Electronic Design

Experimental Conductive Polymer Promises Novel Variable-Resistance Products

An experimental material functions as a lightweight, malleable conductor that can detect, measure, and respond to a range of pressures. This composite is easily shaped into granular form and can be affixed to fabrics, plastics, and other solids. Scientists experimenting with the matter foresee the material being used to create imaginative products such as roll-up musical keyboards or clothing that monitors bodily functions.

The substance is called Peratech, after its creator, the Peratech Co. of North Yorkshire, England. Developed as a prototype for a different product, the unique properties of Peratech were discovered during random testing for electrical properties, says its inventor, David Lussey. Years later, the company is manufacturing the composite routinely and in increasingly large batches.

Generally, composite materials consisting of polymeric binder and metallic filler are fabricated in a conducting or a nonconducting form. The quantity of metallic particles in the composites may or may not be sufficient to provide an unbroken path for current flow. In contrast, Peratech polymers are made so that conductive pathways are not created throughout the samples despite the amount of metallic filler used. This is achieved by covering the metallic particles with a very thin layer of polymer.

In its natural state, Peratech is an insulator. Because the polymer coatings are extremely thin, the material is very sensitive to deformation. Actions such as compressing, stretching, or twisting lower its resistance. In this way, the resistance can be reduced until the substance behaves like a metal.

Peratech can be designed to display a vast range of resistance under normal pressure. The resistance can be reduced from millions of ohms to less than 1 Ω under the pressure of a finger (see the figure).

The conduction mechanism is predominately field-induced quantum tunneling, which affects the exponential decrease of resistance with increasing compression. Such behavior lends itself to applications involving proportional control of electronic devices.

Peratech expects its materials to replace conventional variable-resistance interfaces based upon mechanical contactors. The materials offer reduced wear and increased performance and reliability. They also will provide designers with the ergonomics of a truly moldable switch. The company envisions a future filled with tactile-based wearable interaction and soft-touch interfaces. It's projected that the company is close to attaining a commercially viable product.

For more information on the development of Peratech materials, visit www.peratech.com.

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