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What are high-frequency electromagnetic fields?
- Electric and magnetic fields in the frequency range between 100 kilohertz and 300 gigahertz are referred to as high-frequency fields.
- High-frequency electromagnetic fields are radiated by an antenna in most cases. In free space they propagate at the speed of light, in the course of which they are able to transmit energy and information over long distances.
- With increasing distance from a transmitter, the field strengths drop off rapidly. In free space the power flux density decreases with the square of the distance, that is, with double the distance it decreases to one-fourth.
Electric and magnetic fields in the frequency range between 100 kilohertz and 300 gigahertz are referred to as high-frequency fields. As electric and magnetic fields are closely coupled at high frequencies, they are also called "electromagnetic" fields.
Frequency and wavelength of electromagnetic fields are interlinked by the velocity of propagation (in free space that is the speed of light) and describe the wave character of the fields. At high frequencies the wavelengths are small, at low frequencies they are correspondingly larger. In the case of propagation in free space the wavelengths range between 3 kilometres and 1 millimetre.
Using high-frequency fields in modern communications
High-frequency electromagnetic fields are radiated by an antenna in most cases. In free space they propagate at the speed of light, in the course of which they are able to transmit energy and information over long distances. This property is mainly used in modern communications – such as
- radio, television, mobile communications as well as
- cordless phones and wireless computer networks (Wireless LAN or WLAN).
Short range devices also use high-frequency electromagnetic fields, such as radio modules according to the Bluetooth standard.
Owing to the multitude of possible applications of high-frequency electromagnetic fields, nowadays people are surrounded by a large variety of transmitters operating at various transmitting powers and frequencies (see table in the article sources of high-frequency fields). The intensity or strength of the fields is either given
- in the form of electric field strength (unit of measurement: volts per metre, V/m) or magnetic field strength (unit of measurement: ampere per metre, A/m or
- in the form of power flux density, unit of measurement: watts per square metre, W/m2).
Power flux density is the product of electric and magnetic field strength.
Propagation of high-frequency electromagnetic fields
With increasing distance from a transmitter, the field strengths drop off rapidly. In free space the power flux density decreases with the square of the distance, that is, with double the distance it decreases to one-fourth. As many antennas, owing to their design, radiate in various preferential directions, the intensity in the area around the transmitter can vary strongly even at identical distances to the source. Hence, the field strengths at a certain point can usually not be inferred from distance alone.
High-frequency electromagnetic fields can also be reflected or absorbed by objects in the propagation direction. Which mechanism predominates depends, among others, on the material properties of the object in question. The propagation of high-frequency fields in real environments, therefore, differs significantly from the simple case stated above, the propagation in free space.
Electrically conductive materials, such as metals, reflect high-frequency electromagnetic fields. Metal foils or metal mesh, but also metal-coated window panes (for thermal insulation) can thus completely or partially shield high-frequency electromagnetic fields.
State of 2018.06.25