A new type of solution-concentration sensor using the effects of generation and detection of bulk acoustic waves with interdigital transducers

A new type of solution-concentration sensor using a layered planar structure consisting of piezoelectric substrate–liquid solution layer–piezoelectric substrate is presented. Two interdigital transducers (IDTs) are deposited, respectively, at the two parallel interfaces of the layered structure. Under given conditions, the first IDT deposited at one interface and driven by a tone burst can generate a high frequency bulk acoustic wave (BAW) pulse into the solution layer only. This BAW pulse propagates through the solution layer and impinges on the second IDT deposited at the other interface. The second IDT then produces an electrical pulse output, containing information of the solution concentration of the liquid layer via the carrier phase delay of the BAW pulse propagation. Based on the theoretical consideration, a high sensitivity solution-concentration sensor using BAW generation and detection with the IDTs is designed and fabricated. Its feasibility and performance are also experimentally examined.