Multiple-frequency ultrasonic sensor system

1. An apparatus comprising:

an ultrasonic sensor system, comprising:

an ultrasonic transceiver layer;

a thin-film transistor (TFT) layer proximate a first side of the ultrasonic transceiver layer; and

a high-impedance layer proximate a first area of a second side of the ultrasonic transceiver layer, wherein the high-impedance layer has a higher acoustic impedance than an adjacent layer and wherein the first area corresponds to a low-frequency area of the ultrasonic sensor system.

2. The apparatus of claim 1 , wherein the high-impedance layer is not proximate a second area of the ultrasonic transceiver layer and wherein the second area corresponds to a high-frequency area of the ultrasonic sensor system.

3. The apparatus of claim 1 , wherein the TFT layer has a first thickness in the first area of the ultrasonic sensor system and wherein the TFT layer has a second thickness in a second area of the ultrasonic sensor system, the second area corresponding to a high-frequency area.

4. The apparatus of claim 1 , wherein the TFT layer has a thickness in a range of 50 to 1000 microns.

5. The apparatus of claim 1 , wherein the ultrasonic transceiver layer has a first thickness in the low-frequency area and a second thickness in a high-frequency area.

6. The apparatus of claim 1 , wherein the ultrasonic transceiver layer has first through N th thicknesses in first through N th areas of the ultrasonic sensor system, each of the first through N th areas corresponding with one of first through N th peak frequencies.

7. The apparatus of claim 1 , further comprising an adhesive layer residing between the ultrasonic transceiver layer and the high-impedance layer, wherein the adhesive layer has a first thickness in the low-frequency area and a second thickness in a high-frequency area.

8. The apparatus of claim 7 , wherein the adhesive layer has first through N th thicknesses in first through N th areas of the ultrasonic sensor system, each of the first through N th areas corresponding with one of first through N th peak frequencies.

9. The apparatus of claim 1 , wherein the high-impedance layer comprises a high-impedance ink.

10. The apparatus of claim 9 , wherein the high-impedance ink functions as an acoustic layer and as a conductive layer.

11. The apparatus of claim 1 , further comprising a backer layer, wherein the high-impedance layer resides between the backer layer and the ultrasonic transceiver layer.

12. The apparatus of claim 11 , wherein the backer layer has a first thickness in the low-frequency area and a second thickness in a high-frequency area.

13. The apparatus of claim 12 , wherein the backer layer has first through N th thicknesses in first through N th areas of the ultrasonic sensor system, each of the first through N th areas corresponding with one of first through N th peak frequencies.

14. The apparatus of claim 11 , wherein the high-impedance layer has a higher acoustic impedance than the backer layer.

15. The apparatus of claim 11 , further comprising a conductive layer residing between the high-impedance layer and the first area of the second side of the ultrasonic transceiver layer.

16. The apparatus of claim 1 , further comprising a conductive layer residing between the ultrasonic transceiver layer and the high-impedance layer, wherein the conductive layer has a first thickness in the low-frequency area of the ultrasonic sensor system and wherein the conductive layer has a second thickness in a high-frequency area of the ultrasonic sensor system.

17. The apparatus of claim 16 , wherein the conductive layer has first through N th thicknesses in first through N th areas of the ultrasonic sensor system, each of the first through N th areas corresponding with one of first through N th peak frequencies.

18. The apparatus of claim 1 , wherein the high-impedance layer is adjacent the first area of the second side of the ultrasonic transceiver layer.

19. The apparatus of claim 1 , further comprising a light source system configured to cause photoacoustic emissions in a target object.

20. The apparatus of claim 1 , further comprising a display stack proximate the TFT layer, wherein the TFT layer resides between the ultrasonic transceiver layer and the display stack.

21. The apparatus of claim 1 , further comprising a control system configured to:

control the ultrasonic transceiver layer to transmit an ultrasonic wave, a first portion of the ultrasonic wave being transmitted in a first direction through the TFT layer, the first portion of the ultrasonic wave comprising a first peak frequency; and

receive, from the ultrasonic transceiver layer, first signals corresponding to reflections of the first portion of the ultrasonic wave from a surface of a portion of a target object positioned on an outer surface of the apparatus.

22. The apparatus of claim 21 , wherein the control system is configured to perform an authentication process that is based, at least in part, on the first signals.

23. The apparatus of claim 21 , wherein the control system is configured to obtain fingerprint data based on portions of the first signals received within a time interval corresponding with fingerprints.

24. The apparatus of claim 21 , wherein a second portion of the ultrasonic wave is transmitted in a second direction towards the high-impedance layer and wherein the high-impedance layer and one or more layers between the high-impedance layer and the ultrasonic transceiver layer are configured to cause a reflected second portion of the ultrasonic wave to comprise a second peak frequency that is lower than the first peak frequency.

25. The apparatus of claim 21 , wherein the control system is configured to:

receive, from the ultrasonic transceiver layer, second signals corresponding to reflections of the second portion of the ultrasonic wave from an interior of the portion of the target object; and

perform an authentication process that is based, at least in part, on the second signals.

26. The apparatus of claim 25 , wherein the second signals comprise sub-epidermal layer information corresponding to reflections of the second ultrasonic wave received from the portion of the target object within a time interval corresponding with a sub-epidermal region.

27. The apparatus of claim 1 , wherein the apparatus resides within a mobile device.

28. A method of controlling an ultrasonic sensor system, the method comprising:

controlling an ultrasonic transceiver layer to transmit an ultrasonic wave, a first portion of the ultrasonic wave being transmitted in a first direction through a thin-film transistor (TFT) layer, the first portion of the ultrasonic wave comprising a first peak frequency, wherein a second portion of the ultrasonic wave is transmitted in a second direction towards a high-impedance layer and wherein the high-impedance layer and one or more layers between the high-impedance layer and the ultrasonic transceiver layer are configured to cause a reflected second portion of the ultrasonic wave to comprise a second peak frequency that is lower than the first peak frequency; and

receiving, from the ultrasonic transceiver layer, first signals corresponding to reflections of the first portion of the ultrasonic wave from a surface of a portion of a target object positioned on an outer surface of an apparatus that includes the ultrasonic sensor system;

receiving, from the ultrasonic transceiver layer, second signals corresponding to reflections of the second portion of the ultrasonic wave from an interior of the portion of the target object; and

performing an authentication process that is based, at least in part, on the first signals and the second signals.

29. The method of claim 28 , further comprising obtaining fingerprint data based on portions of the first signals received within a time interval corresponding with fingerprints.

30. The method of claim 28 , wherein the second signals comprise sub-epidermal layer information corresponding to reflections of the second ultrasonic wave received from the portion of the target object within a time interval corresponding with a sub-epidermal region.