§ 5.12.4 Environmental Effects - the SPS Microwave Beam
Commonly, questions have been raised about whether the beam would be hazardous to people or birds. Studies to date have showed the 2.45 GHz prototype beam to be safe. However, before discussing this topic, it is important to understand the basics about radio and microwave beams.
This section puts the SPS beam into a bigger perspective in a general sense. The physics and biophysics of microwaves is discussed in much more detail in a later section of this chapter for anyone wanting to explore this further.
The SPS beam is basically a radio beam. When people hear the word "microwave", they think of a microwave oven. The SPS beam intensity does not need to have the power intensity anything near a microwave oven, and current designs have the intensity as hundreds of times less above the rectenna, indeed a power intensity about one-tenth that of sunlight. Also, a microwave oven is designed to operate at a frequency which is absorbed by water (which is why dry stuff doesn't heat up well in a microwave). The SPS will operate at a frequency designed to NOT be absorbed by water in the atmosphere, and to pass through clouds and rain.
Microwave frequencies are harmlessly used in communications, using different microwave frequencies which avoid absorption by water in the atmosphere so that they travel a long distance. The SPS beam will use a frequency tuned for minimal absorption by the atmosphere, clouds and storms.
The rectenna would be located over crops and perhaps cows, and can be safe -- the beam power intensity could be less than noontime sunlight (but for 24 hours and converted to electricity far more efficiently than sunlight). Animals underneath the rectenna would probably be fine, though birds flying above the rectenna may have to adjust to added warmth, particularly on hot days. Whether or not it will be necessary to discourage birds from flying through is not clear at this time.
Microwaves cause heating, but not much else. The intensity would not be anything near that inside a microwave oven -- a microwave oven operates at power densities hundreds of times higher.
Microwaves are NOT like ultraviolet and other "ionizing" radiation which you get from walking in the sun.
The reason why microwave "radiation" is safer is that it is of much lower frequency or energy than the ultraviolet light you receive from sunlight outdoors, and from the x-rays coming from your TV and computer screen. X-ray and ultraviolet radiation are ionizing radiation which can disrupt molecules in the body. Microwave radiation by the SPS is even less potent than infra-red radiation from heaters and stoves. If the SPS beam is significantly absorbed by biota, it would produce only heating, and usually not significant heating.
The current beam designs put the beam intensity to be one tenth that of sunlight, at 23 milliWatts per square centimeter (mW/cm2) at the center, and just 0.1 (mW/cm2) at the edge of the rectenna complex, and dropping quickly with distance. The U.S. and Canadian governments' safety standards allow unlimited occupational exposure to microwaves in the 2.45 GHz range of 10 milliWatts per square centimeter. Sweden, the United Kingdom, Germany, France and the Netherlands have nearly the same standards. Some countries have lower standards, but without basis or enforcement. All have probably put in a conservative "safety factor".
A microwave oven can leak 5 mW/cm2 and still conform to safety standards. (103)
The figure below shows the power density of the beam.
Birds have been put into wind tunnels; they flew comfortably in a simulated SPS beam. The intensity had to be increased before the birds tried to land to cool off. Monkeys have reproduced in rooms with microwave beams similar to that of the SPS. Wild birds have made nests in military radar transmitters operating at higher intensities (at the transmitter) than the SPS beam, and reproduced without problems.
There are some reports stating that some biological effects may be produced from microwaves (short radio waves) that are modulated at certain modulation amplitudes and frequencies. However, modulated beams can be made to have special properties unlike unmodulated beams, and the SPS would use only unmodulated waves of low amplitude -- modulated waves have no utility for the SPS. (If still worried, then put metal foil in your attic to reflect practically all the SPS farfield spillover.)
Frankly, it doesn't make much sense to worry about the SPS beam if you go out in the sunlight or eat the typical American diet with all kinds of food additives that are chemically less understood than the possible effects of radio waves on biota. You will clearly absorb much more harmful radiation by walking outside in sunshine. However, some elements of the press today give alarmist coverage of the effects of electromagnetic radiation from your house's power wires going through the walls, so I expect to read a lot about the SPS beam in the future. Of course, it's good for everything to be questioned and studied, but it's also important for the general public to be educated in a balanced way and to keep everything in relative perspective. I have no doubt that there will be sensational press based on ignorance regarding the SPS beam.
