The application types of polyurethane absorbing materials are mainly divided into sheets and non-echo anechoic chambers. Since materials of different thicknesses have different attenuation effects on cavity resonance in different frequency bands, flexible absorbing materials of different thicknesses can be selected for different applications. Generally speaking, the effective thickness of the flexible absorbing material is proportional to the wavelength of the target application, or inversely proportional to the frequency. One of the main applications of anechoic anechoic chambers is EMC testing. Among them, the most commonly used are anechoic anechoic chamber tests in the fields of automobiles, microwave antennas, radar, aerospace, etc., and all electronic products (such as electronic components, medical imaging equipment, communications Equipment, digital cameras, mobile phones) also require related darkroom tests. At the same time, the various parameter standards of the darkroom test will be different according to the different test targets.
The goal of solving the cavity resonance problem is to reduce the voltage standing wave ratio (VSWR) at the key point. These key points may be active devices, microstrip filters, or even the input or output of simple feedthrough lines connected to other circuit elements. If the size of the cavity can be reduced, the cutoff point may be raised to a very high value without causing cavity resonance problems in the circuit. However, it is usually impossible to increase the size of the cavity without adversely affecting the circuit.
Repositioning a specific circuit element to a different position in the cavity can also solve this problem. In addition, cleverly dividing the space is also very helpful to suppress standing waves, but these two methods will increase the engineering design time and may delay production.
The use of microwave absorbing materials in the cavity has proven to be very effective in suppressing cavity resonance. Absorbing materials (especially magnetic types) have extremely high permittivity and permeability, and high loss value. According to the basic definitions of permittivity and permeability, they represent the capacity to store electrical energy and magnetic energy, respectively. Introducing this concept into the cavity case, the solution of the electromagnetic field equation shows that the energy mainly exists in materials with high permittivity or high permeability. This will reduce the available energy in the empty area of the cavity (containing the microwave circuit), thereby reducing impedance changes and the impact on the circuit.