Ultrasonic fingerprint sensor with low-frequency vibration source

1. An apparatus, comprising:

an ultrasonic transmitter configured to transmit ultrasonic waves in the range of 1 MHz to 30 MHz;

a low-frequency vibration source configured to generate low-frequency vibrations in the range of 5 Hz to 2000 Hz;

wherein the ultrasonic transmitter and the low-frequency vibration source are mechanically coupled;

an ultrasonic receiver; and

a control system including one or more general purpose single- or multi-chip processors, digital signal processors (DSPs), one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs) or other programmable logic devices, one or more discrete gates or transistor logic, one or more discrete hardware components, or combinations thereof, the control system being configured to:

control the ultrasonic transmitter for transmission of first ultrasonic waves;

control the low-frequency vibration source for generation of first low-frequency vibrations;

synchronize the generation of the first low-frequency vibrations and the transmission of the first ultrasonic waves, wherein synchronizing the generation of first low-frequency vibrations and the transmission of first ultrasonic waves comprises:

controlling the low-frequency vibration source for generation of the first low-frequency vibrations during a first time interval; and

controlling the ultrasonic transmitter for transmission of the first ultrasonic waves during a second time interval that at least partially coincides with the first time interval;

receive ultrasonic receiver signals from the ultrasonic receiver, the ultrasonic receiver signals including signals corresponding to reflections of the first ultrasonic waves from a target object in contact with an outer surface of the apparatus; and

perform an authentication process based, at least in part, on the ultrasonic receiver signals.

2. The apparatus of claim 1 , wherein the low-frequency vibration source comprises one or more of a haptic device, a speaker, a piezoelectric actuator, an eccentric rotating mass or a linear resonant actuator.

3. The apparatus of claim 1 , wherein the low-frequency vibration source is configured to cause at least one of localized low-frequency vibration of only a portion of the apparatus or to cause global low-frequency vibration of the entire apparatus.

4. The apparatus of claim 1 , wherein the low-frequency vibration source and the ultrasonic transmitter are included in a single device.

5. The apparatus of claim 1 , wherein the control system is further configured to:

determine a contact quality metric corresponding to at least one of an image quality metric or a feature quality metric; and

determine whether to actuate the low-frequency vibration source based, at least in part, on the contact quality metric.

6. The apparatus of claim 1 , wherein the control system is configured to control the low-frequency vibration source to generate at least one of a single frequency or multiple frequencies.

7. The apparatus of claim 1 , wherein the control system is configured to control the low-frequency vibration source to generate low-frequency vibrations at least one of intermittently or continuously.

8. The apparatus of claim 1 , wherein the control system is configured to extract features from the ultrasonic receiver signals and wherein the authentication process is based, at least in part, on the features.

9. The apparatus of claim 8 , wherein the control system is configured to:

determine at least one feature quality metric;

determine whether the at least one feature quality metric is below a feature quality metric threshold; and, responsive to determining that the at least one feature quality metric is below the feature quality metric threshold,

controlling the low-frequency vibration source for generation of second low-frequency vibrations having a higher amplitude than the amplitude of the first low-frequency vibrations.

10. The apparatus of claim 1 , wherein the control system is configured to:

determine at least one feature quality metric;

use the feature quality metric as a feedback signal for the low-frequency vibration source; and

control the low-frequency vibration source based, at least in part, on the feedback signal.

11. The apparatus of claim 1 , wherein an ultrasonic transceiver layer comprises the ultrasonic transmitter and the ultrasonic receiver.

12. An authentication method, comprising:

controlling an ultrasonic transmitter for transmission of first ultrasonic waves;

controlling a low-frequency vibration source for generation of first low-frequency vibrations;

synchronizing the generation of the first low-frequency vibrations and the transmission of the first ultrasonic waves, wherein synchronizing the generation of first low-frequency vibrations and the transmission of first ultrasonic waves comprises:

controlling the low-frequency vibration source for generation of the first low-frequency vibrations during a first time interval; and

controlling the ultrasonic transmitter for transmission of the first ultrasonic waves during a second time interval that at least partially coincides with the first time interval;

receiving ultrasonic receiver signals from an ultrasonic receiver, the ultrasonic receiver signals including signals corresponding to reflections of the first ultrasonic waves from a target object in contact with an outer surface of an apparatus; and

performing an authentication process based, at least in part, on the ultrasonic receiver signals.

