Thursday, July 26, 2007
Solar Cell Efficiency Approaching 50
University of Delaware (UD) researchers have managed to crank up the efficiency of silicon solar cells to a record-breaking 42.8 percent under standard terrestrial sunlight conditions. The new record is an important milestone on the path to the 50 percent efficiency goal set by the Defense Advanced Research Projects Agency (DARPA) under its Very High Efficiency Solar Cell (VHESC) program to develop affordable, portable solar cell battery chargers.
The new results put the pieces in place for a solar cell module with a net efficiency 30 percent greater than any previous module efficiency and twice the efficiency of state-of-the-art silicon solar cell modules. DARPA is initiating the next phase of the development program by funding the newly formed DuPont-University of Delaware VHESC Consortium to transition the lab-scale work to an engineering and manufacturing prototype model.
Given that around 20 percent of the weight of a modern soldier's pack is batteries, it's easy to see why the military is interested in the VHESC solar cell. The DARPA program aims to dramatically reduce the battery logistics pipeline and provide the soldier with more power at reduced weight, thus improving mobility, survivability and the availability of power-hungry electronic technologies on the battlefield.
UD's Allen Barnett explained that the VHESC solar cell uses a novel lateral optical concentrating system that splits incoming light into three different "energy bins" of high, medium and low, and directs them onto cells of different light sensitive materials that together cover the solar spectrum. Importantly, the concentrator is stationary with a wide acceptance angle optical system that captures large amounts of light and eliminates the need for complicated tracking devices.
Previous high-efficiency cells used a concentration device that required sophisticated tracking optics, a concentrating lens the size of a table and were more than a foot thick. By contrast, the UD consortium's devices are far thinner at less than 1 centimeter. The low profile and lack of moving parts translates into portability, which means these devices easily could go on a laptop computer or a rooftop.
"This technology has the potential to change the way electricity is generated throughout the world. This is a solar cell that works," Barnett boasted, adding that the 50 percent efficiency mark was just the beginning.
Source: University of Delaware
NEW technology is making us forgetful, a survey has found.
The under-30s, who rely on phones, BlackBerrys and ipods to store information are the worst.
Only one in three could name four telephone numbers of friends before they had to look it up.
And a worrying five per cent of under 30s could not even remember their home address. But the over 50s did the best - recalling six numbers.
Prof Ian Robertson, expert in neuropsychology, said: "People are relying on technology for their memory. But the less you use your memory the poorer it becomes."
Wireless power transfer over two-meter distance, from the coil on the left to the coil on the right, where it powers a 60W light bulb. Members of the team that performed the experiment are obstructing the direct line of sight between the coils; front row: Peter Fisher (left) and Robert Moffatt; second row: Marin Soljacic; third row: Andre Kurs (left), John Joannopoulos and Aristeidis Karalis. Photo / Aristeidis Karalis
Imagine a future in which wireless power transfer is feasible: cell phones, household robots, mp3 players, laptop computers and other portable electronics capable of charging themselves without ever being plugged in, freeing us from that final, ubiquitous power wire. Some of these devices might not even need their bulky batteries to operate.
A team from MIT's Department of Physics, Department of Electrical Engineering and Computer Science, and Institute for Soldier Nanotechnologies (ISN) has experimentally demonstrated an important step toward accomplishing this vision of the future. The team members are Andre Kurs, Aristeidis Karalis, Robert Moffatt, Prof. Peter Fisher, and Prof. John Joannopoulos (Francis Wright Davis Chair and director of ISN), led by Prof. Marin Soljacic. Realizing their recent theoretical prediction, they were able to light a 60W light bulb from a power source seven feet (more than two meters) away; there was no physical connection between the source and the appliance. The MIT team refers to its concept as "WiTricity" (as in wireless electricity). The work will be reported in the June 7 issue of Science Express, the advance online publication of the journal Science.
The story starts one late night a few years ago, with Soljacic (pronounced Soul-ya-cheech) standing in his pajamas, staring at his cell phone on the kitchen counter. "It was probably the sixth time that month that I was awakened by my cell phone beeping to let me know that I had forgotten to charge it. It occurred to me that it would be so great if the thing took care of its own charging." To make this possible, one would have to have a way to transmit power wirelessly, so Soljacic started thinking about which physical phenomena could help make this wish a reality.
