JPH04273699A - Ultrasonic wave checking device - Google Patents

Abstract

PURPOSE:To check an ultrasonic wave at a same transmission reception wave face by independently sending and receiving two ultrasonic waves having a different frequency band and a sufficiently wide specific band. CONSTITUTION:An ultrasonic wave probe 10 is formed by employing a laminate piezoelectric vibrator laminated with a composite piezoelectric layer 15 made of a piezoelectric ceramic material and a high polymer material and a piezoelectric ceramic layer 13 via an electrode layer 14. Two ultrasonic waves with two frequency bands whose center frequency differs are sent/received independently by applying selectively a drive voltage to the piezoelectric ceramic layer 13 and the entire laminated piezoelectric vibrator via a switch 21 so as to check the ultrasonic wave in the B mode or the Doppler mode.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic inspection apparatus for inspecting an object by transmitting and receiving ultrasonic waves using a piezoelectric vibrator, and more particularly to an ultrasonic probe and its drive circuit.

0002

[Prior Art] Ultrasonic inspection equipment uses an ultrasonic probe mainly composed of piezoelectric vibrators to transmit ultrasonic waves toward an object and receive reflected waves from interfaces with different acoustic impedances. This is a device that inspects an object by imaging the internal state of the object. As such ultrasonic inspection devices, medical diagnostic devices for inspecting the inside of the human body, ultrasonic flaw detection devices for the purpose of detecting flaws inside metal welds, etc. have been put into practical use.

The basic operation of a medical ultrasonic diagnostic apparatus is to acquire and display a B-mode image, that is, a tomographic image of the human body. In this operation mode (referred to as B mode), it is required to obtain high-resolution images with high sensitivity so that subtle changes in the body due to lesions and voids can be clearly observed deep down.

On the other hand, recently, in addition to B-mode, a color flow mapping (CFM) method has been developed that uses the Doppler effect to display blood flow information such as blood flow velocity in two-dimensional color for the heart, liver, carotid artery, etc. With the development of , diagnostic ability has improved dramatically. In Doppler mode, which obtains such CFM images, echo signals from small blood cells, such as a few microns in diameter, are used, so the signal level obtained is lower than in B mode, so high sensitivity is particularly required. There is.

[0005] In order to obtain a high-resolution image in B mode, it is necessary to increase the distance resolution and azimuth resolution of the ultrasonic beam. The easiest way to improve these resolutions is to increase the frequency of the ultrasonic frequency band. However, since the ultrasonic attenuation constant is large in a living body, increasing the frequency causes problems such as deterioration of S/N and reduction in penetration due to ultrasonic attenuation. Therefore, especially in the Doppler mode where high sensitivity is required, the reference frequency is set to a frequency lower than the center frequency of the frequency band of the ultrasound probe. The reason for this is that the lower the frequency, the less attenuation of the ultrasound in the living body, so the Doppler image is less susceptible to the S/N reduction due to ultrasound attenuation.

[0006] Due to the above circumstances, in reality, a high-frequency ultrasound probe is used when B-mode image resolution is required depending on the condition of the subject, and when Doppler mode sensitivity is required. In general, operations such as using a low-frequency ultrasonic probe are performed.

[0007] If one ultrasonic probe can transmit and receive ultrasonic waves of two types of frequency band components, it would be possible to selectively obtain a high-resolution B-mode image and a high-sensitivity Doppler image with one probe. becomes possible. Several manufacturers manufacture and sell duplex-type ultrasonic probes based on this idea, in which two types of transducers with different resonance frequencies are installed in one probe.

However, since this type of ultrasonic probe uses transducers with different resonance frequencies arranged at different positions, the ultrasonic transmission/reception wave planes are different for each of the B-mode image and Doppler image. Therefore, it is not possible to observe the same tomographic plane in both B mode and Doppler mode, which is not preferable for better diagnosis.

On the other hand, by using a laminated piezoelectric element,
An ultrasonic probe that transmits and receives ultrasonic waves having two different frequency bands using the same piezoelectric vibrator has been proposed (see, for example, Japanese Patent Laid-Open No. 60-41399). Using such an ultrasound probe, it is possible to obtain a B-mode signal on the high frequency side of two separated frequency bands and a Doppler signal on the low frequency side, making it possible to observe the same tomographic plane in both modes. becomes possible.

[0010] Since this ultrasonic probe uses the electro-mechanical conversion efficiency of one piezoelectric transducer divided into two in two frequency bands, it is different from an ordinary ultrasonic probe with a single frequency characteristic. In comparison, each frequency band becomes narrower. For this reason, in the B-mode image, the wave length (tailing of the echo signal)
Problems such as a decrease in resolution, a deterioration in S/N, and a decrease in penetration arise due to the increase in the length of the signal.

