Bias control of electrostatic transducers

• US 20030048698A1
• Filed: 09/07/2001
• Published: 03/13/2003
• Est. Priority Date: 09/07/2001
• Status: Active Grant

• Current Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Original Assignee: Siemens Medical Systems, Inc. (Siemens AG)
• Inventors: Bolorforosh, Mirsaid Seyed, Phelps, Robert N., Barnes, Stephen R.
• Granted Patent: US 6,795,374 B2
• Time in Patent Office: Days
• US Class Current: 367/181
• CPC Class Codes: B06B 1/0215 for generating pulses, e.g. bursts of oscillations, envelopes
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: B06B 2201/51 Electrostatic transducer
• CPC Class Codes: B06B 2201/76 Medical, dental
• CPC Class Codes: G01S 15/8915 using a transducer array
• CPC Class Codes: G01S 15/895 characterised by the transmitted frequency spectrum
• CPC Class Codes: G01S 7/52033 Gain control of receivers for seismic signals G01V1/245
• CPC Class Codes: G01S 7/52038 involving non-linear properties of the propagation medium or of the reflective target
• CPC Class Codes: G01S 7/52039 exploiting the non-linear response of a contrast enhancer, e.g. a contrast agent diagnostic techniques involving the use of contrast agents A61B8/481
• CPC Class Codes: H04R 2201/021 Transducers or their casings adapted for mounting in or to a wall or ceiling
• CPC Class Codes: H04R 23/00 Transducers other than those covered by groups H04R9/00 - H04R21/00 diaphragms for transducers of the distributed-mode type H04R7/045

Abstract

A method and system for controlling bias voltage for use with an electrostatic transducer are provided. The bias voltage is dynamically varied or set as a function of imaging mode, depth gain compensation, elevational apodization, azimuthal apodization, timing with respect to the transmit waveform, center frequency of transmit and receive waves and desired modulation. Opposite polarity on sub-elements is also provided for removing signals from electromagnetic interference and crosstalk between elements.

Claims

1. An ultrasound method for operating a multiple element capacitive membrane ultrasound transducer (cMUT), the method comprising:

(a) applying a bias voltage to a multiple element electrostatic transducer during one of a transmit and a receive event; and

(b) varying the bias voltage as a function of time.

2. The method of claim 1 wherein (a) comprises applying the bias voltage to each of a plurality of elements.

3. The method of claim 1 wherein (a) comprises applying the varied bias voltage during the receive event and further comprising:

(c) applying a second bias voltage in a transmit mode different than the bias voltages of (a).

4. The method of claim 3 wherein (a) and (c) comprise applying the second bias voltage for transmission at a first frequency and applying the bias voltage of (a) for reception at a second frequency that is a harmonic of the first frequency.

5. The method of claim 1 further comprising:

(c) applying aperture apodization as a function of different bias voltages for each of the multiple elements.

6. The method of claim 1 wherein (b) comprises controlling gain as a function of target depth.

7. The method of claim 1 wherein (b) comprises varying the bias voltage during a single receive event.

8. The method of claim 1 wherein (b) comprises increasing the bias voltage with increasing time.

9. The method of claim 1 further comprising:

(c) applying different bias voltages to different elevationally spaced sub-elements of one of the multiple elements.

10. The method of claim 9 further comprising:

(d) varying the bias voltage of (c) as a function of an imaging mode of operation.

11. The method of claim 5 further comprising:

(d) varying the bias voltage of (c) as a function of an imaging mode of operation.

12. The method of claim 3 further comprising:

(d) applying a transmit waveform to one of the multiple elements; and

(e) changing from the bias voltage of (a) to the second bias voltage of (c) substantially simultaneously with a beginning of (d).

13. The method of claim 1 further comprising:

(c) generating a radio frequency signal; and

(d) applying the radio frequency signal with the bias voltage signal of (a).

14. The method of claim 1 further comprising:

(c) reversing a polarity of the bias voltage of (a) for a sub-element of one of the multiple elements.

