INDEX

Ser No Contents Page No

01 Abstract 02

02 Introduction 02

03 History 03

04 Application in Electronic components 06

05 Infrared 15

06 Optical imaging 15

07 Dispersive Signal Technology 16

08 Acoustic Pulse Recognition 16

09 Ergonomics and usage 18

10 Conclusion 21

11 Referance 21

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INDE

Abstract

1. Touch screen interfaces are becoming increasingly common among portable and desktop computing systems. The global production of touch screen systems has increased exponentially in the recent years.

2. In this technical paper, the history and evolution of touch screen technology over the years have discussed. Moreover, the various types of touch screens and technologies behind that are also addressed. The comparison of various types will give one a technical edge over selecting from a wide array of touch screen interface devices.

Introduction

3. A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreens can also sense other passive objects, such as a stylus. Touchscreens are common in devices such as all-in-one computers, tablet computers, and smartphones.

4. The touchscreen has two main attributes. First, it enables one to interact directly with what is displayed, rather than indirectly with a pointer controlled by a mouse or touchpad. Secondly, it lets one do so without requiring any intermediate device that would need to be held in the hand. Such displays can be attached to computers, or to networks as terminals. They also play a prominent role in the design of digital appliances such as the personal digital assistant (PDA), satellite navigation devices, mobile phones, and video games.

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History of Touch Screen Technology

1960s

5. Historians consider the first touch screen to be a capacitive touch screen invented by E.A. Johnson at the Royal Radar Establishment, Malvern, UK, around 1965 - 1967. The inventor published a full description of touch screen technology for air traffic control in an article published in 1968.

1970s

6. In 1971, a "touch sensor" was developed by Doctor Sam Hurst (founder of Elographics) while he was an instructor at the University of Kentucky. This sensor called the "Elograph" was patented by The University of Kentucky Research Foundation. The "Elograph" was not transparent like modern touch screens, however, it was a significant milestone in touch screen technology. The Elograph was selected by Industrial Research as one of the 100 Most Significant New Technical Products of the Year 1973.

7. In 1974, the first true touch screen incorporating a transparent surface came on the scene developed by Sam Hurst and Elographics. In 1977, Elographics developed and patented a resistive touch screen technology, the most popular touch screen technology in use today.

8. In 1977, Siemens Corporation financed an effort by Elographics to produce the first curved glass touch sensor interface, which became the first device to have the name "touch screen" attached to it. On February 24, 1994, the company officially changed its name from Elographics to Elo TouchSystems.

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1980s

9. In 1983, the computer manufacturing company, Hewlett-Packard introduced the HP-150, a home computer with touch screen technology. The HP-150 had a built in grid of infrared beams across the front of the monitor which detected finger movements. However, the infrared sensors would collect dust and require frequent cleanings.

1990s

10. The nineties introduced smart phones and handhelds with touch screen technology. In 1993, Apple released the Newton PDA, equipped with handwriting recognition; and IBM released the first smart phone called Simon, which featured a calendar, note pad, and fax function, and a touch screen interface that allowed users to dial phone numbers. In 1996, Palm entered the PDA market and advanced touch screen technology with its Pilot series.

2000s

11. In 2002, Microsoft introduced the Windows XP Tablet edition and started its entry into touch technology. However, you could say that the increase in the popularity of touch screen smart phones defined the 2000s. In 2007, Apple introduced the king of smart phones, the iPhone, with nothing but touch screen technology.

12. Touch-screen monitors have become more and more commonplace as their price has steadily dropped over the past decade. There are sevral basic systems that are used to recognize a person's touch:

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13. In electrical engineering, resistive touchscreens are touch-sensitive computer displays composed of two flexible sheets coated with a resistive material and separated by an air gap or microdots. When contact is made to the surface of the touchscreen, the two sheets are pressed together. On these two sheets there are horizontal and vertical lines that when pushed together, register the precise location of the touch. Because the touchscreen senses input from contact with nearly any object (finger, stylus/pen, palm) resistive touchscreens are a type of "passive" technology.

