Touchscreen Types-Tracing the History of Touch Display Panel

In today’s era, touchscreens have become an omnipresent part of our lives. From the smartphones we use daily to the self – checkout machines in shopping malls, with their intuitive and direct interaction methods, they have completely transformed the way we interact with technological devices and occupied an indispensable position in the modern world.

I. Definition and Principle of Touchscreens

A touchscreen is an interface that combines display and input functions, usually presented in the form of a transparent display screen. Users can interact with devices by identifying touch inputs on the screen surface. In most cases, it utilizes the electrical properties of the human body, especially the conductivity of fingertips, to detect touch actions. When a fingertip touches the screen, the device can recognize this conductive behavior and register it as a valid input.

Its operation relies on three key components: the touch sensor, the controller, and the software. The touch sensor, also known as the touch panel, contains a touch – sensitive surface that can detect changes in electrical properties such as current, voltage, capacitance, or resistance. The controller, as a hardware component, converts the electrical signal changes detected by the touch panel into recognizable touch gesture signals, such as tapping, sliding, zooming, etc. After receiving these signals, the software processes them and executes corresponding functions. It can also send instructions to the device as needed, achieving operations like starting a motor, switching screen information, turning off the device, adjusting brightness, and volume.

II. Working Process of Touchscreens

1. Activation of the Touch Sensor: When a user touches the screen surface, it triggers changes in the electrical properties of the touch sensor.
2. Processing by the Controller: The hardware controller captures the changes in the electrical signals of the touch panel, identifies specific touch gestures, and converts them into signals to be sent to the software.
3. Response of the Software: The software receives the signals, processes them, and then executes specific functions or tasks.

III. Types of Touchscreen Technologies

(1) Resistive Touchscreens

Resistive touchscreens operate by detecting the pressure applied to the screen. They consist of two flexible layers, usually made of polyester and glass, with a thin layer of conductive material, such as indium tin oxide (ITO), coated on the surface. The two layers are separated by tiny spacer dots. When pressure is applied to the screen, the top flexible layer comes into contact with the bottom layer, causing a change in the resistance between the two conductive layers. The touchscreen controller determines the precise location of the touch by analyzing this change. Resistive touchscreens are relatively inexpensive and support various input methods, such as fingers, styluses, or gloved operations. However, compared with other technologies, their sensitivity and clarity are not as good.

(2) Capacitive Touchscreens

Capacitive touchscreens respond by identifying changes in capacitance in the screen’s electrostatic field caused by touch. Different from resistive touchscreens, they do not rely on pressure to detect touch events. When a user touches the screen with a finger or a conductive stylus, the capacitance at the point of contact changes. The capacitive touch controller detects this change, processes the input, and determines the exact location of the touch. Capacitive touchscreens are widely used in smartphones, tablets, and other electronic devices due to their high sensitivity, high accuracy, and fast response. They also support multi – touch functions, allowing users to perform operations like two – finger zooming. However, they have poor compatibility with non – conductive materials, such as ordinary gloves and regular pens.

(3) Projected Capacitive (PCAP)

Projected capacitive touchscreens use an electrode grid to detect touch inputs. These electrodes, usually made of transparent conductive materials, are laid on a thin glass or plastic sheet covering the display. When a finger or stylus touches the screen, the capacitance between the electrodes changes. The controller circuit detects this change, calculates the touch position, and sends the corresponding input to the device. Projected capacitive touchscreens are highly accurate, sensitive, and durable. They are often used in high – end applications such as smartphones, tablets, and industrial control panels and support multi – touch gestures. Compared with ordinary capacitive touchscreens, their electrode structure and arrangement are different, and they are more sensitive and accurate.

(4) Infrared Touchscreens

Infrared touchscreens detect touch inputs with a grid composed of light – emitting diodes (LEDs) and photodetectors. LEDs emit infrared light beams arranged in horizontal and vertical arrays around the edges of the screen, and the photodetectors on the opposite side continuously receive these beams. When a user touches the screen, the finger or stylus blocks the infrared light beams, causing an interruption in the grid. The system calculates the coordinates of the touch point based on the interrupted beams and sends the information to the device’s processing unit to execute corresponding operations. Infrared touchscreens are highly durable, resistant to scratches, dust, and water. They support touch operations with almost any object, and the screen has good light transmittance and high – quality images because there is no additional glass or film layer on the screen surface. However, they may be affected by strong light and are more suitable for indoor environments and large – screen applications.

