What types of touch screens are there? Types of touch screens. Which touch screen is better?
Almost the entire world of high technology has already been captured by the fashion for touch screens. Nowadays, almost every player or cell phone has a touchscreen, and the general scope of application of such display technology is much more significant. There are now different types of touch screens on the market, the operation of which depends on the technology they use.
It is a device focused on input and output of information through a pressure-sensitive display. The screens of modern devices not only display images, but also provide opportunities to interact with them. Initially, such a connection was provided through the buttons familiar to everyone, then a different type of manipulator appeared, called a mouse, which greatly facilitated the process. This device requires a horizontal surface to operate, which is completely inconvenient when using a mobile phone. This is where the addition to the regular screen in the form of a touchscreen comes in handy. The touch element is not inherently a screen, it is an additional device that is placed externally on top of the display, while it protects and is intended for entering coordinates by touching it with an input device or finger. There are different types of touch screens. It's worth looking at them in a little more detail.
Types of touch screens and their use in electronic devices
Initially, touchscreen technology was used for pocket computers, but now it has become much more widely used, from music players to cameras. Since such a control mechanism is very convenient, it is used for modern ATMs, tablet terminals, various electronic directories and other devices. Touch screen technology is very convenient in cases where you need instant access to the controlled device without any preparation and with maximum interactivity: the controls change depending on which function is activated.
Types of touch screens: capacitive, resistive, projected capacitive and others (less popular). In addition to these types, there are also infrared and matrix displays, but their accuracy is so low that their scope of application is completely limited.
Resistive touch screens
These displays are the simplest devices. Such a panel includes a conductive substrate and a plastic membrane, which have a certain resistance. When the membrane is pressed, a short circuit is made with the substrate, which forces the conductive electronics to react to the resistance that has arisen between the edges of these elements, then calculating the coordinates of the point on which the press was made. Such screens are very simple in design, they are cheap, and also have excellent resistance to dirt. The main advantage of this type of sensor is that it is sensitive to all touches. The disadvantage is the high sensitivity to mechanical damage, which requires the use of special panels. Such panels work well at low temperatures.
Capacitive sensor technology works completely differently. It is based on the principle that a large-capacity object can conduct electric current. An electrically conductive layer is applied to the glass, and alternating voltage is applied to all four corners. When the screen touches a grounded object of higher power, current leaks. The control electronics registers these leaks, determining the coordinates.
This article briefly and clearly described the main types of touch screens that have gained the most popularity.
Before considering a capacitive or resistive screen, you need to decide what touch technology is in general. Everything is clear here: this is the screen that determines the coordinates of the press. In scientific terms, this refers to a method of controlling the interface with which the user can click directly on the place of interest. At the moment, there are several methods for implementing touch screens. It is worth considering each separately.
Resistive technology
To decide which type of screen, capacitive or resistive, is best for you, you need to consider them. The second option involves the use of a certain production technology. At the bottom there is a glass panel, on top of which there is a transparent flexible membrane. There is a conductive coating on the panel and membrane, that is, resistive. When you press the screen, a short circuit occurs at a certain point. If you know the voltage on the electrodes on one side and measure it on the membrane, you can track one coordinate. Two coordinates will require turning off one group of electrodes to turn on another. The microprocessor does all this automatically as soon as the voltage on the membrane changes. Resistive screens do not allow multi-touch.
Features of resistive technology
Like any other type of implemented device, there are certain features that are positive or negative depending on the situation. The advantages are usually low-cost production, as well as the ability to press with anything, since you only need to push the membrane. Positioning accuracy is increased through the use of styluses.
Negative points
The main disadvantages include a low degree of light transmission, a high rate of scratches on the surface, the ability to click on one point no more than 35 million times, and the inability to implement multi-touch. If you can't decide whether to choose a capacitive or resistive screen, then it is also important to note that it is impossible to use gestures such as sliding, since you need to press your finger on the screen and drag it without releasing it. In devices with such controls, it is better to use software that requires minimal use of “swipe” gestures.