15. An ultrasound multiple element capacitive membrane ultrasound transducer (cMUT) system, the system comprising:

at least one membrane ultrasound element configured to receive acoustic energy and output a responsive electrical signal; and

a voltage bias source connected with the at least one membrane ultrasound element, the voltage bias source operative to vary a bias voltage as a function of time during one of a transmit event and a receive event.

16. The system of claim 15 wherein the voltage bias source comprises a digital-to-analog converter.

17. The system of claim 15 wherein the voltage bias source is operative to vary the bias during a receive event and apply a second bias voltage in a transmit mode, the second bias voltage different than the bias voltages during a receive mode.

18. The system of claim 17 wherein the voltage bias source is operative to apply the second bias voltage for transmission at a first frequency and applying the bias voltage for reception at a second frequency that is a harmonic of the first frequency.

19. The system of claim 15 wherein the voltage bias source is operative to apply aperture apodization as a function of different bias voltages for different ones of the multiple elements.

20. The system of claim 15 wherein the voltage bias source is operative to varying the bias voltage during a single receive event.

21. The system of claim 15 wherein the voltage bias source is operative to increase the bias voltage with increasing time.

22. The system of claim 15 wherein the at least one membrane ultrasound element comprises at least two elevationally spaced sub-elements;

and wherein the voltage bias source is operative to apply different bias voltages to different ones of the elevationally spaced sub-elements.

23. The system of claim 15 wherein the voltage bias source is operative to vary the bias voltage as a function of an imaging mode of operation.

24. The system of claim 17 further comprising:

a beamformer operative to apply a transmit waveform to the at least one membrane ultrasound element;

wherein the voltage bias source is operative to change from the bias voltage of receive mode to the second bias voltage of the transmit mode substantially simultaneously with a beginning of the transmit waveform.

25. The system of claim 15 further comprising:

a signal source connected with the bias voltage source to the at least one-membrane ultrasound element, the signal source operative to generate a radio frequency signal.

26. The system of claim 15 wherein the at least one membrane ultrasound element comprises at least two sub-elements connected with the bias voltage source with a reversed polarity.

27. An ultrasound method for operating a multiple element capacitive membrane ultrasound transducer (cMUT), the method comprising:

(a) applying a bias voltage to a multiple element electrostatic transducer; and

(b) applying different bias voltages to different elevationally spaced sub-elements of one of the multiple elements.

28. The method of claim 27 wherein (a) comprises applying a plurality of bias voltages to each of a plurality of elements including elevationally spaced sub-elements.

29. The method of claim 27 further comprising:

(c) applying different bias voltages in a transmit than in receive modes.

30. The method of claim 29 wherein (c) comprises applying a first set of bias voltages pursuant to (b) for transmission at a first frequency and applying a second set of bias voltages pursuant to (b) for reception at a second frequency that is a harmonic of the first frequency.

31. The method of claim 27 further comprising:

(c) applying azimuthal aperture apodization as a function of different bias voltages for each of the multiple elements.

32. The method of claim 27 wherein (b) comprises elevationally apodizing the sub-elements.

33. The method of claim 27 further comprising:

(c) varying at least one of the bias voltages of (b) as a function of time.

34. The method of claim 27 further comprising:

(d) varying at least one of the bias voltages of (b) as a function of an imaging mode of operation.

35. The method of claim 31 further comprising:

(d) varying at least one of the bias voltages of (c) as a function of an imaging mode of operation.

36. The method of claim 29 further comprising:

(d) applying a transmit waveform to one of the multiple elements; and

(e) changing from the bias voltages of (b) to the bias voltages of (c) substantially simultaneously with a beginning of (d).

37. The method of claim 27 further comprising:

(c) generating a radio frequency signal; and

(d) applying the radio frequency signal with at least one of the bias voltages of (b).

38. The method of claim 27 further comprising:

(c) applying at least one of the bias voltages of (b) for a sub-element with both a first polarity and a reversed polarity.

