An-Najah National University Faculty of Graduate Studies Electric and Magnetic Field Radiation Leakage from Microwave Ovens at Homes in Palestine By Muna Fozan Ahmad Darawshe Supervisor Prof. Issam Rashid Abdelraziq Co- Supervisor Dr. Mohammed Abu-Jafar This Thesis is submitted in Partial Fulfillment of Requirements for the Degree of Master in Physics, Faculty of Graduate Studies, An-Najah National University - Nablus, Palestine. 2014 III Dedication To my father who illuminated my path of success. I would like to thank My mother who taught me to survive no matter what the circumstances have changed. Thanks to my brothers who dreamed of this more than I do and to my sisters who helped and gave me hope. Special thanks to my friends and my teachers who lit our path science and knowledge. To all my family and everyone who helped me make this work possible. IV Acknowledgments I would like to thank my supervisor Prof. Issam Rashid Abdelraziq for helping me to achieve my dream, and for his support, guidance, patience and encouragement. I would also like to thank him for his valuable time allotted to help me complete this research. I'd also like to extend my thanks to my co-supervisor Dr. Mohammed Abu-Jafar for his suggestions and continued encouragement to achieve this thesis; it is a great honor for me to work with them. Special thanks to homeowners who hosted to make some measurements on microwave ovens at their homes, to make this work possible. V االقرار أًا الوْقع ادًاٍ هقذم الزسالت التي تحول العٌْاى: Electric and Magnetic Field Radiation Leakage from Microwave Ovens at Homes in Palestine ها توت االشارة اليَ أقز بأى ها اشتولت عليَ ُذٍ الزسالت ، اًوا ُي ًتاج جِذي الخاص ، باستثٌاء حيثوا ّرد ، ّأى ُذٍ الزسالت ككل ، أّ أي جزء هٌِا لن يقذم هي قبل لٌيل أي درجت علويت أّ بحث علوي لذٓ أي هؤسست تعليويت أّ بحثيت أخزٓ . Declaration The work provided in this thesis, unless otherwise referenced, is the researcher's own work, and has not been submitted elsewhere for any other degree or qualification. Student’s name: : اسم الطالب Signature: : التوقيع Date: : التاريخ VI List of Contents No. Subject Page Dedication III Acknowledgment IV Declaration V List of Contents VI List of Tables VII List of Figures VIII List of Abbreviations IX Abstract XI Chapter One: Introduction 1 1.1 Literature review 3 1.2 Research objectives 9 Chapter two: Theory 10 2.1 Non-ionizing radiation 10 2.2 How does microwave oven work? 12 2.3 The interaction of the electromagnetic fields with human body 14 2.4 Specific absorption rate (SAR) 18 Chapter Three: Methodology 20 3.1 The studied microwave ovens 20 3.2 Instrumentations 21 3.3 Statistical analysis 25 3.4 Standard values 25 Chapter Four: Results and Discussion 28 4.1 Results of power density measurements 28 4.2 Results of power density measurement with age of ovens 30 4.3 Results of power density measurements with operating power 34 4.4 Results of power density measurements with different manufacturers 38 4.5 Calculation the specific absorption rate 41 Chapter Five: Conclusion and Recommendations 48 5.1 Conclusion 48 5.2 Some observations 49 5.3 Recommendations 50 References 52 Appendix 63 ب الولخص VII List of Tables No. Table Caption Page 2.1 Typical sources of electromagnetic fields 11 3.1 Reference levels for general public exposure to time-varying electric and magnetic fields 29 3.2 The safety standard values of SAR in major countries and international organizations 27 4.1 The power density of radiation leakages from 115 microwave ovens at distances 5 cm and 20 cm 28 4.2 The measured and calculated parameters for microwave ovens with the same operating power at 5 cm distance from oven 31 4.3 The measured and calculated parameters for microwave ovens with the same operating power at 20 cm distance from oven 2 4.4 The measured and calculated parameters for microwave ovens with the same age at 5 cm distance from oven 34 4.5 The measured and calculated parameters for microwave ovens with the same age at 20 cm distance from oven 35 4.6 The measured and calculated parameters for microwave ovens with the same manufacturer at 5 cm distance from oven 39 4.7 The measured and calculated parameters for microwave ovens with the same manufacturer at 20 cm distance from oven 4 4.8 The values of SAR for some tissues of human body exposure to EMR from ovens of the same operating power at 5 cm distance from oven 42 4.9 The values of SAR for some tissues of human body exposure to EMR from ovens of the same operating power at 20 cm distance from oven 43 4.10 The values of SAR for some tissues of human body exposure to EMR from ovens of the same age at 5 cm distance from oven 44 4.11 The values of SAR for some tissues of human body exposure to EMR from ovens of the same age at 20 cm distance from oven 45 4.12 The values of SAR for some tissues of human body exposure to EMR from ovens of different manufactures at 5 cm distance from oven 46 4.13 The values of SAR for some tissues of human body exposure to EMR from ovens of different manufactures at 20 cm distance from oven 47 VIII List of Figures No. Figure Caption Page 1.1 Schematic diagram of typical microwave ovens 3 2.1 Electromagnetic spectrum 11 2.2 The range of microwaves 12 2.3 Water molecules align with direction of electric field 13 2.4 Water molecules in an oscillating electric field 13 2.5 Standing waves in microwave oven 14 3.1 Acoustimeter AM-10 RF meter 22 3.2 Hioki 3423 Lux Hitester digital illumination meter 23 3.3 Microwave leakage detector EMF-810 23 3.4 Sound pressure level meter 24 3.5 Scan probe EM-E 25 4.1 The measured power density of radiation leakage as a function of distance from one oven 23 4.2 The average of the measured power density of radiation leakage as a function of distance from group of ovens operating at the same power 700 W 30 4.3 The me The average of the measured power density leakage as a function of age for groups of ovens at the same operating power 700 W (14 ovens of unknown age were excluded) at distance 5 cm from ovens 33 4.4 The average of the measured power density leakage as a function of age for groups of ovens at the same operating power 700 W (14 ovens of unknown age were excluded) at distance 20 cm from ovens 33 4.5 Average power density leakage as a function of operating power at distance 5 cm from oven 36 4.6 Average power density leakage as a function of operating power at distance 20 cm from oven 36 4.7 The measured power density for 115 microwave ovens versus operating power at distance 20 cm 37 4.8 Average power density leakage as a function of average operating power for group of ovens at the same age (14 ovens of unknown age were excluded) at distance 20 cm from oven 38 IX List of Abbreviation Symbol Abbreviation AC Alternating Current A/m Ampere per meter CENELEC European Committee for Electrotechnical Standardization dB Decibel DNA Deoxyribonucleic Acid E Electric Field ELF Extremely Low Frequency EMF Electromagnetic Field EMR Electromagnetic Radiation FDA Food and Drug Administration g/cm 3 Gram per centimeter cube H Magnetic Field HF High Frequency I Intensity ICDs Implantable Cardiovascular Defibrillators ICNIRP International Commission on Non–Ionizing Radiation Protection IEEE Institute of Electrical and Electronics Engineers IR Infrared Kg/m 3 Kilogram per meter cube LF Low Frequency MF Medium Frequency NRPB National Radiological Protection Board OSHA Occupational Safety and Health Administration P Power Density RF Radio Frequency ROS Reactive Oxygen Species SAR Specific Absorption Rate SAR* Specific Absorption Rate for Human Skin SAR** Specific Absorption Rate for Human Brain SAR*** Specific Absorption Rate for Human Eye Sclera SCENIHR Scientific Committee on Emerging and Newly Identified Health Risks S/m Siemens per meter T4 Thyroxine UHF Ultra High Frequency UK United Kingdom U.S. United State UV Ultraviolet X VHF Very High Frequency V/m Volt per meter W/m 2 Watt per meter square W/kg Watt per kilogram ɳ Field Resistance Linear Attenuation Coefficient Conductivity of the Tissue Mass Density of the Tissue XI Electric and Magnetic Field Radiation Leakage from Microwave Ovens at Homes in Palestine By Muna Fozan Ahmed Darawshe Supervisor Prof. Issam Rashid Abdelraziq Co- Supervisor Dr. Mohammed Abu-Jafar Abstract The amount of radiation leakage, the electric field, magnetic field and the specific absorption rate (SAR) were investigated from 115 microwave ovens in domestic use in Palestine. The power density of radiation leakage from microwave ovens was measured using instruments. The age of ovens were between 1 month and 13 years old including 14 ovens with unknown age, with operating power ranging from 700 W to 1350 W of different types, manufacturers, and models. The power density of radiation from ovens was measured at different distances at the height of center of door screen. Electric field, Magnetic field and SAR were calculated at distances 5 cm and 20 cm from ovens. These values were much less than the specified Electromagnetic Field levels (EMF) of International Commission on Non–Ionizing Radiation Protection (ICNIRP) for 2.45 GHz radiofrequency. The power density of radiation leakages from microwave ovens does not depend on the oven age and operating power of ovens. 