[0011] Furthermore, since the reference frequency is generally fixed in Doppler mode, the frequency band that can be used in Doppler mode is narrow in this ultrasonic probe, so a slight deviation in the frequency band has a large effect on the sensitivity. There is also the problem of doing so.

0012

[Problems to be Solved by the Invention] As described above, in the conventional technology, when a plurality of piezoelectric vibrators with different resonance frequencies are used to obtain two frequency bands with one ultrasonic probe, each frequency band It is not possible to observe the same part in
Further, in an ultrasonic probe in which one laminated piezoelectric vibrator is operated in two frequency bands, there is a problem in that the fractional band of each frequency band is narrow and good images cannot be obtained.

[0013] The present invention uses an ultrasonic probe that can independently transmit and receive ultrasound having two different frequency bands on the same transmitting and receiving wave surface, and that has a sufficiently wide ratio band of each frequency band. It is an object of the present invention to provide an ultrasonic inspection apparatus that can perform inspections in B mode or Doppler mode favorably.

[0014]

[Means for Solving the Problems] An ultrasonic inspection apparatus according to the present invention has a laminated piezoelectric vibration system in which a piezoelectric ceramic layer and a composite piezoelectric layer made of a piezoelectric ceramic material and a polymeric material are laminated with electrode layers interposed therebetween. An ultrasonic probe is constructed using a single piezoelectric ceramic layer and is driven by a drive circuit that selectively applies a drive voltage to the single piezoelectric ceramic layer and the entire laminated piezoelectric vibrator. Further, it is desirable that the composite piezoelectric layer has such a thickness and acoustic impedance that it functions as an acoustic matching layer when the piezoelectric ceramic layer alone is driven.

[0015]

[Operation] In an ultrasonic probe composed of a laminated piezoelectric vibrator consisting of a piezoelectric ceramic layer and a composite piezoelectric layer, when only the piezoelectric ceramic layer is driven, vibrations with relatively high frequency components can be obtained. On the other hand, when the entire laminated piezoelectric vibrator is driven, vibrations of relatively low frequency components can be obtained due to the total thickness of the piezoelectric ceramic layer and the composite piezoelectric layer. As a result, ultrasonic waves of two different frequency bands are transmitted and received independently by the same ultrasound probe on the same transmission and reception plane, and in different operating modes such as B mode and Doppler mode, the same part of the object observation becomes possible.

In this case, since the electromechanical conversion efficiency of the piezoelectric ceramic layer is not divided into two in both frequency bands,
In both the high-frequency side and the low-frequency side, a fractional band comparable to that of a general single-frequency-band ultrasonic probe can be obtained. If conditions are selected so that the composite piezoelectric layer acts as an acoustic matching layer when a single piezoelectric ceramic layer vibrates, unnecessary vibrations will be prevented, resulting in good frequency characteristics, especially on the high frequency side. It is advantageous above.

[0017] Therefore, for example, in B mode using high frequency ultrasonic waves, a B mode signal with high resolution and high S/N can be obtained, and sufficient penetration can be ensured. In the Doppler mode that uses low-frequency ultrasound, even if the frequency band shifts slightly, the bandwidth is originally wide, so a decrease in sensitivity due to a shift in the frequency band with respect to the reference frequency can be avoided.

[0018]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an ultrasonic inspection apparatus according to an embodiment of the present invention, showing an ultrasonic probe and a transmission/reception system.

In FIG. 1, an ultrasonic probe 10 has a piezoelectric ceramic layer 13 provided on a backing material 11 with an external electrode layer 12 interposed therebetween, and a composite piezoelectric layer 15 and an external It has a structure of a laminated piezoelectric vibrator formed by laminating electrode layers 16. Piezoelectric ceramic layer 13
consists only of piezoceramic material. Composite piezoelectric layer 1
5 is formed by a piezoelectric ceramic material part 17 and a polymer material part 18.

[0020] Such a laminated piezoelectric vibrator is made by manufacturing a piezoelectric ceramic vibrator having electrodes on both sides and a vibrator using a 1-3 type composite piezoelectric body having electrodes on both sides to a predetermined thickness. It can be obtained by adhesively laminating these.

[0021] As another method, for example, JP-A-60-
A laminated piezoelectric ceramic vibrator with an integrally formed internal electrode, such as the laminated piezoelectric vibrator having the configuration disclosed in Publication No. 41339, is manufactured, and a diamond blade is used to apply resin vertically and horizontally to only one ceramic layer, leaving the internal electrode. A similar laminated piezoelectric vibrator can be obtained by forming electrodes on the surface after filling the material.

