Non-contact Temperature Measuring System Based On Surface Acoustic Wave

Surface With the rapid development of modern industry, science and technology, new demands are put forward for temperature measurement in many specific areas. Conventional liquid thermometers, thermocouple temperature sensor, colorimetric thermometers, infrared thermometers and other measuring methods can not be well suited to certain areas of the temperature of the non-contact real-time measurement. Therefore, research and development of new temperature measurement technology and system is of important academic significance and extensive practical value in many fields.In recent years, people carry out research on surface acoustic wave (SAW) devices for wireless sensor technology at home and abroad. Inspired by that the resonance frequency of SAW devies varies with temperature, we can achieve passive wireless temperature measurement. So this paper combines a SAW resonator and FPGA to study non-contact real-time temperature measurement technology and system based on SAW resonator and FPGA. The main contents and research results are as follows.This paper proposes a new method for non-contact temperature measurement in real time based on a SAW resonator and FPGA. The method uses a SAW resonator as a temperature sensor and achieve non-contact real-time sensor of temperature according to the characteristics that the resonance frequency varies with temperature. By the signal transmitting and receiving integrated chip, the integration and stability of signal receiving and processing circuit is improved. FPGA development board is used in the system for the first time. The amplitude shift keying (ASK) rather than mechanical switch is adopted to realize high-speed switching between transmitting signals and receiving signals. Strong transmitting signals no longer interfere with weak receiving signals. Thus, the response speed and measure performance of the system are highly improved.A new type of non-contact real-time temperature measurement and monitoring system is developed. The system consists of a FPGA development board, a ASK control port, signal transmission and power amplifier modules, RF transmitting and receiving antennas, a SAW temperature sensor, signal reception and difference frequency circuit modules, computer and software.When the ASK signal that FPGA outputs is high, the signal transmitting circuit generates high-frequency transmission signal of which the center frequency is about 433 MHz. It is amplified to about 10 mW by power amplifier module and then transmitted by antenna (TS signal). After the helical antenna on SAW resonator has received the signal, it excites SAW resonator to generate surface acoustic wave via interdigital transducer (IDT). When ASK signal turns low, TS signal is instantly stopped from transmitting. While the surface acoustic wave that the SAW resonator produces will last for a while. Then it is transmitted by the helical antenna connected with SAW resonator and then received by antenna (RS signal). The signal reception and difference frequency circuit subtracts the signal with intrinsic signal and gets intermediate frequency signal (IS signal). IS signal can be directly input to FPGA and then to computer after processed by FPGA. IS signal is transformed in the software. As fis is corresponding with the temperature of measured object, the temperature can be measured and monitored in real time.Experiments were carried out on the wireless temperature measurement and monitoring system based on SAW and FPGA. The resonant frequencies of SAW temperature sensor at different temperatures are measured with thermostatic plate. Experiments show that this system can implement temperature measurement up to 120?, with an resonance frequency-temperature coefficient of-5.7 kHz/?. The measurement resolution of temperature is better than 0.5?. The temperature of high-power laser was measured and monitored with the system, and perfect results were got. These research results demonstrate that this system provides a new method of real-time temperature measuring, monitoring and security alarming for optoelectronic, electromechanical, electrical and electronic devices.