1 Chapter One Introduction Microwave ovens became indispensable device in most kitchens, because of their ease of use. Users of microwave ovens may concern about potential health hazards from the exposure to microwave radiation leakage. Microwaves are a form of electromagnetic radiation (EMR) because of its ability to penetrate several things like rain, snow, clouds, and smoke. It is used in communication industry for transmitting information from one place to another. In addition, microwave ovens are used for cooking and heating food in homes (Dimple and Singh, 2012). Microwave ovens are amazing household appliance devices used to heat up foods. Percy Spencer working for Raytheon, in 1947 invented the first microwave oven after Second World War from radar technology, called Radarange. Years later, the size and price of microwave ovens were decreased, enabling each house to have a microwave oven. Microwave oven is a device that works on alternating current (AC) that uses microwave radiation at frequency 2.45 GHz, i.e. λ = 12.23 cm to heat and cook food in a short time by oscillating the water molecules contained in the food (Vollmer, 2004). Rays of microwave are absorbing by water, fats and sugars, this means that the molecules of these substances that contain water are electric dipoles and therefore rotate as they try to align themselves with the alternating electric field of the microwaves. Absorbing these rays through the atoms and molecules of the material dispersed energy, make them oscillate significantly, which collide with each other 2 and produce heat necessary to be cooked (Aitkan and Ironmonger, 1996) Fig. (1.1). Many people are concerned about the effect of EMR leakage from microwave ovens. They believe that these leakage radiations may interfere with other electronic apparatus and it may cause health risks when they use microwave ovens in their houses, restaurants and in cafeterias (Vollmer, 2004). This includes concern on whether harmful chemicals would be formed or nutritional quality of food would be lowered during microwave cooking, the food cannot be altered chemically while heated in a microwave oven (Vollmer, 2004). The part that causes leaked of radiations is the door of microwave oven, which made of glasses and covered by metal grids. This metal grid consists of holes, which are small compared with the wavelength of the microwaves so it is like metal plate. The door has λ/4 radiation traps (Thuery and Grant, 1992). The use of a quarter-wavelength chokes away with the requirement for clean metal-to-metal contact and allows small gaps at the door interface (Bangay and Zombolas, 2004). The oven door is the most dangerous place for microwave leakage but magnetic fields can occur all around the oven. This is not good news for children, who love to watch the foods bubbling inside oven. In addition to oven leakage, microwaving causes adverse effects in food (Vollmer, 2004). 3 Fig. (1.1): Schematic diagram of typical microwave ovens (Vollmer, 2004) 1.1 Literature review Mahajan and Singh found in their research that the long-term exposure of low frequency electromagnetic fields (EMFs) would cause health problems especially lack or fatigue, irritability, aggression, hyperactivity, sleep disorders and emotional instability. Large numbers of individuals are becoming hypersensitive to EMR. They showed that the RF energy heats up the tissues in a similar manner, a microwave oven heats the food and it can be dangerous in case of prolong exposure. Tissues can be damaged if exposed to RF energy because they are not capable of dissipating large amount of heat generated. This can lead to skin burns, deep burns and heat strokes. Eyes are most affected by the RF energy because the lack of blood flow to cool the cornea can lead to cataract (Mahajan and Singh, 2012). Exposure to electromagnetic fields has shown to be in connection with Alzheimer disease, motor neuron disease and Parkinson disease (WHO, 2007). Various studies show that exposure to EMR reduce melatonin levels 4 in people. Melatonin protects the brain against damage leading to Alzheimer disease; hence, degenerative diseases such as Alzheimer and Parkinson disease as well as cancer have linked to suppressed melatonin production in the body (Wood et al., 1998) (Wilson et al., 1990). Another study found that the RF Exposure could adversely affect the heart: Pacemaker, implantable cardiovascular defibrillators (ICDs) and impulse generators, and become arrhythmic. This study showed that these radiations may stop pacemaker from delivering pulses in regular way or may generate some kind of external controlling pulse putting the patient to death (Altamura et al., 1997). A study showed that heating garlic for 60 second in microwave oven could block garlic's ability to inhibit in vivo binding of mammary carcinogen. This study demonstrated that this blocking of the ability of garlic was consistent with inactivation of alliinase. Heating destroyed garlic's active allyl sulfur formation, which relate to its anticancer properties (Song and Milner, 2001). Microwave absorption effect is much more significant by the body parts, which contain more fluid (water, blood, etc.) like the brain that consists of about 90% water. Effect is more pronounced where the movement of the fluid is less, for example, eyes, brain, joints, heart, abdomen, etc. The effect has shown to be much more severe for children and pregnant women by Neha and Girish Kumar in their study (Neha and Girish, 2009). A study showed that the effects of radiations are not observed in the initial years of exposure as the body has certain defense mechanisms, and the 5 pressure is on the stress proteins of the body namely the heat shock proteins (Leszczynski et al., 2002). Effects of radiation accumulate over time and risks are more pronounced after 8 to 10 years of exposure (Hardell et al., 2009). Researchers indicate that changes in exposure level might be more important than duration of exposure for producing effects in human beings (Cook et al., 1992). The regular and long-term use of microwave devices (mobile phone, microwave oven) at domestic level can have negative impact upon biological system especially on brain. Increased reactive oxygen species (ROS) play an important role by enhancing the effect of microwave radiations, which may cause neurodegenerative diseases (Kesari et al., 2013). A survey showed that electromagnetic waves of frequency 130 KHz and 150 KHz, which are used for radio navigation system spread in the atmosphere, and affect the people who are living near the radiator of signal. These frequencies have harmful effects on some selected tissues of the human beings. SAR of body fluid, cerebral spinal fluid and gall bladder tissues become greater to the safe limit announced by some international agencies (Kumar et al., 2012). ELF and EMF induce effects in the comet assay are reproducible under specific conditions and occasional triggering of apoptosis rather than by the generation of DNA damage (Focke et al., 2010). A study indicated that the EMF exposure in preimplantation stage could have detrimental effects on female mouse fertility, and embryo development by decreasing the number http://www.ncbi.nlm.nih.gov/pubmed?term=Cook%20MR%5BAuthor%5D&cauthor=true&cauthor_uid=1510736 6 of blastocysts and increasing the blastocysts DNA fragmentation (Borhani et al., 2011). Another study showed a relationship between exposure to radiofrequency fields during work with radiofrequency equipment and radar and reduced fertility (Møllerløkken and Moen, 2008). In 2003, Charles and his group found positive associations between the highest level of exposure to EMFs and risk of mortality from prostate cancer (Charles et al., 2003). In the same year, a study showed that exposed mothers during pregnancy to the highest occupational level of ELF-MF, increase risk of childhood leukemia among children (Infante-Rivard and Deadman, 2003). A study by Mousa on the radiated electromagnetic energy from some typical mobile base stations around the city of Nablus, his study found that the power density emitted by the base stations is lower than permitted levels (Mousa, 2011). Microwaves radiation leakage from ovens decrease body weight, increase thyroxin (T4) and cortisol levels, and therefore has deleterious health effects. They showed in the study that radiation leakage from oven ranged from 6.5 to 57.5 mW/cm 2 . Cortisol and T4 levels were significantly increased in the test group compared to the control group, respectively (Jelodar and Nazifi, 2010). A study showed that the contribution of the magnetic field from microwave ovens for inducing some current density in the human body which is small (one µT induces a current density of ±5 µA.m -2 ) (NRPB, 2001). When a man is just at a couple of centimeters of unshielded operating ovens, a http://www.ncbi.nlm.nih.gov/pubmed?term=M%C3%B8llerl%C3%B8kken%20OJ%5BAuthor%5D&cauthor=true&cauthor_uid=18240289 