JP2002248100A - Ultrasonic transducer and ultrasonic transducer system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic transducer for detecting a harmonic signal having high S/N ratio and high selectivity. SOLUTION: The ultrasonic transducer has a transmission ultrasonic vibrator for transmitting a fundamental ultrasonic wave with center frequency f0 and a receiving ultrasonic vibrator for receiving a harmonic signal with center frequency nf0 ((n): an integer of 2 or more), and the receiving ultrasonic vibrator has a receiving piezoelectric vibrator, and a transmission piezoelectric vibrator and the receiving piezoelectric vibrator are arranged on the same plane of satisfy (g33r .Vr .Qr )/(g33t .Vt .Qt )>=n.(1+R) (wherein, g33t and Vt are respectively the voltage output coefficient and acoustic velocity of the transmission piezoelectric vibrator, g33r and Vr are respectively the voltage output coefficient and acoustic velocity of the receiving piezoelectric vibrator, (n) is their harmonic degree, R is an aperture area ratio and Qt and Qr are respectively the resonance sharpnesses of the transmission ultrasonic vibrator and the receiving ultrasonic vibrator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to an ultrasonic transducer for use in harmonic imaging ultrasonic diagnosis, it transmits the basic ultrasonic waves having a center frequency f _0,
The center frequency n generated in the object by this basic ultrasonic wave
The present invention relates to an ultrasonic transducer that detects nonlinear ultrasonic waves having f ₀ (n: an integer of 2 or more).

[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 "Clinics of Electronics, Special Issue on Ultrasound-Latest Ultrasound-: 1999, Japanese Society of Ultrasound Medicine Academic Lecture, Distribution Text".

In tissue harmonic imaging, an ultrasonic pulse having a center frequency f ₀ is transmitted to living tissue without using an ultrasonic contrast agent, and a harmonic component nf ₀ (n: This is a technique for obtaining a diagnostic image by extracting a relationship between the amplitude and the echo signal reception time by displaying a tomographic image.

At present, this ultrasonic diagnostic method is used only for extracorporeal use, and the second harmonic (n = 2), that is, an ultrasonic wave having a center frequency of 2f ₀ is used. In previous ultrasonic transducer, ultrasonic reception of transmission and the center frequency 2f ₀ of the ultrasonic center frequency f ₀ is effected by the same ultrasonic transducer. For this reason, it is necessary that the ultrasonic transducer used has an extremely wide band. Since it is difficult to design and manufacture such an ultrasonic transducer, an ultrasonic transducer is expensive.

[0005] In the field of tissue harmonic imaging, in order to further improve the resolution,
Although the use of third-order harmonic signal is expected, ultrasonic i.e. ultra-wideband ultrasonic transducer capable of detecting the third-order harmonic of the center frequency 3f ₀ has not yet been realized.

Furthermore, since the performing of the same ultrasonic transducer ultrasonic reception of transmission and the center frequency 2f ₀ of the ultrasonic wave of the center frequency f _0, the fundamental wave and various unwanted vibration to the received ultrasonic signal It is inevitable that they are superimposed, and a means for removing them is required. Such a situation is the same in contrast nick imaging using the above-described contrast agent.

[0007] Japanese Patent Application Laid-Open No. H11-155863 discloses a transducer in which such disadvantages are improved, a transmitting ultrasonic transducer and a receiving ultrasonic transducer are housed in one case, and efficiently receives harmonic components. An ultrasonic transducer that can be used is disclosed. FIG. 18 shows the configuration of this ultrasonic transducer.

As shown in FIG. 18, an ultrasonic transducer 1000 includes a transmitting piezoelectric vibrator 1002,
The receiving polymer piezoelectric vibrator 100 arranged in front of the
4, and the receiving polymer piezoelectric vibrator 1004 and the transmitting piezoelectric vibrator 1002 are arranged in layers via an acoustic matching layer 1006.

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

The transmitting piezoelectric 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 relationship with the resonance frequency of the ultrasonic contrast agent. I have. On the other hand, the receiving polymer piezoelectric vibrator 1004 is a non-resonant type piezoelectric vibrator,
Harmonic components generated based on the non-linear behavior of the ultrasound contrast agent may also be received.

The ultrasonic transducer 1000 is
Since the transmission and reception piezoelectric vibrators are provided separately, the sensitivity is higher than that of an ultrasonic transducer that uses a single piezoelectric vibrator to transmit and receive. Harmonic signals can be detected.

[0012] The ultrasonic transducer 1000
By having the acoustic matching layer 1006 between the transmitting piezoelectric vibrator 1002 and the receiving polymer piezoelectric vibrator 1004, generation of unnecessary vibration due to the difference in acoustic impedance between the two vibrators is suppressed. In addition, only a part where the injected ultrasound contrast agent exists, such as a blood vessel in a human body or a cancer tissue in which capillaries are concentrated in a peripheral part, can be drawn more clearly than other parts.

[0013]

However, FIG.
In the conventional ultrasonic transducer shown in (1), the transmitting ultrasonic vibrator and the receiving ultrasonic vibrator are arranged in an overlapping manner, so that when the transmitted ultrasonic wave passes through the receiving piezoelectric vibrator, The result is that the receiving piezoelectric vibrator is excited and is modulated by the vibration. This means that vibrations of the resonance frequency of the ultrasonic transducer film for reception are mixed from the beginning in the transmission ultrasonic waves. That is, this means that it cannot be determined whether the signal detected by the receiving piezoelectric vibrator is a harmonic signal from an ultrasonic contrast agent or a signal mixed during transmission.

When the fundamental ultrasonic waves are used in so-called tissue harmonic imaging (THI), which detects nonlinear ultrasonic waves generated while the ultrasonic waves propagate in the living tissue, the fundamental ultrasonic waves propagate in the living tissue. As well known, the sound pressure level of the non-linear ultrasonic wave generated at the same time is as small as about -20 dB, so that it is necessary to select and detect this harmonic without fail.

However, in the conventional ultrasonic transducer shown in FIG. 18, since the receiving ultrasonic transducer has non-resonant non-linear characteristics, the received signal also has a higher harmonic signal level than the fundamental wave by -20 dB. The situation of being low remains unchanged, and there is no particular configuration for detecting the harmonic signal with high selectivity. In this case, signal processing is required so that the harmonic signal level is equal to or higher than the fundamental wave.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an ultrasonic transducer which can realize high S / N and high selectivity without a special signal processing circuit. It is.

