Flexible and wearable sensors measure and track body motion, a task made more complex by the human anatomy’s numerous potential contortions. For a wearable sensor to work properly, it must be able to deform accordingly. Wearable technologies such as “smart” garments are an emerging market, as evidenced by the recent availability of clothing that connects with other devices and the Internet.
A new material was developed that is capable of sensing in real time, and can perform “multimodal” sensing, or sensing a variety of stimuli such as continuous contact and stretching in all directions. The material, called iSoft, does not require wiring or electronics within the material, providing the ability to create and customize soft sensors.
Unlike some soft sensors developed previously, iSoft can handle continuous contact, and also can be easily modified for custom purposes after manufacture. The sensor uses a piezoresistive elastomer that, when touched, changes electrical resistance that provides sensing data.
The technology features an electrical impedance tomography (EIT) technique to estimate changes of resistance distribution on the sensor caused by fingertip contact. The system also uses an algorithm called a dynamic baseline update for EIT that compensates for “rebound elasticity,” which normally causes a signal delay while the elastomer returns to its original shape. These baseline updates are triggered by fingertip contact and movement detections.
The material supports unidirectional stretching sensing using a model-based approach that works separately with continuous contact sensing. A software toolkit enables users to design and deploy personalized interfaces. The team also developed a low-cost way to fabricate the piezoresistive-elastomer-based soft sensors for instant interactions.
The performance of contact and stretching sensing was validated through a series of experiments and evaluations. The sensor is a thin, rubbery sheet with electrodes around the periphery. It harnesses a material called carbon-filled silicone rubber, a non-toxic piezoresistive material that has been widely explored in research for various types of low-cost sensors. Limitations in interactions have been mainly due to a rebound elasticity of the material, which causes a slow recovery of the sensing signals after material deformations.
The dynamic baseline update process solves the problem, while the EIT technique makes it possible to fabricate sensors in a single-volume manner, or using electrodes only on the periphery of the material, eliminating the need for invasive wires and sensors within the material.