What if the beam wanders off from the rectenna? The beam can't wander off target with a significant intensity because it needs constant feedback from the rectenna for focusing. (A phased-array system is necessary for successful focusing onto the rectenna at such distances.) If it wanders off, then it immediately defocusses and disperses to a tiny fraction of its operating intensity. It also can't be used as a weapon for this reason. Even if it were re-engineered to point anywhere with the same focussing, the transmitters would be designed to operate at a relatively benign frequency (e.g., 2.45 GHz) which would not pose a credible threat to anyone. Again, the only thing that will significantly absorb the 2.45 GHz frequency beam is a receiving antenna designed for it.
Conceivably, another weapon could be mounted on the SPS to use its electricity, but that would be a major political move that would be quite unlikely to be implemented except in dire circumstances. Verification measures can insure that no weapons systems are mounted on the satellite. It's hard to hide from view in space. On site inspection is also possible.
What is "radiation"?
This section is a follow-on to the discussion earlier in this chapter on the effects of the microwave beam, and you should read that section before this one.
"Radiation" is often a mis-used term. For example, when you sit next to a fireplace, you get infra-red "radiation". You get "radiation" by sleeping next to your spouse, which is welcome on cold winter nights!
The figure below shows the range of electromagnetic radiation (EMR) from destructive gamma rays at one extreme, to visible light and infra-red heat in the middle, to radio waves used for communications on the opposite extreme. Microwaves are within the radio wave spectrum.
The SPS beam of 2.45 GHz is located in the microwave area of the radio communications spectrum, near the TV and FM radio frequencies, and falls within the 2.3 GHz to 2.5 GHz bandwidth allocated for police, taxi, citizen's band, mobile, radiolocation, amateur, amateur-satellite and ISM (industrial, scientific and medical) applications -- the UHF band. The vast majority of these other applications do not use 2.45 GHz but use other frequencies near to 2.45 GHz. The potential effects on these communications is discussed in a later section of this book.
The effects of EMR on animals and inanimate materials have been thoroughly studied over the decades. To understand this work, you must understand some of the basics of physics.
EMR, whether it be sunlight or heat from your fireplace, is both a wave and a kind of particle. When you warm up beside your fireplace, you are actually absorbing particles of invisible infra-red light. These particles are called "photons" (and should NOT be confused with "protons"!). The same is true of your TV -- your antenna absorbs photons emitted by your TV station's transmitter or sent to your TV by cable.
The energy of each photon "particle" depends on its wavelength or frequency. The word frequency is more commonly used here. (Low frequency means long wavelength; high frequency is short wavelength.)
It's confusing, so I'll stick to "frequency". Just remember: Higher frequency means higher energy per photon. Lower frequency means lower energy per photon.
Visible sunlight has higher frequency photons than infrared heat from your fireplace, so it takes more photons from your fireplace to warm you up. However, being a few feet from a fireplace can beat being under the sun if the coals are putting out far more photons than you would get standing in sunlight. (Notably, your eyes can't see most of the photons coming from the fireplace, but do react to the higher energy photons from the sun in vastly smaller quantities.)
High frequency photons can do damage to your body, but low frequency photons cannot. Low frequency photons can warm you up without damaging cells. For example, you can get skin cancer from being in the sun on a cold winter day, but not by sitting next to a fireplace no matter how hot the fireplace. Yet, the sun can't warm you nearly as well as the fireplace. You can get a thousand times more photons next to a fireplace and not get skin cancer. That's because the photons of the fireplace are each not energetic enough to twist the genetic code in cells when each photon strikes, whereas the ultraviolet-frequency photons in sunlight can. If you get close enough to the fireplace, you could cook yourself, but you won't get that mysterious skin-damaging ailment called "sunburn" or skin cancer.
It's like hitting a rock. You can spend a lot of energy slapping the rock all day with a belt and not produce much of a result besides heating the surface and tiring yourself, or you can hit it just once with a hammer and break it.
