As notebook computers become thinner and lighter, the ever-present bulky power adapters used for line current approach the weight of the laptops, but smaller and lighter adapters may be on the way, thanks to piezoelectric technology, according to a Penn State electrical engineer.
"Electromagnetic transformers are shrinking slightly, but there are theoretical limitations in reducing the general size," says Dr. Kenji Uchino, professor of electrical engineering. "A piezoelectric motor and transformer can be much smaller and lighter."
Transformers are needed to convert the 115-volt, 60-cycle power available from a standard U.S. wall receptacle to the 13 to 14 volts direct current used by laptops.
"Eventually we would like to make it the size of a pen, but that is far away," says Uchino. "When we can do that, the adapter will be a component of the laptop, not attached to the cord as a separate piece. Right now, we can reduce the adapters to one-fourth of their current size."
Uchino notes that while his group targets the laptop or notebook computer market, these smaller adapters are suitable for any appliance that requires an ac to dc converter and transformer.
Reporting in The Proceedings of the 5th International Conference on Intelligent Materials, Uchino, who heads the International Center for Actuators and Transducers at Penn State; T. Ezaki, Taiheiyo Cement Corporation, Japan; and A. Vazquez Carazo, Face Electronics, described their piezoelectric transformer.
Piezoelectric material moves when under an electric voltage, and, when displaced by outside pressure, these materials produce an electric voltage.
Transformers are made from piezoelectric materials by applying a chopped electric voltage to one side of a piezoelectric wafer. This on and off voltage creates a vibration in the material, which is converted to an ac voltage on the other side of the wafer. The amount of increase or decrease in the voltage transformed is dependent on the gap between the electrodes.
Most laptops require about 15 volts direct current with less than one amp of current and about 12 watts of power. By manipulating the length and width of the piezoelectric chip, the researchers can convert 115 volts to 15 volts. A rectifier then converts the alternating current to direct current.
The original piezoelectric devices were rectangular, but they could not produce sufficient power, so the researchers switched to a circular configuration.
"Smaller, less complex piezoelectric devices are already in use as step up transformers in some laptops to light the monitors which can take 700 volts to turn on and 50 to 150 volts to continue their operations," says Uchino.
One advantage of piezoelectric PC power adapters is that they do not produce the heat that conventional electromagnetic transformers produce. Electromagnetic power adapters not only produce heat, but also noise and interference. Piezoelectric power adapters operate in the ultrasonic range so humans cannot hear any sound produced and they do not produce electromagnetic interference.
"These power adapters were developed for the American and Japanese market where the line voltage is 100 to 125volts and 50 to 60 cycles," says Uchino. "Eventually, we also developed power adapters that convert 220 volts and 50 cycles so they can be used in the European market."
Other devices that could use these smaller, lighter power converters include printers, CD and DVD players, tape recorders and other appliances that operate on both battery and wall plugs.
The piezoelectric PC power adapter was developed at Penn State in collaboration with Face Electronics of Virginia and Taiheiyo Cement Corporation, Japan. Taiheiyo is planning to mass-produce the devices in 2004.
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