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Generally, piezoelectric materials - those that generate electrical energy when pressure is applied to them - start to lose effectivity in high-temperature environments. A team from Pennsylvania State University and QorTek work past these limitations.

Penn State reports that its Materials Research Institute director Clive Randall led the effort in partnership with Pennsylvania-based electronics manufacturer QorTek, a local company specialized in the development of smart material devices and high-density power electronics.

Piezoelectrics: From Space to Personal Wearables

"NASA's need was how to power electronics in remote locations where batteries are difficult to access for changing," Randall said in the Penn State news release. He adds that the space administration also looks for self-powering sensors to monitor systems like its engine stability monitors and other devices used during rocket launches and similar high-temperature situations that render piezoelectric materials inefficient due to excessive heat.

Piezoelectrics have been widely used for sensors and energy-harvesting mechanisms, such as roads that also power street lamps or self-powering pacemakers that draw power from heartbeats. These materials have generally been used to measure pressure, temperature, acceleration, or mechanical strain applied to a surface. The same technology has also been used to power miniaturized ultrasound detectors.

In their work, the Penn State and QorTek team integrated piezoelectrics into their design of an energy harvester called a "bimorph," which allows the device to work as a sensor, an energy harvester, or an actuating device. It was called a bimorph because of two piezoelectrics assembled together, shaped, and assembled so that both layers are optimized for changing applications. The same energy harvesting mechanism could be used as the power source for sensing or actuating applications.

However, this bimorph also suffers from the same high-temperature limitations as any other piezoelectrics. Current materials are usually limited to a maximum effective operating temp range of 176 degrees Fahrenheit (80 degrees Celsius) to 248 degrees F (120 degrees C).

"A fundamental problem with piezoelectric materials is their performance starts to drop pretty significantly at temperatures above 120 C, to the point where above 200 C (392 F) their performance is negligible," explains QorTek chief technical officer Gareth Knowles, adding that their new work could present a solution for the NASA requirements.

Developing High-Temperature Piezoelectrics

The new piezoelectric material developed by the Penn State and QorTek team supposedly maintain near-constant performance at temperatures of up to 482°F (250°C). Furthermore, while it has also started showing slight drops in performance above this temperature, it still works as a sensor or energy harvesters up to temperatures exceeding 572°F (300°C). Details of the new piezoelectric material are reported in the Journal of Applied Physics.

"The compositions performing just as well at these high temperatures as they do at room temperature is a first, as no one has ever managed piezoelectric materials that effectively operate at such high temperatures," Knowles added. Researchers based it on the ferroelectric system Bi(Me)O3-PbTiO3 in a piezoceramic composition to achieve the new material.

Randall explains that piezoelectric working even in high-temperature environments could also serve as more efficient alternatives for other existing applications.

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