Touch Screens

By Joseph Dotzel

3/27/14

Audience and Scope The purpose of this article is to inform is to inform users how touch screens actually function. The concept of the touch screen was created as early as 1965 and since then has become a normal object in the average person’s life. Whether it be a touchscreen at a bank, on a computer, or on a phone touchscreens have become ingrained into our society, but few people actually stop to think about how they actually work. This article will cover the three major types of touch screens, resistive, surface acoustic and capacitive, and will describe the differences and how each touch screen functions.

Resistive Touch ScreensThe first and most traditional type of touch screen is the analog resistive touch screen. This type of touch screen is created by having two layers of materials that make up the screen. The bottom layer is typically made of glass and the top layer of the screen is made of a plastic film. These two layers are separated by an air-gap or spacers that keep the two layers separated. On the inside of each layer is covered with a grid of electrical conductors. In the past this grid was made from fine metal wires but nowadays they are created from a transparent conductor material such as indium tin oxide.

The grid for glass layer is oriented perpendicular to the plastic layer. A current is run through one of the layers and the resistance is measured by analog-to-digital converters. Upon pressing down on the screen the two screens come into

contact and the drop of resistance allows the x and y coordinates to be calculated.

Capacitive Touch ScreensThe next type of touch screen is known as a projected capacitance touch screen. This type of touch screen has quickly dominated that market since its appearance. It is created by using a single piece of glass. On each side of this, a layer of thin transparent conducting material is applied, usually made of indium tin oxide. These conductor are applied at right angles to each other just as with the resistive touch screens.

While the resistive touch screens worked by measuring the resistance of the screen, the capacitive touch screens, as their name suggests, rely on the principle of capacitance to sense the touches input on the screen. It works by applying an electrical charge to the screen. The charge builds as it has nowhere to flow. Bringing a conductor close to the screen absorbs a little of the charge built up on the touch screen. In this case the conductor is the user’s finger. This change is measured and an x and y location is determined. Furthermore, each conductor for the touch screen is measured separately. This allows multiple touches to be registered on the touch screen.

Surface Acoustic Wave Touch ScreensThis Touch Screen is known as the Surface Acoustic Wave touch screen, and it is quickly becoming a common alternative to the projected capacitance touch screens. The screen is created using two transducers in one corner placed perpendicularly to each other and on the opposite corner two receivers are placed. In addition to these, sound wave reflectors are placed along the edges of the glass screen.

Instead of measuring resistance or capacitance to register the users touch, this screen uses sound. Ultrasonic sound is emitted from the two transducers, one in the x direction and one in the y direction. These sound waves are then reflected into the receivers. When the user touches the screen, some of both of the x and y sound waves are absorbed. The drop in amplitude is measured and the x and y coordinates are determined. This technology is also capable of multi touch inputs.

Pros and Cons

ConclusionThe technology of touch screens has vastly improved in recent years and has become ingrained into our society. It appears in everywhere from banks to in our very pockets. One thing for sure is that they will not be disappearing any

Resistive

ProsRecognizes all types of touch inputCheapConsCan only sense one touch inputRequire regular recalibrationRepeated use can break the conductors on the screenAir gap adds thickness to deviceAir gap causes refraction, creating visible artifactsLight can reflect between the glass and plastic layers

Capacitive

ProsMulti TouchHigh Light TransmissionDurable solid state technologyConsOnly recognize conductors touch inputsCostHigh processing power

Sound Acoustic Wave

ProsMulti TouchDurable due to non layered designRecognizes glovessuperior image clarity and light transmissionCons Only able to identify Soft-touch inputs, Small area inputs such as stylus or pens would not be recognizedTouch screen is not completely sealable and can be affected by dirt, dust, and water

time soon. Keeping this in mind, knowing how they work will allow you to further understand the world that you are living in today.

ReferencesInformation not know was obtained from the following websiteshttp://www.computerworld.com/s/article/9231961/How_it_works_The_technology_of_touch_screens?taxonomyId=12&pageNumber=3 http://touchsystems.com/surfaceacousticwave.phphttp://www.tvielectronics.com/Touch_Screen.htmlhttp://www.elotouch.com/technologies/intellitouch/default.asp

Images were obtained from the following locationshttp://www.computerworld.com/common/images/site/features/2012/10/ts_standard_pro-cap_508.jpghttp://www.analog.com/library/analogdialogue/archives/44-02/AD44_02_BB_FIG_01.jpghttp://upload.wikimedia.org/wikipedia/commons/thumb/c/cd/Capacitor_schematic_with_dielectric.svg/430px-Capacitor_schematic_with_dielectric.svg.pnghttp://www.eizo.com/global/library/basics/basic_understanding_of_touch_panel/06.jpghttp://touchsystems.com/images/saw.jpg