Effect of variable resistance and capacitance on return loss of monitoring side antenna

Abstract

A “smart gear monitoring system” has been developed that consists of an observation antenna and a crack detection sensor with another antenna printed on gears. When the characteristics of the observation antenna were measured with the magnetic coupling between the two antennas printed on POM plates, it was found that the return loss changed significantly depending on whether the crack detection sensor was damaged or not. The obtained results, however, have not been examined in detail. In this paper, the effect of the characteristics of gear sensors on the return loss of the observation antenna is discussed through the experimental results. First, two spiral antennas with the same geometrical shape were printed on POM plates. One was connected to a network analyzer and the other was connected to a variable resistor or variable capacitor. Then, the return loss of the observation antenna was measured while the magnetic coupling was caused by bringing the antenna pairs close to each other. Furthermore, the effect the return loss of the observation antenna was investigated and evaluated by changing the value of the resistance and capacitance. Consequently, the results have shown that the resonance frequency of the coupled system was affected in corresponding with the variation of the capacitance and the Q value was apparently affected in corresponding with the variation of the resistance, respectively.