Design, Fabrication and Characterisation of Multi-Parameter Optical Sensors Dedicated to E-Skin Applications

Abstract

For many years there has been a strong research interest in soft electronics for artificial skin applications. However, one challenge with stretchable devices is the limited availability of high performance, stretchable, electrical conductors and semiconductors that remain stable under strain. Examples of such electronic skin require excessive amounts of wires to address each sensing element—compression force and strain—in a conventional matrix structure. Here, we present a new process for fabricating artificial skin consisting of an optical waveguide architecture, enabling wide ranging sensitivity to external mechanical compression and strain. The manufacturing process allows design of a fully stretchable polydimethylsiloxane elastomer waveguide with embedded gratings, replicated from low cost DVD-Rs. This optical artificial skin allows the detection of compression forces from 0 to 3.8 N with controllable sensitivity. It also permits monitoring of elongation deformations up to 135%. This type of stretchable optical sensor is highly robust, transparent, and presents a large sensing area while limiting the amount of wires connecting to the sensor. Thus, this optical artificial skin presents far superior mechanical properties compared to current electronic skin.

Soft Optical Waveguides for Biomedical Applications, Wearable Devices, and Soft Robotics: A Review

“…Microstructured planar soft waveguides typically have complex and diverse waveguide structures that are tens of microns in size. In recent years, inkjet printing, [54][55][56] laser direct writing, [57,58] and photolithography [59,60] have emerged as efficient techniques for fabricating these structures. Common microstructures found in optical waveguides are diffraction gratings.…”

“…Reproduced with permission. [ 60 ] Copyright 2022, MDPI. e) Phase shift sensing of temperature based on gel polymer waveguide.…”

“…An artificial skin with a grating structure made from a fully stretchable PDMS material has been recently fabricated. [ 60 ] This optical artificial skin has a tailored sensitivity that can detect compression forces ranging from 0 to 3.8 N, while also allowing for monitoring of deformations with up to 135% elongation. Particularly, a special mechanism for detecting the strain applied to the waveguide is the direct colorimetric method, which is essentially a wavelength measurement.…”

“…d) Wavelength and color sensing of compression and deformation based on PDMS waveguide with grating structure using e-beam lithography. Reproduced with permission [60]. Copyright 2022, MDPI.…”