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SMALLER, LIGHTER POWER ADAPTER 181 retired mechanical engineer, says Dynaglass was developed in the mid-1990s, but some of the technology is based on research by the Soviet military and space programs. He learned about the material while helping a friend ship medical supplies to Russia. “Later on, we discovered that the material could be used to store energy,” says Baldwin, who then formed a company— Columbus, Ohio-based Dynelec—to explore the technology’s potential. Baldwin boasts that Dynaglass is a remarkable power source. A Dynaglass battery, he says, is infinitely rechargeable and might be able to generate up to 30 times more energy than a lead-acid battery of comparable size and weight. The device, which can be produced in a wide range of sizes, also contains no acids or other dangerous chemicals, making it pollution free. “It just reacts like glass,” Baldwin says. But since Dynaglass isn’t brittle like ordinary glass, it’s durable and won’t shatter when dropped. While a working Dynaglass battery would be warmly received by mobile device manufacturers and users, Keith Keefer, a scientist based in Richland, Washington, is skeptical that Baldwin’s technology is all that it’s purported to be. He notes that several inventors have created similar devices, and that none of the devices has lived up to its promise. “No one has ever really made it work,” he says. Yet Baldwin is looking to interest manufacturers in his technology. “A glass producer could use this to enter the energy industry at practically no additional cost,” he says. 8.2.2 Ion Trek Mobile phones, CD players, and flashlights all wear down batteries far faster than we might wish. Researchers at the U.S. Department of Energy’s Idaho National Engineering and Environmental Laboratory, however, have overcome another barrier to building more powerful, longer-lasting lithium-based batteries. The team, led by inorganic chemist Thomas Luther, has discovered how lithium ions move through the flexible membrane that powers their patented rechargeable lithium battery. Luther describes the translucent polymer membrane as an “inorganic version of plastic kitchen wrap.” The team, including chemists Luther, Mason Harrup, and Fred Stewart, created it by adding a ceramic powder to a material called MEEP ([bis(methoxyethoxyethoxy)phosphazene]), an oozy, thick oil. The resulting solid, pliable membrane lets positively charged lithium ions pass through to create the electrical circuit that powers the battery but rebuffs negatively charged electrons. This keeps the battery from running down while it sits on the shelf—overcoming a major battery-life storage problem. For years, rechargeable lithium battery performance has been disappointing because the batteries needed recharging every few days. After conquering the discharge challenge, the team attacked the need for greater battery power to be commercially competitive. Their membrane didn’t allow sufficient passage of lithium ions to produce enough power, so they needed to under- 182 ENERGY TO GO—POWER GENERATION stand exactly how the lithium ions move through the membrane on a molecular level. First, they analyzed the MEEP membrane using nuclear magnetic resonance—the equivalent of a hospital MRI—to zero in on the best lithium ion travel routes. The results supported the team’s suspicion that the lithium ions travel along the membrane’s “backbone.” The MEEP membrane has a backbone of alternating phosphorus and nitrogen molecules, with oxygenladen “ribs” attached to the phosphorus molecules. Further analysis with infrared and raman spectroscopy (techniques that measure vibrational frequencies and the bonds between different nuclei) helped confirm that the lithium ions are most mobile when interacting with nitrogen. Lithium prefers to nestle into a “pocket” created by a nitrogen molecule on the bottom with oxygen molecules from a MEEP rib on either side. Armed with this new understanding of how lithium moves through the solid MEEP membrane, the team starting making new membrane versions to optimize lithium ion flow. This should make the team’s lithium batteries much more powerful. The team’s research results are a major departure from the conventionally accepted explanation of lithium ion transport that proposed the lithium/MEEP transport mechanism as jumping from one rib to the next using the oxygen molecules as stepping stones. Harrup, Stewart, and Luther are optimistic their battery design will ultimately change the battery industry. The team projects that its polymer membrane will be so efficient at preventing battery run down, that batteries could sit unused for up to 500 months between charges with no loss of charge. Because the membrane is a flexible solid, it can be molded into any shape, which could open up new applications for batteries. The membrane is also very temperature tolerant, which could potentially solve portable power need problems in the frigid cold of space. The team is already working with several federal agencies on applications for its lithium battery designs. 