A flexible future: The new challenge for display technology
26 March 2010
Wafer-thin display media such as rear projection film (RPF), and more recently organic LED (OLED) technology, offer many exciting new design possibilities, as Ian Crosby discusses.
RPF has opened new creative freedoms particularly for designers in the digital-signage community, to make compelling presentations on screens having imaginative shapes or curved surfaces. OLED technology, which enables flexible powered displays suitable for small portable devices or larger products, will allow designers to realise even more futuristic visions such as daily-refreshable electronic newspapers that may be rolled up.
Despite the excitement caused by these innovations, end users can be expected to want more. The logical next step will be to add interactive capabilities to flexible display media; as these types of screens become commonplace, people will naturally want to touch - and will expect a response.
Adding Interactivity
Integrating a touch screen with a display is an established and implicit method of turning a one-way image into a two-way experience. Many types of equipment, such as self-service kiosks, ticketing terminals, industrial computers and some consumer products, already employ touch screens to promote speed, and ease of use, inviting a higher degree of customer interaction.
To choose the optimum touch screen technology from the alternatives available, designers must always consider aspects of the operating environment, such as moisture, dirt, dust, ambient light levels, and the potential for accidental or deliberate damage that may be caused by users. New opportunities and applications taking advantage of flexible displays such as RPF and OLEDs will add further criteria that touch system designers should consider.
Touch sensors using infrared or surface acoustic wave (SAW) detection systems, need a frame or bulky bezel structure to house necessary edge-mounted electronics. Increasingly, this is at odds with the form factor and flexibility benefits offered by RPF or OLED technologies, particularly given the modern preference for sleek, smooth-fronted designs, whether the displays are touch interactive or not.
As well as the bezel consideration, designers should also understand that touch technologies which are reliant upon front-face detection may not be compatible with curved display designs, even though they can be used successfully with rigid screen formats.
The addition of touch interaction to a screen that will be exposed to weather, dirt or damage poses an even greater challenge. Hence, to achieve a satisfactory solution in applications such as interactive storefront displays, a technology capable of sensing touch through the window will allow the touchscreen and its components to be positioned inside the store, away from any potential harm.
The Utilisation of PCT
Touch detection through projected capacitance has become widely used in modern, personal electronic devices, such as smart phones and notebook computers. Zytronic’s proprietary Projective Capacitive Technology (PCT) was originally developed approximately 10 years ago, in response to the demand for bringing touch sensing capability to applications requiring larger displays, located in harsh environments, such as outdoor ATMs, industrial computing, and interactive public terminals for ticketing and information display. Unlike resistive, infrared and surface-capacitive sensors, the PCT sensor has no front-face-active components. Instead, it has a matrix of copper capacitors arranged in an XY grid. At 10 µm in diameter (approximately one quarter the thickness of a human hair), the capacitive sensors are near invisible, allowing users to benefit from the full brightness of the display.
Figure 1 illustrates a cross section of the sensing array, which generates a capacitive field sensitive enough to detect touch through up to 20 mm of glass. The sensor matrix connections terminate at one edge of the touchscreen, leading into a controller IC that runs proprietary firmware and scans each capacitor. This can detect minute changes in capacitance caused by the proximity of a finger. Unlike conventional surface capacitive touchscreen solutions, which rely upon actual finger touch, PCT’s projected field can detect a touch even if the user is wearing gloves - the technology is therefore highly suitable for industrial and outdoor applications. An increase in the number of capacitors allows touchscreens to be built for display sizes ranging from 5 inches to 82 inches, in almost any form factor without the need for special tooling or masks – a major benefit for designers wishing to quickly design, test and implement a customised touchscreen system.
In conventional flat-fronted display touchscreens, the PCT sensing array is embedded within a laminated panel. The outer layer can be glass, polycarbonate or acrylic, depending on the end application requirements. If needed, anti-glare, anti-reflective or strengthened glass treatments can also be specified. As the sensing array is situated behind the front panel, it is well protected from hazards such as scratching or chemical spills. PCT units can also be sealed to meet IP67 or NEMA 4x enclosure standards.
These attributes have enabled the benefits of PCT-based touchscreen interactivity to reach a wide range of applications previously deemed impractical, especially in heavy duty industrial or outdoor environments, or settings where the display will be exposed to harsh weather conditions or potential vandalism.
Flexibility in Touchscreens
The PCT capacitor array can be deposited onto a variety of substrate types, including flexible ones, in an almost limitless variety of sizes and form factors. This now gives designers the means to combine interactivity with display media such as RPF. Flexible PCT sensors have been combined with RPF and an adhesive front face to enable an interactive display capable of operating through glass such as a store window.
The example shown in Figure 2 is ZYPROFILM, a combined RPF/PCT laminate built as a single flexible foil with a shielded tail providing the connection to the touchscreen controller. The foil can be quickly and easily applied to the inside of the store window. Importantly, it can also be rolled into a cardboard tube for fast, low-cost despatch using a regular postal service; unlike more conventional storefront displays, such as large TFT-LCDs or plasma panels. Power to the sensor matrix, plus the necessary linkage to the computer that generates the images and software content go through a USB or Serial connection. Figure 3 shows how the digital projector and combined RPF/PCT laminate interact to present a large, possibly curved, touch-sensitive, computer-generated display.
The techniques developed to create this type of interactive rear-projection foil can also be applied to flexible OLED displays, and may be used in the future to deliver further innovation in user-interface designs. For example, certain established electronics brands have already developed prototype TV monitors which can be bent in any direction and potentially wrapped around the user’s arm or other objects. Elsewhere, mobile phone manufacturers have created concept handsets which can be opened up like books to reveal a single display that has double the area of the handset package. It is only a matter of time before products such as these will require touch functionality, and consequently, the touchscreen solutions described in this article are likely to see widespread market uptake.
Ian Crosby is Sales and Marketing Director of Zytronic
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