JPH0537999A - Wide band ultrasonic probe - Google Patents

Abstract

PURPOSE:To obtain sufficiently high distance resolving power in water even when center frequency to be used is low by forming Langevin oscillator structure forming resonance blocks constituted of plastic on both the sides of a pair of piezo-electric oscillators. CONSTITUTION:The Langevin structure is constituted of symmetrically forming the resonance blocks 10a, 10b consisting of plastic on both the sides of a pair of piezo-electric oscillators 1a, 1b. The acoustic impedance ZB of the blocks 10a, 10b is determined so that the value of a specific band f/f0 becomes >=0.2 in the prescribed using center frequency f0 found out from a transmission function T(f) in a transmitting/receiving system using water as a propagation medium. For instance, the blocks 10a, 10b are constituted of plastic using an epoxy compound material in which the acoustic impedance ZB is 4.2X10<6>(kg/m<2>/sec). Thereby even when the frequency f0 is low, sufficiently high distance resolving power can be obtained in water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband ultrasonic probe using a Langevin transducer structure in which water is used as a propagation medium.

[0002]

2. Description of the Related Art Conventionally, as an ultrasonic probe used in a water immersion type ultrasonic probe, for example, that shown in FIG. 9 is used. In the ultrasonic probe of FIG. 9, 1 is, for example, P
A piezoelectric vibrator using ZT, which is fixed to the back plate 2 and, on the opposite side, two impedance conversion blocks 3 and 4 for gradually approaching the acoustic impedance of water serving as a propagation medium.
Is provided.

Here, the thickness l of the piezoelectric vibrator 1 is l = λ / 2
And the thickness of each of the impedance conversion blocks 3 and 4 is set to λ / 4. However, in such a conventional ultrasonic probe, the operating frequency fo
Is high, there is no problem, but when the used frequency fo is lowered to increase the propagation distance in water, for example, fo = 30
When the frequency is lowered to kHz, the thickness l of the piezoelectric vibrator 1 is
When the sound velocity V of the piezoelectric vibrator is 4000 [m / s], l = λ / 2≈V / (2fo) = 67 mm, which makes it impossible to manufacture such a thick piezoelectric vibrator. Since it is too thick, it becomes difficult to polarize when a voltage is applied, and it cannot be used at a low frequency.

In order to solve this problem, the Langevin oscillator shown in FIG. 10 has been put into practical use. In the Langevin oscillator of FIG. 10, 1a and 1b are a pair of piezoelectric oscillators having a predetermined thickness, and duralumin (acoustic impedance 17 × 10 ⁶ [k
g / m ² / sec]), the resonance blocks 5a, 5
It has a symmetrical structure with b integrated, and the total length of the vibrator is λ /
It is set to 2.

Aluminum may be used for the resonance blocks 5a and 5b. According to such a Langevin oscillator, the operating frequency f is increased without increasing the thickness of the piezoelectric oscillator.
It is possible to lower o such as fo = 30 kHz, and it is possible to lengthen the underwater propagation distance of ultrasonic waves.

[0006]

However, in such a conventional Langevin oscillator, since the Q indicating the sharpness of the transfer function with respect to the used center frequency is very large, ultrasonic vibration propagating in water is generated. However, there is a problem in that the received pulse width of ultrasonic vibration becomes long and the range resolution is poor.

FIG. 11 shows a time change of a reception voltage when an ultrasonic wave is emitted into water by using a conventional Langevin oscillator and is received. A tone burst including one cycle of a 27 kHz sine wave is shown. When a wavy electric pulse is applied, the reception voltage shown as the sensitivity falls below the -20 dB line after τ time, and the time τ until it falls below the -20 dB line is defined as the pulse width τ.

In the case of the conventional Langevin oscillator, the pulse width τ is widened, for example, τ = 337 [μsec]. Therefore, the distance resolution d in water is d.
_res is as low as d _res = 0.25 [m].

FIG. 12 shows the relationship of the transfer function with respect to the frequency of the conventional Langevin oscillator. When the use center frequency fo = 26.6 kHz, the relationship of the transfer function with respect to the illustrated frequency is obtained. From this characteristic, the frequencies f1 and f2 determined by the −6 dB line of the peak amplitude are f1 = 25.4 kHz and F2 = 27.8 kHz, and therefore the bandwidth Δf is Δf = 2.4 kHz. Then, when the ratio band (Δf / fo) is obtained, Δf / fo = 0.09, and the sharpness Q becomes a narrow band characteristic showing a very high value of Q = fo / Δf = 11.1, Wider width and lower range resolution.

