A low-power chip could be used for implantable medical sensors.

Pico power: This tiny processor, called the Phoenix, uses 90 percent less energy than the most efficient chip on the market today. It could enable implantable medical sensors powered by tiny batteries.
Credit: Mingoo Seok

Before long, sensors may be implanted in our bodies to do things like measure blood-glucose levels in diabetics or retinal pressure in glaucoma patients. But to be practical, they’ll have to both be very small–as tiny as a grain of sand–and use long-lasting batteries of similarly small size, a combination not commercially available today.

Now researchers at the University of Michigan have made a processor that takes up just one millimeter square and whose power consumption is so low that emerging thin-film batteries of the same size could power it for 10 years or more, says David Blaauw, professor of electrical engineering and computer science at Michigan and one of the lead researchers on the project.

But when this processor, dubbed the Phoenix, is coupled with a battery, the whole package would only be a cubic millimeter in volume. At this scale, Blaauw says, it could be feasible to build the chip into a thick contact lens and use it to monitor pressure in the eye, which would be useful for glaucoma detection. It could also be implanted under the skin to sense glucose levels in subcutaneous fluid. More broadly, this low-power approach to processor design could be used in environmental sensors that monitor pollution, or structural health sensors, for instance.

The processer uses only about 30 picowatts (a picowatt is one-millionth of one-millionth of a watt) of power when idle. When active, the processor consumes only 2.8 picojoules of energy per computing cycle. That amount is about a tenth of the energy used by the most energy-efficient chips on the market, says Jan Rabaey, a professor of electrical engineering and computer science at the University of California, Berkeley, who was not involved in the research.

The Michigan team’s main idea was to design a chip that runs at an extremely low voltage. While microprocessors for personal computers may require two volts of electricity per operation, the Phoenix only needs 500 millivolts, or 75 percent less.

At this voltage, parts of the chip don’t operate well, explains Blaauw, so his team redesigned the chip’s memory, which is smaller than most processor memory, and its internal clock so that it could operate with minimal electrical input. The chip’s clock–the timepiece that synchronizes number-crunching operations–has been reduced to an extremely slow rate of 100 kilohertz, as opposed to the gigahertz rates of personal computers. This approach makes sense for sensors, says Blaauw. “If we wanted to monitor pressure in the eye . . . we only need to take readings every few minutes,” he says.

Additionally, the researchers paid close attention to the energy loss that occurs while the chip is in sleep mode, or not collecting or processing data. Transistors in the newest computers are made using a 45-nanometer process in which features on a chip are 45 nanometers in size. While this allows for more transistors on a smaller chip, it also results in electrical leakage, due to the physics of the materials at this scale. Blaauw and his team opted for larger transistors made using a 180-nanometer process, from a previous generation of chips. These transistors are in a “sweet spot,” says Blaauw. They are big enough to have minimal leakage and yet small enough for the researchers to fit a large number on a one-millimeter-square chip.

To further minimize leakage, the researchers added special transistors that completely shut off the power supply to the processing transistors when the chip is in standby mode. This is a common approach, says Blaauw, but his team took it to the extreme and dedicated much more of the chip than usual to these “power-gating” transistors. “If a normal [chip] designer would look at this, he’d say, ‘You’re out of your mind,’” Blaauw says. “But it gives us the power-savings trade-off we need.” In sum, the researchers combined a number of already existing tricks and fine-tuned them to achieve the record-breaking low power consumption.

The Michigan team, which is also led by Dennis Sylvester, professor of electrical engineering and computer science, still must add a battery to the Phoenix, and it needs to develop a way for data to be offloaded from the chip for further analysis. Once this is done, the researchers can work on full integration within a biological system, which could take years.

Berkeley’s Rabaey, who is writing a book on low-power processors, says that the work is significant. “What has impressed me is that they’ve driven this to quite extreme numbers,” he says. “The energy consumption is extremely low. Nobody else has come even close to this.” Rabaey notes that this processor is intended for specialty sensor applications and that it won’t show up in a cell phone anytime soon. However, it’s an important step toward building implantable medical sensors whose batteries can last for years.

The idea of this low voltage chip is not new, says Rabaey: it’s been used successfully in the watch industry for decades. But within the past few years, academic and industry interest in such design has blossomed as engineers are exploring more varied and ubiquitous uses of sensors, devices that require energy-saving tricks in order to be practical.

