This section was edited by Associate Editor Jeffrey Winters.

INSTRUMENTATION AND CONTROL

Jet Thermometer

Jet engines are hard systems to monitor. When the machine is operating, it's a forbidding environment for transducers. But the failure of just one part of the system can spell disaster.

To get a better sense of when bearings inside a jet engine are approaching the end of their productive lives, the U.S. Air Force and engineers at Purdue University in West Lafayette, Ind., have teamed up to develop a minuscule wireless sensor tough enough to function inside an engine.

It's hot in there: The Air Force is working with a team at Purdue to develop a microsystem that can monitor bearing conditions in a jet engine.

The work with the Air Force is an offshoot of an earlier microelectromechanical system designed by Farshid Sadeghi, a mechanical engineering professor at Purdue. That system was intended to monitor the bearings supporting the gyroscopes inside orbiting satellites. When those bearings fail, the gyro seizes up and the satellite tumbles out of its stable orbit. By sending a signal that a bearing is going bad, the sensor can warn controllers on Earth that it is time to switch to a backup gyroscope.

An Air Force grant in 2006 directed the engineers to look at how a similar system could work in a jet environment. MEMS systems have had a difficult time functioning in conditions as harsh as those within a jet engine, with its high temperatures, extreme stresses, and ubiquitous oil.

Indeed, one of the mandates from the Air Force was for the new sensor to work at more than 570°F, an increase of more than 160° over the current sensor technology. At such high temperatures, supplying electricity for a sensor becomes problematic as batteries don't perform well when they are subjected to that sort of heat. The solution the Purdue team hit upon was to ditch the battery entirely, relying instead on generating current via inductive coupling.

The design is also innovative for being so small; it can be installed close to the bearings themselves without disturbing them and so can provide a direct measurement of the bearings' temperature. (Current systems measure this indirectly by sampling the temperature of lubricating oil.)

It may be a few years before these sensors can be incorporated into the next generation of engines for fighter planes and attack helicopters. But if the design proves successful, similar MEMS-based monitoring systems could make their way into commercial aircraft and even cars. 

Medical Metal Detector

Broken bones are often held in place with a number of stainless steel or titanium screws. Five to 10 percent of the time, however, these bits of hardware can do more harm than good, either triggering an infection or causing searing pain. Removing those troublesome screws can be a chore, as scar tissue can obscure their exact location, leading to time-consuming and invasive surgery.

A team of biomedical engineering students from Johns Hopkins University in Baltimore believes they have developed the right tool for finding and removing these screws. The technology, it turns out, is based on the beachcomber's familiar metal detector.

The battery-powered device employs a current pulsing through a coil of wire to create a small magnetic field. When the coil nears a piece of metal, the frequency of the pulsation shifts; the closer the object, the greater the shift. Following this signal, a surgeon using the device can home in on the head of the screw.

The device, which is now in working prototype form, sits inside a non-metallic, needle-like tube. When the detector finds the head of the screw, the coils are withdrawn and a minuscule screwdriver is inserted through the tube to remove the hardware.

A private company is planning a round of market research to gauge interest in the device from orthopedic surgeons. 

Anyone who has spent a night in a hospital knows the experience of trying to sleep while hooked up to various medical monitors. New sensors developed at the University of Arkansas in Fayetteville might change all that, however. The sensors, which can monitor such vital readings as temperature and respiration rate, could be incorporated into tee shirts.

The present-day state-of-the-art for microsensors—silicon-based MEMS devices—aren't flexible and are hard to integrate into comfortable, wearable materials. Researchers from the university's Organic Electronics and Devices Laboratory have used a non-silicon semiconductor, an organic molecule called pentacene, and combined it with carbon nanotubes to create a sensor that can be made directly on a flexible plastic substrate.

Respiration is monitored through a strain sensor that converts mechanical deformation into an electrical signal. The research team found that small sensors were more sensitive to such changes than large ones were.

The temperature sensor is a thin-film transistor in which the current allowed to flow is sensitive to changes in temperature. The temperature and respiration data can be sent through a small antenna in the fabric to a wireless network, so the information can be monitored constantly. In time, such a system could eliminate another nighttime hospital ritual: the 3 a.m. check of one's vital signs.

