Ultrasonic wave transducer system and ultrasonic wave transducer

• US 20020007118A1
• Filed: 07/09/2001
• Published: 01/17/2002
• Est. Priority Date: 03/15/2000
• Status: Active Grant

• Current Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Original Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Inventors: Adachi, Hideo, Wakabayashi, Katsuhiro
• Granted Patent: US 6,443,900 B2
• Time in Patent Office: Days
• US Class Current: 600/443
• CPC Class Codes: B06B 1/0611 in a pile
• CPC Class Codes: B06B 1/0681 and a damping structure
• CPC Class Codes: G01S 15/8922 the array being concentric or annular
• CPC Class Codes: G01S 15/895 characterised by the transmitted frequency spectrum
• CPC Class Codes: G10K 11/30 using refraction, e.g. acoustic lenses
• CPC Class Codes: G10K 11/32 characterised by the shape of the source

Abstract

There is disclosed an ultrasonic transducer system for harmonic imaging, comprising: an ultrasonic transducer comprising a transmitting ultrasonic vibrator for transmitting a fundamental ultrasound having a center frequency f₀, and a receiving ultrasonic vibrator for receiving a harmonic signal having a center frequency nf₀ (n is an integer of 2 or more); and control means for controlling the ultrasonic transducer, wherein the transmitting ultrasonic vibrator comprises a transmitting piezoelectric resonator, the receiving ultrasonic vibrator comprises a receiving piezoelectric resonator, the transmitting and receiving piezoelectric resonators are superposed in layers and disposed, and the control means supplies a drive signal to the transmitting piezoelectric resonator only for a time t₁, holds a state between electrodes of the receiving piezoelectric resonator in a low resistance state including a short circuit for a predetermined time t₂ (>t₁) after the drive signal is supplied, and holds the state between the electrodes of the transmitting piezoelectric resonator in a high resistance state including an open circuit after an elapse of the predetermined time t₂, until the next drive signal is supplied to the transmitting piezoelectric resonator.

Claims

1. An ultrasonic transducer system for harmonic imaging, comprising:

an ultrasonic transducer comprising a transmitting ultrasonic vibrator for transmitting a fundamental ultrasound having a center frequency f₀, and a receiving ultrasonic vibrator for receiving a harmonic signal having a center frequency nf₀ (n is an integer of 2 or more); and

control means for controlling the ultrasonic transducer,

wherein said transmitting ultrasonic vibrator comprises a transmitting piezoelectric resonator, said receiving ultrasonic vibrator comprises a receiving piezoelectric resonator, the transmitting piezoelectric resonator and the receiving piezoelectric resonator are superposed and disposed in layers, and

said control means supplies a drive signal to the transmitting piezoelectric resonator only for a time t₁, holds a state between electrodes of the receiving piezoelectric resonator in a low resistance state including a short circuit for a predetermined time t₂ = (>

t₁) after the drive signal is supplied, and holds the state between the electrodes of the transmitting piezoelectric resonator in a high resistance state including an open circuit after an elapse of the predetermined time t₂, until the next drive signal is supplied to the transmitting piezoelectric resonator.

2. The ultrasonic transducer system according to claim 1, wherein said control means comprises an inductance circuit for holding the state between the electrodes of the receiving piezoelectric resonator in a low resistance state including the short circuit state for a specific time.

3. The ultrasonic transducer system according to claim 1, wherein said control means comprises an on/off control device, disposed in a final stage of a circuit for supplying the drive signal to the transmitting piezoelectric resonator, for holding the high resistance state including the open circuit.

4. The ultrasonic transducer system according to claim 1, wherein said receiving piezoelectric resonator comprises a polymeric piezoelectric material.

5. The ultrasonic transducer system according to claim 1, wherein said receiving piezoelectric resonator comprises a composite piezoelectric material.

6. The ultrasonic transducer system according to claim 4, wherein said polymeric piezoelectric material is directly disposed on the surface of the transmitting piezoelectric resonator on an ultrasonic emission side.

7. The ultrasonic transducer system according to claim 4, wherein said polymeric piezoelectric material is disposed on the surface of the transmitting piezoelectric resonator on an ultrasonic emission side via an acoustic matching layer.

8. The ultrasonic transducer system according to claim 6, wherein said polymeric piezoelectric material comprises a polymeric film in which a piezoelectric property is spontaneously generated by polarizing a surface energy.

9. The ultrasonic transducer system according to claim 7, wherein said polymeric piezoelectric material comprises a polymeric film in which a piezoelectric property is spontaneously generated by polarizing a surface energy.