14 For example, during operation of a four-wire touchscreen, a uniform, unidirectional voltage gradient is applied to the first sheet. When the two sheets are pressed together, the second sheet measures the voltage as distance along the first sheet, providing the X coordinate. When this contact coordinate has been acquired, the uniform voltage gradient is applied to the second sheet to ascertain the Y coordinate. These operations occur within a few milliseconds, registering the exact touch location as contact is made.

15. Resistive touchscreens typically have high resolution (4096 x 4096 DPI or higher), providing accurate touch control. Because the touchscreen responds to pressure on its surface, contact can be made with a finger or any other pointing device.

16. SAWs were first explained in 1885 by Lord Rayleigh, who described the surface acoustic mode of propagation and predicted its properties in his classic paper. Named after their discoverer, Rayleigh waves have a longitudinal and a vertical shear component that can couple with any media in contact with the surface. This coupling strongly affects the amplitude and velocity of the wave, allowing SAW sensors to directly sense mass and mechanical properties.

SAW Devices

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17. SAW devices use SAW wave in electronic components to provide a number of different functions, including as delay lines, filters, correlators and DC to DC converters.

Application in electronic components

18. This kind of wave is commonly used in devices called SAW devices in electronic circuits. SAW devices are used as filters, oscillators and transformers, devices that are based on the transduction of acoustic waves. The transduction from electric energy to mechanical energy (in the form of SAWs) is accomplished by the use of piezoelectric materials.

Schematic picture of a typical SAW device design.

19. Electronic devices employing SAWs normally use one or more interdigital transducers (IDTs) to convert acoustic waves to electrical signals and vice versa by exploiting the piezoelectric effect of certain materials (quartz, lithium niobate, lithium tantalate, lanthanum gallium silicate, etc.). These devices are fabricated by photolithography, the process used in the manufacture of silicon integrated circuits.

20. SAW filters are now used in mobile telephones, and provide significant advantages in performance, cost, and size over other filter

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technologies such asquartz crystals (based on bulk waves), LC filters, and waveguide filters.

21. Much research has been done in the last 20 years in the area of surface acoustic wave sensors.[3] Sensor applications include all areas of sensing (such as chemical, optical, thermal, pressure, acceleration, torque and biological). SAW sensors have seen relatively modest commercial success to date, but are commonly commercially available for some applications such as touchscreen displays.

SAW device applications in radio and television

22. This is a typical photo of SAW (surface acoustic wave) resonator commonly used in garage door opener remote control and rf modules.

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23. A typical inner photo of fixed frequency RF remote control (315mhz,433mhz,etc.) which uses SAW (surface acoustic wave) resonator to stabilize transmitting frequency.

24. SAW resonators are often used in radio transmitters where tunability is not required. They are often used in applications such as garage door opener remote controls, short range radio frequency links for computer peripherals, and other devices where channelization is not required. Where a radio link might use several channels, quartz crystal oscillators are more commonly used to drive a phase locked loop. Since the resonant frequency of a SAW device is set by the mechanical properties of the crystal, it does not drift as much as a simple LC oscillator, where conditions such as capacitor performance and battery voltage will vary substantially with temperature and age.

25. SAW filters are also often used in radio receivers, as they can have accurately determined and narrow pass bands. This is helpful in applications where a single antenna must be shared between a transmitter and a receiver operating at closely spaced frequencies. SAW filters are also frequently used in television receivers, for extracting subcarriers from the signal; until the analog switchoff, the extraction of digital audio subcarriers from the intermediate frequency strip of a television receiver or video recorder was one of the main markets for SAW filters. They are also often used in digital receivers, and are well suited to superhet applications. This is because the intermediate frequency signal is always at a fixed frequency after the local oscillator has been mixed with the received signal, and so a filter with a fixed frequency and high Q provides excellent removal of unwanted or interference signals.

26. In these applications, SAW filters are almost always used with a phase locked loop synthesized local oscillator, or a varicap driven oscillator.

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SAW Geographics

27. In seismology surface acoustic waves travelling along the Earth's surface play an important role, since they can be the most destructive type of seismic wave produced by earthquakes.