http://www.ncbi.nlm.nih.gov/pubmed?term=Moen%20BE%5BAuthor%5D&cauthor=true&cauthor_uid=18240289 7 much higher current density may induce (up to 500 µT induce a current density of 5 µA.m -2 (Decat and Van Tichelen, 1995). A study by Skotte surveyed microwave ovens used in restaurants and cafeterias, and found that for most of the large ovens leakage is in the range between 0.2 to 2 mW/cm 2 (Skotte, 1981). Another study by Muhammad and his group found that, only one microwave oven gives a value of 10.19 mW/cm 2 which exceeds the standard value (Muhammad et al., 2011). Some ovens were found to radiate more than the specified limit, and that was attributed to oven age and the lack of cleaning and proper maintenance (Osepchuk, 1978). Correlation was observed between measured leakage and oven age. There is no apparent correlation was found between measured leakage and operating power (Alhekail, 2001). Research demonstrated that the extended exposure to RF signals at an average SAR of at least 5.0 W/kg, are capable of inducing chromosomal damage in human lymphocytes (Tice et al., 2002). Annual surveys investigated in the United Kingdom (UK) from 1980– 1987, showed that only a small number of the inspected ovens leaked in excess of 5 mW/cm 2 at 5 cm from the surface of oven (Moseley and Davison, 1989). Survey conducted at the United State Fermi National Accelerator Laboratory between 1974 and 1985, it was found that the mean maximum leakage within 5 cm of the oven surface was 0.2 ± 3.1 mW/cm 2 (Miller, 1987).zAlhekail studied the leakage from 106 microwave ovens and showed that only one oven exceeded the 5 mW/cm 2 emission limit. He 8 found that the probability of finding an oven that leaks more than 5 mW/cm 2 is 0.6 % (Alhekail, 2001). This is a relatively high probability, when compared to the one found by Matthes where leakage measurements were performed on ovens brought in for cost-free check (Matthes, 1992). Alhekail found that several ovens leaking more than 1 mW/cm 2 (Alhekail, 2001). Matthes studied 130 ovens. Ovens power was 350W- 1200W, and the age of the ovens was between 5 - 18 years, his study reported that all checked ovens were found to leak less than 1 mW/cm 2 (Matthes, 1992). Survey was conducted in Ottawa, Canada, on 60 before-sale microwave ovens and 100 used ovens. None of the before-sale ovens were found to emit microwave radiation in excess of the maximum allowed leakage. They found only one used oven leaked in excess of the maximum allowed leakage. Six before-sale ovens from three different manufacturers were found to be noncompliant with the labeling requirements (Thansanodte et al., 2000). Gilbert showed in his research that microwave ovens leaked radiation when door of ovens closed. His study was made of 187 commercials use ovens. He found that 20 % leak 10 mW/cm 2 or more, within two inches from the closed oven (Gilbert, 1970). Astudy by Lahham and Sharabati about the amount of radiation leakage from 117 microwave ovens in domestic and restaurant use in the West Bank, Palestine. The amount of radiation leakages at a distance of 1 m was found to vary from 0.43 to 16.4 µW/cm 2 with an average value of 3.64 http://rpd.oxfordjournals.org/search?author1=Adnan+Lahham&sortspec=date&submit=Submit http://rpd.oxfordjournals.org/search?author1=Afifeh+Sharabati&sortspec=date&submit=Submit 9 µW/cm 2 . Leakages from all tested microwave ovens except for seven ovens (∼6 % of the total) were below 10 µW/cm 2 . The highest radiation leakage from any tested oven was ∼16.4 µW/cm 2 . This study confirmed a linear correlation between the amount of leakage and both oven age and operating power with a stronger dependence of leakage on age (Lahham and Sharabati, 2013). 1.2 Research objectives The effect of electromagnetic radiation (leakage) from microwave ovens has been raised. Many people are concerned about the impact of radiation leaking from microwave ovens on their health. The aims of this study are: 1. Investigating radio frequency radiation leakage from 115 microwave ovens, at homes in Palestine. 2. Measuring the power density of radiation leakage as a function of distance from ovens, oven age and operating power of ovens. 3. Calculating the electric fields, magnetic fields of electromagnetic radiations leakage from ovens. 4. Calculating the SAR of some human body tissues and organs; human skin, human brain and human eye sclera. 5. Comparing the results of this work with the international standards of ICNIRP in tables (3.1) and (3.2). http://rpd.oxfordjournals.org/search?author1=Adnan+Lahham&sortspec=date&submit=Submit 11 Chapter Two Theory 2.1 Non-ionizing radiation There are typical sources of electromagnetic fields with frequency and intensity. The lower part of the frequency spectrum is considered non- ionizing EMR, with its energy levels are below than the required for effects at the atomic level. The non-ionizing EMR are classified into frequency bands, namely (SCENIHR, 2007):  Radio frequency (RF) (100 kHz < F ≤ 300 GHz), which including low frequency (LF), medium frequency (MF), high frequency (HF), very high frequency (VHF), ultra high frequency (UHF) and microwave and millimeterwave (30 kHz to 300 GHz), as shown in table (2.1).  Intermediate frequency (IF) (300 Hz < F ≤ 100 kHz)  Extremely low frequency (ELF) (0< F ≤ 300 Hz)  Static (0 Hz)  Optical radiations: infrared (IR) (760 - 10 6 ) nm, visible (400 – 760) nm, (Ng, 2003). 11 Table (2.1): Typical sources of electromagnetic fields (SCENIHR, 2007) Frequency range Frequencies Some examples of exposures sources Static 0 Hz VDU (video displays); MRI and other diagnostic / scientific instrumentation; Industrial electrolysis; Welding devices ELF 0-300 Hz Powerlines; Domestic distribution lines, Domestic appliances; Electric engines in cars, train and tramway; Welding devices IF 300 Hz-100 KHz VDU; anti theft devices in shops, hands free access control systems, card readers and metal detectors; MRI; Welding devices RF 100 KHz-300 GHz Mobile telephony; Broadcasting and TV; Microwave oven; Radar, portable and stationary radio, transceivers, personal mobile radio; MRI Microwaves are form of electromagnetic radiation (non ionizing radiation), these waves are radio wave that wavelengths range from 1 mm to 1 meter, and the frequency is 300 MHz to 300 GHz (Dimple and Singh, 2012). The electromagnetic spectrum is shown in Figs. (2.1) and (2.2) (Zamanian and Hardiman, 2005). Fig. (2.1): Electromagnetic spectrum 12 Fig. (2.2): The range of microwaves 2.2 How does microwave oven work? The microwave oven is a versatile, time saving kitchen appliance that uses for thawing, cooking or reheating foods by exposing it to microwave radiation. The source of the radiation in a microwave oven is the magnetron tube, which is the heart of microwave oven. Magnetron is a tube that generates microwave radiations, in which electrons affected by magnetic and electric fields to produce radiation at about 2.45 GHz, and channeled by the waveguides. They are usually metal tubes of rectangular cross section, into the cooking chamber, which has metallic walls (Aitkan and Ironmonger, 1996). When these waves incident the metal walls they will be absorbed very effectively. Interaction will happened between the electric field of the waves and the free electron of the metal. These electrons re- radiated these waves in phase and at the same frequency so the microwaves reflected (Vollmer, 2004). Most food contains water even dry food, water H2O is a polar molecule with two hydrogen positive atoms and single oxygen negative atom. The water molecules are in constant motion and are normally randomly 13 oriented. When these molecules exposure to EMF which are generated from magnetron, they will experience a torque from the electric field and will become aligned with direction of this field. Water molecules are oriented by the electric field Fig. (2.3), the direction of the electric field is changing rapidly about 2.45 billion times per second. Then polar water molecules follow the oscillation of the electric field, they collide more frequently with the molecules (water and other) around them. This microwaves have frequency equals the resonance frequency of water, Fig. (2.4) (Vollmer, 2004). Fig. (2.3): Water molecules align with direction of electric field Fig. (2.4): Water molecules in an oscillating electric field 14 The molecules move faster and faster and the temperature increases, which causes heating. Inside a microwave oven, the electromagnetic waves resonate and form standing waves from reflections at the walls, these standing waves are simplified by the fact that the wavelength of the microwaves is roughly the same as the linear dimensions of the chamber. The microwave oven cooks all food evenly, but the nodes and antinodes of the standing waves can cause the food to burn in some places but to remain cool in others, without a turntable the food will not be cooked uniformly (Vollmer, 2004), Fig. (2.5). Fig. (2.5): Standing waves in microwave oven 2.3 The interaction of the electromagnetic fields with human body RF energy is produced by many manufactured sources, which radiate EMR of different frequencies and intensities. including cellular phones and base stations, television and radio broadcasting facilities, radar, medical equipment, coffee makers, refrigerators, cloth washers and dryers, microwave ovens, RF induction heaters, … etc (Consumer and Clinical Radiation Protection Bureau, 2009). 