10. The ultrasonic transducer system according to claim 1, wherein said transmitting ultrasonic vibrator and said receiving ultrasonic vibrator comprise a damping layer (backing layer) disposed on the back surface of the transmitting piezoelectric resonator, and an acoustic lens disposed on the front surface of the receiving piezoelectric resonator in common.

11. The ultrasonic transducer system according to claim 10, wherein said acoustic lens comprises an acoustic matching function.

12. The ultrasonic transducer system according to claim 10, wherein said acoustic lens comprises an opening surface having a constant curvature radius, and the curvature radius of the opening surface has a value equal to an average value of an acoustic focal length for the ultrasound having the center frequency f₀ and an acoustic focal length for the ultrasound having the center frequency nf₀ (n is an integer of 2 or more).

13. The ultrasonic transducer system according to claim 10, wherein said acoustic lens comprises an opening surface having a curvature radius which partially differs.

14. An ultrasonic transducer for harmonic imaging, comprising:

a transmitting ultrasonic vibrator including a transmitting piezoelectric resonator, for transmitting a fundamental ultrasound having a center frequency f₀; and

a receiving ultrasonic vibrator including a receiving piezoelectric resonator, for receiving a harmonic signal having a center frequency nf₀ (n is an integer of 2 or more),

wherein one of said transmitting piezoelectric resonator and said receiving piezoelectric resonator has an annular band shape, the other one of said transmitting piezoelectric resonator and said receiving piezoelectric resonator has a disc shape, and the disc-shaped piezoelectric resonator is disposed inside the annular band shaped piezoelectric resonator.

15. The ultrasonic transducer according to claim 14, wherein said transmitting piezoelectric resonator comprises the annular band shaped piezoelectric resonator, and said receiving piezoelectric resonator comprises the disc shaped piezoelectric resonator.

16. The ultrasonic transducer according to claim 14, further comprising an acoustic lens disposed in front of the transmitting piezoelectric resonator and the receiving piezoelectric resonator and provided with an acoustic matching function, wherein said transmitting ultrasonic vibrator and said receiving ultrasonic vibrator partially include the acoustic lens.

17. The ultrasonic transducer according to claim 14, wherein said transmitting ultrasonic vibrator further comprises a damping layer disposed on the back surface of the transmitting piezoelectric resonator, said receiving ultrasonic vibrator further comprises a damping layer disposed on the back surface of the receiving piezoelectric resonator, and these damping layers have different thickness values.

18. The ultrasonic transducer according to claim 14, wherein said acoustic lens comprises an opening surface having a curvature radius which partially differs.

19. The ultrasonic transducer according to claim 18, wherein said acoustic lens comprises a first portion positioned in front of the transmitting piezoelectric resonator and a second portion positioned in front of the receiving piezoelectric resonator, the first portion of the acoustic lens comprises the opening surface having a constant curvature radius R_t, and the second portion of the acoustic lens comprises the opening surface having a constant curvature radius R_r smaller than the curvature radius R_t.

20. The ultrasonic transducer according to claim 19, wherein said receiving piezoelectric resonator projects forward from the transmitting piezoelectric resonator.

21. The ultrasonic transducer according to claim 19, wherein said curvature radius R_t of the opening surface of the first portion of the acoustic lens has a value equal to an acoustic focal length for the ultrasound having the center frequency f₀, and said curvature radius R_r of the opening surface of the second portion of the acoustic lens has a value equal to an acoustic focal length for the ultrasound having the center frequency nf₀ (n is an integer of 2 or more).

22. The ultrasonic transducer according to claim 19, wherein said first portion of the acoustic lens has a thickness which is ¼

of a wavelength corresponding to the frequency f₀ on average, and said second portion of the acoustic lens has a thickness which is ¼

of a wavelength corresponding to the frequency nf₀ on average.

23. The ultrasonic transducer according to claim 14, wherein said acoustic lens comprises an opening surface having a constant curvature radius.

24. The ultrasonic transducer according to claim 23, wherein said acoustic lens comprises a first portion positioned in front of the transmitting piezoelectric resonator and a second portion positioned in front of the receiving piezoelectric resonator, the first portion of the acoustic lens has an average thickness T_t equal to ¼

of a wavelength of the ultrasound having the fundamental frequency f₀, and the second portion of the acoustic lens has an average thickness T_r equal to ¼

of a wavelength of the ultrasound having the fundamental frequency nf₀ (n is an integer of 2 or more).

