er- sions of solar cells in the laboratory and achieved 17 percent efficiency at con- verting light to electricity. They have also built bright light-emitting diodes (LEDs) on silicon substrates that have a display quality comparable to that of traditional LEDs. 8.2 SMALLER, LIGHTER POWER ADAPTER As notebook computers become thinner and lighter, the ubiquitous power adapter remains stubbornly heavy and bulky. In fact, it's not hard to see the day when notebooks are actually more compact than their power adaptors. But smaller and lighter adapters may soon be on the way, thanks to a little known power-generation approach known as piezoelectric technology. 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. "Electromagnetic transformers are shrinking slightly, but there are theoretical limitations in reducing the general size," says Kenji Uchino, a professor of electrical engineering at Pennsylvania State University. However, ENERGY TO GO-POWER GENERATION a piezoelectric motor and transformer can be much smaller and lighter, he notes. Piezoelectric material moves when placed under an electric voltage. Addi- tionally, when displaced by outside pressure, piezoelectric 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 1 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. "Smaller, less complex piezoelectric devices are al