15 When an electric or magnetic field penetrates into the body, it is attenuated and a part of it is absorbed inside the body tissue (Kumar et al; 2008). There are three basic coupling mechanisms, through which electric and magnetic fields interact directly with living matter: coupling to low- frequency electric fields, low-frequency magnetic fields and absorption of energy from electromagnetic fields (Sinik and Despotovic, 2002). The interaction of electric fields with the human body causes: flow of electric charges, polarization of bound charge, and the reorientation of electric dipoles in tissue. The magnitudes of these different effects depend on electrical conductivity and permittivity of the body (Sinik and Despotovic, 2002). These electrical properties of the body vary with the type of body tissue and the frequency of the applied field, for example, human body consists of homogeneous tissue like muscle tissue and three layer tissue like skin and fat (Klemm and Troester, 2006). External electric fields induce a surface charge on the body; these results an induced current in the body, the distribution of which depends on exposure conditions, the size and shape of the body, and the body’s position in the field (Sinik and Despotovic, 2002). The interaction of magnetic fields with the human body results an induced electric fields and circulating electric currents. Their magnitudes are proportional to the radius of the loop, the electrical conductivity of the tissue, and the rate of change and magnitude of the magnetic flux density. The exact path and magnitude of the resulting current induced in any part 16 of the body will depend on the electrical conductivity of the tissue (Sinik and Despotovic, 2002). Exposure to electromagnetic fields at frequencies above about 100 kHz can lead to significant absorption of energy and temperature increases. In general, exposure to a uniform electromagnetic field results in a non- uniform deposition and distribution of energy within the body (Sinik and Despotovic, 2002). The intensity of radiation that absorbed by a sample depends on the chemical density of the sample, its thickness, the cross section of absorption, and on the wavelength of the radiation of the sample (Harrison et al., 2011). The beam will lose intensity due to two processes: the substance can absorb the light, or the light can be scattered by the substance when a narrow (collimated) beam of light passes through a substance. However, how much of the lost intensity was scattered, and how much was absorbed can be measured. Attenuation coefficient measures the total loss of narrow-beam intensity, including scattering as well (Bohren and Huffman, 1998). The measured intensity of transmitted through a layer of material with thickness x, related to the incident intensity according to the inverse exponential power law that usually referred to as Beer-Lambert law: 2.1 Where, x is the path length of radiation and the attenuation coefficient (or linear attenuation coefficient). 17 The linear attenuation coefficient and mass attenuation coefficient are related such that the mass attenuation coefficient is simply , where is the density in g/cm 3 . When this coefficient is used in the Beer-Lambert law, then "mass thickness" (defined as the mass per unit area) replaces the product of length time's density (Bohren and Huffman, 1983). Beer observed that, the amount of radiation that absorbed by a sample is proportional to the concentration of dissolved substance (Harrison et al., 2011). As an electromagnetic wave travels through space, energy transferred from the source to other objects (receivers). The rate of this energy transfer depends on the strength of the electromagnetic field components. Microwave radiation is measured as power density, which is essentially the rate of energy flow per unit area. Power density is the product of the electric field strength (E) times the magnetic field strength (H) (OSHA, 1990). P = E H 2.2 Where, P is the power density in W/m 2 , E is the electric field strength in V/m, and H is the magnetic field strength in A/m (OSHA, 1990). The power density can be written as: P = ɳ H 2 2.3 ɳ is the field resistance taken as ( ) 1/2 = 377 Ω for free space (in air) (ICNIRP, 1998). http://en.wikipedia.org/wiki/Mass_attenuation_coefficient 18 2.4 Specific absorption rate (SAR) The frequently usage of microwave ovens generates concern about potential health effects on humans. It has become necessary to ensure that these devices do not expose their users to potentially harmful levels, and the known health effects center around tissue heating. A measure of this heating effect is known as specific absorption rate (SAR). SAR is one of the important parameter that should be measured, when human and biological objects are exposed to electromagnetic radiation from microwave oven, they are absorbed electromagnetic energy. SAR is defined as the time derivative of the incremental energy (dW) absorbed by or dissipated in an incremental mass (dm) contained in a volume (dV) of a given mass density ( ). It can be defined as (Seabury and ETS-Lindgren, 2005): SAR = ( ) = ( ) 2.4 SAR is related to electric fields at a point, which is the power of electromagnetic radiation absorbed per mass of tissue. SAR can be calculated as (Bangay and Zombolas, 2004): SAR = 2.5 Where SAR is the Specific absorption rate in (W/Kg), is the conductivity of the tissue in (1/Ω.m), E is electric field strength in (V/m), and is the mass density of the tissue in (Kg/m 3 ). The appropriate parameters for the conductivity , and the tissue density of all different materials used for 19 the calculation must be known. Equation (2.5) represents the rate at which the electromagnetic energy is converted into heat, through interaction mechanisms. It provides a quantitative measure of all interaction mechanisms that are dependent on the intensity of the internal electric field (Kumar et al., 2008). There are some international radiation exposure safety standard available in major countries as; Europe, America, Korea and Japan. The international organizations are; European Committee for Electrotechnical Standardization (CENELEC), International Commission on Non-Ionizing Radiation Protection (ICNIRP) and Institute of Electrical and Electronics Engineers (IEEE), that are mainly defined from the thermal point of view. For examples, the general public exposure limit of whole body average SAR is 0.08 W/kg, while the localized SAR for head and trunk is 2 W/kg (Chiang and Tam, 2008). In the case of the eye, the limit for the average SAR over 10 grams of tissue is 2 W/kg in the frequency range from 0.5 to 3.5 GHz (IEEE, 2005) (ICNIRP, 1988), these standard values of SAR in different organizations and countries are shown in Table (3.2). 21 Chapter Three Methodology 3.1 The studied microwave ovens In this study, 115 microwave ovens of different types and models were tested in domestic use in Nablus, Palestine. The age of ovens ranged from 1 month to 13 years, with 14 ovens of unknown age. Operating power of ovens ranged from 700 W to 1350 W. The power density leakage from microwave ovens was measured at different distances at the height of center of door screen; a detector is set up to measure EMR leakage in different directions from microwave ovens. The principle of heating food in microwave ovens depends on the presence of water molecules in it, therefore the leakage power density from microwave ovens was measured by putting water in a plate in the cavity of ovens; any source of electromagnetic fields was turned off in homes such as; TV and wireless internet. All the inspected ovens were adjusted to operate at maximum output power, by touch power level pad and select a high cooking power level. The measurements were made using acoustimeter and microwave leakage detector EMF-810. The light intensity was measured in different sites of the houses especially in the kitchens using hioki 3423 lux hitester digital illumination meter, values of light intensity are found to be within the range (500 – 750) lux. The noise pressure level was measured in all tested houses using sound pressure level meter and, it was within the range (50 - 60) dB, which is considered quiet place. The intensity level of light and sound noise level 21 were measured to make sure that; they don't influence the measured values. It has been found by some researchers that there are an effect from exposure to sound, light intensity and other sources of EMR (Sadeq et al., 2013) (Sadeq, 2011) (Ibrahim et al., 2013) (Sheikh et al., 2013) (Sheikh, 2013) (Abdelraziq et al., 2003) (Abdelraziq et al., 2000) (Qamhieh et al., 2000) (Sa'abnah, 2011) (Suliman, 2014) (Thaher, 2014) (Subha, 2014) (Abu hadba, 2014) (Al-Faqeeh, 2013) (Abo-Ras, 2012). The power of EMR was measured near these microwave ovens. Data was collected and logged in the special data collection sheet which was designed. The sheet included information about the oven of various models such as manufacturer, dates of manufacturing, country of origin, operating power, frequency, age, number of users, daily use, age of users, location of the oven at home, user awareness and physical condition, this sheet is shown in Appendix (C). Microwave oven has label of information and labels of awareness, some ovens did not have labels of awareness, and there is no warning labels in the local language were fixed on any of the surveyed ovens. 