SAW in microfluids

28. In recent years, attention has been drawn to using SAWs to drive microfluidic actuation and a variety of processes. Owing to the mismatch of sound velocities in the SAW substrate and fluid, SAWs can be efficiently transferred into the fluid, to create significant inertial force and fluid velocities. This mechanism can be exploited to drive fluid actions such as pumping, mixing, jetting, as well as others.

29. This article is about the sensing technology used in human interfaces. For the device used in distance measurements, see Capacitive displacement sensor.

30. In electrical engineering, capacitive sensing is a technology based on capacitive coupling that is used in many different types of sensors, including those to detect and measure: proximity, position or displacement, humidity, fluid level, and acceleration. Capacitive sensing as a human interface device (HID) technology, for example to replace the computer mouse, is growing increasingly popular. Capacitive touch sensors are used in many devices such as laptop trackpads, digital audio players, computer displays, mobile phones, mobile devices and others. More and more design engineers are selecting capacitive sensors for their versatility, reliability and robustness, unique human-device interface and cost reduction over mechanical switches.

31. Capacitive sensors detect anything which is conductive or has a dielectric different than that of air. While capacitive sensing applications can replace mechanical buttons with capacitive

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alternatives, other technologies such as multi-touch and gesture-based touchscreens are also premised on capacitive sensing.

Sensor Design

32. Capacitive sensors can be constructed from many different media, such as copper, Indium tin oxide (ITO) and printed ink. Copper capacitive sensors can be implemented on standard FR4 PCBs as well as on flexible material. ITO allows the capacitive sensor to be up to 90% transparent (for one layer solutions). The size and spacing of the capacitive sensor are both very important to the sensor's performance. In addition to the size of the sensor, and its spacing relative to the ground plane, the type of ground plane used is very important. Since the parasitic capacitance of the sensor is related to the electric field's (e-field) path to ground, it is important to choose a ground plane that limits the concentration of e-field lines with no conductive object present.

33. Designing a capacitance sensing system requires first picking the type of sensing material (FR4, Flex, ITO, etc.). One also needs to understand the environment the device will operate in, such as the full operating temperature range, what radio frequencies are present and how the user will interact with the interface.

34. There are two types of capacitive sensing system: mutual capacitance, where the object (finger, conductive stylus) alters the mutual coupling between row and column electrodes, which are scanned sequentially; and self- or absolute capacitance where the object (such as a finger) loads the sensor or increases the parasitic capacitance to ground. In both cases, the difference of a preceding absolute position from the present absolute position yields the relative motion of the object or finger during that time. The technologies are elaborated in the following section.

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Surface capacitance35. In this basic technology, only one side of the insulator is coated with a conductive layer. A small voltage is applied to the conductive layer, resulting in a uniform electrostatic field. When a conductor, such as a human finger, touches the uncoated surface, a capacitor is dynamically formed. Due to the sheet resistance of the surface, each corner is measured to have a different effective capacitance. The sensor's controller can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the panel; the larger the change in capacitance, the closer the touch is to that corner. As it has no moving parts, it is moderately durable. But it has limited resolution, is prone to false signals from parasitic capacitive coupling, and needs calibration during manufacture. It is therefore most often used in simple applications such as industrial controls and kiosks.

Projected capacitance

36. Projected capacitive touch (PCT) technology is a capacitive technology which allows more accurate and flexible operation, by etching the conductive layer. An X-Y grid is formed either by etching one layer to form a grid pattern of electrodes, or by etching two separate, perpendicular layers of conductive material with parallel lines or tracks to form the grid; comparable to the pixel grid found in manyliquid crystal displays (LCD).

