Soft Inductive Coil Spring Strain Sensor Integrated with SMA Spring Bundle Actuator

Highly Inductive Coil Spring Strain/Compress Sensors Integrated with Shape Memory Alloy and Shape Memory Polymers-CNTs

Future wearable electronic gadgets offer great potential for using stretchable, strain-sensitive materials to instantly detect human motion and record physiological information. This paper presens a strain/compress sensor made from a Shape memory alloy (SMA) coil spring covered with silver pastes and the composite of carbon nanotubes and Shape memory polymer (SMP). The combination of the shape memory materials that expand or contract automatically by temperature improved the mechanics of the sensor. First, the proposed sensors showed an excellent ability to broad-range strain of 250% and compress of 50% with a relative inductance (∆L/L0 ) range from -35% to 50%, respectively. Durability during 1000 loading and unloading cycles at 200% strain is included. Secondly, by monitoring changes in resistance, inductance, and time, it is determined how many silver layers appropriate for transformation should be in order to improve the recovery time of the SMA coil spring. Moreover, the presence of CNTs in the composite-covered outer of sensors helps to reduce the influence of the relation between resistance and temperature in the range from 30 °C to 110 °C. Finally, a device is suggested for monitoring arm and triceps brachii muscle movements based on the stretchable area as a key parameter.

Coil Formation of a Silicone String Using UV-Ozone Treatment

Microcoils are used in various mechanical devices. However, existing methods for producing microcoils from polymers often require expensive equipment. In this study, microcoils were prepared using a cost-effective and simple method. The material used was silicone, which is a biocompatible polymeric material. Silicone was solidified inside glass capillaries to form thin, straight strings with a diameter of 140 μm. The string was then transformed to a coil shape by oxidation using UV-ozone treatment while it was prestretched and pretwisted. The resilience force from the prestretching and pretwisting forces caused the string to bend and twist, respectively. As a result of the combination of these deformation modes, a coil was formed. As an application of the coils, an actuator was prepared, which repeatedly transforms between straight and coiled shapes. The actuation was caused by the swelling/deswelling of silicone with hexane. A large strain of 54% was obtained.