Radio-frequency and microwave-frequency photons have much lower energy than those from the "infrared" radiation from your fireplace, your TV infra-red remote control, or even those radiating from your spouse.
Walking down the street during daylight exposes you to far more damaging radiation from the sun than microwave oven "radiation" ever will.
Microwaves are used in electronic ovens because they are not so readily absorbed by food, compared to gas fired (infrared) ovens. Microwaves travel through food, whereas infrared "heat" is absorbed at the surface. That may sound bad, but actually it's good. Microwaves are advantageous if you want to heat something up in the middle nearly as fast as the outside. But you have to make a lot of photons, and reflect them between the walls of the inside of the microwave to get enough heating. (That's why you can't put metal into a microwave, as it screws up the reflection pattern. If your microwave has plastic inside walls, such a distortion of the reflective "standing waves" can melt the plastic walls inside the oven.)
Conservative government safety guidelines allow microwave ovens to leak 5 milliWatts per square centimeter (mW/cm2). That's unlike to warm you up or affect vital electronics like pacemakers or police radio. The outer fence of the rectenna would have 0.1 mW/cm2, and dropping rapidly with distance. The middle of the beam is 23 mW/cm2.
In the figure above, the low energy EMR is shown on the left, and high energy EMR on the right. The scale is not proportional but "logarithmic". For example, the SPS is in the 109 area, whereas infrared is in the 1012 area. A difference of 3 means "three zeros", i.e., that an infrared photon is 1000 TIMES more energetic than a microwave photon. 109 = 1,000,000,000 whereas 1012 = 1,000,000,000,000.
On the left are generally harmless radiation used for communications. In the middle is visible light. To the right is hazardous x-rays and gamma rays. (Nuclear waste atoms produce gamma rays.)
One term used in radiation discussions is "ionizing radiation". "Ionization" is the ability to knock an electron off of an atom, thereby creating a charged and reactive atom. (A charged atom is called an "ion".)
A molecule is a set of atoms in a stable arrangement. For example, genetic material in an animal's cells are large molecules. Generally, if a photon is capable of ionizing an atom, it is also capable of hitting a molecule hard enough to modify it. An ionized atom can also modify material next to it. This could damage the overall function of the cell if not repaired by cell repair mechanisms. Cells behave and reproduce according to the molecules they are made of, and modification of these molecules in the wrong way can cause them to go crazy and possibly do things like become cancerous.
This "ionizing radiation" is on the right side of the figure above. Photons on the left half are not energetic enough to do such things. The SPS beam is not ionizing, nor even close to being ionizing.
Temperature is physically the motion of atoms and molecules. The faster they are moving, the warmer they are. When low energy photons hit molecules, they just speed them up a little. To speed them up enough to "cook" them requires an extremely intense bombardment of photons -- one right after another after another… on a given molecule, usually by a visible light flame. Standing outside a microwave oven and absorbing its leakage simply won't cook you, and neither will an SPS beam.
However, a tiny dose of ultraviolet, x-ray, or gamma ray photons causing NO measurable temperature change can possibly wreak havoc on an animal's body in the form of genetic damage and cancer.
To be really exhaustive, let me get a little more technical in this paragraph. I am a physicist, after all. The energy of photons is usually stated in "electron volts", or eV (the energy gained by an electron accelerated through a field of one volt). 0.08 eV is needed to change a molecular hydrogen bond, and 10 eV to ionize it. An infrared photon from your spouse at 37C (98F) has about 0.03 eV. A SPS beam photon has an energy of 0.00001 eV.
"Microwave radiation" from an SPS beam seems trivial in today's modern world.
Of course, gamma rays from nuclear power plant waste, chemical pollutants from coal fired power plants, and food additives create significant risks to animals.
Years upon years of study have turned up no adverse effects of continuous wave microwaves besides heating in extreme cases. The exposure of the general population to the SPS beam will cause no measurable heating -- infinitesimally small. You'll get more heating from infrared radiation by the person across the room. The SPS won't help on cold winter nights, except to power your electric heater.
