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Illumination & Displays

Bandage-sized flexible touch display

A soft-actuator-based tactile human-machine interface offers innovative information-technology solutions.
9 January 2008, SPIE Newsroom. DOI: 10.1117/2.1200812.1442

We currently use our visual and auditory senses when interacting with primary information-technology devices such as computers, game players, and mobile phones. However, the implementation of ‘touch feel’—a major human sensory function—for human-machine interfaces has long been a core research interest. Touch is now being exploited as the major function of the human interface in high-end mobile phones such as the Apple® iPhone® and Samsung's Haptic Phone, among others. However, the state of the art remains focused on just sensing the touch, and displays aimed at transferring the feel of touch lag far behind expectations.


Figure 1. Tactile display worn on a fingertip.

Our tactile display realizes touch transfer (see Figure 1).1 The device is a flexible polymer film consisting of tiny actuator cells (black dots, see Figure 2). The key material is a dielectric elastomer, an electroactive polymer.2 Like most polymers, the dielectric elastomer is hyperelastic, implying that it can withstand significant elastic strain yet still recover its original shape. When a voltage is applied, the film compresses down and expands outward. The film thus puts pressure on the wearer's skin, inducing a ‘touch feel’ without using any electromechanical transmission. Overcoming the rigidity and bulkiness of current devices, the new display is soft and flexible enough to be wrapped around almost any part of the human body such as the fingertip, palm, or arm. The display can convey touch information to the wearer when worn on the fingertip like a thimble.


Figure 2. Overview of a tactile cell. (a) Cross-sectional view of a tactile stimulating cell. (b) Tactile-cell assembly.

A typical implementation with 20 actuator cells is as shown in Figure 3. Its active area is 14×11mm2 to cover most of the fingertip area dedicated to feeling touch. As if using a thimble, the user inserts a fingertip into the display by lining up the active area with the fingertip's touch-sensitive area. The tactile feel is generated by actuating the 20 cells independently, driven by the pattern of touch required. Depending on the application, either simple up-down actuation or overall vibration can be generated. We have developed an electronic circuit driving the tactile cells3 to achieve this.

This simple stimulation mechanism—which does not require complex electronics—is one of the greatest advantages of the soft tactile display compared with other currently available devices. Its other benefits include efficient power usage, cost effectiveness, and easy fabrication. We hope that the soft display might lead to the development of new user interfaces for mobile information-technology devices, game interfaces, and communication tools for the visually impaired (e.g., Braille displays). It could also have applications in robotics, virtual reality, and telesurgery.3,4


Figure 3. Operational 20-cell fingertip touch display.

Hyouk Ryeol Choi, Igmo Koo, Jachoon Koo
School of Mechanical Engineering
Sungkyunkwan University
Suwon, South Korea
Hyouk Ryeol Choi is a professor. He was previously a researcher at LG Electronics Central Research Laboratories and a Japan Society for the Promotion of Science fellow at the National Institute of Advanced Industrial Science and Technology (Japan).
Igmo Koo is a PhD student in the Intelligent Robotics and Mechatronic System Laboratory under supervision of Hyouk Ryeol Choi.
Jachoon Koo is an associate professor.
Jae-do Nam
Department of Polymer System Engineering
Sungkyunkwan University
Suwon, South Korea

Jae-do Nam is the director of the Gyeonggi Regional Research Center, supported by the Kyunggi provincial office.