Passive wireless UV SAW sensor

This paper presents studies of a passive wireless ultraviolet (UV) surface acoustic wave (SAW) sensor operating in the frequency range 436–440 MHz. The sensor contains two SAW delay lines (DLs). The first DL is measuring, and the second is the reference. In the measuring DL, receiving–transmitting inter-digital transducer (IDT) is connected to the antenna and the sensing element zinc oxide film. In the reference DL, the receiving–transmitting IDT is connected to another antenna and does not contain a UV-sensitive element. Two methods of information reading from the sensor are proposed: based on the Fourier transform of the frequency dependence of the parameter S11 of the reader antenna and using reading pulses of 1.5-μs duration, which have carrier frequencies corresponding to the central frequencies of the measuring and reference channels. The sensor can measure UV intensities from 10 to 40,000 μW/cm 2 with a maximum sensitivity of 6000 ppm / (μW/cm 2 ) at low intensities, and which rapidly decreases as the UV intensity increases (less than 100 ppm at the UV intensity of 40,0000 µw/cm 2 ).