Absorbing materials to solve the problem of metal interference in high-frequency RFID at 13.56MHz

Due to being a passive electronic tag, the energy required for the operation of the chip and memory in the electronic tag needs to be provided by the reader/writer. The communication between the reader/writer and the electronic tag is achieved through the principle of electromagnetic coupling, and the energy of the electronic tag is generated by the coil antenna of the reader/writer through electromagnetic coupling. The high-frequency electromagnetic field is generated by the antenna coil of the reader/writer, and then the magnetic field passes through the cross-section of the coil and the space around the coil. According to the tag's usage frequency of 13.56MHz and wavelength of 22.1m, which is much greater than the distance between the reader antenna and the electronic tag, the electromagnetic field between the reader antenna and the antenna can be treated as a simple alternating magnetic field.

By adjusting the antenna coil and capacitor of the electronic tag to form a resonant circuit, tuned to the designated transmission frequency of 13.56MHz of the reader/writer, the voltage generated on the inductance of the coil in the tag reaches the maximum value according to the resonance of the circuit. The power transmission efficiency between the antenna coil of the reader and the electronic tag is proportional to the number of turns of the coil in the tag, the area enclosed by the coil, the relative angle between the two, and the distance between them. This is also the reason why RFID tags have a certain limit on the reading distance. For RFID electronic tags used at 13.56MHz, their maximum read and write distance is usually around 10 centimeters, and the chip's current consumption is approximately 1mA. As the frequency increases, the required inductance of the electronic tag coil decreases in the number of turns, typically ranging from 3 to 10 turns at that frequency.

The reading distance of RFID tags is not only related to themselves, but also to their environment. When using inductively coupled radio frequency identification systems, it is often required to directly install the antenna of the reader or electronic tag on a metal surface. However, it is impossible to directly install magnetic antennas on metal surfaces. Because the magnetic flux of the antenna passing through the metal surface will generate induced eddy currents, according to Lenz's law, eddy currents will have a counter effect on the field of the antenna and rapidly attenuate the magnetic field on the metal surface. As a result, the data reading distance between the reader and the electronic tag will be severely affected, and there may even be misreading or reading failure. Whether the magnetic field generated by the coil installed on the metal surface itself or the field approaching the metal plate from the outside (electronic tags on the metal surface), the result is the same.

The absorption principle of absorbing materials in RFID

 Absorbing materialIt is a magnetic functional material with high magnetic permeability, usually made by uniformly filling some absorbents on polymer materials through special processes. Compared with traditional absorbing materials, this type of high-performance absorbing material for 13.56MHz has different performance characterization and usage principles.

Traditional absorbing materials are mainly used in military confrontations to cover up and confuse enemy radar reconnaissance aircraft, warships, and armored tanks. They have a high frequency of use in the microwave range and are analyzed using far-field models.