Circuit Optimal Design Of The Passive Wireless Temperature, Humidity And Pressure Sensor System

The sensor technology has penetrated into industry and daily life in all aspects, including automotive, computer, intelligent mobile phone, weather detection, defense security. With the increasingly widespread application of sensor, defects of the traditional active wired sensors have become increasingly prominent; people put forward many new requirements on sensor performance, such as miniaturization, integration, digitization, intelligent, low power passive and so on. The volume of traditional active wired sensor is large, of which the data transmission is through wires or cables. It is not easy or even unable to measure the harsh environment, organism and sealed environment. Passive wireless sensor has the advantages of small volume, no power supply and remote sensing, so it is facilitate to measure hermetic environment.Passive wireless sensor is mainly divided into two categories:the first category is the LC resonant passive wireless sensor; the second category is the passive wireless sensor based on backscatter modulation. The sensor used in LC resonant sensor system is generally capacitive sensor or inductive sensor. Change of sensor parameters lead to resonant frequency changes and the resonant frequency is measured through an external device. The default of this kind passive wireless sensor is that bulky external device or complex circuit is needed and it is difficult to achieve dual channel data transmission or multi-parameter measurement. Passive wireless sensor system based on backscatter modulation has overcome these shortcomings of the LC resonant sensor. This kind of system is the combination of sensor technology and radio frequency identification technology. The principle of energy and data wireless transmission between RFID technology and passive wireless sensor is the same, and the difference between RFID technology and passive wireless sensor is the data source. In this dissertation, a wireless passive multi-parameter sensor system based on backscattering modulation is designed, and the system has done a lot of optimization. The system is mainly designed for spraying room, and it is used to measure the temperature, relative humidity and air pressure of the spraying room. The main research contents and innovations of this paper are as follows:First, the development direction of the traditional sensor technology is introduced, and then the application of passive wireless sensors is illustrated. Types of passive wireless sensor are introduced, and then the development status of wireless passive sensor system based on backscatter modulation is presented. Then the related technique and theory about passive wireless sensor system based on backscattering modulation are analyzed. A kind of passive wireless multi-parameter sensor system suitable for measuring sealed environment is proposed, and the system is mainly used for temperature, humidity and pressure measurement of the sealed environment. The system mainly consists of two parts:primary system and secondary system. The energy and data wireless transmission between the primary system and secondary system is realized by inductive coupling. Primary system provides energy for secondary system through the carrier, and secondary system uses sensors to collect environmental data. The data is converted to digital frequency signal by interface circuit of sensor, and time-division multiplexing circuit is used to achieve multi-parameter measurement. The secondary system transfers the data to the primary system by load modulation. Every part of the system of the circuit structure and function is illustrated in detail, and simulation software is used to verify the feasibility of the circuit. Then the performance of the system are improved through optimize the power amplifier, sensor interface circuit and so on. After optimization design, the circuit debugging and system testing are done, including how to debug the circuit parameters, calibration and testing of the sensors. The testing of system of wireless data transmission distance, the testing of the accuracy and resolution of the system and the testing of the system in closed spraying room are illustrated in detail. Backscatter modulation readout technology realizes a wireless range of 4 cm from the battery-free sensing system to the primary system. The test results show that the sensitivity of temperature, humidity and pressure sensor is:0.18kHz/?,0.1kHz/%RH and 0.056kHz/hPa, respectively. At the end of this paper the work is summarized, and the methods how to optimize the passive wireless sensor system based on backscattering modulation is discussed.