Understanding the features of this technology, it is worth noting that it can be implemented in several ways that have certain differences. A capacitive touchscreen can be simply capacitive or projected capacitive. The first option involves the use of certain elements. A transparent resistive material, such as an alloy of tin oxide or indium, is placed on top of the glass panel. Electrodes are placed in the corners, which apply a small alternating voltage to the conductive layer. If the screen is touched by a conductive object, a leakage occurs, and the closer this object is to the electrode, the lower the screen resistance, that is, the current strength increases noticeably. And this is all called a capacitive screen, since alternating current is conducted by an object with a larger capacitance. Most often we are talking about a finger.
Features of capacitive screens
Like other types of technologies, in this case we are talking about a combination of advantages and disadvantages. The advantages over others include high light transmittance, significant click life, simplicity and ease of operation using the “flipping” method. There are also disadvantages here: you only need to use your fingers or specialized styluses. A regular capacitive screen does not support multi-touch technology. There are often accidental clicks. For example, the system can recognize a gesture as “scrolling” even when it is not intended, since it is difficult to keep the finger strictly in one place after pressing.
Projected capacitive touch screen
In this case, the device differs quite greatly from the previous ones. The inner side of the screen is a grid of electrodes. If an object of greater capacitance touches the electrode, a capacitor is formed with a constant capacitance. Such screens are used outdoors, as they allow the installation of glass with a thickness of up to 18 mm, which not only produces the hardest possible surface, but also ensures vandal resistance.
Features of projected capacitive sensors
In this case, as in all others, there are certain advantages and disadvantages that you should be aware of. The advantages include the ability to implement multi-touch, respond to pressure with a glove, a high degree of light transmission, as well as the durability of the screen itself. Such screens are able to respond to the approach of fingers without actually pressing. The threshold for when a touch completes occurs is usually software configurable. The extreme point is usually the screen itself, since pushing through it is completely useless.
If we consider a projective-capacitive screen, it also has certain disadvantages, which are usually called complex and rather expensive electronics, the inability to use a regular stylus, and the likelihood of accidental clicks.
Multi-touch technology
It is impossible to determine the appropriate type of touch screen, capacitive or resistive, without addressing the issue regarding the implementation of this technology. Multitouch is the ability to make multiple touches. This implementation involves tracking the coordinates of several clicks simultaneously. If such technology is implemented in a smartphone or tablet, then it can be used to imitate playing a musical instrument, for example, a guitar. This needs to be looked into in more detail.
You can take a regular capacitive or resistive screen. If you first press, for example, in the upper left corner, and then, without lifting your finger, press the lower right corner with another, then the electronics will determine the center of the screen as the coordinates, that is, the middle of the segment between these pair of touches. This will be visible if you run a special application that tracks the coordinates of the click. However, the question arises: how is image scaling implemented if only one click is recognized anyway?
Everything is simple here. This is the most common software trick. You pressed the capacitive screen - the electronics detected this. This will be point "A". Now, without releasing your finger, you press in another place, which will be point “B”, it turns out that at this moment the point of pressing instantly moved to the side, forming “C”. It was at this moment, when there was no actual release of the finger, but the pressing point instantly moved, that is processed in software as a multi-touch. Further, if point “C” becomes closer to “A”, then the movement of the fingers is determined, that is, in the case of an image, the picture must be reduced, and vice versa. One more point: if point “C” describes an arc around one of the points, then the program defines this as the rotation of one finger around the other, which necessitates rotating the picture in the appropriate direction.
Using resistive and capacitive screens
Professional developers traditionally use the first type, as it allows you to control any object under different weather conditions. Resistive technology uses a larger number of sensors per square centimeter compared to capacitive technology, so the display can display tiny icons that can be pressed with a needle. For example, the Windows Mobile operating system was designed with this feature in mind, so it works well with resistive screens. Such displays are almost insensitive to accidental clicks. However, many developers are now aiming to create applications that target capacitive touch screens. This is already becoming a problem for devices made using resistive technology.
