Communications of the ACM
Technical Perspective: The Future of Large-Scale Embedded Sensing
The dream of computational material has been in the air for decades, dating at least to the Smart Matter program at Xerox PARC in the late 1990s. Inspired by the complexity of biological skin, my own team (see Sensate Media, Communications, Mar. 2005, p. 70) and others have looked to integrate distributed sensing into large flexible membranes, a trend that continues in research today (see the IEEE 2019 Proceedings on Flexible Electronic Skin). Most of these devices, however, are actively powered. The SATURN system described in the following paper works passively, energized essentially by static electricity generated as layers move relative to each other during vibration, hearkening perhaps to, at a smaller scale, electret microphones, which exploit charge trapped on their foil membrane to produce a vibration-dependent voltage. Using only two components—an FET and matching inductor—the authors are able to modulate the resonance of a RF antenna that can be embedded in the material and read out via passive backscatter from an external transmitter, allowing a material to work as an audio pickup without a power source.
Traditional work in this area has tended to exploit piezoelectric polymers like PVDF, which generate voltage under strain. Triboelectrics present a different approach, although provide probably an even higher source impedance that would challenge power conversion even more. SATURN sidesteps this entirely, using the generated voltage directly at the gate of the resonance-modulating FET (ironic, in that we usually work to avoid destructive static charge there—but the potentials are much lower here). Hence, the key contribution of this paper is a means of transmitting audio features from a passive triboelectric-generating material.
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