Sensitive skin is a large-area, flexible array of sensors with data processing capabilities, which can be used to cover the entire surface of a machine or even a part of a human body. Depending on the skin electronics, it endows its carrier with an ability to sense its surroundings via the skin’s proximity, touch, pressure, temperature, chemical/biological, or other sensors. Sensitive skin devices will make possible the use of unsupervised machines operating in unstructured, unpredictable surroundings among people, among many obstacles, outdoors on a crowded street, undersea, or on faraway planets. Sensitive skin will make machines “cautious” and thus friendly to their environment. This will allow us to build machine helpers for the disabled and elderly, bring sensing to human prosthetics, and widen the scale of machines’ use in service industry. With their ability to produce and process massive data flow, sensitive skin devices will make yet another advance in the information revolution. This paper surveys the state of the art and research issues that need to be resolved in order to make sensitive skin a reality.
Sensitive Skin material will hold embedded sensors and related signal processing hardware. It needs to be flexible enough for attaching it to the outer surfaces of machines with moving parts and flexible joints. The skin must stretch, shrink, and wrinkle the way human skin does, or to have other compensating features. Otherwise, some machine parts may become exposed due to the machine's moving parts, and have no associated sensing. Wiring must keep its integrity when Sensitive Skin is stretched or wrinkled. This requirement calls for novel wire materials, e.g. conductive elastomers or vessels carrying conductive liquid, or novel ways of wire design with traditional materials, such as helical, stretchable wires.
The success of integrated circuits has been in large part based on the ability to integrate more devices using thin film technology into a single product. Following this model, one would want to directly integrate the devices for the sensors, intelligence, etc directly onto the substrate /fabric with the interconnect. This approach may have a systems advantage over the hybrid approach in that one can locate the sensors /intelligence wherever one wants them, as opposed just to local areas represented by the attached chips. Furthermore, the high costs and reliability issues associated with hybrid assembly could be avoided.
This approach is very application specific and depends on materials compatibility issues, To achieve flexibility, etc., it may be necessary to fabricate “hard” islands of devices on a “soft” substrate. Rather than directly integrate all functions onto one substrate, one attractive approach would be to fabricate multiple thin film substrates with different functions, which could then be bonded together in a continuous fashion to achieve the integrated system. Besides the compatibility issue, a critical issue for sensor/ intelligence integration is that of pattern definition. The ability to directly print either an etch mask or the electronic materials themselves, in patterned form might be an enabling technology which could lead to much lower cost products. Although it is unlikely that the line widths achievable with printing would approach those of conventional IC manufacturing, resulting in lower performance of the electronics or perhaps of the sensors manufactured with the technique, the lower performance might be sufficient for many applications.