The present invention has been made in view of the above conventional problems, and is intended for an ultrasonic probe having a structure as a Langevin oscillator, and is sufficient in water even if the center frequency fo is low. It is an object of the present invention to provide a wideband ultrasonic probe capable of obtaining high range resolution.

[0011]

To achieve this object, the present invention is constructed as follows. The reference numerals in the drawings of the embodiments are also shown. First, according to the present invention, as shown in FIG.
It is intended for a broadband ultrasonic probe having a Langevin structure in which 0b is symmetrically provided.

In the present invention as such a wide band ultrasonic probe, at a predetermined use center frequency fo obtained from the transfer function T (f) of the transmission / reception system using water of the Langevin oscillator as a propagation medium. The acoustic impedance Z _B of the resonance blocks 10a and 10b is set so that the value of the ratio band Δf / fo becomes 0.2 or more.
The resonance blocks 10a and 10b that provide wide-band characteristics with a value of f / fo of 0.2 or more are made of an epoxy compound material having an acoustic impedance Z _B of 4.2 × 10 ⁶ [kg / m ² / sec], for example. It may be made of the used plastic.

Further, as shown in FIG. 13, the pair of piezoelectric vibrators 1a and 1b may be a single piezoelectric vibrator 1a only.

[0014]

According to the broadband ultrasonic probe of the present invention having such a configuration, the electroacoustic equivalent circuit of the Langevin oscillator is specified by the four-terminal circuit so that, for example, Langevin using water as a propagation medium. The transfer function T (f) of the transmission / reception system of the oscillator is obtained, and the ratio band (Δf / fo) can be calculated from this transfer function T (f). Therefore, the relationship between the acoustic impedance Z _{B of the} resonance block and the specific band is plotted, and the maximum of the acoustic impedance Z _B of the resonant block corresponding to the minimum value 0.2 of the specific band (Δf / fo) at which the sharpness Q can be sufficiently reduced. The value can be obtained, and the resonance block may be configured using a material having an acoustic impedance Z _{B that} is equal to or less than the maximum value.

A resonance block whose ratio band is 0.2 or more.
Acoustic impedance Z_M The maximum value of
9 × 10 when the frequency fo = 31.7 kHz⁶ [Kg
/ M ² / Sec] and may be set to a value less than this.
As a material satisfying this condition, for example, an acoustic impedance
Space Z_M Is 4.2 × 10 ⁶ [Kg / m² / Sec]
Resonant block using epoxy compound material
By making it, the distance resolution in water can be increased almost three times.
You can

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an embodiment showing an embodiment of a wide band ultrasonic probe of the present invention. In FIG. 1, 1a and 1b are piezoelectric vibrators, for example, PZT is used,
The acoustic impedance Zo of PZT is approximately Zo = 40 × 10 ⁶ [kg / m ² / sec].

The pair of piezoelectric vibrators 1a and 1b are integrally bonded and fixed, and the resonance blocks 10a and 10b are symmetrically fixed to the outside of each piezoelectric vibrator 1a and 1b. That is, the broadband ultrasonic probe of the present invention has the same oscillator structure as the conventional Langevin oscillator shown in FIG. The difference from the conventional Langevin oscillator is that in the broadband ultrasonic probe of the present invention, the frequency characteristics of the transfer function T (f) when the water is used as the propagation blocks of the resonance blocks 10a and 10b are different from each other. The acoustic impedance Z _M is set so as to obtain a wide band characteristic of 0.2 or more in the band (Δf / fo). As a material for realizing the acoustic impedance Z _{M in} which the ratio band (Δf / fo) is 0.2 or more, for example, plastic resonance blocks 10a and 10b made of an epoxy compound material may be used.

In the embodiment shown in FIG. 1, the use center frequency f
When o is fo = 31.7 kHz, the total length l of the wideband ultrasonic probe is l = λ / 2 as shown in the figure. Further, the thickness l1 and the diameter D1 of the piezoelectric vibrators 1a and 1b at this time are l1 = 2 mm and D1 = 24 mm, respectively, and the length l2 and the diameter D2 of the resonance blocks 10a and 10b are l2 = 17 mm and D2 = It will be 20 mm.

Next, as shown in the embodiment of FIG. 1, in the resonance blocks 10a and 10b of the wideband ultrasonic probe having the Langevin oscillator structure of the present invention, a specific band (Δf / f) is applied.
acoustic impedance Z _M such that o) is 0.2 or more
The principle of wide band characteristics using the material will be described in detail. First, the inventors of the present application considered the equivalent circuit shown in FIG. 2 as an equivalent circuit of an ultrasonic probe using a Langevin oscillator.