37. The greater resolution of PCT allows operation with no direct contact, such that the conducting layers can be coated with further protective insulating layers, and operates even under screen protectors, or behind weather and vandal-proof glass. Due to the top layer of a PCT being glass, PCT is a more robust solution versus resistive touch technology. Depending on the implementation, an active or passive stylus can be used instead of or in addition to a finger. This is common with point of sale devices that require signature capture. Gloved fingers may or may not be sensed, depending on the implementation and gain settings. Conductive

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smudges and similar interference on the panel surface can interfere with the performance. Such conductive smudges come mostly from sticky or sweaty finger tips, especially in high humidity environments. Collected dust, which adheres to the screen due to the moisture from fingertips can also be a problem. There are two types of PCT: self capacitance, and mutual capacitance.

Mutual capacitance38. Mutual capacitive sensors have a capacitor at each intersection of each row and each column. A 12-by-16 array, for example, would have 192 independent capacitors. A voltage is applied to the rows or columns. Bringing a finger or conductive stylus near the surface of the sensor changes the local electric field which reduces the mutual capacitance. The capacitance change at every individual point on the grid can be measured to accurately determine the touch location by measuring the voltage in the other axis. Mutual capacitance allows multi-touch operation where multiple fingers, palms or stylus can be accurately tracked at the same time.

Self-capacitance

39. Self-capacitance sensors can have the same X-Y grid as mutual capacitance sensors, but the columns and rows operate independently. With self-capacitance, the capacitive load of a finger is measured on each column or row electrode by a current meter. This method produces a stronger signal than mutual capacitance, but it is unable to resolve accurately more than one finger, which results in "ghosting", or misplaced location sensing.

Circuit Design

40. Capacitance is typically measured indirectly, by using it to control the frequency of an oscillator, or to vary the level of coupling (or attenuation) of an AC signal.

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41. The design of a simple capacitance meter is often based on a relaxation oscillator. The capacitance to be sensed forms a portion of the oscillator's RC circuit or LC circuit. Basically the technique works by charging the unknown capacitance with a known current. (The equation of state for a capacitor is i = C dv/dt. This means that the capacitance equals the current divided by the rate of change of voltage across the capacitor.) The capacitance can be calculated by measuring the charging time required to reach the threshold voltage (of the relaxation oscillator), or equivalently, by measuring the oscillator's frequency. Both of these are proportional to the RC (or LC) time constant of the oscillator circuit.

42. The primary source of error in capacitance measurements is stray capacitance, which if not guarded against, may fluctuate between 10 pF to 10 nF. The stray capacitance can be held relatively constant by shielding the (high impedance) capacitance signal and then connecting the shield to (a low impedance) ground reference. Also, to minimize the unwanted effects of stray capacitance, it is good practice to locate the sensing electronics as near the sensor as possible.

43. Another measurement technique is to apply a fixed-frequency AC-voltage signal across a capacitive divider. This consists of two capacitors in series, one of a known value and the other of an unknown value. An output signal is then taken from across one of the capacitors. The value of the unknown capacitor can be found from the ratio of capacitances, which equals the ratio of the output/input signal amplitudes, as measured by an AC voltmeter. More accurate instruments may use a capacitance bridge configuration, similar to a Wheatstone bridge. The capacitance bridge helps to compensate for any variability that may exist in the the applied signal.

Comparison with other touch screen technologies

44. Since capacitive screens respond to only materials which are conductive (human finger used most commonly), they can be

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cleaned with cloths with no accidental command input. Capacitive touchscreens are more responsive than resistive touchscreens. standard stylus cannot be used for capacitive sensing unless it is tipped with some form of conductive material, such as anti-static conductive foam. However, capacitive styli—different from standardstyli—can be used as well as finger input on capacitive screens. Capacitive touchscreens are more expensive to manufacture and offer a significantly lesser degree of accuracy than resistive touchscreens.[7] Some cannot be used with gloves, and can fail to sense correctly with even a small amount of water on the screen.

Power supplies with high electronic noise can reduce accuracy.

Capacitive stylus

45. A Capacitive stylus is a special type of stylus that works on capacitive touchscreens primarily designed for fingers, as on iPhone and most Android devices. They are different from standard styli designed for resistive touchscreens.

46. According to a report by ABI Research, styli are especially needed in China for handwriting recognition because of the nature of its writing system.

