Principle of electromagnetic wave absorption and reflection
[Electromagnetic waves are energy]
What is electromagnetic waves? The most important thing about electromagnetic waves is that they are energy. For example, for infrared light with a frequency slightly lower than visible light. The warmth of the flame is felt by the infrared rays emitted by the flame. The electromagnetic waves around us are much lower in frequency than infrared rays, so the body does not feel as heat when exposed to electromagnetic waves. However, there are a few percent of those who are sensitive to electromagnetic waves, and these people seem to feel electromagnetic waves in their peripheral nerves and brains. In the case of mild symptoms, the author is also, but when you are tired, using your mobile phone will make your hands messy. Wavesafe transmits via the hand instead of reducing head exposure, so naturally the amount to the hands with a lot of peripheral nerves increases as the amount to the head decreases.
Examples of direct action of electromagnetic wave energy include microwave ovens and high-frequency heating furnaces. The 2.45 GHz electromagnetic wave used by the microwave increases the temperature by vibrating water molecules. In the high-frequency heating furnace, an alternating current of 10 kHz to 100 kHz is passed through the coil around the object to be heated, and an induction current is passed through the object to perform joule heating. Rather than heating the object to be heated from the outside, it is directly superheated by the current induced in the interior, so there is little energy loss and it is an excellent method for instantly overheating. For microwave ovens, rewrite the section.
[Electromagnetic waves are waves]
Another characteristic of electromagnetic waves is that they have wave properties. When electromagnetic waves travel through space, the nature of waves appears. Because it is a wave, the characteristics of electromagnetic waves are determined by frequency and wavelength. The relationship between the velocity, wavelength, and frequency of electromagnetic waves in air or vacuum is expressed by the equation: v (velocity) = f (frequency) · λ (wavelength). Since the speed v is constant at about 300,000 km per second, the frequency f and the wavelength λ are inversely related. The frequency f is the number of times a wave repeats per second, and the wavelength is a break of waves. As an easy-to-understand value, the wavelength λ of 1 GHz (gigahertz) electromagnetic waves used by mobile phones is 30 cm. The wavelength of 50Hz alternating current used at home is 6,000km. Since the length of the outer circumference of the earth is about 40,000 km, 50 Hz electromagnetic waves surround the earth with seven or fewer waves.
Even if the same electromagnetic wave is used, if the frequency is changed, the usage and influence will be greatly different. Broadly speaking, frequencies above 1 MHz are used for signal transmission, and below that are used for high-frequency heating, switching regulators, or commercial power transmission such as 50 and 60 Hz.
The characteristics of the space where electromagnetic waves are transmitted are expressed in units called impedance. Impedance is the ease with which electromagnetic waves can flow or the ease with which they pass. The impedance of air and vacuum through which electromagnetic waves propagate is 377 ohms, and this value does not change with frequency. Metal is 0 ohms. Electromagnetic waves are reflected without entering the metal from the air because the impedance value is discontinuous (changes suddenly) between air and metal. The radar uses this principle, and the radar sends electromagnetic waves from itself, and receives the electromagnetic waves that are reflected back when hitting a metal plane or ship, and knows the existence of the other party.
[Principle of antenna]
The amount of reflection of electromagnetic waves decreases as the metal becomes smaller, but the reflection becomes very large for metals with an integral multiple of the wavelength or the same length. This is an example of the strong nature of electromagnetic waves. Here, if the rod-shaped metal is half the wavelength, the characteristic impedance of the rod at that frequency is 377 ohms, which is the same as the wall made of air, and the electromagnetic wave is not affected and remains as it is. Pass through. Therefore, if you cut the middle of the rod and connect the amplifier, it becomes a receiver, and if you connect it with a resistor, the electromagnetic energy is converted into heat and absorbed by the resistor. The half-wavelength bar acts as an antenna. Antennas are most prominent in the nature of electromagnetic waves.
[Relationship between human body and electromagnetic waves]
There are many electromagnetic sources in the UHF band from 300MHz to 3GHz, such as TV broadcasts, police and fire fighting radios, and mobile phones. In particular, it has an impact when you make a call with your mobile phone. A maximum of 0.8 W of electromagnetic wave travels through the head.
The electromagnetic waves used by radar are often reflected from metals of the same length and integer multiples. This can be said to resonate once on a metal of the same length as the wavelength and then radiate again. The adult body is 60% water, but contains salt, so it is the same as a good conductor, that is, a metal. The size of the human body is 60cm around the head, 30cm around the elbow, 90cm around the waist, and an integral multiple of the 1GHz wavelength of 30cm. Each part of the upper body must be long enough to resonate with electromagnetic waves. I understand.
Unlike antenna rods, the human body is thick and should resonate at longer wavelengths. The trouble is that the 800MHz frequency used for calls is 37.5cm, so it will resonate even better. In addition, the electromagnetic wave around 1.5 GHz used in the LTE mode when connected to the smartphone’s Internet is a wavelength that resonates with the infant’s head and body. I want to pay attention to this point.