A multi-sensor tactile system based on fiber Bragg grating sensors for soft tissue palpation

Superficial tissue palpation is a clinical examination to detect tumors in soft tissue, like breast, by applying variable forces on its surface. Recently, instrumented tactile probes based on different technologies (e.g., electrical and optical sensors) were developed to quantitatively detect changes in the tissue stiffness, improving the chances of early tumor diagnosis. Among many options to develop tactile probes, fiber Bragg grating (FBG) sensors are gaining increasing traction, thanks to their superior potentials (e.g., high sensitivity, small dimensions, electromagnetic immunity interferences, and multiplexing capability). This study proposed a multi-FBG sensors tactile system for superficial breast palpation, as an optimization of a previously designed prototype, in terms of dimensions and number of sensors. It represents the first step towards the creation of a matrix of sensors for optimizing the tumor identification. In details, a three-FBG array was integrated into a 3Dprinted structure to simultaneously investigate multiple measurement sites, enhance the system spatial resolution, and minimize the probe encumbrance. The design of the system was guided by a finite element analysis. Then, a metrological characterization was performed, focusing on the investigation of the FBGs sensitivity to force and analysis of the crosstalk effects among sensors within the same structure. Subsequently, palpation tests on phantoms mimicking soft tissues with a tumor were conducted, revealing the ability of the fabricated system to detect stiffer materials within flexible substrates. These findings make the proposed system an ideal candidate for diagnostic tissue palpation.