New technology could provide a way to harness wave energy.

Catching waves: A U.K.-based company has come up with a simple design for a device that harnesses wave power: a water-filled rubber tube floating just under the ocean’s surface. Waves create bulges inside the tube that travel along it and drive a turbine attached at the other end.
Credit: Engineering and Physical Sciences Research Council, UK

The ocean’s waves have enough energy to provide two trillion watts of electricity, according to the Department of Energy’s office of Energy Efficiency and Renewable Energy. Extracting that enormous resource of power, however, has proved to be a herculean challenge.

A new device being developed by U.K.-based Checkmate SeaEnergy could help tap a portion of this wave power. The device, aptly named the Anaconda, is a long, water-filled rubber tube closed at both ends. It currently exists as a small laboratory-scale model, but it could eventually be 200 meters long and seven meters in diameter. At such a size, it will be capable of generating one megawatt of power at about 12 cents a kilowatt-hour, which is competitive with electricity costs from other wave-power technologies.

The one-megawatt Anaconda, which will use about 110 tons of rubber, should be lighter and cheaper than other wave-exploiting designs, says John Chaplin, a civil-engineering professor at the University of Southampton, in the United Kingdom, who is testing the lab-scale device. It is also simpler, with fewer moving parts and hinges, which means less maintenance. Since it is a pliant rubber tube, it should be able to survive severe weather conditions. “We don’t really know how Anaconda works in big waves yet, but intuitively, it seems likely that it’s going to be able to survive big waves,” Chaplin says.

The Anaconda will face plenty of competition from other wave-power devices that have already reached commercial-scale deployment. Scotland-based Pelamis Wave Power’s snakelike device was the first to provide power to the grid when it was installed off the coast of Orkney, Scotland, in 2004. In October 2007, Pelamis deployed three of its 750-kilowatt devices–770-ton, 120-meter-long chains of metal cylinders–off the coast of Portugal. Other companies, such as Finavera Renewables of Vancouver, AWS Ocean Energy of Scotland, and Ocean Power Technologies of Pennington, NJ, are testing bobbing buoy-type devices. In addition, others are developing technology to exploit tidal energy.

The Anaconda floats horizontally just below the ocean’s surface, tethered to the ocean floor at one end, facing oncoming swells, with a turbine attached, at the other. A wave hitting the tube creates a bulge in the water inside. The bulge travels down the tube with a speed that depends on the diameter of the tube, wall thickness, and elasticity of the material, Chaplin says. The tube is designed so that the speed of the bulge is the same as the speed of the wave. The wave travels outside the tube alongside the bulge, making the bulge bigger and bigger, so that it drives the turbine with maximum power.

The power wave: A group of wave-energy devices, each capable of generating one megawatt of power, could be deployed a few kilometers away from coasts.
Credit: Engineering and Physical Sciences Research Council, UK

Chaplin is testing a model that is 25 centimeters wide and about eight meters long. So far, it seems to do what a simple theory predicts that it should, Chaplin says. The lab tests will last three years.

Deployed along the U.S. coast, wave devices could provide the United States–and the world–with a substantial renewable-energy boost. The contiguous United States has a wave-energy resource of 2,100 terawatt-hours per year–about half the country’s total electricity consumption, says Roger Bedard of the power-industry-funded nonprofit Electric Power Research Institute.

But how much of the ocean’s energy can be exploited in the United States is open to speculation, Bedard says. The technology is still immature and does not have nearly as much support from the government as solar and wind power do. What’s more, its implementation faces tremendous regulatory and social hurdles in the United States. Bedard estimates that about 250 terawatt-hours of energy in the United States could reasonably come from waves–about as much as the country gets from hydropower.

Researchers have found a way to boost light from OLEDs

Beam me up: A new OLED design could help the devices emit far more light. Electron microscope images show the top of the OLED with organic and aluminum layers (top) and an organic grid before depositing the organic and aluminum layers (middle). The bottom image shows polymer micro lenses on the surface of the glass substrate.
Credit: University of Michigan/Nature Photonics

Energy efficiency and flexible lighting applications have long been the promise of organic light emitting diodes (OLEDs). The technology hasn’t lived up to its promise, however, because in typical OLEDs, only 20 percent of the light generated is released from the device. That means that most light is trapped inside the bulb, making it highly inefficient.

