Editing Touchscreen (section)

==Technologies==
{{Cleanup|date=January 2024|reason=Grammar & punctuation}}
There are a number of touchscreen technologies, with different methods of sensing touch.<ref name=Sears1990/>

===Resistive===
{{Main|Resistive touchscreen}}
A [[resistive]] touchscreen panel is composed of several thin layers, the most important of which are two transparent electrically resistive layers facing each other with a thin gap between them. The top layer (the layer that is touched) has a coating on the underside surface; just beneath it is a similar resistive layer on top of its substrate. One layer has conductive connections along its sides, while the other along the top and bottom. A voltage is applied to one layer and sensed by the other. When an object, such as a fingertip or stylus tip, presses down onto the outer surface, the two layers touch to become connected at that point.<ref>{{Cite web|title=What is touch screen? - Definition from WhatIs.com|url=https://whatis.techtarget.com/definition/touch-screen|access-date=2020-09-07|website=WhatIs.com|language=en}}</ref> The panel then behaves as a pair of [[voltage divider]]s, one axis at a time. By rapidly switching between each layer, the position of pressure on the screen can be detected.

Resistive touch is used in restaurants, factories, and hospitals due to its high tolerance for liquids and contaminants. A major benefit of resistive-touch technology is its low cost. Additionally, they may be used with gloves on, or by using anything rigid as a finger substitute, as only sufficient pressure is necessary for the touch to be sensed. Disadvantages include the need to press down, and a risk of damage by sharp objects. Resistive touchscreens also suffer from poorer contrast, due to having additional reflections (i.e. glare) from the layers of material placed over the screen.<ref>Lancet, Yaara. (2012-07-19) [http://www.makeuseof.com/tag/differences-capacitive-resistive-touchscreens-si/ What Are The Differences Between Capacitive & Resistive Touchscreens?] {{webarchive|url=https://web.archive.org/web/20130309025853/http://www.makeuseof.com/tag/differences-capacitive-resistive-touchscreens-si/|date=2013-03-09}}. Makeuseof.com. Retrieved on 2013-08-16.</ref> This type of touchscreen has been used by Nintendo in the DS family, the [[Nintendo 3DS line|3DS family]], and the [[Wii U GamePad]].<ref>{{cite web|url=https://www.engadget.com/2011/06/13/nintendo-3ds-has-resistive-touchscreen-for-backwards-compatibili/|title=Nintendo 3DS has resistive touchscreen for backwards compatibility, what's the Wii U's excuse?|author=Vlad Savov|publisher=AOL|work=Engadget|date=13 June 2011 |access-date=29 July 2015|url-status=live|archive-url=https://web.archive.org/web/20151112064552/http://www.engadget.com/2011/06/13/nintendo-3ds-has-resistive-touchscreen-for-backwards-compatibili/|archive-date=12 November 2015}}</ref>

Due to their simple structure, with very few inputs, resistive touchscreens are mainly used for single touch operation, although some two touch versions (often described as multi-touch) are available.<ref>{{cite web|url=https://www.dush.co.jp/english/library/005/|title=Multi-touch Resistive Touchscreen with 12/15 x/y matrix|access-date=2023-04-16}}</ref><ref>{{cite web|url=https://slashgear.com/fujitsu-multitouch-resistive-touchscreens-bring-cheap-pinch-zooming-to-windows-7-notebooks-17114578/|title=Multi-touch Resistive Touchscreen with x/y matrix|access-date=2010-11-01}}</ref> However, there are some true multi-touch resistive touchscreens available. These need many more inputs, and rely on x/y multiplexing to keep the I/O count down.

One example of a true multi-touch resistive touchscreen<ref>{{cite web|url=https://www.schurter.com/en/data/download/rmt-multitouch-technology|title=Resistive-touchscreens|access-date=2023-07-08}}</ref> can detect 10 fingers at the same time. This has 80 I/O connections. These are possibly split 34 x inputs / 46 y outputs, forming a standard 3:4 aspect ratio touchscreen with 1564 x/y intersecting touch sensing nodes.

===Surface acoustic wave===
{{Main|Surface acoustic wave}}

Surface acoustic wave (SAW) technology uses [[ultrasound|ultrasonic]] waves that pass over the touchscreen panel. When the panel is touched, a portion of the wave is absorbed. The change in ultrasonic waves is processed by the [[MIDI controller|controller]] to determine the position of the touch event. Surface acoustic wave touchscreen panels can be damaged by outside elements. Contaminants on the surface can also interfere with the functionality of the touchscreen.

