A High-Sensitivity Tactile Sensor Array Based on Fiber Bragg Grating Sensing for Tissue Palpation in Minimally Invasive Surgery

This paper presents a novel and high-sensitivity optical tactile sensor array based on fiber Bragg grating (FBG) to explore and localize tissue abnormalities during tissue palpation in a minimally invasive surgery. This sensor consists of five separate tactile cells with the same configuration, associated fixations, and holder parts. Each tactile cell is mainly composed of a spiral elastomer, a suspended optical fiber inscribed with an FBG element, and a contact head connecting the elastomer with a threaded connection. The two ends of the fiber were glued on the two sides of the spiral elastomer to form a tight suspension status. This configuration can effectively avoid the FBG chirping failure and achieve a higher sensitivity compared with the conventional direct FBG-pasting methods. The corresponding theoretical model has been derived, and the finite element method based simulation has been performed to facilitate the structure design and investigate both static and dynamic performances. Both static calibration experiments and dynamic loading experiments have been conducted to characterize the sensor's performance. The prototyped sensor can achieve a high resolution of up to 0.93 mN and is able to operate within a force measurement range of 0-5 N with a maximum relative error of less than 8.22%. The further surface estimation experiments and in-vitro palpation implementation on a silicone phantom embedded with simulated tumors have validated the effectiveness of the proposed design. The in-vitro experiments have demonstrated an excellent capacity to detect tumors with an embedded depth of up to 8 mm.