Infrared touch screen

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47. Infrared sensors mounted around the display watch for a user's touchscreen input on this PLATO V terminal in 1981. The monochromatic plasma display's characteristic orange glow is illustrated.

48. An infrared touchscreen uses an array of X-Y infra red LED and photodetector pairs around the edges of the screen to detect a disruption in the pattern of LED beams. These LED beams cross each other in vertical and horizontal patterns. This helps the sensors pick up the exact location of the touch. A major benefit of such a system is that it can detect essentially any input including a finger, gloved finger, stylus or pen. It is generally used in outdoor applications and point of sale systems which can't rely on a conductor (such as a bare finger) to activate the touchscreen. Unlike capacitive touchscreens, infrared touchscreens do not require any patterning on the glass which increases durability and optical clarity of the overall system.

Optical imaging49. This is a relatively modern development in touchscreen technology, in which two or more image sensors are placed around the edges (mostly the corners) of the screen. Infrared back lights are placed in the camera's field of view on the other side of the screen. A touch shows up as a shadow and each pair of cameras can then be pinpointed to locate the touch or even measure the size of the touching object (see visual hull). This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for larger units.

Dispersive signal technology50. Introduced in 2002 by 3M, this system uses sensors to detect the mechanical energy in the glass that occurs due to a touch. Complex algorithms then interpret this information and provide the actual location of the touch.[15] The technology claims to be

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unaffected by dust and other outside elements, including scratches. Since there is no need for additional elements on screen, it also claims to provide excellent optical clarity. Also, since mechanical vibrations are used to detect a touch event, any object can be used to generate these events, including fingers and stylus. A downside is that after the initial touch the system cannot detect a motionless finger.

Acoustic pulse recognition51. This system, introduced by Tyco International's Elo division in 2006, uses piezoelectric transducers located at various positions around the screen. The transducers create a standing wave on the screen, that is interupted by a touch, and turned into an electronic signal location.[16] The screen hardware then uses an algorithm to determine the location of the touch based on the transducer signals. The touchscreen itself is made of ordinary glass, giving it good durability and optical clarity. It is usually able to function with scratches and dust on the screen with good accuracy. The technology is also well suited to displays that are physically larger. As with the Dispersive Signal Technology system, after the initial touch, a motionless finger cannot be detected. However, for the same reason, the touch recognition is not disrupted by any resting objects.

Construction

52. There are several principal ways to build a touchscreen. The key goals are to recognize one or more fingers touching a display, to interpret the command that this represents, and to communicate the command to the appropriate application.

53. In the most popular techniques, the capacitive or resistive approach, there are typically four layers;

a) Top polyester coated with a transparent metallic conductive coating on the bottom

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b) Adhesive spacerc) Glass layer coated with a transparent metallic conductive

coating on the topd) Adhesive layer on the backside of the glass for mounting.

54. When a user touches the surface, the system records the change in the electrical current that flows through the display.

55. Dispersive-signal technology which 3M created in 2002, measures the piezoelectric effect — the voltage generated when mechanical force is applied to a material — that occurs chemically when a strengthened glass substrate is touched.

56. There are two infrared-based approaches. In one, an array of sensors detects a finger touching or almost touching the display, thereby interrupting light beams projected over the screen. In the other, bottom-mounted infrared cameras record screen touches.

57. In each case, the system determines the intended command based on the controls showing on the screen at the time and the location of the touch.

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Development

58. Most touchscreen technology patents were filed during the 1970s and 1980s and have expired. Touchscreen component manufacturing and product design are no longer encumbered by royalties or legalities with regard to patents and the use of touchscreen-enabled displays is widespread.

59. The development of multipoint touchscreens facilitated the tracking of more than one finger on the screen; thus, operations that require more than one finger are possible. These devices also allow multiple users to interact with the touchscreen simultaneously.

60. With the growing use of touchscreens, the marginal cost of touchscreen technology is routinely absorbed into the products that incorporate it and is nearly eliminated. Touchscreens now have proven reliability. Thus, touchscreen displays are found today in airplanes, automobiles, gaming consoles, machine control systems, appliances, and handheld display devices including the Nintendo DS and the later multi-touch enabled iPhones; the touchscreen market for mobile devices is projected to produce US$5 billion in 2009.

