Micromachined Tactile Sensor for Soft-Tissue Compliance Detection

Compliance detection becomes very essential in minimally invasive surgery (MIS). It can help in detection of cancerous lumps and/or for deciding on tissue healthiness. In this paper, a micromachined piezoresistive tactile sensor, with two serpentine springs and 500-μm cubic mesas, has been designed for detecting the compliance of soft tissue independent of the applied distance between the sensor and the tissue. The measuring range of the sensor is chosen to be associated with the soft-tissue properties. The sensor parameters are optimized to give high sensitivity and linearity of the sensor output. The design is simulated using ANSYS for checking the sensor performance. Then, the sensor is fabricated and tested by three types of specimens, namely, specimen chips with known stiffness, silicone rubber specimens, and chicken organ specimens (leg and heart). For the specimen chips and silicone rubber specimens, the sensor distinguished between different stiffnesses independent of the applied displacement in the range of 50-200 μm. The sensor measured Young´s modulus up to 808 kPa with an average error of ±7.25%. For the chicken leg and heart, the sensor distinguished between them under the applied displacement from 100 to 200 μm, and they were calculated as 12 ±1 kPa and 81 ±8 kPa, respectively.