University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Tuesday, October 15th 2019
3:30 pm:
CESTA Seminar in 110 PAN
Speaker: Joey Talghader, Electrical and Computer Engineering, UMN
Subject: Distributed Sensing: When are our sensors too small to be smart?

Distributed sensor networks are proliferating in products and systems through the economy, and their technological capabilities are rising at a rapid rate. At present, most sensors are either directly connected to the networks of which they are a part, for example in automobiles, or they are large and complex enough that they have on-board power and can connect periodically to the global telecommunication system, for example in remote weather stations. These types of sensors are often called "smart" sensors because they can take advantage of power supplies, communications devices, microelectronic data processing, software, and other resources that are part of their individual unit or the system to which they are directly or indirectly connected.

However, future systems may have sensors that travel passively, say by fluid flow, wind, or water and, further, have dimensions of a few microns or less. Such sensors cannot be “smart” in the traditional way we define the term. The difficulty is not merely miniaturization; instead, there are fundamental issues of diffraction for remote communication and volume power density for batteries or photovoltaic cells that prevent independent operation.

This talk will discuss these issues and present two examples of distributed sensors that must operate in environments where smart sensing is difficult. The first sensors are semi-autonomous particles for sensing metal-ion concentration in fluids. The devices were designed to be released in numbers to collect statistical data as they flow through microchannels. They incorporate a monolithically integrated photovoltaic (PV) power supply and use a resonant cantilever mass sensor to detect electrodeposited metal at the tip of a cantilever. Individual devices correctly predict, within about a factor of two, the metal ion concentration even when operating off of scavenged light from a room lamp. The current sensors operate at powers of about 50nW, and are integrated into a total volume below 0.046mm3. The second sensors are also particles but designed to measure temperature inside explosions, perhaps the harshest environment on earth. The sensor particles are embedded in or around an explosive device and disperse with the explosion. The thermoluminescence (TL) of the oxide microparticles gives direct information on temperature and time because the trapped charges that ultimately give rise to TL have a probability of detrapping that follows an Arrhenius-type relationship. The effects of maximum temperature on the intensity ratios of various luminescent peaks have been compared with first-order kinetics theory and predict temperatures to within 5% or better.

These types of passive, “dumb” sensors are absolutely necessary in certain critical environment but present challenges of incorporation into traditional distributed networks. We hope to contribute to CESTA by addressing some of these challenges.

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