[0017]

SUMMARY OF THE INVENTION The present invention provides, in part,
An ultrasonic transducer for harmonic imaging, which transmits a basic ultrasonic wave having a center frequency f ₀ in response to an input of an electric signal, and a center frequency nf generated on an object by the basic ultrasonic wave ₀ (n
Is an integer of 2 or more), the receiving ultrasonic transducer for receiving a harmonic signal, the transmitting ultrasonic transducer has a transmitting piezoelectric transducer, and the receiving ultrasonic transducer is receiving. has a use piezoelectric vibrator, a piezoelectric vibrator for transmitting and receiving piezoelectric vibrator is arranged on the same plane, the receiving piezoelectric vibrator and transmitting piezoelectric vibrator, (g _33r · V _r・ Q _r ) / (g _33t
· V _t · Q _t ) ≥ n · (1 + R), where g
_33t and V _t is the voltage output coefficient and sound speed of each transmitting piezoelectric vibrator, g _33r and V _r is the voltage output coefficient and sound speed of each receiving piezoelectric vibrator, n represents the harmonic order, R represents an opening area ratio
A (opening area of the opening area / transmitting piezoelectric vibrator receiving piezoelectric vibrator), and there resonance sharpness Q _t and Q _r for receiving the respective transmitting ultrasonic transducer ultrasonic vibrator.

According to another aspect of the present invention, there is provided an ultrasonic transducer system comprising the above-described ultrasonic transducer and drive control means for driving and controlling the ultrasonic transducer. An ultrasonic wave in which the 2f ₀ component is suppressed is generated by the transmitting ultrasonic transducer.

In a more preferred ultrasonic transducer system, the transmitting ultrasonic vibrator has means for giving the transmitting piezoelectric vibrator at least a gradient function characteristic relating to at least one of a piezoelectric constant and a dielectric constant.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION [First Embodiment] The present inventors have modified the above-described conventional ultrasonic transducer in which a transmitting ultrasonic transducer and a receiving ultrasonic transducer are arranged in an overlapping manner. As a further improvement, Japanese Patent Application No. 2000-72854 proposes an in-plane separation type ultrasonic transducer in which a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator are arranged on the same plane. The configuration is shown in FIG.

As shown in FIG. 1, an ultrasonic transducer 300 includes a transmitting ultrasonic vibrator for transmitting a basic ultrasonic wave, a receiving ultrasonic vibrator for receiving a harmonic signal, and Housing 306 to accommodate
And The transmitting ultrasonic vibrator has a transmitting piezoelectric vibrator 302 and a backing layer (damping layer) 310 disposed on the back surface thereof. Further, the receiving ultrasonic vibrator has a receiving piezoelectric vibrator 304 and a backing layer (damping layer) 312 disposed on the back surface thereof.

The transmitting piezoelectric vibrator 302 has an annular plate shape, the receiving piezoelectric vibrator 304 has a disk shape, and the receiving piezoelectric vibrator 304 is a transmitting piezoelectric vibrator. 3
02. On the front surfaces of the transmitting piezoelectric vibrator 302 and the receiving piezoelectric vibrator 304, a concave acoustic lens 308 made of, for example, epoxy resin or the like is arranged.

Further, each of the transmitting ultrasonic transducer and the receiving ultrasonic transducer partially has an acoustic lens 308. That is, the receiving ultrasonic vibrator has a part of the acoustic lens 308 located in front of the receiving piezoelectric vibrator 304, that is, a circular central portion, and the transmitting ultrasonic vibrator is
Acoustic lens 3 located in front of transmitting piezoelectric vibrator 302
08, that is, a ring-shaped peripheral portion.

The transmitting ultrasonic vibrator transmits a basic ultrasonic wave having a center frequency f ₀ according to the input of the electric signal, and the receiving ultrasonic vibrator transmits a central frequency generated on the object by the basic ultrasonic wave. A harmonic signal having nf ₀ (n is an integer of 2 or more) is received.

The transmitting ultrasonic vibrator and the receiving ultrasonic vibrator, that is, the structure including the transmitting piezoelectric vibrator 302, the receiving piezoelectric vibrator 304, the acoustic lens 308, the backing layer 310, and the backing layer 312 are as follows. It is fixed inside the housing 306 via an insulating layer 314.

The receiving piezoelectric vibrator 304 has a disk-shaped piezoelectric material and a pair of electrodes formed on the entire surface of the receiving piezoelectric vibrator 304. Similarly, the transmitting piezoelectric vibrator 302 It has a strip-shaped piezoelectric material and a pair of electrodes formed on the entire opposing surface. The front side of the receiving piezoelectric vibrator 304, that is, the electrode on the ultrasonic wave emitting surface side is electrically connected to the front side of the transmitting piezoelectric vibrator 302, that is, the electrode on the ultrasonic wave emitting surface side by the wiring 316. The front electrode of the vibrator 302 is connected to the housing 3 by the wiring 318.
06 is electrically connected.

The two-core coaxial cable 320 extending through the housing 306 includes a lead 322 and a lead 3
24 and a shield wire 326, the lead wire 322 is electrically connected to an electrode on the rear side of the transmitting piezoelectric vibrator 302 via a wiring 332, and the lead wire 324 is electrically connected to the receiving piezoelectric vibrator via a wiring 334. The shield wire 326 is electrically connected to the electrode on the rear side of the
6 are electrically connected. Further, the housing 30
The space 336 inside 6 is filled with a sealing material such as epoxy resin.

FIGS. 2A and 2B schematically show the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator of the in-plane separation type ultrasonic transducer shown in FIG. As shown in FIG. 2A, the transmitting piezoelectric vibrator 302 has an annular shape, the receiving piezoelectric vibrator 304 has a disk shape, and the receiving piezoelectric vibrator 304 Are located inside the transmitting piezoelectric vibrator 302. In FIG. 2B, not only the secondary or tertiary harmonic signal 314 but also the ultrasonic waves of all the frequency components included in the transmission ultrasonic wave 312 are converted into harmonic signals by the receiving disk-shaped piezoelectric vibrator 304. Reach by overlapping.

In the in-plane separation type ultrasonic transducer,
As can be seen from FIG. 2A, the opening area of the transmitting piezoelectric vibrator is smaller than that of the in-plane transmitting / receiving integrated ultrasonic transducer that transmits and receives over the entire opening. FIG.
As shown in (B), the thickness of the receiving piezoelectric vibrator decreases as the order of the received harmonic signal increases.

In the following, consideration will be given to the sensitivity reduction due to the decrease in the opening area of the transmitting piezoelectric vibrator and the thickness of the receiving piezoelectric vibrator.
It is shown that a good sensitivity can be obtained by appropriately selecting the piezoelectric material described above.

The opening area of the transmitting piezoelectric vibrator 302 is represented by _St
Assuming that the opening area of the receiving piezoelectric vibrator 304 is S _r , the transmission ultrasonic energy is almost _St / compared to a conventional in-plane transmission / reception integrated ultrasonic transducer having an opening area of S _t + S _r. ( _St + _Sr ).

Output voltage V _out of receiving piezoelectric vibrator 304
Is represented by the following equation (1).

V _out = q _r / C _r = d _{33 r} · T · S _r / (εS _r / t _r ) = g _33r · t _r · T (1) where q _r is piezoelectrically converted Receiving piezoelectric vibrator 304
Charge generated on the electrode, the piezoelectric vibrator 30 for C _r is received
Ε is the dielectric constant of the receiving piezoelectric vibrator 304,
d _33r piezoelectric constant of the receiving piezoelectric vibrator, g _33r voltage output coefficient of the receiving piezoelectric vibrator, t _r is the thickness of the receiving piezoelectric vibrator, T is an ultrasonic receiver stress.