Various methods of transmitting power wirelessly have been known for centuries. Perhaps the best known example is electromagnetic radiation, such as radio waves. While such radiation is excellent for wireless transmission of information, it is not feasible to use it for power transmission. Since radiation spreads in all directions, a vast majority of power would end up being wasted into free space. One can envision using directed electromagnetic radiation, such as lasers, but this is not very practical and can even be dangerous. It requires an uninterrupted line of sight between the source and the device, as well as a sophisticated tracking mechanism when the device is mobile.
In contrast, WiTricity is based on using coupled resonant objects. Two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with extraneous off-resonant objects. A child on a swing is a good example of this. A swing is a type of mechanical resonance, so only when the child pumps her legs at the natural frequency of the swing is she able to impart substantial energy. Another example involves acoustic resonances: Imagine a room with 100 identical wine glasses, each filled with wine up to a different level, so they all have different resonant frequencies. If an opera singer sings a sufficiently loud single note inside the room, a glass of the corresponding frequency might accumulate sufficient energy to even explode, while not influencing the other glasses. In any system of coupled resonators there often exists a so-called "strongly coupled" regime of operation. If one ensures to operate in that regime in a given system, the energy transfer can be very efficient.
While these considerations are universal, applying to all kinds of resonances (e.g., acoustic, mechanical, electromagnetic, etc.), the MIT team focused on one particular type: magnetically coupled resonators. The team explored a system of two electromagnetic resonators coupled mostly through their magnetic fields; they were able to identify the strongly coupled regime in this system, even when the distance between them was several times larger than the sizes of the resonant objects. This way, efficient power transfer was enabled. Magnetic coupling is particularly suitable for everyday applications because most common materials interact only very weakly with magnetic fields, so interactions with extraneous environmental objects are suppressed even further. "The fact that magnetic fields interact so weakly with biological organisms is also important for safety considerations," Kurs, a graduate student in physics, points out.
The investigated design consists of two copper coils, each a self-resonant system. One of the coils, attached to the power source, is the sending unit. Instead of irradiating the environment with electromagnetic waves, it fills the space around it with a non-radiative magnetic field oscillating at MHz frequencies. The non-radiative field mediates the power exchange with the other coil (the receiving unit), which is specially designed to resonate with the field. The resonant nature of the process ensures the strong interaction between the sending unit and the receiving unit, while the interaction with the rest of the environment is weak. Moffatt, an MIT undergraduate in physics, explains: "The crucial advantage of using the non-radiative field lies in the fact that most of the power not picked up by the receiving coil remains bound to the vicinity of the sending unit, instead of being radiated into the environment and lost." With such a design, power transfer has a limited range, and the range would be shorter for smaller-size receivers. Still, for laptop-sized coils, power levels more than sufficient to run a laptop can be transferred over room-sized distances nearly omni-directionally and efficiently, irrespective of the geometry of the surrounding space, even when environmental objects completely obstruct the line-of-sight between the two coils. Fisher points out: "As long as the laptop is in a room equipped with a source of such wireless power, it would charge automatically, without having to be plugged in. In fact, it would not even need a battery to operate inside of such a room." In the long run, this could reduce our society's dependence on batteries, which are currently heavy and expensive.
At first glance, such a power transfer is reminiscent of relatively commonplace magnetic induction, such as is used in power transformers, which contain coils that transmit power to each other over very short distances. An electric current running in a sending coil induces another current in a receiving coil. The two coils are very close, but they do not touch. However, this behavior changes dramatically when the distance between the coils is increased. As Karalis, a graduate student in electrical engineering and computer science, points out, "Here is where the magic of the resonant coupling comes about. The usual non-resonant magnetic induction would be almost 1 million times less efficient in this particular system."
WiTricity is rooted in such well-known laws of physics that it makes one wonder why no one thought of it before. "In the past, there was no great demand for such a system, so people did not have a strong motivation to look into it," points out Joannopoulos, adding, "Over the past several years, portable electronic devices, such as laptops, cell phones, iPods and even household robots have become widespread, all of which require batteries that need to be recharged often."
As for what the future holds, Soljacic adds, "Once, when my son was about three years old, we visited his grandparents' house. They had a 20-year-old phone and my son picked up the handset, asking, 'Dad, why is this phone attached with a cord to the wall"' That is the mindset of a child growing up in a wireless world. My best response was, 'It is strange and awkward, isn't it" Hopefully, we will be getting rid of some more wires, and also batteries, soon.'"
