MADISON - Working to help cell-phone users take advantage of the limitless minutes now included in many calling plans, University of Wisconsin-Madison engineers have developed a device that can significantly improve the quality of the transmitted signal on even less battery power.
"When you've been talking on a cell phone for a long time, you can feel how hot it gets," notes Zhenqiang "Jack" Ma, an assistant professor of electrical and computer engineering at UW-Madison. "This kind of overheating has always been a barrier to improving wireless communications."
Wireless communications devices, such as cell phones or cordless computer keyboards, rely on a small electrical part called a power amplifier. The amplifier, composed of tiny energy cells, is responsible for sending signals. In the case of cell phones, it turns on when the user hits the "send" button.
Because the power amplifier does the heavy lifting when it comes to communicating via a mobile phone, it may not be surprising that it also consumes the most battery power.
This power drain, as Ma explains, poses challenges to improving the capabilities of cell phones. According to the Wisconsin engineer, more electrical current converges in the center of the power amplifier when the device is overpowered. As a result, it heats up and, in some cases, even burns out.
To prevent this overheating, the makers of power amplifiers add current-controlling devices called ballasting resistors. Ma says that while these resistors stabilize the internal temperature, they also sacrifice power output. Less power, he explains, means weaker cell-phone signals and batteries that need to be charged more often.
One of the few ways to improve cell-phone technology - including the amount of data that can be transmitted, battery efficiency and hardware cost - is to overcome the overheating within power amplifiers, eliminating the need for the power-limiting resistors, says Ma, noting that the last major advance in this area occurred in 1989.
What Ma, along with his graduate students, developed could mark the next step in power amplification technology. After reading through dozens of scientific papers and analyzing heat transfer within power amplifiers housed in wireless communication devices, Ma and his students found a way to significantly reduce the rising temperatures inside amplifiers from the increased electrical current.
"If the heat transfer mechanism within the devices is fully understood," Ma says, "the solution to overcome the overheating becomes quite obvious." The solution the Wisconsin engineers came up with was to rearrange the energy cells within a power amplifier so that any heat produced dissipates uniformly, rather than moving towards the center. This rearrangement reduces the overall temperature, which enhances overall performance.
"We have found a new power device structure that can counterbalance heat transfer, restoring the degradation in capability associated with the present design," says Ma.
Both theoretical models and a prototype Ma and his collaborators have created confirm that this new structure can increase the output of the power amplifier while reducing its input - energy from an internal battery. The end result could mean cell phones that receive more data, reach towers farther away and stay powered longer.
With the new design, patented and to be licensed by UW-Madison intellectual property manager, the Wisconsin Alumni Research Foundation, Ma says that cell phones not only will be better, but also cheaper to make, and will provide a very competitive edge to companies that utilize the new development.
Ma, a cell phone user himself, is excited about this advance in power amplifiers and predicts that within the next 10 years the new structure designed by the Wisconsin engineers could become the industry standard for any type of wireless communications device.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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