Above 1 000 RF plasma generators Domestic microwave ovens (2 450 MHz) Commercial microwave ovens (2 450 MHz) Rubber vulcanization (2 450 MHz) RF excited ultraviolet curing 4 Characteristics of radiation In general, the radiation characteristics of ISM equipment depend on operating frequency, waveform of RF source, structure of radiator, surrounding structure of radiator, etc. Also, the radiation characteristics depend on distance from ISM equipment. the conventional antenna theory, the space surrounding a radiator is subdivided into three regions: a) reactive near-field; b) radiating near-field (Fresnel); c) (Fraunhofer) regions as shown in Fig. 1. Therefore, the radiation characteristics impacting on radiocommunication devices may be different according to the distance between radiators and victims. 1 Field regions of an antenna 4.1 Induction heating Induction heating is a process which is used to bond, harden, or soften metals or other conductive materials with the application of the transformer theory. When an alternating electrical current is applied to the primary of a transformer, an alternating magnetic field is created. According to Faraday’s Law, if the secondary of the transformer is located within the magnetic field, an electric current will be induced, which is called an eddy current. In basic induction heating equipment, the coil serves as the transformer primary and the target conductor to be heated becomes a short circuit secondary. Since the shape of the induction heating coil is similar to a circular loop antenna, the radiation characteristics of induction heating coil are also similar to those of a circular loop antenna. Especially, since the operating frequency for induction heating is lower than 1 MHz, the wavelength is greater than 300 m, which is very large compared with the radius of induction heating coil. Therefore, the induction heating coil can be considered as a small circular loop antenna. 2 Geometry for circular loop antenna When a radiocommunication system locates near the induction heating coil (kr << 1), the predominant electromagnetic fields to influence the device can be approximated as: (1) (2)
mP7/sP7: the expected mean and standard deviation values that buildings provide a certain degree of additional attenuation. In 16-4-4, mP5 is computed as: a) < Bnoise < Bmeas mP5 = 10 log(Bwant/Bnoise) where: Bwant: the bandwidth of the considered radio receiver for the wanted signal Bnoise: the bandwidth of the broadband disturbance the measurement bandwidth of measuring device. The relationships are as follows: b) Bmeas < Bnoise < Bwant mP5 = 10 log(Bnoise/Bmeas) c) Bnoise > and Bwant, respectively, mP5 = 10 log(Bwant/Bmeas) The value of mP6 is calculated by x•20 log(r/d) and the exact values of other parameters used in equation (20) are unfortunately not known. We believe that the parameters except for mP5 and mP6 would be determined by practical experiment and experience. Table 3 gives a representative example of the limit calculated by using the CISPR model above 1 GHz. TABLE 3 An example of the limit calculated by CISPR model above 1 GHz Actual field strength of the wanted signal, (EW) Gain of disturbance source, P1(dB) Mean value, mw (dB(V/m)) Standard deviation, sw (dB) Mean value, mP1 (dB) Standard deviation, sP1 (dB) 16 2 3 0.1 Gain of victim antenna, P2(dB) Victim is mobile, P3(dB) Mean value, mP2 (dB) Standard deviation, sP2 (dB) Mean value, mP3 (dB) Standard deviation, sP3 (dB) 3 0.1 5 0.1 Emission limit, P4(dB) Type of emission broadband correction, P5(dB) Mean mP4 (dB) Standard deviation, sP4 (dB) Mean value, mP5 (dB) Standard deviation, sP5 (dB) 1 0.1 1.000 0.1 Distance to victim, P6(dB) Building attenuation, P7(dB) Mean value, mP6 (dB) Standard deviation, sP6 (dB) Mean value, mP7 (dB) Standard deviation, sP7 (dB) 16.478 0.1 4.000 0.1 Limit for disturbance measured, ELimit (dB(V/m)) 40.3398