There have been extensive studies looking for effects on people and animals due to mobile telephones held up to their ears (which work in the microwave spectrum), FM radio station transmitting antennas located in neighborhoods, and even birds nesting in airport radar horns. Over 35 million industrial microwave heaters and dryers are used in the plastics, paper, and other industries. About 30 million citizens band radios are licensed to operate and transmit at 4,000 milliWatts (i.e., 4 Watts), as compared to the 23 milliWatt per square centimeter SPS beam at its peak in the center.
No good scientific study has turned up anything alarming. I have read sensational press by demagogic reporters covering weird reports (often by people trying to get research money) of mysterious effects that defy basic theory, without addressing the fact that decades of good scientific studies have turned up nil. Remember, studies must have a statistically significant number of "typical" subjects, a controlled environment to eliminate other factors, and a second "control group" exposed to an identical environment except the microwaves. And the results must be reproducible by an independent group of unbiased scientists.
To illustrate this point, there was a high profile study as a result of a bizarre situation. The Russians irradiated the American Embassy in Moscow with continuous microwave beams from 1953 to 1979, probably for electronic jamming though press speculation was that Russian research had found microwaves to interfere with thinking. Health concerns arose. The first study compared the effects to a control group not exposed to microwave radiation. The surprising results were that the control group people experienced "many times more effects than the exposed individuals". Of course, that study showed the importance of statistically larger samples and psychosomatic effects.
Concerned citizens are also misled by alarmist and sensational writings such as The Zapping of America (118) by well known journalist Steven Broder.
The U.S. Environmental Protection Agency, in response to public controversy on EMR bioeffects due to microwaves and other "Radio Frequency Radiation (RFR)", wrote a piece entitled "Misconceptions" which puts it this way: "Accounts of purported deleterious effects of RFR exposure on humans sometimes appear that, on investigation, are found to be either specious or not due to RFR exposure. Moreover, some of these accounts persist or are repeated well after investigations have shown them to be incorrect." (117)
I'd recommend that you listen to the scientists whose professional credibiilty is on the line before listening to someone with an apparent bias or trying to sell a sensational article or tabloid newspaper.
Likewise, conservatively worded statements by scientists should not be misinterpreted. Establishing the absence of harmful or deleterious effects is extensively time-consuming and expensive, as opposed to establishing their existence.
What has been studied? Genetic and cytogenetic effects, cancer, teratogenesis (fetus development), ocular effects, nervous system effects, brain-related effects, hematological (blood) effects, behavior, endocrinological effects, cell membrane and other cellular effects. The only effects found (e.g., blood serum protein levels) were for doses much higher than people would experience by a SPS, and those effects were the same as what happens to the body if it warms beyond normal temperature, e.g., during a fever. In other words, the effects of heating. You can produce those effects by sitting in a sauna. Cells and the body's organs behave differently at different temperatures, which is why our bodies regulate our temperature to within a tenth of a degree. Turn down the microwave levels to decent intensities and the symptoms go away. "Almost all of the credible reported microwave exposure effects are ascribed to the heating produced by the microwave energy." (111)
The Office of Technology Assessment report cited above states "Most U.S. microwave experts acknowledge the need for research on low-level effects, but remain skeptical about their biological significance, especially at the proposed SPS single frequency of continuous radiation." (116)
The Environmental Protection Agency received funding to study the SPS beam's health risks on both the general public and fulltime workers on-site at the rectenna. (Workers would spend most of their time underneath the rectenna which absorbs about 85% of the beam.) Their final report states:
"Since there appear to be no intrinsic, metagenic or carcinogenic effects of microwaves [below exhorbitantly high levels], the problem of such effects can be dismissed for the ordinary level of exposure of human [workers] within the rectenna area of SPS (0.01 to 1.0 mW/cm2)." (120)
"Overall, the epidemiologic evidence does not offer any reliable evidence that the ordinary level of exposure of humans within the rectenna area of SPS (0.01 to 1.0 mW/cm2) would cause any harm." (123)
They looked at the most sensitive elements of the human body, e.g., pregnant mothers working below or even above the rectenna:
"In summary, teratogenic (fetal and baby development) effects of microwaves appear to occur reliably only at relatively high power-density levels, probably greater than 23 mW/cm2. In relation to the problem of SPS, it appears very likely that neither the ordinary level of exposure of humans (0.01 to 1.0 mW/cm2) nor the maximum level (23 mW/cm2) would cause any teratogenic effects in humans." (121)
"Within the rectenna area of SPS, neither the exposure ... nor the maximum exposure (23 mW/cm2) has any realistic probability of inducing [a serious health problem] in workers in the area." (122)
"For humans and animals outside the SPS rectenna site, it would seem that effects on the nervous system are unlikely. Beneath the rectenna panels, the power density is also probably too low to expect effects on the nervous system." (124)
"Microwaves would have no effect on evoked [brain voltages] or EEGs [i.e., electroencephalographs]. For ordinary exposure within the rectenna area (0.1 to 1.0 mW/cm2) there is little or no probability of an effect on either blood-brain barrier or brain histology [i.e., the microscopic structure of tissue]." (125) (There was a report on the effects of certain modulated microwaves on the blood-brain barrier that was read far and wide, unrelated to SPSs.)