3.2 Instrumentations Five Instruments were used in our test and measurements. These instruments are briefly described in the following: 1. Acoustimeter AM-10 RF meter is dedicated RF radiation meter. This meter is used to measure radiation from different sources. It measures RF radiation from 200 MHz right up to 8 GHz ±3 dB, and measures average exposure levels from 1 to 100,000 microwatts per 22 square meter [ μW/m2 ], peak exposure levels from 0.02 to 6.00 volts per meter [ V/m ]. Acoustimeter is shown in Fig. (3.1) (Acoustimeter User Manual, 2011). Fig. (3.1): Acoustimeter AM-10 RF meter (Acoustimeter User Manual, 2011) 2. Hioki 3423 lux hitester digital illumination meter is used to measure the light intensity in selected homes. This instrument is suited for a wide range of application. It measures a broad range of luminosities, from the low light provided by induction lighting up to a maximum intensity of 199,900 lux, with accuracy ±4%. This instrument is shown in Fig. (3.2) (Hioki 3423 Lux Hitester Instruction Manual, 2006). 23 Fig. (3.2): Hioki 3423 Lux Hitester Digital Illumination Meter (Hioki 3423 Lux Hitester Instruction Manual, 2006) 3. Microwave leakage detector EMF-810. This instrument is used to measure electromagnetic field value for the microwave frequency, precisely on the frequency value 2.45 GHz, and to detect the leakage of microwave oven with accuracy < 2 dB. Accuracy tested less than 2.45 ± 50 MHz and measurement range from 0 to 1.999 mW/cm 2 . Microwave leakage detector, which is used in this study, is shown in Fig. (3.3) (Microwave Leakage Detector Operation Manual). Fig. (3.3): Microwave leakage detector EMF-81 (Microwave Leakage Detector Operation Manual) 24 4. Sound pressure level meter that is used to measure the sound level in dB of selected homes, (Quest Technologies U.S.A, Model 2900 type 2) with accuracy of ± 0.5 dB at 25 °C. This device gives the readings with a precision of 0.1 dB. This instrument is shown in Fig. (3.4) (Instructions manual for sound level meter, 1998b). Fig. (3.4): Sound pressure level meter (Instructions manual for sound level meter, 1998b) 5. Scan probe EM-E, model CTM020. It is used to detect the presence of an electromagnetic field, and provides audio and visual indication of relative field strength. The scan probe offers a green / yellow / red 5-LED light bar and audible tone, which changes pitch with field strength. Scan probe is shown in Fig. (3.5) (Instruction Manual for Scan Probe, China, 2006) 25 Fig. (3.5): Scan probe EM-E (Instruction Manual for Scan Probe, China, 2006) 3.3 Statistical analysis The data was analyzed by using excel program. Excel was used to find the relation between the power density of radiation leakages and the distance from microwave ovens, the age of ovens and the operating power of ovens. Electric field, magnetic field and SAR were calculated at distance 5 cm and 20 cm by using excel program. 3.4 Standard values The maximum amount of leakage (emission) from microwave ovens has been specified by the United State code of federal regulation (CFR) 21 part 1030, at distances of 5 cm from the oven to be 1 mW/cm 2 before the oven is sold, and 5 mW/cm 2 throughout its operating life (FDA, 1992). In addition, by ICNIRP, limit general public exposure to RF power to 1 mW/cm 2 at 2.45 GHz radiofrequency (ICNIRP, 1998). Table 3.1 shows the reference levels for general public exposure to time varying electric and magnetic fields (ICNRP, 1998). The reference levels for limiting exposure are obtained from the basic restrictions for the condition of maximum coupling of the field to the exposed individual, thereby providing maximum protection (Vecchia, 2007). 26 Table (3.1): Reference levels for occupational and general public exposure to time-varying electric and magnetic fields (ICNIRP, 1998) Equivalent plane wave power flux density Seq (W/m 2 ) H-field strength (A/m rms) E-field strength (V/m rms) Frequency range Exposure category - 1.63/f 614 100 KHz -1 MHz Occupational 1000/f 2 1.63/f 614/f 1 MHz -10 MHz 10 0.163 61.4 10 MHz -400 MHz f /40 0.00814 x f 0.5 3.07 x f 0.5 400 MHz -2 GHz 50 0.364 137 2 GHz -300 GHz - 4.86 86.8 100 KHz -150 KHz General public - 0.729/f 86.8 150 KHz -1 MHz - 0.729/f 86.8 / f 0.5 1 MHz – 10 MHz 2 0.0729 27.4 10 MHz - 400 MHz f /200 0.00364 x f 0.5 1.37 x f 0.5 400 MHz -2 GHz 10 0.163 61.4 2 GHz -300 GHz 27 Table (3.2) shows the safety standard values of SAR in major countries and international organizations. Table (3.2): The safety standard values of SAR in major countries and international organizations (ICNIRP, 1998) Classification Korea Japan U.S. CENELEC ICNIRP IEEE Frequency range (Hz) 10 5 ~ 10 10 10 5 ~ 3 x 10 8 10 5 ~ 6 x 10 8 10 6 ~ 3 x 10 11 10 5 ~ 10 10 10 5 ~ 3 x 10 6 Normal use (W/kg) Whole body 0.08 0.08 0.08 0.08 0.08 0.08 Head/ trunk 1.6 2 1.6 2 2 2 Limbs 4 4 4 4 4 4 Occupation al user (W/Kg) Whole body 0.4 0.4 0.4 0.4 0.4 0.4 Head/ trunk 8 10 8 10 10 10 Extremities 20 20 20 20 20 20 Note: Head/trunk refers to body parts excluding the limbs; the SAR standard for limbs is the average maximum value for 1 gram of human tissue in Korea and the U.S. while in Japan, CENELEC, ICNIRP and IEEE limbs is based on the average maximum value for 10 grams of human tissue. 28 Chapter Four Results and Discussion This chapter represents the results and discussion of this study. Results of power density measurements, the electric, magnetic fields and SAR are calculated and explained in section (4.1). Results of power density measurements with age of ovens and operating power are shown in sections (4.2) and (4.3). Results of power density measurements, calculated electric field, magnetic field and SAR for different manufacturers are shown in section (4.4). The calculated SAR is shown in section (4.5). 4.1 Results of power density measurements Our study was carried out for 115 microwave ovens in domestic use at homes in Palestine, by Acoustimeter AM-10 RF meter at different distances. In this study, the power density of radiation leakage from 115 microwave ovens at distances 5 cm and 20 cm are shown in table (4.1). Table (4.1): The power density of radiation leakages from 115 microwave ovens at distances 5 cm and 20 cm Distance from oven (cm) The lowest value of P (mW/m 2 ) The highest value of P (mW/m 2 ) An average value of P (mW/m 2 ) 5 1.54 76.01 50.92 20 1.57 67.82 34.86 14 ovens with unknown age 5 1.54 69.95 47.32 20 1.57 53.16 28.59 These values are much less than standard values in table (3.1). A study in Germany reported that all checked ovens were found to leak less than 1 mW/cm 2 (Matthes, 1992). 29 The age of ovens were between 1 month and 13 years old including 14 ovens with unknown age, with operating power ranging from 700 W to 1350 W, and of different types, models and manufacturers. The electric field and magnetic fields were calculated using equations (2.2) and (2.3). The highest calculated values of electric field were 5.35 V/m at 5 cm distance from oven, and 5.06 V/m at 20 cm distance from oven. The lowest calculated values of electric field were 0.77 V/m at 5 cm, and 0.76 V/m at 20 cm. The highest calculated values of magnetic field were 141.20 x 10 -4 A/m at 5 cm distance from oven, and 134.10 x 10 -4 A/m at 20 cm far from oven. The lowest calculated values of magnetic field were 20.00 x 10 - 4 A/m at 5 cm distance from oven, and 11.50 x 10 -4 A/m at 20 cm distance from oven. All of these values were less than the standard values according to table (3.1). The measured power density of radiation leakage as a function of distance from one of the ovens is shown in Fig. (4.1); the data of this figure is given in table (a1) in Appendix (A). The average of the measured power density of radiation leakage as a function of distance, for the group of ovens operating at the same power 700 W, is shown in Fig. (4.2), the data of this figure is tabulated in table (a2) in Appendix (A). 31 Fig. (4.1): The measured power density of radiation leakage as a function of distance from one oven Fig. (4.2): The average of the measured power density of radiation leakage as a function of distance from group of ovens operating at the same power 700 W Figs. (4.1) and (4.2) indicate that the measured power density of radiation leakage decrease with distance from the ovens. The power density as a function of distance from one oven was the same for a group of ovens operating at the same power. A study showed that the measured power density decreases with distance from microwave oven (Lahham and Sharabati, 2013). 