Degree of protection
It is important to understand that for tablet computers and communicators, the display is the most vulnerable part. A capacitive screen is a more preferable option in terms of reliability. Its performance in any conditions is noticeably higher, and resistive models may fail, for example, if you carry them downwards with glass. Capacitive screen is a fail-safe option. Even if it is broken, it will continue to perform its functions. If you are deciding whether to choose a capacitive or resistive screen, it is worth noting that in field conditions the first will be the best option.
conclusions
To summarize, it can be noted that both display implementation options have their advantages and disadvantages. While a capacitive screen is a whole set of possibilities, a resistive screen is focused on use in certain situations. Usually it all depends on the interface used in the gadget. easy to use, its pressing area is noticeably smaller than that of a finger, however, with good responsiveness of the surface, it is convenient to do without this device. The constant improvement of resistive displays has led to the emergence of models that are quite hard, that is, resistant to scratches, but also responsive. Such options have become very convenient to use.
The need to use a special stylus for capacitive screens sometimes causes considerable inconvenience, since it usually does not come with the device. And resistive technology involves both accompaniment with a special device and the ability to press with any hard object. One of the reasons many people choose a capacitive touchscreen is multi-touch, however it is worth noting that most often this is a software implementation, as already described, and with the right approach it can be applied to a resistive one. Projected capacitive technology has not yet become as accessible as we would like.
Based on the difference in how information is entered, screen sensors are divided into two types: resistive screens and capacitive ones.
Resistive type
Resistive type - a screen that responds to pressure from almost any hard object. As a rule, phones with this sensor come with a stylus - a special stick.
What can be attributed to the advantages of such a display: price! they are so inexpensive to produce and fill an extremely large niche.
Another important advantage is that they are very resistant to contamination. To put it quite simply, if you see (at least somehow) the buttons, then they work!
Regarding the disadvantages, it is worth noting that the light conductivity is not very high.
There are two types of resistive screens: four-wire and five-wire
Capacitive type
Capacitive type - just like the resistive type, there are two types of capacitive screens - surface capacitive type, and projected capacitive type.
Surface capacitive type: The screen uses the principle of conducting alternating electric current by an object with high capacitance.
The capacitive type sensor is a glass panel covered with a layer of conductor. Electrodes located at the corners of the screen supply alternating voltage to it. When a person touches with a finger or any other leading object, a flow of current occurs. The current in all corners of the screen is recorded by special sensors and transmitted to the controller, which calculates the coordinates of the touch point.
The capacitive type of screen is more reliable (designed for 200 million touches on one point versus 35 million), does not allow liquids to pass through and is resistant to non-conductive contaminants. Another advantage of this type is that the screen transparency is 90%.
Now about the disadvantages - the screen will not work when you are wearing a glove, this is the first drawback. The second disadvantage is that multi-touch is not possible on it.
Projected capacitive type: A grid of electrodes is applied inside the screen. Together with the human body, these electrodes create a capacitor.
The features of this type include: advantages - screen transparency is about 90%, an unusually wide temperature range, many screens can be operated even when you are wearing gloves. Multitouch appeared here. And finally, these screens are very durable.
The disadvantages include the price of such a sensor and the complexity of production.
Therefore, if you are choosing which touch screen to get a phone with, I personally advise you to get a projected capacitive type.
The screens of modern devices can not only display images, but also allow you to interact with the device through sensors.
Initially, touch screens were used in some pocket computers, and today touch screens are widely used in mobile devices, players, photo and video cameras, information kiosks, and so on. Moreover, each of the listed devices can use one or another type of touch screen. Currently, several types of touch panels have been developed, and, accordingly, each of them has its own advantages and disadvantages. In this article we will look at what types of touch screens there are, their advantages and disadvantages, and which type of touch screen is better.
There are four main types of touch screens: resistive, capacitive, with the detection of surface acoustic waves and infrared . In mobile devices, only two are most widespread: resistive and capacitive . Their main difference is the fact that resistive screens recognize pressure, while capacitive screens recognize touch.