8.3 FUEL CELLS Although PC vendors are eager to breathe new life into their aging systems, particularly modestly equipped notebooks, at least one highly anticipated technology may not make it into the mainstream as soon as many vendors would like. Micro fuel cell technology has been aggressively touted as a convenient and easily renewable power source. The devices, which generate electricity through a chemical reaction between oxygen and a fuel such as hydrogen or methanol, can power a notebook for up to 40 hours. Yet, it’s unlikely that large numbers of users will be “filling up” notebook PCs, PDAs, and other mobile devices anytime soon. Roadblocks for use include fuel cell size, the lack of a universal standard, customer education issues, and safety and security concerns as users bring devices containing volatile fluids into buildings and onto airplanes and other vehicles. MICROCOMBUSTION BATTERY 183 All of these drawbacks have made many notebook vendors skeptical about fuel cell technology. “Fuel cells are not likely to be relevant for mainstream mobile devices for several years,” says Jay Parker, notebook products director for Round Rock, Texas-based Dell Computer. He believes it will be hard to change notebook users’ ingrained habits. “Customers will need to become acclimated to refueling rather than recharging.” Parker notes, however, that Dell is continuing to evaluate various fuel cell technologies. Howard Locker, chief architect of Armonk, New York-based IBM’s personal computing division, says fuel cells will never become popular because users will have to pay for each refill. “Today, when you charge a battery, it’s free,” he says. “Folks are already at nine hours on a battery, so how much better does it need to get?” Locker’s opinion of fuel cell technology: “It’s a nonstarter.” Two notebook makers, however, are undeterred by the naysayers and plan to push ahead with fuel cell technology. Toshiba and NEC have each announced they will start selling fuel cell-equipped notebooks during 2004. 8.4 MICROCOMBUSTION BATTERY The search for a better battery is getting a push from the U.S. Defense Advanced Research Project Agency (DARPA), which has given Yale University’s engineering department $2.4 million to develop readily rechargeable microcombustion batteries. The Yale research is part of DARPA’s Palm Power program, which addresses the military’s need for lighter and more compact electrical power sources. “DARPA is shooting for something that weighs as little as a few ounces to power the growing number of communications and weapons systems that tomorrow’s soldiers will carry,” says Alessandro Gomez, director of the Yale Center for Combustion Studies and a professor of mechanical engineering. Microcombustion technology generates heat by slowly burning tiny amounts of liquid hydrocarbons. The heat is then converted into electricity by other energy conversion schemes such as thermoelectric and thermophotovoltaic. By taking advantage of the abundant power densities offered by hydrocarbon fuels, a microcombustion battery with millimeter-level dimensions could provide the same power and operating time as a conventional battery up to 10 times its size. And microcombustion cells could be quickly refueled with an eyedropper. The Department of Defense plans to use microcombustion batteries in everything from tactical bodyware computers to Micro Air Vehicles—six-inchlong unmanned reconnaissance aircraft. The technology, once perfected, should spill over quickly into business and consumer products, Gomez says. “Laptop computers, cell phones, and a variety of other portable electronics products could all benefit.” 184 ENERGY TO GO—POWER GENERATION Yale scientists are concentrating on developing the most effective combustion technology, while researchers at other institutions are working on techniques for converting thermal energy into electrical energy. “Conventional battery technology has reached a dead end,” says Gomez. “We’re looking to develop a power source that’s every bit as innovative as the latest military systems.” 