(5) Surface Acoustic Wave (SAW)

Surface acoustic wave touchscreens use ultrasonic waves to detect touch inputs on the screen surface. The screen is made of a layer of glass or other transparent materials with a thin reflective material layer on the surface. Ultrasonic waves are generated by transducers at the corners of the screen and propagate on the glass surface. When a finger, stylus, or other object touches the screen, part of the ultrasonic waves is absorbed, causing a disturbance in the wave pattern. The transducers detect this disturbance and calculate the position and type of the touch input. SAW touchscreens have high clarity, strong durability, and good reliability, with fast response speeds and the ability to detect slight touches and gestures. However, they are relatively expensive and not very suitable for use in harsh environments with a lot of dust and water.

(6) Optical Imaging Touchscreens

Optical imaging touchscreens use camera – like sensors and image – processing algorithms to detect touch inputs, similar to infrared touchscreens in principle. When a user touches the screen surface, the sensors detect the changes in light and shadow caused by the touch. These touchscreens have good durability and are not easily worn out by physical contact. They are often used in public kiosks, interactive displays, and game applications. However, their response speed and sensitivity may be inferior to other types, and they do not support multi – touch gestures.

IV. Development History of Touchscreens

The history of touchscreens dates back to the 1960s. At that time, early touch – based input devices were developed for use in control panels and other specialized applications.

1. 1960: Bell Telephone Laboratories (now AT&T) released one of the earliest versions of a touchscreen and patented it in 1962 (US 3016421A). This touchscreen used a grid of straight lights shining down onto the screen surface and only supported stylus operation, not finger touch. When the stylus interrupted the light beam in the grid, the photodetector recorded the touch.
2. 1965: Eric Johnson, from the Royal Radar Establishment in Malvern, UK, developed the first touchscreen that could be operated by a finger for traffic control. He first described the working principle of capacitive touchscreens in 1965 and further elaborated on it with photos and diagrams in an article in 1967. He applied for a patent in the UK in 1965 (GB3352465) and received a US patent in 1969 (US3482241A).
3. 1971: Dr. Samuel Hurst invented the first resistive touchscreen, which was not transparent at that time. In 1974, he developed a transparent resistive touchscreen.
4. 1972: The University of Illinois developed a touchscreen for the educational terminal system PLATO IV. There was a 16×16 infrared sensor array composed of LEDs and phototransistors on the edges of the screen, which could detect the touch of objects close to the screen.
5. 1973: Two engineers from CERN (European Organization for Nuclear Research), Frank Beck and Bent Stumpe, created a transparent capacitive touchscreen based on Stumpe’s previous work in a TV factory in the early 1960s. CERN began manufacturing them in 1973.
6. 1974: Dr. Samuel Hurst created the first resistive touchscreen with a transparent surface and applied for a patent (US3911215A) for the company he founded, Elographics Inc., which was granted in 1975.
7. 1982: The Input Research Group at the University of Toronto created the first multi – touch system using a frosted – glass panel and a rear – mounted camera, marking the beginning of multi – touch technology.
8. 1980s – 1990s: During this period, a large amount of research was carried out to improve the accuracy and functionality of touchscreen technology.

Conclusion

Capacitive and projected capacitive touchscreens have risen to prominence as the preeminent touchscreen display technology, thanks to their high precision and rapid responsiveness. Resistive touchscreens trail closely behind in popularity. Although infrared, surface acoustic wave, and optical imaging touchscreens are less commonly employed and less mainstream, they possess distinct applications and thus retain a niche yet loyal market segment.

Touchscreens have become ubiquitous, gracing industrial control panels, ATMs, medical equipment, and consumer electronics alike. They have transformed the way we engage with technology, firmly establishing themselves as an indispensable element of our everyday existence.