Researchers at the University of Michigan and Princeton University believe that they’re on to a way to break the OLED-efficiency logjam. The scientists have designed an OLED that boosts illumination by 60 percent using a combination of an organic grid working in tandem with small micro lenses that guide the trapped light out of the device.

Stephen Forrest, a professor of electrical engineering and physics at Michigan, and Yuri Sun, from Princeton University, described the work in the August issue of Nature Photonics.

In OLEDs, white light is generated by using electricity to send an electron into nanometer-thick layers of organic materials that behave like semiconductor materials. Typically, the light in the substrate is internally reflected and runs parallel and not perpendicular. That’s the crux of the problem because the light can’t escape in the vertical direction without some coaxing. In Forrest’s devices, the grids refract the trapped light, sending it to the five micrometers dome-shaped micro lenses. The light is sent off in a vertical orientation that helps release the trapped rays.

Forrest and his coworkers report that the technology emits about 70 lumens from a watt of power. In comparison, incandescent lightbulbs emit 15 lumens per watt. Fluorescent lights put out roughly 90 lumens of light per watt but have liabilities: they produce harsh light, lack longevity, and use environment-damaging substances like mercury.

Forrest says that the next step in the research is to use OLEDs that are more efficient than those the team used in the current project. Looking beyond the research lab work on these OLEDs, he is cautiously optimistic that it should be possible to scale up the manufacturing of the devices, and that production costs for manufacturing the new OLEDs will be competitive.

Today, an estimated 22 percent of the electricity produced goes to lighting buildings. A highly efficient form of OLED lighting could significantly reduce the electricity demand and boost savings. Another factor influencing broad adoption of LEDs is the fact that they outlast incandescent bulbs. Over the next 20 years, the rapid adoption of LED lighting in the United States could reduce electricity demands by 62 percent and thus eliminate 258 million metric tons of carbon emissions, according to the Department of Energy.

It will take several years to replace current lighting in office buildings and homes with OLEDs. But the continued progress in increasing the efficiencies of the devices is encouraging to researchers. “Luckily, OLEDs are the light that just keeps giving,” says Forrest, who has spent much of his professional research career focused on OLEDs. “There is so much to be done and so much that’s been done, but this is nonetheless a quite exciting advancement.”

NaNoTuBe TecHnoLogy

New research suggests that networks of single-walled carbon nanotubes printed onto bendable plastic perform well as semiconductors in integrated circuits. Researchers from the University of Illinois at Urbana-Champaign (UIUC) and Purdue University, whose work appears this week in Nature, say that these nanotube networks could replace organic semiconductors in applications such as flexible displays.

Development of flexible electronics has recently focused on organic molecules because, unlike silicon, they are compatible with bendable plastic substrates. Flexible electronics have potential in such applications as low-power electronic newspapers or PDAs that roll up into the size and shape of a pen. The problem with existing organic-electronic devices, however, is that “they aren’t well developed for long-term reliability, and they perform far worse than silicon,” says John A. Rogers, an engineering professor at UIUC and co-author of the Nature paper.

Carbon-nanotube networks, on the other hand, combine the performance of silicon with the flexibility of organic films on plastic. Rogers says that the speed of the nanotube device compares favorably with the speed of commercially used single-crystal silicon circuits. The transistors can also switch between on and off states in the range of several kilohertz, which is similar to the range of those used for liquid crystal displays and radio frequency identification (RFID) sensors. However, the on-off current ratio for carbon nanotubes is still a few orders of magnitude lower than that for silicon transistors.

The researchers made the networks by depositing nanotubes onto plastic by standard printing methods, which could lead to low-cost, large-scale fabrication. And the printed circuits can bend to a radius of about five millimeters without compromising the electrical performance of the device. “This method is good for flexible electronics that need to be printed over a large area,” says Ali Javey, an assistant professor of electrical engineering at the University of California, Berkeley.

Using a technique called transfer printing, the researchers deposited randomly aligned carbon nanotubes onto a 50-micrometer-thick sheet of plastic, and then patterned gold electrodes and other circuit components onto the substrate. Because about one-third of the nanotubes in any network are metallic, which can short out the transistors, the researchers then etched narrow parallel lines through the network with soft lithography. By cutting the nanotubes, they can effectively eliminate the possibility of a purely metallic pathway connecting two electrodes while preserving the performance of the device.

