Improved sensitivity of TSM sensors using a composite Sensor-Actuator Hybrid Structure (SAHS)

Thickness shear mode (TSM) sensors are widely employed as biosensors. One of the most important operational parameters of biosensors is their sensitivity. Due to the fact that TSM sensors have maximum sensitivity at the center of the sensing electrode, there has been increased research efforts focused on the development of techniques for controlling the distribution of the measurand over the sensor surface. This paper discusses the improvement of TSM sensor performance via the construction of a simple, inexpensive, sensor-actuator hybrid structure (SAHS). The SAHS consists of a piezoelectric ceramic radial mode, ring-shaped, actuator affixed to a TSM AT-cut quartz sensor. The ring actuator operating at a given frequency generates a specific force-pattern over the TSM sensor surface. A finite element analysis (FEA) is used to simulate various force patterns, identify the appropriate ones and determine the corresponding driving frequencies of the ring actuator. The simulation results show that the SAHS is capable of concentrating micron and sub-micron sized particles to high sensitivity locations at and around the center of the sensor. A structure incorporating a ring-actuator (6.35 times 2.4 times 1 mm) with a TSM sensor, operated at 100 MHz, has been experimentally tested with micrometer sized inorganic particles, namely, polystyrene and silica, and biological bacterial spores, Escherichia Coli. The response of the sensor, to particle loading, has been improved by means of manipulation and clustering of particles. Furthermore, particle distribution over the SAHS was recorded and was consistent with the FEA simulation results.