Signal control in micromachined ultrasonic transducer

• US 7,764,003 B2
• Filed: 04/03/2007
• Issued: 07/27/2010
• 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): Dougherty; Thomas M
• Application Number:
  US11/695,919
• Publication Number:
  US 20070228877A1
• Time in Patent Office: 1,211 Days
• Field of Search: 310/309, 600/437, 600/459, 367/140, 735/70
• 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 transducers (cMUT) uses signal control methods to reduce harmonic distortion of the output signal. The method uses an AC transmission input signal characterized with a frequency ω and takes the second-order frequency component with frequency 2ω, rather than the first-order frequency component with the base frequency ω, as the desired output pressure signal. A frequency ω is preferably equal to ω₀/2, where ω is the desired cMUT output frequency. Various examples of AC transmission input signals, in combination with or without a DC bias signal, that are suitable for producing a large second-order frequency component and small (ideally zero) first-order frequency component are disclosed.

Claims

1. A method for operating a capacitive micromachined ultrasonic transducer (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 V_tx(t) having a base frequency ω

to one of the first electrode and the second electrode of the cMUT, wherein V_tx(t) defines an output signal function V_tx(t)² which has a dominating second-order frequency component having an output signal frequency 2ω

; and

allowing the movable electrode of the cMUT to move in response to the applied transmission input signal to actuate the medium.

2. The method as recited in claim 1, wherein the base frequency ω

is about half of a desired operating frequency ω

₀ of the cMUT, such that the output signal frequency 2ω

is close to the desired operating frequency ω

₀.

3. The method as recited in claim 1, wherein the transmission input signal V_tx(t) is solely contributed by an AC signal source without applying a separate DC bias voltage in a transmission mode.

4. The method as recited in claim 1, wherein applying a transmission input signal V_tx(t) is enabled by switching the cMUT system to a transmission mode.

5. The method as recited in claim 1, wherein the cMUT system has a DC signal source providing a DC bias voltage which is switchably connected to one of the first electrode and the second electrode of the cMUT, the method further comprising:

disconnecting the DC bias voltage from the cMUT before applying the transmission input signal V_tx(t).

6. The method as recited in claim 1, further comprising:

before applying the transmission input signal V_tx(t) to the cMUT, shifting the transmission input signal to result in a shifted transmission input signal V_tx(t)−

V_dc; and

applying a DC bias voltage V_dc to the same electrode of the cMUT such that the net transmission input signal applied to the cMUT is V_tx(t).

7. The method as recited in claim 1, further comprising:

before applying the transmission input signal V_tx(t) to the cMUT, shifting the transmission input signal to result in a shifted transmission input signal V_tx(t)−

V_dc; and

applying a DC bias voltage −

V_dc to the other electrode of the cMUT such that the net transmission input signal applied to the cMUT is V_tx(t).

8. The method as recited in claim 1, wherein the output signal function V_tx(t)² has a negligible first-order frequency component of the base frequency ω

.

9. The method as recited in claim 1, wherein the transmission input signal V_tx(t) comprises a component W(t)×

V_tx sin(ω

t), where W(t) is a gated time window function.

10. The method as recited in claim 1, wherein the transmission input signal V_tx(t) comprises a Gaussian-shaped sine signal defined as

11. The method as recited in claim 1, wherein the transmission input signal V_tx(t) comprises an absolute-value signal.

12. The method as recited in claim 1, wherein the transmission input signal V_tx(t) comprises an absolute-value signal component W(t)×

2V_p-p×

abs(sin(ω

t)), where W(t) is a gated time window function, and V_p-p is a peak-to-peak amplitude.

13. The method as recited in claim 1, wherein the transmission input signal V_tx(t) comprises an absolute-value signal defined as

14. A method for operating a capacitive micromachined ultrasonic transducer (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:

generating a voltage signal V(t);

shifting the initial signal V(t) to obtain a shifted transmission input signal V(t)−

V_sh;

applying the shifted transmission input signal V(t)−

V_sh to one of the first electrode and the second electrode of the cMUT;

applying a DC bias voltage V_dc to one of the first electrode and the second electrode of the cMUT such that the net transmission input signal applied on the cMUT is V_tx(t)=V(t)−

V_sh+V_dc, or V_tx(t)=V(t)−

V_sh−

V_dc, wherein V_tx(t) defines an output signal function V_tx(t)² which has a dominating second-order frequency component having an output signal frequency 2ω

; and

allowing the movable electrode of the cMUT to move in response to the applied transmission input signal to actuate the medium.

15. The method as recited in claim 14, wherein the DC bias voltage V_dc and the shifted transmission input signal V(t)−

V_sh are applied to the same electrode of the cMUT, V_dc is substantially the same as V_sh to cancel each other, such that V_tx(t)=V(t)−

V_sh+V_dc is approximately the same as the V(t).

16. The method as recited in claim 14, wherein the DC bias voltage V_dc and the shifted transmission input signal V(t)−

V_sh are applied to the opposite electrodes of the cMUT, V_dc is substantially the same as −

V_sh to cancel each other, such that V_tx(t)=V(t)−

V_sh−

V_dc is approximately the same as the V(t).

17. The method as recited in claim 14, wherein generating the voltage signal V(t) comprises amplifying an interim voltage signal V_int(t).

18. The method as recited in claim 14, further comprising:

generating an initial voltage signal V_i(t) having a voltage swing from −

V_i to +V_i;

converting the initial voltage signal V_i(t) to an absolute-value voltage signal |V_i(t)| having a voltage swing from 0 to V_i;

generating an interim voltage signal V_int(t) by shifting the absolute-value voltage signal |V_i(t)| to obtain the interim voltage signal V_int(t) as defined by |V_i(t)|−

Vs; and

amplifying the interim voltage signal V_int(t) to obtain the voltage signal V(t).

19. 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;

an AC signal source for generating the transmission input signal to be applied to one of the first electrode and the second electrode of the cMUT; and

a DC signal source for providing a DC bias voltage to be applied to one of the first electrode and the second electrode of the cMUT, wherein, when applied, the transmission input signal and the DC bias voltage together result in a total transmission input signal V_tx(t) having a base frequency ω

, and wherein V_tx(t) defines an output signal function V_tx(t)² which has a dominating second-order frequency component having an output signal frequency 2ω

.

20. The cMUT as recited in claim 19, wherein the DC signal source and the DC bias voltage is switchably connected to the cMUT, the DC bias voltage being disconnected to the cMUT in the transmission mode.