Uses Two Relay Switches For A Multifunctional LC Passive Wireless Sensor System

Simultaneous detection of multipara-meters is required in more and more practical applications,especially in sensor network.An LC passive wireless multifunction sensor system is desired in areas such as implantable devices or wearable devices and commercial scale monitoring of food quality,monitoring in agriculture purposes and for industrial machinery monitoring.Compared with implementation by several sensors,it can be simplify the detecting system and has lower cost and smaller size along with the extended interrogation distance,which is required for further achievements.This thesis concerns itself with modeling and simulation of the multifunction LC passive wireless sensing system using two relay switches.The main objective of the thesis/project is to model and simulate the LC passive wireless sensing System to demonstrate the multiple resonant frequencies for simultaneously measurement of the multiple parameters of interest.In this project the LC-type passive wireless sensing system have been developed for the detection of triple parameters simultaneously by three different capacitive sensors controlling by two switches.The sensing system includes inductor coils,three capacitors and two switches.The sensor Coil is connected with three different capacitors in parallel consecutively and two switches are in series to each other,which lead to construct three different LC resonant circuits.The read out coil is magnetically coupled with the sensor coil to wirelessly interrogate the sensors and induced voltages for the operation of both switches.Three different resonant frequencies using three individual simulations setup for accurate results has been carried out using ADS,which can be utilized for the measurement of the Pressure,Relative Humidity and Temperature sensors simultaneously.The two electromagnetic relay switches are operating over two different threshold value of voltages,which will make it possible to simultaneously measured three parameters using three variable capacitive sensors connected with sensor coil and controlled by both of the switches.Mathematical analysis has been carried out using MATHLAB to analyze the working principle multifunction of LC sensing System.To present the modal,the PCB inductor,two Switches and three variable capacitors for detection of three different external parameters are constructed on wire board.The first resonant frequency is 30MHz during both of the mechanical switches are turned off,the variable capacitor C,is 30 PF,C2 and C3 are fixed at 50 PF and the parasitic capacitances of both switches has been taken into account.By turning on the 1st switch(SW1),we have the 2nd resonant frequency is of 27MHz by adjusting C2 variable at 30 PF,however C1 and C3 are fixed at 50 PF.When both of the switches SW1 and Sw2 are turned on,we have another different resonant frequency response is about 25MHz by fixing C1 and C2 at 50 PF and C3 is variable at 30 PF.The output results are closely related and verified with the simulations results.This multifunction LC sensors system is detecting three different resonant frequencies simultaneously and independently.