A novel surface acoustic wave sensor with embedded microcavities for size differentiation of solid microparticles

Here we present a novel method for sensing of solid microparticles using surface acoustic wave (SAW) devices. In contrast to the standard mass loaded delay line approach, microcavities with varying geometrical shapes and sizes are formed between SAW interdigitated transducer (IDT) pairs. The system operation relies on the resonance condition occurring inside the microcavity through coupling of Rayleigh waves to the sample, and the output phase angle is used for obtaining measurement results. We show through measurements that it is possible to interact with polystyrene solid microbeads trapped inside the microcavity and extract information about the size of the sample. Experimental results are compared and verified with finite element method (FEM) simulations. In essence, this novel approach resulted in a micro acoustic microscopy device with the capability of analyzing sample volumes less than 10 pL in a non-invasive manner. Experimental phase shifts of 0.14°±0.05°, 0.81°±0.26°, and 3.54°±0.49° were obtained in rectangular microcavities for 10 μm, 15 μm, and 20 μm microbeads, respectively The proposed system was designed, simulated, fabricated, and tested successfully.