[0022] The electrode layers 12, 14, and 16 are connected to the ultrasonic inspection apparatus body 20 via a cable led out to the outside of the ultrasonic probe 10. Ultrasonic inspection device main body 2
0 is provided with a switch 21 and a transmitting circuit 22 and a receiving circuit 23 which are drive circuits. The lower external electrode layer 12 is connected to the transmitting circuit 22 and the receiving circuit 23, and the internal electrode layer 14 and the upper external electrode layer 16 are selectively connected to the transmitting circuit 22 and the receiving circuit 23 by a switch 21.

Next, the operation of this embodiment will be explained. Figure 1
In the configuration, when the switch 21 is switched to the A side and the transmitting circuit 22 and the receiving circuit 23 are connected between the electrode layers 12-16, the electrode layers 12, 14, 16, the piezoelectric ceramic layer 13, and the composite piezoelectric layer 15 A driving voltage is applied from the transmitting circuit 22 to the entire constructed laminated piezoelectric vibrator. Therefore, since the entire laminated piezoelectric vibrator operates as a vibrator,
The resonance frequency has a value that depends on the total thickness of the piezoelectric ceramic layer 13 and the composite piezoelectric layer 15 and the average sound velocity of each of these layers 13 and 15.

On the other hand, by switching the switch 21 to the B side,
When the transmitting circuit 22 and the receiving circuit 23 are connected between the electrode layers 14-16, a driving voltage is applied to the piezoelectric ceramic layer 13, so that only the piezoelectric ceramic layer 13 operates as a vibrator. The resonance frequency at this time is determined by the thickness of the piezoelectric ceramic layer 13 and its sound velocity. In this case, the composite piezoelectric layer 15 is configured such that the composite piezoelectric layer 15 forms an acoustic matching layer with respect to the center frequency of the oscillated ultrasonic wave.
If the thickness and acoustic impedance of the composite piezoelectric layer 15 are selected in advance, the composite piezoelectric layer 15 will not affect the resonant frequency, as will be described later.

Since the resonant frequency of the transducer in each of the above cases uniquely determines the center frequency of the ultrasonic probe, the center frequency of the ultrasonic probe can be changed by changing the switch 21. It will be possible.

To give a specific example, for example, when the longitudinal sound velocity is 4
, 500 m/sec of a resonant frequency 5 MHz vibrator (thickness: 450 μm) consisting of only a piezoelectric ceramic layer, and a 1-3 type composite piezoelectric layer (thickness: 190 μm) with a longitudinal sound velocity of 3,800 m/sec. We manufactured an ultrasonic probe with laminated transducers. The thickness of the composite piezoelectric layer of 190 μm is a value corresponding to 1/4 of the wavelength within the composite piezoelectric layer at a frequency of 5 MHz, and is a value determined from the λ/4 acoustic matching condition (λ: wavelength).

[0027] Here, when only the piezoelectric ceramic layer is driven, the center frequency of the ultrasonic probe is 5 MHz. When driving the entire laminated vibrator consisting of a laminated body of a piezoelectric ceramic layer and a composite piezoelectric layer, the total thickness of the laminated body is 64 mm.
Since the average sound speed is approximately 4,290 m/sec, the resonant frequency is 3.35 MHz.

[0028] Also, with the above conditions, the acoustic matching condition is set to 3.
Assuming λ/4, the thickness of the composite piezoelectric layer is 570 μm, the total thickness of the laminate of the composite piezoelectric layer and the piezoelectric ceramic layer is 1,020 μm, and the average sound velocity is 4,100 m/sec.
c, the resonant frequency when the entire laminated vibrator is driven is 2 MHz.

As described above, by switching the electrode position to which the driving voltage from the transmitting circuit 22 is applied using the switch 21, it is possible to select two types of center frequencies of the ultrasonic waves to be transmitted and received. Therefore, for example, in an ultrasonic diagnostic apparatus having B mode and Doppler mode, in the B mode, the switch 21 is switched to the B side to drive only the piezoelectric ceramic layer 13, and in the Doppler mode, the switch 21 is switched to the A side.
By switching to the side and driving the entire laminated piezoelectric element, operation in both modes can be realized with one ultrasonic probe 10.

In this case, when the piezoelectric ceramic layer 13 alone vibrates, the composite piezoelectric layer 15 acts as an acoustic matching layer, so that unnecessary vibrations caused by the composite piezoelectric layer 15 are not generated, and good vibration can be obtained. . Therefore, it is possible to transmit and receive ultrasonic waves at a high frequency to obtain a high-resolution B-mode image and in a wide band to ensure sufficient penetration. In addition, by driving the vibrator independently when the center frequency is high or low, sensitivity and fractional bandwidth equivalent to that of a normal vibrator can be secured, so in Doppler mode that drives the entire laminated piezoelectric element, This can reduce the decrease in sensitivity due to a shift in the frequency band of the ultrasonic probe with respect to the reference frequency.