13. The method of claim 12 , further comprising detecting background noise in the ultrasonic receiver signals based, at least in part, on the first low-frequency vibrations.

14. The method of claim 12 , wherein controlling the low-frequency vibration source comprises at least one of causing localized low-frequency vibration of only a portion of the apparatus or global low-frequency vibration of the entire apparatus.

15. The method of claim 12 , wherein controlling the low-frequency vibration source and controlling the ultrasonic transmitter comprise controlling a single device.

16. The method of claim 12 , wherein controlling the low-frequency vibration source comprises causing the low-frequency vibration source to generate the first low-frequency vibrations in the plane of the outer surface or perpendicular to the plane of the outer surface.

17. The method of claim 12 , wherein controlling the low-frequency vibration source comprises causing the low-frequency vibration source to generate at least one of a single frequency or multiple frequencies.

18. The method of claim 12 , wherein controlling the low-frequency vibration source comprises causing the low-frequency vibration source to generate low-frequency vibrations at least one of intermittently or continuously.

19. The method of claim 12 , further comprising extracting features from the ultrasonic receiver signals, wherein the authentication process is based, at least in part, on the features.

20. The method of claim 19 , further comprising:

determining at least one feature quality metric;

using the feature quality metric as a feedback signal for the low-frequency vibration source; and

controlling the low-frequency vibration source based, at least in part, on the feedback signal.

21. The method of claim 19 , further comprising:

determining at least one feature quality metric;

determining whether the at least one feature quality metric is below a feature quality metric threshold; and, responsive to determining that the at least one feature quality metric is below the feature quality metric threshold,

controlling the low-frequency vibration source for generation of second low-frequency vibrations having a higher amplitude than the amplitude of the first low-frequency vibrations.

22. One or more non-transitory media having software stored thereon, the software including instructions for controlling one or more devices to perform an authentication method, the authentication method comprising:

controlling an ultrasonic transmitter for transmission of first ultrasonic waves;

controlling a low-frequency vibration source for generation of first low-frequency vibrations;

synchronizing the generation of the first low-frequency vibrations and the transmission of the first ultrasonic waves, wherein synchronizing the generation of first low-frequency vibrations and the transmission of first ultrasonic waves comprises:

controlling the low-frequency vibration source for generation of the first low-frequency vibrations during a first time interval; and

controlling the ultrasonic transmitter for transmission of the first ultrasonic waves during a second time interval that at least partially coincides with the first time interval;

receiving ultrasonic receiver signals from an ultrasonic receiver, the ultrasonic receiver signals including signals corresponding to reflections of the first ultrasonic waves from a target object in contact with an outer surface of an apparatus; and

performing an authentication process based, at least in part, on the ultrasonic receiver signals.

23. An apparatus, comprising:

transmitting means for transmitting ultrasonic waves in the range of 1 MHz to 30 MHz;

generating means for generating low-frequency vibrations in the range of 5 Hz to 2000 Hz;

receiving means for receiving ultrasonic waves; and

control means for:

controlling the transmitting means for transmission of first ultrasonic waves;

controlling the generating means for generation of first low-frequency vibrations;

synchronizing the generation of the first low-frequency vibrations and the transmission of the first ultrasonic waves, wherein synchronizing the generation of first low-frequency vibrations and the transmission of first ultrasonic waves comprises:

controlling the low-frequency vibration source for generation of the first low-frequency vibrations during a first time interval; and

controlling the ultrasonic transmitter for transmission of the first ultrasonic waves during a second time interval that at least partially coincides with the first time interval;

receiving ultrasonic receiver signals from the receiving means, the ultrasonic receiver signals including signals corresponding to reflections of the first ultrasonic waves from a target object in contact with an outer surface of the apparatus; and

performing an authentication process based, at least in part, on the ultrasonic receiver signals.