25. The ultrasonic transducer according to claim 24, wherein an opening surface of the acoustic lens has a curvature radius equal to a radius of a spherical surface which circumscribes a circle obtained by connecting a point of the average thickness T_t of the first portion of the acoustic lens, and a circle obtained by connecting a point of the average thickness T_r of the second portion of the acoustic lens.

26. An ultrasonic transducer for harmonic imaging, comprising:

a plurality of transmitting ultrasonic vibrators for transmitting a fundamental ultrasound having a center frequency f₀; and

a plurality of receiving ultrasonic vibrators for receiving a harmonic signal having a center frequency nf₀ (n is an integer of 2 or more),

wherein said transmitting ultrasonic vibrators and said receiving ultrasonic vibrators are alternately disposed in a radial form.

27. The ultrasonic transducer according to claim 26, wherein each of said transmitting ultrasonic vibrators comprises a transmitting piezoelectric resonator, and an acoustic lens disposed in front of the transmitting piezoelectric resonator, each of said receiving ultrasonic vibrators comprises a receiving piezoelectric resonator, and an acoustic lens disposed in front of the receiving piezoelectric resonator, and the acoustic lens of the receiving ultrasonic vibrator has a curvature radius smaller than a curvature radius of the acoustic lens of the transmitting ultrasonic vibrator.

28. The ultrasonic transducer according to claim 27, wherein said transmitting ultrasonic vibrator further comprises a damping layer disposed on the back surface of the transmitting piezoelectric resonator, said receiving ultrasonic vibrator further comprises a damping layer disposed on the back surface of the receiving piezoelectric resonator, and these damping layers have different thickness values.

29. An ultrasonic transducer for harmonic imaging, comprising:

a transmitting ultrasonic vibrator for transmitting a fundamental ultrasound having a center frequency f₀ in response to input of an electric signal; and

a receiving ultrasonic vibrator for receiving a harmonic signal having a center frequency nf₀ (n is an integer of 2 or more) generated in an object by the fundamental ultrasound,

wherein said transmitting ultrasonic vibrator comprises a transmitting piezoelectric resonator, said receiving ultrasonic vibrator comprises a receiving piezoelectric resonator, the transmitting piezoelectric resonator and the receiving piezoelectric resonator are disposed on the same plane, and the transmitting piezoelectric resonator and the receiving piezoelectric resonator satisfy (g_33r·

V_r·

Q_r)/(g_33t·

V_t·

Q_t)≧

n·

(1+R), in which g_33t and V_t denote a voltage output coefficient and a sound velocity of the transmitting piezoelectric resonator, g_33r and V_r denote a voltage output coefficient and a sound velocity of the receiving piezoelectric resonator, n denotes a harmonic order, R denotes an opening area ratio (an opening area of the receiving piezoelectric resonator/an opening area of the transmitting piezoelectric resonator), and Q_t and Q_r denote resonance sharpness of the transmitting ultrasonic vibrator and the receiving ultrasonic vibrator, respectively.

30. The ultrasonic transducer according to claim 29, wherein in said transmitting ultrasonic vibrator, a mechanical resonance sharpness Q in the center frequency is between 1 and 5.

31. The ultrasonic transducer according to claim 30, wherein a material of the transmitting piezoelectric resonator has a piezoelectric constant d₃₃ which satisfies d₃₃>

200 ×

10<sub>−

12</sub> [m/V], and a mechanical quality factor Qm which satisfies 70<

Qm<

1000.

32. The ultrasonic transducer according to claim 30, wherein said transmitting ultrasonic vibrator further comprises a backing layer disposed on the back surface of the transmitting piezoelectric resonator, and the backing layer has an ultrasonic attenuation ratio larger than 5 dB/cm/MHz, and an acoustic impedance Zd which is ⅓

or less of an acoustic impedance Zp of the transmitting piezoelectric resonator.

33. The ultrasonic transducer according to claim 30, wherein said transmitting piezoelectric resonator comprises an energy trapped electrode.

34. The ultrasonic transducer according to claim 29, wherein said receiving ultrasonic vibrator has a center frequency of 2f₀, and a mechanical resonance sharpness Q in the center frequency is between 1 and 5.

35. The ultrasonic transducer according to claim 29, wherein said receiving ultrasonic vibrator has a center frequency of 3f₀, and a mechanical resonance sharpness Q in the center frequency is between 1 and 5.

36. The ultrasonic transducer according to claim 34 or 35, wherein a piezoelectric material of the receiving piezoelectric resonator has a high voltage output coefficient g₃₃, and a high longitudinal wave sound velocity.

