Fingerprint Cards patent application for lower-cost ultrasonic biometric sensing system published in U.S.
A patent application filed by Fingerprint Cards for an acoustic fingerprint technology which could be used for relatively low-cost in-display smartphone biometrics has been published by the U.S. Patent and Trademark Office (USPTO).
The filing for an ‘Acoustic Fingerprint Representation Acquisition Technique’ refers back to a patent application filed by the company in Sweden in 2019. It describes a system with a region for fingerprint placement on a device, and an ultrasound transmitter transducer like a piezoelectric slab with a resonance frequency coupled to a transducer region in the device. The transducer region is laterally spaced apart from the touch region, with connected drive, receiver and processing circuitry.
The transmitter and receiver transducers may be separate, and the thickness of transducers is a determining factor in their resonant frequency, according to the application.
Ultrasonic sensing could provide performance advantages over capacitive and other technologies, according to the application, as prints could be captured from moist fingers or palms, for instance. The inventors write that Fingerprint Cards is particularly interested in ultrasonic biometric sensors for touch surfaces on devices. Ultrasonic sensors could also enable a larger sensing area without proportionally increasing the cost.
Based on those potential advantages “and other drawbacks of the prior art,” the invention is intended “to achieve improved acquisition of a fingerprint representation of a finger surface, in particular providing for the detection of finer features of the finger surface,” according to the filing.
The key innovation seems to be the finding “that a piezoelectric slab type ultrasound transducer having a fundamental mode resonance frequency can be controlled to provide a fundamental mode oscillation with a frequency spectrum having a peak frequency that is higher than the fundamental mode resonance frequency, and that this can be done with substantially the same performance as would be attainable with a thinner slab type ultrasound transducer having a fundamental mode resonance frequency at the desired frequency.” The inventors believe this is due to compensation through the use of more energy, which thicker transducers of this type can provide. This means more standard-thickness piezoelectric slabs could be used to gain the advantages of ultrasonic sensing, without the usual increase in manufacturing cost.
The company was reported as far back as mid-2018 to be working on ultrasonic fingerprint sensors for in-display implementation to mobile devices like smartphones.