JP5776542B2 - Ultrasonic probe and ultrasonic inspection device - Google Patents

Description

  The present invention relates to an ultrasonic probe using a MUT (Micromachining Ultrasonic Transducer) element and an ultrasonic inspection apparatus using the same. In particular, the present invention relates to a wide band and high sensitivity of an ultrasonic probe for three-dimensional observation of a living body.

  The ultrasonic inspection apparatus transmits an ultrasonic beam from the ultrasonic probe to the subject, receives an ultrasonic signal reflected from the inside of the subject (hereinafter referred to as an ultrasonic echo), and receives information on the inside of the subject. It is a device to obtain. In this ultrasonic inspection apparatus, the higher the frequency of the ultrasonic wave transmitted from the ultrasonic probe, the higher the resolution. However, when performing in-vivo observation of a living body, the depth of arrival of the ultrasonic wave is shallower as the frequency of the ultrasonic wave is higher. The lower, the deeper. Therefore, in order to obtain a high-resolution image from a deep part to a shallow part, an ultrasonic probe capable of transmitting and receiving broadband ultrasonic waves is desired.

  Conventionally, an ultrasonic probe is configured by arranging a large number of piezoelectric vibrators made of a piezoelectric ceramic represented by PZT (lead zirconate titanate). In this configuration, as a method of expanding the band of ultrasonic waves to be transmitted and received, a configuration in which transducers having different resonance frequencies are arranged in the slice direction (for example, Patent Document 1), or a transducer having different resonance frequencies in the array direction is arranged. The structure (for example, patent document 2) etc. which do is proposed.

  However, such a method can be realized with a one-dimensional probe in which transducers are arranged in a row, but it is difficult to realize with a two-dimensional array probe that has been increasingly demanded in recent years. In order to make a conventional one-dimensional probe structure two-dimensional as it is, there are problems in terms of microfabrication, wiring, and electrical impedance. There are vibrators with distributions in the slice direction and vibrators with different thicknesses. In addition, the difficulty level increases and is not realistic.

  As a configuration suitable for such a two-dimensional array probe, a pMUT (Piezoelectric Microtransducing Ultratransducer) element and a cMUT (Capacitive Microtransducing Ultracapacitor Ultratransducer element) have recently been used. These transducers are formed by using a semiconductor manufacturing technique, and have advantages such as the possibility of increasing the number of arrays and the ease of integration with circuits. On the other hand, when such a transducer is used as an ultrasonic probe, it has a problem that it is difficult to satisfy simultaneously the high resonance frequency, the wide frequency band to be transmitted / received, the size of transmission output and reception sensitivity, etc. doing.

  As a countermeasure against this, pMUT has been proposed to improve sensitivity by structuring a piezoelectric layer (for example, Patent Document 4). Moreover, in cMUT, the structure which aimed at coexistence of a resonance frequency maintenance and a sensitivity improvement by providing a recessed part in the membrane surface and reducing the density of a membrane is proposed (for example, patent document 4).

JP-A-6-121390 JP 2005-277788 A JP 2011-15423 A JP 2009-182838 A

  As described above, the conventional bulk type vibrators described in Patent Documents 1 and 2 have problems such as fine processing, wiring, and electrical impedance, and are not suitable for a two-dimensional array probe.

  Further, although the cMUT described in Patent Document 3 can realize an improvement in reception sensitivity and wideband characteristics, when viewed as a transmission element, the sound pressure of the output ultrasonic wave is greatly inferior as compared with a conventional bulk type configuration.

  Moreover, although the pMUT element described in Patent Document 4 can be expected to have a larger transmission output than the cMUT, no mention is made regarding compatibility with wideband characteristics.

  The present invention solves the above-described conventional problems, and provides a two-dimensional array probe that improves the transmission output and reception sensitivity of a MUT element, particularly a pMUT, and has both wideband characteristics. An object of the present invention is to provide an ultrasonic inspection apparatus capable of obtaining a wide range and clear ultrasonic image by using this ultrasonic probe.

  In order to achieve the above object, an ultrasonic probe of the present invention includes a plurality of unit transducers arranged two-dimensionally, and the unit transducers are formed at least on a pedestal portion and the pedestal portion. A diaphragm, a first piezoelectric film formed on the upper surface of the diaphragm, a second piezoelectric film, a first electrode formed on the upper surface of the first piezoelectric film, and the second piezoelectric body It has a plurality of MUT (Micromachining Ultrasonic Transducer) elements composed of second electrodes formed on the upper surface of the film, and the first electrode and the second electrode are not electrically connected. With this configuration, the generated ultrasonic wave can be shortened and the transmitted ultrasonic wave can be broadened.

