Modulation in micromachined ultrasonic transducers

• US 7,956,510 B2
• Filed: 04/03/2007
• Issued: 06/07/2011
• Est. Priority Date: 04/04/2006
• Status: Active Grant

• Current Assignee: Kolo Medical, Ltd.
• Original Assignee: Kolo Technologies, Inc.
• Inventors: Huang, Yongli
• Primary Examiner(s): Budd; Mark
• Application Number:
  US12/296,099
• Publication Number:
  US 20090048522A1
• Time in Patent Office: 1,526 Days
• Field of Search: 310/309, 600/437, 600/459
• US Class Current: 310/309
• CPC Class Codes: B06B 1/0238 of a single frequency, e.g. a sine-wave
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: G01N 29/2406 Electrostatic or capacitive probes, e.g. electret or cMUT-probes
• CPC Class Codes: Y10T 29/49005 Acoustic transducer

Abstract

A capacitive micromachined ultrasonic transducer (cMUT) system uses a modulation technique to increase cMUT sensitivity. An AC carrier signal is applied to the cMUT through a modulation signal port to modulate the signal. The higher frequency of the AC carrier signal carries the real signal to a high frequency range to increase the output current signal level. The real signal is later recovered by demodulation. The technique is applicable in both the reception mode and the transmission mode.

Claims

1. A capacitive micromachined ultrasonic transducer (cMUT) system comprising:

a cMUT having a first electrode and a second electrode;

at least one of a transmission input signal port and a reception signal port connected to one of the first electrode and the second electrode, wherein the transmission input signal port is adapted for applying a transmission input signal to the cMUT in a transmission mode, and the reception signal port is adapted for receiving an output signal from the cMUT in a reception mode, and wherein the transmission input signal has a non-modulated transmission frequency ftx, and the output signal has a non-modulated reception frequency frx; and

an AC signal source for generating an AC carrier signal to be applied to the cMUT through a modulation signal port connected to one of the first electrode and the second electrode of the cMUT, wherein the AC carrier signal has a carrier frequency fcarrier which is different from the non-modulated transmission frequency ftx and the non-modulated reception frequency fxr.

2. The cMUT system as recited in claim 1, comprising both the transmission input signal port and the reception signal port, and a port switch to switch between the transmission input signal port and the reception signal port.

3. The cMUT system as recited in claim 1, wherein the modulation signal port and the at least one of the transmission input signal port and the reception signal port are connected to the same electrode of the cMUT.

4. The cMUT system as recited in claim 1, wherein the at least one of the transmission input signal port and the reception signal port are connected to the first electrode of the cMUT, and the modulation signal port is connected to the second electrode of the cMUT.

5. The cMUT system as recited in claim 1, wherein the modulation signal port is directly connected to the one of the first electrode and the second electrode of the cMUT.

6. The cMUT system as recited in claim 1, wherein the modulation signal port is connected to the one of the first electrode and the second electrode of the cMUT through a shorting protection circuit.

7. The cMUT system as recited in claim 1, further comprising a DC signal source for generating a DC bias signal.

8. The cMUT system as recited in claim 7, wherein the DC bias signal is applied together with the AC carrier signal as a combined modulation signal to the cMUT.

9. The cMUT system as recited in claim 1, wherein, when the cMUT is at a reception operation mode, the output signal has a real signal component and a modulated signal component carrying the real signal component, which contains information of a pressure signal sensed by the cMUT, the cMUT system further comprising:

a demodulator connected to the reception port for extracting the real signal component from the modulated signal component.

10. The cMUT system as recited in claim 1, wherein, when the cMUT is at a reception operation mode, the output signal has a non-modulated signal component and a modulated signal component carrying a real signal component containing information of a pressure signal sensed by the cMUT, the cMUT system further comprising:

a band-pass filter connected to the reception port for filtering out the non-modulated signal component.

11. The cMUT system as recited in claim 1, wherein the AC carrier signal has a frequency significantly higher than an operating frequency of the cMUT.

12. The cMUT system as recited in claim 1, wherein the AC carrier signal has an optimal frequency at which the AC carrier signal and a capacitance change of the cMUT generates a modulated signal component at desirably high signal level.

13. The cMUT system as recited in claim 1, further comprising:

an inductive device connected to the cMUT for tuning impedance of the cMUT.

14. The cMUT system as recited in claim 13, wherein the inductive device is micromachined on a substrate.

15. A capacitive micromachined ultrasonic transducer (cMUT) system comprising:

a cMUT array having a plurality of cMUTs built on a first substrate, each cMUT having a first electrode and a second electrode;

at least one of a transmission input signal port and a reception signal port connected to one of the first electrode and the second electrode of each cMUT, wherein the transmission input signal port is adapted for applying a transmission input signal to the connected cMUT in a transmission mode, and the reception signal port is adapted for receiving an output signal from the connected cMUT in a reception mode; and

an AC signal source for generating an AC carrier signal to be applied to each cMUT through a modulation signal port connected to one of the first electrode and the second electrode of each cMUT; and

an inductive device array having a plurality of inductive devices built on a second substrate, each inductive device being connected to one of the plurality of cMUTs in the cMUT array, each inductive device having an inductance suitable for tuning impedance of the respective cMUT.

16. The cMUT system as recited in claim 15, wherein the inductive device array is micromachined on the second substrate.

17. The cMUT system as recited in claim 15, wherein the inductive device array and the cMUT array are wire-bonded to electrically connect each inductive device and the respective cMUT.

18. The cMUT system as recited in claim 15, wherein the inductive device array and the cMUT array are directly bonded through contact bonding pads to electrically connect each inductive device and the respective cMUT.

19. A method for transmitting an ultrasonic signal using a cMUT system including a cMUT having a first electrode and a second electrode, at least one of the first electrode and the second electrode being movable and interfacing with a medium, the method comprising:

applying a transmission input signal having a transmission frequency to one of the first electrode and the second electrode of the cMUT;

applying an AC modulation signal having a carrier frequency to one of the first electrode and the second electrode of the cMUT, wherein the carrier frequency is higher than the transmission frequency; and

allowing the movable electrode of the cMUT to move in response to the applied transmission input signal and the AC modulation signal to generate an ultrasonic wave in the medium.

20. The method as recited in claim 19, wherein the transmission frequency is about half of an operating frequency of the cMUT.

21. The method as recited in claim 19, further comprising:

selecting an amplitude of the AC modulation signal such that a desired DC bias pressure is applied on the cMUT.

22. A method for sensing a pressure using a cMUT system including a cMUT having a first electrode and a second electrode, at least one of the first electrode and the second electrode being movable, the method comprising:

allowing a pressure signal to be applied on the movable electrode of the cMUT to generate a capacitance change of the cMUT, the capacity change having a pressure signal frequency frx;

applying an AC modulation signal having a carrier frequency fcarrier;

receiving a first output signal which is contributed by both the capacitance change and the AC modulation signal, wherein the first output signal has a modulated component at the modulated frequency fcarrier−

frx or fcarrier+frx; and

demodulating the first output signal to generate a second output signal having a component at the pressure signal frequency frx.

23. The method as recited in claim 22, wherein the carrier frequency fcarrier is significantly higher than the pressure signal frequency frx.

24. The method as recited in claim 22, wherein the AC modulation signal has an optimal frequency at which the modulated component at the modulated frequency fcarrier−

frx or fcarrier+frx has a desirably high signal level.

25. The method as recited in claim 22, wherein the pressure signal frequency frx is in the range of Hz≦

fr≦

20 kHz.