Just as the blind have long learned to paint an image in their minds by tracing their hands over a person or object, so, too, can tactile sensors yield images through contact mechanics. To effectively create innovative products that exploit capacitive tactile sensor technology, however, inspired engineers must first select the optimal materials and construction for a tactile pressure sensor.
Among the advantages of capacitive tactile pressure sensors is the variety of design options available for materials and shapes. Furthermore, while many firms chose to print their tactile sensors on films, cloth material offers the benefit of seamlessly contouring to a plethora of shapes, including that of the human body. With this in mind, capacitive tactile sensors from PPS are available in four material and construction options: conformable sensors made from conductive cloth; stretchable sensors engineered from Lycra; industrial sensors developed using Kapton; and hybrid sensors that combine both conductive cloth and Kapton.
Conformable Tactile Pressure Sensors
PPS’s conformable TactArray pressure sensors (CTS) are constructed from soft and flexible conductive cloth that measures approximately one-millimeter thick. Two types of conductive cloth are actually incorporated in these conformable pressure sensors, however. A woven high-density nickel- or copper-plated yarn is used for the electrode while a knitted silver-plated material is employed for shielding. In addition, these materials can also be waterproofed using a thin latex material akin to a silicone bladder.
Conformable tactile pressure sensors offer the key advantage of providing relatively high sensor performance in a flexible package that is moldable to multi-curved surfaces. In particular, they can wrap around cylindrical objects or shapes with multiple radii of curvature—a feature that has enabled the development of medical probes that can follow the natural curvature of the human body, for example. PPS’s conformable pressure sensors function with maximum pressures (FSR) from 1 psi to 200 psi within temperature ranges of –20° to 100°C.
Stretchable Tactile Pressure Sensors
For increased flexibility, PPS offers stretchable TactArray pressure sensors (STS). Engineered from extremely soft and conductive silver-metalized Lycra, these tactile pressure sensors can stretch to 10% with negligible baseline shift.
At about three-millimeters thick, the stretchable pressure sensors are thicker than their conformable counterparts and, thus, have more-limited layout options. They also have a slightly more-restricted temperature range of –20° to 50°C and feature maximum pressures (FSR) from 5 psi to 50 psi.
These stretchable sensors, however, accommodate bending, flexing, and stretching surfaces. As a result of this flexibility, stretchable sensors are ideal for applications in which they are embedded into objects that are going to be deformed slightly through use, such as a seat cushion, mattress, or tight clothing. They can be built in both 1-D and 2-D layouts and cover areas of up to 50 cm × 40 cm.
Industrial Tactile Pressure Sensors
Optimized for applications requiring tactile sensors that can withstand extremely high temperatures and pressures, Industrial TactArray Pressure Sensors (ITS) feature a flat and rigid Kapton construction. Kapton, a polyimide film, is characterized by its stability across a wide temperature range and serves as the foundation for the flexible circuit industry.
Industrial pressure sensors are able to measure pressure distribution up to 2000 psi in temperatures up to 200°C. Furthermore, at a thickness of just 0.3 mm, they are the thinnest sensor construction option. And while these industrial pressure sensors are by no means as flexible as stretchable and conformable pressure sensors, they can accommodate moderate bending, making them fairly robust.
Hybrid Tactile Pressure Sensors
The final tactile sensor construction in PPS’s portfolio is the hybrid tactile pressure sensor, which combines the best of both material worlds. Developed for use in low-to-moderate pressure ranges, hybrid pressure sensors leverage the benefits of both cloth and Kapton. These sensors consist of a flexible or rigid Kapton circuit board base with a cloth upper electrode and are best suited for use in designs that require the sensor to be integrated into a product.
While conductive cloth materials are already advancing innovative tactile applications, PPS is looking to meet the demands of the burgeoning trend toward wearable computing. To that end, PPS continues to conduct research on new conductive cloth materials and patterns for even greater versatility and flexibility, for a more-tactile future.
For a visual guide to capacitive tactile sensor construction, check out our video below.