Stretch sensors are a type of sensor designed to measure soft structures, including soft robots and the human body. StretchSense, a company from New Zealand, has developed commercially available stretch sensors that can measure either stretch, bend, shear, or pressure. These stretch sensors are essentially flexible capacitors. When the sensor deforms (due to stretching or squeezing) its capacitance value changes. The sensor sends data about its capacitance to a Bluetooth enabled device, and the StretchSense App translates the data to give a user highly precise information about what the sensor is detecting. StretchSense sensors can be made in various sizes, elasticities, and sensitivities depending on desired application.
The inside of the stretch sensor consists of a stretchable signal electrode sandwiched between two ground electrodes which are separated by silicone dielectric insulators. Since the sensor is essentially a flexible parallel plate capacitor, the two dimensions that change when the sensor is stretched are thickness and area of the conductive layers. Stretching the sensor increases area and decreases thickness which both contribute to an increase in capacitance. Since capacitors resist a change in voltage, the capacitance can be indirectly measured through an applied voltage. By applying a voltage to the sensor and comparing the actual voltage output to what would be expected without a capacitor, the capacitance of the sensor can be determined.
StretchSense offers two versions of stretch sensor: A silicone based sensor and a fabric based sensor. The silicone variety offers a set of mounting holes to attach to your system, while the fabric variety has a thin sew-able region on each side of the sensor which is perfect for integrating with wearable applications.
Silicone stretch sensor
Fabric stretch sensor
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