As was demonstrated dramatically last summer with the collapse of a highway bridge in Minneapolis, annual visual inspections are not sufficient to make sure static spans don't start to become, well, dynamic. Continual monitoring using remote strain sensors has been promoted as a solution.

The problem is that maintaining energy-using sensors can be difficult in remote locations. After all, what good is a bridge monitor with a run-down battery? Indeed, if such sensors became the standard, millions of batteries for bridge sensors would have to be replaced each year, putting an additional maintenance burden on transportation departments hard-pressed to fill in potholes.

Bridge monitor: Harvesting the energy of vibration from passing traffic may one day power sensors that report the soundness of critical structures.

Engineers at Clarkson University in Potsdam, N.Y., have developed an innovative way around that problem. Instead of running the sensors off batteries, the wireless monitors they have built are powered by a virtually limitless energy resource: the traffic rumbling over the bridges themselves.

Energy harvesting for remote applications has received a lot of attention of late; one well-publicized scheme involved a generator attached to a frame backpack. But unlike most other proposals for harvesting energy by using small vibrations to move minuscule magnets through a coil, the Clarkson plan has immediate real-world advantages over other power sources.

In an experiment conducted last June, engineering professors Edward Sazonov and Pragasen Pillay and their students attached a tubular linear generator to a steel girder on the Route 11 bridge outside of Potsdam. Each time a car or truck rolled over the bridge, the vibrations would cause a coil suspended on a spring to oscillate through the center of a hollow magnet, inducing an alternating current. The current was low, but there was enough to power the monitor and a transmitter for sending the data back to the lab.

During high traffic periods in the afternoon, such vibrations generated enough electricity to provide for as many as 40 measurements each hour.

The technology has been licensed to AmbioSystems, a small start-up company that hopes to market the sensor-powering system. 

Palpitating Cells

When a cancer metastasizes, diseased cells travel through the body and invade healthy organs. In that event, doctors have to make a quick decision to treat the cancer aggressively. But one of the signs of metastasis—a buildup of fluid in the chest and abdomen—isn't a proof-positive signal. And the difference between cancer cells and normal cells is hard to discern using standard laboratory equipment.

Doctors from the University of California, Los Angeles, reported in December that they had developed a bio-sensing technique that might one day be able to differentiate rapidly dividing cancer cells from normal cells. What's more, the technique, first published in Nature Nanotechnology, uses a tool most often employed in studying surfaces at the atomic scale.

Sense of touch: UCLA researchers are using an atomic force microscope to aid the ability to distinguish cancer cells like these from healthy cells.

To diagnose metastatic cancer, technicians will draw fluid from the abdominal cavity, isolate and stain cells from that fluid, and examine them under an optical microscope. Even when stained, the cancer cells have only subtle visible differences from normal cells. In fact, this procedure identifies cancerous cells only 70 percent of the time they are present.

Jianyu Rao, a researcher at UCLA's Jonsson Comprehensive Cancer Center, realized there were other, physical differences between cancer cells and normal ones. For one, meta- static cancer cells are more pliant—so soft and flexible that they can literally squeeze their way into the tightest of spaces—to better invade cells. If technicians could somehow gently poke the cells they were examining, they could more readily diagnose metastasizing cancers.

The problem was finding an instrument that could push against the cells without bursting them. The problem is akin to looking at tomatoes in a market, said James Gimzewski, a member of the California NanoSystems Institute at UCLA. One may look as red and firm as the next, but a gentle squeeze will quickly expose the tomato that is overripe.

Working with Gimzewski, Rao and his colleagues began testing live cells using an atomic force microscope, a nanoscale tool that employs a silicon cantilever to characterize the properties of a surface. The cantilever arm was slowly brought close to the cells. Those that were healthy resisted the movement of the arm; the cancerous ones "felt" squishy. The physical characteristics of the two types of cells were so striking that all the cancerous cells were softer than the softest normal cell.

The hope is that this technique can be developed to the point where it not only provides a fast and definitive test for cancer, but that it will also be able to differentiate between various kinds of cancer. This would enable doctors to prescribe the treatment that most aggressively attacks the specific cancer, rather than use a more general kind of chemotherapy.

Networked Railcars

There is a steady stream of railcars at the Croda Inc. plant in Mill Hall, Pa. The railcars bring in liquids—some of which are flammable—that are processed into specialty chemicals. To ensure that the liquids are being stored safely, the temperatures of the railcars must be checked at least once a day. And, until recently, that meant sending a worker to inspect each and every car at the plant.