Furthermore the frequency of the received ultrasonic wave and f _r, when the longitudinal wave acoustic velocity of the piezoelectric vibrator material and _{V r, t r = λ /} 2 = V r / 2f r ··· (2) So (1 ) _{equation, V out = g 33r · t} r · T = g 33r · V r · T / 2f r ··· (3) to become.

[0035] Further ultrasound receiving stress T is considered to be proportional to the opening of the transmission piezoelectric _{vibrator, V out = g 33r · V} r · T / 2f r = g 33r · V r · S r · P 0 / 2f r _{= g 33r · V r · S} t · d 33t · V drive / 2f r ··· (4) Further, if the received ultrasonic wave is a n-order harmonic _{signal, V out = g 33r · V} r · S t D _33t V _drive / 2nfr _r (5) Here, _St is the aperture of the transmitting piezoelectric vibrator, P ₀ is the ultrasonic sound pressure per unit area generated by the transmitting piezoelectric vibrator,
d _33t is the piezoelectric constant of the transmitting piezoelectric vibrator, and V _drive is the drive voltage applied to the transmitting piezoelectric vibrator.

From the equations (4) and (5), in the case of receiving an n-th order harmonic signal, the reception frequency becomes n times, and the output voltage V _out becomes 1 / n.

In comparison with the in-plane transmission / reception integrated ultrasonic transducer, the area of the transmission aperture is S _t / (S _t + S _r ) times that of the in-plane transmission / reception integrated ultrasonic transducer. The output voltage _Vout further decreases.

Usually, a piezoelectric vibrator made of the same piezoelectric material is used for the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator. Based on this assumption, for example, when S _t = S _r, detection ultrasonic frequency f _r is 2f _0, V _out is 1/4 (= - 12dB)
To decline.

Here, as a comparison object of the in-plane separation type ultrasonic transducer shown in FIGS. 2A and 2B, only the basic ultrasonic wave shown in FIGS. 3A and 3B is used. Consider an in-plane separation type ultrasonic transducer for detecting the following. This ultrasonic transducer corresponds to a general pulse echo transducer integrated on the entire surface.

In this ultrasonic transducer, both the transmitting piezoelectric vibrator 322 and the receiving piezoelectric vibrator 324 have the same thickness and the same piezoelectric material, for example, longitudinal wave velocity V _t = 426.
0 [m / s], voltage output coefficient g _33t = 30 × 10 ⁻³ [Vm /
N] PZT-based piezoelectric material.

In the ultrasonic transducers shown in FIGS. 3A and 3B, the receiving piezoelectric vibrator 324 can be used for transmission, so that the transmission and reception are the same as the fundamental wave pulse echo diagnosis using the conventional integrated ultrasonic transducer. , FIG. 3 (A) and FIG.
The transmission aperture area of the ultrasonic transducer of (B) is substantially _St + _Sr.

The reception voltage V in the case of such a fundamental wave reception
_r1 is, (4) the subscript r at a convenience subscript t in the _{equation, V r1 = g 33t · V} t · (S t + S r) · Q t · d t · V drive / 2f t ··· ( 6). Here, Q _t is an ultrasonic transducer, i.e. overall resonance sharpness of mechanical vibrations, including a backing layer and an acoustic matching layer.

On the other hand, if the received voltage in the case of n-th order harmonic reception and V _rn, in the same manner as _{(6), V rn = g 33r · V} r · S t · Q r · d t · V drive / 2nf _t (7)

The ultrasonic transducers shown in FIGS. 2 (A) and 2 (B) compensate for a decrease in sensitivity by using a signal higher than the fundamental wave reception voltage in the ultrasonic transducers shown in FIGS. 3 (A) and 3 (B). It is preferable that an nth-order harmonic signal can be received at the level. For this purpose, the ultrasonic transducer shown in FIGS. 2A and 2B only needs to satisfy V _rn / V _r1 ≧ 1.

[0045] By substituting in this relationship (6) and _{(7), V rn / V r1 = (} g 33r · V r · (S t + S r) · Q r / n) / (g 33t · V _{t · S t · Q t)} ≧ 1 ··· (8) next, after _{all, (g 33r · V r ·} Q r) / (g 33t · V t · Q t) ≧ n · (1 + R) ··· (9) Here, R = _St / _Sr.

The mechanical resonance sharpness Q _t of the transmitting piezoelectric vibrator 302, when it 5 or more, tail stringing becomes longer transmission ultrasonic pulse, exacerbating the depth resolution, also when he 1 or less,
The band of the fundamental wave ultrasonic wave becomes too wide, and the amount of the fundamental wave component mixed at 2f0 increases, thereby lowering the S / N. Therefore, the value of Q _t is may be in the between 1 and 5.

When the mechanical resonance sharpness Q _r of the receiving piezoelectric vibrator 304 is 5 or more, the tailing of the reception voltage V _rn becomes long, and the resolution in the depth direction is deteriorated.
The band of the reception voltage V _rn becomes too wide, the ratio of the fundamental wave component increases, and the S / N decreases. Thus, the value of Q _r is 1
Or between 5 and 5.

The material of the transmitting piezoelectric vibrator is d ₃₃ > 200.
It is preferable to have a piezoelectric constant d ₃₃ and a mechanical quality factor Qm satisfying × 10 ⁻¹² [m / V], 70 <Qm <1000.

When the value of Qm of the piezoelectric vibrator is large,
By mitigating the damping effect of the backing layer,
It is preferable to adjust the value of Q _t. The backing layer 310 has a high ultrasonic attenuation rate and a low acoustic impedance Z to reduce the damping effect more than usual and increase the resonance sharpness.
d, for example, it is preferable to have an acoustic impedance Zd of 1/3 or less of the acoustic impedance Zp of the transmitting piezoelectric vibrator 302. Suitable materials for the backing layer 310 include, for example, a composite resin obtained by mixing a suitable amount of tungsten powder with a highly flexible epoxy resin. The tungsten powder is preferably mixed in such an amount that the acoustic impedance of the backing layer 310 is about 1/3 of the acoustic impedance of the piezoelectric vibrator and the attenuation rate is about 8 dB / cm / MHz. Here, if the attenuation rate is 5 dB / cm / MHz or less, Q becomes too large, the time-axis pulse width becomes long, and the resolution in the distance direction deteriorates. The material of the backing layer 310 is not limited to the above-described composite material, and may be, for example, a composite material in which alumina or zirconia powder is mixed.

Since the receiving disk-shaped piezoelectric vibrator 304 has a narrow band filter characteristic at the center frequency 2f ₀ or 3f ₀ , only the 2f ₀ or 3f ₀ component is selectively converted into a voltage signal. . The ultrasonic vibration on the back side of the piezoelectric vibrator reflects the amplitude of the ultrasonic vibration transmitted to the backing layer side and the reflection to the piezoelectric vibrator side due to the relative relationship between the acoustic impedance Zp of the piezoelectric vibrator and the acoustic impedance Zd of the backing layer. The ratio is one of the criteria for determining the mechanical resonance sharpness Q of the transmitting ultrasonic transducer.
When Zd is 1/3 or less of Zp, the reflected ultrasonic component becomes larger, and the mechanical resonance sharpness Q of the transmitting ultrasonic transducer can be controlled to an optimal value of 2 to 5.

