Digital phase detection for high-precision surface acoustic wave sensor systems

We are developing a highly sensitive surface acoustic wave (SAW) sensor system for biomedical and industrial applications. One of the key components of such a system is the signal read-out unit based on digital phase detection, which is needed to quantitatively determine tiny mass change on the sensor. To find a method that produces the highest precision, we have compared several digital phase detection methods (fast-Fourier transform, zero-crossing and sine-wave fitting) and found the zero-crossing method to be the most promising one. Using this method, a phase detection limit of 0.03deg has been achieved on an AlN/sapphire SAW sensor operating at 255.05 MHz. And the minimum phase detection limit of our system could reach 0.01deg at the same frequency