JP2001258879A - Ultrasonic transducer system and ultrasonic transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic transducer technology allowing the detection of a harmonics signal with higher sensitivity than heretofore. SOLUTION: This ultrasonic transducer has a transmitting piezoelectric vibrator 102, a receiving piezoelectric vibrator 104, a housing 106 for accommodating the piezoelectric vibrators 102, 104, and a concave acoustic lens 108. The transmitting piezoelectric vibrator 102 has resonance frequency ft, and the receiving piezoelectric vibrator 104 has resonance frequency nft [(n) is an integer of 2 or more]. Driving voltage is applied to the transmitting piezoelectric vibrator 102 only for a time t1. During a specified time t2(>t1) from the application of the driving voltage, a low resistance state including short circuit is maintained between electrodes of the receiving piezoelectric vibrator 104, and until the following driving voltage is applied to the transmitting piezoelectric vibrator 102 after the lapse of the specified time t2, a high resistance state including release is maintained between the electrodes of the transmitting piezoelectric vibrator 102.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an ultrasonic transducer and an ultrasonic transducer system used for harmonic imaging ultrasonic diagnosis.

[0002]

2. Description of the Related Art Harmonic imaging ultrasonic diagnostic methods have recently attracted attention. This diagnostic method is roughly divided into
It is classified into contrast harmonic imaging using a contrast agent and tissue harmonic imaging which detects and displays an image by detecting nonlinearity of elastic properties of living tissue. The situation is described in detail in "Special Issue on Clinical Ultrasound of Electronics -Latest Ultrasound-: Textbook distributed at the 1999 Annual Meeting of the Japanese Society of Ultrasound Medicine".

[0003] In tissue-harmonic imaging, an ultrasonic pulse having a center frequency f0 is transmitted to living tissue without using an ultrasonic contrast agent, and a harmonic component nf0 (n is 2 or more) included in the returned echo signal. ) Is extracted, and a diagnostic image is obtained by displaying a relationship between the amplitude and the echo signal reception time on a tomographic image. For extracorporeal use, diagnostic devices equipped with this function are already on the market. The tissue harmonic imaging diagnostic method enables relatively clear observation of cardiac structures such as the left ventricular wall even in obese cases, elderly people, or smokers, where echo images have often been unclear due to noise contamination.

At present, this diagnostic technique is used only for extracorporeal use, and only the second harmonic (n = 2) is used. In order to receive this second harmonic efficiently, it is necessary to transmit in the lower half of the band of the ultrasonic transducer and receive in the upper half. For this purpose, a broadband ultrasonic transducer has been used, and drive control for widening the band has been performed.

However, at present, the bandwidth and sensitivity cannot be said to be sufficient. Further, when dealing with harmonics of n ≧ 3, a large fractional bandwidth greater than the fractional bandwidth of the currently optimally designed ultrasonic transducer is required. This is extremely difficult to achieve with conventional ultrasonic transducer design and manufacturing techniques. As a next best measure, it is possible to widen the band by devising the drive waveform, but widening causes a decrease in sensitivity.

Normally, the harmonic signal is 15 to 20 dB in the second order and 15 to 2 in the third order compared to the fundamental frequency signal.
It is said that 0 dB sensitivity decreases. Therefore, the decrease in sensitivity due to the above-mentioned widening of the band causes further deterioration of the diagnostic image, which is not preferable.

Further, when transmission and reception are performed by the same piezoelectric vibrator, a harmonic signal is mixed with a harmonic signal, and a special device is required to extract only a weak harmonic signal from the harmonic signal with high accuracy. . The above problem cannot be avoided as long as f0 transmission and 2f0 reception are performed by the same piezoelectric vibrator.

Japanese Patent Application Laid-Open No. H11-155863 discloses an ultrasonic wave in which a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator are housed in a single case to efficiently receive a harmonic component. 1 discloses a transducer.
FIG. 14 shows the configuration of this ultrasonic transducer.

As shown in FIG. 14, an ultrasonic transducer 1000 includes a transmitting piezoelectric ultrasonic vibrator 100.
2 and a receiving polymer piezoelectric vibrator 1004 disposed in front of it.
04 and the transmitting piezoelectric ultrasonic vibrator 1002 are arranged in layers with an acoustic matching layer 1006 interposed therebetween.

The front electrodes of the transmitting piezoelectric ultrasonic vibrator 1002 and the receiving polymer piezoelectric vibrator 1004 are both connected to a ground lead wire 1008 and are kept at the ground potential. An electrode on the rear side of the transmitting piezoelectric ultrasonic vibrator 1002 is connected to a transmitting shield wire 1010, and a driving voltage is supplied through the transmitting shield wire 1010. An electrode on the rear side of the receiving polymer piezoelectric vibrator 1004 is a receiving shield wire 1012.
, Through which a received signal is extracted.

The transmitting piezoelectric ultrasonic vibrator 1002 has a resonance frequency or an anti-resonance frequency that matches the resonance frequency of the ultrasonic contrast agent or a frequency having a specific relation to the resonance frequency of the ultrasonic contrast agent. Have. On the other hand, the receiving polymer piezoelectric vibrator 1004 is a non-resonant type piezoelectric vibrator, and can also receive a harmonic component generated based on the non-linear behavior of the ultrasonic contrast agent.

[0012] The ultrasonic transducer 1000
Since the acoustic matching layer 1006 is provided between the transmitting piezoelectric ultrasonic vibrator 1002 and the receiving high-molecular piezoelectric vibrator 1004, injection of cancerous tissue in which blood capillaries are concentrated in blood vessels in the human body or in the peripheral part. Only the portion where the ultrasonic contrast agent is present can be drawn more clearly than other portions.

[0013]

Since the ultrasonic transducer 1000 has a separate transmitting piezoelectric vibrator and a receiving piezoelectric vibrator, it is possible to use a single piezoelectric vibrator which has been generally used in the past. Compared with an ultrasonic transducer that performs transmission and reception, it is expected that the bandwidth can be easily widened and characteristics suitable for harmonic imaging are exhibited.

However, since the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator are arranged in layers, during transmission, when transmitting the ultrasonic wave through the receiving piezoelectric vibrator, residual vibrations occur in the transmitted ultrasonic wave. At the time of reception, when receiving ultrasonic waves reach the transmitting piezoelectric vibrator, residual vibrations are superimposed on the received ultrasonic waves. Such superposition of the residual vibration causes a great degradation in resolution. This fact has been confirmed experimentally and by simulations by the present inventors.

As described above, the ultrasonic transducer 1000 disclosed in Japanese Patent Application Laid-Open No. H11-155863 has the acoustic matching layer 1006 between the transmitting piezoelectric vibrator 1002 and the receiving piezoelectric vibrator 1004. Although it is possible to eliminate the reflection at the boundary between the transmitting piezoelectric vibrator 1002 and the receiving piezoelectric vibrator 1004, no measure is taken against residual vibration. In addition, the document does not teach or suggest measures against residual vibration.

An object of the present invention is to have a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator housed in the same case,
It is an object of the present invention to provide an ultrasonic transducer technology capable of detecting a harmonic signal with high sensitivity without being affected by resolution degradation caused by residual vibration.

[0017]

SUMMARY OF THE INVENTION The present invention, in one aspect, is an ultrasonic transducer system, comprising: a transmitting piezoelectric vibrator for transmitting ultrasonic waves having a resonance frequency ft disposed in layers with each other; and a resonance frequency nft ( n is an integer of 2 or more)
An ultrasonic transducer having a receiving piezoelectric vibrator for receiving ultrasonic waves, and control means for controlling the ultrasonic transducer, wherein the control means applies a drive voltage to the transmitting piezoelectric vibrator only during time t1. During the predetermined time t2 (> t1) from the application of the drive voltage, the electrodes of the receiving piezoelectric vibrator are maintained in a low resistance state including a short circuit,
After the lapse of the predetermined time t2, until the next drive voltage is applied to the transmitting piezoelectric vibrator, an ultrasonic transducer system that holds the electrodes of the transmitting piezoelectric vibrator in a high resistance state including an open state is used. is there.

