Chances are that inside your digital camera is a small ultrasonic motor that silently focuses the lens. The same motors are in your cell phone, video camera, and personal digital assistant. These miniature motors operate with ever increasing efficiency on very little current using high energy density piezoelectric materials. In Penn State’s International Center for Actuators and Transducers (ICAT), the materials, designs, and devices are developed that make possible the continued miniaturization of consumer electronics – from laptop computers to cell phones to the latest motorized medical devices.
A transducer is a device that converts one type of energy into another. Your ear is a type of transducer, converting sound waves into electrical energy using a (recently discovered) flexoelectric effect. Actuators convert energy into motion, think of them as motors. Kenji Uchino, professor of electrical engineering and director of ICAT, is a pioneer in the development of ultrasonic transducers and actuators. Beginning in the early 1980s, he was among the first researchers to put piezoelectric materials together with actuators to move something mechanically.
In the 1950s, C.A. Rosen and colleagues developed the concept of an ultrasonic transformer. A Rosen-type transformer utilizes a piezoelectric ceramic that vibrates at a certain resonant frequency when exposed to an electric field. This type of transformer can step-up or step-down the voltage between the input and output of the transformer without using wires or magnetism (Uchino & Carazo 2003). Current transformers can step up from 9 volts to close to 500 volts.
Uchino tells the story of a Japanese electronics company that commercialized Rosen’s invention in the 1970s, putting ceramic transformers into color televisions that they introduced with great fanfare during the Tokyo Olympics. However, all of the sets had to be recalled within a few months when the brittle ceramic transformers failed. This stumble effectively stalled the development of piezoelectric transformers for a generation, according to Uchino. This is typical of most failures in manufacturing, he maintains. “When you are young and fail at something, later on as you become upper management, experiment in that area is suppressed. ‘Oh, I tried this,’ you say. ‘It doesn’t work.’ It takes that generation to retire or die before work in that area can go on.” This was the case with the piezo transformer as the technology faded out for two and a half decades. At about the time of that first failure, Uchino began his academic career and immediately turned his attention to learning why the ceramics failed and how to test new piezoelectric materials. He introduced a testing method called constant current measurement, which developed into constant motion current. With these calculations, new compositions could be tested and improved upon.
Electromagnetic motors like the ones in household appliances and power tools convert electrical energy to magnetic energy via a coiled wire, and then convert that energy into mechanical energy to do something, such as turn a mixer blade. Large electromagnetic motors can operate with more than 90 percent efficiency. However, that efficiency drops as the motors shrink and the wire coils become more resistive to the flow of electrons. Small electromagnetic motors are relatively complicated and lose much of their energy as heat (i.e., Joule heat in a coil). In a 30 watt mobile device, such as a laptop, the efficiency is below 30 percent, while in a 100 milliwatt electromagnetic watch motor, for instance, the efficiency becomes less than one percent.
At the size scale where electromagnetic motors become inefficient, ultrasonic motors come into their own. Ultrasonic motors fill the niche between micron-size devices (MEMS) and devices that require more than 30 watts of power. That range is a perfect fit for portable Zoom lens focus mechanism for a cell phone camera electronics, such as digital cameras and cell phones, laptop displays, and miniaturized devices that need to deliver high performance on very little power.
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