The piezoelectric material of the receiving piezoelectric vibrator 304 is Q
m is large, a large voltage output coefficient g _33, may is longitudinal wave sound velocity is large material. The voltage output coefficient g ₃₃ is g ₃₃ > 3
It is preferable to satisfy 0 × 10 ⁻³ [V / Nm]. Preferred materials, for example, the formula _{K (Nb 1-x Ta x} ) O 3,
There is a piezoelectric single crystal represented by 0 ≦ x ≦ 0.2. Another preferred material is lead titanate-based piezoelectric ceramics. Yet another preferred material is a Bi ₄ Ti ₃ O ₁₂ or _{Ma 1-x Mb x Bi 2} McO 8, 0 ≦ x ≦ 0.2 in Formula bismuth layered ferroelectric represented (BLSF) . Here, Ma and Mb are alkaline earth metal elements such as Sr and Ba, and Mc is a + 5-valent metal element such as Ta and Nb.

When the value of Qm of the piezoelectric vibrator is large,
By mitigating the damping effect of the backing layer,
It is preferable to adjust the value of Q _r. The backing layer 312 has a high ultrasonic attenuation rate and a low acoustic impedance Z in order to reduce the damping effect and increase the resonance sharpness.
d, for example, it is preferable to have an acoustic impedance Zd of 以下 or less of the acoustic impedance Zp of the receiving piezoelectric vibrator 304. Suitable materials for the backing layer 312 include, for example, a composite resin obtained by mixing a suitable amount of tungsten oxide powder or barium ferrite powder with highly flexible epoxy resin. The material of the backing layer 312 is not limited to the above-described composite resin, and may be, for example, a composite resin obtained by mixing alumina or zirconia powder.

As a specific example, the transmitting piezoelectric vibrator 30
The piezoelectric material of No. 2 is PZT ceramics, and the piezoelectric material of the receiving piezoelectric vibrator 304 is a longitudinal wave velocity V _t = 5900 [m /
s] and a potassium single niobate (KNbO ₃ ) piezoelectric single crystal having a voltage output coefficient g _33t = 55 × 10 ⁻³ [Vm / N].

Here, when Q _t = 1 and Q _r = 5, and these values and their material constants are substituted into the left side of the equation (9),
The left side = 12.7. When R = 1, that is, when the transmission aperture area = the reception aperture area, n = 6, so that good reception is possible up to the sixth harmonic signal. If the actual value is too large for Q _r is the time-axis pulse width is increased, so will reduce the depth resolution, the value of Q _r is preferably small. When lowered to Q _r = 2.5,
The left side of equation (9) is 6.4, and n = 3.
Good reception is possible up to the third harmonic signal.

Further, Q _t = 2, R of the transmitting ultrasonic transducer
If = 1, then Q _r = 3.2 and n = 2, so that good reception up to the third harmonic signal is possible. Further, when R = 0.5, that is, when the reception aperture area S _r is _の of the transmission aperture area, Q _t = 2, Q _r = 2.4, and n
= 2, good reception is possible up to the second harmonic signal.

These transducer characteristics do not need to rely on undeveloped technology and can be sufficiently realized by conventional transducer manufacturing technology.

As can be understood from the above description, in the in-plane separation type ultrasonic transducer for harmonic imaging, by using the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator satisfying the expression (9), the entire aperture is opened. Harmonic signals can be received at the same reception voltage as that of the fundamental wave transmission / reception.

[First Modification] FIGS. 4A and 4B show a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator of an in-plane separation type ultrasonic transducer according to a modification of the present embodiment. Show. In the in-plane separation type ultrasonic transducer of this modification, the transmitting piezoelectric vibrator 362 of the transmitting ultrasonic vibrator is a PZT ceramics disk vibrator, and the receiving ultrasonic vibrator for receiving a harmonic signal is received. The piezoelectric vibrator 364 for KN
This is an annular piezoelectric vibrator made of bO ₃ , and the transmitting piezoelectric vibrator 362 is located inside the receiving piezoelectric vibrator 364, contrary to the above-described embodiment.

[0059] When the opening area ratio _{R (= S r / S t} ) of 0.5, the relative configuration of Q _t and Q _r, the same extent as if the entire opening and the fundamental wave transmitted and received as described above At the signal level,
Harmonic signals can be received.

When a general PZT ceramic vibrator is formed in an annular shape, a divided vibration occurs near a resonance frequency.
In many cases, good resonance characteristics cannot be obtained. But,
By using KNbO ₃ for the annular piezoelectric vibrator as in the present modification, the resonance characteristics are greatly improved. This fact has been experimentally confirmed by the present inventors.

[Second Modification] Next, a transmitting piezoelectric vibrator according to a modification of the present embodiment will be described with reference to FIGS.

In the present embodiment, the ring-shaped transmitting piezoelectric vibrator has a full-surface electrode formed on the entire surface thereof. In a modification of the present embodiment, as shown in FIG. The ring-shaped transmitting piezoelectric vibrator 370 has an energy trapping electrode structure 372.

Here, the term “energy trapping electrode structure” refers to an electrode that partially covers the face of the piezoelectric material and satisfies the expression (10) described later.

This energy trapping electrode structure 372
Has a pair of electrode plates disposed to face each other with an annular piezoelectric body 374 interposed therebetween. One of the pair of electrode plates, for example, the front side electrode plate is, as shown in FIG. It has a plurality of circular electrodes 382 and thin wires 384 connecting adjacent circular electrodes 382. In addition, the other of the pair of electrode plates, for example, the back side electrode plate, for example, as shown in FIG.
A thin wiring 394 for connecting the adjacent circular electrodes 392 is provided.

As can be seen from FIGS. 6 and 7, the circular electrode 3
82 and the circular electrode 392 are arranged facing each other with the piezoelectric body 374 interposed therebetween, and the wiring 384 and the wiring 394 intersect at only one position in the projection thereof, and except for this, the wiring between the piezoelectric body 374 and It does not have a part that sandwiches and faces each other.

Further, the thickness h of the piezoelectric body 374 satisfies the following expression, where a is the diameter of the electrode, and Δ is the rate of decrease in frequency due to electrode formation.

[0067]

(Equation 1)

Such a piezoelectric vibrator is formed, for example, by forming electrodes on the entire front and back surfaces of an annular PZT piezoelectric body having a thickness satisfying the above equation, polarizing the electrodes, and then performing a process such as photolithography. It is formed by selectively etching the entire surface electrodes on the front side and the back side.

The diameter of the circular electrode 382 is selected to be about １ to / of the width w of the ring of the piezoelectric body 374, and the diameter of the circular electrode 392 is such that one of a pair of circular electrodes In order not to protrude, a value smaller than the diameter of the circular electrode 382 by 5 to 10% is selected in consideration of a displacement at the time of etching.