Resistive touch screens
This technology is most widespread among mobile devices, which is explained by the simplicity of the technology and low production costs. A resistive screen is an LCD display on which two transparent plates are superimposed, separated by a dielectric layer. The top plate is flexible, as the user presses on it, while the bottom plate is rigidly fixed to the screen. Conductors are applied to surfaces facing each other.
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Resistive touch screen |
The microcontroller supplies voltage in series to the electrodes of the top and bottom plates. When the screen is pressed, the flexible top layer flexes and its inner conductive surface touches the lower conductive layer, thereby changing the resistance of the entire system. The change in resistance is recorded by the microcontroller and thus the coordinates of the touch point are determined.
The advantages of resistive screens include simplicity and low cost, good sensitivity, and the ability to press the screen with either a finger or any object. Among the disadvantages, it is necessary to note poor light transmission (as a result, you have to use a brighter backlight), poor support for multiple clicks (multi-touch), they cannot determine the force of pressing, as well as fairly rapid mechanical wear, although in comparison with the life of the phone, this disadvantage is not so important, since the phone usually fails faster than the touch screen.
Application: cell phones, PDAs, smartphones, communicators, POS terminals, TabletPC, medical equipment.
Capacitive touch screens
Capacitive touch screens are divided into two types: surface-capacitive and projected-capacitive . Surface capacitive touch screens They are glass on the surface of which a thin transparent conductive coating is applied, on top of which a protective coating is applied. Along the edges of the glass there are printed electrodes that apply low-voltage alternating voltage to the conductive coating.
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Surface capacitive touch screen |
When you touch the screen, a current pulse is generated at the point of contact, the magnitude of which is proportional to the distance from each corner of the screen to the point of contact, thus, it is quite simple for the controller to calculate the coordinates of the point of contact and compare these currents. The advantages of surface capacitive screens include: good light transmission, short response time and long touch life. Among the disadvantages: the electrodes placed on the sides are not suitable for mobile devices, they are demanding on external temperature, they do not support multi-touch, you can touch them with your fingers or a special stylus, and they cannot determine the pressing force.
Application: Information kiosks in secure areas, at some ATMs.
Projected capacitive touch screens They are glass with horizontal leading lines of conductive material and vertical defining lines of conductive material applied to it, separated by a layer of dielectric.
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Projected capacitive touch screen |
Such a screen works as follows: a microcontroller sequentially applies voltage to each of the electrodes in the conductive material and measures the amplitude of the resulting current pulse. As the finger approaches the screen, the capacitance of the electrodes located under the finger changes, and thus the controller determines the location of the touch, that is, the coordinates of the touch are intersecting electrodes with increased capacitance.
The advantage of projected capacitive touch screens is their fast touch response speed, multi-touch support, more accurate coordinate determination compared to resistive screens, and pressure detection. Therefore, these screens are used to a greater extent in devices such as the iPhone and iPad. It is also worth noting the greater reliability of these screens and, as a result, a longer service life. Among the disadvantages, it can be noted that on such screens you can only touch with your fingers (drawing or writing by hand with your fingers is very inconvenient) or with a special stylus.
Application: payment terminals, ATMs, electronic kiosks on the streets, touchpads of laptops, iPhone, iPad, communicators and so on.
SAW touch screens (surface acoustic waves)
The composition and operating principle of this type of screen is as follows: piezoelectric elements are placed at the corners of the screen, which convert the electrical signal supplied to them into ultrasonic waves and direct these waves along the surface of the screen. Reflectors are distributed along the edges of one side of the screen, which distribute ultrasonic waves across the entire screen. On the opposite edges of the screen from the reflectors there are sensors that focus ultrasonic waves and transmit them further to the transducer, which in turn converts the ultrasonic wave back into an electrical signal. Thus, for the controller, the screen is represented as a digital matrix, each value of which corresponds to a specific point on the screen surface. When a finger touches the screen at any point, waves are absorbed, and as a result, the overall pattern of propagation of ultrasonic waves changes and as a result, the transducer produces a weaker electrical signal, which is compared with the digital matrix of the screen stored in memory, and thus the coordinates of touching the screen are calculated.
