Power/Performance Bits: April 23

Miniature spectrometer; RFID for IoT; solar and silver.


Tiny spectrometer
Engineers at the University of Wisconsin-Madison, Sandia National Laboratories, and Huazhong University of Science and Technology developed a miniature spectrometer small enough to integrate with the camera on a typical cellphone without sacrificing accuracy. This miniature sensor is CMOS compatible.

“This is a compact, single-shot spectrometer that offers high resolution with low fabrication costs,” said Zhu Wang of the University of Wisconsin-Madison.

Spectrometers usually rely on prisms or gratings to split light emitted from an object into discrete bands, each corresponding to a different wavelength. A camera’s photodetector can capture and analyze those bands. To resolve the difference among a mixture of different colors, spectrometers usually must be relatively large with a long path length for light beams to travel and separate.

New compact and low-cost devices could help turn ordinary cell phones into advanced analytical tools. (Photo source: Zongfu Yu / University of Wisconsin-Madison)

The new spectrometer measures just 200 micrometers on each side and uses arrays of photodetectors, each of which has a unique responsivity created by complex optical interference in photonic-crystal slabs positioned immediately on top of the photodetector pixels. This forces incoming light to bounce back and forth several times before reaching the sensor. Those internal reflections elongated the path along which light traveled without adding bulk, boosting the devices’ resolution.

The device is also capable of hyperspectral imaging, which collects information about each individual pixel in an image order to identify materials or detect specific objects amidst a complicated background.

Next, the team plans to improve the device’s spectral resolution as well as the clarity and crispness of the images it captures.

RFID for IoT
Researchers at the University of Michigan, University of Washington, and Intel propose a way more sensitive RFID tags could be used to sense the presence and movement of people in a room and detect the movement of objects.

Called IDAct, the system involves ceiling-mounted RFID readers and battery-free RFID sticker tags that cost a few cents apiece. In addition to expanding the range of items that can be part of a home’s IoT, the researchers see potential for the technology in elder care, where it could be used to unobtrusively monitor medications and daily activities to help seniors stay independent longer.

In a recent test, the system accurately detected specific activities more than 96% of the time. The test involved outfitting a volunteer’s apartment with a series of readers then tagging individual items. They collected 26 hours of data from each room while users were present, and also collected two hours of data from empty rooms as a control.

“You could imagine assistive tools that could help the elderly stay in their own homes longer by monitoring their daily activities with this technology,” said Alanson Sample, associate professor of electrical engineering and computer science at U-M. “It could detect changes in eating, sleeping or medication, for example, before the situation deteriorates and they end up in the emergency room.”

IDAct can detect minute fluctuations in the signal coming back from tags to detect when an object is moved or whether a person is touching it. It can also detect changes in a room’s electromagnetic field to infer when someone is present.

“Every object causes electromagnetic interference in a specific way,” Sample said. “We can use that information, along with information from RFID tags, to get a very detailed picture of what’s going on in a given space.”

The signals are then analyzed by a machine learning algorithm run by an onsite computer to infer what’s happening in a room. In the testing phase, this processing was done on a laptop, but Sample envisions that the necessary hardware eventually will be integrated into the RFID reader itself.

The team plans to look for industry partners that could build out the technology for use in elder care settings.

Solar and silver
Researchers at the University of Kent and University of Piraeus investigated the role rising demand for solar panels is playing on the worldwide price of silver.

Silver is used heavily in solar panels, with around 20g per panel. The silver component alone equates to around 6.1% of the total cost of the price of building each unit.

In their analysis, the researchers used data from quarterly silver prices measured from the London Bullion Market, installed solar energy capacity and solar gross electricity production between 1990 and 2016 to map correlations in demand and costs.

The price of silver rose at the same time as increased demand for solar panels, such as after the 2008 global recession and higher oil prices in 2011.

If silver prices continue to rise, the researchers warn that solar panel production costs could increase to the point where government intervention would be needed to keep making transitions to renewable energy cost-effective. Alternatively, it may push research towards development of solar panels using alternative materials, but any such work is years away from commercialization.

“The research shows that silver price rises are directly linked to the increase demand for solar panels,” said Iraklis Apergis, a PhD candidate at Kent. “This will likely have major implications for the longer-term use of solar panels and may require new alternative technologies to ensure solar panel production is cost-effective, or government subsidies.”

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