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(Pocket-lint) - With the notch trend introduced by the Apple iPhone X in full swing, attention is now turning to the next big mobile trend, in-display fingerprint sensors. Samsung has been said to developing its own sensor for some time now - it was originally said to be debuting in the Galaxy S8, to no avail - and most recently was said to be appearing in the Galaxy Note 9.

Those rumours have now been quashed by a report from Korea, which says we'll have to wait until the Galaxy S10 to see something from the South Korean tech giant. Apple is also said to be wading in on the technology too, although it's unlikely we'll see in-display sensors in any of this year's new iPhone launches.

The reason for the two companies taking their time in releasing these sensors, is because they're said to be developing ultrasonic ones. Ultrasonic sensors were introduced by Qualcomm at MWC Shanghai, and they have the potential to dominate the in-display sensor market. Companies such as Vivo and Huawei have already integrated similar sensors in their phones, but these are optical and not ultrasonic.

It's unlikely Apple will be working with Qualcomm to develop a sensor, due to their rocky relationship, so is likely working on one of its own. Samsung is also rumoured to be working on its own sensor, because it plans to integrate it into its other future products, not just phones. 

Optical sensors shine light on the fingerprint and match it with an image stored in the phone's memory, if it matches, the phone unlocks. Ultrasonic sensors are a lot more accurate, as like their name suggests, they create an ultrasonic map of the fingerprint which picks up a lot more detail. This means the sensor will still work when fingers are wet or have some butter on if you've been eating your morning toast. 

Ultrasonic sensors can also work through glass, making them ideal for use in phones. However they are expensive and difficult to make, so it's no surprise that they're only predicted for the high-end flagships for now. 

The Samsung Galaxy S10 should be announced in March or April 2019, so there is still a fair bit of time to wait to see if the company integrates an ultrasonic sensor. We'll no doubt see plenty of leaks and rumours in the preceding months, so we'll keep our eyes peeled for any developments. 

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Writing by Max Langridge.