EMC Absorber (withstand High-power Irradiation) - ZXB

Abstract: This article introduces a novel radio-wave absorbing material for anechoic chamber, named ZXB absorber. Compared with PU absorber, this non - woven fabric based absorber material has better performance in power capacity, fire-retardancy andenvironmental protection than polyurethane absorbers. It meets the requirements of NRL Report NO 8093 Test 1, 2 and 3 and other related standards. ZXB absorber has the same reflectivity performance as conventional PU absorber, but it has no unpleasant smell, powder that falls off, nor drooping tips in the long-term use . I t is also clean and humidity resistant. Developed in 1999, this type of absorber has been successfully used in over 100 anechoic chambers for radar, satellite, wireless communication and antenna measurement and EMC test application.

The design concept of adopting pyramid absorber in anechoic chamber is first proposed by Tiley JW and he won the U.S. Patent in March,1949. For over 50 years, with the requirement of high-performance radar development and technology advance, PUabsorber immersed with Carbon has achieved high absorption rate, but it could not withstand several kilowatts per square meter of microwave power irradiation. Therefore, it could not meet the requirements of developing & producing modern weapons. In 1999, Nanjing Lopu developed a novel absorbing material, ZXB absorber, which is made of n on - woven fabrics and special mineral . ZXB absorber maintains the same absorbing properties as PU absorber, but ZXB absorber has better performance in power capacity, fire-retardancy and environmental protection and etc. Since developed, it has been applied in over 100 various types of anechoic chamber, with application area of over 100,000 square meters. Such ZXB absorber has been widely applied in aerospace, electronics, IT, RF and other fields.

1. ZXB absorber physical properties
The Z XB pyramid absorbing material is a type of electric loss absorbers, and pyramid structure is applied to perfectly match radio waves. With vertical incidence its wave impedance gradually changes from 377 ohm to 2 ohm , avoiding reflection on the absorber's surface. For those radio waves entering into the absorbing material, with its good electrical conductivity, such absorbing material rapidly transforms the electromagnetic energy to Ohm energy, thus to attenuate the radio waves. Assume the reflectivity of absorber is R, when its thickness wavelength ratio t/ λ =0.2, R=-1 4 dB; when t/ λ =1, R=-3 1 dB; when t/ λ = 7 , R=-50dB. For detail reflection loss relationship, please refer to the following figure.

2 , ZXB absorber safety performance
Such absorber has good fire-resistant performance, as it is made up of inorganic substances. Tested according to GB/T2406-93 << Plastic combustion performance test method, the oxygen index method >>, with oxygen index over 60% , it can meet the
requirement of GB8624-1997 << Flammability of building materials classification method >> , it is B1 Flame retardant materials . It can withstand high-power irradiation. Under the microwave power irradiation of below 15kw/sqm, it won't take any cooling facilities. The testing of flame ignition & spread, conductance and Internal heat , it shows its performance is superior to the requirements of test I voltage-resistant, test II difficulty of flame ignition and propagation, test III flame-resistant test of Navy laboratory report NRL8093 (1977). Therefore, no matter the irradiation of strong lighting, strong current, flame and strong microwave, it won't bring combustion. It is absolute safety materials, and it can be used in microwave anechoic chambers,, without any fire worries. Adopting such absorber can greatly simplify the anti-fire system in the anechoic chambers. It has been passed the review of some anti-fire safety departments.

3 , ZXB absorber environmental performance
Tested according to GB/T14677-93 "air emission monitoring and analysis methods", chamber's inside health environment is able to meet the Chinese living standards . Such absorber won't pollute the environment, even scrapped in the future. It is an environmental protection type absorbing materials. It has stability chemical properties , no odor, no harmful gases released, no powder off, non-fade phenomenon, it also doesn't absorb moisture, with cleanliness degree up to 100,000.

4 , ZXB absorber's structure and properties
It can meet more than 10 years' service life, and the absorb er won't bend, and shed within 10 years' service life. The absorber has neatly arranged pyramid, with good visual effects and light reflective . It also has flush bottom , no residue , clean appearance, uniform color , as well as smooth feel ing, without fade phenomenon. During the warranty period, there is no cracks, no discoloration, no deformation.

Such absorber can be applied in antenna far-field measurement microwave anechoic chamber, far-field measurement microwave anechoic chamber, RCS measurement microwave anechoic chamber, and EMC measurement anechoic chamber, and etc (If left figure, it is the first anechoic chamber we adopted such ZXB absorber, which was built in 2000, achieved good economic and social benefits. The largest anechoic chamber (In right figure) adopting such ZXB absorber was built in 2005, with size 54m *10.8m * 10.90 (L*W*H), it is built for antenna far-field measurement .