Touch switches are found in smartphones and a variety of other devices. They are conducive to aesthetic design, convenient to use, and are growing rapidly in popularity. However, they are vulnerable to water and perspiration and largely unusable when gloves are worn. PiezoTap™, currently under development at TDK, is a piezo switch based on piezoelectric technology that is expected to expand the potential of touch switches.
Technical challenges facing the touch switch, a buttonless switch
A touch switch (also known as a touch sensor) refers to a switch (sensor) that is activated when a person or object comes into contact with it. They are drawing substantial attention as they can replace mechanical buttons, improving product design and ease of use.
Because touch switches require no firm force to operate—all they need is gentle contact—they are commonly found in lights, automatic doors and elevators. In particular, capacitive touch switches that respond to touches on screens have come into widespread use in smartphones and tablets in recent years. Capacitive touch switches work by detecting the change in capacitance that occurs when a fingertip and a sensing area come into proximity.
Capacitive touch switches, however, bear a significant shortcoming: they are vulnerable to water and perspiration, and usage with gloves requires special conductive gloves. With ordinary gloves, capacitance changes between the finger and the sensing area become difficult to detect, rendering the switch inoperable. Also, the presence of water or perspiration may cause erratic responses. Since compact touch switches are expected to be utilized in wearable devices, outdoor products, and products used near water, there is a growing need to address issues surrounding these types of applications.
Ultracompact, slim piezo switch solution built on the piezoelectric effect
PiezoTap™, a compact, highly sensitive piezoelectric switch under development at TDK, solves the problems touch switches have had with gloves and wet conditions. PiezoTap is an ultracompact, slim piezo switch built on the piezoelectric effect instead of the capacitance method. It can be used even when gloves are worn or in wet environments, thanks to how it detects pressure utilizing the piezoelectric effect—converting the minute mechanical stress caused by the force from a touch into a voltage using a piezoelectric element. By mounting PiezoTap inside the enclosure of a sealed device, applications where touch switches could not be installed in the past will become possible, greatly expanding the breadth of product design.
PiezoTap also features an ultracompact and slim design, weighing only 0.046 grams and measuring 7 by 7 by 0.2 millimeters, and can be installed regardless of the enclosure’s material. It can be mounted without cutting any holes in the enclosure, greatly improving the degree of freedom of design for products requiring small touch switches.
It is expected to be a great fit for a wide range of applications, including TWS (true wireless earphones), which are often used outdoors; wearable devices like smart glasses and smart watches; products used in the proximity of water, such as refrigerators, cooking appliances, washing machines, electric toothbrushes and bathroom remote controls; and car dashboards.
●Comparison of the occurrence of erroneous results between a bare finger, gloves compatible with touchscreens, and gloves incompatible with touchscreens, when each are dry and wet
●Evaluation criteria OK: Intended action successful NG: Unintended results (e.g., single tap interpreted as long press)
Promising future of an innovative piezo switch
1st. Section, Piezo Products Development Department
Piezo & Protection Devices Business Group
PiezoTap is a product currently under development, with mass production scheduled to begin in 2023. Atsushi Tamura, one of PiezoTap’s developers with the Piezo & Protection Devices Business Group, explains. “PiezoTap is expected to contribute not only to the miniaturization and waterproofing of wearable devices such as TWS, smart watches and smart glasses, but also to improved designs of home appliances like refrigerators and washers. While our current focus is on consumer products, we are looking to branch out to automotive displays and instrument panels in our next steps.”
TDK is broadening the possibilities of new product designs and user experiences with PiezoTap—an unprecedented, ultracompact piezo switch built on piezoelectric technology.