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SAW touch screen |
The advantages include high transparency, since the screen does not contain conductive surfaces, durability (up to 50 million touches), and surfactant touch screens allow you to determine not only the coordinates of pressing, but also the pressing force.
Among the disadvantages, we can note the lower accuracy of determining coordinates than capacitive ones, that is, you won’t be able to draw on such screens. A big disadvantage is malfunctions when exposed to acoustic noise, vibrations or when the screen is dirty, i.e. Any dirt on the screen will block its operation. Also, these screens only work correctly with objects that absorb acoustic waves.
Application: SAW touch screens are mainly found in secure information kiosks, educational institutions, gaming machines and so on.
Infrared touch screens
The design and operating principle of infrared touch screens is quite simple. Along two adjacent sides of the touch screen there are LEDs that emit infrared rays. And on the opposite side of the screen there are phototransistors that receive infrared rays. Thus, the entire screen is covered with an invisible grid of intersecting infrared rays, and if you touch the screen with your finger, the rays overlap and do not hit the phototransistors, which is immediately registered by the controller, and thus the coordinates of the touch are determined.
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Infrared touch screen |
Application: Infrared touch screens are mainly used in information kiosks, vending machines, medical equipment, etc.
Among the advantages we can note the high transparency of the screen, durability, simplicity and maintainability of the circuit. Among the disadvantages: they are afraid of dirt (therefore they are used only indoors), cannot determine the force of pressing, average accuracy in determining coordinates.
P.S. So, we have looked at the main types of the most common sensor technologies (although there are also less common ones, such as optical, strain gauge, induction, and so on). Of all these technologies, resistive and capacitive ones are most widely used in mobile devices, as they have high accuracy in determining the point of contact. Of these, projected capacitive touch screens have the best characteristics.
The text was prepared based on materials from open sources by Technological methodologists Karabin A.S., L.V. Gavrik, S.V. Usachev
The iPhone 2G was the first mobile phone to operate entirely on a touch screen. More than ten years have passed since its presentation, but many of us still do not know how the Touchscreen works. But we encounter this intuitive input tool not only in smartphones, but also in ATMs, payment terminals, computers, cars and airplanes - literally everywhere.
Before touchscreens, the most common interface for entering commands into electronic devices was various keyboards. Although they seem to have nothing in common with touchscreens, in fact, how similar a touchscreen is to a keyboard can be surprising. Let's look at their device in detail.
The keyboard is a printed circuit board on which several rows of switches-buttons are installed. Regardless of their design, membrane or mechanical, when you press each of the keys, the same thing happens. An electrical circuit is closed on the computer board under the button, the computer registers the passage of current in this place of the circuit, “understands” which key is pressed and executes the corresponding command. In the case of a touch screen, almost the same thing happens.
There are about a dozen different types of touch screens, but most of these models are either outdated and not used, or are experimental and are unlikely to ever appear in production devices. First of all, I will talk about the structure of current technologies, those that you constantly interact with or at least may encounter in everyday life.
Resistive touch screen
Resistive touch screens were invented back in 1970 and have changed little since then.
In displays with such sensors, a couple of additional layers are located above the matrix. However, I’ll make a reservation that the matrix is not at all necessary here. The first resistive touch devices were not screens at all.
The bottom sensor layer consists of a glass base and is called the resistive layer. A transparent metal coating is applied to it that transmits current well, for example, from a semiconductor such as indium tin oxide. The top layer of the touchscreen, with which the user interacts by pressing the screen, is made of a flexible and elastic membrane. It is called the conductive layer. An air gap is left in the space between the layers, or it is evenly dotted with microscopic insulating particles. Along the edges, four, five or eight electrodes are connected to the sensor layer, connecting it with sensors and a microcontroller. The more electrodes, the higher the sensitivity of the resistive touchscreen, since changes in voltage across them are constantly monitored.