SAW devices have a wide range of applications, including [[Analog delay line|delay lines]], filters, correlators and [[DC to DC converter]]s.

===Capacitive touchscreen===
[[File:Capacitive touchscreen.jpg|thumb|Capacitive touchscreen of a mobile phone]]
[[File:Casio TC500 Touch Sensor Watch.jpg|thumb|The Casio TC500 Capacitive touch sensor watch from 1983, with angled light exposing the touch sensor pads and traces etched onto the top watch glass surface]]
{{Main|Capacitive sensing}}

A capacitive touchscreen panel consists of an [[insulator (electrical)|insulator]], such as [[glass]], coated with a transparent [[electrical conductor|conductor]], such as [[indium tin oxide]] (ITO).<ref>{{cite journal |last1=Hong |first1=Chan-Hwa |last2=Shin |first2=Jae-Heon |last3=Ju |first3=Byeong-Kwon |last4=Kim |first4=Kyung-Hyun |last5=Park |first5=Nae-Man |last6=Kim |first6=Bo-Sul |last7=Cheong |first7=Woo-Seok |title=Index-Matched Indium Tin Oxide Electrodes for Capacitive Touch Screen Panel Applications |journal=Journal of Nanoscience and Nanotechnology |date=1 November 2013 |volume=13 |issue=11 |pages=7756–7759 |doi=10.1166/jnn.2013.7814 |pmid=24245328 |s2cid=24281861 }}</ref> As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen's [[electrostatic]] field, measurable as a change in [[capacitance]]. Different technologies may be used to determine the location of the touch. The location is then sent to the controller for processing. Some touchscreens use silver instead of ITO, as ITO causes several environmental problems due to the use of indium.<ref>{{cite web|url=https://www.fujifilm.eu/eu/news/article/fujifilm-reinforces-the-production-facilities-for-its-touch-panel-sensor-film-exclear|title=Fujifilm reinforces the production facilities for its touch-panel sensor film "EXCLEAR"|website=FUJIFILM Europe}}</ref><ref>{{cite web|url=https://www.fujifilm.com/about/research/report/062/pdf/index/ff_rd062_008_en.pdf |title=Development of a Thin Double-sided Sensor Film "EXCLEAR" for Touch Panels via Silver Halide Photographic Technology |publisher=www.fujifilm.com |access-date=2019-12-09}}</ref><ref>{{cite web|url=https://fujifilm-innovation.tumblr.com/post/142053562369/whats-behind-your-smartphone-screen-this|title=What's behind your smartphone screen? This... &#124;|website=fujifilm-innovation.tumblr.com}}</ref><ref>{{cite web|url=https://www.fujifilmholdings.com/en/sustainability/valuePlan2016/process/policy01/environment2016/02.html|title=Environment: [Topics2] Development of Materials That Solve Environmental Issues EXCLEAR thin double-sided sensor film for touch panels &#124; FUJIFILM Holdings|website=www.fujifilmholdings.com}}</ref> The controller is typically a [[complementary metal–oxide–semiconductor]] (CMOS) [[application-specific integrated circuit]] (ASIC) chip, which in turn usually sends the signals to a CMOS [[digital signal processor]] (DSP) for processing.<ref>{{cite journal |last1=Kent |first1=Joel |title=Touchscreen technology basics & a new development |journal=CMOS Emerging Technologies Conference |date=May 2010 |volume=6 |pages=1–13 |url=https://books.google.com/books?id=ekdkWGqw29EC&pg=PA34 |publisher=CMOS Emerging Technologies Research|isbn=9781927500057 }}</ref><ref>{{cite news |last1=Ganapati |first1=Priya |title=Finger Fail: Why Most Touchscreens Miss the Point |url=https://www.wired.com/2010/03/touchscreens-smartphones/ |access-date=9 November 2019 |magazine=[[Wired (magazine)|Wired]] |date=5 March 2010 |archive-url=https://web.archive.org/web/20140511114207/http://www.wired.com/2010/03/touchscreens-smartphones/ |archive-date=2014-05-11 |url-status=live}}</ref>

Unlike a [[resistive touchscreen]], some capacitive touchscreens cannot be used to detect a finger through electrically insulating material, such as gloves. This disadvantage especially affects usability in consumer electronics, such as touch tablet PCs and capacitive smartphones in cold weather when people may be wearing gloves. It can be overcome with a special capacitive stylus, or a special-application glove with an embroidered patch of conductive thread allowing electrical contact with the user's fingertip.