In FIG. 1, the electrode 382 on the ultrasonic wave emitting side is connected to the front side electrode of the disk-shaped piezoelectric vibrator 304 arranged inside the annular piezoelectric vibrator by the wiring 416, and is connected to the housing 306 by the wiring 418. Connected.

In a ring-shaped piezoelectric vibrator having a normal whole-surface electrode, divided vibration sometimes occurs at a resonance frequency. The generation of such divided vibrations not only reduces the transmission ultrasonic sound pressure, but also shifts the ratio of the resonance frequency of the transmission ultrasonic vibrator to the resonance frequency of the reception ultrasonic vibrator from 1: 2. Transmission of the fundamental wave and reception of the harmonic signal.

Since the annular piezoelectric vibrator of this modification has an energy trapping electrode structure, split vibration near the resonance frequency hardly occurs. This enables the ratio of the resonance frequency of the transmitting ultrasonic transducer to the resonance frequency of the receiving ultrasonic transducer to be accurately maintained at 1: 2, which is preferable for realizing effective harmonic imaging.

As described above, by using the electrodes of the piezoelectric vibrator as the energy confining electrodes, the annular piezoelectric vibrator does not have any unnecessary vibration components superimposed thereon, and emits a fundamental ultrasonic wave consisting of only a longitudinal ultrasonic wave component. It can be generated efficiently.

In this modification, a transmitting piezoelectric vibrator having an energy confining electrode has been exemplified as an improvement measure of the transmitting piezoelectric vibrator.
The receiving piezoelectric vibrator may have an energy trapping electrode. A large _Qr is obtained by the receiving piezoelectric vibrator having the energy trapping electrode, and thus a large reception voltage _Vrn is obtained.

The respective components of the embodiment of the present invention are as follows.
Naturally, various modifications and changes are possible.

For example, in the present embodiment, the ultrasonic transducer has a circular opening, but the shape of the opening is not limited to a circle. The aperture of the ultrasonic transducer may have, for example, a rectangular, elliptical, or strip shape. Further, the ultrasonic transducer is an electronic scanning array type transducer, and each element constituting the array is arranged in the same plane as in the present embodiment, and a fundamental wave transmitting transducer is arranged. And a harmonic receiving vibrator.

[Second Embodiment] This embodiment is an ultrasonic transducer system including the ultrasonic transducer described in the first embodiment, which is suitable for harmonic imaging ultrasonic diagnosis.

This ultrasonic transducer system has:
As shown in FIG.
And a pulser circuit 402 for supplying a driving pulse signal to the transmitting piezoelectric vibrator 302 of the ultrasonic transducer 300
And In one example, the pulser circuit 402 can generate a high-voltage spike wave and adjust its pulse width and fall time as needed. Pulsar circuit 402
In another example, may generate a high voltage trapezoidal wave and adjust its pulse width and fall time as needed. In still another example, the pulser circuit 402 can generate a high-voltage burst wave and adjust its burst length and window function as needed.

The ultrasonic transducer system further includes a receiver circuit 404 for receiving an output signal of the receiving piezoelectric vibrator 304 of the ultrasonic transducer 300, and a signal processing circuit 40 for processing a signal from the receiver circuit 404.
6 and an image processing circuit 408 for imaging a signal from the signal processing circuit 406. The image obtained by the image processing circuit 408 is displayed on a monitor screen that is not finally displayed.

The present invention is directed to an ultrasonic diagnosis using a secondary or tertiary harmonic signal. In ultrasonic diagnosis, the fundamental wave ultrasound, other frequency components except for the center frequency f0, that does not particularly include a frequency component of 2f ₀ and 3f ₀ is desired. In particular, two fundamental waves
as containing the frequency components of f ₀ and 3f _0, upon reception,
A harmonic signal to be detected, can not distinguish between frequency components of 2f ₀ and 3f ₀ which are mixed from the beginning to the fundamental wave ultrasound.

[0081] For this reason, in the application to the ultrasonic diagnostic of second harmonic signal, it is desirable that the ultrasonic wave transmitted from the transmitting ultrasonic vibrator contains no frequency component of 2f _0. Similarly, in the use of the ultrasonic diagnostic third order harmonic signals, it is desirable that the ultrasonic wave transmitted from the transmitting ultrasonic vibrator contains no frequency component of 3f _0.

FIG. 9A shows a drive voltage waveform 41 of a spike wave which is an example of a drive signal supplied to the transmitting piezoelectric vibrator.
2 is shown. FIG. 9B shows a frequency characteristic of the driving voltage waveform 412 of the spike wave, and shows a negative slope 416 near the first dip frequency and a first dip frequency 4.
22, a second dip frequency 424, and a first peak frequency 426 are shown. Such a trapezoidal wave is a waveform generally used in a pulse echo diagnostic method as a realistic drive signal waveform, since a δ function or a rectangular wave as an ideal drive waveform cannot be strictly realized.

As can be seen from FIG. 9B, the frequency characteristics of the drive voltage waveform 412 of the spike wave show a peak / dip characteristic and an overall drooping characteristic. It is well known that the frequency characteristics of the δ function do not exhibit peak / dip characteristics or overall droop characteristics. It has been found that the peak / dip characteristic has a pulse width on the time axis, and that the overall droop characteristic and the blunting of the level change at the peak / dip frequency have a falling slope. .

The spectrum T (jω) of the transmitted ultrasonic signal is
As shown in the following equation (11), the response signal spectrum H (jω) at the time of driving the δ function is multiplied by the spectrum D (jω) of the driving waveform.

T (jω) = H (jω) · D (jω) (11) From this equation, if D (jω) has a dip at 2f ₀ , that is, a level drop in the frequency characteristic, The transmission waveform T (jω) also has a dip at that frequency,
As a result, it is understood that the 2f ₀ component of the transmitted fundamental ultrasonic wave is suppressed.

As shown in FIG. 9B, by using a drive signal waveform having a spectrum in which the frequency of the first dip 422 is 2f ₀ , the transmission spectrum T (jω) in which the 2f ₀ component is suppressed can be obtained. can get.

FIG. 11 shows the fall time t _f of the first dip frequency in the frequency characteristic of the spike wave drive signal.
Are shown. From the characteristic curve of the first dip frequency shown in FIG.
In the detection of the next harmonic signal, by setting a fall time tf in 99Ns, it can be seen that the fundamental ultrasound 2f ₀ component is suppressed is obtained. As a result, −2.5 [dB / MHz] × (10 MHz−5 MHz)
= -12.5 dB level down can be realized. On the other hand, the level reduction in the dip is also reduced, but it is clear that the level reduction of -12.5 dB or more can be realized by both effects.

As described above, by appropriately selecting the fall time of the spike wave, it is possible to generate a fundamental ultrasonic wave in which the 2f ₀ component or the 3f ₀ component is suppressed.

FIG. 10A shows a drive voltage waveform 432 of a trapezoidal wave which is another example of the drive signal supplied to the transmitting piezoelectric vibrator. FIG. 10B shows the frequency characteristics of the drive voltage waveform 432 of the trapezoidal wave. The negative slope 436 near the first dip frequency, the first dip frequency 442, the second dip frequency 444, and the One peak frequency 446 is shown.