  In addition, a control unit that controls a drive signal transmitted to the second electrode is further provided, and the control unit can control the applied voltage in accordance with the passage of time after transmitting the ultrasonic wave into the subject. To do. With this configuration, a frequency band with high reception sensitivity can be effectively set according to the depth at which the ultrasonic echo returns, and apparently wide bandwidth and high sensitivity characteristics can be obtained.

  The ultrasonic inspection apparatus according to the present invention performs beam forming processing using the ultrasonic probe, a receiving unit that digitally converts a signal detected by the ultrasonic probe, and a signal digitally converted by the receiving unit. The signal processing unit includes an image processing unit that generates a three-dimensional image based on the three-dimensional data obtained by the signal processing unit, and a display unit that displays the three-dimensional image. With this configuration, a wide and clear ultrasonic image can be obtained.

  The ultrasonic probe and ultrasonic inspection apparatus of the present invention can shorten the generated ultrasonic wave to form a transmission wave having a wide band.

  Furthermore, at the time of reception, by shifting the frequency band with high reception sensitivity with the passage of time, it is possible to set according to the depth of return of ultrasonic echo, and apparently wideband and highly sensitive signal detection is possible Become.

  Therefore, by using the ultrasonic probe according to the present invention, it is possible to realize a high quality ultrasonic inspection apparatus in a wide range from a shallow part to a deep part.

1 is a block diagram showing a schematic configuration of an ultrasonic inspection apparatus according to a first embodiment of the present invention. 1 is a configuration diagram showing the overall configuration of an ultrasonic probe according to a first embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which showed the structure of the vibrator | oscillator unit concerning Embodiment 1 of this invention, (a) is a top view, (b) is a side view in AA cross section. 2A and 2B are cross-sectional views of the pMUT element 31 according to the first embodiment of the present invention, in which FIG. 1A is an explanatory diagram showing pressure acting on the piezoelectric film 35 when a voltage is applied, and FIG. And an explanatory diagram showing the accompanying deformation FIG. 6 is a top view showing another structure of the unit resonator according to the first embodiment of the invention. FIG. 6 is a top view showing still another structure of the unit resonator according to the first embodiment of the invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same reference number is attached | subjected to the same component and description is abbreviate | omitted.

(Embodiment 1)
FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic inspection apparatus 10 according to the first embodiment of the present invention. The ultrasonic inspection apparatus 10 transmits an ultrasonic wave to the subject 11, generates an ultrasonic probe 12 that receives an ultrasonic signal reflected inside the subject 11, and a drive signal for transmitting the ultrasonic wave. The signal is supplied to the main electrode of the ultrasonic probe 12, and the signal detected by the main electrode of the ultrasonic probe 12 is amplified and digitally converted and output, and the signal output from the transmitter / receiver 13 is digitally used. A signal processing unit 14 that performs beam forming, an image processing unit 15 that performs a rendering process of a three-dimensional image based on the three-dimensional data generated by the signal processing unit 14, and a processing that is based on the processed image data. An image display unit 16 that displays an image, and generates a drive signal to be transmitted to the sub-electrode of the ultrasonic probe 12 when transmitting and receiving the ultrasonic wave. A sub transmission portion 18 to be supplied to the lobe 12, and a control unit 17 for controlling the transmission and reception unit 13 and the sub-transmission unit 18 to generate a driving signal at a predetermined timing.

  Further, the transmission / reception unit 13, the sub-transmission unit 18, the signal processing unit 14, the image processing unit 15, the image display unit 16, and the control unit 17 are stored in the inspection apparatus main body 19. A plurality of signal line cables are connected together by a probe cable covering them.

  FIG. 2 is a configuration diagram showing the overall configuration of the ultrasonic probe 12 according to the first embodiment of the present invention. As shown in FIG. 2, the ultrasonic probe 12 is independent of the transducer unit 22 that transmits and receives ultrasonic waves into the probe case 21 and the main electrode and the sub electrode of the unit transducer in the transducer unit 22. And a printed circuit board 24 on which a plurality of signal lines for inputting and outputting electrical signals are printed. Further, the ultrasonic probe 12 is connected to the inspection apparatus main body 19 via a probe cable 25.

