Stretchable Thermoplastic Elastomer Optical Fibers for Sensing of Extreme Deformations

Abstract

The design of advanced materials with coupled optical and mechanical properties is an important challenge in materials science; especially, the implementation of soft materials in optics has recently gained significant interest. Soft optical systems are particularly versatile in sensing, where large and repeated deformations require dynamically responsive materials. Here, stretchable step‐index optical fibers, which are capable of reversibly sustaining strains of up to 300% while guiding light, are demonstrated. A continuous and scalable melt‐flow process is used to coextrude two thermoplastic elastomers, thereby forming the fibers' high index core‐low index cladding structure. Deformation of the fibers through stretching, bending, and indentation induces detectable, predictable, reversible, and wavelength‐dependent changes in light transmission. Quantitative knowledge about the coupling of the fibers' mechanical and optical properties forms the basis for the design of fiber‐based sensors that are capable of reliably assessing extreme mechanical stimuli. The fibers utility in sensing scenarios is demonstrated in a knee brace for continuous knee motion tracking, a glove for control of a virtual hand model, and a tennis racket capable of locating ball impacts. Such devices can greatly improve quantitative assessment of human motion in rehabilitation, sports, and anywhere else where large deformations need to be monitored reliably.

Wearable and Stretchable Strain Sensors: Materials, Sensing Mechanisms, and Applications

“…[1,11,37] Recently, soft and stretchable optical strain sensors have also received considerable interest in wearable and soft robotic applications because of their merits, such as resistance to environmental factors (e.g., temperature and humidity) and minimized sensitivity to electromagnetic interference ( Figure 1). [28,38,39] In view of the above statements, this Review only emphasizes resistive, capacitive, and optical strain sensors.…”

“…Since the introduction of novel fabrication techniques in electronics (e.g., soft lithography and 3D printing), flexible polymeric waveguides have been investigated for wearable strain sensing applications. [20,28,38] The principal sensing mechanism is based on the changes in the transmission of strain sensors upon deformation measured by the generated light power difference between the light source and photodetector. [28] The most recently reported stretchable optical strain sensors have shown promising results in terms of resolution and dynamic performance.…”

A Review on Measuring Affect with Practical Sensors to Monitor Driver Behavior

“…For example, a wearable capacitive sensor was demonstrated to detect restless leg motion [87]. Soft, deformable optical materials made it possible to measure shape changes in a leg-worn athletic tape caused by weight bearing [88], and hand motions in a glove [89] equipped with all-polymer strain sensors. Body motions like fidgeting and slouching are also visible in images; Fernández et al [1] gives a comprehensive overview of camera-based sensors for detecting motions relevant to driver fatigue and inattention.…”

Stretchable and Temperature‐Sensitive Polymer Optical Fibers for Wearable Health Monitoring

“…However, conventional inorganic optical waveguides, made of silicon or glass, are highly stiff and rigid, which makes them intrinsically incompatible with the soft and elastic skins. To address these limitations, stretchable polymers such as hydrogels and elastomers have been employed for the fabrication of optical waveguides that could endure large strain deformations. For example, in a previous research, we have demonstrated a highly stretchable and biocompatible optical fiber based on a hybrid hydrogel of alginate and polyacrylamide that showed a remarkable stretchability of more than 700% .…”