According to another aspect of the present invention, there is provided an ultrasonic transducer, comprising: a transmitting piezoelectric vibrator for transmitting ultrasonic waves having a resonance frequency ft; and an ultrasonic transducer having a resonance frequency nft (n is an integer of 2 or more). One of the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator has an annular shape, and the other of the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator has a disc shape. The disk-shaped piezoelectric vibrator is an ultrasonic transducer arranged inside the annular piezoelectric vibrator.

According to still another aspect of the present invention, there is provided an ultrasonic transducer, comprising: a plurality of transmitting piezoelectric vibrators for transmitting ultrasonic waves having a resonance frequency ft;
a plurality of receiving piezoelectric vibrators for receiving ultrasonic waves of ft (n is an integer of 2 or more), wherein the transmitting piezoelectric vibrators and the receiving piezoelectric vibrators are radially and alternately arranged. It is a transducer.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] This embodiment is an ultrasonic transducer system suitable for harmonic imaging ultrasonic diagnosis, which includes an ultrasonic transducer and a control system thereof. Below,
First, an ultrasonic transducer will be described, and then a control system thereof will be described.

[Structure] As shown in FIG. 1, the ultrasonic transducer comprises a transmitting piezoelectric vibrator 102, a receiving piezoelectric vibrator 104, and these piezoelectric vibrators 102 and 10.
4 and a concave acoustic lens 108.

The transmitting piezoelectric vibrator 102 is, for example, a piezoelectric element made of piezoelectric ceramics such as lead zircon titanate PZT or a bismuth layered structure, or a single crystal such as quartz, lithium niobate, or PZT. Receiving piezoelectric vibrator 104
Is, for example, a polymer piezoelectric element made of a polymer resin such as polyvinylidene fluoride or vinylidene cyanide, or a composite piezoelectric element in which columnar piezoelectric ceramics are distributed in an epoxy resin or the like.

The transmitting piezoelectric vibrator 102 and the receiving piezoelectric vibrator 104 are laminated with an acoustic matching layer 110 interposed therebetween, and a damping layer 112 is provided on the back surface of the transmitting piezoelectric vibrator 102. This laminated structure is fixed in the housing 106 by an insulating layer 114 lined on the inner wall of the housing 106. The insulating layer 114 insulates the housing 106 from the electrodes of the piezoelectric vibrators 102 and 104. The acoustic lens 108 includes the receiving piezoelectric vibrator 104.
It is arranged on the front of.

The electrode on the ultrasonic wave emitting side of the transmitting piezoelectric vibrator 102 and the electrode on the opposite side of the ultrasonic wave emitting side of the receiving piezoelectric vibrator 104 are electrically connected to the housing 106 by wiring 116. And is kept at the same potential.
The two-core coaxial cable 118 has a lead wire 122 electrically connected to an electrode on the side opposite to the ultrasonic wave emitting side of the transmitting piezoelectric vibrator 102, and a lead wire 124 connected to the receiving piezoelectric vibrator 1.
04 is electrically connected to the electrode on the ultrasonic wave emitting side, and the shield line 120 is electrically connected to the housing 106.

The transmitting piezoelectric vibrator 102 has a resonance frequency ft
And the receiving piezoelectric vibrator 104 has a resonance frequency nft (n
Is an integer of 2 or more). For example, the transmitting piezoelectric vibrator 102 has a resonance frequency of 5 MHz, and the receiving piezoelectric vibrator 104 has a resonance frequency of 10 MHz. The resonance frequencies of the piezoelectric vibrators 102 and 104 are adjusted by controlling their thickness.

The receiving piezoelectric vibrator 104 may be formed by bonding a piezoelectric polymer film in a polarized state in advance by bonding. However, the transmitting piezoelectric vibrator 104 is affected by the pressure at the time of bonding, the influence of air bubbles, and the effect of the adhesive layer. In some cases, the structure and characteristics as designed cannot be stably obtained due to damage to the vibrator, uneven thickness of the adhesive layer, and the like. In such a case, it is desirable to form a piezoelectric polymer layer capable of surface energy poling. This method is described in the literature "JunyaIDE et al: Jpn J. Appl. Phys.
Vol.38 (1999) pp2049-2052 ", and a polymer material such as polycyanophenyl sulfide is formed on the electrode formed on the surface of the acoustic matching layer 110, and the upper electrode is formed after curing. The polarization state can be spontaneously realized after the film formation by the effect of the surface energy without performing the polarization treatment. Since it can be formed by spin coating or the like, it is easier to realize a target structure than a method of bonding a piezoelectric polymer film in a polarized state by adhesion. This polymer material is used for the acoustic matching layer 110.
A drop is dropped on an electrode (not shown) formed on the surface, spin-coated at an appropriate number of revolutions, and an upper electrode is further formed to form the receiving piezoelectric vibrator 104.

Next, the setting of the radius of curvature of the spherical surface of the acoustic lens 108 will be described with reference to FIG. FIG. 5A shows the radius of curvature R of the acoustic lens disposed on the front surface of the disk-shaped piezoelectric vibrator.
And the relationship between the focal length F in the ultrasonic propagation medium of water,
The horizontal axis D (= a ² / λR ′, a: aperture radius, λ: wavelength in the propagation material of the ultrasonic wave, R ′: R ′ is the apparent radius of curvature of the lens
= 2.25R, R: radius of curvature of the acoustic lens) and the vertical axis F / R ', which is derived from the well-known Rayleigh equation. FIG. 5B shows the relationship between the focal point and the actual radius of curvature of the acoustic lens for the cases of 5 MHz and 10 MHz.
From FIG. 5 (B), in order to focus on the same position, for example, a position of 30 mm at any frequency, a different radius of curvature, for example, 16 mm for 10 MHz, 5 MH
It can be seen that it is desirable to set z to 40 mm. However, the aperture surfaces for transmitting and receiving ultrasonic waves are shared. For this reason, the acoustic lens 108 is set to an intermediate value between the two radii of curvature, for example, 25 mm, and realizes an optimum focus imaging state in this structure.

Although the average value is used in the above description, the radius of curvature may be partially changed so that the center is optimal for reception and the periphery is optimal for transmission (or vice versa).

The above description is for the case where a harmonic signal of 10 MHz has been generated from the time of transmission. In practice, however, the harmonic signal is gradually generated due to the nonlinearity of the elastic modulus of the living body together with the propagation distance of the ultrasonic wave. Is not far away. However, since the distance from the focal point at the fundamental frequency increases with the order of the harmonics signal, the defocus of the two becomes large with it, thereby canceling out the improvement of the ultrasonic image resolution by the harmonics imaging.

Next, a control system for controlling transmission and reception of the above-described ultrasonic transducer will be described with reference to FIG.

FIG. 6A schematically shows the configuration of the control system. As shown in FIG. 6A, the control system includes an on / off control device 150 for controlling the transmitting piezoelectric vibrator 102.
And a selector 160 for controlling the signal flow of the receiving piezoelectric vibrator 104. On-off control device 1
50 supplies the high voltage Vd supplied from the terminal 152 to the transmitting piezoelectric vibrator 102 according to the control signal Vt input from the terminal 154. The selector 160 converts the received signal of the receiving piezoelectric vibrator 104 into the branch 1 connected to the amplifier according to the control signal Vr input from the terminal 162.
64 and one of the grounded branches 166.

FIG. 6B shows an on / off control device 150.
And a timing chart of control signals Vt and Vr input to the selector 160. As can be seen from this timing chart, a pulse having a pulse width t1 is input to the terminal 154 of the on / off control device 150 and a pulse width t2 (>) to the terminal 162 of the selector 160 at a period of t3.
The pulse of t1) is input. The timing chart shows the control waveform of a single rectangular wave.
According to the method disclosed by the present inventors in Japanese Patent Application No. 10-178861, a bipolar double pulse voltage waveform is more preferable.