Here is the screen with the resistive touchscreen turned on. Nothing is happening yet. Electric current flows freely through the conductive layer, but when the user touches the screen, the membrane on top bends, the insulating particles part, and it touches the bottom layer of the touchscreen and comes into contact. This is followed by a change in voltage at once on all electrodes of the screen.
The touchscreen controller detects voltage changes and reads readings from the electrodes. Four, five, eight meanings and all different. Based on the difference in readings between the right and left electrodes, the microcontroller will calculate the X-coordinate of the press, and based on the differences in voltage on the upper and lower electrodes, it will determine the Y-coordinate and thus tell the computer the point at which the layers of the touch screen layer touched.
Resistive touch screens have a long list of disadvantages. So, in principle, they are not able to recognize two simultaneous clicks, let alone a larger number. They don't do well in the cold. Due to the need for a layer between the sensor layers, the matrices of such screens noticeably lose brightness and contrast, tend to glare in the sun, and generally look noticeably worse. However, where image quality is of secondary importance, they continue to be used due to their resistance to stains, their ability to be used with gloves and, most importantly, their low cost.
Such input devices are ubiquitous in inexpensive mass-produced devices, such as information terminals in public places, and are still found in aging gadgets, such as cheap MP3 players.
Infrared touch screen
The next, much less common, but nevertheless relevant touch screen option is the infrared touchscreen. It has nothing in common with a resistive sensor, although it performs similar functions.
The infrared touchscreen is constructed from arrays of LEDs and photosensitive photocells located on opposite sides of the screen. LEDs illuminate the surface of the screen with invisible infrared light, forming something like a spider's web or coordinate grid on it. This is reminiscent of a security alarm, as they are shown in spy action films or computer games.
When something touches the screen, whether it's a finger, a gloved hand, a stylus, or a pencil, two or more beams are interrupted. Photocells record this event, the touchscreen controller finds out which of them are not receiving enough infrared light and, based on their position, calculates the area of the screen in which an obstacle has arisen. The rest is to match the touch with what interface element is on the screen at that location - the software's job.
Today, infrared touch screens can be found in those gadgets whose screens have a non-standard design, where adding additional touch layers is technically difficult or impractical - in e-books based on E-link displays, for example, Amazon Kindle Touch and Sony Ebook. In addition, devices with similar sensors, due to their simplicity and maintainability, attracted the attention of the military.
Capacitive touch screen
If in resistive touch screens the computer registers the change in conductivity that follows a press on the screen directly between the layers of the sensor, then capacitive sensors record the touch directly.
The human body and skin are good conductors of electricity and have an electrical charge. You usually notice this by walking on a wool carpet or taking off your favorite sweater and then touching something metal. We are all familiar with static electricity, have experienced its effects ourselves and have seen tiny sparks flying off our fingers in the dark. A weaker, imperceptible exchange of electrons between the human body and various conductive surfaces occurs constantly and this is what capacitive screens record.
The first such touchscreens were called surface capacitive and were a logical development of resistive sensors. In them, only one conductive layer, similar to the one used previously, was installed directly on top of the screen. Sensitive electrodes were also attached to it, this time at the corners of the touchpad. The sensors that monitor the voltage on the electrodes and their software were made noticeably more sensitive and could now detect the slightest changes in the flow of electric current across the screen. When a finger (another conductive object, such as a stylus) touches the surface with a surface capacitive touchscreen, the conductive layer immediately begins to exchange electrons with it, and the microcontroller notices this.
The advent of surface capacitive touchscreens was a breakthrough, but due to the fact that the conductive layer applied directly on top of the glass was easily damaged, they were not suitable for the new generation of devices.
To create the first iPhone, projected capacitive sensors were required. This type of touchscreen has quickly become the most common in modern consumer electronics: smartphones, tablets, laptops, all-in-one PCs and other household devices.