  Here, the vibrator unit 22 includes a vibrator array in which unit vibrators composed of a plurality of pMUT elements are two-dimensionally arranged, and each unit vibrator has a main electrode in addition to a grounded common electrode. There are two types of electrodes, an electrode and a sub-electrode. An ultrasonic pulse is generated by applying a pulsed voltage to the main electrode, and an ultrasonic wave generated by supplying a drive voltage subjected to delay processing to the main electrode from the transceiver 13. Can be focused and deflected. With this configuration, the ultrasonic probe 12 is configured to perform sector scanning by transmitting ultrasonic waves in a three-dimensional direction.

  In addition, when transmitting and receiving ultrasonic waves, a predetermined signal, which will be described later, is transmitted to the sub-electrode so that broadband ultrasonic waves can be transmitted and received.

  3A and 3B are explanatory views showing the structure of the vibrator unit 22 according to the first embodiment of the present invention, in which FIG. 3A is a top view and FIG. 3B is a side view in the AA section.

  As shown in FIGS. 3A and 3B, the vibrator unit 22 is configured by, for example, two-dimensionally arranging unit vibrators 32 including four pMUT elements 31. Each pMUT element includes a main electrode 33 made of a metal thin film such as platinum (Pt), gold (Au), and aluminum (Al), a sub electrode 34, a piezoelectric ceramic represented by PZT (lead zirconate titanate), and the like. The piezoelectric films 35a and 35b are made of a metal film such as copper (Cu), chromium (Cr), and the like. The diaphragm 36 also serves as a common electrode, and a pedestal 37 made of a rigid material.

  Further, the main electrode 33 and the sub electrode 34 of the pMUT element 31 are connected to each unit vibrator, and are individually connected to the printed circuit board 24 shown in FIG. 2 from the lead portion 33a and the lead portion 34a. The lead-out portion of the diaphragm 36 that also serves as a common electrode is connected to the ground line of the printed circuit board 24. With this configuration, a voltage can be applied independently for each main electrode and sub electrode of the unit vibrator 32, and the corresponding piezoelectric films 35a and 35b can be driven.

  Note that the materials of the main electrode 33 and the sub electrode 34, the piezoelectric film 35, and the diaphragm 36 described above are examples, and any materials may be used as long as they have the same function.

  Next, the operation of the ultrasonic inspection apparatus 10 according to the first embodiment configured as described above will be specifically described with reference to FIGS. 1 to 3 and FIG. 4. 4A and 4B are cross-sectional views of the pMUT element 31 according to the first embodiment of the present invention. FIG. 4A is an explanatory diagram showing the pressure acting on the piezoelectric film 35 when a voltage is applied, and FIG. It is explanatory drawing which showed the moment which acts, and the deformation | transformation accompanying it.

  1 to 3, first, the control unit 17 controls the transmission / reception unit 13 so that a pulse signal is generated at a predetermined timing. The transmission / reception unit 13 performs a delay process for focusing and deflecting the ultrasonic wave, and the probe. A drive signal is transmitted to the ultrasonic probe 12 via a signal line collected in the cable 25. At this time, a drive signal is similarly transmitted from the sub-transmission unit 18 by a signal from the control unit 17. The delay-processed drive signal transmitted from the transmission / reception unit 13 is sent to the main electrode 33 of the transducer unit 22 via the printed circuit board 24, and the drive signal transmitted from the sub-transmission unit 18 is transmitted through the same path. It is sent to the electrode 34. The piezoelectric films 35a and 35b are distorted by the voltage applied to the main electrode 33 and the sub electrode 34, and an ultrasonic wave is generated from each unit vibrator with a predetermined time difference. A predetermined wavefront is formed by the phase distribution of the ultrasonic waves, and an ultrasonic beam is transmitted into the subject 11.

  The operation of transmitting this ultrasonic wave will be specifically described with reference to FIG. First, in FIG. 4A, when a drive signal is transmitted to the main electrode 33, a pulsed voltage is applied in the thickness direction of the piezoelectric film 35a accordingly. Distorted in the direction of shrinking. At this time, a voltage having a potential opposite to that of the main electrode 33 is applied to the sub electrode 34, and the piezoelectric film 35b is distorted in a direction extending in the plane. When the piezoelectric films 35a and 35b are distorted in the direction of the arrow shown in FIG. 4A, moments as shown by the arrows in FIG. 4B are respectively applied to the portions of the diaphragm 36 that are in contact with the piezoelectric films 35a and 35b. Is generated, and the diaphragm 36 is instantaneously bent to generate ultrasonic waves.