Source: Massachusetts Institute of Technology.
MIT is "a university polarized around science, engineering, and the arts." MIT has five schools (Science, Engineering, Architecture and Planning, Management, and Humanities, Arts, and Social Sciences) and one college (Whitaker College of Health Sciences and Technology), but no schools of law or medicine.
MIT is governed by a 78-member board of trustees known as the MIT Corporation which approve the budget, degrees, and faculty appointments as well as electing the President. MIT's endowment and other financial assets are managed through a subsidiary MIT Investment Management Company (MITIMCo). The chair of each of MIT's 32 academic departments reports to the dean of that department's school, who in turn reports to the Provost under the President. However, faculty committees assert substantial control over many areas of MIT's curriculum, research, student life, and administrative affairs.
MIT students refer to both their majors and classes using numbers alone. Majors are numbered in the approximate order of when the department was founded; for example, Civil and Environmental Engineering is Course I, while Nuclear Science & Engineering is Course XXII. Students majoring in Electrical Engineering and Computer Science, the most popular department, collectively identify themselves as "Course VI." MIT students use a combination of the department's course number and the number assigned to the class number to identify their subjects; the course which many American universities would designate as "Physics 101" is, at MIT, simply "8.01
Technorati : John Joannopoulos and Aristeidis Karalis. Photo / Aristeidis Karalis, Wireless power transfer over two-meter distance, from the coil on the left to the coil on the right, where it powers a 60W light bulb. Members of the team that performed the experiment are obstructing the direct line of sight between the coils; front row: Peter Fisher (left) and Robert Moffatt; second row: Marin Soljacic; third row: Andre Kurs (left)
The new price on PS3 ,Sony claims huge sales bump after PS3 price cut ,a $100 price drop for the 60 gigabyte PS3 on July 9th
Sony claims that Playstation 3 sales have increased by more than 135% at the company's top five retailers since they announced a $100 price drop for the 60 gigabyte PS3 on July 9th.
They also say that Playstation hardware sales have increased by 161%, software by 15% and peripherals by 60%.
"The new price on the 60 GB PS3, coupled with our very strong software showing from E3, is certainly paying dividends in terms of impressive sales across the board at retail," says SCEA head Jack Tretton. "This jump in sales bodes very well for us heading into the fall as we launch an impressive arsenal of hardware and software, leading off with the new 80 GB PS3 in August along with the unveiling of highly anticipated games such as Lair and Warhawk. That will be followed by Heavenly Sword in September and six more exclusive first-party PS3 games in October, including Ratchet & Clank Future: Tools of Destruction."
The Nintendo Wii led the way in the console sales race last month, selling 381,800 consoles, doubling the Xbox 360, and quadrupling the Playstation 3.
If Sony's claims are accurate, then it is possible that it will catch the Xbox 360 in monthly sales, at least for this month. June NPD numbers showed the Xbox 360 sold 198,400 units, compared to the Playstation 3's 98,500.
The sales increase might not be sustainable however, as the company revealed that the new $599 80 gigabyte bundle will be the only version of the console availble after the 60 gigabyte model sells out.
Sony has to hope that the Playstation can continue the hot streak the earned since the price drop, or it will trail Nintendo and Microsoft for the second straight Holiday season.
<b>PlayStation 3Inside News</b>
Manufacturer Sony, Foxconn and ASUSTeK for SCEI
Type Video game console
Generation Seventh generation era
First available November 11, 2006
November 17, 2006
March 23, 2007
Controller input Up to 7
Online service PlayStation Network
Units sold 3.8 million+ (details)
Units shipped 5.5 million+ (details)
Top-selling game Resistance: Fall of Man
compatibility Most PlayStation games
Most PlayStation 2 games
Predecessor PlayStation ,
Kevin Rose at Digg is saying the popular user-driven news site has just signed a three-year exclusive ad deal with Microsoft. Bye-bye Google. Don't think it will hurt Google's bottom line much, and Mike Arrington at TechCrunch thinks it's another money-losing deal for the software giant, which also did a similar deal with Facebook. But neither is this a ringing endorsement of Google from one of the stars of Web 2.0, with 17 million unique monthly users. "No dancing monkey ads, and the design will remain uncluttered," Rose vows, no doubt anticipating the usual Microsoft-bashing in Digg comments on the post.