0 10 20 30 40 50 60 70 80 90 100 0 50 100 150 200 250 Po we r d en sit y ( mW /m 2 ) Distance from oven (cm) 0 10 20 30 40 50 60 70 0 50 100 150 200 250 Av er ag e p ow er d en sit y lea ka ge (m W /m 2 ) Distance from oven (cm) http://rpd.oxfordjournals.org/search?author1=Adnan+Lahham&sortspec=date&submit=Submit 31 4.2 Results of power density measurements with age of ovens The age of all ovens was between 1 month and 13 years old including 14 ovens with unknown age. The electric field and magnetic field were calculated using equations (2.2) and (2.3). The average power density of radiation leakages from all ovens of different ages of the same operating power, the magnitudes of electric field and magnetic field are shown in tables (4.2) and (4.3), at distances 5 cm and 20 cm far from ovens. Table (4.2): The measured and calculated parameters* for microwave ovens of the same operating power at 5 cm distance from oven Parameters*: P = Power density leakage, E = Electric field, H = Magnetic field Avg. H (A/m) X 10 -4 Avg. E (V/m) Avg. P (mW/m 2 ) Avg. Age (months) No. of Ovens Operating Power (W) 112.64 4.25 49.09 34 50 700 127.50 4.81 61.33 156 1 750 113.41 4.27 49.70 38 15 800 116.41 4.39 51.42 20 8 850 120.83 4.56 56.15 35 20 900 107.00 4.04 43.22 156 1 950 124.01 4.68 58.49 65 5 1000 119.43 4.50 53.77 60 1 1350 89.15 3.58 34.75 Un- known age 6 700 118.57 4.47 53.53 5 800 128.00 4.84 62.02 1 850 121.00 4.56 55.17 1 900 135.40 5.10 69.11 1 1000 32 Table (4.3): The measured and calculated parameters* for microwave ovens of the same operating power at 20 cm distance from oven Avg. H (A/m) X 10 -4 Avg. E (V/m) Avg. P (mW/m 2 ) Avg. Age (months) No. of Ovens Operating Power (W) 91.09 3.40 33.46 34 50 700 89.21 3.36 30.00 156 1 750 97.44 3.64 39.17 38 15 800 98.95 3.73 37.44 20 8 850 96.92 3.67 37.95 35 20 900 90.00 3.39 30.55 156 1 950 103.10 3.89 40.92 65 5 1000 110.86 4.18 46.33 60 1 1350 53.95 1.54 13.74 Un- known age 6 700 97.63 3.68 36.71 5 800 105.00 3.95 41.45 1 850 109.00 4.09 44.39 1 900 113.44 4.28 48.51 1 1000 Parameters*: P = Power density leakage, E = Electric field, H = Magnetic field The Average power density of EMR leakages from ovens is much less than the recommended values in table (3.1), at distances 5 cm and 20 cm far from ovens. The magnitudes of electric and magnetic field of radiation leakages from all ovens in tables (4.2) and (4.3) are less than the standard values of general public in table (3.1). It is clear that the electric field is < 61.4 V/m and the magnetic field is < 0.163 A/m. The values of average power density, electric field and magnetic of radiations at distances 5 cm is larger than the values at 20 cm far from ovens, however it is still less than the standard values according to table (3.1) The relation between the power density of radiation leakage from ovens and age of ovens are shown in Figs. (4.3) and (4.4). These figures show the averaged measured power density leakage as a function of age for groups 33 of ovens of the same operating power 700 W (14 ovens of unknown age were excluded), at distances 5 cm and 20 cm from ovens. Data of Figs. (4.3) and (4.4) are given in tables (b1) and (b2) in Appendix (B). Fig. (4.3): The average of the measured power density leakage as a function of age for groups of ovens at the same operating power 700 W (14 ovens of unknown age were excluded) at distance 5 cm from ovens Fig. (4.4): The average of the measured power density leakage as a function of age for groups of ovens at the same operating power 700 W (14 ovens of unknown age were excluded) at distance 20 cm from ovens 0 10 20 30 40 50 60 <1 1 1.5 2 2.5 3 4 5 6 7 8 10Av er ag e m ea su re d po we r de ns ity (m W /m 2 ) Age (Years) Operating power = 700 W 0 10 20 30 40 50 60 <1 1 1.5 2 2.5 3 4 5 6 7 8 10 Av er ag e m ea su re d po we r de ns ity (m W /m 2 ) Age (Years) Operating power = 700 W 34 Figures (4.3) and (4.4) show the independent of leakages on age of oven for ovens operating at same power 700 W, at 5 cm and 20 cm distances from ovens. From these figures, there is no statistically significant relation between power density leakages from ovens and age. The independent of power density on age is clear in figure (4.4). 4.3 Results of power density measurements with operating power The operating powers of all ovens in this study ranging from 700 W to 1350 W of different types, models and manufacturers. The average of the measured power density, the average of the calculated electric field, magnetic field of radiations leakage from all ovens of the same age, are given in tables (4.4) and (4.5) at distances 5 cm, and 20 cm far from ovens. Table (4.4): The measured and calculated parameters* for microwave ovens of the same age at 5 cm distance from oven Avg. H (A/m) X 10 -4 Avg. E (V/m) Avg. P (mW/m 2 ) Avg. Operating power (W) No. of Ovens Age in Months 112.54 4.24 49.12 774 17 1-12 115.22 4.34 51.00 796 12 12 124.23 4.68 58.48 767 6 18 107.18 4.04 44.03 789 9 24 55.02 2.07 11.41 700 1 30 118.60 4.48 54.48 777 24 36 112.89 4.26 49.42 800 11 44 117.97 4.45 53.31 844 9 60 114.17 4.30 49.18 800 2 72 127.02 4.78 60.94 800 2 84 116.33 4.40 51.45 767 3 96 120.00 4.54 54.69 700 1 120 123.00 4.63 56.81 800 1 144 122.26 4.61 56.73 900 3 156 108.01 4..07 47.32 782 14 Un-known age Parameters*: P = Power density leakage, E = Electric field, H = Magnetic field 35 Table (4.5): The measured and calculated parameters* for microwave oven of the same age at 20 cm distance from oven Avg. H (A/m) X 10 -4 Avg. E (V/m) Avg. P (mW/m 2 ) Avg. Operating power (W) No. of Ovens Age in Months 88.85 3.35 33.17 774 17 1-12 92.73 3.50 34.03 796 12 12 113.02 4.26 48.49 767 6 18 89.02 3.30 31.18 789 9 24 30.50 1.15 3.51 700 1 30 97.67 3.68 37.96 777 24 36 88.53 3.34 33.24 800 11 48 100.54 3.79 39.20 844 9 60 81.22 3.05 26.15 800 2 72 108.41 4.09 44.63 800 2 84 87.67 3.34 30.79 767 3 96 98.00 3.69 36.05 700 1 120 114.00 4.31 49.33 800 1 144 70.11 2.64 27.56 900 3 156 81.38 2.85 28.59 782 14 Un- known age Parameters*: P = Power density leakage, E = Electric field, H = Magnetic field The magnitudes of average power density, average electric and magnetic field of radiation leakages from all ovens of the same age in tables (4.4) and (4.5) were much less than the standard values of general public in table (3.1). Average power density, Average electric and magnetic field of EMR leakages from all ovens of the same age at distance 5 cm are larger than at 20 cm far from ovens, nevertheless it is still less than the standard values in table (3.1). The measured power density leakage from microwave oven as a function of operating power are shown in figures (4.5) and (4.6), at 5 cm and 20 cm 36 distances from group of ovens have the same age which is one year. Data of these figures are given in tables (b3) and (b4) in Appendix B. Fig. (4.5): Average power density leakage as a function of operating power at distance 5 cm from oven Fig. (4.6): Average power density leakage as a function of operating power at distance 20 cm from oven 45 45.5 46 46.5 47 47.5 48 48.5 49 700 800 850 900 Av er ag ed o f t he m ea su re d po we r de ns ity (m W /m 2 ) Operating power (W) Age of oven = 12 Month 0 10 20 30 40 50 60 700 800 850 900 Av er ag ed o f t he m ea su re d po we r de ns ity (m W /m 2 ) Operating power (W) Age of oven = 12 Month 37 The figures (4.5) and (4.6) show the independent of leakages on operating power of ovens at distance 5 cm and 20 cm, no statistically significant relation was observed between the power density of radiation leakage and operating power of ovens from figures (4.5) and (4.6). It is more pronounced in figure (4.8) for all ovens and in figures (4.7) for group of ovens at the same age. The measured power density of all ovens with operating power are shown in figure (4.7), data of this figure is shown in table (b5) in Appendix (B). Fig. (4.7): The measured power density for 115 microwave ovens versus operating power at distance 20 cm The averaged of the measured power density leakage as a function of average operating power for groups of ovens at the same age (14 ovens of unknown age were excluded), are shown in figure (3.8), data of this figure are given in table (b6) in Appendix (B). 0 10 20 30 40 50 60 70 80 500 700 900 1100 1300 1500 Po we r d en sit y ( mW /m 2 ) Operating Power (W) 38 Fig. (4.8): Average power density leakage as a function of average operating power for group of ovens at the same age (14 ovens of unknown age were excluded) at distance 20 cm from oven 4.4 Results of power density measurements with different manufacturers The type, daily use and manufacturer of ovens are parameters that affect on the value of radiation emissions from microwave ovens. The average electric field magnetic field of all ovens of different manufacturers are calculated and given in tables (4.6) and (4.7) at distances 5 cm, and 20 cm far away from ovens. 