Research On Chipless RFID Temperature Sensor

RFID temperature sensor is a novel sensor which uses transfer characteristic of electromagnetic wave to realize contactless temperature detection.RFID temperature sensor is not popular because of high cost,complicated craft and narrow applied place.Chipless temperature sensor can settle those problems and chiplss temperature sensor become hot spot in this field at home and abroad.This thesis includes four parts which are the design of chipless temperature structure,the fabrication of temperature sensitive material,the printing fabrication of temperature sensor and the test of temperature sensibility of sensor.This thesis have done a lot of research about low cost chipless RFID temperature.Three types of split ring resonator which are square split single-ring resonator,square split-double and circle split ring resonator are designed to 2.45GHz by electromagnetic simulation software.The equivalent circuit models of three split ring resonators are studied and researched,and then we prove the rationality of three types of split ring resonator we designed.Then the resonance characteristic of tree types of split ring resonator is compared and the square split single-ring resonator whose resonance characteristics is the best is selected to be the basics of temperature sensor.A batch of single split ring resonators are made by screen printing technique.The resonant frequency of square split single-ring resonator is tested and it is found that the resonant frequency of the resonators we made is at about 2.45GHz and the simulation value,theoretical value and test value of the resonant frequency are the same with each other basically.So it is proved that the square split single-ring resonator we designed and made can be the basic structure of chipless RFID temperature sensor.The thermal mechanism of temperature sensor which is loaded temperature sensitive material is simulated and it is found the resonant frequency goes down obviously with the conductivity of the sensitive material goes up.Multi-walled carbon nanotube by screen printing technique is made and the temperature sensing mechanism of multi-walled carbon nanotube is researched in theory and we found that the conductivity of multi-walled carbon nanotube goes up with the temperature goes up,which has negative temperature effect.The resonator and multi-walled carbon nanotube are made in turn by screen printing technique and three temperature sensors whose number of multi-walled carbon nanotube layer is one,two and three are made.The temperature sensitivity test system of temperature sensor is established with vector network analyzer,Tx/Rx antenna and temperature controlling unit to test the temperature sensitivity of these three temperature sensors.lt is found that the resonant frequency of these three temperature sensors goes left with the temperature goes up,which is the same with the result in theory.Then it is studied that how the layer of multi-walled carbon nanotube affect the performance of the sensors and it is found that the temperature sensor whose multi-walled carbon nanotube is one layer performs best and has the highest sensitivity.The resonant frequency decline from 2415 MHz to 2375MHz and the total frequency shift of this sensor is about 40MHz.The chipless RFID temperature sensor we designed in this thesis has three features which are low cost,simple structure and better temperature sensitivity,and the sensor has certain application potential in wireless temperature detection.