With the rapid advancements in electronics industry and radio communication technology, our life has become more abundant than ever before. On the other hand, serious social problems such as electromagnetic interference (EMI) and electromagnetic susceptibility (EMS) have arisen due to the increased use of electromagnetic waves. Therefore, countermeasure against electromagnetic waves obstacle is embossed to be important subject. International organizations such as CISPR, FCC, and ANSI have provided the standards for the EM wave environments and for countermeasure of the electromagnetic compatibility (EMC).
Especially, UHF(433 MHz and 860 MHz ~ 960 MHz) band RFID system is widely accepted by industries such as port logistics, circulation, and mobile RFID field advantage of long communication range, high speed transmission of data. Particulary, port logistics RFID systems have several EMC problem such as decrease of communication range and errors by mutiple reflection. Port logistics RFID systems which have hundreds of antennas are positioned in small area, cause the interferences between readers and tags. Thus, to avoid severe communication interruption between RFID systems, we must study carefully. To avoid the communication interruption, EM wave absorber is applicable among readers. Besides, communication range of RFID system is reduced when RFID Tag approached metal plate. In this case, the EM wave absorber can increase the communication range of RFID system when it inserts between tag and metal plate.
In this study, the EM wave absorbers are designed and fabricated for preventing reader to reader interference by dense mode and the reduction of the communication range when RFID Tag approached metal plate. The EM wave absorber samples are fabricated with difference composition ratios of Amorphous metal powder and CPE, the S-parameters of samples are measured. Absorption abilities are simulated by substituting different thicknesses of the EM wave absorbers, and the EM wave absorbers are manufactured based on the simulated results.
As a result, the developed EM wave absorber for port logistics RFID system has the composition ratio of Amorphous metal powder(flake shape) : CPE = 87.5 : 12.5 wt.% and a thickness of 5.1 mm and, absorption ability is 22.5 dB in frequency band 433 MHz.