8.5 POWER MONITOR As people increasingly rely on sophisticated mobile phones and PDAs to handle an array of tasks, knowing exactly how much battery power remains inside a device becomes ever more critical, especially before accessing important information or initiating a wireless transaction. Texas Instruments is looking to help mobile device users accurately monitor their power usage. The company has developed the first fully integrated battery fuel gauge for single-cell lithium ion and lithium polymer battery packs. The chip-based gauge is designed to help users observe remaining battery capacity and system run time (time to empty). The chip, named bqJunior, promises to help manufacturers reduce the development time and total cost of implementing a comprehensive battery fuel gauge system in mobile devices. “As battery-powered consumer devices become more complicated and dynamic, designers of those products will require the right intelligent hardware to provide accurate information about the battery and system run times to better manage available power,” says Peter Fundaro, worldwide marketing manager for Texas Instrument’s battery management products. Fundaro notes that Texas Instrument’s product simplifies the design of a cost-effective accurate battery fuel gauge in single cell by “offering a solution that performs all the necessary intelligent calculations on-chip, significantly reducing the amount of calculations performed by the host-side microcontroller.” Unlike a standard battery monitor, bqJunior incorporates an on-board processor to calculate the remaining battery capacity and system run-time. The device measures the battery’s charge and discharge currents to within 1 percent error using an integrated low-offset voltage-to-frequency converter. An analog-to-digital converter measures battery voltage and temperature. Using the measurement inputs, the bqJunior runs an algorithm to accurately calculate remaining battery capacity and system run time. bqJunior compensates remaining battery capacity and run times for battery discharge rate and temperature variations. Because the device performs the algorithm and data set calculations, there’s no need to develop and incorporate code to implement those tasks in the host system processor, which helps reduce development time and total implementation cost. The host system processor simply reads the data set in bqJunior to retrieve remaining battery capacity, run time, and other critical information that’s fundamental to comprehensive battery and power management, including available power, COOLING TECHNOLOGIES 185 average current, temperature, voltage, and time to empty and full charge. bqJunior includes a single wire communications port to communicate the data set to the system host controller. The fuel gauge operates directly from a single lithium ion cell and operates at less than 100 microamps. It features three lowpower standby modes to minimize battery consumption during periods of system inactivity. Other bqJunior features include a low-offset voltage-to-frequency converter (VFC) for accurate charge and discharge counting. Also provided are an internal time base and an on-chip configuration EEPROM that allows application-specific parameters. bqJunior takes advantage of Texas Instrument’s new LBC4 copper CMOS process node, which helps achieve higher integration, lower power, and enhanced performance. 8.6 COOLING TECHNOLOGIES Two new technologies developed at the Georgia Institute of Technology promise to remove heat from electronic devices and could help future generations of laptops, PDAs, mobile phones, telecom switches, and high-powered military equipment keep their cool in the face of growing power demands. The technologies—synthetic jet ejector arrays (SynJets) and vibrationinduced droplet atomization (VIDA)—are designed to keep telecom devices cool despite relentless miniaturization. “There is a lot of concern in the electronics industry about thermal management,” says Raghav Mahalingam, a Georgia Tech research engineer and the technology’s codeveloper. “New processors are consuming more power, circuit densities are getting higher, and there is pressure to reduce the size of devices. Unless there is a breakthrough in low-power systems, conventional fan-driven cooling will no longer be enough.” Processors, memory chips, graphics chips, batteries, radio frequency components, and other devices found in electronic equipment generate heat that must be dissipated to avoid damage. Traditional cooling techniques use metallic heat sinks to conduct thermal energy away from the devices, then transfer it to the air via fans. However, cooling fans have a number of limitations. For instance, much of the circulated air bypasses the heat sinks and doesn’t mix well with the thermal boundary layer that forms on the fins. Fans placed directly over heat sinks have “dead areas” where their motor assemblies block airflow. Additionally, as designers boost airflow to increase cooling, fans use more energy, create more audible noise, and take up more space. 