Types of Touch Screen Technology

Touch screens are found in all kinds of devices from ATM machines and cash registers to diagnostic tools in automobile repair shops. They are also used in many media houses, where they allow reporters to report on the weather or news events without having to move away from the screen.

Capacitive

Capacitive touch screen technology is the standard for most modern devices and has supplanted resistive technology. It offers a number of advantages over other technologies, including better durability and lower power consumption.

A capacitive touchscreen works by detecting the slight change in charge caused by your finger touching the surface of the screen. This change in charge is like the static electricity that makes up our bodies, and it allows the processor to accurately locate where your finger is touching.

To do this, a capacitive touch screen uses a conductive layer of indium tin oxide (ITO) and an insulator layer of glass. When your finger touches this, it creates a capacitor, and the human skin acts as a dielectric, affecting the circuit’s overall capacitance.

The touch sensor is connected to a microcontroller that monitors variations in the circuit’s charge-discharge times, and when the value deviates from the standard, it sends a signal to the main controller indicating that you have touched the screen.

Another major advantage of capacitive touch screens is that they can work in a wide range of environments, ranging from dusty rooms to a moist kitchen. The screen can also survive a small crack in the case without failing to function.

Capacitive touchscreens are also easier to clean than resistive screens because they can be wiped with a damp cloth or a soft, nonabrasive soap and water solution. However, it is important to ensure that the screen and edges are completely dry before you use them again.

In addition, they can be easily repaired with an adhesive layer if needed, so they are a good option for high-end devices.

The touchscreen panels of these devices feature a patterned conductive matrix behind the front glass, which is monitored by the touch controller firmware. When a finger or stylus is pressed onto the screen, a minute change in the capacitive field generated by the matrix occurs, and the touch controller firmware determines the finger position using the grid intersections that correspond to each touch location.

A variety of technologies are used for touchscreens, but most rely on electrode grid patterns on etched conductive layers. These are typically called projected-capacitive (PCT) or mutual capacitive. The grids are positioned across each other, resulting in horizontal and vertical patterns that match the touch positions.

Resistive

The most common type of touch screen technology, resistive touchscreens are used in a wide range of consumer and industrial applications. They are particularly popular in point-of-sale (POS) terminals, as well as digital still cameras and GPS devices.

Resistive touchscreens consist of two conductive layers separated by dielectric spacer dots, typically made of indium tin oxide (ITO). When pressure is applied to the top layer by a finger or other object such as a stylus or pen, these two layers come into contact. This creates a change in resistance (an increase in voltage), which the sensor layer detects and the tablet or mobile phone processor can use to determine the X-Y coordinates of that touch.

With their simple structure and low cost, resistive touch screens are a popular choice for portable applications and industrial settings. They offer a reliable user experience in harsh environments, where liquids or debris might interfere with other types of touch screens. They are also ideal for users wearing gloves, as they can be activated using bare fingers, nails or even a stylus.

Because of their simplicity, resistive touch screens are easy to design Touch screen and manufacture. They are available in 4-, 5-, 6- and 8-wire designs, which vary in sensitivity, durability and noise suppression.

They are sensitive to both a single touch point and multi-touch inputs, which can be beneficial in fast-paced applications. However, their single-touch operation limits them to basic touch actions, such as pinching and zooming.

Additionally, they are susceptible to dents and scratches in certain conditions. The film substrate commonly used as a top surface is less transmissive than glass, which can lead to reduced brightness and haze.

While resistive touchscreen technology remains a popular option for many applications, it’s losing market share to projected capacitive technologies, which are becoming the preferred touch-enabled interface choice across most devices. Projected-capacitance touchscreens don’t suffer from the limitations of their predecessors, and they offer high-end devices more features than resistive screens. Consequently, system designers must balance component integration costs against functional performance to provide the best user experience for their customers.

Surface Acoustic Wave (SAW)

The SAW sensor is a type of sensor that detects events through the interaction of acoustic waves and an electrical signal. This technology is very common in electronic circuit devices, such as filters, oscillators, and transformers.

SAW sensors can be divided into two categories: delay line and resonant type. The delayed line-type SAW sensor has a piezoelectric substrate and an interdigital transducer (IDT), which converts the excitation signal into an acoustic wave. The acoustic wave then propagates along the piezoelectric substrate, and its energy is reflected by the reflective gate.

When an acoustic wave reaches the piezoelectric substrate, the amplitude of the acoustic wave decays exponentially with the depth of the piezoelectric material. The penetration depth of SAW is just a couple of wavelengths, which makes it an ideal candidate for acoustic radio frequency (RF) filtering applications in wireless communication systems.

In addition to RF filters, SAWs and bulk acoustic waves find increasing applications in life sciences and microfluidics for sensing or mixing of tiny amounts of liquids. These thumbnail-sized ‘lab-on-a-chip’ (LOC) devices revolutionize diagnostic quests in medicine.

However, there are some limitations to SAW sensors. Unlike other types of sensors, SAW sensors have limited success in liquid environments. This is because the SAWs propagate through a liquid’s surface, which leads to complex flow line patterns in the fluid.

To overcome this limitation, a new generation of SAW sensors is aimed at measuring chemical reaction processes in liquids. They have high resolution, high accuracy, and low power consumption.

For example, FLOWave is a compact and lightweight in-line flowmeter that uses acoustic-surface technology to measure the flow of liquids. It is CIP/SIP capable, and can conform to the strictest hygiene standards.

Another advantage of this type of sensor is that it can be easily inserted in different liquids. The one-piece stainless steel tube body enables highly accurate measurements and no pressure drops, which is especially useful for CIP/SIP operations.

SAWs are a powerful tool for studying material properties, from linear elastic behavior to fracture. They also are the basis for the development of acoustic cavitation phenomena, which induce micron-sized cavities in fluid bulk by using high-power acoustic waves.

Infrared

Infrared touch screens are one of the most common technologies used in commercial applications. They work by detecting interruptions in an invisible light beam that is created by LED lights embedded into the frame of the display screen. These IR LEDs emit horizontal and vertical invisible IR beams, which form grids across the surface of the overlay, and photodetectors are installed across from them to detect interruptions in the light beams as a touch event happens.

Another benefit of IR technology is that it does not require any conductor such as a finger, apparatus or a stylus to operate the device. This eliminates the need for patterning on the glass, making it stronger and more durable than capacitive devices which are more susceptible to breakage when dropped from a height.

However, IR touch screens are not as accurate as capacitive or resistive devices, and the signal can be interrupted by dirt and dust, or Touch screen by moving objects such as a mouse. These problems can be resolved by using a specialized anti-jamming mode in the display, which works by only transmitting a fixed frequency signal to the sensors on the screen.

Additionally, infrared touch screens can be operated with wet or dirty fingers and gloves. This makes them ideal for industrial and medical applications, which require high reliability and safety.

For example, infrared touch screen technology is used in plant control systems, factory automation, and ATM. It is also a good choice for interactive whiteboards, which are widely used in business meetings and distance learning.

Compared with capacitive and resistive technologies, infrared technology is considered more reliable and less expensive. It can support up to 40-point touch input and can be activated by a bare finger, gloved finger or stylus.

Infrared technology is also more resistant to electrostatic and magnetic noises, and can be used for multi-touch operations. This means that multiple people can use a single device at the same time, and it also improves battery life because there is no need to constantly re-calibrate the screen. Furthermore, infrared touchscreens can be applied to large size panels.