Also in this trapezoidal wave, a specific relationship is established between the first dip frequency and the fall time similarly to the above-described spike wave. Therefore, by appropriately selecting the fall time, it is possible to generate a fundamental ultrasonic wave in which the 2f ₀ component or the 3f ₀ component is suppressed.

FIG. 12A shows a drive voltage waveform of a burst wave which is still another example of the drive signal supplied to the transmitting piezoelectric vibrator, and FIG. 12B shows the frequency characteristic. Is shown. In this case, since the nucleus of the burst wave 452 is a sine wave, the ideal driving signal waveform has an extremely small side lobe, about -30 dB, and a small main lobe bandwidth.

In this burst wave, the burst length t
p and the first dip frequency have the relationship shown in FIG. Therefore, the first dip frequency can be controlled by adjusting the burst length tp. Therefore, by using a drive signal having such a spectrum D (jω), it is possible to obtain a transmission wave in which frequency components of 2f ₀ and 3f ₀ are almost completely suppressed.

In the ultrasonic transducer system of the present embodiment, the pulser circuit 402 has the center frequency f ₀
And a drive pulse signal having a frequency characteristic having a first dip frequency of 2f ₀ is supplied to the transmitting ultrasonic transducer. As a result, the transmission ultrasonic transducer generates an ultrasonic wave in which the 2f ₀ component is suppressed.

Alternatively, the pulser circuit 402 may supply a driving pulse signal having a frequency characteristic whose center frequency is at f ₀ and whose first dip frequency is at 3f ₀ to the transmitting ultrasonic transducer. As a result, the transmitting ultrasonic transducer generates an ultrasonic wave in which the 3f ₀ component is suppressed.

According to the present embodiment, by controlling the drive signal waveform, it is possible to transmit an ultrasonic wave in which the 2f ₀ component and the 3f ₀ component are suppressed, and as a result, the ultrasonic wave is generated on the object by the fundamental ultrasonic wave. Second and third harmonic signals with high S
/ N can be received.

Note that each configuration of the embodiment of the present invention
Naturally, various modifications and changes are possible.

For example, in the present embodiment, the ultrasonic transducer has a circular opening, but the shape of the opening is not limited to a circle. The aperture of the ultrasonic transducer may have, for example, a rectangular, elliptical, or strip shape. Further, the ultrasonic transducer is an electronic scanning array type transducer, and each element constituting the array is arranged in the same plane as in the present embodiment, and a fundamental wave transmitting transducer is arranged. And a harmonic receiving vibrator.

[Third Embodiment] An ultrasonic transducer according to the present embodiment will be described with reference to FIG.
The ultrasonic transducer of the present embodiment is similar to the ultrasonic transducer described in detail with reference to FIG. 1 in the first embodiment, and FIG.
The members indicated by the same reference numerals as those of the above indicate equivalent members.

The ultrasonic transducer of the present embodiment has a thin-film spiral heater 502 inside the acoustic lens 308. One end of the heater 502 is electrically connected to the surface electrode of the transmitting piezoelectric vibrator 302 via a thin conductor 504, and the other end is connected to the housing 306 via a thin conductor 506. The spiral-shaped thin-film heater 502 preferably includes a transmitting piezoelectric vibrator 302.
Are disposed as close as possible to the transmitting piezoelectric vibrator 302 as long as they do not come into contact with the electrode on the ultrasonic emission surface side.

The heater 502 is connected to the transmitting piezoelectric vibrator 30.
2 to give a temperature gradient along its thickness direction,
At least one of the piezoelectric constant and the dielectric constant functions to provide a gradient function characteristic.

It is known that the vibration characteristics can be changed by giving the piezoelectric constant and the dielectric constant of the piezoelectric vibrator a function of a gradient. (Akira Yamada: "Piezoelectric Functional Gradient Broadband Ultrasonic Transducer", 2000 Commemorative, Advanced Technology Symposium "Piezoelectric Materials and Elastic Wave Devices" Text (February 2000) P31-38).

[0102] In FIG. 15, dashed line 512 shows the impedance characteristics of the piezoelectric vibrator having no tilt function, the solid line 514 shows the impedance characteristics of the piezoelectric vibrator having the functionally gradient characteristics of the piezoelectric constant e ₃₃ I have.

As can be seen from FIG. 15, in the piezoelectric vibrator having the tilt function characteristic, the tertiary piezoelectric vibration 516 which is largely generated in the piezoelectric vibrator having no tilt function characteristic is suppressed. Therefore, the tertiary piezoelectric vibration 516 can be suppressed by providing the transmitting piezoelectric vibrator with the tilting function characteristic.

The ultrasonic transducer of the present embodiment imparts a tilting function characteristic to the transmitting piezoelectric vibrator 302 by heating by the heater 502, thereby suppressing tertiary piezoelectric vibration.

The transmission and reception of ultrasonic waves in the ultrasonic transducer of the present embodiment is the same as that of the ultrasonic transducer shown in FIG. 1, and therefore description thereof is omitted to avoid duplication. I will explain only.

When a drive signal, for example, a burst wave signal is applied between the housing 306 and the wiring 332 to the transmitting piezoelectric vibrator 302, the wiring 332, the piezoelectric vibrator 302, and the conductor 5
04, the spiral-shaped thin-film heater 502, the conducting wire 506, and the housing 306 flow in this order. The electric current is converted into Joule heat by flowing through the spiral flake heater 502. Since the spiral flake heater 502 is arranged near the transmitting piezoelectric vibrator 302, heat generated by the spiral flake heater 502 is efficiently transmitted to the transmitting piezoelectric vibrator 302.

On the other hand, on the back surface of the transmitting piezoelectric vibrator 302, a backing layer 310 made of a resin in which tungsten powder is dispersed at a high density in, for example, silicone resin having good thermal conductivity is joined. Further, the space 336 inside the housing 306 is also filled with a material having good heat conductivity such as silicone resin. Therefore, the heat transmitted through the transmitting piezoelectric vibrator 302 is radiated well from the back side.

As a result, a temperature gradient is generated in the thickness direction of the transmitting piezoelectric vibrator 302, and the transmitting piezoelectric vibrator 302 is provided with a dielectric function, a piezoelectric constant, or a gradient function characteristic relating to both. Therefore, as described with reference to FIG. 15, the tertiary piezoelectric vibration of the transmitting piezoelectric vibrator 302 is suppressed. As a result, the transmitting ultrasonic transducer generates an ultrasonic wave in which the 3f ₀ component is suppressed.

In the present embodiment, the transmitting piezoelectric vibrator 30
While the second tertiary piezoelectric vibration is suppressed, the second piezoelectric vibration 518 of the transmitting piezoelectric vibrator 302 is excited. Therefore, the ultrasonic transducer of the present embodiment was described in the second embodiment, it may be combined with the drive control for suppressing a component of 2f _0.

