Okay, but how do touch screens actually work?

Swipe: verb; the act of moving one’s finger across a touch screen.

Okay, but how do touch screens actually work?
[Image Credit: Flickr via Adactio ]
By | Posted January 17, 2012
Posted in: Ever Wondered?
Tags: , , ,

I recently overheard a woman on the subway telling her friend that her toddler “swipes” everything in their house – the coffee table, books, plates and even her own mother, trying to make her disappear like an image on a touch screen. The story got me thinking that for many of us, our knowledge of what’s going on behind that glossy display isn’t much more than a toddler’s.

Before I started researching how touch screens worked, I figured there was one universal technology behind the “swipable” phenomenon. Instead it turns out there are half a dozen, and more being researched every day. The two most commonly used systems are resistive and capacitive touch screens. For the sake of simplicity, I will focus here on these two systems and finish with where experts think touch screen technology is headed.

1. Resistive

These are the most basic and common touch screens, the ones used at ATMs and supermarkets, that require an electronic signature with that small grey pen. These screens literally “resist” your touch; if you press hard enough you can feel the screen bend slightly. This is what makes resistive screens work – two electrically conductive layers bending to touch one another, as in this picture:

Resistive touch screen technology [Image Credit: Chassis Plans]

One of those thin yellow layers is resistive and the other is conductive, separated by a gap of tiny dots called spacers to keep the two layers apart until you touch it. (A thin, scratch-resistant blue layer on top completes the package.) An electrical current runs through those yellow layers at all times, but when your finger hits the screen the two are pressed together and the electrical current changes at the point of contact. The software recognizes a change in the current at these coordinates and carries out the function that corresponds with that spot.

Resistive touch screens are durable and consistent, but they’re harder to read because the multiple layers reflect more ambient light. They also can only handle one touch at a time – ruling out, for example, the two-finger zoom on an iPhone. That’s why high-end devices are much more likely to use capacitive touchscreens that detect anything that conducts electricity.

2. Capacitive

Unlike resistive touch screens, capacitive screens do not use the pressure of your finger to create a change in the flow of electricity. Instead, they work with anything that holds an electrical charge – including human skin. (Yes, we are comprised of atoms with positive and negative charges!) Capacitive touch screens are constructed from materials like copper or indium tin oxide that store electrical charges in an electrostatic grid of tiny wires, each smaller than a human hair.

Capacitive touch screen technology [Image credit: Electrotest]

There are two main types of capacitive touch screens – surface and projective. Surface capacitive uses sensors at the corners and a thin evenly distributed film across the surface (as pictured above) whereas projective capacitive uses a grid of rows and columns with a separate chip for sensing, explained Matt Rosenthal, an embedded project manager at Touch Revolution. In both instances, when a finger hits the screen a tiny electrical charge is transferred to the finger to complete the circuit, creating a voltage drop on that point of the screen. (This is why capacitive screens don’t work when you wear gloves; cloth does not  conduct electricity, unless it is fitted with conductive thread.) The software processes the location of  this voltage drop and orders the ensuing action. (If you’re still confused, watch this video.)

3. What’s next? Sizing Up

Newer touch screen technologies are under development, but capacitive touch remains the industry standard for now. The biggest challenge with touch screens is developing them for larger surfaces  –  the electrical fields of larger screens often interfere with its sensing capability.

Software engineers from Perceptive Pixel, which designs multi-touch screens, is using a technology called frustrated total internal reflection (FTRI) for their larger screens, which are as big as 82-inches. When you touch an FTRI screen you scatter light – and several cameras on the back of the screen detect this light as an optical change, just as a capacitive touch screen detects a change in electrical current.

Frustrated total internal reflection [Image Credit: Jeff Han Laboratory, formerly NYU now Perceptive Pixel]

82 inches? That’s the perfect size for a swipeable coffee table.

Posted in: Ever Wondered?

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  1. Great explanation of technology that we use every day. I was thinking about this topic just the other day and never looked into it, now I don’t have too!

    Steve, January 19, 2012 at 11:33 am
  2. Are latex & nitrile some of those conductive materials? At work I wear latex or nitrile coated cotton/polyester gloves and I can use my iPhone without removing my gloves.

    Tim S., January 24, 2012 at 2:43 pm
  3. Hi Tim,

    The answer to your question is not quite that straightforward — any capacitive touch screen, like your iPhone, registers a touch based on the dielectric constant and thickness of the material in contact. The dielectric constant is the extent to which a material can create electric flux — and most touch screens are tuned so your finger needs to be within .5mm or closer (in air) to sense a touch. So since your latex and nitrile gloves, for instance, are extremely thin, your finger is still close enough to the screen for it to register. The commercial touchscreen gloves, on the other hand, aren’t using latex or nitrile material, they’re using a conductive thread that can pick up the electrical current from your hands and make the screen think the entire glove is just part of your hand. So, when using gloves on a touchscreen, they either need to be really thin (like yours) or really conductive (like the ones advertised) – latex and nitrile work well, but I don’t think they’re going to keep your hands very warm!

    Allison T. McCann, January 27, 2012 at 1:20 pm
  4. Thanks for a simple answer to a question I’ve wondered about more than once. And thank you Allison for your comments about the iPhone. I can interact with my iPhone through something as thick as a cotton shirt but I’m thinking it might be porous enough to be mildly conductive.

    Trevor Gallant, January 30, 2012 at 8:29 am
  5. I am trying to understand why I cannot use or better yet, why don’t touch screens work for me? I understand the information you supplied, even without gloves, the touch screen doesn’t register me. Why?

