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This article provides an overview of electromagnetic radiation to help readers better understand its properties and potential effects.
Electromagnetic waves are fundamental to modern life, especially in the 5G era of IoT. Devices like smartphones, computers, tablets, and smartwatches are common examples of their application. However, electromagnetic waves are also a form of electromagnetic radiation. The term "radiation" often causes concern, largely due to the known dangers of nuclear radiation, such as the events at Chernobyl.
Electromagnetic radiation can be classified into two types: ionizing and non-ionizing. The electromagnetic spectrum is vast, ranging from long-wavelength radio waves to short-wavelength gamma rays. This includes radio waves used for broadcasting and wireless communications, microwaves, infrared, visible light, ultraviolet light, X-rays, and gamma rays. Non-ionizing radiation does not have enough energy to remove electrons from atoms or alter molecular structures. In contrast, ionizing radiation can remove electrons from atoms, changing molecular structures and directly damaging cells in organic matter. Examples of ionizing radiation include ultraviolet light, X-rays, and gamma rays. The radio waves and visible light encountered in daily life are forms of non-ionizing radiation, which pose a lower risk to the human body. However, their effects should not be entirely disregarded.
Potential Health Effects of Mobile Phone Radiation
The paper "Cell phones: modern man's nemesis?" outlines several potential health effects of mobile phone electromagnetic radiation.
Cardiovascular System Effects
In a 1998 experiment by Braune et al., human volunteers exposed to 900 MHz RF-EMW for 35 minutes showed an increase in blood pressure (both systolic and diastolic). The blood pressure rose by 5-10 mmHg, accompanied by a significant reduction in capillary perfusion due to vasoconstriction.
Effects on Sleep
An experiment by Huber et al. in 2000 found that while there were no significant changes in overall sleep quality, 30 minutes of exposure to 900 MHz electromagnetic radiation significantly increased the time it took to fall asleep, potentially leading to insomnia with long-term exposure.
Impact on Neurohormone Secretion
Increased Cancer Risk
The carcinogenic potential of mobile phone radiation is one of the most controversial areas of research. Addressing public concern, Hardell et al. (2006) conducted an epidemiological questionnaire-based study and concluded that astrocytoma (Grade III-IV) and acoustic neuroma showed a positive correlation with mobile phone usage.
One case study involved a woman with multifocal breast cancer. This was unusual as she had no genetic predisposition. Her doctors noted a strange pattern in the cancer cells that matched the outline of her mobile phone. The woman confirmed she frequently carried her phone in her bra, leading them to connect the device to her cancer.
Impact on Male Fertility
Although the effects of mobile phone electromagnetic radiation on the male reproductive system are not definitively established in many reports, a 2009 study examined 150 men who regularly wore their phones on their belts. Scientists found that these men had reduced bone mineral density in the pelvic bone on the side where they carried their phones.
Why Does Weaker Signal Mean Higher Phone Radiation?
Mobile phones achieve wireless communication by connecting with base stations, which then route signals to the intended recipient. This process involves two main sources of electromagnetic radiation: the downlink signal from the base station to the phone, and the uplink signal from the phone to the base station. This means that during a call, we are exposed to radiation from both the base station and the phone itself. Public concern often focuses on base station radiation, leading to instances where communities have demanded their removal due to health fears.
Let's first examine base station radiation. For a typical 5G base station, the average power per channel is about 5W. With 64 channels, the total power is 320W, or approximately 55 dBm. While this seems high, electromagnetic wave path loss is inversely proportional to the square of the distance.
In reality, the radiation from 5G base stations is very low. According to China Telecom, 5G base station power and radiation levels are well within the national safety limits. Measurements taken 10 meters from a 5G base station show radiation levels of approximately 1-1.5 μW/cm2.
However, the impact of a mobile phone on the human body is more significant due to its close proximity. According to the latest 5G mobile phone transmission power standards defined by 3GPP for Sub-6 GHz spectrum: Power Class 3 is 23 dBm, and Power Class 2 is 26 dBm. Power Class 1, which would theoretically be higher, is not yet defined. Current 5G commercial use primarily involves eMBB services on Sub-6G bands. The following describes the maximum transmit power for mainstream 5G bands (e.g., FDD n1, n3, n8; TDD n41, n77, n78) in six different scenarios.
- 5G FDD (SA mode): Max transmit power is Class 3 (23 dBm).
- 5G TDD (SA mode): Max transmit power is Class 2 (26 dBm).
- 5G FDD + 5G TDD CA (SA mode): Max transmit power is Class 3 (23 dBm).
- 5G TDD + 5G TDD CA (SA mode): Max transmit power is Class 3 (23 dBm).
- 4G FDD + 5G TDD DC (NSA mode): Max transmit power is Class 3 (23 dBm).
- 4G TDD + 5G TDD DC (NSA mode): Max transmit power is defined as Class 3 (23 dBm) in Release 15, but can be supported up to Class 2 (26 dBm) in Release 16.
This means that the weaker the signal, the higher the power the phone must transmit to communicate with the base station. When the signal is poor, your phone operates at maximum power, which can be up to 26 dBm (398 mW). This is approximately 1000 times the radiation power received from a base station at a 10-meter distance. According to tests by telecom operators, a phone in standby mode has a radiation value of about 17.1 μW/cm2, which increases to about 93.1 μW/cm2 during a call. The farther the phone is from a base station (and thus the weaker the signal), the higher its radiation value during a call. Therefore, from a purely radiation exposure perspective, the phone itself is a much more significant source than a distant base station.
Radiation Standards and Context
Even at maximum power, mobile phone radiation remains within safe limits. Industry experts in China have noted that the country's mobile communication base station radiation standards are based on IEC recommendations. Standards in the US, EU, and Japan are 12 to 15 times less strict. This is often because base station siting is more difficult in those regions, requiring larger coverage radiuses and higher transmission power. The specific mobile communication base station radiation limits are:
- United States and Japan: 600 μW/cm2
- European Union: 450 μW/cm2
- China: 40 μW/cm2
In practice, base station radiation is far below China's standard, and even further below European and American standards. With the denser deployment of 5G, each base station can operate at lower power. Higher frequencies also lead to greater propagation loss. Measurements show that radiation 10 meters from a 5G base station is about 1-1.5 μW/cm2. Furthermore, base stations use adaptive power control to reduce their transmit power for terminals that are close by.
Base station radiation levels are also lower than those of many common household appliances. For example, a microwave oven can have a radiation level of 268 μW/cm2 at a distance of 1 meter. China's base station radiation standard is only about 1/6 of that level.
Therefore, base stations are not the primary source of concern for everyday radiation exposure. It is more important to be aware of the radiation sources in our immediate vicinity.