The temperature gradient to be applied to the transmitting piezoelectric vibrator 302 strongly depends on the dielectric constant of the transmitting piezoelectric vibrator 302 and the temperature characteristics of the piezoelectric constant. In general, it is known that the lower the Curie point of a piezoelectric vibrator, the greater the temperature dependence of the dielectric constant and piezoelectric constant, and the smaller the temperature difference applied to the front and back surfaces of the piezoelectric vibrator.

For example, in order to give the transmitting piezoelectric vibrator 302 a tilting function characteristic having a dielectric constant of 3200 on the front surface and 2200 on the back surface, the temperature characteristic of the dielectric constant of the transmitting piezoelectric vibrator 302 should be about 1 ° C. When it changes by 1%, the temperature difference given to the front and back surfaces may be about 26 ° C.

According to the present embodiment, the third-order piezoelectric vibration is suppressed by providing the transmitting piezoelectric vibrator with a gradient function characteristic with respect to the dielectric constant and / or the piezoelectric constant, and further to the second embodiment. By using the drive control described in (1) together, an ultrasonic pulse close to an ideal waveform consisting of only the fundamental wave component is transmitted from the transmitting ultrasonic transducer.

Note that each configuration of the embodiment of the present invention
Naturally, various modifications and changes are possible.

For example, in the present embodiment, the ultrasonic transducer has a circular opening, but the shape of the opening is not limited to a circle. The aperture of the ultrasonic transducer may have, for example, a rectangular, elliptical, or strip shape. Further, the ultrasonic transducer is an electronic scanning array type transducer, and each element constituting the array is arranged in the same plane as in the present embodiment, and a fundamental wave transmitting transducer is arranged. And a harmonic receiving vibrator.

In this embodiment, the means for giving a temperature gradient is an example of a spiral flake heater. However, the means for giving a temperature gradient may be another means, for example, a Peltier element. In particular, the Peltier element has one end serving as a cooling end and the other end serving as a heating end, and thus has high heat utilization efficiency and good controllability. Therefore, it can be said that the Peltier element is suitable means when there is a margin in the external dimensions of the transducer.

[Modification of this Embodiment] As a modification of the ultrasonic transducer of this modification, a transmitting piezoelectric vibrator having a gradient function characteristic in at least one of a piezoelectric constant and a dielectric constant is provided. The ultrasonic transducer that is used will be described.

In the present embodiment described above, for the purpose of suppressing the tertiary piezoelectric vibration of the transmitting piezoelectric vibrator 302, an ultrasonic wave having a means for giving the transmitting piezoelectric vibrator 302 a tilting function characteristic is provided. Although a transducer has been shown, in order to achieve the same purpose, instead of an ultrasonic transducer having such means, the transmitting piezoelectric vibrator itself has at least one of a piezoelectric constant and a dielectric constant. May have a gradient function characteristic.

The ultrasonic transducer of this modification has the same structure as the ultrasonic transducer shown in FIG. 1, except that the transmitting piezoelectric vibrator 302 is replaced by a piezoelectric vibrator having a tilt function characteristic. I have. FIG. 16 shows a transmitting piezoelectric vibrator 302 of the ultrasonic transducer of FIG.
14 shows a partial cross-section of a functionally graded piezoelectric vibrator 520 having functionally graded characteristics, which can be replaced with FIG.

The functionally graded piezoelectric vibrator 520 has a pair of electrodes 522a and 522b and a piezoelectric layer 524 sandwiched between them, and the piezoelectric layer 524 is composed of a plurality of stacked layers. The piezoelectric thin films 526a, 526b,.
526z, and each of the piezoelectric thin films is slightly different from the adjacent piezoelectric thin film in the dielectric constant and / or the piezoelectric constant along the laminating direction.

For example, the piezoelectric thin films 526a, 526b,
.., 526z are almost the same except for the Curie temperature except for the dielectric constant, and the uppermost, that is, the piezoelectric thin film 526a on the ultrasonic emission surface side has a dielectric constant of 3200, The piezoelectric thin film 526z has a dielectric constant of 2200, and has the functionally graded characteristic shown in FIG. 17 as a whole.

The piezoelectric vibrator 520 itself having the function of tilting itself has a larger function than the function of tilting created by applying a temperature gradient to the piezoelectric vibrator having no function of tilting. Due to the slope, the third order piezoelectric vibration 516 is more dramatically suppressed.

The piezoelectric layer of the functionally graded piezoelectric vibrator is not limited to a laminate of piezoelectric thin films having different dielectric constants or piezoelectric constants or both. At least one of the piezoelectric constant and the dielectric constant is used. It is only required that one side has a tilting function characteristic. For example, it may be formed by diffusing impurity ions from one surface of a plate-shaped piezoelectric body.

[0123]

According to the present invention, an ultrasonic transducer having high S / N and high selectivity is provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of an in-plane separation type ultrasonic transducer according to a first embodiment.

FIGS. 2A and 2B schematically show a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator in the in-plane separation type ultrasonic transducer according to the first embodiment, and FIG. It is a front view of a piezoelectric vibrator, (B) is 2B-2 of (A).
It is sectional drawing which followed the B line.

FIG. 3 shows an in-plane separation type ultrasonic transducer for detecting only a basic ultrasonic wave as a comparative object of the first embodiment, and FIG. 3A is a front view of a piezoelectric vibrator of the ultrasonic transducer. FIG. 3B is a sectional view taken along line 3B-3B of FIG.

4A and 4B schematically show a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator in an in-plane separation type ultrasonic transducer according to a modified example of the first embodiment, and FIG. 4A shows a transmitting piezoelectric vibrator. And FIG. 4B is a cross-sectional view taken along line 4B-4B of FIG.

FIG. 5 is a plan view of a transmitting piezoelectric vibrator having an energy trapping electrode structure, which is a modification of the second embodiment.

6 is a view corresponding to a portion surrounded by a broken line in FIG. 5, and shows a layout of an electrode plate on the front side of the energy trapping electrode structure.

FIG. 7 is a diagram corresponding to a portion surrounded by a broken line in FIG. 5, and shows a layout of an electrode plate on the back side of the energy trapping electrode structure.

FIG. 8 illustrates an ultrasound transducer system including the ultrasound transducer of FIG.

FIG. 9A shows a driving voltage waveform of a spike wave which is an example of a driving signal supplied to a transmitting piezoelectric vibrator;
(B) shows the frequency characteristic.

FIG. 10 shows a change in the first dip frequency with respect to the fall time for the spike wave shown in FIG.

FIG. 11A shows a drive voltage waveform of a trapezoidal wave which is another example of the drive signal supplied to the transmitting piezoelectric vibrator, and FIG. 11B shows the frequency characteristics thereof.

FIG. 12A shows a drive voltage waveform of a burst wave as still another example of the drive signal supplied to the transmitting piezoelectric vibrator, and FIG. 12B shows the frequency characteristics thereof.

FIG. 13 relates to the spike wave shown in FIG.
4 illustrates a change in a first dip frequency with respect to a burst wavelength.

FIG. 14 is a sectional view of an in-plane separation type ultrasonic transducer according to a third embodiment.

FIG. 15 shows impedance characteristics of a piezoelectric vibrator having a tilt function characteristic in a piezoelectric constant and a piezoelectric vibrator having no tilt function characteristic.