[Operation] A bipolar double pulse voltage is applied to the transmitting piezoelectric vibrator according to, for example, the method disclosed in Japanese Patent Application No. 10-178861 by the present inventors. Since the transmitting piezoelectric vibrator has a relatively large Qm, this voltage application method can generate an ultrasonic pulse having a large sound pressure amplitude and a large band. Since the actual Qm greatly depends not only on the Qm of the piezoelectric vibrator but also on the degree of damping of the damping layer 112, for example, even with a piezoelectric vibrator having a Qm of several tens, it is possible to weaken the degree of damping and obtain the same effect. It is.

The transmitted ultrasonic wave is transmitted to the receiving
Of ultrasonic wave when transmitting through ultrasonic transducer
Waves periodically deform in the receiving ultrasonic transducer
Generates a surface charge of a polarity that restricts the surface charge. This charge is piezoelectric
Electric field in a direction that restricts the change in polarization state in the oscillator
And mechanical displacement is unlikely to occur due to the inverse piezoelectric effect.
A hard state. Meanwhile, the surface charge
Is discharged by an external circuit.
It does not produce an electric field in the direction of
Thus, a hard state is not induced. That is, the piezoelectric vibration
The pressure depends on how the charge generated between the electrodes of the rotor is treated.
A difference appears in the hardness of the electric vibrator. This phenomenon is a piezoelectric vibrator
This is a peculiar phenomenon that occurs in the stiffener of a piezoelectric vibrator.
Is c ^E(Electric field 0) and c^D(Electrical displacement 0), c^E= (1-K^Two) c^D (K: electromechanical coupling constant) is a well-known phenomenon. Ultrasonic waves
The thickness of the piezoelectric vibrator through which ultrasonic waves pass is sufficient compared to the length
When the thickness is large, there is almost no effect of the generation of the surface charge,
As in the present embodiment, the thickness of the piezoelectric vibrator is about 1 / 4λ.
In the case of degrees, it has a big impact.

FIG. 8 shows a simulation result obtained by calculating the influence. In FIG. 8, the vertical column shows the relationship between the state of charge processing between the electrodes of the receiving piezoelectric vibrator 104 during transmission and the state of charge processing between the electrodes of the transmitting piezoelectric vibrator 102 during reception. That is, (a), (b),
(c) shows the state of charge processing between the electrodes of the receiving piezoelectric vibrator 104 during transmission, the state of charge processing between the electrodes of the transmitting piezoelectric vibrator 102 during the reception / short / short, (d), (e), (f)
Is short / open, (g), (h), (i) is open / open, (j), (k), (l) is an ultrasonic pulse for transmission only when open / short (left column) , The reception-only ultrasonic pulse (middle row) and the transmission / reception total ultrasonic pulse (right row). It is clear from FIG. 8 that in the case of short / short and open / short, residual vibrations appear from (b) and (k), respectively, and it cannot be said that this is a preferable method of treating charges between electrodes. Note that the short state is a low resistance state including a short circuit, and the open state is a high resistance state including an open state.

[0036]

[Table 1]

Table 1 shows characteristic values of these pulse waveforms, that is, Vpp: maximum pulse amplitude, CF: center frequency,
PW: -20 dB pulse width. Vpp
Based on the general idea that large and small PW lead to wide band and high sensitivity, this table shows that the short / open inter-electrode charge processing method, It can be seen that it is most preferable that the ultrasonic transducer 104 is controlled so that the electrodes are short-circuited, and the receiving ultrasonic transducer 102 is controlled to be open between the electrodes during reception. This phenomenon is basically different from the effect obtained by providing the acoustic matching layer 112 at the boundary between the transmitting ultrasonic transducer 102 and the receiving ultrasonic transducer 104 in principle,
This is an indispensable control method.

Next, the operation according to this embodiment will be described with reference to FIG.

The on / off control device 150 is connected to the terminal 15
2, a DC voltage Vd is applied, and a control signal Vt whose pulse width or the like is controlled is input to a terminal 154. The control signal Vt is a rectangular wave, an impulse wave, a bipolar double pulse wave, or the like. For example, as shown in FIG.
This is a rectangular wave having a period of t3 and a pulse width of t1. The transmitting piezoelectric vibrator 102 generates an ultrasonic pulse 174 according to the pulse waveform of the input control signal Vt.

The transmission ultrasonic pulse 174 has a center frequency f
t, which is reflected at the acoustic discontinuity interface 172 of the biological tissue 170 and, due to the non-linearity of the elastic properties of the living body, relatively disperses the harmonic signal at the frequency nft (n is an integer of 2 or more). It becomes an echo signal 176 that contains a lot,
It is received by the receiving piezoelectric vibrator 104. The receiving piezoelectric vibrator 104 has a resonance frequency having a frequency nft (n is an integer of 2 or more) as a center frequency, and thus selectively receives the harmonic signal and converts it into an electric signal.

The selector 160 guides the received signal of the receiving piezoelectric vibrator 104 to one of the branches 164 and 166 in accordance with the control signal Vr input to the terminal 162.
The control signal Vr is a rectangular wave having a pulse width of t2 having the same cycle as the cycle t3 of the control signal Vt, and is synchronized with the control signal Vt. The selector 160 guides the received signal to the grounded branch 166 during a time t2 corresponding to "H", and a subsequent signal processing unit such as an amplifier during a time t4 = t3-t2 corresponding to "L". To the branch 164 connected to

The pulse width t2 of the control signal Vr is
The pulse width t is set to be longer than the pulse width t1, which corresponds to at least the time required for the ultrasonic waves generated by the transmitting piezoelectric vibrator 102 to completely pass through the receiving piezoelectric vibrator 104.

The control signal Vr input to the terminal 162 is
At the timing when the echo signal 176 is received by the receiving piezoelectric vibrator 104, the signal is switched to “L”. Therefore, the received signal Vout from the receiving piezoelectric vibrator 104 is guided to a subsequent signal processing unit such as an amplifier. .

As described above, it is preferable that the gap between the electrodes of the transmitting piezoelectric vibrator 102 at the time of reception is controlled to be in an open state or a state close thereto. While the echo signal 176 is received by the receiving piezoelectric vibrator 104, the control signal Vr is “L”, so that the electrodes of the transmitting piezoelectric vibrator 102 are kept substantially open.

In this control, it is preferable that a control device capable of obtaining a large output voltage and a large output voltage when the output resistance is low when the output resistance is on and not when the output resistance is on is used for the last stage of the transmission drive circuit, instead of the transformer coupling. Such a control device includes, for example, a high-speed power MOSF having a large output voltage.
ET is suitable.

The piezoelectric polymer constituting the receiving piezoelectric vibrator 104 has a large piezoelectric g constant and a large receiving sensitivity, but has a small Qm, and therefore has low selectivity with respect to the receiving frequency. Therefore, in some cases, it is effective to connect an inductance in parallel to the receiving piezoelectric vibrator 104 in order to improve the selectivity. Further, the Qm of the composite piezoelectric material is more preferable because it is larger than the Qm of the polymer piezoelectric material and has relatively high selectivity.

Hereinafter, a modification of the present embodiment will be described with reference to the drawings. In the drawings, members equivalent to those described above are denoted by the same reference numerals, and a detailed description thereof will be omitted in the following description to avoid duplication.

FIG. 2 shows a first modification of the ultrasonic transducer. The ultrasonic transducer of this modification includes a convex acoustic lens 132 and an acoustic lens 132.
And a buffer layer 134 provided between the receiving piezoelectric vibrators 104. Convex acoustic lens 132
Means that the sound speed of the lens material is 1500 m / s
It corresponds to the case smaller than ec. Buffer layer 134
Improves the bonding between the acoustic lens 132 and the receiving piezoelectric vibrator 104.

