Shulou(Shulou.com)11/24 Report--

Hello, everyone, this is Radio Frequency School.

Today, we will popularize the knowledge about electromagnetic radiation. Through this article, I hope that we can better understand electromagnetic radiation and better protect ourselves.

When we talk about electromagnetic waves, we talk more about how convenient electromagnetic waves have brought to our lives, especially in the 5G era of the Internet of everything, our mobile phones, computers, ipad, children's watches, are the best examples of electromagnetic wave applications, but also the nearest electromagnetic wave. But when we give electromagnetic waves another name, everyone may feel uncomfortable. In fact, electromagnetic wave is a kind of electromagnetic radiation. The word radiation is particularly disconcerting. Students who have seen the American TV series Chernobyl must be frightened by the great harm that nuclear radiation brings to people.

Electromagnetic radiation can be divided into two cases, one is ionizing radiation, the other is non-ionizing radiation. In a broad sense, electromagnetic radiation includes a very wide range of frequencies and a wide range of wavelengths, ranging from tens of meters of long wave radiation to gamma rays with only a few emitters. This includes radio waves and microwaves used in television broadcasting and wireless communications, as well as ultraviolet, infrared, visible light, X-rays, gamma rays and so on. Non-ionizing radiation can not separate electrons from the atoms of an object and does not change the molecular structure of the object, while ionizing radiation can separate electrons from the atoms of the object, change the molecular structure of the object, and directly cause damage to the cells in organic matters. for example, ultraviolet, X-rays and gamma rays are ionizing radiation. Fortunately, the radio waves and visible light that we are most exposed to in our daily life belong to non-ionizing radiation and do less harm to the human body. But you can't turn a blind eye.

What harm does the radiation from mobile phones do to the human body? The article "Cell phones: modern man's nemesis?" lists the possible types of damage to the human body caused by electromagnetic radiation from mobile phones, as shown in the following figure:

Harm to cardiovascular system

In a 1998 experiment, Braun et al exposed human volunteers to RF-EMW and reported elevated blood pressure (systolic and diastolic) at 900 MHz exposure to RF-EMW35. The blood pressure increased by 5 °10 mmHg, accompanied by a significant decrease in capillary perfusion due to vascular consumption.

Harm to sleep

Although Hu Bo et al did not find any significant change in sleep quality in the 2000 experiment, exposure to 900MHz electromagnetic radiation for 30 minutes would significantly increase the time to fall asleep and cause insomnia for a long time.

Affect the secretion of neurohormones

Increase the probability of cancer

Carcinogenic potential cell phone radiation is one of the most contradictory aspects of various studies conducted in several groups. Concerned about the public concern that cell phone exposure may lead to cancer, Hardell et al (2006) conducted a study based on an epidemiological questionnaire and concluded that astrocytoma (III-IV) and acoustic neuroma do show a positive correlation with cell phone use.

In one case, a woman had multifocal breast cancer. This is strange because she has no tendency to suffer from cancer. Although this is still possible, her doctor noticed a strange pattern in her cancer cells. On closer inspection, I found that it was the outline of her mobile phone. It's strange for them. However, the woman explained that she often keeps her phone in her bra. So they can connect these dots from her cell phone to her cancer cells.

Affect the reproductive function of men

Although the effects of electromagnetic radiation of mobile phones on the male reproductive system have not been clarified in many reports. But do you dare to do this experiment? In 2009, there was a study of 150 men who tied their phones to their belts for long periods of time. The scientists found that in these men, the bone mineral density of the pelvis on one side of the mobile phone was reduced.

Why is the weaker the signal, the greater the radiation from the phone? Why can our mobile phones communicate wirelessly? The main reason is that the mobile phone can communicate with the base station, and then the base station transmits your signal to the phone you want to call.

The electromagnetic radiation mainly includes the downlink signal sent by the mobile base station to your mobile phone and the uplink signal sent by the mobile phone to the mobile base station. In other words, when we make a phone call, we will be exposed to two aspects of electromagnetic radiation, one is the radiation from the base station, the other is the radiation from the mobile phone. With regard to the radiation of the base station, everyone may be more concerned about it, so there are a lot of demolition of the base station. After all, life and health come first, and I really panic in the face of this thing on top of my head.

