Date of Award
Doctor of Philosophy (PhD)
In a world that is increasingly dominated by advances made in digital systems, this work will explore the exploiting of naturally occurring physical phenomena to pave the way towards a self-powered sensor for Cyber-Physical Systems (CPS). In general, a sensor frontend can be broken up into a handful of basic stages: transduction, filtering, energy conversion, measurement, and interfacing. One analog artifact that was investigated for filtering was the physical phenomenon of hysteresis induced in current-mode biquads driven near or at their saturation limit. Known as jump resonance, this analog construct facilitates a higher quality factor to be brought about without resorting to the addition of multiple stages and poles in the filter. Exploiting this allows a filter that mimics mammalian cochlea using nW of power, and the viability of such a filter was demonstrated in the application of speaker recognition. Features were extracted using a silicon cochlea analog frontend, which outperformed features from traditional linear filters when classification was done with a Gini-SVM.
To realize the measurement stage of the frontend, a previously reported technology, the Piezoelectric-Floating-Gate (PFG) was employed. The PFG matches physics of Impact-
Ionized Hot-Electron Injection (IIHEI) in silicon metal-oxide field effect transistors with a piezoelectric transducer to drive nonvolatile data-logging measurements. The PFG implementation is self-powered in the sense that the energy required for sensing comes from the signal being observed, which allows for continuous, zero-downtime measurements of signals that exceed the IIHEI threshold and can drive nW loads. Moreover, since it directly matches the transduction stage to measurement, it obviates the need for an explicit energy conversion stage in the frontend. Multiple interfacing technologies were evaluated, including: wired, self-powered radio-frequency (RF) backscatter, periodic 915 MHz active RF, and a hybrid model that uses energy scavenging to determine if an interrogator is within range before transmitting. A multi-year deployment of this sensor frontend for structural health monitoring is currently active on the Mackinac Bridge in northern Michigan and demonstrates successful transition from laboratory to practice for a CPS.
Finally, a modification to the PFG topology to include filtering aspects borrowed from earlier study was proposed and fabricated on a standard 0.5 μm CMOS process. Measurements show that the PFG sensor can be endowed with frequency discriminating capabilities to better focus on signals of interest. The modifications also give rise to a means for higher sensitivity (input stimuli below IIHEI threshold) data-logging that would vastly expand the potential application space.
Roger D. Chamberlain, Baranidharan Raman, William D. Richard, Xuan Zhang,