Potential for ultra-compact piezoelectric tactile switches usable with wet hands

“Touch switches are used in smartphones and various other devices. They are beautifully designed, easy to use, and are rapidly gaining popularity. However, they are susceptible to water and perspiration and are largely unusable with gloves on. PiezoTap™, currently under development by TDK, is a piezoelectric switch based on piezoelectric technology that is expected to expand the potential of touch switches.

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Touch switches are used in smartphones and various other devices. They are beautifully designed, easy to use, and are rapidly gaining popularity. However, they are susceptible to water and perspiration and are largely unusable with gloves on. PiezoTap™, currently under development by TDK, is a piezoelectric switch based on piezoelectric technology that is expected to expand the potential of touch switches.

Buttonless Switches—Technical Challenges for Touch Switches

A touch switch (also called a touch sensor) is a switch (sensor) that activates when a person or object comes into contact with it. Such switches are gaining attention as a replacement for mechanical buttons, improved product design, and ease of use.

Because the touch switch does not require force when operating, it only needs to be touched lightly, so it is usually used in electric lights, automatic doors and elevators. In particular, capacitive touch switches, which respond to screen touches, have been widely used in smartphones and tablets in recent years. Capacitive touch switches work by detecting the change in capacitance as the fingertip approaches the sensing area.

However, capacitive touch switches have one distinct disadvantage: they are susceptible to water and perspiration, and special conductive gloves are required if gloves are required. With ordinary gloves, the change in capacitance between the finger and the sensing area becomes difficult to detect, making it impossible to operate the switch. In addition, water or perspiration can cause unstable responses. Since compact tactile switches will be used in wearable devices, outdoor products, and products that may come into contact with water, there is an urgent need to solve the problems of such applications.

Ultra-Compact, Slim Piezo Switch Solution Based on Piezoelectric Effect

PiezoTap™ is a compact, high-sensitivity piezoelectric switch being developed by TDK Corporation to solve the problem that touch switches cannot be used in gloved and wet conditions. PiezoTap is an ultra-compact, low profile piezoelectric switch based on the piezoelectric effect rather than the capacitive method. It uses piezoelectric elements to convert tiny mechanical stress from touch into voltage, and uses the piezoelectric effect to detect pressure, so the switch can be used even when wearing gloves or in wet environments. By installing the PiezoTap within the enclosure of a sealed device, applications that previously could not be fitted with a tactile switch can now be used, greatly expanding the breadth of product design.

In addition, PiezoTap weighs only 0.046 grams and measures 7 x 7 x 0.2 mm, so it can be installed in any casing. It can also be installed without opening holes in the housing, which greatly improves the design freedom of products that require the use of small touch switches.

The product is expected to have a wide range of applications, including TWS (true wireless earphones) that are often used outdoors; wearable devices such as smart glasses and smart watches; products that may come into contact with water, such as refrigerators, kitchenware, washing machines, electric toothbrushes, bathroom remotes, etc.; and car dashboards.

PiezoTap™ works based on the piezoelectric effect

The piezoelectric effect is a phenomenon in which a voltage is generated by mechanically deforming a piezoelectric element, such as a quartz crystal or some types of ceramics, by applying pressure. Piezoelectric elements detect tiny stresses from touch.

Comparison Results of Piezoelectric and Capacitive Methods

・ Comparison of erroneous results with bare fingers, wearing touchscreen compatible gloves, and wearing non-touchscreen compatible gloves under dry and wet conditions
・Evaluation Criteria Determination: Expected Action Success Failed: Unexpected Result (e.g. a single touch is interpreted as a long press)

An innovative piezoelectric switch with development prospects

PiezoTap is currently in development, with mass production scheduled to begin in 2023.

One of the developers of PiezoTap, Atsushi Tamura from the Piezo and Protection Devices Division explains. “We expect that PiezoTap will not only contribute to the realization of small and waterproof wearable devices such as TWS, smart watches and smart glasses, but also improve the design of home appliances such as refrigerators and washing machines. Although we are currently focusing on consumer products, In the next step we hope to expand to automotive displays and dashboards.”

TDK’s PiezoTap is a pioneering ultra-compact piezoelectric switch based on piezoelectric technology, and we will also broaden the possibilities of new product design and user experience by utilizing this product.

PiezoTap™ Piezo Switch

PiezoTap is a compact, slim, high sensitivity (high output voltage) piezoelectric switch that can be mounted on housings made of a variety of materials, including metal, plastic and glass. This product is currently under development and specifications are subject to change without notice.