Selected operating frequency depends primarily on the following four factors:
    ( A ) the volume of processed material and thickness. Because microwave penetration depth of the material used and the processing of the frequency of the dielectric constant of the material to be processed and the dielectric loss , and therefore, when the material is in 915MH2 and 2450MHz dielectric constant and dielectric loss care little difference , the choice to 915MHZ obtain a larger penetration depth , do that the material can be heated larger ,
    ( 2 ) The water content and dielectric loss of materials , in general, the greater the moisture content of the process material , the greater the dielectric loss ; when the frequency is higher, the greater the dielectric loss . Therefore shopping for materials containing large amounts of water can be used to 915MHZ; However, when the water content is low , the material for the 915M her microwave on less absorbed, so because of the choice of 2450MHz. However, some materials , such as those containing o. 1mol / L of brine , 915MKz but the loss of the medium 1 times when 2450MH2 . Others such as meats , which have a similar situation. Therefore, the choice of what exactly the frequency , it is best to test the defined channel .
    ( 3 ) the total production volume and costs. Because microwave tubes may be able to get the power and frequency. For example . Magnetron frequency of 915MHz single tube can get 30kw or 60kw of power , while the 2450MHz magnetron 5kw single tube can only get about power . And the general efficiency of the magnetron 915MHz 2450MH2 higher than 10% -20 % in order to obtain the frequency of 2450MHz 30kw power above , it must be used in parallel or in a few magnetron klystron higher prices . Thus , a large number of materials in the processing , often use 915MHz, 2450MHz , or used in conjunction with 915MHs , the total cost can be reduced .
    ( 4 ) equipment size . Generally , 2450MHz and the magnetic wave than 915MHz over small , so the size of the heater generally smaller :