61. The ability to accurately point on the screen itself is also advancing with the emerging graphics tablet/screen hybrids.

Ergonomics and usage

Finger stress62. An ergonomic problem of certain types of (resistive) touchscreens is their stress on human fingers when used for more than a few minutes at a time, as significant pressure can be required, depending upon the technologies involved. This can be alleviated for some users with the use of a pen or other device to add leverage and more accurate pointing. The introduction of such items can sometimes be problematic, depending on the desired use (e.g.,

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public kiosks such as ATMs). Also, more accurate control is achieved with a stylus, because a finger is a rather broad and ambiguous point of contact with the screen itself, but requires the user to possess fine motor skills to hold such a stylus.

Fingernail as stylus

63. Pointed nail for easier typing. The concept of using a fingernail trimmed to form a point, to be specifically used as a styluson a writing tablet for communication, appeared in the 1950 science fiction short story Scanners Live in Vain.

64. These ergonomic issues of direct touch can be bypassed by using a different technique, provided that the user's fingernails are either short or sufficiently long. Rather than pressing with the soft skin of an outstretched fingertip, the finger is curled over, so that the tip of a fingernail can be used instead. This method does not work on capacitive touchscreens.

65. The fingernail's hard, curved surface contacts the touchscreen at one very small point. Therefore, much less finger pressure is needed, much greater precision is possible (approaching that of a stylus, with a little experience), much less skin oil is smeared onto the screen, and the fingernail can be silently moved across the screen with very little resistance, allowing for selecting text, moving windows, or drawing lines.

66. The human fingernail consists of keratin which has a hardness and smoothness similar to the tip of a stylus (and so will not typically scratch a touchscreen). Alternatively, very short stylus tips are

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available, which slip right onto the end of a finger; this increases visibility of the contact point with the screen.

Fingerprints67. Touchscreens can suffer from the problem of fingerprints on the display. This can be mitigated by the use of materials with optical coatings designed to reduce the visible effects of fingerprint oils, or oleophobic coatings as used in the iPhone 3G S, which lessen the actual amount of oil residue, or by reducing skin contact by using a fingernail or stylus.

Combined with haptics68. Touchscreens are often used with haptic response systems. An example of this technology would be a system that caused the device to vibrate when a button on the touchscreen was tapped. The user experience with touchscreens lacking tactile feedback or haptics can be difficult due to latency or other factors. Research from the University of Glasgow Scotland [Brewster, Chohan, and Brown 2007] demonstrates that sample users reduce input errors (20%), increase input speed (20%), and lower their cognitive load (40%) when touchscreens are combined with haptics or tactile feedback [vs. non-haptic touchscreens].

Gorilla arm69. The Jargon File dictionary of hacker slang defined "gorilla arm" as the failure to understand the ergonomics of vertically mounted touchscreens for prolonged use. The proposition is that the human arm held in an unsupported horizontal position rapidly becomes fatigued and painful, the so-called "gorilla arm". It is often cited as a prima facie example of what not to do in ergonomics. Vertical touchscreens still dominate in applications such as ATMs and data kiosks in which the usage is too brief to be an ergonomic problem.

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70. Discomfort might be caused by previous poor posture and atrophied muscular systems caused by limited physical exercise. Fine art painters are also often subject to neck and shoulder pains due to their posture and the repetitiveness of their movements while painting.

Screen protectors

71. Some touchscreens, primarily those employed in smartphones, use transparent plastic protectors to prevent any scratches that might be caused by day-to-day use from becoming permanent.

Conclusion

72. The touch screen interface is going to revolutionise the electronic interactive devices in a big way. The future multi touch systems which has limit of imagination as drawback are going to substantially dominate the field. The exponential growth of touch screens are just an indication of the future of these devices.

References www.wikipedia.com

fujitsu microelectronics

howstuffworks.com

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