JPH03133300A - Composite piezoelectric ultrasonic probe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a composite piezoelectric ultrasonic probe constructed by laminating a polymer piezoelectric material and a ceramic piezoelectric material.

(Prior art) Linear array type ultrasound probes, convex array type ultrasound probes, and phased array type ultrasound probes have been conventionally used for linear electronic scanning and phased array electronic scanning. An array-type device in which a ceramic piezoelectric material such as titanium/lead zirconate or lead titanate is formed into a rectangular shape has been used for both transmitting and receiving purposes. These materials are the most widely used because of their high electro-mechanical coupling coefficients.

On the other hand, polyvinylidene fluoride (hereinafter abbreviated as PVDF)
and polyvinylidene sulfide-ethylene trisulfide copolymer (
Research has also progressed in recent years on ultrasonic probes using polymeric piezoelectric materials, such as PVDF-TrFE. These polymer piezoelectric materials generally have a small Q value (resonance sharpness), so they do not cause so-called tailing in the ultrasonic pulse waveform.
<、The pulse length is short and the resolution is good, and the specific acoustic impedance (=density x sound velocity) is 4 to 5 x 10'
kg/rd ・TAEC and that of living organisms (1.5X 1
Since it is relatively close to 0' kg/-.5ec), it has the advantage of being easy to achieve acoustic matching.

The aforementioned ceramic piezoelectric material has a large electro-mechanical coupling coefficient, but its high Q value causes tailing in the ultrasonic pulse waveform, lengthening the pulse length and reducing resolution, and its inherent acoustic impedance is higher than that of a living body. more than io times (approximately 30X
10'kgz/5ac), it has the disadvantage that it is difficult to achieve acoustic matching.

Conventionally, in order to compensate for these shortcomings, as shown in FIG. Efforts have been made to match the acoustic impedance as close to the living body as possible by adding a first matching layer 23, a second matching layer 24, etc. as acoustic matching layers to the surface side of the body, but this is still not sufficient. do not have.

Here, the backing material 22 is provided for the purpose of damping vibrations and absorbing sound waves, but as the braking performance is increased and the Q value is lowered, the sensitivity inevitably decreases, so that the braking performance and the Q value are There is a trade-off with sensitivity.

On the other hand, polymer piezoelectric materials have a significant disadvantage of low sensitivity due to their small electro-mechanical coupling coefficients, and are currently not suitable for use alone.

In order to overcome the drawbacks of using a ceramic piezoelectric material or a polymer piezoelectric material alone, Japanese Patent Laid-Open No. 59-1370
There is an ultrasonic probe known as No. 39. This ultrasonic probe uses a ceramic piezoelectric material as a transmitting transducer and a polymer piezoelectric material as a receiving transducer.With such a composite configuration, each piezoelectric The aim is to create a highly sensitive ultrasound probe by complementing only the strengths of the body.

(Problem to be Solved by the Invention) However, in the ultrasonic probe disclosed in JP-A-59-137039, for example, a ceramic piezoelectric material and a polymer piezoelectric material are arranged at adjacent positions on the same plane. Since the structure is such that the echoes of the ultrasound emitted from the ceramic piezoelectric material are received by the adjacent polymeric piezoelectric material, there are problems in that it is difficult to receive echoes from the desired depth of focus and the directivity is poor. Generally, the configuration is complicated, making it difficult to manufacture and increasing costs.

The present invention has been made to solve the above problems, and its purpose is to create a ceramic piezoelectric material by laminating a polymer piezoelectric material and a ceramic piezoelectric material and using them as a whole for both transmission and reception. It has the individual advantages of body and polymer piezoelectric material, and is
A compound piezoelectric ultrasonic probe that eliminates the poor directivity and manufacturing defects of the compound ultrasonic probe shown in No. 39, and has high sensitivity, wide band, short pulse length, and high resolution. Our goal is to provide the following.

(Means for Solving the Problems) In order to achieve the above object, a first invention provides a first invention in which a polymer piezoelectric material and a ceramic piezoelectric material each having an electrode formed on both surfaces are laminated with their polarization directions facing each other, and the laminated The electrodes on the surfaces are commonly connected, and the electrodes on the other side are also commonly connected, and the laminated polymer piezoelectric material and ceramic piezoelectric material are used for transmitting and receiving ultrasonic waves.

Further, a second invention provides a device which can also be used for transmitting and receiving ultrasonic waves by laminating the polymer piezoelectric body and the ceramic piezoelectric body through an acoustic matching layer having a thickness that is approximately 1/4 of the ultrasonic wavelength. When transmitting and receiving ultrasonic waves, a time delay is created in the signal transmission system of the transmitting circuit and receiving circuit connected to the polymer piezoelectric material, taking into account the propagation time of the ultrasonic waves within the matching layer. It is something that

(Function) According to the first or second invention, by laminating the polymer piezoelectric material and the ceramic piezoelectric material to serve both as transmitting and receiving functions, the advantages of each piezoelectric material can be utilized, and the sensitivity can be reduced. It has a relatively small Q value and wideband frequency characteristics, so there is no tailing in the transmitted and received waveforms.
A probe with high resolution and directivity can be realized.

