What makes the iPhone so great? Touch screen technology. Touch screens are changing the way we interact with technology and with iPhone, Apple has opened the floodgates of innovation for the function and design of handheld devices.

In many other products and across all industries, touch screens are becoming ubiquitous. Applications include interactive mall directories, voting booths, industrial terminals, and GPS mapping devices. Consumers are getting more accustomed to the self-service environment as more kiosks and terminals become available at airports, grocery stores and even libraries. There is even evidence that a significant percentage of the public now prefers touch screen kiosks to dealing directly with a customer service agent, and some grocery stores and home improvement stores have replaced express lanes with touch screen self-service kiosks.

Apple’s innovative iPhone features a 3.5-inch (diagonal) widescreen multi-touch display that offers 480 — 320-pixel resolution at 163 ppi.

The Seattle- Tacoma airport recently underwent a dramatic renovation and replaced many of their traditional ticket counters with touch screen kiosks. This allows the airlines to reduce the number of employees on staff and speed the check-in process for all customers. Employees now stand next to customers at a touch screen kiosk instead of working behind a counter, assisting with check-in only as needed.

Understanding the technology behind touch screens will better enable companies to assess and incorporate touch screens into their products and work environments. Many industrial settings and commercial applications that at one time were not qualified for touch screen interfaces are now prime candidates.

Touch screens can be classified into seven primary technologies from the more basic resistive touch screens to the newer developments in force panel technology.

Resistive

The most common and often the least expensive touch screen technology, resistive touch can be found in many PDAs, retail registers, credit card readers, and ATMs. The technology senses touch when a user presses the screen, bringing together two layers of sensing resistive film that determine the location of the touch. Resistive screens are susceptible to damage from sharp objects, repeated use, or excessive force. The clarity and readability of the display is also compromised because the layers used to register touch reduce transparency.

Capacitive

Microsoft Surface is a 30-inch touch-sensitive display that turns an ordinary tabletop into an interactive computer.

The Apple iPhone is an impressive advance in the use of capacitive touch and popularized multi-touch commands for the general public. Capacitive touch screens come in two flavors: surface capacitive and projected capacitive. Capacitive touch panels sense the change in the alternating current applied to a conductive layer in the panel when it is touched by a finger. Capacitive screens are longer-lasting than resistive screens, but these screens can also be compromised by moisture on the touch surface. Another drawback is the screens cannot sense a touch if the user is wearing a glove. For the iPhone, Apple contracted the screens to the German company, Balda.

Infrared

The most common technology for infrared involves emitting infrared light across the surface of the touch screen and using an array of vertical and horizontal light sensors to detect interruptions in the light. The touch screens are very transparent and can be quite durable and are often found in military applications. This technology is susceptible to debris on the surface or anything that will disrupt the light waves traveling across the surface. One recent introduction with an integrated infrared screen is the 8000i from Northstar. This marine navigation system is able to maintain a bright display, is not affected when a boat starts bouncing around on the water, remains cool during long use, and can even be operated if the user is wearing gloves.

Surface Acoustic Wave

Surface acoustic wave touch screens operate similar to infrared, except instead of infrared light, they send acoustic waves across the touch surface. When a finger touches the surface, waves are absorbed and a series of transducers and reflectors detects the point. The surface needs to be made of glass and is susceptible to scratches or debris on the surface. The touch surface can be rugged and the technology will sense most any object and work over wide temperature extremes.

Optical Imaging

Optical imaging uses a system of imaging sensors and infrared light across the touch surface to sense touch. Cameras are used to detect changes in the light on the surface, or shadows, and locate the touch. One intriguing application was the Microsoft Surface introduced in 2007. This new application makes a coffee table into a touch sensitive computer that can sense touch commands as well as the presence of objects and technology products resting on the surface. For example, the screen can sense a digital camera and download the images stored on the camera right onto the "desktop" of the screen. This download of images appears as a pile of virtual pictures ready to be arranged with the user's fingers.

Bending Wave

The two most popular bending wave technologies are 3M's dispersive signal technology and Elo's acoustic pulse recognition. These applications use transducers at the edges to detect bending waves disrupted by the user's touch on a glass plate and a digital signal processor determines touch location. The touch surface can be very rugged and the transparent touch panels are as clear as glass. The dispersive signal technology can eliminate problems related to on-screen contaminants and surface damage. The acoustic pulse recognition can be scaled from a PDA size to 42" and offers palm rejection during signature capture. Palm rejection is a touch screen's ability to differentiate a stylus from other objects that might come in contact with the screen, such as the palm of your hand.

Force Panel

While the technology for force panel began in the 1960s, only recently has the technology become commercially viable with a unique set of improvements over previous touch screen technologies. Force-based touch panels measure the force from a touch with multiple sensors and can measure how hard the user is pressing against the panel. Panels can include irregular surfaces or elevated elements that remain touch sensitive. For example, custom-built buttons in any shape or size can be integrated into the design of the touch surface. InfiniTouch, introduced by QSI Corporation in 2007, is the first functioning application of force panel technology in the United States. InfiniTouch is the only touch technology that measures the actual touch force rather than using an indirect measurement.

Other interesting developments in touch screen technology include frustrated total internal reflection developed by NYU Courant Institute of Mathematical Sciences and the MERL DiamondTouch. Frustrated total internal reflection allows for multi-touch and multi-user input, but necessitates working in a dark room with plenty of room for rear projection. The DiamondTouch is also a multi-user application, but with a system of antennas and receivers the display can distinguish between the touches of different users. DiamondTouch is a front projection system and requires the users to maintain a capacitive connection to a receiver, typically through their chair.

Each of these seven main touch screen technologies exhibits unique strengths and weaknesses depending on a potential application. The iPhone uses capacitive in part because of the multi-touch functionality; the military relies on infrared for many applications, despite the high cost, to ensure brightness in the displays; and the InfiniTouch provides improved durability and design flexibility.

The epidemic of touch screens continues to spread in everyday life with new applications on the market every day. With the new introductions of products like JazzMutant's Lemur, Apple's iPhone, and QSI Corporations's InfiniTouch, the boundaries of touch screen technology continue to expand.

This article was written by Garrick Infanger, Force Panel Project Manager, QSI Corporation (Salt Lake City, UT). For more information, contact Mr. Infanger at garrick. This email address is being protected from spambots. You need JavaScript enabled to view it., or click here .