0 10 20 30 40 50 60 70 80 600 650 700 750 800 850 900 950 av er ag e p ow er d en sit y l ea ka ge (m W /m 2 ) Average operating power (W) 39 Table (4.6): The measured and calculated parameters* for microwave ovens of different manufacturers at 5 cm distance from oven Manuf- acturer No. of Ovens Avg. Operating power (W) Avg. Age (months) Avg. P (mW/m 2 ) Avg. E (V/m) Avg. H (A/m) X 10 -4 LG 41 777 34 51.92 4.41 116.93 Kennedy 9 744 35 38.63 3.74 99.24 Daeivoo 8 850 29 56.95 4.51 119.59 Konka 4 850 16 55.25 4.56 120.85 Pilot 4 700 19 54.99 4.51 119.73 Universal 4 775 51 53.30 4.47 118.47 Crystal 3 900 37 57.85 4.66 123.65 Electra 3 800 18 47.38 4.20 111.29 Hemilton 3 767 34 45.79 4.01 109.11 Gold star 3 800 24 38.65 3.60 95.51 Hyundai 3 700 24 36.84 3.69 97.91 Sharp 2 750 24 68.50 5.08 134.76 Sanyo 2 900 90 63.18 4.87 129.41 Prestige 2 775 102 58.62 4.70 122.25 Galanz 2 900 54 55.09 4.57 120.86 Morphy richards 1 900 36 72.79 5.24 138.95 Panasonic 1 1000 156 65.65 4.98 131.96 Prisma 1 700 60 56.11 4.60 122.00 Typhoon 1 700 3 51.42 4.40 117.00 Mega 1 700 12 48.99 4.30 113.99 Technolax 1 1000 48 48.72 4.29 113.68 Kenon 1 700 96 43.56 4.05 107.00 compact 1 950 156 43.22 4.04 107.00 Parameters*: P = Power density leakage, E = Electric field, H = Magnetic field 41 Table (4.7): The measured and calculated parameters* for microwave ovens of different manufacturers at 20 cm distance from oven Manuf- acturer No. of Ovens Avg. Operating power(W) Avg. Age (months) Avg. P (mW/m 2 ) Avg. E (V/m) Avg. H (A/m) X 10 -4 LG 41 777 34 36.70 3.63 95.89 Kennedy 9 744 35 25.80 2.98 78.98 Daeivoo 8 850 29 47.26 4.10 110.51 Pilot 4 700 19 42.22 3.94 104.43 Konka 4 850 16 38.61 3.80 100.83 Universal 4 775 51 30.27 3.19 84.93 Crystal 3 900 37 382.00 3.78 100.24 Electra 3 800 18 32.75 3.39 91.19 Hemilton 3 766 34 29.16 2.93 77.64 Gold star 3 800 24 27.62 3.02 79.96 Hyundai 3 700 24 20.49 3.69 97.91 Sanyo 2 900 90 48.02 4.25 112.66 Sharp 2 750 24 46.87 4.20 111.43 Galanz 2 900 54 36.01 3.68 97.70 Prestige 2 775 102 19.17 2.57 68.11 Morphy richards 1 900 36 65.55 4.97 131.86 Panasonic 1 1000 156 52.09 4.43 117.54 Typhoon 1 700 3 46.20 4.17 112.00 Prisma 1 700 60 40.62 3.91 103.80 Technolax 1 1000 48 32.47 3.50 92.80 compact 1 950 156 30.55 3.39 90.00 Mega 1 700 12 21.01 2.82 74.66 Kenon 1 700 96 16.03 2.46 65.00 Parameters*: P = Power density leakage, E = Electric field, H = Magnetic field The type, model, usage time and manufacturer are parameters that affect on the values of power density of radiation emissions from microwave ovens. The average power density of all ovens of different manufacturers is shown in tables (4.5) and (4.6); from these tables Morphyrichards have the highest values of average power density, average electric and magnetic field at 41 distances 5 cm and 20 cm far from oven. However, it is still much below than the recommended values in table (3.1). The measured power density, calculated electric and magnetic field of radiation leakages from all ovens with different manufacturer according to table (4.6) and (4.7) were less than the standard values of general public as shown table (3.1). 4.5 Calculation the specific absorption rate SAR values were calculated using equation (2.5) according to ρ and σ values as follows; SAR for human's brain, ρ = 1030 kg/m 3 and σ = 0.77 1/Ωm, while SAR for human's skin ρ = 1100 kg/m 3 and σ = 0.872 1/Ωm, and SAR for human's eye sclera ρ = 1100 kg/m 3 and σ = 1.173 1/Ωm (Angelone et al., 2004). SAR values are given in tables (4.8), (4.9), (4.10), (4.11), (4.12) and (4.13). Tables (4.8) and (4.9) show the average SAR of some human tissues that exposure to EMR leakages from microwave ovens of the same age at distances 5 cm and 20 cm from ovens. SAR was calculated for some tissues of human body; human's skin, human's brain and human's eye sclera. 42 Table (4.8): The values of SAR for some tissues of human body exposure to EMR from ovens of the same operating power at 5 cm distance from oven Avg. SAR*** (W/Kg) X 10 -4 Avg. SAR** (W/Kg) X 10 -4 Avg. SAR* (W/Kg) X 10 -4 Avg. Age (months) No. of Ovens Operating Power (W) 99 69 73 34 50 700 123 86 92 156 1 750 101 71 75 38 15 800 103 72 77 20 8 850 113 79 84 35 20 900 87 61 65 156 1 950 118 82 87 65 5 1000 108 76 80 60 1 1350 70 47 52 Un-known age 6 700 108 75 80 5 800 125 87 93 1 850 111 78 82 1 900 139 97 103 1 1000 SAR*: SAR for human skin SAR**: SAR for human brain SAR***: SAR for human eye sclera 43 Table (4.9): The values of SAR for some tissues of human body exposure to EMR from ovens of the same operating power at 20 cm distance from oven Avg. SAR*** (W/Kg) X 10 -4 Avg. SAR** (W/Kg) X 10 -4 Avg. SAR* (W/Kg) X 10 -4 Avg. Age (months) No. of ovens Operating Power (W) 68 47 51 34 50 700 60 42 45 156 1 750 76 53 56 38 15 800 74 52 55 20 8 850 76 53 57 35 20 900 61 43 46 156 1 950 82 58 61 65 5 1000 108 65 69 60 1 1350 15 11 12 Un-known age 6 700 74 52 55 5 800 83 58 62 1 850 89 63 63 1 900 98 68 72 1 1000 SAR*: SAR for human skin SAR**: SAR for human brain SAR***: SAR for human eye sclera All magnitudes of the calculated SAR in tables (4.7) and (4.8) for human's skin, human's brain and human's eye sclera were much less than the recommended levels of exposure in table (3.2). These results were much less than 0.08 W/ Kg for human's skin, 2 W/ Kg for human's brain and human's eye sclera. Values of SAR in table (4.8) are greater than in tables (4.9), nevertheless it is still below than the recommended values according to table (3.2). Tables (4.10) and (4.11) show the average SAR for some human tissues that exposure to EMR leakages from groups of microwave ovens have the same operating power at distances 5 cm and 20 cm from ovens. SAR was 44 calculated using equation (2.5) for some tissues of human body, human's skin, human's brain and human's eye sclera. Table (4.10): The values of SAR for some tissues of human body exposure to EMR from ovens of the same age at 5 cm distance from oven Avg. SAR*** (W/Kg) X 10 -4 Avg. SAR** (W/Kg) X 10 -4 Avg. SAR* (W/Kg) X 10 -4 Avg. Operating power (W) No. of Ovens Age in Months 99 69 73 774 17 1-12 103 72 76 796 12 12 118 82 87 767 6 18 89 62 66 789 9 24 23 16 17 700 1 30 110 77 81 777 24 36 99 73 74 800 11 48 107 75 80 844 9 60 99 69 73 800 2 72 122 86 91 800 2 84 103 72 77 767 3 96 110 77 82 700 1 120 114 80 85 800 1 144 114 80 85 900 3 156 95 67 71 782 14 Un- known age SAR*: SAR for human skin SAR**: SAR for human brain SAR***: SAR for human eye sclera 45 Table (4.11): The values of SAR for some tissues of human body exposure to EMR from ovens of the same age at 20 cm distance from oven Avg. SAR*** (W/Kg) X 10 -4 Avg. SAR** (W/Kg) X 10 -4 Avg. SAR* (W/Kg) X 10 -4 Avg. Operating power (W) No. of Ovens Age in Months 133 94 104 774 17 1-12 135 95 101 796 12 12 196 137 145 767 6 18 125 88 93 789 9 24 14 10 10 700 1 30 153 107 114 777 24 36 134 94 99 800 11 48 158 111 117 844 9 60 105 74 78 800 2 72 179 126 133 800 2 84 124 87 92 767 3 96 145 102 108 700 1 120 198 139 147 800 1 144 166 116 124 900 3 156 105 73 78 782 14 Un- known age SAR*: SAR for human skin SAR**: SAR for human brain SAR***: SAR for human eye sclera SAR for human skin, human brain and human eye sclera in tables (4.10) and (4.11) were much less than the safety values of SAR as shown in table (3.2). The average SAR of some tissues of human body that exposure to EMF leakages from ovens of different manufacturers, SAR are calculated and given in tables (4.12) and (4.13) at distances 5 cm, and 20 cm far from ovens. 46 Table (4.12): The values of SAR for some tissues of human body exposure to EMR from ovens of different manufactures at 5 cm distance from oven Manuf- acturer No. of Ovens Avg. Operating power (W) Avg. Age (months) Avg. SAR* (W/Kg) X 10 -4 Avg. SAR** (W/Kg) X 10 -4 Avg. SAR*** (W/Kg) X 10 -4 LG 41 777 34 78 74 105 Kennedy 9 744 35 58 54 78 Daeivoo 8 850 29 85 80 111 Konka 4 850 16 88 78 111 Pilot 4 700 19 82 77 111 Universal 4 775 51 80 75 107 Crystal 3 900 37 86 81 116 Electra 3 800 18 71 67 95 Hemilton 3 767 34 68 65 92 Gold star 3 800 24 56 54 78 Hyundai 3 700 24 55 52 74 Sharp 2 750 24 102 97 138 Sanyo 2 900 90 94 89 127 Prestige 2 775 102 87 82 118 Galanz 2 900 54 83 78 112 Morphy richards 1 900 36 109 103 146 Panasonic 1 1000 156 98 93 132 Prisma 1 700 60 84 79 113 Typhoon 1 700 3 77 72 103 Mega 1 700 12 73 69 98 Technolax 1 1000 48 73 69 98 Kenon 1 700 96 65 61 88 compact 1 950 156 65 61 87 47 Table (4.13): The values of SAR for some tissues of human body exposure to EMR from ovens of different manufactures at 20 cm distance from oven Manuf- acturer No. of Ovens Avg. Operating power (W) Avg. Age (months) Avg. SAR* (W/Kg) X 10 -4 Avg. SAR** (W/Kg) X 10 -4 Avg. SAR*** (W/Kg) X 10 -4 LG 41 777 34 52 52 72 Kennedy 9 744 35 47 36 52 Daeivoo 8 850 29 70 67 95 Pilot 4 700 19 63 59 85 Konka 4 850 16 58 54 78 Universal 4 775 51 45 43 68 Crystal 3 900 37 57 54 76 Electra 3 800 18 49 46 66 Hemilton 3 767 34 44 41 59 Gold star 3 800 24 41 39 56 Hyundai 3 700 24 31 29 41 Sanyo 2 900 90 72 68 97 Sharp 2 750 24 70 66 94 Galanz 2 900 54 54 51 72 Prestige 2 775 102 29 27 39 Morphy richards 1 900 36 98 92 132 Panasonic 1 1000 156 78 73 105 Typhoon 1 700 3 96 65 93 Prisma 1 700 60 61 57 82 Technolax 1 1000 48 49 46 65 compact 1 950 156 46 43 61 Mega 1 700 12 31 30 42 Kenon 1 700 96 24 23 32 SAR*: SAR for human skin SAR**: SAR for human brain SAR***: SAR for human eye sclera The maximum values of SAR for human skin, human brain and human eye sclera when expose to EMR leakages are from Morphyrichards oven at distance 5 cm and 20 cm from ovens. However these values are still less than recommended level of SAR in table (3.2). SAR for human skin, human brain and human eye sclera in tables (4.12), (4.13), were much less than the recommended levels of exposure in table (3.2). 