January R&D Round UpJanuary 11, 2008 By: Melanie Martella, Sensors
Happy New Year! To start 2008 out right, I'm going to give you a quick summary of the science stories that caught my eye: measuring the elasticity of MEMS, achieving better ultrasound scans, designing nano-scale sensors, and using cyclists to help monitor air pollution.
Young's Modulus of Thin Films
NIST researchers are spearheading the development of SEMI Standard MS4-1107, "Test Method for Young's Modulus Measurements of Thin, Reflecting Films Based on the Frequency of Beams in Resonance." By measuring the maximum amplitude of the resonating beams of the MEMS structure as they oscillate out of plane, you obtain a resonance frequency which can be used to calculate the Young's Modulus of the thin film. The same group has created a Web-based tool to help you convert data interferometer data into thin-film properties. A better understanding of the mechanical properties of these films will lead to better design and fabrication systems. Which can only be a good thing, since MEMS-based sensors and components seem to be more prevalent, these days.
Super lens for Ultrasound
Sébastien Guenneau, a mathematician at the University of Liverpool led a team in modeling metamaterials that could bend sound waves backwards. The New Scientist article, "Acoustic superlens could mean finer ultrasound scans" explains the research in more detail, but the gist is that, by controlling the structure of acoustic materials, and specifically the pattern of matter and voids within them, it's possible to create materials with a negative refractive index. Potential applications of these materials could include improved soundproofing, earthquake protection, and greatly improved images from existing ultrasound and seismic probes. As the article says, "Although the work is so far mathematical, the team is confident its acoustic metamaterial can be built. The model is based on the known properties of silica and the voids cut into it are accompanied by stiff bars with properties similar to carbon nanotubes."
Nano-scale Sensor Design
Researchers at Purdue University claim to have found the "missing framework" for systematically improving sensor design rather than using trial and error. Ashraf Alam and Pradeep Nair have developed a new method for modeling sensor designs ("Sensor design gets systematic," published in EE Times). So far they've used their modeling technique to assess why certain configurations of nanoscale sensors work better than others, specifically why a single cylindrical nanotube makes a better chemical sensing element than one with a planar form factor. Researchers know that smaller sensing elements work better for devices in which a target molecule sticks to the element, but nobody had a conclusive explanation as to why. Alam and Nair used their model to consider the question and then verified their results experimentally. ""What happens when you have a small cylindrical sensor like a nanotube or nanowire is that the molecules you are trying to sense can come from any direction—which per unit area makes it more likely to sense a molecule than a traditional planar sensor," said Alam." The team discovered that the sensor using a single cylindrical nanotube sensing element was 100 times as sensitive as that using a traditional planar sensing element.
I think this approach is fascinating and, if experiments continue to confirm the modeling results, could smooth the improvement of sensor designs.
Cyclists Monitoring Pollution
In a clever twist on sensor networking, the Cambridge Mobile Sensing (CamMobSens) project at Cambridge University in the UK uses small, Bluetooth-enabled wireless pollution sensors and GPS devices that communicate with the cellphones of bicycle couriers. As the cyclists travel around town, the sensors on their phones measure the concentrations of various air pollution chemicals, GPS units provide location, and both communicate the data to the cellphone via Bluetooth. Software on the phones lets them constantly report air quality back to the lab. A New Scientist article, "Cyclists' cellphones help monitor air pollution" discusses the project in greater detail. As more of us live in urban areas, the ability to monitor and assess the air quality becomes more important for public health authorities. Increased air pollution has been linked to increased rates of asthma, for instance. I have seasonal allergies and I find that exposure to higher than normal concentrations of ozone makes my allergy symptoms much, much worse.
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