  Then, the piezoelectric film 35b is driven by controlling the voltage applied to the sub electrode 34 immediately after transmitting the ultrasonic wave, and the vibration of the diaphragm 36 immediately after transmitting the ultrasonic wave is suppressed. By effectively suppressing vibration of the diaphragm 36, a short pulse of ultrasonic waves is transmitted.

  Here, in the present embodiment, by driving using the piezoelectric films 35a and 35b, the displacement of the diaphragm 36 can be increased as compared with the case where the piezoelectric film is disposed only in the center, and the transmission output Has improved. In addition, immediately after ultrasonic transmission, the piezoelectric film 35b is driven to suppress vibrations, whereby the transmission wave is made shorter than usual so that signals with a wide band can be transmitted.

  The sub-electrode 34 and the piezoelectric film 35b are preferably arranged so that the end faces are aligned with the projected positions of the boundary line 39 between the pedestal 37 and the space 38 on the diaphragm 36. Since this position becomes a vibration node of the diaphragm 36, the moment generated in the piezoelectric film 35b can be effectively transmitted to the diaphragm 36.

  In addition, the signal transmitted to the sub-electrode during ultrasonic transmission can use a signal obtained by inverting the potential of the signal transmitted to the main electrode, and the signal for damping is also transmitted to the main electrode. Those with the phase shifted may be used. With such control, the configuration of the sub transmission unit can be simplified.

  The ultrasonic wave transmitted from the ultrasonic probe 12 is reflected by the reflective tissue inside the subject 11, propagates to the surface of the subject 11 as an ultrasonic echo, and vibrates the transducer unit 22.

  At this time, the sub transmission unit 18 transmits a drive signal so that a voltage corresponding to the passage of time after transmitting the ultrasonic wave is applied to the sub electrode 34. The piezoelectric film 35 to which a voltage is applied in the thickness direction by the sub electrode 34 expands and contracts in the in-plane direction to give tensile or compressive stress to the vibration plate 36, and changes the apparent rigidity of the vibration plate 36 with time.

  When the diaphragm 36 of each pMUT element is vibrated by ultrasonic echoes, the central piezoelectric film 35a is pulled and compressed in a plane to generate distortion, and a voltage is generated in the thickness direction of the piezoelectric film 35a according to this distortion. To do. At this time, the vibration according to the ultrasonic echo can be detected by detecting the voltage between the main electrode 33 and the diaphragm 36.

  By the way, although the ultrasonic wave transmitted from the ultrasonic probe 12 has a higher resolution as the frequency is higher, the depth of arrival is shallower as the frequency is higher and deeper as the frequency is lower. Therefore, a signal detected in a short time after transmitting an ultrasonic wave into the subject has a high frequency component, but a high frequency component of the signal detected with time decreases. Therefore, when the frequency characteristic of the reception sensitivity of the transducer unit 22 is shifted from a high frequency band to a low frequency band as time passes after ultrasonic transmission, high reception sensitivity can be realized in a wide frequency band. .

  In the present embodiment, the sub-transmission unit 18 controls the voltage applied to the sub-electrode 34 in accordance with the passage of time after ultrasonic transmission to apply stress to the diaphragm 36 of the pMUT element 31, thereby resonating the pMUT element 31. Shift the frequency over time. As a result, the center frequency of the reception sensitivity changes with time, and ultrasonic echoes generated in a wide range from a shallow part to a deep part are detected with high sensitivity.

  Referring back to FIG. 1 again, the signal detected by the ultrasonic probe 12 is sent to the transmission / reception unit 13, amplified and digitally converted by the transmission / reception unit 13, and the ultrasonic transmission path (hereinafter referred to as sound ray) by the signal processing unit 14. The beam forming process is performed on the area along the line.

  The above operation is performed while scanning the sound ray of the ultrasonic wave transmitted from the ultrasonic probe 12 in the subject, and information on the entire examination region is calculated and stored in the image memory in the signal processing unit 14. . The three-dimensional data stored in the image memory is subjected to a three-dimensional image rendering process by the image processing unit 15, and an image is displayed on the image display unit 16.

  As described above, the ultrasonic inspection apparatus 10 according to the first embodiment can shorten the pulse length when transmitting and receiving ultrasonic waves into the subject. Thereby, a broadband ultrasonic wave can be transmitted. Also, when receiving ultrasonic echoes, it is possible to detect ultrasonic echoes generated in a wide range from shallow parts to deep parts with high sensitivity by shifting the frequency characteristics of reception sensitivity over time. it can. Thereby, it is possible to realize an ultrasonic inspection apparatus capable of acquiring a wide range of high-quality three-dimensional images.

