Creating a Soft Tactile Skin Employing Fluorescence Based Optical Sensing

Currently, optical tactile sensors propose solutions to measure contact forces at the tip of flexible medical instruments. However, the sensing capability of normal pressures applied to the surface along the tool body is still an open challenge. To deal with this challenge, this letter proposes a sensor design employing an angled tip optical fiber to measure the intensity modulation of a fluorescence signal proportional to the applied force. The fiber is used as both emitter of the excitation light and receiver of the fluorescence signal. This configuration allows to (i) halve the number of optical fibers and (ii) improve the signal to noise ratio thanks to the wavelength shift between excitation and fluorescence emission. The proposed design makes use of soft and flexible materials only, avoiding the size constraints given by rigid optical components and facilitating further miniaturization. The employed materials are bio-compatible and guarantee chemical inertness and non-toxicity for medical uses. In this work, the sensing principle is validated using a single optical fiber. Then, a soft stretchable skin pad, containing four tactile sensing elements, is presented to demonstrate the feasibility of this new force sensor design.