In this modification, the acoustic matching layer 110 in FIG. 1 is not provided between the transmitting piezoelectric vibrator 102 and the receiving piezoelectric vibrator 104, but the transmitting piezoelectric vibrator 102 and the receiving piezoelectric vibrating It is more preferable to have an acoustic matching layer between the elements 104. Since the silicone resin used as the material of the convex acoustic lens 132 generally has poor adhesion to other resin materials, the acoustic lens 132 and the receiving piezoelectric vibrator 104 are preliminarily heated and bonded to a polyimide resin film as a buffer layer. Should be joined.

FIG. 3 shows a second modification of the ultrasonic transducer. The ultrasonic transducer of this modification does not have an acoustic lens, and the receiving piezoelectric vibrator 1
Only the insulating layer 136 is formed on the front surface of the substrate 04. This ultrasonic transducer can be provided at a low cost for the purpose of detecting biological information that has not been conventionally obtained by using a harmonics signal without making the lateral resolution much a problem.
Also in this modification, it is more preferable to have an acoustic matching layer between the transmitting piezoelectric vibrator 102 and the receiving piezoelectric vibrator 104.

FIG. 4 shows a third modification of the ultrasonic transducer. The ultrasonic transducer of this modification includes a transmitting piezoelectric vibrator 138 and a receiving piezoelectric vibrator 14.
0 and the insulating layer 142 are both concave. This structural feature allows the ultrasound transducer to focus ultrasound without an acoustic lens. Also in this modification,
It is more preferable to have an acoustic matching layer between the transmitting piezoelectric vibrator 138 and the receiving piezoelectric vibrator 140.

FIG. 7A schematically shows a configuration of a modified example of the control system, and FIG. 7B shows a timing chart of the control signal Vt.

In this control system, the receiving piezoelectric vibrator 104
Does not include the selector 160, but instead has a transformer 180 connected in parallel and a capacitor 182 connected to the secondary side of the transformer 180. The other configuration is the same as the control system shown in FIG.

The transformer 180 has a small primary-side inductance, and has an impedance ωL with respect to the frequency ft during transmission (L is the primary-side inductance of the transformer 180).
Is set to an inductance value that can be regarded as substantially in a short state. The capacitor 182 has a frequency n
ft (n is an integer of 2 or more).

In this control system, the receiving piezoelectric vibrator 104
Out of the received signal, only the component of nft (n is an integer of 2 or more), that is, the harmonics signal is selectively boosted by the secondary-side tuning circuit (transformer 180 and capacitor 182), and is output as an output Vout by an amplifier or the like. It is sent to the signal processing unit.

[Effect] The ultrasonic transducer has a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator arranged in layers, and the control system short-circuits the electrodes of the receiving piezoelectric vibrator during ultrasonic transmission. Or a state close to it for a specific time, and at the time of ultrasonic reception, control is performed to keep the electrodes of the transmitting piezoelectric vibrator open or close to the state for a specific time, thereby eliminating noise components due to residual vibration and Since the aperture structure is the same and transmits and receives ultrasonic waves throughout the aperture,
It is possible to receive a harmonic signal having a large output.

Although the present embodiment has described the configuration of a single type ultrasonic transducer for mechanical sector scanning, the technology described in the present embodiment is applicable to an array type ultrasonic transducer for electronic scanning. However, the present invention is not limited to a single type ultrasonic transducer for mechanical sector scanning. In addition, the basic form and the structure of the modification in the present embodiment can be variously combined, and various configurations of ultrasonic transducers for harmonic imaging are possible in accordance with a diagnosis target site and diagnosis accuracy. It is included as another modification.

[Second Embodiment] The present embodiment relates to an ultrasonic transducer suitable for harmonic imaging ultrasonic diagnosis.

[Structure] As shown in FIG. 9, the ultrasonic transducer includes a transmitting piezoelectric vibrator 202, a receiving piezoelectric vibrator 204, and these piezoelectric vibrators 202 and 20.
4 and a concave acoustic lens 208.

The transmitting piezoelectric vibrator 202 is made of, for example, lead zircon titanate (PZT) which is polarized by applying electrodes on both surfaces.
This is a piezoelectric element made of ceramics. The receiving piezoelectric vibrator 204 is made of a piezoelectric material having a larger piezoelectric g constant than a transmitting piezoelectric vibrator such as lead zircon titanate (PZT) ceramics of the same material or another composition, or a single crystal or a composite piezoelectric material. It is a piezoelectric element.

The transmitting piezoelectric vibrator 202 has an annular shape, the receiving piezoelectric vibrator 204 has a disk shape, and the receiving piezoelectric vibrator 204 is located inside the transmitting piezoelectric vibrator 202.

A damping layer 210 is provided on the back of the transmitting piezoelectric vibrator 202, and a damping layer 212 is provided on the back of the receiving piezoelectric vibrator 204.

Since the receiving ultrasonic wave has an integral multiple of the frequency of the transmitting ultrasonic wave, the damping degree of the damping layer 212 on the back surface of the receiving piezoelectric vibrator 204 is
May be set to be weaker than the damping degree of the damping layer 210 on the back surface, for example, the thickness of the layer may be set relatively thin, or a damping material having a relatively small ultrasonic attenuation may be used. This makes it possible to use an insulating damping layer in which alumina is dispersed in an epoxy resin as a material of the damping layer 212, and can also avoid the influence of electric crosstalk via the damping layer.

The acoustic lens 208 includes the piezoelectric vibrator 202,
It is arranged on the front surface of 204 and is made of, for example, epoxy resin. In the acoustic lens 208, a lens portion located on the front surface of the transmitting piezoelectric vibrator 202 has a radius of curvature rT, and a lens portion located on the front surface of the receiving piezoelectric vibrator 204 has a radius of curvature rR. Both lens portions are concave. The transmitting ultrasonic wave is transmitted by the transmitting piezoelectric vibrator 2.
02 and the focal point F2 by the wavelength λT corresponding to the radius of curvature rT and the frequency fT, and the received ultrasonic wave also corresponds to the aperture of the receiving piezoelectric vibrator 204, the radius of curvature rR and the frequency nfT (n is an integer of 2 or more). It is designed so as to connect to the focal point F2 determined by the wavelength .lambda.T / n.

Further, in order to give the acoustic lens a function of acoustic matching, the lens portion having a radius of curvature rT and the lens portion having a radius of curvature rR of the acoustic lens are each 1 / 4λ corresponding to the frequency on average. It is desired to have a thickness of The frequency of the target harmonics signal is 2fT
Then, the average thickness tR of the lens portion on the front surface of the receiving piezoelectric vibrator 204 is desirably equal to the transmitting piezoelectric vibrator 20.
2 is 1/2 of the average thickness tT of the front lens portion. If this condition and the condition that the focus coincides are satisfied, a step may occur at the boundary between two lens portions having different radii of curvature. To correct this shift, the surface position of the receiving piezoelectric vibrator 204 protrudes from the surface position of the transmitting piezoelectric vibrator 202 by the length td. Here, the average thickness tR is, as shown in FIG. 9B, from the surface of the receiving piezoelectric vibrator 204 to the middle between the bottom of the concave surface of the curvature radius rR and the upper end of the concave surface of the curvature radius rR. Is the distance. The average thickness tT is from the surface of the transmitting piezoelectric vibrator 202 to the virtual bottom of the radius of curvature rT and the upper end of the concave surface of the radius of curvature rT (from the lens effective end to the transmitting piezoelectric vibrator). And the distance to the middle.

The structure including the transmitting piezoelectric vibrator 202, the receiving piezoelectric vibrator 204, and the acoustic lens 208 is composed of an insulating layer 2
14 and is fixed inside the housing 206. The front electrode of the receiving piezoelectric vibrator 204 is a wiring 216.
Is connected to the front electrode of the transmitting piezoelectric vibrator 202, and the front electrode of the transmitting piezoelectric vibrator 202 is connected to the wiring 2.
It is connected to the housing 206 by 18. The two-core coaxial cable 220 has a lead wire 222 connected to the rear electrode of the transmitting piezoelectric vibrator 202, a lead wire 224 connected to the rear electrode of the receiving piezoelectric vibrator 204, and a shield wire 226 connected to the housing. 206.