  In this embodiment, the voltage applied to the sub-electrode at the time of reception is controlled according to the passage of time. However, the voltage applied to the sub-electrode is modulated at a frequency sufficiently higher than the frequency of ultrasonic waves to be transmitted and received. The echo signal may be detected by changing the frequency of the signal detected by the main electrode. In this way, the vibration type sensor is excellent in resolution and temperature characteristics, the output signal is alternating current, and the frequency varies according to the sound pressure of the ultrasonic echo, so that digital signal processing becomes easy.

  In the present embodiment, the pMUT element 31 has a square shape, but this shape may be a rectangle, a hexagon as shown in FIG. 5, or other shapes. Further, the number of pMUT elements 31 included in one unit vibrator is not limited to four and may be more than that. For example, as shown in FIG. 6, it may be configured to include nine pMUT elements 31.

  In the present embodiment, the AD conversion of the detected signal is performed by the transmission / reception unit 13 in the inspection apparatus body 19. However, when the number of unit transducers 32 in the ultrasonic probe 12 is large, the analog signal remains as it is. If it is going to transmit a detection signal, many signal lines will be needed and the probe cable 25 will become thick and hard. As a result, handling becomes worse, so that part or all of the functions of the transmission / reception unit 13 may be provided integrally with the ultrasonic probe 12 and the digitally converted signal may be communicated by the probe cable 25. .

  As described above, according to the present invention, a highly sensitive two-dimensional array probe can be realized over a wide band. Thereby, it is possible to realize an ultrasonic diagnostic apparatus having a wide range and high image quality from a shallow part to a deep part.

DESCRIPTION OF SYMBOLS 10 Ultrasonic inspection apparatus 11 Subject 12 Ultrasonic probe 13 Transmission / reception part 14 Signal processing part 15 Image processing part 16 Image display part 17 Control part 18 Sub transmission part 19 Inspection apparatus main body 21 Probe case 22 Transducer unit 24 Printed circuit board 25 Probe Cable 31 pMUT element 32 Unit vibrator 33 Main electrode 33a Lead part 34 Sub electrode 34a Lead part 35 Piezoelectric film 35a Piezoelectric film 35b Piezoelectric film 36 Diaphragm 37 Pedestal 38 Space 39 Boundary line

Claims (10)

An ultrasound probe for in-vivo observation of a subject,
A plurality of unit vibrators arranged two-dimensionally,
The unit vibrator includes at least a pedestal part, a diaphragm formed on the pedestal part, a first piezoelectric film and a second piezoelectric film formed on an upper surface of the diaphragm, and the first piezoelectric element. A plurality of MUT (Micromachining Ultrasound Transducer) elements comprising a first electrode formed on the upper surface of the body film and a second electrode formed on the upper surface of the second piezoelectric film;
The ultrasonic probe, wherein the first electrode and the second electrode are not electrically connected. The ultrasonic probe according to claim 1, wherein ultrasonic waves are generated by transmitting different drive signals to the first electrode and the second electrode, respectively. In each of the MUT elements, the second piezoelectric film is disposed around the first piezoelectric film, and the first electrodes of the adjacent MUT elements in the same unit vibrator, and the second electrode The ultrasonic probe according to claim 1, wherein the two are electrically connected. The ultrasonic probe according to claim 3, wherein the second piezoelectric film is disposed in a region where the pedestal portion is projected on the diaphragm. The ultrasonic probe according to claim 2, wherein the drive signal transmitted to the first electrode is transmitted to the second electrode with a phase shift. 3. The ultrasonic probe according to claim 2, wherein when applying a voltage to the first electrode, a voltage having a potential opposite to a voltage applied to the first electrode is applied to the second electrode. . A controller for controlling a drive signal transmitted to the second electrode;
The ultrasonic probe according to claim 2, wherein the control unit controls an applied voltage according to a lapse of time after transmitting an ultrasonic wave into the subject. A controller for controlling a drive signal transmitted to the second electrode;
The ultrasonic probe according to claim 2, wherein the control unit periodically modulates an applied voltage so that the diaphragm vibrates at a specific frequency. 9. The ultrasonic probe according to claim 1, a receiving unit that digitally converts a signal detected by the ultrasonic probe, and signal processing that performs beam forming processing using the signal digitally converted by the receiving unit. And an image processing unit that generates a three-dimensional image based on the three-dimensional data obtained by the signal processing unit, and a display unit that displays the three-dimensional image. The ultrasonic inspection apparatus according to claim 9, wherein the receiving unit is disposed in the ultrasonic probe.

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