    Carrie P, February 2, 2012 at 10:32 pm
  6. This is just awesome, Lehman can understand the concept of touch screen.

    Kishor, July 20, 2012 at 9:14 am
  7. Thanks for explanation of how touch screens worked

    phen, December 4, 2012 at 11:57 am
  8. How do capacitive touch screens work with screen guards?

    Bharat, May 23, 2013 at 12:47 am
  9. very well explained…
    resistive touchscreen are clearly more sturdy… I had a Nokia 5230 and i used it for 3 years..I dropped it off a chairlift from atleast 200 ft….The screen wasnt even scratched


    hameed1989, June 4, 2013 at 8:46 am
  10. A few days ago an unnatural thing happened. I was connecting my USB keyboard to the backside of my CPU. As usual when I touched it I got a little shock which was bearable. Then I took my mobile phone, which has a Capacitive touchscreen. But the phone started to behave weird. It seems that it was being touched automatically!! It seemed someone invisible was touching it vigorously !! After that I restart my phone, cleaned the screen several times. Now, some corner area isn’t responding. I want a description about this incident….

    Abrar, October 2, 2014 at 1:09 pm
  11. Nice explanation indeed. We understand the basic idea now. But that flash video was not really helpful because of poor presentation. Thanks for the article by the way..

    Rahul, January 31, 2015 at 11:03 am
  12. @ Carrie P.: Carrie, I have seen where some people couldn’t get their touchscreens to work and thought their phones were broken. I told them to moiturize their hands and try again. Turned out they happen to have very dry finger tips, that day. Also, do your fingers get cold easily? If so, you may have poor circulation in your hands and should see your Physician.

    As stated it the article, our bodies are made up of Atoms. Unless you’re an alien, with synthetic blood that has been designed with an alternative to the Atom or your creator made you with rubber fingers, you carry an electric charge. If you are, indeed, an alien, you may want to have your fingers redesigned, to work with our archaic technology. ;-)

    I know someone who is working with a synthetic fluid and has had encouraging success, thus far. He’s 12 years old, too. He could be the creator of the next and greatest touchscreen. He carries my blood, so, I know he’s not an alien – even though I wonder, at times. Reading 4-500 WPM and comprehending them, at the age of 5 and scoring in the top 19% in the country, on the college entrance exam, in 7th grade, isn’t exactly the norm. I have no doubt he will be remebered as one of the great-minds of his generation.


    John Curtis, May 7, 2015 at 10:00 am
  13. Why does the surface that is touching the capacitive screen have to be flat? I can use the flat area of a piece of aluminum foil that my finger is touching to control the screen but not a tip of the same piece of foil right next to a flat area that worked and held in the same way.


    Ralph, May 15, 2015 at 1:24 pm
  14. Is it that enough charge can’t flow though a small area like the tip of a piece of aluminum foil fast enough to activate the circuitry?

    Ralph, May 15, 2015 at 1:34 pm
  15. how capacitive touch screen work with plastic protector because it is a bad conductor so the charge is transferred from body to screen through plastic protector

    abdul rehman, May 19, 2015 at 6:36 am
  16. I thought this website was great! Keep up the good work! Helped me with my science homework.

    Regan Leavy, May 30, 2015 at 10:43 pm
  17. @Ralph. Yes it can. It is metal with an electrical charge.

    Regan Leavy, May 30, 2015 at 10:50 pm
  18. I have low blood pressure that likes to get even lower when there is a stressor…those times, can’t hardly use my iPhone

    Mind, June 5, 2015 at 8:28 am
  19. I race cars, my car the requires a tablet (Nexus 7) to display the data inside the car. I am not able to manipulate the screen with my racing gloves on and no one makes a nomex glove with capacitive touch capabilities. Could I add conductive thread to index finger tip to make this work?

    Tom, June 9, 2015 at 10:07 am
  20. An electrician friend argued that
    A touchscreen operated on heat. He got mad when I tried to correct him.

    Clifford a. Kirkland, July 9, 2015 at 6:29 pm
  21. please I want more understanding on capacitive systems.

    muelz Aaron, July 12, 2015 at 4:17 am
  22. @Tom Just try to pull a nitrile glove (those blue examination golves) over your normal gloves.
    In the case of a friend who is paragliding this helped. He can use his mobile while in the air by just wearing nitrile gloves over the thik leather gloves.

    Marco, July 13, 2015 at 5:45 am
  23. I am wondering whether resistive touchscreen would be replaced by capacitive touchscreen in the future? Capacitive touchscreen has more advantages and we use capacitive technology in some of our products.

    Helen, July 23, 2015 at 10:31 pm
  24. This is a brilliantly structured article.

    Cheven Ramrathan, July 28, 2015 at 7:55 am
  25. @Clifford Lol I had the same argument with my husband! He shut up when I pointed out the fact that his stylus is not warm so he is wrong! This is a great explanation of how they work. Thanks for proving me right!!!

    Joanie S., August 23, 2015 at 8:24 am
  26. Brilliant article. I would love to know more if it is possible for a touch-system that does not requires any kind of surface to interact upon. This might totally sound insane, but looking at the future. This totally might be another possibility.

    Sudipto, August 29, 2015 at 6:44 pm
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    running walking shoes, September 3, 2015 at 6:20 am
  28. Couldn’t have explained it better. Thanks!

    Frank S., September 14, 2015 at 8:51 am

    Carl j. jones, September 16, 2015 at 1:38 pm
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