39. An ultrasound multiple element capacitive membrane ultrasound transducer (cMUT) system, the system comprising:

at least one membrane ultrasound element comprising at least two elevationally spaced sub-elements; and

a voltage bias source connected with the at least one membrane ultrasound element, the voltage bias source operative to apply different bias voltages to different ones of the elevationally spaced sub-elements.

40. The system of claim 39 wherein the voltage bias source comprises a digital-to-analog converter.

41. The system of claim 39 wherein the voltage bias source is operative to applying different bias voltages in a transmit mode than in a receive mode.

42. The system of claim 41 wherein the voltage bias source is operative to apply bias voltages for transmission at a first frequency and applying bias voltages for reception at a second frequency that is a harmonic of the first frequency.

43. The system of claim 39 wherein the voltage bias source is operative to apply azimuthal aperture apodization as a function of different bias voltages for different ones of the multiple elements.

44. The system of claim 39 wherein the voltage bias source is operative to vary at least one of the bias voltages as a function of time.

45. The system of claim 39 wherein the voltage bias source is operative to vary at least one of the bias voltages as a function of an imaging mode of operation.

46. The system of claim 41 further comprising:

a beamformer operative to apply a transmit waveform to the at least one membrane ultrasound element;

wherein the voltage bias source is operative to change from the bias voltages of receive mode to the bias voltages of the transmit mode substantially simultaneously with a beginning of the transmit waveform.

47. The system of claim 39 further comprising:

a signal source connected with the bias voltage source to the at least one-membrane ultrasound element, the signal source operative to generate a radio frequency signal.

48. The system of claim 39 wherein the at least one membrane ultrasound element comprises at least first and second bias sub-elements, the first bias sub-element connected with the bias voltage source with a reversed polarity than the second bias sub-element.

49. An ultrasound method for operating a multiple element capacitive membrane ultrasound transducer (cMUT), the method comprising:

(a) applying a bias voltage to a multiple element electrostatic transducer; and

(b) varying the bias voltage as a function of an imaging mode of operation.

50. The method of claim 49 further comprising:

(c) applying aperture apodization as a function of different bias voltages for each of the multiple elements;

wherein the different bias voltages for each of the multiple elements is varied in accordance with (b).

51. The method of claim 49 further comprising:

(c) applying different bias voltages to different elevationally spaced sub-elements of one of the multiple elements;

wherein the different bias voltages of (c) are varied in accordance with (b).

52. An ultrasound multiple element capacitive membrane ultrasound transducer (cMUT) system, the system comprising:

at least one membrane ultrasound element; and

a voltage bias source connected with the at least one membrane ultrasound element, the voltage bias source operative to vary a bias voltage as a function of an imaging mode of operation.

53. The system of claim 52 wherein the at least one membrane ultrasound element comprises at least two elevationally spaced sub-elements;

and wherein the voltage bias source is operative to apply different bias voltages to different ones of the elevationally spaced sub-elements.

54. An ultrasound method for operating a multiple element capacitive membrane ultrasound transducer (cMUT), the method comprising:

(a) applying a bias voltage to a multiple element electrostatic transducer; and

(b) generating a radio frequency signal; and

(c) applying the radio frequency signal with the bias voltage.

55. The method of claim 54 wherein (c) comprises applying the radio frequency signal in a receive mode.

56. An ultrasound multiple element capacitive membrane ultrasound transducer (cMUT) system, the system comprising:

at least one membrane ultrasound element;

a voltage bias source connected with the at least one membrane ultrasound element; and

a signal source connected with the bias voltage source to the at least one-membrane ultrasound element, the signal source operative to generate a radio frequency signal.

57. The system of claim 56 wherein the signal source is operative to generate the radio frequency signal while the system is in a receive mode.

58. An ultrasound method for operating a multiple element capacitive membrane ultrasound transducer (cMUT), the method comprising:

(a) applying a first bias voltage to at least one of the multiple elements in a receive mode;

(b) applying a second bias voltage in a transmit mode, the second bias voltage different than the first bias voltages;

(c) applying a transmit waveform to one of the multiple elements in the transmit mode; and

(d) changing from the first bias voltage to the second bias voltage substantially simultaneously with a beginning of the transmit waveform.

