Design of SH-SAW phononic devices for highly sensitive and ultra-low power sensing applications

SAW biosensors based on a shear horizontal wave have been developed to detect breast cancer markers, E. Coli bacteria, and in DNA hybridization studies. A current trend in these biosensing systems is to move away from clinical laboratories where expensive bulky equipment and highly skilled personnel are needed and move to point-of-care-testing (POCT). Monitoring a physiological signal such as blood glucose levels in a patient with a wireless sensor provides a good example. A major challenge to the incorporation of wireless sensors for biosensing/medical applications is power consumption. Inspired by the concept of phononic crystals (PCs), we incorporate microcavities in the form of periodic inclusions in a SAW devices made of 90 ° ST-X Quartz and 36° YX LiTaO₃. We utilize a three-dimensional (3-D) finite element model (FEM) to compare insertion loss (IL) and mass sensitivity of SAW sensors having microcavities and show that significant improvements in sensitivity and power consumption can be obtained. The resulting metamaterial has properties different than those of the host material; in particular, density and elastic properties. To harness the potential of PCs within a SAW sensing device, we have systematically evaluated properties such as size, periodicity and nature of the filling materials because these affect the center frequency, power consumption, width of the bandgap, and sensor sensitivity among other things. Our simulation and experimental results suggest the possibility of tuning the acoustic band-gap and acoustic confinement to realize novel SAW and SH-SAW phononic sensors having low insertion loss and high sensitivity.