6I-3 Low-Cost Transceiver Unit for SAW-Sensors Using Customized Hardware Components

This paper presents a low-cost transceiver unit for wireless surface acoustic wave (SAW) sensors. Different types of radar principles are compared. Due to the simplicity of the hardware, the FMCW (Frequency Modulated Continuous Wave) concept is selected. It is shown that the linearity of the frequency sweep of the oscillator is the crucial point for the sensor resolution. Consequently, this contribution gives special attention to the signal generation. The customized hardware components - a mixer, a hybrid, a band-pass filter and two amplifiers - affect the signal-to-noise ratio while the readout range of the system additionally depends on the gain of the antennas. An ADC (Analog to Digital Converter) and a DSP (Digital Signal Processor) complete the hardware setup. The system is tested with delay-line temperature sensors based on the phase evaluation of the reflections. The first prototype of the interrogation unit achieves a temperature accuracy of about 0.2degC, a readout distance of 3 meters and its overall costs do not exceed 1000 euro