8.6.1 SynJets Developed by Mahalingam and Ari Glezer, a professor at Georgia Tech’s School of Mechanical Engineering, SynJets are more efficient than fans, producing two to three times as much cooling with two-thirds less energy input. Simple and with no friction parts to wear out, a synthetic jet module in prin- 186 ENERGY TO GO—POWER GENERATION ciple resembles a tiny stereo speaker in which a diaphragm is mounted within a cavity that has one or more orifices. Electromagnetic or piezoelectric drivers cause the diaphragm to vibrate 100 to 200 times per second, sucking surrounding air into the cavity and then expelling it. The rapid cycling of air into and out of the module creates pulsating jets that can be directed to the precise locations where cooling is needed. The jet cooling modules take up less space in cramped equipment housings and can be flexibly conformed to components that need cooling—even mounted directly within the cooling fins of heat sinks. Arrays of jets would provide cooling matched to component needs, and the devices could even be switched on and off to meet changing thermal demands. Although the jets move 70 percent less air than fans of comparable size, the airflow they produce contains tiny vortices that make the flow turbulent, encouraging efficient mixing with ambient air and breaking up thermal boundary layers. “You get a much higher heat transfer coefficient with synthetic jets, so you do away with the major cooling bottleneck seen in conventional systems,” says Mahalingam. The ability to scale the jet modules to suit specific applications and to integrate them into electronic equipment could provide cooling solutions over a broad range of electronic hardware ranging from desktop computers to PDAs, mobile phones, and other portable devices that are now too small or have too little power for active cooling. SynJets could be used by themselves to supplement fans or even in conjunction with cooling liquid atomization. “We will fit in where there currently is no solution or improve on an existing solution,” says Jonathan Goldman, a commercialization catalyst with Georgia Tech’s VentureLab, a program that helps faculty members commercialize the technology they develop. Beyond the diaphragm, the system requires an electronic driver and wiring. Goldman expects the jets to be cost competitive with fans and easier to manufacture. Further energy savings could be realized by using piezoelectric actuators. One of the practical implications of this technology could be to forestall the need to use costlier heat sinks made from copper. “The industry could continue to use aluminum and retain its advantages of design simplicity, lower cost, and lower weight,” says Goldman. 8.6.2 VIDA In applications like high-powered military electronics, automotive components, radars, and lasers, power dissipation needs exceed 100 watts per square centimeter and may surpass 1,000 watts per square centimeter. For such higher demands, vibration-induced droplet atomization (VIDA) could be used. This sophisticated system uses atomized liquid coolants—such as water—to carry heat away from components. Also developed at Georgia Tech by Glezer’s group, VIDA uses high-frequency vibration produced by piezoelectric actuators to create sprays of tiny cooling liquid droplets inside a closed cell attached to an electronic component in need of cooling. COOLING TECHNOLOGIES 187 The droplets form a thin film on the heated surface, allowing thermal energy to be removed by evaporation. The heated vapor then condenses, either on the exterior walls of the cooling cell or on tubes carrying liquid coolant through the cell. The liquid is then pumped back to the vibrating diaphragm for reuse. “A system like this could work in the avionics bay of an aircraft,” says Samuel Heffington, a Georgia Tech research engineer. “We have so far been able to cool about 420 watts per square centimeter and ultimately expect to increase that to 1,000 watts per square centimeter.” SynJets and VIDA have both been licensed to Atlanta-based Innovative Fluidics, which will use them to develop products that will be designed to meet a broad range of electronic device cooling needs. 8.6.3 Wiggling Fans Another promising approach to device cooling is based on tiny, quiet fans that wiggle back and forth to help cool future laptop computers, mobile phones, and other portable electronic gear. The devices, developed by researchers at Purdue University, aim to remove heat by waving a small blade in alternate directions, like the motion of a classic hand-held Chinese fan (Fig. 8-1). They consume only about 1/150th as much Figure 8-1 Tiny, quiet fan that will help cool future laptop computers, mobile phones and other portable electronic gear. 188 ENERGY TO GO—POWER GENERATION electricity as conventional fans, and they have no gears or bearings, which produce friction and heat. Because the new fans work without motors that contain magnets, they do not produce electromagnetic “noise” that can interfere with electronic signals in computer circuits. The cramped interiors of laptop computers and cell phones contain empty spaces that are too small to house conventional fans but large enough to accommodate the new fans, some of which have blades about an inch long. Placing the fans in these previously empty spaces has been shown to dramatically reduce the interior temperatures of laptop computers. The wiggling fans will not replace conventional fans. Instead, they