High frequency currents
What are high frequency currents?
Currents with a frequency higher than 10,000 Hz are called high frequency currents (HFC). They are obtained using electronic devices.
If you place a wire inside a coil through which a high-frequency current flows, then eddy currents… Eddy currents heat up the wire. The heating rate and temperature can be easily adjusted by changing the current in the coil.
Most refractory metals can be melted in an induction furnace. To obtain highly pure substances, melting can be done in a vacuum and even without a crucible, by suspending the molten metal in a magnetic field. The high heating rate is very convenient when rolling and forging metal. By choosing the shape of the coils, you can solder and weld parts under the best temperature conditions.
Induction melting furnace
A current flowing through a wire creates a magnetic field B. At very high frequencies the effect of the eddy electric field E generated by a change in the field B becomes noticeable.
The influence of the E field increases the current on the surface of the conductor and weakens it in the middle.At a sufficiently high frequency, the current flows only in the surface layer of the conductor.
The method for surface hardening of steel products was invented and proposed by the Russian scientist V.P. Vologdin. At high frequency, the induction current heats only the surface layer of the workpiece. After rapid cooling, an unbreakable product with a hard surface is obtained.
Curing machine
See here for more details: Induction heating and tempering installations
The action of high-frequency currents on dielectrics
Dielectrics are affected by a high-frequency electric field, placing them between the plates of the capacitor. Part of the energy of the electric field is spent in this case to heat the dielectric. HFC heating is particularly good if the thermal conductivity of the substance is low.
High frequency heating of dielectrics (dielectric heating) is widely used for drying and gluing wood, for the production of rubber and plastics.
High frequency currents in medicine
UHF therapy is dielectric heating of body tissues. Direct and low-frequency currents above a few milliamperes are lethal to humans. High-frequency current (≈ 1 MHz), even at a power of 1 A, causes only tissue heating and is used for treatment.
«Electroknife» is a high-frequency device widely used in medicine. It cuts the tissues and tightens the blood vessels.
Other applications of high frequency currents
Grain treated with HDTV before sowing significantly increased yield.
Induction heating of gas plasma allows high temperatures to be obtained.
A 2400 MHz field in a microwave electric oven cooks the soup right on the plate in 2-3 minutes.
The action of the mine detector is based on the change in the parameters of the oscillating circuit when the coil is brought to the metal object.
High frequency currents are also used for radio communications, television and radar.