Finite element simulation of a highly sensitive SH-SAW delay line sensor with SiO _2 micro-ridges

The paper presents 3D finite element simulation of an SH-SAW delay line sensor to investigate coupled resonance with SiO _2 micro-ridges designed along the wave propagation direction on a 36 ^∘ -YX LiTaO _3 substrate. Time response simulation is used to calculate the displacements and voltages at the output IDT. The device generates a shear wave with horizontal displacement component ten times greater than vertical displacement component. Mass loading is simulated by applying an equivalent surface mass density of double-stranded DNA uniformly on the SiO _2 ridges. At critical ridge height, both substrate and ridge vibrate in unison leading to a sharp change in the phase shift from negative to positive causing coupled resonance. In the presence of coupled resonance, the device offers high mass sensitivity of 1295 m ^2 /kg which is about 20 times greater in comparison to the mass sensitivity of a conventional SiO _2 based Love wave device. The increase in mass sensitivity at coupled resonance is attributed to the increase in the area-averaged stress at the interface of micro-ridge and substrate, going above 8.5 MPa. As ridge height is varied, a transition occurs in the mode of vibration leading to a 5 dB swing in the insertion loss of the device near the coupled resonant height.