Design of an Ultrasonic Concentrator for Vibro-Tactile Sensors Using Electro-Mechanical Analogy

Vibro-tactile sensors have been utilized to measure the mechanical properties of soft materials based on the shift of resonant frequency. However, their low signal to noise ratio (SNR) has impeded them from critical applications where accurate measurements are required. One of the ways to improve the SNR is to add an ultrasonic concentrator as a mechanical filter to the vibro-tactile sensor. In order to maximize the SNR, the concentrator should be optimally designed; however, systematic design approach of the concentrator has rarely been considered so far. In this paper, a hybrid design approach employing both analytical analysis and numerical simulation is presented. For analytical analysis, impedance analogy was used to facilitate the designing process, and the numerical simulation using FEA was conducted to carry out the parametric refinement of the design. The performance of the final design was verified by mechanical and electrical characteristics tests. Tests results indicate that the longitudinal resonance mode of the sensor was significantly enhanced and the increase in its mechanical quality factor was achieved by the ultrasonic concentrator. The tactile sensing experiments on the silicone rubber samples showed the high potential of the vibro-tactile sensor in estimating the elastic moduli of soft materials in the range of 5-100 kPa, which is not readily available with conventional testing methods.