First, the present inventors put together an ultrasonic probe using a Langevin oscillator into a simple 4-terminal equivalent circuit using F parameters (A, B, C, D) as shown in FIG. It was Next, a configuration as shown in FIG. 3 will be considered in order to evaluate the ratio band and the pulse width τ of the received waveform in the transmission / reception system using the Langevin oscillator. In FIG. 3, 13
Is a transmission circuit, and the transmission voltage Vs of the used center frequency fo
Can be expressed by using the constant voltage power supply 14 that generates the voltage and the internal impedance Zs, and drives the transmission oscillator 16 using the Langevin oscillator. The transmission oscillator 16 is placed in water 17 as a propagation medium, and the reception oscillator 18 is disposed in the water 17 facing the transmission oscillator 16.
A Langevin oscillator is also used as the reception oscillator 18, a reception circuit 19 having a reception impedance Zl is connected to the reception oscillator 18, and a reception voltage Vl is obtained at both ends of the reception impedance Zl.

When the equivalent circuit represented by the F parameter shown in FIG. 2 is applied to the transmission / reception system of the Langevin oscillator using water as the propagation medium shown in FIG. 3, the equivalent circuit of the transmission / reception system shown in FIG. 4 is obtained. You can Regarding the equivalent circuit of the transmission / reception system of FIG. 4, F parameters (A, B, C, D) of the equivalent circuit of the Langevin oscillator using the transfer function T (f) for the transmission oscillator 16 and the reception oscillator 18 are used. It is expressed as T (f) = Vl / Vs = (2Z M Zl) / [AZ M + B + Zs (CZ M + D)] · [AZ M + B + Zl (CZ M + D)] transmission of the transmitting and receiving system using a Langevin transducer in this manner When the function T (f) is obtained, the ratio band (Δf / fo) can be calculated by obtaining the values of the F parameters (A, B, C, D) of the equivalent circuit of FIG. 2 at the used frequency fo. . The calculation of this ratio band (Δf / fo) is performed in the above (1).
In the formula, the transfer function T (f) at the use frequency fo is obtained, and the frequencies f1 and f2 before and after the use center frequency fo which gives the value of the transfer function T (f) lowered by −6 dB with this value as the peak value are obtained. , Δf / fo = (f2-f1) / fo.

Next, plotting the value of the ratio band (Δf / fo) which can be calculated from the transfer function T (f) of the equation (1) in the case of the used center frequency fo = 31.7 kHz, the characteristic shown in FIG. 5 is obtained. To be In FIG. 5, as the acoustic impedance Z _B of the resonance blocks 10a and 10b decreases, the ratio band value increases.

Here, the specific band (Δf / fo) represents the frequency characteristic of ultrasonic vibration propagating in water, and the specific band (Δf / fo)
The wider the value of f / fo), the wider the band characteristic. If the propagation characteristics of ultrasonic vibration are wideband characteristics, the pulse width τ
Since the distance can be shortened and the distance resolution in water can be improved, in the present invention, for example, the ratio band (Δf / f
o) has a minimum value of Δf / fo = 0.2, and the acoustic impedance Z _B of the resonance blocks 10a and 10b is determined so as to provide a ratio band of 0.2 or more.

The acoustic impedance of the piezoelectric vibrator is 40 ×
In the case of 10 ⁶ [kg / m ² / s], the specific band (Δf /
The acoustic impedance Z _B of the resonance blocks 10a and 10b that gives fo) = 0.2 is Z _B = 10 × 10 ⁶ [kg / m ² / sec]. Therefore, acoustic impedance Z _B below this value
The resonance blocks 10a and 10b may be formed using a material having

Specifically, as shown in the embodiment of FIG. 1, an epoxy compound material can be used, and the acoustic impedance Z _B of the epoxy compound material is Z _B = 4.2 × 10 ⁶ [kg / m ² / sec], it is included in the range 20 of the vibrator of the present invention shown in FIG. 5, and in this case, the relative bandwidth (Δf / f
o) is as high as 0.48, and a sufficient wide band characteristic can be obtained.

Incidentally, the conventional Langeva shown in FIG.
Using duralumin or aluminum in the oscillator
The acoustic impedance of the resonance blocks 5a and 5b is 16 ×
10 ^-6[Kg / m² / Sec] or more, and as shown in FIG.
Specific band in the range 30 of the conventional Langevin oscillator shown
The range (Δf / fo) is slightly larger than 0.1.
Therefore, the propagation characteristics of ultrasonic vibration become narrow band characteristics,
The width τ becomes long and the range resolution becomes extremely low.