[Operation] The ultrasonic wave having the center frequency fT transmitted from the transmitting piezoelectric vibrator 202 is converged by the acoustic lens 208 and focuses on the position F2. An echo signal including a harmonic signal transmitted through a living tissue having a large nonlinear effect is transmitted via an acoustic lens 208 to a receiving piezoelectric vibrator 204 having a resonance frequency of nfT (n is an integer of 2 or more).
And is converted into an electric signal.

When the receiving piezoelectric vibrator 204 is made of a material having the same sound speed as the transmitting piezoelectric vibrator, the thickness of the receiving piezoelectric vibrator 204 is set to approximately 1 / n of the thickness of the transmitting piezoelectric vibrator 202. You. Thereby, the receiving piezoelectric vibrator 2
04 selectively receives a frequency component of nfT (n is an integer of 2 or more).

Also, the acoustic lens also determines the radii of curvature rT and rR so that the focal point for the transmission frequency of the center frequency fT and the focal point for the reception frequency of the center frequency nfT (n is an integer of 2 or more) coincide with each other. Resolution is obtained. Further, since the average thickness of the acoustic lens is set to 1 / 4λ for each frequency, transmission and reception with a wide band and high sensitivity can be performed.

In this embodiment, the transmitting piezoelectric vibrator 20
2 and the receiving piezoelectric vibrator 204 are arranged so as to be separated from each other in substantially the same plane, so that the ultrasonic waves generated by the transmitting piezoelectric vibrator 202 pass through the receiving piezoelectric vibrator 204 or are reflected there. Nothing. Therefore, it is not necessary to control the state between the respective electrodes, such as open / short, and the control is extremely easy.

In this embodiment, the receiving piezoelectric vibrator 20
By making the piezoelectric g constant of No. 4 larger than the piezoelectric g constant of the transmitting piezoelectric vibrator 202 and using a piezoelectric material having a large mechanical quality factor Qm, the selectivity of harmonic signal reception is further increased.

By making the applied signal a bipolar double pulse, a transmission ultrasonic wave having a large amplitude can be obtained.
It is possible to increase the amplitude of the harmonic signal in proportion. This leads to an improvement in the S / N of the harmonic signal, and makes it possible to obtain good harmonic imaging.

Hereinafter, a modification of the present embodiment will be described with reference to the drawings. In the drawings, members equivalent to those described above are denoted by the same reference numerals, and a detailed description thereof will be omitted in the following description to avoid duplication.

FIG. 10 shows a first modification of the ultrasonic transducer. In the ultrasonic transducer of this modification, the acoustic lens 230 has the same radius of curvature over the entire aperture. The acoustic lens 230 is a circle in which the average thickness tT of the front surface of the transmitting piezoelectric vibrator 202 is connected along a donut shape to a quarter of the wavelength λ of the ultrasonic wave having the fundamental frequency fT. Spheres circumscribed so that the average thickness tR of the front surface of the ring 204 is a circle connecting a quarter of the wavelength λ of the ultrasonic wave having the fundamental frequency nfT (n is an integer of 2 or more) along a donut shape. Has a curvature surface having a radius of curvature as a radius of curvature. Here, the average thickness tR is, as shown in FIG. 10, from the surface of the receiving piezoelectric element 204 to the bottom of the concave surface of the acoustic lens 230 and its upper end (from the effective end to the receiving piezoelectric element 204). And the average thickness tT is from the surface of the transmitting piezoelectric element 202 to the bottom of the acoustic lens 230 and its upper end (however,
The distance from the transmission piezoelectric element 202 to an intermediate point between the transmission piezoelectric element 202 and the lens effective end).

As a result, the spatial resolution is slightly reduced, but the acoustic matching condition is approximately satisfied, and high-sensitivity reception of harmonic signals can be performed. Also, the acoustic lens 2
Since the radius of curvature of 30 is the same over the entire opening, machining is easy, and therefore, an inexpensive ultrasonic transducer for harmonic imaging ultrasonic diagnosis can be provided.

FIG. 11 shows a second modification of the ultrasonic transducer. The ultrasonic transducer according to the present modification includes a ring-shaped receiving piezoelectric vibrator 232 and a disc-shaped transmitting piezoelectric vibrator 234.
4 is located inside the receiving piezoelectric vibrator 232. In the acoustic lens 236, the lens portion located on the front surface of the transmitting piezoelectric vibrator 234 has a spherical curvature radius rT, and the lens portion located on the front surface of the receiving piezoelectric vibrator 232 has a spherical curvature radius rR. These lens portions are both convex.

Although the original purpose of the acoustic lens 232 is to converge the ultrasonic waves, it is more preferable that the acoustic lens 232 also functions as an acoustic matching layer. The thickness of the acoustic matching layer for the harmonic signal is smaller than the thickness of the acoustic matching layer for the fundamental frequency. The acoustic lens 232 has a thicker lens portion near the center and a thinner lens portion at the peripheral portion. For this reason, the transmitting piezoelectric vibrator 234 is disposed at the center, and the receiving piezoelectric vibrator 232 is disposed at the peripheral part.

FIG. 12 shows a main part of a third modification of the ultrasonic transducer. The main part of the ultrasonic transducer of the present modification is a part accommodated in the housing, and has a circular transmitting part 248 and a ring-shaped receiving part 250 surrounding the transmitting part 248. The receiving unit 250 includes a central portion of the vibrator 242,
It comprises a peripheral portion of the piezoelectric vibrator 242 and a damping layer 252 provided on the back surface thereof.

The piezoelectric vibrator 242 has a disk shape, and has, on its front surface, an electrode 244 common to the transmitting unit 248 and the receiving unit 250, and on its back surface, the circular electrode 246 of the transmitting unit 248 and the receiving unit 250. And an annular electrode 256. The receiving unit 250 of the piezoelectric vibrator 242 has a thickness of 1 / n of the thickness of the transmitting unit 248, and nft (n is 2 or more) with respect to the fundamental transmission ultrasonic wave ft transmitted from the transmitting unit 248. ) Can be selectively received.

The damping layer 252 includes the piezoelectric vibrator 242
Has a concave depression at a central portion corresponding to the transmitting portion 248, and the outer annular portion is joined to the receiving portion 250 of the piezoelectric vibrator 242, and the bottom of the concave depression is a piezoelectric vibrator 242. Is not in contact with the transmission unit 248 of the
8, a void 254 is formed on the back surface.

In this structure, the transmission section 248 has a large mechanical quality factor Qm, and can radiate a large-amplitude and wide-band transmission ultrasonic wave by performing the aforementioned bipolar double-pulse drive control. In this modification, the damping layer 252
Has a concave depression at the center corresponding to the transmitting unit 248, but may have a through hole.

FIG. 13 shows a main part of a fourth modification of the ultrasonic transducer. The main part of the ultrasonic transducer of this modification is a part housed in the housing, and has four transmitting units 260 and four receiving units 270. The transmitting section 260 and the receiving section 270 both have the same fan shape, and they are arranged alternately in a radial pattern. That is, the fan-shaped transmitting unit 260 and the receiving unit 270
Are alternately arranged along the angular direction.

The transmitting section 260 is provided on the transmitting piezoelectric vibrator 262 for transmitting the fundamental ultrasonic wave of the frequency ft, the transmitting acoustic lens 264 disposed on the front surface thereof, and the rear surface of the transmitting piezoelectric vibrator 262. And a damping layer 266. The transmitting acoustic lens 264 has a surface radius of curvature rT centered on the point F2, and transmits a sound ray 2 to an ultrasonic wave of the fundamental frequency ft transmitted from the transmitting piezoelectric vibrator 262.
At 68 focus on point F2.