48 Chapter Five Conclusion and Recommendations 5.1 Conclusion This survey tested 115 microwave ovens of domestic use in Palestine. The maximum power density, electric field, magnetic field and SAR of radiation leakages from all ovens at distances 5 cm and 20 cm, were found less than the specified limit for the general public exposure. Values of power density leakage from all tested ovens with different ages, operating power, models, daily use, number of users and manufacturer were less than the specified value, the power density leakages from all ovens at 5 cm is < 10 W/m 2 in table (3.1), there is no concern from EMR leakage from microwave ovens. Usage time of every microwave oven was recorded. The users of microwave ovens spent short time near these ovens; a slight daily use of microwave ovens at homes was found; the maximum duration of use was for an hour and intermittently. Therefor the power density of radiation leakage from microwave ovens was slight. The maximum value of SAR for human skin was less when compared to the standard value 0.08 W/Kg, all values of calculated SAR for human brain and human eye sclera were much less than the recommended levels of exposure, which is 2 W/Kg according to table (3.2) for standard values of SAR. There is no concern about exposure to radiation leakage from microwave ovens when they are used in cooking and heating; because of the short time 49 of use of ovens. The amount of radiation leakage does not depend on oven age. There is no statistically significant relation found between operating power and radiation leakages from ovens. 5.2 Some observations In this study some survey observations were noted:  It is found that some people buy used ovens; in this study 14 ovens with unknown age.  Some ovens had broken doors glasses but no abnormal leakage was detected.  Some people put a wet towel on the door of the microwave oven when they turn it on; they believe it reduces the radiation leaking from these ovens.  Some ovens have been damaged and the measurements were not taken, so they did not taken into consideration in this study.  A few of the ovens had problems with their doors that small piece of paper placed in the door to force the doors to be closed.  The lower parts of some ovens are damaged.  Some ovens are found above electrical devices, such as television and refrigerator.  Some ovens stop working although there is a timer.  Some ovens have used doors which relate to other ovens.  Small numbers of people are using plastic and metal pots to heat food in microwave oven. 51 The above mentioned points made us to exclude these ovens from the sample of ovens. 5.3 Recommendations The suggestions and recommendations mentioned below may reduce the EMR leakage from microwave ovens and its effect on human health. Even though, the results do not exceed the exposure standard values: 1. It is useful for the manufacturers to make labels of information and warnings in local language, to make it easier for people to understand and read the warnings. 2. It is recommended to stay away from the microwave oven a distance of not less than 20 cm while using it, and to stay away from the oven while it is running, and avoid stand next it to cook the food, especially for the children. 3. It is better in future to avoid putting the microwave ovens near other electrical devices; operating microwave oven may cause an interference of the electromagnetic radiation leakage with other radiation. 4. It is prohibited in future to operate the oven while the door is open; this leads to harmful exposure to microwave radiation. It is particularly important that the oven door close properly. 5. 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P (mW/m 2 ) 0 59.50 2 53.90 5 48.08 10 42.54 15 37.55 20 32.86 25 27.54 30 31.21 40 20.48 45 17.40 50 14.31 70 10.18 90 7.65 100 6.15 130 3.58 150 2.49 200 1.78 Distance from oven (cm) P (mW/m 2 ) 0 76.02 2 72.08 5 69.06 15 58.62 20 53.84 25 48.02 30 46.02 40 39.02 45 36.95 50 32.04 70 22.62 90 18.07 100 10.04 130 6.10 150 2.02 200 0.99 64 Appendix (B) Table (b1): The average measured power density at distance 5 cm from ovens and age of oven Table (b2): The average measured power density at distance 20 cm from ovens and age of oven Age of Ovens (Years) Avg. P (mW/m 2 ) <1 33.02 1 27.58 1.5 41.37 2 20.89 2.5 3.51 3 32.66 4 39.65 5 41.76 6 14.26 7 52.07 8 30.02 10 36.05 Age of Ovens (Years) Avg. P (mW/m 2 ) <1 48.61 1 47.53 1.5 53.87 2 37.18 2.5 11.41 3 52.75 4 52.60 5 54.16 6 45.49 7 53.13 8 51.34 10 54.69 65 Table (b3): The average measured power density at distance 5 cm from ovens and operating power Operating Power (W) Avg. P (mW/m 2 ) 700 46.45 800 47.45 850 48.49 900 47.45 Table (b4): The average measured power density at distance 20 cm from ovens and operating power Operating Power (W) Avg. P (mW/m 2 ) 700 28.77 800 50.02 850 38.93 900 39.22 Table (b5): The measured power density for 115 microwave ovens and operating power at distance 20 cm Operating Power(W) P(mW/m 2 ) 700 46.32 700 54.30 700 53.13 700 44.27 700 34.21 700 45.15 700 33.31 700 43.56 700 59.12 700 31.20 700 53.23 700 18.91 700 54.69 700 63.22 700 45.49 700 36.11 700 49.81 700 52.17 700 1.54 700 32.62 66 700 44.57 700 32.56 700 41.09 700 44.77 700 53.00 700 51.42 700 61.03 750 60.00 800 37.38 800 42.91 800 55.91 800 56.89 800 53.24 800 56.81 800 9.04 800 59.76 800 43.67 800 36.66 850 62.02 900 16.09 900 51.67 900 46.32 900 45.70 900 32.64 900 55.17 900 55.02 950 43.22 1000 43.24 1350 53.77 700 65.51 700 70.61 700 56.16 700 10.30 700 38.32 700 59.88 700 64.22 700 29.46 700 44.70 700 34.00 700 59.87 700 32.14 67 700 52.70 700 26.22 700 51.10 700 48.99 700 57.05 700 53.52 700 70.05 700 66.71 700 48.40 700 58.15 700 67.60 700 73.61 700 11.41 700 58.90 700 53.12 700 63.18 700 56.11 800 62.91 800 59.02 800 58.40 800 42.33 800 29.08 800 76.01 800 51.65 800 48.05 800 69.95 800 71.48 850 46.34 850 47.04 68 Operating Power (W) P (mW/m 2 ) 850 39.09 850 69.06 850 59.02 850 52.39 850 48.32 850 50.11 900 68.60 900 72.79 900 52.88 900 68.97 900 57.32 900 68.75 900 72.07 900 64.23 900 58.05 900 66.76 900 65.66 900 49.78 900 52.39 900 57.31 1000 65.65 1000 65.27 1000 69.54 1000 69.11 1000 48.72 69 Table (b6): Average power density leakage, average operating power for group of ovens at the same age (14 ovens of unknown age were excluded) at distance 20 cm from oven Operating power (W) Avg. P (mW/m 2 ) 774 60.97 796 34.03 767 48.49 789 31.18 700 3.51 777 65.46 800 63.62 844 67.82 800 38.03 800 52.07 767 44.02 700 36.05 800 49.33 900 27.56 71 Appendix C Paper to collect data and information about microwave oven Dates of manufacturing : Ovens number : Manufacturer : Country of origin : Number of users : Age of oven : Location of the oven at home : Daily use : Age of user : Operating power : Frequency : User awareness : Electric field (E): Magnetic field (H) : Power density (mW/cm 2 ) : Leakage ( 𝜇W/m 2 ) Distance from oven (cm) 0 2 5 10 15 20 25 30 40 45 50 70 90 100 130 150 200 الوطنية النجاح جامعة العميا الدراسات كمية المجال الكهربائي والمغناطيسي لإلشعاعات المتسربة من أفران الميكروويف في المنازل في فمسطين اعداد منى فوزان أحمد دراوشة اشراف راشد عبد الرازق عصام د.أ جعفر ابو محمد .د بكمية الفيزياء في الماجستير درجةالحصول عمى لمتطمبات استكماال االطروحة هذه قدمت فمسطين – نابمس في الوطنية النجاح في جامعة العميا الدراسات 2014 ب‌ المجال الكهربائي والمغناطيسي لإلشعاعات المتسربة من أفران الميكروويف في المنازل في فمسطين اعداد فوزان أحمد دراوشةمنى اشراف أ.د عصام راشد عبد الرازق د. محمد أبو جعفر الممخص المجال المغناطيسي ومعدل و المجال الكهربائي، وحساب كمية التسرب اإلشعاعي، قياسلقد تم لقياس . فمسطين -نابمس ستخدام المنزلي فيفرن ميكروويف لإل 115االمتصاص النوعي من المقاسة يتراوح عمر األفران. Acoustimeterجهاز ستخدم اكمية التسرب اإلشعاعي من األفران -700تتراوح بين هاقوة تشغيمو (العمرمستعمل غير معروف ا فرن 14بينهم ) سنة 13 -شهر من وقد تم قياس كثافة تدفق الطاقة لإلشعاعات . من أنواع ونماذج مختمفة األفران كانت، واط 1350 ، ومعدل المجال المغناطيسي، حساب المجال الكهربائي، و المتسربة من األفران عند مسافات مختمفة كانت هذه القيم أقل بكثير من . من األفرانسم 20سم و 5االمتصاص النوعي عمى بعد من المجنة الدولية لمحماية من الموصى بها (EMF) الت الكهرومغناطيسيةامستويات المج كثافة تدفق وتبين من النتائج أن غيغاهيرتز. 2.45( عند تردد ICNIRPاإلشعاع غير المؤين ) تشغيل األفران. درةعمى كل من عمر الفرن وقال تعتمد الطاقة لإلشعاعات الكهرومغناطيسية