Let's talk about the radiation of the base station first. For the current 5G base station, the average power of the order channel is about 5W, while that of the 64 channel is 320W, which is about 55dBm. It looks big, but because the path loss of the electromagnetic wave is proportional to the square of the distance

Where d represents distance, f represents frequency, and c represents the speed of light. Path loss varies with distance and frequency.

According to the above formula of path loss, let's take a look at how much radiation a 5G base station operating at 2.6G would ideally do to us. The following is an ideal power value based only on the path loss in free space. We see that even if it is only 10 meters away from the base station, the radiation from the base station reaches the human body only 0.2 milliwatts.

In fact, 5G base stations have less radiation to the human body. China Telecom said that the power and radiation of 5G base stations are already very small and are within the safe value set by the state. At present, the measured radiation within 10 meters near the 5G base station is about 1-1.5 uW / cm.

However, mobile phones have a greater impact on the human body, because the distance is closer. For many people nowadays, mobile phones are carried with them anytime, anywhere. According to the latest transmission power standard of 5G mobile phone, according to the definition of 3GPP: in the Sub6G spectrum, the power level 3, the size is 23dBm, the power level 2, the size is 26dBm, and the power level 1, which is theoretically more powerful, has not been defined yet. At present, 5G business mainly focuses on the eMBB service of mobile phones in the Sub6G band. The following article will focus on this scenario, which can be described in six types for the mainstream 5G band (such as FDD N1, N3, and N8, TDD n41, n77 and n78, etc.).

5G FDD (SA mode): maximum transmit power is level 3, that is, 23dBm

5G TDD (SA mode): maximum transmit power is level 2, that is, 26dBm

5G FDD + 5G TDD CA (SA mode): the maximum transmit power is level 3, i.e. 23dBm

5G TDD + 5G TDD CA (SA mode): the maximum transmit power is level 3, i.e. 23dBm

4G FDD + 5G TDD DC (NSA mode): the maximum transmit power is level 3, i.e. 23dBm

4G TDD + 5G TDD DC (NSA mode): the maximum transmission power defined by R15 is level 3, that is, the maximum transmission power that can be supported by 23dBm NSA R16 version is level 2, namely 26dBm.

In other words, in order to communicate with the base station, the worse the signal of the mobile phone is, the more power it needs to transmit. This means that when the signal is poor, your phone's maximum power is about 26dBm, which is equal to 398MW, which is about 1000 times the radiation of a 10-meter base station. In fact, according to telecom tests, the standby radiation value of the phone is about 17.1 microwatts per square centimeter and 93.1 microwatts per square centimeter when talking. The farther away the phone is from the base station, the worse the signal, and the greater the radiation value during the call. So, if you are really worried, it is better to smash your own phone than to demolish the base station.

But please rest assured that even if the mobile phone power increases, the amount of radiation is also within the safe range. Many relevant people in the domestic communications industry have already said that China's mobile communication base station radiation standards are in accordance with IEC standards, while EU standards, American standards, and Japanese standards are 12 to 15 times higher than China's. The reason is that the location of the base station in the above countries and regions is very difficult, the radius of the base station is very large, and the transmission power is also very large. According to national radiation standards for mobile communication base stations, the United States and Japan are 600 microwatts per square centimeter, the European Union is 450 microwatts per square centimeter, and China is 40 microwatts per square centimeter.

In fact, the radiation of the base station is much smaller than the Chinese standard, and much less than the European and American standard. At the same time, the 5G base station is denser, each base station has lower transmission power, higher frequency and greater propagation loss. according to the actual measurement, the measured radiation within 10 meters near the 5G base station is about 1-1.5 microwatts / square centimeter. For the terminals close to the base station, the base station will adaptively reduce the transmission power.

Not only that, the radiation level of the base station is even smaller than that of many household appliances we use on a daily basis. Microwave ovens with relatively large radiation levels are 268 microwatts per square centimeter at a distance of 1 meter. In China, the standard for base station radiation is only 1 milliwatt of microwave oven radiation, which is much lower than that produced by microwave ovens.

So the base station is not scary. More attention should be paid to the sources of radiation around us.

This article is from the official account of Wechat: radio Frequency School (ID:RF_Center), author: RF Carpenter

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