The receiving section 270 includes a receiving piezoelectric vibrator 272 for selectively receiving harmonic ultrasonic waves having a frequency nft (n is an integer of 2 or more), a receiving acoustic lens 274 disposed on the front surface thereof, And a damping layer 276 provided on the rear surface of the piezoelectric vibrator 272. The receiving acoustic lens 274 has a surface curvature radius rR centered on the point F1.
And for harmonic ultrasound at frequency nft:
The sound ray 278 focuses on the point F2.

This structure is composed of a transmitting unit 260 and a receiving unit 27
The aperture area of 0 is the same for transmission and reception, and the focal point can be matched only by the lens surface shape.

[Effect] In the ultrasonic transducer of the present embodiment, the transmitting section and the receiving section are separated in the plane.
By optimizing the shape of the acoustic lens placed in front of the piezoelectric vibrator, not only can transmission and reception be performed efficiently, but also the spatial resolution where the focal points of the fundamental ultrasonic wave and the harmonic ultrasonic wave match are good and the output is good. A large harmonic signal can be received.

Although the present embodiment has described the configuration of the single type ultrasonic transducer for mechanical sector scanning, the contents described in this embodiment are the same as those of the fourth embodiment except for the fourth modification.
The present invention can be applied to an array type ultrasonic transducer for electronic scanning, and is not limited to a single type ultrasonic transducer for mechanical sector scanning. In addition, the configurations of the present embodiment and its modifications can be variously combined, and various configurations of ultrasonic transducers for harmonic imaging are possible in accordance with a diagnosis target site and diagnostic accuracy. It shall be included as another modification of the embodiment.

Although some embodiments have been described in detail with reference to the drawings, the present invention is not limited to the above-described embodiments, and may be carried out without departing from the scope of the invention. Including all implementations.

Therefore, the following can be said about the ultrasonic transducer of the present invention.

1. An ultrasonic transducer having a structure in which a transmitting piezoelectric vibrator having a resonance frequency ft and a receiving piezoelectric vibrator having a resonance frequency nft (n is an integer of 2 or more) are arranged in a layer on the same structure.

[Effects] When an ultrasonic pulse of approximately ft is transmitted from a transmitting ultrasonic vibrator having a resonance frequency ft to a living tissue, the ultrasonic pulse propagates through the living tissue so that the elasticity of the living tissue is nonlinear. Ft and ft
An ultrasonic echo signal in which harmonic signals of almost an integral multiple of the above are mixed is received. Since the resonance frequency of the receiving piezoelectric vibrator is substantially an integral multiple of the resonance frequency ft of the transmitting ultrasonic vibrator, it is possible to selectively detect only the harmonic signal of substantially an integral multiple of ft. . In addition, since the transmission and reception apertures of the ultrasonic wave coincide with each other and the aperture of the ultrasonic transducer is fully utilized, an ultrasonic pulse having a large sound pressure can be transmitted. This means that the sound pressure of the received harmonics signal increases, and the harmonics signal, which is weaker than the reference frequency, can be processed with a relatively high S / N. Further, since the beam axes of the transmitted and received ultrasonic beams coincide with each other, the lateral resolution is improved.

[0092] 2. The low-resistance state including the short circuit is connected to the ultrasonic transducer described in the first item, and the gap between the electrodes of the receiving piezoelectric vibrator is kept for a specific time after applying the driving voltage to the transmitting piezoelectric vibrator. Control means for an ultrasonic transducer, characterized in that it is controlled so as to be controlled.

[Operation and Effect] When ultrasonic waves pass through the piezoelectric vibrator in an electrically constrained state, the electric constrained state periodically changes depending on the relationship between the wavelength of the transmitted ultrasonic wave and the vibrator thickness. Correspondingly, the sound speed of the piezoelectric vibrator changes periodically,
Residual vibration may appear. By short-circuiting the electrodes of the receiving piezoelectric vibrator, it is always unrestricted,
Residual vibration does not occur when transmitting ultrasonic waves, and as a result, ultrasonic diagnosis with good S / N and excellent spatial resolution can be performed.

The low resistance state referred to here is between several tens of kΩ or less between the two electrodes, and the high resistance state is several hundred kΩ between the two electrodes.
That's all.

3. The control means of the ultrasonic transducer described in paragraph 2 controls the electrode of the transmitting piezoelectric vibrator to be kept in a high resistance state including an open state after the specific time has elapsed until the next transmission is performed. Ultrasonic transducer control means.

[Operation and Effect] The control means of the ultrasonic transducer keeps the electrodes of the transmitting piezoelectric vibrator in the high resistance state including the open state until the next transmission is performed after the lapse of the specific time. Since the piezoelectric vibrator is kept in a hard state, residual vibration does not occur at the time of reception, and as a result, ultrasonic diagnosis with a good S / N and excellent spatial resolution can be performed.

4. In the control means of the ultrasonic transducer according to the second aspect, an inductance circuit performs control so as to maintain a low resistance state including a short circuit between the electrodes of the receiving piezoelectric vibrator for a specific time. Control means for the acoustic transducer.

[Effects] When connected to a receiving circuit via an inductance circuit, a resonance system is formed by the inductance circuit and the capacitance of the receiving piezoelectric vibrator, so that optimum reception band characteristics can be obtained. This shuts off the fundamental wave,
Only the harmonic signal can be detected with high selectivity. At the same time, the inductance circuit can be connected to the receiving piezoelectric vibrator to keep the inter-electrode resistance low.

5. 4. An on / off control device for controlling the ultrasonic transducer according to claim 3, wherein the control is performed such that the high resistance state including the open state is maintained. Control means for an ultrasonic transducer.

[Function / Effect] Since the last stage of the circuit for applying the drive voltage to the transmitting piezoelectric vibrator comprises an on / off control device, the device is controlled so as to be in the on state at the time of transmission and turned off at the time of reception to thereby receive the signal. It is possible to prevent the residual vibration from being superimposed on the signal, and as a result, it becomes possible to perform an ultrasonic diagnosis having a good S / N and an excellent spatial resolution.

6. 2. The ultrasonic transducer control unit according to claim 1, wherein the receiving piezoelectric vibrator is one of a polymer piezoelectric substance and a composite piezoelectric substance.

[Function and Effect] By using either the polymer piezoelectric material or the composite piezoelectric material as the receiving piezoelectric vibrator, the receiving sensitivity can be increased and the harmonic signal can be detected with high sensitivity.

7. 7. The ultrasonic transducer according to claim 6, wherein the polymer piezoelectric body has a structure in which the polymer piezoelectric body is disposed directly or through an acoustic matching layer on a surface of the transmitting piezoelectric vibrator on the ultrasonic wave emitting side. Transducer.

[Function and Effect] In general, the acoustic impedance of a polymer piezoelectric substance is close to the acoustic impedance of a living body. Therefore, by using this as a receiving piezoelectric vibrator and disposing it on the side that comes into contact with the living tissue, it is possible to suppress the occurrence of multiple reflection near the surface and to achieve high contrast resolution near the body surface.

8. 8. The ultrasonic transducer according to claim 7, wherein the piezoelectric polymer is made of a polymer film that spontaneously generates piezoelectricity due to surface energy polarization.

[Function and Effect] Since no adhesive layer is interposed, stable transmission / reception characteristics can be obtained. Furthermore, immediately after the formation of the piezoelectric polymer layer, the polarization state is spontaneously reached by the action of surface energy, and the polarization state can be developed without applying an external electric field.
In addition, since there is no bonding step, bubbles are not entangled at the time of bonding and the sensitivity and the band are not deteriorated. Also, since no adhesive pressure is applied to the transmitting piezoelectric vibrator on the back side, the manufacturing process can be simplified without causing damage to the transmitting piezoelectric vibrator such as cracks, and it is low cost and has good reproducibility for harmonic imaging. An ultrasonic transducer can be obtained.

9. 2. The ultrasonic transducer according to claim 1, wherein a damping layer is provided on a back surface of the transmitting piezoelectric vibrator, and an acoustic lens having an acoustic matching function is provided on a front surface of the receiving piezoelectric vibrator. Transducer.

