• Print
  • Downlaod
  • A- A A+
How Much Do You Know about EM Radiation?: About EM Waves
With the widespread use of wireless networks, electromagnetic radiation in the microwave band has become ubiquitous in our living environment. (photograph provided by Wu, Mei-chih)
With the widespread use of wireless networks, electromagnetic radiation in the microwave band has become ubiquitous in our living environment. (photograph provided by Wu, Mei-chih)

Some news about Wi-Fi that has spread from Denmark to Taiwan has panicked many Internet users: Five Danish high school girls performed an experiment indicating that Wi-Fi radiation may kill plants! The reporter who wrote this story also added: "According to domestic experts, long-term exposure to Wi-Fi radiation may cause cancer!" Sensational stories like this are once again fanning people's fear of radiation. Radiation—which consists of electromagnetic waves—is actually a ubiquitous part of our living environment. Do these waves actually pose a constant threat to human health?

Elegant mathematics, wonderful electromagnetic waves

  Mathematics is the soul of science, and the deeper one delves into science, the more mathematics is needed for a complete description. The mid-19th century scientist James Clerk Maxwell developed Maxwell's equations, which are of profound importance to the electrical and electronics industries. One of the most interesting things about these equations is that they predicted the existence of electromagnetic radiation before it was discovered experimentally.
Prof. Ma Tzu-chuang of the Department of Electrical Engineering at National Taiwan University of Science and Technology has extensively researched electromagnetic radiation, and one of the things he likes best about electromagnetic waves is that they have "elegant mathematics." According to Prof. Ma, "It is wonderful that the behavior of electromagnetic waves can be described and predicted using mathematics alone. Many fields of science lack this extraordinary feature."

In spite of its aesthetic beauty, this field of science nevertheless perplexes most of even the smartest students. Prof. Ma noted with touch of resignation, that out of the students in his Department of Electrical Engineering, only five in a hundred can fully grasp the complex and powerful mathematical portrayal of electromagnetic waves, and even fewer can see the close linkage between complex mathematical equations and physical phenomenon involving electromagnetic waves in space.

The ubiquity of electromagnetic waves 

As their name suggests, electromagnetic waves consist of electrical and magnetic fluctuations. In simple language, when electric and magnetic fields vary with time, they will give rise to waves in space; these waves carry energy, move at the speed of light, and do not require a medium to sustain their transmission.

Electromagnetic radiation is only a general term, and actually encompasses a wide variety of waves. In practice, electromagnetic waves are classified on the basis of their vibrational frequency. Frequency is given in units of Hertz (Hz), which represents the number of vibrations per second. A low frequency implies relatively few vibrations per second, and vice versa. Frequency has an important physical characteristic: The amount of energy carried by each unit of electromagnetic radiation is proportional to its frequency.

These unseen, unfelt electromagnetic waves of different frequencies actually fill our living environment. As an example, because power transmission lines and transformers use 50-60 Hz ultra-low frequency electric currents to generate electromagnetic radiation,  our electrical appliances and products tend to use the same frequency, or even a multiple of that frequency (such as 150-180 Hz), and thus produce electromagnetic radiation at that frequency.

If we start to move toward higher frequencies, we reach the 106-108 Hz band, which encompasses such commonly encountered forms of radiation as AM and FM radio waves, the identification signals used by the Taipei Metro's "Easy Card" RFID system, and digital TV signals. For their part, 2G, 3G, and 4G mobile phones, Wi-Fi wireless networks, and Bluetooth all use microwave radiation in the 109-1010 Hz band. It's probably now apparent that although many of the household appliances, communications equipment, and signal transmission devices that we depend on in our daily lives emit various kinds of electromagnetic waves, they also provide indispensable services.

If we then shift our attention to even higher frequencies, the 1011-1016 Hz band contains far infrared, infrared, visible light, and UV radiation wavelengths, which can induce various responses in our sensory organs. We can only see radiation in the visible light waveband (such as a rainbow) with our naked eye, While infrared and UV radiation cannot be seen, their effects can still be sensed. For instance, infrared causes us to feel heat, while UV will give us sunburn. It is worth mentioning that if the frequency of electromagnetic radiation is as high as or higher than the UV waveband, the radiation will cause a certain amount of injury to the unprotected human body.

Continuing to yet higher frequencies, we reach the point where, in accordance with quantum physics' wave-particle duality, electromagnetic waves acquire the characteristics of particles. When frequency exceeds 1016 Hz, we term electromagnetic waves "ionizing radiation" (electromagnetic waves with a frequency of under 1016 Hz can similarly be termed "nonionizing radiation"). The electromagnetic waves comprising ionizing radiation have high energies, and are sufficiently powerful to be able to penetrate the human body. For instance, the x-rays commonly used in medicine are a form of ionizing radiation. In addition, γ (gamma) radiation, which has even greater energy, consists of byproducts of radioactivity decay, and is even more hazardous.

These ultra-high-energy electromagnetic waves can easily penetrate the human body. When they pass through cells, the great energy of the radiation will break DNA chains, possibly cause cellular mutations, and severely affect health. It stands to reason that exposure to this radiation is very hazardous.
In summary, because the microwave radiation the public commonly encounters in everyday life has a relatively low frequency, and consequently carries only one ten millionth of the unit energy carried by hazardous UV radiation, the potential harm of microwave radiation is simply not sufficient to cause worry.

Are electromagnetic waves really hazardous to humans?

