Using Multi Repeaters For Enhancing The Remote Distance Of Lc Passive Wireless Sensors

LC sensors are widely used in industrial manufacturing,aerospace,and biomedical engineering field.Usually,the planar spiral inductor connected with a variable capacitor designs the LC sensor.The LC Passive wireless sensor does not need physical connection and power supply,which makes the measurement in the harsh environment become possible.With its excellent properties such as smaller size,battery-free,and longer lifetime,LC passive wireless sensors are emerging technology to solve measurement problems in the harsh environment,such as rotating parts,high-temperature environments,and another occasions.An Inductor-Capacitor(LC)passive wireless sensor system consists of LC resonant tank and the readout coil.Parameter of interest causes changes in the sensitive element of LC sensor,resulting in a shift in the resonant frequency.The interrogation between the LC sensor and the readout coil is based on the mutual inductance.Usually,the readout distance of the LC sensor is limited due to the small size of the LC sensor,which is about the diameter of the inductor.Other key parameters that influence the readout distance is the substrate material,parasitic capacitance and its parasitic resistance.The main method to extending the readout distance is to improve the magnetic field in the space,and enhance the mutual coupling between the readout coil and the sensor inductor.Previous papers use a repeater coil to enhance the mutual coupling.In this thesis,a new method is proposed to extend the readout distance by using two repeaters.The proposed repeater is consist of a variable capacitor and an inductor.When the resonant frequency of the repeater is consistent with the LC sensor's resonant frequency,the strong magnetic coupling happens,which enhance the signal intensity.Using two repeaters can further enhance the magnetic field in the space,which realize a longer readout distance than that using only one repeater.The schematic model and the layout model is simulated by using ADS(Advance Design System)software.In experiments,the repeater is composed of a PCB planar inductor and a varactor.The capacitance of the varactor is controlled by the driving voltage.The LC sensor is consist of a PCB planar inductor and a sensitive capacitor.Experiment and simulation results show that the readout distance of the LC passive wireless sensor is improved by using two resonator coils.The strength of the received signal by using two resonator coils is higher than by using one resonator coil,due to the stronger magnetic coupling.