The top layer of this type of touchscreen screen has a protective function and can be made of tempered glass, such as the famous Gorilla Glass. Below are the thinnest electrodes that form a grid. At first they were placed on top of each other in two layers, then to reduce the thickness of the screen they began to be placed on the same level.
Made from semiconductor materials, including the aforementioned indium tin oxide, these conductive hairs create an electrostatic field where they intersect.
When a finger touches the glass, due to the electrically conductive properties of the skin, it distorts the local electric field at the points of closest intersection of the electrodes. This distortion can be measured as the change in capacitance at a single grid point.
Because the electrode array is made quite small and dense, such a system is able to track touch very accurately and can easily pick up multiple touches at once. In addition, the absence of additional layers and interlayers in the sandwich of the matrix, sensor and protective glass has a positive effect on image quality. True, for the same reason, broken screens, as a rule, are completely replaced. Once put together, the projected capacitive touch screen is extremely difficult to repair.
Now the advantages of projective-capacitive touchscreens do not sound like anything surprising, but at the time of the iPhone’s presentation they provided the technology with tremendous success, despite the objective disadvantages - sensitivity to dirt and humidity.
Pressure-sensitive touch screens - 3D Touch
The ideological predecessor of pressure-sensitive touch screens was Apple's proprietary technology, called Force Touch, used in the company's smart watches, MacBook, MackBook Pro and Magic Trackpad 2.
Having tested interface solutions and various scenarios for using pressure recognition on these devices, Apple began implementing a similar solution in its smartphones. In the iPhone 6s and 6s Plus, pressure recognition and measurement became one of the touchscreen functions and received the commercial name 3D Touch.
Although Apple did not hide the fact that the new technology only modifies the capacitive sensors we are used to and even showed a diagram that generally explained the principle of its operation, details about the design of touch screens with 3D Touch appeared only after the first iPhones of the new generation were disassembled by enthusiasts .
In order to teach the capacitive touch screen to recognize clicks and distinguish between several degrees of pressure, engineers from Cupertino needed to rebuild the touch screen sandwich. They made changes to individual parts of it and added another, new layer to the capacitive one. And, interestingly, when doing this, they were clearly inspired by outdated resistive screens.
The grid of capacitive sensors remained unchanged, but it was moved back, closer to the matrix. An additional array of 96 individual sensors was integrated between a set of electrical contacts that monitor where the display is touched and the protective glass.
Its task was not to determine the location of a finger on the iPhone screen. The capacitive touchscreen still handled this perfectly well. These plates are necessary to detect and measure the degree of bending of the safety glass. Apple specifically for the iPhone ordered Gorilla Glass to develop and produce a protective coating that would retain the same strength and, at the same time, be flexible enough for the screen to respond to pressure.
This development could have been the end of the material about touch screens, if not for another technology that was predicted to have a great future several years ago.
Wave touch screens
Surprisingly, they don't use electricity and don't even have anything to do with light. Surface Acoustic Wave system technology uses surface acoustic waves propagating along the surface of the screen to detect the point of touch. The ultrasound generated by the piezoelectric elements at the corners is too high to be detected by human hearing. It spreads back and forth, bouncing off the edges of the screen multiple times. The sound is analyzed for anomalies caused by objects touching the screen.
There are not many disadvantages to wave touch screens. They begin to make mistakes after the glass is heavily soiled and in conditions of strong noise, but at the same time, in screens with such a sensor there are no additional layers that increase the thickness and affect the image quality. All sensor components are hidden under the display frame. In addition, wave sensors allow you to accurately calculate the area of contact between the screen and a finger or other object and, based on this area, indirectly calculate the force of pressing the screen.
We are unlikely to encounter this technology in smartphones due to the current fashion for frameless displays, but several years ago Samsung experimented with the Surface Acoustic Wave system in monoblocks, and panels with acoustic touchscreens are also sold as components for slot machines and advertising terminals. Now