[Function and Effect] By providing a damping layer on the back surface of the transmitting piezoelectric vibrator, the pulse width of the transmitting ultrasonic pulse is shortened, the spatial resolution in the depth direction is increased, and the acoustic lens having the acoustic matching function is provided. By the formation, an ultrasonic transducer having high sensitivity and good convergence can be obtained, and good lateral spatial resolution can be obtained.

10. 10. The ultrasonic transducer according to claim 9, wherein the surface of the acoustic lens is a concave or convex spherical surface having a radius of curvature R, and R is an acoustic focal point at ft and an acoustic focal point at nft (n is an integer of 2 or more). An ultrasonic transducer characterized by being set to a value indicating an acoustic focus which is an average value.

[Effects] The transmission ultrasonic wave is ft, the reception frequency is nft (n is an integer of 2 or more), and when the radius of curvature of the spherical surface of the acoustic lens is the same, the focal point for transmission and the focal point for reception are different. Position. This leads to deterioration of the uniformity of the ultrasonic image. In the layered structure, it is impossible to integrally form a lens structure having a radius of curvature corresponding to each layer at the same position. Accordingly, the radius of curvature of the lens is set such that the surface of the insulating layer is a spherical surface having a concave or convex radius of curvature R and R is ft.
By setting a value indicating the acoustic focus, which is the average value of the acoustic focus at nft and nft (n is an integer of 2 or more), good ultrasonic image uniformity can be obtained.

(11) 10. The ultrasonic transducer according to claim 9, wherein the surface of the acoustic lens has a partially different radius of curvature.

[Operation and Effect] Since the surface of the acoustic lens has different radii of curvature at different positions, the acoustic focus connected at the frequency ft of the transmitted ultrasonic wave and the acoustic wave connected at the received ultrasonic wave nft (n is an integer of 2 or more). It is possible to match the target focus. This improves the lateral resolution.

12. In an ultrasonic transducer having a transmitting piezoelectric vibrator having a resonance frequency ft and a receiving piezoelectric vibrator having a resonance frequency nft (n is an integer of 2 or more) in the same structure, the relative arrangement thereof is such that the annular plate and the An ultrasonic transducer characterized by being in a relation of a disk arranged inside an inner diameter.

[Operation and Effect] Since the relative positions of the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator are in the relation of the annular plate and the disk disposed inside the inner diameter thereof, the transmitting ultrasonic wave and the receiving ultrasonic wave are not used. It does not transmit or reflect through the piezoelectric vibrator, so that it is not necessary to take measures against residual vibration. Further, an acoustic matching layer between the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator is not required, the structure is simplified, and the transmission of the fundamental wave and the reception of the harmonic signal can be performed with high reliability.

13. 13. The ultrasonic transducer according to claim 12, further comprising an acoustic lens having an acoustic matching function on upper surfaces of the transmitting and receiving piezoelectric vibrators.

[Function and Effect] The ultrasonic lens function narrows the ultrasonic beam to improve the lateral resolution, and the acoustic matching function enables high-sensitivity transmission and reception.

14. 14. The ultrasonic transducer according to claim 13, wherein the orbicular plate is a transmitting piezoelectric vibrator, and a disk disposed within the inner diameter is a receiving piezoelectric vibrator.

[Function and Effect] The resonance frequency of the transmitting piezoelectric vibrator is ft, and the receiving frequency of the receiving piezoelectric vibrator is nf when the average thickness of the acoustic lens disposed on the front surface is t.
(n is an integer of 2 or more), so that the average thickness of the acoustic lens disposed on the front surface is t / n. Since the transmitting piezoelectric vibrator as the annular plate is disposed outside and the receiving piezoelectric vibrator as the circular plate is disposed inside, if the sound speed of the acoustic lens material is higher than the sound speed of the living tissue, the above thickness relationship is applied. Thus, the acoustic lens structure has a thicker peripheral portion and a thinner central portion. This means that the surface shape of the acoustic lens can be made concave,
It becomes possible to add an acoustic matching function to the acoustic lens.

15. 13. The ultrasonic transducer according to claim 12, further comprising a damping layer having different thicknesses or different damping characteristics on the back surfaces of the two piezoelectric vibrators.

[Function and Effect] Since the frequency of the received harmonic signal is nft (n is an integer of 2 or more), which is higher than the frequency of the transmitted ultrasonic wave, if the same material is used, the thickness of the damping layer on the back of the transmitting piezoelectric vibrator is reduced. It is possible to make it thinner.
Alternatively, an insulating damping layer having a low damping ability can be used. As a result, it is possible to reduce the electrical crosstalk between the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator that has reached the damping layer, and it is possible to make it difficult for the fundamental signal to be put on the harmonic signal.

16. 14. The ultrasonic transducer according to claim 13, wherein a surface of the acoustic lens has a partially different radius of curvature, and a focal point of the transmitting ultrasonic wave by the acoustic lens coincides with a focal point of the receiving ultrasonic wave by the acoustic lens. Wherein the radius of curvature of both acoustic lenses is set.

[Function and Effect] The frequency of the transmitted ultrasonic pulse is ft. When the radius of curvature Rt of the acoustic lens is set so that the focal point of the transmitted ultrasonic wave is at a specific position A, the focal point of the received ultrasonic wave is positioned. In order to match A, the radius of curvature Rr of the acoustic lens must be set to a value different from Rt. Therefore, by adopting a structure having different radii of curvature between the spherical portion on the transmitting piezoelectric vibrator and the spherical portion on the receiving piezoelectric vibrator as described in this section, the focal points of the transmission fundamental wave and the harmonic reception signal coincide. As a result, good spatial resolution and uniformity of the ultrasonic image can be obtained.

17. 14. The ultrasonic transducer according to claim 13, wherein a surface of the receiving piezoelectric vibrator protrudes toward an ultrasonic transmitting side from a surface of the transmitting piezoelectric vibrator.

[Function and Effect] In the acoustic lens structure of the sixteenth aspect, if the aperture size and the inner diameter of the ring-shaped piezoelectric vibrator are determined, the focal position is uniquely determined. When diagnosing a living tissue at a different deep position, it is desirable that the design can be changed so as to have a focal position corresponding thereto. By adopting a structure in which the surface of the receiving piezoelectric vibrator protrudes toward the ultrasonic transmitting side from the surface of the transmitting piezoelectric vibrator as in this section,
It is possible to satisfy the acoustic matching condition at the time of reception corresponding to nf (n is an integer of 2 or more) without changing the radius of curvature of the concave surface.

18. In the ultrasonic transducer described in Item 16, the radius of curvature rR of the concave or convex surface of the acoustic lens on the receiving piezoelectric vibrator is smaller than the radius of curvature rT of the concave or convex surface of the acoustic lens on the transmitting piezoelectric vibrator. An ultrasonic transducer characterized in that:

[Effects] The frequency of the transmitted ultrasonic pulse is ft. When the radius of curvature rT of the concave shape is set so that the focal point of the transmitted ultrasonic wave is at a specific position A, the focal point of the received ultrasonic wave is positioned. In order to make A coincide with A, the relationship that the radius of curvature of the concave surface is rR> rT is required. Therefore, the focal point of the transmitted ultrasonic wave coincides with the focal point of the received ultrasonic wave by making the spherical portion on the transmitting piezoelectric vibrator and the spherical portion on the receiving piezoelectric vibrator satisfy rR> rT as described in this section. This makes it possible to obtain a harmonic imaging ultrasound diagnostic image having good lateral resolution and uniformity of the ultrasonic image.

19. In an ultrasonic transducer having a transmitting piezoelectric vibrator having a resonance frequency ft and a receiving piezoelectric vibrator having a resonance frequency nft (n is an integer of 2 or more) in the same structure, their relative arrangement is radially and alternately arranged. An ultrasonic transducer characterized by being in a relationship.

