SENSORS AND SENSIBILITY
By Charles Nevsimal
When it comes to life, Dr. Stephen Heinrich, professor of civil, construction and environmental engineering, prefers to turn autopilot off. Whether by indulging in 19th-century French literature, 1950s jazz or long contemplative walks, slowing down from the warp-speed tendencies of our culture is integral to Heinrich’s day. Taking time to reflect ... consider ... plan. “I have come to appreciate the importance of intention,” says Heinrich, whose research in theoretical and applied mechanics has become an incarnation of intention in the past 25 years. Heinrich and his team are working to develop an effective solution for detecting air pollutants, water toxins and blood-borne disease markers using microcantilever beams as chemical sensors. “Think of a diving board,” he says. “A tiny diving board, several thousandths of a millimeter in size. That’s the scale of the structures we study.” Here’s how they work: The microcantilever — fabricated from silicon or a polymer — is coated with a chemically sensitive layer that will absorb certain target substances if they are present in the surrounding air or liquid. The amount absorbed, dependent upon the substance’s concentration, is measured by comparing the difference in the microcantilever’s mass before and immediately after the sample is collected. Any increase in mass denotes a corresponding concentration of the target substance. Says Heinrich: “A slight increase in mass is recognizable as a shift in natural frequency. After the microcantilever is put into a resonant vibrational state using various actuation methods, the frequency shift may be monitored and the associated mass increase and ambient concentration determined — if the underlying mechanics are fully understood.” By measuring the shift, Heinrich and his team can deduce chemical concentrations in gas and liquid environments. “My involvement,” he says, “is understanding how the device’s design and the environmental properties affect the microcantilever’s vibrational response through theoretical modeling: structural mechanics, fluid mechanics, mathematics — the areas in which my professional passion lies.” What does Heinrich’s research mean for the world? It could make it a safer place to live. “As an example,” he says, “chemical sensing devices such as these could be deployed to help monitor water distribution systems or large transportation networks like New York City’s subway system, thereby ensuring rapid responses to environmental hazards or providing safeguards against terrorist acts.” A safer place to live means a better place to slow down, which means more time to enjoy life’s finer intricacies: a Chet Baker solo ... a fine Bordeaux ... enjoying the Brewers. More time to pursue excellence in research and teaching at Marquette. For Stephen Heinrich, a dream come true.
Chemically sensitive microbeams may be a more sound solution for detecting environmental toxins and disease markers.
November 2011 // 14