A low-quality [[switching-mode power supply]] unit with an accordingly unstable, noisy [[voltage]] may temporarily interfere with the precision, accuracy and sensitivity of capacitive touch screens.<ref>{{Cite web|last=Andi|date=2014-01-24|title=How noise affects touch screens|url=https://www.westfloridacomponents.com/blog/noise-affects-touch-screens/|access-date=2020-10-24|website=West Florida Components|language=en-US}}</ref><ref>{{cite web |title=Touch screens and charger noise {{!}} |url=https://www.epanorama.net/blog/2013/03/12/touch-screens-and-charger-noise/ |website=epanorama.net |date=2013-03-12}}</ref><ref>{{cite web |title=Aggressively combat noise in capacitive touch applications |url=https://www.edn.com/aggressively-combat-noise-in-capacitive-touch-applications/ |website=EDN.com |date=2013-04-08}}</ref>

Some capacitive display manufacturers continue to develop thinner and more accurate touchscreens. Those for [[mobile device]]s are now being produced with 'in-cell' technology, such as in Samsung's [[AMOLED#Super AMOLED|Super AMOLED]] screens, that eliminates a layer by building the capacitors inside the display itself. This type of touchscreen reduces the visible distance between the user's finger and what the user is touching on the screen, reducing the thickness and weight of the display, which is desirable in [[smartphone]]s.

A simple parallel-plate capacitor has two conductors separated by a dielectric layer. Most of the energy in this system is concentrated directly between the plates. Some of the energy spills over into the area outside the plates, and the electric field lines associated with this effect are called fringing fields. Part of the challenge of making a practical capacitive sensor is to design a set of printed circuit traces which direct fringing fields into an active sensing area accessible to a user. A parallel-plate capacitor is not a good choice for such a sensor pattern. Placing a finger near fringing electric fields adds conductive surface area to the capacitive system. The additional charge storage capacity added by the finger is known as finger capacitance, or CF. The capacitance of the sensor without a finger present is known as parasitic capacitance, or CP.

====Surface capacitance====
In this basic technology, only one side of the insulator is coated with a conductive layer. A small voltage is applied to the layer, resulting in a uniform electrostatic field. When a conductor, such as a human finger, touches the uncoated surface, a capacitor is dynamically formed. 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. As it has no moving parts, it is moderately durable but 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 [[interactive kiosk|kiosks]].<ref>{{cite web|url=http://electronicdesign.com/Articles/Index.cfm?AD=1&ArticleID=18592|title=Please Touch! Explore The Evolving World Of Touchscreen Technology|publisher=electronicdesign.com|access-date=2009-09-02|url-status=dead|archive-url=https://web.archive.org/web/20151213043947/http://electronicdesign.com/Articles/Index.cfm?AD=1&ArticleID=18592|archive-date=2015-12-13}}</ref>

Although some standard capacitance detection methods are projective, in the sense that they can be used to detect a finger through a non-conductive surface, they are very sensitive to fluctuations in temperature, which expand or contract the sensing plates, causing fluctuations in the capacitance of these plates.<ref>{{cite web|url=https://www.electronics-tutorials.ws/capacitor/cap_4.html|title=formula for relationship between plate area and capacitance|date=26 July 2013 }}</ref> These fluctuations result in a lot of background noise, so a strong finger signal is required for accurate detection. This limits applications to those where the finger directly touches the sensing element or is sensed through a relatively thin non-conductive surface.

==== Mutual capacitance ====
An electrical signal, imposed on one electrical conductor, can be capacitively "sensed" by another electrical conductor that is in very close proximity, but electrically isolated—a feature that is exploited in mutual capacitance touchscreens. In a mutual capacitive sensor array, the "mutual" crossing of one electrical conductor with another electrical conductor, but with no direct electrical contact, forms a [[capacitor]] (see [[touchscreen#Construction]]).