[Function and Effect] Since the plurality of transmitting piezoelectric vibrators and the plurality of receiving piezoelectric vibrators are arranged alternately in a radial pattern, the average aperture diameter of the transmitted ultrasonic wave and the average aperture diameter of the received ultrasonic wave are one. As a result, the degree of freedom in designing the acoustic lens in front of each piezoelectric vibrator is increased, and various ultrasonic transducers for harmonic imaging having different focal regions can be realized.

20. The ultrasonic transducer according to claim 19, wherein the ultrasonic transducer has an acoustic lens having a radius of curvature rT on the front surface of the transmitting piezoelectric vibrator and a radius of curvature rR on the front surface of the receiving piezoelectric vibrator and having a relationship of rR <rT. An ultrasonic transducer characterized by having each.

[Operation and Effect] Since the plurality of transmitting piezoelectric vibrators and the plurality of receiving piezoelectric vibrators are arranged alternately in a radial pattern, the average aperture diameter of transmitted ultrasonic waves and the average aperture diameter of received ultrasonic waves are one. Radius of curvature r on the front face of the transmitting piezoelectric vibrator.
T, since the front side of the receiving piezoelectric vibrator has acoustic lenses having a relationship of rR <rT with a radius of curvature of rR on the front surface of the receiving piezoelectric vibrator, the focal point of the transmitted ultrasonic wave can be matched with the focal point of the received ultrasonic wave. , And a harmonic imaging ultrasonic diagnostic image having a good lateral resolution can be obtained.

21. The same structure includes a transmitting piezoelectric vibrator having a resonance frequency ft and a receiving piezoelectric vibrator having a resonance frequency nft (n is an integer of 2 or more), and an acoustic lens disposed on the front surface of the ultrasonic wave emitting side thereof. An ultrasonic transducer, wherein a damping layer which is electrically isolated from each other is disposed on a back surface of each of the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator.

[Effects] No electrical crosstalk occurs between the transmitting and receiving piezoelectric vibrators, and it is possible to prevent the fundamental frequency from being mixed into the nft (n is an integer of 2 or more) harmonic reception signal. .

22. A control unit connected to an ultrasonic transducer having a transmitting piezoelectric vibrator having a resonance frequency ft and a receiving piezoelectric vibrator having a resonance frequency nft (n is an integer of 2 or more) in the same structure; Control means characterized in that the voltage waveform applied to the device is a trapezoidal wave or a double pulse.

[Function / Effect] A transmission ultrasonic signal having a large amplitude and a wide band can be obtained, the amplitude of a weak harmonic signal can be increased, and a high-sensitivity, favorable S / N S / N harmonic imaging ultrasonic diagnostic image can be obtained. Can be obtained.

[0135]

According to the present invention, although the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator are housed in the same case, the ultrasonic wave which is not adversely affected by the resolution degradation due to the residual vibration is provided. Transducer technology is provided. According to the ultrasonic transducer and the ultrasonic transducer system, the harmonic signal can be detected with higher sensitivity than before.

[Brief description of the drawings]

FIG. 1 shows a side cross section of an ultrasonic transducer according to a first embodiment.

FIG. 2 shows a side cross section of a first modification of the ultrasonic transducer according to the first embodiment.

FIG. 3 shows a side cross section of a second modified example of the ultrasonic transducer according to the first embodiment.

FIG. 4 shows a side cross section of a third modification of the ultrasonic transducer according to the first embodiment.

5A and 5B are diagrams for explaining setting of a radius of curvature of the acoustic lens shown in FIG. 1; FIG. 5A is a diagram illustrating a radius of curvature R of an acoustic lens disposed on a front surface of a disk-shaped piezoelectric vibrator; The relationship of the focal length F in the ultrasonic propagation medium of FIG.
(= A ² / λR ′, a: aperture radius, λ: wavelength of ultrasonic wave in the propagation material, R ′: apparent radius of curvature of the lens, R ′ = 2.
25R, R: radius of curvature of the acoustic lens), vertical axis F / R '
(B) is a graph showing the relationship between the focal point and the radius of curvature of the acoustic lens in the case of 5 MHz and 10 MHz.

6 is a diagram for explaining a control system that controls transmission and reception of the ultrasonic transducer shown in FIG. 1,
(A) schematically shows a configuration of a control system, and (B) shows a timing chart of on / off control devices and control signals Vt and Vr input to a selector.

7A and 7B are diagrams for explaining a modification of the control system that controls transmission and reception of the ultrasonic transducer shown in FIG. 1; FIG. 7A schematically shows a configuration of a control system of the modification; (B) shows a timing chart of the control signals Vt and Vr input to the on / off control device.

FIG. 8 shows a simulation result in which the effect of surface charges generated on a piezoelectric vibrator through which ultrasonic waves are transmitted is calculated, and the state of charge processing between the electrodes of the receiving piezoelectric vibrator 104 during transmission / transmission during reception. Regarding the charge processing state between the electrodes of the credit piezoelectric vibrator 102, (a), (b), (c) are short / short, (d), (e), (f) are short / open,
(g), (h), (i) are open / open, (j), (k),
(l) shows the transmission-only ultrasonic pulse (left column), the reception-only ultrasonic pulse (middle column), and the total transmission / reception ultrasonic pulse (right column) when open / short.

9A and 9B are views for explaining an ultrasonic transducer according to a second embodiment, in which FIG. 9A shows a side cross section of the ultrasonic transducer, and FIG. 9B is an enlarged view of a central portion of the acoustic lens. Is shown.

FIG. 10 shows a side cross section of a first modified example of the ultrasonic transducer according to the second embodiment.

FIG. 11 shows a side cross section of a second modified example of the ultrasonic transducer according to the second embodiment.

FIG. 12 shows a side cross section of a third modified example of the ultrasonic transducer of the second embodiment.

FIG. 13 is a view for explaining a fourth modification of the ultrasonic transducer according to the second embodiment, and FIG.
Shows the upper surface of the ultrasonic transducer, and (B) shows
FIG. 3A is a side cross-sectional view of the ultrasonic transducer taken along the line BB of FIG.

FIG. 14 shows a side cross section of a conventional ultrasonic transducer.

[Explanation of symbols]

 102 Transmitting piezoelectric vibrator 104 Receiving piezoelectric vibrator 108 Acoustic lens 150 ON / OFF control device 160 Selector

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04R 17/00 330 H04R 17/00 330J

Claims (3)

[Claims] 1. A transmitting piezoelectric vibrator for transmitting ultrasonic waves having a resonance frequency ft and a resonance frequency nft disposed in layers with each other.
(n is an integer of 2 or more) an ultrasonic transducer having an ultrasonic transducer for receiving ultrasonic waves, and an ultrasonic transducer system having control means for controlling the ultrasonic transducer; A drive voltage is applied to the transmitting piezoelectric vibrator only for t1, and for a predetermined time t2 (> t1) from the application of the driving voltage, the electrodes of the receiving piezoelectric vibrator are
After the predetermined time t2 elapses and the drive voltage is applied to the transmitting piezoelectric vibrator after the elapse of the predetermined time t2, the electrodes of the transmitting piezoelectric vibrator are maintained in a low resistance state including a short circuit. An ultrasonic transducer system that holds in state. 2. A transmitting piezoelectric vibrator for transmitting an ultrasonic wave having a resonance frequency ft, and a receiving piezoelectric vibrator for receiving an ultrasonic wave having a resonance frequency nft (n is an integer of 2 or more). One of the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator has a ring shape, and the other of the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator has a disc shape, and the disc-shaped piezoelectric vibrator has a ring-shaped piezoelectric vibrator. An ultrasonic transducer located inside the transducer. 3. A plurality of transmitting piezoelectric vibrators for transmitting ultrasonic waves having a resonance frequency ft, and a plurality of receiving piezoelectric vibrators for receiving ultrasonic waves having a resonance frequency nft (n is an integer of 2 or more). An ultrasonic transducer in which a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator are alternately arranged radially.