"It's a tough job, especially when the weather is bad," said Denny Fetters, an instrument and electrical designer at the plant. Monitoring the temperature manually involves a worker climbing to the top of a railcar and inserting an instrument into a slot in the car. Even though there had been no serious accidents at the plant due to the monitoring, Fetters said, "Whenever you put someone in harm's way, there's a probability that someone is going to slip."

That probability has been greatly reduced, thanks to a new monitoring system that the Mill Hall plant has adopted in the past year. Instead of daily temperature readings taken by hand, engineers at the plant now have minute-by-minute measurements sent to them via a wireless network.

Fetters said that Croda had been looking for an improved monitoring system for some time. Because the railcars are moved around the site, hard-wiring a sensor to them was not an option. Instead, the company was one of the first in North America to adopt a wireless technology solution offered by Emerson Process Management, a division of St. Louis-based Emerson. An extension of the company's existing digital plant architecture, Emerson's "smart wireless" system combined reliable monitoring devices with wireless transmitters as part of a self-organizing communications network.

The result has been a better data stream for monitoring the condition of the materials at the plant site and a $15,000-per-year reduction in maintenance costs. Now, temperature monitoring requires just two climbs on the railcar: one to put the wireless monitor in place when the car comes in, and one to take the monitor off when the car departs.

The experience has been so positive that Fetters looks forward to extending the concept to the entire plant. "Once we have batteries with a long-enough working life," Fetters said, "I can't see putting in any more wires."

Border agents and security screeners employ sniffing dogs for a reason: Sometimes the clearest and most apparent sign of a hidden stash of drugs or explosives is its odor. But there are places such as factories where dogs aren't suitable, and dangerous gases worth detecting to which no one would willingly subject an animal.

The answer to such situations has long been artificial noses. But such devices have been expensive to produce. Now, a prototype nose developed by engineers at the Massachusetts Institute of Technology may point the way to mass producing gas sensors that can sniff out carbon monoxide, nitrogen oxide, and hazardous industrial fumes.

The sensor consists of an array of thin films, each of which responds to gases differently. Individual substances can then be identified by the combination of sensors they trip. The research team, led by Henry Tuller, a professor of materials sciences and engineering, designed a sensor to study gases in diesel exhaust by depositing layers of barium carbonate on a quartz chip. The team found that to make the detector sufficiently sensitive, they needed a more porous film with a larger surface area.

To add texture, the research team deposited a thin film not on a chip, but on a layer of micrometer-scale plastic spheres. After burning away the plastic, they were left with a porous, textured film just a few tens of nanometers thick.

The team still needed a fast way to add these gas-sensitive layers to a detector. They hit upon using a specialized inkjet printer used by another research team for building organic electric devices. The printer can lay down "inks" made up of gas-sensitive materials onto a chip with great precision. The research team is working toward using the inkjet technology to print a large array of gas-detecting films on a three-dimensional surface.

Seniors May Get Monitored

As baby boomers pass through the end of middle age, an increasing number of Americans will begin to need constant attention to their health. For that reason, Dallas-based Parks Associates, an international market research company, is predicting that within five years, millions of senior citizens will be using networked health monitors.

Granted, there are plenty of Americans who could benefit from such monitors today. Up to now, however, the sensors available have not been light, cheap, or reliable enough to break into the mass market. What's more, until recently, getting the sensor's signals from the device to a medical professional usually involved tying up a copper phone line.

But in a market report released in December, Parks Associates forecasts that advances in sensor technology— especially in the ability to link home-based monitors to wireless networks—will help overcome those obstacles. Parks predicts that by 2012, more than 3 million seniors will be using networked health monitors in their homes.

Among the potential kinds of devices that could become widespread are home respiratory and heart-rate monitors, blood glucose sensors, and applications to record the amount of daily activity.

Indeed, the main stumbling block to adoption seems to be societal, not technological. Consumers must come to trust the effectiveness and reliability of home health sensors, and overcome the initial feeling that such monitoring is unnecessarily intrusive. And the health care system must figure out who should pay for the service: individuals out of their own pockets, private insurers, or the government-funded Medicare program.