59. The method of claim 58 wherein (a) and (b) comprise applying the first and second bias voltages, respectively, to each of a plurality of the multiple elements.

60. The method of claim 58 wherein (d) comprises changing from the first bias voltage to the second bias voltage in synchronization with a leading edge of the transmit waveform.

61. The method of claim 58 wherein (b) comprises applying the second bias voltage for transmission at a first frequency and (a) comprises applying the first bias voltage for reception at a second frequency that is a harmonic of the first frequency.

62. The method of claim 58 further comprising:

(e) applying aperture apodization as a function of different bias voltages for each of the multiple elements.

63. The method of claim 58 further comprising:

(e) varying the first bias voltage as a function of depth.

64. The method of claim 58 wherein the second bias voltage is less than the first bias voltage and the beginning of the transmit waveform comprises a decreasing voltage.

65. The method of claim 58 further comprising:

(e) applying different bias voltages at one time to different elevationally spaced sub-elements of one of the multiple elements.

66. The method of claim 58 further comprising:

(e) varying the first and second bias voltages as a function of an imaging mode of operation.

67. The method of claim 58 further comprising:

(e) varying the first bias voltage as a function of time during a receive event.

68. The method of claim 58 further comprising:

(e) generating a radio frequency signal; and

(f) applying the radio frequency signal with the first bias voltage.

69. The method of claim 58 further comprising:

(e) reversing a polarity of the first bias voltage for a sub-element of one of the multiple elements.

70. An ultrasound multiple element capacitive membrane ultrasound transducer (cWT) system, the system comprising:

at least one membrane ultrasound element;

a beamformer operative to apply a transmit waveform to the at least one membrane ultrasound element; and

a voltage bias source connected with the at least one membrane ultrasound element, the voltage bias source operative to change from a first bias voltage of a receive mode to a second different bias voltage of a transmit mode substantially simultaneously with a beginning of the transmit waveform.

71. The system of claim 70 wherein the voltage bias source comprises a digital-to-analog converter.

72. The system of claim 70 wherein the voltage bias source is operative to apply the second bias voltage for transmission at a first frequency and applying the first bias voltage for reception at a second frequency that is a harmonic of the first frequency.

73. The system of claim 70 wherein the voltage bias source is operative to apply aperture apodization as a function of different bias voltages for different ones of the multiple elements.

74. The system of claim 70 wherein the voltage bias source is operative to changing from the first bias voltage to the second bias voltage in synchronization with a leading edge of the transmit waveform.

75. The system of claim 70 wherein the at least one membrane ultrasound element comprises at least two elevationally spaced sub-elements;

and wherein the voltage bias source is operative to apply different bias voltages to different ones of the elevationally spaced sub-elements.

76. The system of claim 70 wherein the voltage bias source is operative to vary the bias voltage in the receive mode as a function of an imaging mode of operation.

77. The system of claim 70 wherein the voltage bias source is operative to vary the first bias voltage as a function of time during a receive event.

78. The system of claim 70 further comprising:

a signal source connected with the bias voltage source to the at least one-membrane ultrasound element, the signal source operative to generate a radio frequency signal.

79. The system of claim 70 wherein the at least one membrane ultrasound element comprises at least two sub-elements connected with the bias voltage source with a reversed polarity.

80. An ultrasound method for operating a multiple element capacitive membrane ultrasound transducer (cMUT), the method comprising:

(a) applying a first bias voltage to a first sub-element of at least one element of the multiple element electrostatic transducer array;

(b) reversing a polarity of the first bias voltage for a second sub-element of the at least one element.

81. The method of claim 80 wherein (a) comprises applying the bias voltage at positive and negative polarity to each of a plurality of elements.

82. The method of claim 80 wherein (a) comprises applying the first bias voltage in a receive mode;

further comprising;

(c) applying a second bias voltage in a transmit mode, the second bias voltage different than the first bias voltage.

