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Artistic rendering of a smart liquid microlens

Electrical and Computer Engineering

Autonomous lenses may bring microworld into focus

When Assistant Professor Hongrui Jiang looked into a fly’s eye, he saw a way to make a tiny lens so “smart” that it can adapt its focal length from minus infinity to plus infinity—without external control. Jiang, Biomedical Engineering Professor David Beebe, postdoctoral researcher Liang Dong and doctoral student Abhiskek Agarwal described the technology in the cover story of the Aug. 3 Nature.

At hundreds of microns up to about a millimeter, variable focal length lenses aren’t new; however, existing microlenses require external control systems to function. Because they can tune hydrogels to respond to just about any stimulus parameter, including physical, chemical or biological stimuli, Jiang’s group chose hydrogels to actuate its lens function.

A water-oil interface forms the lens, which resides atop a water-filled tube with hydrogel walls. The tube’s open top, or aperture, is thin polymer. The researchers applied one surface treatment to the aperture walls and underside, rendering them hydrophilic, or water-attracting. They applied another surface treatment to the top side of the aperture, making them hydrophobic, or water-repelling. Where the hydrophilic and hydrophobic edges meet, the water-oil lens is secured, or pinned, in place.

When the hydrogel swells in response to a substance, the water in the tube bulges up and the lens becomes divergent; when the hydrogel contracts, the water in the tube bows down and the lens becomes convergent.

The lenses could advance lab-on-a-chip technologies, optical imaging, medical diagnostics and bio-optical microfluidic systems. The researchers are patenting the technology through the Wisconsin Alumni Research Foundation (WARF). Grants from the UW Graduate School, the Department of Homeland Security-funded National Center for Food Protection and Defense at the University of Minnesota, and from WARF partially funded the research.

Microgrids deliver value to energy consumers

In industry, electricity is measured in quality as well as quantity. A disruption in the power supply can damage sensitive equipment as well as cost many thousands of dollars in lost productivity. Thanks to technology invented by Professor Emeritus Robert Lasseter, large electricity customers across the country could enhance their power quality, yet lower their energy costs. Major U.S. electricity producer American Electric Power and the Consortium for Electric Reliability Technology Solutions (CERTS), an industry-university-government cooperative, are researching, developing and demonstrating Lasseter’s microgrid concept.

Through CERTS, Lasseter developed simple, reliable power electronic control technology that allows a customer to access higher power quality and lower energy cost using combined heat and power sources in a microgrid structure. The microgrid is a system of small generators clustered with loads; it can operate either connected to the utility grid or independent of it. During a grid disturbance, the technology seamlessly disconnects the microgrid from the utility without reducing power quality or disrupting loads within the microgrid. When utility power resumes, the microgrid automatically resynchronizes and seamlessly reconnects to the grid.

Without extensive, expensive custom engineering, the CERTS microgrid provides functionality via peer-to-peer and plug-and-play concepts for each component within the microgrid, says Lasseter. In addition, its design provides high system reliability and flexibility in the placement of distributed generation within the microgrid.

American Electric Power assembled the system and began full-scale testing in summer 2006 at its research and development facility in Gahana, Ohio. Other research participants include Sandia National Laboratories, Northern Power Systems, and TeCogen Inc.

Charting semiconductors on the scale of atoms

As the result of a unique university-industry collaboration, engineers can image nanoscale transistors on semi-conductor chips by mapping them atom by atom. Professor John Booske, and Keith Thompson, David Larson and Tom Kelly of Madison-based Imago Scientific Instruments used the company’s local electrode atom probe (LEAP) microscope to pinpoint individual atoms of boron—a common additive, or dopant, in semiconductors—within a sea of silicon atoms.

For atomic-scale transistors to function properly, boron must be implanted at very high concentrations within the first 200 to 300 atomic layers of the silicon surface. But a critical heating step for making transistors often causes boron atoms to diffuse more deeply, ending up in regions where another dopant, usually arsenic, resides.

When Thompson was a graduate student under Booske, the pair devised a rapid microwave heating technique they believed would limit diffusion; however, the system’s tiny scale left them no way to confirm the boron atoms were staying put. Boron movement and clustering was never experimentally verified, says Thompson. “Physics says that it should happen, but there was never a technique to actually show it happens,” he says.

Enter LEAP, which can analyze roughly 50 million atoms an hour. To create images, the microscope applies voltage to a specially prepared, needle-shaped sample, ripping atoms from the tip of the sample one by one. An electric field then pulls the charged atoms to a detector, which identifies them and records their location in the original specimen.

In the first practical application of the microscope to semiconductors, rather than metallic specimens, the team used LEAP to show, in precise 3-D detail, that rapid-heating techniques do cause boron to spread from its original location. Moreover, the measurements showed that in some situations, the movement of boron atoms can result in undesirable clustering where researchers previously assumed the atoms stayed uniformly spread throughout their intended location.

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