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The microwave auditory effect, also known as the microwave hearing effect or the Frey effect, consists of the human perception of sounds induced by pulsed or modulated radio frequencies. The perceived sounds are generated directly inside the human head without the need of any receiving electronic device.
The crystal detector demodulates the radio frequency signal, extracting the modulation (the audio signal which represents the sound waves) from the radio frequency carrier wave. In early receivers, a type of crystal detector often used was a "cat whisker detector".
A cavity resonator is one in which waves exist in a hollow space inside the device. In electronics and radio, microwave cavities consisting of hollow metal boxes are used in microwave transmitters, receivers and test equipment to control frequency, in place of the tuned circuits which are used at lower frequencies.
Radio wave diffraction is the scattering of radio frequency or lower frequencies from the Earth's ionosphere, resulting in the ability to achieve greater distance radio broadcasting. Sound wave diffraction is the bending of sound waves, as the sound travels around edges of geometric objects. This produces the effect of being able to hear even ...
One of the first crude examples of a BFO, the Goldschmidt tone wheel. Before vacuum tube oscillators were invented, the first CW receivers used a wheel with electrical contacts around its rim, spun at a high speed by a motor, to interrupt a current to create a radio frequency signal to beat with the incoming radio signal. This example, at the ...
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere. [1]: 26‑1 As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering. [2]
Radio waves can be shielded against by a conductive metal sheet or screen, an enclosure of sheet or screen is called a Faraday cage. A metal screen shields against radio waves as well as a solid sheet as long as the holes in the screen are smaller than about 1 ⁄ 20 of wavelength of the waves. [26]
Radio waves in this band have wavelengths from ten to one millimeter, so it is also called the millimeter band and radiation in this band is called millimeter waves, sometimes abbreviated MMW or mmWave. [3] Some define mmWaves as starting at 24 GHz, thus covering the entire FR2 band (24.25 to 71 GHz), among others. [4] [5]