83. The method of claim 82 wherein (c) comprises applying the second bias voltage for transmission at a first frequency and (a) comprises applying the first bias voltage for reception at a second frequency that is a harmonic of the first frequency.

84. The method of claim 81 further comprising:

(c) applying aperture apodization as a function of different bias voltages for each of the multiple elements.

85. The method of claim 80 wherein (b) comprises providing the reversed polarity with a separate voltage source.

86. The method of claim 80 further comprising:

(c) inputting signals from the first and second sub-elements to different inputs of a differential amplifier.

87. The method of claim 81 wherein each of the plurality of elements comprises first and second sub-elements, the first and second sub-elements comprising a plurality of separate interconnected electrodes;

and further comprising;

(d) balancing the electromagnetic coupling between the electrodes of the plurality of elements as a function of spatial off-set of the electrodes of adjacent elements.

88. The method of claim 80 further comprising:

(c) applying different bias voltages to different elevationally spaced sub-elements of one of the multiple elements.

89. The method of claim 80 further comprising:

(d) varying the first bias voltage as a function of an imaging mode of operation.

90. The method of claim 82 further comprising:

(d) applying a transmit waveform to the at least one element; and

(e) changing from the first bias voltage to the second bias voltage substantially simultaneously with a beginning of (d).

91. The method of claim 80 further comprising:

(c) generating a radio frequency signal; and

(d) applying the radio frequency signal with the first bias voltage.

92. The method of claim 80 further comprising:

(c) varying the first bias voltage as a function of time in a receive mode.

93. An ultrasound multiple element capacitive membrane ultrasound transducer (cMUT) system, the system comprising:

at least one membrane ultrasound element comprising first and second sub-elements; and

a voltage bias source connected with the first sub-element with an reverse polarity to the second sub-element.

94. The system of claim 93 wherein the voltage bias source comprises a digital-to-analog converter having positive and negative outputs.

95. The system of claim 93 wherein the voltage bias source comprises first and second voltage sources, the first voltage source operative to output a positive voltage and the second voltage source operative to output a negative voltage.

96. The system of claim 93 further comprising:

a differential amplifier having positive and negative inputs connected with the first and second sub-elements, respectively.

97. The system of claim 93 further comprising:

a transmit beamformer having first and second outputs connected with the first and second sub-elements, respectively, the first output an inverted output of the second output.

98. The system of claim 93 wherein each of multiple elements comprise first and second sub-elements, the first and second sub-elements comprising a plurality of separate interconnected electrodes;

and

wherein electrodes of adjacent elements are off-set to balance the electromagnetic coupling between the electrodes the adjacent elements.

99. The system of claim 93 wherein the voltage bias source is operative to apply a first bias voltage in a receive mode and a second bias voltage in a transmit mode, the second bias voltage different than the first bias voltage.

100. The system of claim 99 wherein the voltage bias source is operative to apply the second bias voltage for transmission at a first frequency and applying the first bias voltage for reception at a second frequency that is a harmonic of the first frequency.

101. The system of claim 93 wherein the voltage bias source is operative to apply aperture apodization as a function of different bias voltages for different ones of the multiple elements.

102. The system of claim 93 wherein the at least one membrane ultrasound element comprises at least two elevationally spaced sub-elements;

and wherein the voltage bias source is operative to apply different bias voltages to different ones of the elevationally spaced sub-elements.

103. The system of claim 93 wherein the voltage bias source is operative to vary a bias voltage as a function of an imaging mode of operation.

104. The system of claim 99 further comprising:

a beamformer operative to apply a transmit waveform to the at least one membrane ultrasound element;

wherein the voltage bias source is operative to change from the first bias voltage to the second bias voltage substantially simultaneously with a beginning of the transmit waveform.

105. The system of claim 93 further comprising:

a signal source connected with the bias voltage source to the at least one-membrane ultrasound element, the signal source operative to generate a radio frequency signal.

106. The system of claim 93 wherein the voltage bias source is operative to vary a bias voltage as a function of time during a receive event.