(Example) Hereinafter, each invention will be described in detail with reference to the drawings.

First, FIG. 1 shows the main parts of an embodiment according to the first invention. In the figure, 1 is a rectangular ceramic piezoelectric body made of titanium, lead zirconate, etc. 1 are arranged in an array with gaps 4 interposed therebetween. Moreover, on the surface side of the ceramic piezoelectric body 1,
A polymeric piezoelectric material 2 such as PVDF is laminated and bonded.

Here, the gap 4 is provided to separate the electrical and acoustic coupling between the rectangular ceramic piezoelectric bodies 1, and is made of an air layer, a resin with high ultrasonic attenuation, or the like.

Furthermore, a backing material 3 mainly composed of rubber or the like is adhered to the back surface of the ceramic piezoelectric body 1.

Note that this ultrasonic probe is used with the polymer piezoelectric material 2 side facing the living body as a diagnosis target, and although not shown in the figure, the ultrasonic probe is used on the surface side of the polymer piezoelectric material 2. An acoustic lens is provided for focusing. Furthermore, an acoustic matching layer may be provided on the surface side of the 11-polymer piezoelectric material 2, if necessary, in order to improve the acoustic matching with the living body.

In addition, PVDF used as the polymer piezoelectric material 2 is relatively flexible, and moreover, the array direction (ceramic piezoelectric material 1
Since the acoustic coupling in the adjacent direction) can be reduced, it is not necessarily necessary to cut and separate the ceramic piezoelectric body 1 into strips as in the case of the ceramic piezoelectric body 1 shown in the figure.

However, if it is desired to further reduce the acoustic coupling in the array direction, as in another embodiment shown in FIG. A structure may be used in which a gap 4a is interposed, and also in this embodiment, an acoustic matching layer may be provided on the polymer piezoelectric body 2a side if necessary.

FIG. 3 is a partial sectional view taken along the line AA in FIG. 2, and illustrates the state of the electrodes connected to each piezoelectric body 1, 2a. Note that the configuration of these electrodes is substantially the same in the embodiment shown in FIG.

In FIG. 3, each piezoelectric body 1, 2a has its own polarization direction P.
, , P are stacked to face each other, one common electrode 6 is formed on the stacked surface S, and the other common electrode 7 is formed on each surface other than the stacked surface 5. It is formed. Then, a high voltage is transmitted between these electrodes 6 and 7.
By applying a pulse, each piezoelectric body 1, 2a is sequentially excited in the array direction, and ultrasonic waves are emitted in the direction of the living body.
In addition, echoes from the living body are generated as vibrations in each piezoelectric body 1, 2a.
The voltage generated between the plane electrodes 6 and 7 is guided to a reception add-on circuit (not shown).

Note that FIG. 4 shows the frequency characteristics of the sensitivity determined from the amplitudes of the transmitted and received voltages. In the same figure, b is the characteristic of a probe using only a ceramic piezoelectric material, and although the sensitivity is high, the Q
The value is not small enough and the frequency band is narrow. Further, C is a characteristic of a probe using only a polymeric piezoelectric material, and has a low sensitivity, a small Q value, and a wide frequency band.

On the other hand, a is a characteristic of the composite piezoelectric ultrasonic probe according to the present invention, and it is clear that the overall sensitivity is high, the Q value is not so large, and it has a sufficiently wide frequency band. Obtaining broadband characteristics on the frequency spectrum means that the transmitted and received pulses become short pulse-like on the time axis, making it possible to obtain a probe with high resolution and no tailing in the waveform. Can be done. Therefore, the probe according to the present invention can be said to be extremely excellent as a probe using the pulse echo method.

Next, FIG. 5 shows the main part of an embodiment according to the second invention, and is a partial sectional view corresponding to the previous FIG. 3.

In this invention, a ceramic piezoelectric body and a polymer piezoelectric body are laminated with an acoustic matching layer interposed therebetween.

That is, in FIG. 5, electrodes 9a and 10a are formed on both sides of the ceramic piezoelectric body 1 laminated on the backing material 3 by vapor deposition or baking, and one electrode 9
An acoustic matching layer 8 having a thickness approximately 1/4 of the ultrasonic wavelength is adhered to the upper surface of a for the purpose of acoustic matching. Furthermore, a polymer piezoelectric material 2b having electrodes 9b and 10b formed on both surfaces is laminated by adhesive on its upper surface.

