Concept designers have been creating renderings of bezel-free iPhones – where the display extends all the way to the edges of the phone – for years now. One major barrier to realizing this vision has, of course, been the Home button with its embedded Touch ID sensor.

Third-party companies have already developed transparent fingerprint sensors capable of being embedded into a smartphone display, and an Apple patent filed in March of last year but only published yesterday describes the exact same approach …

The patent describes three different technologies that can be used for fingerprint sensors, and says that the third of them – ultrasonic imaging – would not only allow the reader to be embedded into the display, but would also be even more accurate than the capacitive sensor used by Touch ID today.

The most accurate but least common finger-scanning technology is ultrasound imaging. In this type of sensor, two transducers are placed on the x- and y-axes of a plate of glass–one each for receiving and transmitting–for propagating ultrasound waves through a glass plate; when the finger is placed on top of the glass, the finger impedes the waves and the receiving transducer can measure the alteration in wave patterns. This type of scanner is very new and largely untested in a variety of conditions, but initial results show promise for the technology. It combines the large plate size and ease of use of the optical scanners with the ability to pervade dirt and residue on the scanner, an advantage of capacitive scanners.

As Patently Apple notes, the patent also describes how a fingerprint sensor – or Biometric Personal Identification Device (BPID) in patenteze – could be used to verify the authenticity of data. One specific application given is that of a driving license, an interesting example given that the British government is working on allowing digital licenses to be stored in Apple’s Wallet app.

An extremely sketchy report last month suggested that this technology could even make its way into the iPhone 7, though this of course conflicts with the majority (though not all) of reports which suggest that the iPhone 7 will feature only minor enhancements over the 6 and 6s.

There would, of course, be additional challenges to a truly bezel-free phone, including the front-facing camera. The usual disclaimer applies to Apple patents: very few of them make it as far as products. Check out another interesting Apple Home button patent here, and two further patents relating to embedded Touch ID over at Patently Apple.

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