"Workers in the rectenna area exposed at the ordinary power density level (0.01 to 1.0 mW/cm2) would probably not experience any effect on performance of trained tasks or speed of learning..." (126)
"Continuous-wave microwaves have no effect on cell membranes or membrane-bound enzymes except that produced by temperature rise..." (130)
"Workers in the rectenna area of SPS exposed at the ordinary power density of microwaves ... would not be expected to show any endocrine [i.e., gland secretion] changes resulting from the exposure." (131)
"[M]icrowave irradiation produces a metabolic adaptation to heat load and a change in serum lipids and proteins... Workers in the rectenna area of the SPS would probably show changes in serum protein levels similar to those reported by Pazderova et al. at both the ordinary (0.01 to 1.0 mW/cm2) and maximum (23 mW/cm2) power-density levels of exposure. There is no evidence that this effect would have any significance for human health." (129)
"Workers who are on medication might be subjected to enhanced action of the drugs at either the ordinary or the maximum power density level." (126)
"[W]orkers exposed to the radiation at ordinary power density levels (0.01 to 1.0 mW/cm2) would probably exhibit no changes in immunological response, particularly if the exposure occurred rather irregularly. If the exposure occurred regularly on a five-day-a-week schedule, there might be some changes in immune responsiveness." (127) It did not say whether the changes might be a stronger or weaker immune system. A warmer body tends to ward off colds. That's why you run a fever when you're sick -- it's a defense mechanism by your body. It's good to stay warm. Some cultures have a history of inducing artificial fever in sick people by wrapping them up.
"... no effect on the immune system could be expected for the general population off the SPS rectenna site." (128)
The EPA turned up nothing worse than the above.
At the other extreme, the EPA has turned up a long list of problems and serious concerns with coal-powered electricity plants, mines, and waste disposal, and the same for nuclear power. Even hydroelectric dams damage the environment, with ecosystem flooding upstream and fish migrations cut off.
The SPS looks like the most environmentally safe large scale source of energy we've ever considered.
Still, we can expect sensational press reports regarding the safety of the microwave beam, so let's look at the most salient topics -- pregnant mothers and birds flying through the beam. They were both studied.
Monkeys were used to look for any effects of 2.45 GHz microwaves during pregnancy and post-natal development, due to their similarities to man in pregnancy and post-natal development.
In the first study, 41 pregnant monkeys were exposed to the SPS beam beginning in the second trimester of the 7-month pregnancy, and continued after birth for 12 months for the babies and 6 months for the mothers. (Nursing is 6 months for monkeys.)
There were 4 groups of monkeys: those exposed to 0.1, 1.0 and 10 mw/cm2, and those exposed to no microwaves. In this first study, they were exposed for 3 hours per day, 5 days per week.
A variety of biological and behavior measures were monitored in both mothers and offspring. "These included weight changes, behavior during irradiation, perceptual-motor development of infants, maternal care, urinary catecholamines, plasma cortisol, PHA-stimulated response of peripheral lymphocytes, and different aspects of electroencephalographic activity."