FIG. 2 shows an ultrasonic probe according to another embodiment of the present invention. This ultrasonic probe further includes an acoustic matching layer 19 on the ultrasonic probe 10 shown in FIG. In general, the optimal conditions for acoustic matching layers differ depending on the number of layers, but a material is selected that has an acoustic impedance value between that of the transducer and the subject, and in the case of a multilayer configuration, the acoustic impedance value is selected so that it changes sequentially. . This acoustic matching layer 19 has the effect of widening the frequency band of the ultrasonic probe without changing its center frequency and increasing its sensitivity. The number of layers in the acoustic matching layer 19 is not limited to a single layer, and may be increased to two, three, and so on.

Here, if the acoustic matching layer 19 is a single layer, when a laminated vibrator driven at a low frequency is driven as a vibrator, the acoustic matching layer is a single layer of only the acoustic matching layer 19. On the other hand, when the piezoelectric ceramic layer 13 driven by high frequency is driven alone as a vibrator, the acoustic matching layer has a two-layer structure of the composite piezoelectric layer 15 and the acoustic matching layer 19. Hereinafter, if the acoustic matching layer 19 is similarly made into two layers, the actual acoustic matching layer will have a two-layer structure in the case of low-frequency drive, and a three-layer structure in the case of high-frequency drive.

The acoustic impedances of the piezoelectric ceramic layer 13 with a sound velocity of 4,500 m/sec and the composite piezoelectric layer 15 with a sound velocity of 3,800 m/sec are each 35 Mr.
ayls and 15 Mrayls. On the other hand, in the case of an ultrasonic diagnostic apparatus, the acoustic impedance of a human body as a subject is generally 1.5 Mrayls. The acoustic impedance of the acoustic matching layer 19 is 15 Mrayls and 1.5 Mrayls, which are the acoustic impedances of the medium on both sides.
A value intermediate between ls and ls is selected. In this case, the arrangement of the laminated structure of the laminated piezoelectric element of this embodiment is such that the composite piezoelectric layer 15, which has an acoustic impedance closer to that of the human body, is located on the ultrasonic wave transmitting/receiving surface side. suitable for Note that the material of the composite piezoelectric layer 15 can be arbitrarily selected as long as it satisfies the above conditions, and in some cases, it may be made of only a polymer material.

Further, in the embodiment, the switch 21 is provided in the main body 20 of the ultrasonic inspection apparatus, but it can also be built into the ultrasonic probe 10. In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

[0035]

[Effects of the Invention] According to the present invention, an ultrasonic probe constructed of a laminated piezoelectric vibrator consisting of a piezoelectric ceramic layer and a composite piezoelectric layer is used, and the piezoelectric ceramic layer alone and the entire laminated piezoelectric vibrator are By adopting a configuration in which they are each driven independently and selectively, it is possible to independently transmit and receive ultrasonic waves in two different frequency bands with wide relative bandwidths on the same transmission and reception wave surface. Therefore, when applied to a medical diagnostic device, for example, B-mode images and CFM images can be favorably obtained for a site within the same tomographic plane.

That is, when obtaining a high-resolution B-mode image, only the piezoelectric ceramic layer is driven to transmit and receive ultrasonic waves with a high center frequency, and images such as a B-mode image with penetration or a highly sensitive CFM image are When you get
The entire laminated piezoelectric vibrator consisting of a piezoelectric ceramic layer and a composite piezoelectric layer is driven to transmit and receive ultrasonic waves with a low center frequency. As a result, in B mode, resolution decreases and S
It is possible to obtain an image with penetration with less deterioration of /N, and in Doppler mode, it is possible to reduce the decrease in sensitivity due to deviation of the frequency band with respect to the reference frequency.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an ultrasonic inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view of an ultrasound probe according to another embodiment of the present invention.

[Explanation of symbols]

10...Ultrasonic probe
11... Backing material 12... External electrode layer
13... Piezoelectric ceramic layer 14... Internal electrode layer
15... Composite piezoelectric layer 16... External electrode layer
17...Piezoelectric ceramic material section 18...Polymer material section
19...Acoustic matching layer

Claims (1)

[Claims] [Claim 1] An ultrasonic inspection device that transmits and receives ultrasonic waves to inspect an object, in which a piezoelectric ceramic layer and a composite piezoelectric layer made of a piezoelectric ceramic material and a polymeric material are laminated with an electrode layer interposed therebetween. An ultrasonic inspection characterized by comprising an ultrasonic probe having a laminated piezoelectric vibrator, and a driving means for selectively applying a driving voltage to the single piezoelectric ceramic layer and the entire laminated piezoelectric vibrator. Device.