Although John Battelle's Federated Media is still involved and apparently will work with Microsoft on Digg sponsorships, some folks are wondering if Federated's role is rather less than it was intended to be. Will update as I hear more.
For now, though, "it's a real coup for Microsoft," Internet marketing consultant Andy Beal told my colleague Tom Giles. "It's a good way to put their product in front of a high-tech savvy audience." On the other hand, it remains to be seen how lucrative an ad magnet Digg will be. Ashkan Karbasfrooshan at watchmojo.com thinks not so much.
As for the odd man out, Yahoo!, Beal says it's in a tough position: "They want to get the partnerships away from Google, but can't afford to cut deals. They need the revenue coming in. With investors watching closely, I don't think Yahoo can afford to be ultra-aggressive."
Clearly, the battle for the ad business of the new crop of Web companies is intensifying. In particular, it will be interesting to see how Google and Microsoft will spend their seemingly boundless budgets--and if and when we'll see one of them blink. Not for a good long while, I think.
An Army veteran who lost part of his leg in Iraq walked with more spring in his step Monday as he unveiled the world's first robotic ankle -- an important advance for lower-limb amputees that was developed by a team at MIT.
Garth Stewart, 24, who lost his left leg below the knee in an explosion in Iraq, demonstrated the new powered ankle-foot prosthesis during a ceremony at the Providence, R.I., Veterans Affairs Medical Center. Stewart walked in the device, which, unlike any other, propels users forward using tendon-like springs and an electric motor. The prototype device reduces fatigue, improves balance and provides amputees with a more fluid gait. It could become commercially available as early as the summer of 2008.
MIT Media Lab Professor Hugh Herr and his team of researchers developed the ankle-foot. Herr, NEC Career Development Professor and head of the biomechatronics research group at the Media Lab, is a VA research investigator. He is also a double amputee who tested his invention: "This design releases three times the power of a conventional prosthesis to propel you forward and, for the first time, provides amputees with a truly humanlike gait," Herr said.
"It's wild," he said, "like you're on one of those moving walkways in the airport."
Because conventional prostheses only provide a passive spring response during walking, they force the amputee to have an unnatural gait and typically to expend some 30 percent more energy on walking than a non-amputee. The new ankle is light, flexible, and -- most importantly -- generates energy for walking beyond that which can be released from a spring alone.
This is accomplished through a device equipped with multiple springs and a small battery-powered motor. The energy produced from the forward motion of the person wearing the prosthesis is stored in the power-assisted spring, and then released as the foot pushes off. Additional mechanical energy is also added to help momentum.
Herr created the device through the Center for Restorative and Regenerative Medicine (CRRM), a collaborative research initiative that includes the Providence VA Medical Center, Brown University and MIT. The center's mission is to improve the lives of individuals with limb trauma through tissue restoration, advanced rehabilitation and new prosthetics that give amputees - particularly war veterans - better mobility and control of their limbs and reduce the discomfort and infections common with current prostheses.
To achieve this goal, the center funds a team of researchers with expertise in tissue engineering, orthopedics, neurotechnology, prosthetic design and rehabilitation. The aim is to bring these complementary techniques together to create "biohybrid" limbs composed of biological and man-made materials - a melding of man and machine.
To meet this goal, the VA has provided an additional $6.9 million to construct a state-of-the-art rehabilitation research building that will house the center on the campus of the Providence VA Medical Center. Construction begins this fall.
"A major goal of the center is to develop artificial limbs that perform like biological ones," said Professor Roy Aaron, M.D., of Brown University, director of the CRRM. "Hugh Herr and his team have met that goal - and done so successfully. This device is a major step forward for Garth Stewart and other amputees."
Joel Kupersmith, M.D., chief research and development officer for VA, said a top priority for the department is providing state-of-the-art prosthetic care for veterans - especially those returning from Iraq and Afghanistan. VA research, he said, is integral to this effort.
"The robotic ankle is a sterling example of how our leading-edge research improves veterans' lives," Kupersmith said. "Up to now, prosthetic devices have not been able to duplicate the complex functions of our feet and ankles as we walk and run. The ingenious computerized design of this new prosthesis changes all of this, as it constantly 'thinks' and responds, allowing the person to walk or run in a more natural and comfortable way."