"None of these measures differed in any systematic way among either dams [i.e., mothers] or offspring of the various treatment groups." However, "in contrast to these results, a greater number of offspring died in the group exposed both pre-and postnatally to 10 mW/cm2 than in any of the other groups." (133)
For comparison, the annual mortality rate during the first year of life for nonexperimental monkeys in the institute's colony over the previous 5 years had averaged 20 to 25%. In this experiment, 22% died in the 0.1 mW/cm2 group, 17% in the 1.0 mW/cm2 group, 56% in the 10 mW/cm2 group, and 0% in the control group of 8 monkeys. "In all but one case, the deaths of infants were completely unexpected and occurred without prior warnings. In each case, the dead infant was found in his home cage in the morning. The only infant that did not die suddenly was in the 10 mW/cm2 group exposed pre- and post-natally; it died when it was 177 days old, after having become gradually weaker over a 9-day period. Gross necropsies were performed on only four of the nine infants that died, and in no case was the cause of death obvious."
Look bad? Word got around on this study, and even I thought I may have missed something in the theory, though the statistics were not that solid. To nonscientists, things looked dismal, but there's a lesson to learn here: All scientific studies need to be done properly and verified. So there was a second study, done on a bigger scale, and performed more carefully.
"Because of the small number of subjects in the different treatment groups the significance of these mortality figures were questionable at the end of the study. Thus, in order to provide a more definitive answer as to the relative safety of pre- and postnatal exposure to 10 mW/cm2 equivalent, a subsequent experiment was undertaken with a larger population of animals in which offspring viability at 10 mW/cm2 was compared with that of sham exposure at 0 level."
The second study also properly irradiated them from the first trimester of pregnancy, the most sensitive for babies.
"In this latter study pregnant monkeys were irradiated for 3 hours daily, 7 days/week beginning in the first trimester of pregnancy in the same chambers used in the first study. After parturition, dams were irradiated with their offspring for 6 months; then the offspring were irradiated alone until 9 months of age... results obtained ... have not verified the original mortality findings. Moreover, as found before, both the general health and growth of offspring did not differ from controls." (135) I heard and found no bad news on these monkeys over time.
In the latter study, those monkeys not exposed to the microwaves actually had more stillbirths and deaths than those exposed to microwaves...
"... Thus, based on these last results, it would not appear that SPS frequency microwaves at power levels of 10 mW/cm2 are lethal to primate offspring chronically exposed pre- and post-natally" unlike the conclusions that some may reach from the first study.
It should be stressed that the general public will be exposed to microwave levels more than a thousand times less than the above, and even SPS workers will not get the above dose.
Birds flying through the beam
Birds will get the biggest exposure to the beam.
Birds are particularly sensitive because their high metabolism during flight can put them at their thermal limit during summer. (Fortunately, they usually migrate during cool weather.) Also, the 2.45 GHz beam has a wavelength near the size of birds, which makes them more absorbant (a phenomenon called resonance). The question hence focusses on the effects of the beam on a summer day, and how well birds can regulate their temperature.
The U.S. Environmental Protection Agency (EPA) studied the effects of SPS beams on birds. "Studies [were conducted] on the effects of acute and chronic exposure to 2.45 GHz fields on the behavioral and navigational capability of birds. Thus far, no major effects on behavior from 1-100 mW/cm2 fields have been detected." (137) "Generally, no statistically significant effects have been detected at power densities of 0.1 to 25 mW/cm2." (138)
The EPA SPS studies are not the only ones. Numerous other documented studies also exist on birds roosting and nesting in high power (above 23 mW/cm2) microwave radar and communications antennas, including the horn, with no apparent effects. (139)
The single most extensive study into 2.45 GHz radiation effects on birds was conducted in 1981, a late contract by EPA in the SPS program. These experiments were designed to provide, where possible, dose-response data for a variety of different behaviors and physiologic aspects, including thermoregulatory behavior (including in flight in a wind tunnel), aversion and attraction to beams, migratory orientation, reproductive behavior and reproduction itself, social interaction, foraging (food search and manipulation), molting (the cyclic loss and replacement of feathers), and lethality. A number of appropriate species were studied.
