Research Of RF Transceiver&Signal Analysis Systems For Wireless Passive SAW Sensors

Surface Acoustic Wave (SAW) sensor is a novel sensor, which can be passive, wireless and suitable for various environments. The structure of SAW sensor is simple and robust, so it can work in poor environments and measure many factors. In decades, SAW sensor is developed rapidly in temperature and press measurements. With the progress of Micro-electromechanical Systems (MEMS) processes and wireless transceiver technology, SAW wireless sensor would play an important role in sensors market.The wireless passive SAW sensor consists of RF (Radio Frequency) transceiver with signal analysis system and SAW sensor device with antenna. Firstly, the RF transceiver transmits an electromagnetic enquiry signal, which is then received by the SAW device and transferred to acoustic signals. Secondly, the transferred acoustic wave propagates on the surface of SAW device, and the properties of propagation are affected by the factors of environments, such as temperature and pressure. Finally, the acoustic wave will transferred back to electromagnetic wave as the reflected signal and received by the RF transceiver, then the sensing information included in reflected signal will be extracted by the signal processing system, which means the factors of the environment is measured.Depending on the factors to be measured, the structure and material of SAW sensor differs. However, the theory of the measurement method is unchanged. Therefore we can design a versatile wireless transceiver and signal processing system, completing the sensing system together with the SAW sensor. In this thesis, the structure characteristics of SAW sensor and the principle of measurement are reviewed firstly. Then, we analyzed the required characteristics of wireless transceiver module and signal processing module depending on the SAW sensor theory. At last, a wireless transceiver integrated with signal processing system is designed, manufactured and tested for temperature sensing application. Results show the system works well, and the measured data fit the theory analysis in good consistency. The main innovation of this thesis is that the FPGA (Field Programmable Gate Array) are used to control the parameters of RF transceiver module as well as to extract sensing information in signal processing module. For this reason, the RF transceiver and signal analysis systems was versatility and flexibility, not only can be applied to SAW devices with different frequency, but also make the system easy to be upgraded.The main work and achievements of this thesis are:1. The wireless passive SAW sensor system are analyzed and discussed theoretically, and a wireless transceiver system integrated with signal processing module to extract the sensing information based on the characteristics of SAW sensor are designed in system level..2. Wireless transmitting circuits were designed and fabricated based on the PLL (Phase Locked Loop) theory. The frequency of the pulse signal was tunable between433-435MHz via FPGA. The wireless transmitting circuits was tested on433.5MHz,434MHz and434.5MHz, and the results turned out that the measured frequency was433.503MHz,434.003MHz and434.503MHz, respectively. The period and emitting width of the pulse signal are also tested, and the results are in good agreement with expectation..3. Wireless receiving circuits were designed and fabricated based on the direct-conversion circuits theory. The receiving circuits were tested under the RF input and LO (Local Oscillator) frequencies are set to433and434MHz respectively. Experimental results show that the demodulated signal is1.00248MHz.4. Signal processing modules like FIR (Finite Impulse Response), FFT (Fast Fourier Transform) and CORDIC (COordinated Rotation DIgital Computer) blocks were designed and implemented. The cutoff frequency and stopband attenuation of FIR were5MHz and-30dB respectively. The FFT module was worked in1024points. The CORDIC module was used to generate the amplitude of the FFT results in frequency domain. The signal process modules were tested by modelsim and matlab cosimulation. 5. The designed system, which includes RF transceiver and signal processing modules, was verified by a typical application of wireless temperature sensing using a433MHz SAW temperature sensor. Experimental results show that the measured data successfully changed with the ambient temperature accordingly, and three typical points are10.3℃,35.5℃and48.2℃, respectively.