Michael E. Selzer, M.D., director of Rehabilitation Research and Development for VA, agreed: "Hugh Herr and his Media Lab group are well-known for their scientific ingenuity and creativity on behalf of amputees. This new technology represents rehabilitation research at its finest, and is yet another milestone in VA's long history of outstanding achievements in this area."
MIT researchers have demonstrated how ordinary spark-ignition automobile engines can, under certain driving conditions, move into a spark-free operating mode that is more fuel-efficient and just as clean.
The mode-switching capability could appear in production models within a few years, improving fuel economy by several miles per gallon in millions of new cars each year. Over time, that change could cut oil demand in the United States alone by a million barrels a day. Currently, the U.S. consumes more than 20 million barrels of oil a day.
The MIT team presented their latest results on July 23 at the Japan Society of Automotive Engineers (JSAE)/Society of Automotive Engineers (SAE) 2007 International Fuel and Lubricants Meeting.
Many researchers are studying a new way of operating an internal combustion engine known as "homogeneous charge compression ignition" (HCCI). Switching a spark-ignition (SI) engine to HCCI mode pushes up its fuel efficiency.
In an HCCI engine, fuel and air are mixed together and injected into the cylinder. The piston compresses the mixture until spontaneous combustion occurs. The engine thus combines fuel-and-air premixing (as in an SI engine) with spontaneous ignition (as in a diesel engine). The result is the HCCI's distinctive feature: combustion occurs simultaneously at many locations throughout the combustion chamber.
That behavior has advantages. In both SI and diesel engines, the fuel must burn hot to ensure that the flame spreads rapidly through the combustion chamber before a new "charge" enters. In an HCCI engine, there is no need for a quickly spreading flame because combustion occurs throughout the combustion chamber. As a result, combustion temperatures can be lower, so emissions of nitrogen pollutants are negligible. The fuel is spread in low concentrations throughout the cylinder, so the soot emissions from fuel-rich regions in diesels are not present.
Perhaps most important, the HCCI engine is not locked into having just enough air to burn the available fuel, as is the SI engine. When the fuel coming into an SI engine is reduced to cut power, the incoming air must also be constrained--a major source of wasted energy.
However, it is difficult to control exactly when ignition occurs in an HCCI engine. And if it does not begin when the piston is positioned for the power stroke, the engine will not run right.
"It's like when you push a kid on a swing," said Professor William H. Green, Jr., of the Department of Chemical Engineering. "You have to push when the swing is all the way back and about to go. If you push at the wrong time, the kid will twist around and not go anywhere. The same thing happens to your engine."
According to Green, ignition timing in an HCCI engine depends on two factors: the temperature of the mixture and the detailed chemistry of the fuel. Both are hard to predict and control. So while the HCCI engine performs well under controlled conditions in the laboratory, it is difficult to predict at this time what will happen in the real world.
Green, along with Professor Wai K. Cheng of the Department of Mechanical Engineering, and colleagues in MIT's Sloan Automotive Laboratory and MIT's Laboratory for Energy and the Environment have been working to find the answer.
A large part of their research has utilized an engine modified to run in either HCCI or SI operating mode. For the past two years, Morgan Andreae (MIT PhD 2006) and graduate student John Angelos of chemical engineering have been studying the engine's behavior as the inlet temperature and type of fuel are changed.
Not surprisingly, the range of conditions suitable for HCCI operation is far smaller than the range for SI mode. Variations in temperature had a noticeable but not overwhelming effect on when the HCCI mode worked. Fuel composition had a greater impact, but it was not as much of a showstopper as the researchers expected.
Using the results of their engine tests as a guide, the researchers developed an inexpensive technique that should enable a single engine to run in SI mode but switch to HCCI mode whenever possible. A simple temperature sensor determines whether the upcoming cycle should be in SI or HCCI mode (assuming a constant fuel).
To estimate potential fuel savings from the mode-switching scheme, Andreae determined when an SI engine would switch into HCCI mode under simulated urban driving conditions. Over the course of the simulated trip, HCCI mode operates about 40 percent of the time.
The researchers estimate that the increase in fuel efficiency would be a few miles per gallon. "That may not seem like an impressive improvement," said Green. "But if all the cars in the US today improved that much, it might be worth a million barrels of oil per day--and that's a lot."
Funded by :This research was supported by Ford Motor Company and the Ford-MIT Alliance, with additional support from BP.