High frequency voltage pulses are applied to these conductors, one at a time. These pulses capacitively couple to every conductor that intersects it.

Bringing a finger or conductive stylus close to the surface of the sensor changes the local electrostatic field, which in turn reduces the capacitance between these intersecting conductors. Any significant change in the strength of the signal sensed is used to determine if a finger is present or not at an intersection.<ref>{{cite web|url=https://onlinedocs.microchip.com/pr/GUID-A8A0085D-58D1-4E41-A07D-B93BFDE11AFE-en-US-4/index.html?GUID-F186B556-F266-4585-830D-1CCE04045D0E|title=Mutual Capacitance|access-date=2023-04-26}}</ref>

The capacitance change at every intersection on the grid can be measured to accurately determine one or more touch locations.
 
Mutual capacitance allows multi-touch operation where multiple fingers, palms or styli can be accurately tracked at the same time.The greater the number of intersections, the better the touch resolution and the more independent fingers that can be detected.<ref>{{cite web|url=https://walkermobile.com/Touch_Technologies_Tutorial_Latest_Version.pdf|title=Touch technologies|access-date=2023-04-26}}</ref>
<ref>{{cite web|url=https://fieldscale.com/learn-capacitive-sensing/self-mutual-capacitive-touch-sensors/|title=Self vs Mutual Capacitance|work=Fieldscale |access-date=2023-04-26}}</ref> This indicates a distinct advantage of diagonal wiring over standard x/y wiring, since diagonal wiring creates nearly twice the number of intersections.

A 30 i/o, 16×14 x/y array, for example, would have 224 of these intersections / capacitors, and a 30 i/o diagonal lattice array could have 435 intersections.

Each trace of an x/y mutual capacitance array only has one function, it is either an input or an output. The horizontal traces may be transmitters while the vertical traces are sensors, or vice versa.

==== Self-capacitance ====
Self-capacitance sensors can have the same layout as mutual capacitance sensors, but, with self-capacitance all the traces usually operate independently, with no interaction between different traces. Along with several other methods, the extra capacitive load of a finger on a trace electrode may be measured by a current meter, or by the change in frequency of an RC oscillator.

Traces are sensed, one after the other until all the traces have been sensed. A finger may be detected anywhere along the whole length of a trace (even "off-screen"), but there is no indication where the finger is along that trace. If, however, a finger is also detected along another intersecting trace, then it is assumed that the finger position is at the intersection of the two traces. This allows for the speedy and accurate detection of a single finger.

Although mutual capacitance is simpler for multi-touch, multi-touch can be achieved using self-capacitance.

Self-capacitive touch screen layers are used on mobile phones such as the [[Sony Xperia Sola]],<ref name="SonyDev">{{Cite web |url=http://developer.sonymobile.com/wp/2012/03/13/imagine-controlling-your-phone-without-touching-the-screen-floating-touch-makes-it-possible-video/ |title=Self-capacitive touch described on official Sony Developers blog |access-date=2012-03-14 |archive-date=2012-03-14 |archive-url=https://archive.today/20120314110416/http://developer.sonymobile.com/wp/2012/03/13/imagine-controlling-your-phone-without-touching-the-screen-floating-touch-makes-it-possible-video/ |url-status=live }}</ref> the [[Samsung Galaxy S4]], [[Galaxy Note 3]], [[Galaxy S5]], and [[Galaxy Alpha]].

Self-capacitance is far more sensitive than mutual capacitance and is mainly used for single touch, simple gesturing and proximity sensing where the finger does not even have to touch the glass surface. Mutual capacitance is mainly used for multitouch applications.<ref>{{cite journal|title=Comparison of self capacitance and mutual capacitance. |doi=10.1017/S1743921315010388 |arxiv=1612.08227 |last1=Du |first1=Li |year=2016 |s2cid=220453196 }}</ref> Many touchscreen manufacturers use both self and mutual capacitance technologies in the same product, thereby combining their individual benefits.<ref>{{cite web|url=http://www.cypress.com/products/cypress-sensing-technologies|title=Hybrid self and mutual capacitance touch sensing controllers }}</ref>

====Use of stylus on capacitive screens====
Capacitive touchscreens do not necessarily need to be operated by a finger, but until recently the special styli required could be quite expensive to purchase. The cost of this technology has fallen greatly in recent years and capacitive styli are now widely available for a nominal charge, and often given away free with mobile accessories. These consist of an electrically conductive shaft with a soft conductive rubber tip, thereby resistively connecting the fingers to the tip of the stylus.