37. The ultrasonic transducer according to claim 36, wherein the material having the high voltage output coefficient g₃₃ and the high longitudinal wave sound velocity is a piezoelectric single crystal represented by a chemical formula K(Nb_1-xTa_x)O₃, 0≦

x ≦

0.2.

38. The ultrasonic transducer according to claim 36, wherein the material having the high voltage output coefficient g₃₃ and the high longitudinal wave sound velocity is a lead titanate based piezoelectric ceramic.

39. The ultrasonic transducer according to claim 36, wherein the material having the high voltage output coefficient g₃₃ and the high longitudinal wave sound velocity is a bismuth layer structure ferroelectric material (BLSF) represented by a chemical formula Bi₄Ti₃O₁₂ or Ma_1-xMb_xBi₂McO₈, 0≦

x ≦

0.2, in which Ma and Mb are alkaline earth metal elements such as Sr and Ba, and Mc is a +5 valence metal element such as Ta and Nb.

40. The ultrasonic transducer according to claim 34, wherein said receiving piezoelectric resonator comprises an energy trapped electrode.

41. The ultrasonic transducer according to claim 34, wherein said receiving ultrasonic vibrator comprises a backing layer disposed on the back surface of the receiving piezoelectric resonator, and a material of the backing layer has an ultrasonic attenuation ratio larger than 5 dB/cm/MHz, and an acoustic impedance Zd which is ⅓

or less of an acoustic impedance Zp of the receiving piezoelectric resonator.

42. An ultrasonic transducer system for harmonic imaging, comprising:

an ultrasonic transducer comprising a transmitting ultrasonic vibrator for transmitting a fundamental ultrasound having a center frequency f₀ in response to input of an electric signal and a receiving ultrasonic vibrator for receiving a harmonic signal having a center frequency nf₀ (n is an integer of 2 or more) generated in an object by the fundamental ultrasound, said transmitting ultrasonic vibrator comprising a transmitting piezoelectric resonator, said receiving ultrasonic vibrator comprising a receiving piezoelectric resonator, said transmitting piezoelectric resonator and said receiving piezoelectric resonator being disposed on the same plane, said transmitting piezoelectric resonator and said receiving piezoelectric resonator satisfying (g_33r·

V_r·

Q_r)/(g_33t·

V_t·

Q_t)≧

n·

(1+R), in which g_33t and V_t denote a voltage output coefficient and a sound velocity of the transmitting piezoelectric resonator, g_33r and V_r denote a voltage output coefficient and a sound velocity of the receiving piezoelectric resonator, n denotes a harmonic order, R denotes an opening area ratio (an opening area of the receiving piezoelectric resonator/an opening area of the transmitting piezoelectric resonator), and Q_t and Q_r denote resonance sharpness of the transmitting ultrasonic vibrator and the receiving ultrasonic vibrator, respectively; and

drive control means for driving/controlling the ultrasonic transducer,

wherein said drive control means generates an ultrasound in which at least a component of 2f₀ is inhibited in the transmitting ultrasonic vibrator.

43. The ultrasonic transducer system according to claim 42, wherein said drive control means supplies a drive pulse signal having a frequency characteristic such that the center frequency is in f₀ and a first dip frequency is in 2f₀ to the transmitting ultrasonic vibrator.

44. The ultrasonic transducer system according to claim 43, wherein said drive control means supplies the drive pulse signal of a burst wave to the transmitting ultrasonic vibrator.

45. The ultrasonic transducer system according to claim 42, wherein said transmitting ultrasonic vibrator comprises means for imparting a functionally gradient characteristic concerning at least one of a piezoelectric constant and a permittivity to the transmitting piezoelectric resonator.

46. The ultrasonic transducer system according to claim 45, wherein said means for imparting the functionally gradient characteristic comprises a heater for imparting a temperature gradient to the transmitting piezoelectric resonator along a thickness direction of the transmitting piezoelectric resonator.

47. The ultrasonic transducer system according to claim 42, wherein said transmitting piezoelectric resonator has an functionally gradient characteristic in at least one of a piezoelectric constant and a permittivity.

48. The ultrasonic transducer system according to claim 47, wherein said transmitting piezoelectric resonator has an inclination piezoelectric material in which at least one of the piezoelectric constant and the permittivity monotonously changes along a thickness direction.

49. The ultrasonic transducer system according to claim 47, wherein said transmitting piezoelectric resonator comprises a plurality of piezoelectric thin plates being laminated on one another and having the functionally gradient characteristic in which at least one of the piezoelectric constant and the permittivity gradually differs.