will be used to enhance the cooling now provided by conventional fans and passive design features, such as heat-dissipating fins. In experiments on laptop computers, the Purdue researchers reduced the interior temperatures by as much as 8 degrees Celsius. “For a very small power expenditure, we are able to get a huge benefit,” says Suresh Garimella, an associate professor of mechanical engineering at Purdue. The fans run on 2 milliwatts of electricity, or 2 1/1,000ths of 1 watt, compared with 300 milliwatts for conventional fans. The fans are moved back and forth by a “piezoelectric” ceramic material that is attached to the blade. As electricity is applied to the ceramic, it expands, causing the blade to move in one direction. Then, electricity is applied in the alternate direction, causing the ceramic material to contract and move the blade back in the opposite direction. This alternating current causes the fan to move back and forth continuously. The operating efficiency of a fan can be optimized by carefully adjusting the frequency of alternating current until it is just right for that particular fan. The piezoelectric fans can be made in a wide range of sizes. The Purdue engineers are developing fans small enough to fit on a computer chip: their blades will only be about 100 micrometers long, which is roughly the width of a human hair. Piezoelectric fans were developed during the 1970s. The first versions were considered noisy, but the Purdue group has developed fans that are almost inaudible. The fans are made by attaching a tiny “patch” of piezoelectric ceramic to a metal or Mylar blade. Two factors affecting the performance of the fans are how much the ceramic patch overlaps the blade and how thick the patch is compared with the blade’s thickness. Another critical factor is precisely where to attach the blade to the patch. Those factors dictate performance characteristics such as how far the blade moves, how much airflow it produces, and how that flow produces complicated circulation patterns. An improperly designed fan could actually make matters worse by recirculating hot air back onto electronic components, notes Arvind Raman, an assistant professor of mechanical engineering at Purdue. The Purdue researchers have developed mathematical techniques that take these factors into consideration when designing fans for specific purposes. “These fans typically have been novelty items,” says Raman. “If you want to COOLING TECHNOLOGIES 189 really be serious about putting them into any practical use, there are so many things you need to understand about how they work and how to optimize them.” Mathematical models developed by Purdue researchers can be used to provide design guidelines for engineers. “What we bring to the table is a knowledge of the modeling of these fans,” says Garimella. “How to analyze the design, to figure out how large a patch should be for how long a blade, how thick the patch should be, and what happens if you modify all these quantities. In short, it’s how to optimize the performance of these fans. Raman and his students developed relatively simple mathematical formulas that make it easier for engineers to begin designing fans for specific jobs. Engineers can use the formulas to do a quick, “back-of-the-envelope” design. “And then you might want to do some fine tuning and tweaking with more detailed analysis,” says Garimella. Chapter 9 The Critical Last Inch—Input and Output Technologies The telecom world spends a lot of time thinking about the “last mile”—that critical distance between the customer and the service provider’s equipment. Yet, for a growing number of telecom device manufacturers (and their customers), the really important factor limiting the use of telecom technology is the “last inch”—the distance that separates the user’s finger from a keyboard or keypad and the user’s eye from a display screen. As telecom devices shrink, “last inch” design issues are becoming increasingly critical. For example, how do you allow people to input alphanumeric data into a button-sized PDA? And, conversely, how does one mount a screen that can display meaningful information on a device that’s no larger than a thumbnail? Researchers around the world are pondering the growing input/ output problem and are arriving at an array of potential solutions. 9.1 A FINGER PHONE Mobile phone manufacturers are beginning to experiment with novel phone form factors in an attempt to better address users’ daily needs. Japan’s NTT DoCoMo, for instance, is developing a radically new type of mobile phone that uses the human hand as an integral part of the receiver. The FingerWhisper, which is being developed at NTT DoCoMo’s Yokosuka, Japan, R&D center, works by requiring its user to stick a finger into his or her ear. Telecosmos: The Next Great Telecom Revolution, edited by John Edwards ISBN 0-471-65533-3 Copyright © 2005 by John Wiley & Sons, Inc. 190