FIG. 16 is a partial cross-sectional view of a functionally graded piezoelectric vibrator that is replaced with the transmitting piezoelectric vibrator of the ultrasonic transducer of FIG. 1 in a modification of the third embodiment.

FIG. 17 shows overall functional characteristics of the functionally graded piezoelectric vibrator of FIG.

FIG. 18 shows a conventional ultrasonic transducer having a transmitting ultrasonic vibrator and a receiving ultrasonic vibrator arranged one on top of the other.

[Explanation of symbols]

 302 Piezoelectric transducer for transmission 304 Piezoelectric transducer for reception

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H04R 17/00 332 H01L 41/08 J UF term (Reference) 4C301 AA03 EE04 EE15 GB14 GB20 GB34 GB36 GB40 HH01 HH47 HH48 JA17 5D019 AA27 BB02 BB10 BB20 FF04

Claims (21)

[Claims] 1. A is a ultrasonic transducer for harmonic imaging, a transmitting ultrasonic transducer for transmitting basic ultrasound having a center frequency f ₀ in response to an input electrical signal, to the object by the base ultrasound A receiving ultrasonic vibrator that receives a harmonic signal having a generated center frequency nf ₀ (n is an integer of 2 or more), and the transmitting ultrasonic vibrator has a transmitting piezoelectric vibrator; The receiving ultrasonic vibrator has a receiving piezoelectric vibrator, the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator are arranged on the same surface, and the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator are arranged. Is (g _{33r
V r · Q r) / (} g 33t · V t · Q t) satisfies the ≧ n · (1 + R) , where the, g _33t and V _t is the voltage output coefficient and sound speed of each transmitting piezoelectric vibrator, g _33r and V _r are the voltage output coefficient and sound velocity of the receiving piezoelectric vibrator, n is the harmonic order,
R is the opening area ratio (opening area of the receiving piezoelectric vibrator / opening area of the transmitting piezoelectric vibrator), and _Qt and _Qr are the transmitting ultrasonic vibrator and the receiving ultrasonic vibrator, respectively. Ultrasonic transducer with resonance sharpness. 2. The transmitting ultrasonic transducer according to claim 1, wherein the mechanical resonance sharpness Q at the center frequency is between 1 and 5.
An ultrasonic transducer according to claim 1. 3. The material of the transmitting piezoelectric vibrator is d ₃₃ > 20.
A piezoelectric constant d ₃₃ satisfying 0 × 10 ⁻¹² [m / V], and 70 <
3. The ultrasonic transducer according to claim 2, having a mechanical quality factor Qm satisfying Qm <1000. 4. The transmitting ultrasonic vibrator further includes a backing layer disposed on a back surface of the transmitting piezoelectric vibrator,
The backing layer has an ultrasonic attenuation rate greater than 5 dB / cm / MHz and an acoustic impedance Z of the transmitting piezoelectric vibrator.
The ultrasonic transducer according to claim 2, wherein the ultrasonic transducer has an acoustic impedance Zd of 1/3 or less of p. 5. The ultrasonic transducer according to claim 2, wherein the transmitting piezoelectric vibrator has an energy trapping electrode. 6. The ultrasonic transducer according to claim 1, wherein the receiving ultrasonic transducer has a center frequency of 2f _{0, and} a mechanical resonance sharpness Q at the center frequency is between 1 and 5. . 7. The ultrasonic transducer according to claim 1, wherein the receiving ultrasonic transducer has a center frequency of 3f _{0, and} a mechanical resonance sharpness Q at the center frequency is between 1 and 5. . Piezoelectric material 8. piezoelectric vibrator for receiving the high voltage output coefficient g _33, longitudinal wave acoustic velocity is faster material ultrasonic transducer according to claim 6 or claim 7. 9. high voltage output coefficient g _33, longitudinal wave acoustic velocity faster material, chemical formula _{K (Nb 1-x Ta x} ) O 3, 0 ≦ x ≦ 0.
The ultrasonic transducer according to claim 8, which is a piezoelectric single crystal represented by 2. 10. high voltage output coefficient g _33, longitudinal wave acoustic velocity faster material is a lead-based piezoelectric ceramics titanate ultrasonic transducer according to claim 8. 11. high voltage output coefficient g _33, longitudinal wave acoustic velocity faster materials, Bi ₄ Ti ₃ O ₁₂ or Ma _1-x Mb x Bi ₂
McO ₈ , a bismuth layered structure ferroelectric (BLSF) represented by the chemical formula of 0 ≦ x ≦ 0.2, wherein Ma and M
b is an alkaline earth metal element such as Sr or Ba, Mc is Ta
The ultrasonic transducer according to claim 8, wherein the ultrasonic transducer is a + 5-valent metal element such as Nb or Nb. 12. The ultrasonic transducer according to claim 6, wherein the receiving piezoelectric vibrator has an energy trapping electrode. 13. The receiving ultrasonic vibrator has a backing layer disposed on the back surface of the receiving piezoelectric vibrator, and the material of the backing layer is an ultrasonic attenuation rate greater than 5 dB / cm / MHz. The ultrasonic transducer according to claim 6, wherein the ultrasonic transducer has an acoustic impedance Zd which is equal to or less than / of an acoustic impedance Zp of the receiving piezoelectric vibrator. 14. An ultrasonic transducer system comprising: the ultrasonic transducer according to claim 1; and drive control means for driving and controlling the ultrasonic transducer, wherein the drive control means includes an ultrasonic wave having at least a component of 2f ₀ suppressed. An ultrasonic transducer system that generates an ultrasonic transducer for transmission. 15. The drive control unit supplies a drive pulse signal having a frequency characteristic having a center frequency of f ₀ and a first dip frequency of 2f ₀ to the transmitting ultrasonic vibrator. 15. The ultrasonic transducer system according to claim 14. 16. The drive control unit supplies a drive pulse signal of a burst wave to a transmitting ultrasonic transducer.
An ultrasonic transducer system according to claim 1. 17. The ultrasonic transmitting device according to claim 14, wherein the transmitting ultrasonic vibrator has means for giving the transmitting piezoelectric vibrator at least a gradient function characteristic relating to one of a piezoelectric constant and a dielectric constant. Sound transducer system. 18. The ultrasonic transducer system according to claim 17, wherein the means for imparting a functional gradient characteristic includes a heater for imparting a temperature gradient to the transmitting piezoelectric vibrator along a thickness direction thereof. 19. The ultrasonic transducer system according to claim 14, wherein the transmitting piezoelectric vibrator has a gradient function characteristic in at least one of a piezoelectric constant and a dielectric constant. 20. The ultrasonic wave according to claim 19, wherein the transmitting piezoelectric vibrator has an inclined piezoelectric material in which at least one of a piezoelectric constant and a dielectric constant monotonically changes along a thickness direction. Transducer system. 21. The ultrasonic transducer system according to claim 19, wherein the functionally graded function includes a plurality of laminated piezoelectric thin plates that have at least one of a piezoelectric constant and a dielectric constant slightly different. .