The reporting is generally for power densities higher than the 23 mW/cm2 peak in the center of the baseline SPS beam. It appears that the 23 mW/cm2 power density did not affect the birds much, but doubling that power density did affect the birds alot.
Each bird's body temperature (1 to 1.5 cm deep) was monitored continually before, during and after exposures to various energy densities. Large birds had more difficulty getting rid of excess heat. Also, orientation of the bird with respect to the polarity of the electric field of the beam was a significant factor in heating. In warm air, birds opened their mouths wide for breathing (gaping). Heat stress and strong panting began for some species at about 50 mW/cm2 and 24C (75F), with some House Finches eventually dying in these conditions. Blue Jays also had serious problems. Some species were fine.
Lethality studies used Dark-Eyed Juncos, but they didn't begin experiencing thermal stress until about 100 to 130 mW/cm2, and lethality for half of them began at 160 mW/cm2 after 7 minutes.
Wind tunnels were built with electric-shock cages to test birds in flight, so they couldn't land when they felt they were getting too hot. 2.45 GHz beams of various energy densities irradiated the flying area, and the temperature and humidity of the air cycled through the fan was varied. The wind speed in the cage was 37 km/hr (23 mph). A number of trained Budgerigars, a species which is relatively highly absorbant to 2.45 GHz radiation, were chosen for the wind tunnel experiments.
"When irradiated by 50 mW/cm2 microwaves, birds began to show high levels of stress at ambient temperatures above 26C [79F] and demonstrated an inability to fly for 10 minutes at air temperatures above 32C [90F]. At air temperatures above 33C [91F], budgerigars required at least 10 minutes to recover fully after flights involving exposures of 50 mW/cm2.
Budgerigars irradiated during flight generally showed higher body temperatures than did birds flown without microwaves when air temperatures were above 28C [82F]. Based on these data at air temperatures above 28C, and vapor pressures between 17 and 23 torr [i.e., a high relative humidity of 65 to 88%, lower at higher temperatures, e.g., 35 to 47% at 38C or 100F], a microwave field of 50 mW/cm could impair bird flight in the field, forcing the bird to engage in thermoregulatory behaviors and land prematurely. The long post-flight cooling period might adversely affect a bird's ability to forage or escape predators. A 50 mW/cm>2 power density is approximately equal to an 8C [14F] rise in ambient temperature to a flying budgerigar. A 25 mW/cm2 power density should approximate the effect of a 4C [7F] rise.
"During conditions of thermal stress, the birds dropped their legs to cool off by exposing their toes and tarsa-metatarsus to the air stream, in addition to flying with their mouths open."
Wintertime is hard on birds, and it has been speculated that rectennas would attract and benefit birds in the winter. Cold conditions were not studied, but it was found that birds knew what's hot and what's not in the beam.
Aversion/attraction tests were conducted by varying the power densities in cages, from zero to 10, 25 and 50 mW/cm2. Blue Jays exhibited an aversion to all three power densities by perching more frequently in or near the zero radiation areas. House Finches exhibited attraction to the 10 mW/cm2 areas over the zero radiation areas, but avoided energy densities of 50 and 25 mW/cm2. That's probably because they're small, and small animals get cold easily -- bigger animals are in effect like small animals with more insulation.
This showed that birds seem to have the good sense to know when they're getting into a hot area, and to get out and find a more comfortable area when given the choice.
In the real world, avoidance or attractive behavior would depend upon temperature, humidity, wind speed, sunshine, and rain or snow.
Birds "molting" (i.e., seasonal loss and replacement of feathers of migratory birds), which involves sensitive mechanisms of the endocrine and autonomic nervous systems, was studied under SPS beam conditions to mock nesting near or on the rectenna, at power densities of 1, 10, and 25 mW/cm2, continuously for 110 to 150 days. House Finches were chosen as the best species for study. All birds completed the molt, with the 1 and 10 mW/cm2 birds doing so at essentially the same time as non-exposed birds. The birds exposed to 25 mW/cm2 completed their molt a little slower, perhaps due to significant microwave heating which induced their system to delay adding heat insulation (i.e., feathers), which would show they can adapt.
