Surface acoustic wave-based sensors using mode conversion in an array of periodic gratings

Novel surface acoustic wave (SAW) sensor platforms with electrode-free sensing surface are being investigated for use in applications in which the sensing environment may be conducting or corrosive. It is shown that, by using a system of four grating arrays, the IDT generated SAW can be directed to the opposite surface where it interacts with a chemical sensing medium before being directed back to the electroded surface. The design principles of these grating-based SAW sensor platforms are discussed. The signal quality and the mass sensitivity of the devices are analyzed and compared to those of a direct path SAW using chemical vapor deposited thin polymer films. Experimental results are presented for the detection of nitrogen dioxide (NO₂) in sub-ppm concentrations on devices fabricated on YZ-LiNbO₃ plates