We live in a world where every screen has to be touched. The problem with this laudable view is that when you use the touch screen, sometimes you get unexpected results. For example, not many people want greasy stains on TV. Another problem is that touch screen technology is expensive and complex. Although this technology has promoted the revolution of smart phones, the cost of turning every surface into smart glass is prohibitive. There has always been a close relationship between innovation and art. However, the limitations of touch screen technology mean that the ubiquitous science fiction level of touch screen is almost impossible.

Working principle of touch screen technology

There are several types of touch screen technology that most people don’t know about. The most commonly used are capacitive, resistive and infrared. There are also near-field imaging, but this is largely for military use. While all of these screen types end up doing the same thing, they work in different ways. So as to make them more suitable for some uses / applications.

Capacitive touch screen

The capacitive screen works with multi-layer glass, and the inner and outer layers of the glass conduct electricity. Thus, the screen behaves like a conductor separated by an insulator. It’s like a capacitor. By touching the screen, the electric field changes and the input is recorded. The capacitive screen allows you to make multiple inputs at once. However, one thing a capacitive screen can’t do is input with a plastic pen. Because plastic is an insulator, the screen does not record input.

What are the main types of touch screens?

Resistive touch screen

Resistive touch screen is the most common technology type in the market. They work by coating conductive glass with a soft layer of conductive polyester, separated by an insulating film. When you touch the screen, the polyester will touch the glass and complete the circuit – that’s how keyboards work. The device can determine where you press on the screen and respond accordingly. That’s why the device doesn’t always respond to the correct input when the two buttons are close together.

Infrared touch screen

The infrared touch screen uses a grid of LEDs and photodetectors. The LED is located on the opposite side of the screen, illuminating an infrared lattice in front of the screen. By touching the screen, the light beam is disconnected, and the device interprets the input according to the position. Because touching the screen destroys the infrared beam without having to complete a circuit, the technology works for any type of input, including non-conductive ones. They are also a limiting factor in terms of where touch screens are installed. There are also some considerations about cost and energy consumption.

Surface acoustic wave technology (or ultrasonic)

In fact, surface acoustic wave technology is not so new. In fact, ultrasound as a technology has been used in many industries for decades. On the touch screen side, the technology works by projecting ultrasonic waves onto the surface of the screen. When you interact with the screen, the sound waves are interrupted, absorbing some of the energy. Then, the control chip of the screen can determine the position of the touch screen.

The size of the ultrasonic sensor at the contact point is only 1.4×2.4×0.49mm (approximately the size of a pen tip), which can work on metal, glass, wood, ceramics and plastics. Make it suitable for most business and home environments. But it’s not that exciting, because existing touch technologies already work in these environments, so unless it’s more common, it’s not impressive. The touchpoints can work in the presence of moisture, oil and dirt, which means that the technology can be used in industries and environments that were not previously practical. To make the device easier to use, it can be connected to anything from industrial machines to military equipment. Because the ultrasonic wave can be projected on the surface of any thickness, it is widely used.

One problem is that the tiny size of the chip means that a single sensor can only record one mechanical button. Therefore, in order to input multiple commands, multiple sensors are needed. However, in order to prevent the processor of the host device from overload, each sensor is designed to work independently and has its own processing capacity, which means that it can only relay input, so it is easier to install. If the technology works as ultrasense systems claims, it could, in theory, reduce the cost of technologies such as tablets and hybrid laptops. It’s just that the existing complex technology can be replaced by a series of touch points around the screen. Unfortunately, despite the innovation, we are still a long way from science fiction level of interaction. Because the technology requires (potentially) hundreds of sensors around the required surface, the possibility of turning a coffee table into a keyboard won’t come soon. It is speculated that the next step will be to produce a “frame” of contact points, which can be placed around an object to make it permanent or temporary – a touch interface. After that, we can expect to see the wireless (wireless charging) smart table enter the furniture market.

Editor in charge: Tzh

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