Foraging (i.e., the ability to search for and manipulate food) appeared unaffected by the beam. Foraging was studied for the White-Throated Sparrow under acute and continuous (up to 4 weeks) exposure, from zero to 25 mW/cm2 power density and under different temperature and humidity environments. Though "foraging efficiency" was found to be influence by changes in temperature and relative humidity, birds exposed to microwaves as compared to non-microwave-treated birds exposed to the same temperature and humidity conditions "showed no significant differences in foraging efficiency between pre-exposures, exposures and post-exposure periods despite significant differences in ambient room and exposure chamber temperatures."
Migratory birds were studied for when they would pass over a rectenna area. Migratory birds use the Earth's magnetic field, the sun, visual landmarks, meteorological cues (e.g., wind and temperature), and/or hearing, varying between species and their domain on Earth. In a planetarium, birds act the same whether or not a line of solar power satellites was superimposed on the stellar background. (A giant SPS could be as bright as Venus in the sky.) However, under both unblocked and blocked views of the sky, the microwave-treated birds showed a dispersion around the correct average direction of orientation. Once outside the beam, they would be OK again.
What about birds who nest on top and in the middle of a rectenna?
Reproductive behavior during mating and success of mating under continuous exposure of 25 mW/cm2, using Zebra Finches, showed "no significant difference in the number of fledglings produced by the irradiated and control [i.e., non-irradiated] pairs of birds." (143)
Quail eggs (Coturnix Quail) were irradiated by 25 or 50 mW/cm2 radiation, each series consisting of 38 exposed eggs and three non-exposed groups of 38 eggs each, the three control groups being exposed to different air temperatures. The microwave-exposed eggs were irradiated for 30 minutes twice per day, with egg temperatures probably not exceeding the desired warmth as regulated by mothers. The hatchability of eggs did not differ from non-exposed eggs, nor did the rate of growth of chicks differ significantly. No evidence of teratogenesis was observed, as no chicks had deformities or weaknesses.
The effects of behavior and flock dominance heirarchy was assessed using White-Throated Sparrow and Dark-Eyed Junco flocks. All birds were marked with identifications, and time was allowed for heirarchy establishment. Periodically, all birds were caged and certain ones were irradiated consistently at different levels up to 25 mW/cm2, after which all birds were uncaged and observed in detail for affects on individual social behavior. No effect on heirarchy was observed, though some appeared to have a change in their level of aggression after exposure of 25 mW/cm2.
At the end of the experiment, "individual birds receiving 25 mW/cm2 were examined for altered behavior, as well as a variety of different somatic and cisceral reflexes and then killed ... each bird was observed for changes in muscle tone, righting reflex, vestibular function, pupillary response to light, corneal opacity and response to pain (cornea)." "At necropsy, major organs were examined and sections prepared for histological examination. No notable differences were observed in the incidence and severity of lesions between control and microwave treated birds ... an examination of the microwave irradiated and control birds revealed no observable gross or histopathological changes in any of the major organs ...
"No differences were observed between control and irradiated birds."
Several past studies on various insects under microwaves at power densities near the SPS had turned up no effects. (145) However, honey bee hives were specifically researched in a 2.45 GHz SPS beam, since honey bees are the major insect pollinator of wild flora and cultivated crops that account for one-third of the USA's food supply. (147) Bees are also sophisticated insects.
Things like reproduction, longevity, navigation, foraging, memory, thermoregulation of the nest, brood rearing, and societal activities were sensitively monitored.
"No evidence has been found to suggest that 2.45 GHz continuous wave microwves at selected power densities from 1-50 mW/cm2 have biological effects on honey bees." (148)
Studies were also done on other biota. For example, studies into the effects of 20 mW/cm2 2.45 fields on the immunology and hematology of small mammals turned up no effects. (149)
Even ultra-sensitive yeasts were exposed to a continuous beam at energy densities of more than 100mW/cm2, and microscopic observations found no mutagenetic or other non-thermal effects.
If you're still afraid, you can cover the inside of your roof with foil to reflect the feeble level of far field microwaves. At the very least, it might prevent psychosomatic symptoms.