===Infrared grid===
[[Image:Platovterm1981.jpg|right|thumb|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.]]

An [[infrared]] touchscreen uses an array of X-Y infrared [[light-emitting diode|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 opaque object including a finger, gloved finger, stylus or pen. It is generally used in outdoor applications and POS systems that cannot rely on a conductor (such as a bare finger) to activate the touchscreen. Unlike [[capacitive sensing|capacitive touchscreens]], infrared touchscreens do not require any patterning on the glass which increases durability and optical clarity of the overall system. Infrared touchscreens are sensitive to dirt and dust that can interfere with the infrared beams, and suffer from parallax in curved surfaces and accidental press when the user hovers a finger over the screen while searching for the item to be selected.

===Infrared acrylic projection===
A translucent acrylic sheet is used as a rear-projection screen to display information. The edges of the acrylic sheet are illuminated by infrared LEDs, and infrared cameras are focused on the back of the sheet. Objects placed on the sheet are detectable by the cameras. When the sheet is touched by the user, [[frustrated total internal reflection]] results in leakage of infrared light which peaks at the points of maximum pressure, indicating the user's touch location. Microsoft's [[Microsoft PixelSense|PixelSense]] tablets use this technology.

===Optical imaging===
Optical touchscreens are a relatively modern development in touchscreen technology, in which two or more [[image sensors]] (such as [[CMOS sensor]]s) are placed around the edges (mostly the corners) of the screen. Infrared backlights are placed in the sensor's field of view on the opposite side of the screen. A touch blocks some lights from the sensors, and the location and size of the touching object can be calculated (see [[Visual hull#In two dimensions|visual hull]]). This technology is growing in popularity due to its scalability, versatility, and affordability for larger touchscreens.

===Dispersive signal technology===
Introduced in 2002 by [[3M]], this system detects a touch by using sensors to measure the [[piezoelectricity]] in the glass. Complex algorithms interpret this information and provide the actual location of the touch.<ref>{{cite web|access-date=2009-03-16|url=http://www.fool.com/investing/general/2008/02/13/innovation-series-touchscreen-technology.aspx|title=Innovation Series: Touchscreen Technology|work=The Motley Fool|date=2008-02-13|last=Beyers|first=Tim|url-status=live|archive-url=https://web.archive.org/web/20090324195620/http://www.fool.com/investing/general/2008/02/13/innovation-series-touchscreen-technology.aspx|archive-date=2009-03-24}}</ref> The technology is 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. Any object can be used to generate touch events, including gloved fingers. A downside is that after the initial touch, the system cannot detect a motionless finger. However, for the same reason, resting objects do not disrupt touch recognition.

===Acoustic pulse recognition===
The key to this technology is that a touch at any one position on the surface generates a sound wave in the substrate which then produces a unique combined signal as measured by three or more tiny transducers attached to the edges of the touchscreen. The digitized signal is compared to a list corresponding to every position on the surface, determining the touch location. A moving touch is tracked by rapid repetition of this process. Extraneous and ambient sounds are ignored since they do not match any stored sound profile. The technology differs from other sound-based technologies by using a simple look-up method rather than expensive signal-processing hardware. As with the dispersive signal technology system, a motionless finger cannot be detected after the initial touch. However, for the same reason, the touch recognition is not disrupted by any resting objects. The technology was created by SoundTouch Ltd in the early 2000s, as described by the patent family EP1852772, and introduced to the market by [[Tyco International]]'s Elo division in 2006 as Acoustic Pulse Recognition.<ref>{{Cite journal|title=Acoustic Pulse Recognition Touchscreens|page=3|publisher=Elo Touch Systems|year=2006|url=http://media.elotouch.com/pdfs/marcom/apr_wp.pdf|access-date=2011-09-27|url-status=live|archive-url=https://web.archive.org/web/20110905005921/http://media.elotouch.com/pdfs/marcom/apr_wp.pdf|archive-date=2011-09-05}}</ref> The touchscreen used by Elo is made of ordinary glass, giving good durability and optical clarity. The technology usually retains accuracy with scratches and dust on the screen. The technology is also well suited to displays that are physically larger.