Since they are so all-pervasive in our living environment, are electromagnetic waves harmful to humans? Addressing this question, Prof. Ma provides several lines of thinking: First, it is important to understand clearly the type of electromagnetic wave and its intensity. While ionizing and nonionizing radiation are both types of electromagnetic waves, but the former have great energy, can easily penetrate the body, and can destroy or damage cells. In contrast, there is still no scientific evidence that nonionizing radiation has been proven to have any harmful effect on the human body.

Even if electromagnetic waves have a similar frequency, they can still have very different effects on the human body if their intensity differs significantly. For instance, while microwave ovens and Wi-Fi base stations both use 2.45 GHz microwaves (note: 1 GHz = 109 Hz), microwave ovens use roughly 100,000 times the power of a Wi-Fi base station when cooking foods. which is why microwave ovens are able to quickly heat foods, while Wi-Fi base stations have extremely little effect on living organisms, because of their very low power. The effects of these two radiation sources therefore cannot be compared on equal terms, and the public should be fully aware of this distinction.

Secondly, according to evidence accumulated by large research teams in many parts of the world over the course of many years, the one and only effect on the human body of the electromagnetic waves used by today's microwave communications is a very minor heating effect. Taking voice calls on a cell phone as an example, cell phones can only achieve several tenths of a degree of temperature increase in normal use. To say that such a tiny temperature change may injure the human body is excessively alarmist, and lacks any rigorous scientific evidence. Furthermore, some people even claim that far infrared, which has a higher frequency and greater energy per unit of radiation, can be used for medical heating, and consumers have avidly purchased products that offer a far infrared therapeutic effect. Isn't there a big contradiction between these two situations?!
Another major issue is the problem of rigorous scientific verification. Prof. Ma therefore feels a high degree of skepticism toward the Danish high school students who claim they have experimentally proven that Wi-Fi electromagnetic waves can kill plants. Ma believes that all scientific experiments must have a very rigorous variable control design, and all inferences and results must be able to withstand repeated examination if they are to have value.

With regard to the Danish experiment, it remains uncertain whether the various environmental variables were adequately controlled during the experimental process. These variables include the length of time the plants are exposed to light, the number of times they were watered each day, and the ambient temperature, all of which may affect the plants' survival. Because of this, he cannot determine from the brief online account whether the Wi-Fi signal was actually connected with the inhibition of the plants' growth, and believes that the hasty conclusion that "electromagnetic waves in the form of Wi-Fi signals can kill plants" is merely sensationalist talk.

Ma emphasizes that there is still no scientific evidence that nonionizing radiation is harmful to humans. Especially during the most recent 20 years, when mobile communications have become ubiquitous, general public health statistics should gradually reveal any statistical concerning the foregoing health issues. Nevertheless, a look at research in many countries does not turn up any conclusions that nonionizing radiation (especially in the microwave waveband) is harmful to human health. As a result, the public has no need to worry about the effects of electromagnetic waves from cell phones or microwave equipment.

Prof. Ma noted that there are countless other factors in our lives that can exert more direct and more severe effects on health, and food, air, and water quality are just a few examples. Especially in the wake of major food safety incidents during the last few years, most people clearly understand that the consumption of unwholesome ingredients and bad eating habits can be extremely harmful to the human digestive system. Furthermore, it has also been found that the particulate air pollution brought to Taiwan by the northeastern monsoon wind may have a very close relationship with increases in certain respiratory diseases.

Because it is extremely difficult to eliminate the influence of many other disease-causing factors in daily life (since people must also eat and breathe) in large-scale statistical experiments seeking to determine whether nonionizing electromagnetic radiation is harmful to humans, Prof. Ma believes that it will be very difficult to obtain more persuasive experimental data in the future. On the other hand, he finds it very hard to imagine that electromagnetic waves have a greater and more significant influence on health than tainted foods and fine particulate matter (PM 2.5) in the air.

The National Communications Commission (NCC) and electromagnetic radiation

Finally, Prof. Ma also discussed electromagnetic radiation frequency management tasks. Because electromagnetic waves have such a broad frequency range, and have such diverse applications, how to ensure that applications will not overlap and communications are not subject to interference? The National Communications Commission (NCC) currently bears responsibility for this important mission, and is the country's highest authority in charge of frequency spectrum management. In order to avoid mutual interference, the NCC must clearly determine which bands are exclusively for use by mobile communications, which bands are for radio broadcasting, and which bands are for use by defense and space applications.

It's worth noting that, in order to avoid unnecessary controls, an international consensus has been reached to make certain specific bands available for use by industry, scientific research, and medicine, and these are known as ISM bands. This also ensures that companies' products and the public have less need to apply to the government to use certain channels. Commonly seen ISM bands include 900 MHz, 2.4 GHz, 5 GHz, and 60 GHz. Thanks to the establishment of ISM bands, we can easily set up and freely use Wi-Fi wireless network base stations and Bluetooth, etc. in our homes.

In summary, electromagnetic waves pervade our living environment, and the widespread use of cell phones, mobile Internet, and various non-contact sensor chips have made various types of electromagnetic radiation even more ubiquitous. While it is easy to be afraid of things that we cannot see, but Prof. Ma reminds us that we should maintain a rational, scientific attitude when confronting these unknown factors, and seek to understand them; this is much more sensible than jumping to rash conclusions and giving free rein to panic.

Translated by Glen E. Lucas
Date:8 Jun 2016

996 visits