Frequency, sometimes referred to as pitch, is the number of times per second that a sound pressure wave repeats itself. The units of frequency are called hertz (Hz). Humans with normal hearing can hear sounds between 20 Hz and 20,000 Hz. Frequencies above 20,000 Hz are known as ultrasound.

frequence

Sound waves fall into three categories: longitudinal waves, mechanical waves, and pressure waves. Keep reading to find out what qualifies them as such. Longitudinal Sound Waves – A longitudinal wave is a wave in which the motion of the medium’s particles is parallel to the direction of the energy transport.

Infrasound

20,000Hz

Yes. Sound can absolutely kill you if it’s loud enough. Sound is created by a pressure wave which vibrates particles as it travels in an accordion-like manner. A vibrating source pushes particles forwards with a high-pressure wave.

The most restrictive limits on whole-body exposure are in the frequency range of 30-300 MHz where the human body absorbs RF energy most efficiently when the whole body is exposed.

At 60 GHz, the oxygen molecule becomes highly absorbent of electromagnetic energy, which weakens the 60 GHz signals over distance, keeping them from overshooting their intended target.

In addition to the very low power levels discussed above, 60 GHz systems do not penetrate the human body. As a result, exposure to 60 GHz is very similar to the exposure to sunlight ” but at 1/10,000 of the energy. Lower-frequency emissions penetrate and may even pass completely through the human body.

An experiment conducted by the Medical Research Institute of Kanazawa Medical University found that 60GHz “millimeter-wave antennas can cause thermal injuries of varying types of levels. The thermal effects induced by millimeterwaves can apparently penetrate below the surface of the eye.”

These 60GHz technologies operate in the unlicensed bands and typically operate between 57 GHz to 66 GHz. Within this frequency range, there are 4 channels allocated. Since the wavelength of 60GHz is approximately 5 millimeters, this technology is sometimes referred to as millimeter-wave (mm-wave).

WiGig, alternatively known as 60 GHz Wi-Fi, refers to a set of 60 GHz wireless network protocols. It includes the current IEEE 802.11ad standard and also the upcoming IEEE 802.11ay standard. The WiGig specification allows devices to communicate without wires at multi-gigabit speeds.

High Security and Interference Resistance Before commercial point-to-point radio links became an attractive option for high speed wireless communications, 60 GHz radios have been used for many years in applications requiring a highly secure communications channel, such Satellite-to-Satellite communications systems.

IEEE 802.11ad is an amendment to the IEEE 802.11 wireless networking standard, developed to provide a Multiple Gigabit Wireless System (MGWS) standard at 60 GHz frequency, and is a networking standard for WiGig networks. After revision, the 60 GHz band covers the frequency of 57 to 71 GHz.

Wireless backhaul: Particularly for small cells, operators can use the 60GHz radios to connect small cells to a fiber hub. (See More Startups Target Small-Cell Backhaul.) Wireless bridges: These are useful for providing extra capacity at events, ad-hoc networks, and private high-speed enterprise links.

60 GHz

At 60 GHz, Oxygen molecules in the atmosphere interact with the RF signals to cause significant attenuation. Due to this attenuation the 60 GHz band is not a good frequency to use for long-range radar or communication applications. At 60 GHz O2 can cause an attenuation of up to 10 dB/km.

At the millimeter wave frequency of 60GHz, the absorption is very high, with 98 percent of the transmitted energy absorbed by atmospheric oxygen. While oxygen absorption at 60GHz severely limits range, it also eliminates interference between same frequency terminals.

Telecommunications. In the United States, the band 36.0–40.0 GHz is used for licensed high-speed microwave data links, and the 60 GHz band can be used for unlicensed short range (1.7 km) data links with data throughputs up to 2.5 Gbit/s.

Fog, mist or even thick cloud does not really have any effect to the 60GHz signal, certainly nowhere near as much as rain can do. With very short distances, such as 100-200m the loss due to rain fade are so minimal, they are not worth even calculating.

Rain fade can affect millimeter wave wireless link availability if the fade is severe enough to interrupt link service. If the link is installed at a range of 500 meters, then there will be a margin of 12.5 dB left to handle even more rain fade.