Here, the polarization directions P - P a of the piezoelectric bodies 1 and 2b are the same, and the electrodes 10a and 1Ob are used as ground electrodes, and the electrodes 9a and 9b are used as electrodes to which a positive high voltage is applied. It will be done. In this case, the electrode 10a
, 10b can be connected in common, but the electrode 9a
, 9b, it is not preferable to connect them in common because it is necessary to give a time delay to the signal during transmission and reception as will be described later. Of course, if it is desired to further improve the acoustic matching with the living body, a second acoustic matching layer may be added above the polymeric piezoelectric material 2b.

The polymer piezoelectric body 2b may be either flat or strip-shaped as shown in FIG. 1 or 2.

In this embodiment, the acoustic matching layer 8 has an acoustic impedance Z intermediate between the acoustic impedance Zo of the ceramic piezoelectric body 1 and that of the polymeric piezoelectric body 2b. For example.

The value Zn=f'-n is used.-For example, 10'kg/nf・
In see units, if Zo=30, Z,=4, then Z, l
= Kasou τ ~11.0.

As a result, compared to the first invention, the acoustic matching between the ceramic piezoelectric body 1 and the polymer piezoelectric body 2b is further improved, and there is no reflection of ultrasonic waves, and the energy transmission efficiency is further improved. The characteristics are also broadband.

However, if ultrasonic waves are simultaneously transmitted or received by both piezoelectric bodies 1 and 2b, the acoustic matching layer 8 interposed between them
The waveforms of the two waveforms are shifted by an amount equal to the propagation time t of the ultrasonic waves inside, and the combined waveform is deteriorated.

Therefore, in order to prevent this, a time delay may be applied to the signal transmission system of the transmitting circuit and the receiving circuit connected to the polymer piezoelectric material 2b on the side closer to the living body, as shown in FIG. Here, although the optimal time delay T is approximately equal to t, there is actually a slight difference depending on the voltage waveforms to be transmitted and received.

In FIG. 6, when transmitting ultrasonic waves, a trigger pulse output from a transmission trigger generator 11 is applied to a pulser 13 that drives a polymer piezoelectric body 2b via a delay circuit 12 that provides the time delay T, Furthermore, the trigger pulse is directly applied to the pulser 14 that drives the ceramic piezoelectric body 1 . As a result, the ultrasonic waves from the piezoelectric bodies 1 and 2b are synthesized in the same phase.

On the other hand, when echoes are received, a delay circuit 15 applies a similar time delay, and an addition amplifier 16 adds and synthesizes the echoes with the same phase.

In this embodiment as well, a frequency characteristic a as shown in FIG. 4 can be obtained, the Q value is not so high, and a probe with a wide band and high sensitivity can be realized.

In each of the above embodiments, the case where the first and second inventions are applied to a linear array type probe has been described, but each invention is applicable to a phased array type probe or a convex array type probe. The same applies to children, etc.

(Effects of the Invention) As described above, according to the first or second invention, a highly sensitive ceramic piezoelectric material and a polymeric piezoelectric material having a small Q value and a wide frequency band are laminated and can be used for both transmitting and receiving purposes. Since it is used as a transducer, it is possible to transmit and receive ultrasonic waves with high sensitivity and short pulse length, and it is possible to provide a highly sensitive ultrasonic probe with extremely high resolution and an ultrasonic diagnostic apparatus.

In addition, since the ultrasonic wave transmitting and receiving surfaces are structurally the same, it has excellent directivity, has a generally simple structure, is easy to manufacture, and can be provided at low cost.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of the first invention, FIG. 2 is a partial sectional view showing another embodiment, FIG. 3 is a partial sectional view taken along line A-A in FIG. 2, and FIG. FIG. 5 is a partial sectional view showing an embodiment of the second invention, FIG. 6 is a block diagram of a transmitting/receiving circuit, and FIG. 7 is a sensitivity-frequency characteristic diagram of the first and second inventions. FIG. 2 is a perspective view showing an example of a sonic probe. 1... Ceramic piezoelectric body 2.2a, 2b... Polymer piezoelectric body 3... Backing material 4.4a... Gap 5... Lamination surface 6, 7.9a, 9b, 10a, 10b- Electrode 8...
Acoustic matching layer p,, p2...polarization direction

Claims (2)

[Claims] (1) In a composite piezoelectric ultrasonic probe equipped with a polymer piezoelectric material and a ceramic piezoelectric material each having electrodes formed on both sides, the polymer piezoelectric material and the ceramic piezoelectric material are arranged so that their respective polarization directions face each other. A composite piezoelectric ultrasonic probe characterized in that the laminated polymer piezoelectric material and ceramic piezoelectric material are used for transmitting and receiving ultrasonic waves. (2) In a composite piezoelectric ultrasonic probe equipped with a polymer piezoelectric material and a ceramic piezoelectric material each having electrodes formed on both sides, the polymer piezoelectric material and the ceramic piezoelectric material are placed between them at an ultrasonic wavelength. Composite piezoelectric type ultrasound characterized by laminating layers through acoustic matching layers having a thickness of approximately 1/4 of probe.