Several challenges still remain before the nanotubes networks are ready for actual products. Devices need to be made in which the performance from device to device doesn’t vary; billions of individual nanotubes have to be made with high purity and the right dimensions for optimal performance. The printing process also needs development, says George Gruner, a professor of physics at the University of California, Los Angeles. Gruner suggests that nanotubes could be dissolved into ink and then printed onto plastic. “These devices have to be cheap and disposable,” especially for devices like RFID tags in food packaging, he adds.

Rogers’s group’s immediate goals are to work toward lower power and higher speed in the devices. “We want to push the limits to see how far we can go,” he says.

GAS: Hybrid Hydrogen Car

Most of us are unhappy about gas prices these days, but Denny Klein just turns on the Hybrid Hydrogen Oxygen System (HHOS) and smiles. With the HHOS Aquygen™ Gas is generated on demand and used as a fuel additive in a standard gasoline or diesel engine. We have applied this breakthrough method in two prototype vehicles—a 1994 Ford Escort Wagon and a 1998 Ford Ranger pickup. The results speak for themselves:

* The current prototype vehicle receives a net increase in horsepower and an average increase of 20 to 30 percent in miles per gallon.
* The HHOS does not affect water or oil temperatures.
* The HHOS can be installed with very little modification to a standard piston engine and so can be retrofitted on nearly any existing automobile.
* Unlike a fuel cell, where hydrogen is stored at a dangerous 10,000 PSI, the HHOS produces Aquygen™ Gas on demand at less than 60 PSI.
* Exhaust contains decreased emissions.

Because the HHOS is evolutionary, not revolutionary, it utilizes the time-tested technology of the internal combustion engine and the existing refueling infrastructure. The HHOS could save billions of dollars in redesign and retooling costs compared to fuel cells.
Application Details

* The HHOS is in patent pending stage with 39 claims pending.
* The HHOS can be sized (i.e., the level of Aquygen™ Gas output required) for smaller or larger engines depending on the horsepower and/or electrical (kW hour) deviations per volume of fuel (gas or diesel) consumed.
* The HHOS enhances proven technology, i.e., the internal combustion engine, which has been proven reliable over trillions of miles for more than 100 years.
* The HHOS can be retrofitted on millions of existing gas and diesel fueled vehicles. Fleet vehicles are being specifically targeted now.
* The HHOS would create more jobs now; there’s a huge retrofit market to tap.
* The HHOS is cost efficient. The economic payback on fleet vehicles could be less than six months!

A New Competitor to LCD

A pixel that uses a pair of mirrors to block or transmit light could lead to displays that are faster, brighter, and more power efficient than liquid crystal displays (LCDs). Researchers at Microsoft Research who published their novel pixel design in Nature Photonics say that their design is also simpler and easier to fabricate, which should make it cheaper.

LCDs corner half of the global TV market and are the most popular technology for cell phones and flat-panel computer monitors. But for three reasons, they do not boast the best image quality. First, the pixels do not turn completely off. Second, it takes 25 to 40 milliseconds on average for the pixels to switch between black and white, which is slow enough to blur fast-moving images. Third, LCDs are almost impossible to use in bright ambient light. “There is nothing in LCD technology that stands out,” says Sriram Peruvemba, vice president of marketing at electronic-paper pioneer E Ink, based in Cambridge, MA. “The only reason it has done well is it’s the lowest price [flat-panel] display today.”

The new telescopic pixels switch completely off and on within 1.5 milliseconds. Michael Sinclair at Microsoft Research says that the ultrafast response time translates to simpler, low-cost color displays. In LCDs, a pixel is made of three subpixels–red, green, and blue–that are lit up simultaneously at different intensities to create, say, yellow. Each subpixel is controlled with a separate transistor circuit, which makes the circuits complex. Because the telescopic display switches so rapidly, you could put red, green, and blue light-emitting diodes behind each pixel, Sinclair says, and have them sequentially light up to create a color shade. “This would reduce the complexity and cost of today’s LCD,” he says.

The telescopic pixels are also significantly brighter. In an LCD, by the time light passes through the polarizing films, the liquid-crystal layer, and the color filters, only 5 to 10 percent of it comes out. The telescopic pixels, on the other hand, let about 36 percent of the light through. “I could get by with a less-powerful backlight, because the telescopic pixel is more efficient,” Sinclair says. The greater brightness would also make the display more visible in bright sunlight.