Of course, even if the specific band (Δf / fo) is less than 0.2, if it is larger than the range 30 of the conventional Langevin oscillator, a certain improvement effect can be expected, but it is not so remarkable, and from a practical point of view. It can be said that it is effective to form the resonance blocks 10a and 10b with a material having an acoustic impedance Z _B that makes the relative band (Δf / fo) 0.2 or more.

FIG. 6 shows an acoustic impedance Z _B = 4.2 × 1 in the resonance blocks 10a and 10b in the embodiment of FIG.
0 ^-6 used frequency fo = 31.7 when molded using the epoxy compound material [kg / m ² / sec]
The reception waveform of the ultrasonic vibration propagated in water at kHz is shown. In FIG. 6, the received waveform of the ultrasonic wave by the wide band ultrasonic probe of the present invention provided with the resonance blocks 10a and 10b made of the epoxy compound material is until the received waveform exceeds the −20 dB line and returns again. The time τ, that is, the pulse width τ becomes τ = 117 [μsec], and the use center frequency fo is slightly different, but the pulse width τ is reduced to about 1/3 as compared with the case of the conventional Langevin oscillator shown in FIG. ing. Further, the distance resolution d _{res in} water in this case is d _res = 0.088 [m], and the distance resolution could be improved almost three times as compared with the conventional example of FIG.

FIG. 7 shows the transfer function with respect to the frequency f when propagating in water when the use center frequency fo = 31.7 kHz in the embodiment of FIG. 1 in which the resonance blocks 10a and 10b are made of an epoxy compound material. . In FIG. 7, the frequencies f1 and f2 of the −6 dB lines on both sides with respect to the center frequency fo = 31.7 kHz are f1 = 24.1 kHz f2 = 39.3 kHz, and therefore Δf is Δf = f2-f1 = 15.2 kHz. This bandwidth Δf is more than 5 times wider than that of the conventional example shown in FIG.

When the specific band (Δf / fo) is specifically obtained, Δf / fo = 0.48, and therefore the sharpness Q becomes Q = 2.09, which is sufficient for the wideband ultrasonic probe of the present invention. It has been confirmed that a wide band characteristic was obtained, and as a result, the range resolution in water was significantly improved.

FIG. 9 is a block diagram of an embodiment showing another embodiment of the present invention. In the embodiment shown in FIG. 1, the piezoelectric vibrator having a pair of piezoelectric vibrators 1a and 1b is replaced by a single piezoelectric element. Transducer 1a
The resonance blocks 10a and 10b are fixed symmetrically on both sides of the piezoelectric vibrator 1a. Even in the embodiment of FIG. 9, the resonance blocks 10a and 10b are made of a material having an acoustic impedance Z _B such that the relative bandwidth (Δf / fo) at the use frequency fo is 0.2 or more, for example, an epoxy compound material.

In addition, the above-mentioned embodiment uses the resonance block 10.
Although an epoxy compound material has been taken as an example of the material constituting a and 10b, the specific bandwidth (Δf / fo) obtained from T (f) given by the above equation (1) is 0.
The resonance blocks 10a and 10b can be made of an appropriate material as long as the material has an acoustic impedance Z _B of 2 or more. Of course, it is desirable that the resonance blocks 10a and 10b are made of a material having an acoustic impedance Z _B that gives a larger ratio band, since the ratio band 0.2 is the minimum value.

[0033]

As described above, according to the present invention, the resonance block of the Langevin oscillator structure is made of a material having an acoustic impedance with a specific band of 0.2 or more, so that it can be used underwater or the like. It is possible to narrow the pulse width of ultrasonic vibration by making the band characteristic of the ultrasonic wave propagating through the center frequency of the ultrasonic wave to be a wide band characteristic, thereby significantly improving the distance resolution of the ultrasonic wave in water.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of a Langevin oscillator expressed by F parameter.

FIG. 3 is an explanatory diagram for obtaining a transfer function of a transmission / reception system using a Langevin oscillator.

4 is an equivalent circuit diagram showing the transmission / reception system of FIG. 3 using the equivalent circuit of the F parameter of FIG.

FIG. 5 is a characteristic diagram showing the relationship between the acoustic impedance used to determine the acoustic impedance of the resonance block used in the probe of the present invention and the ratio band.

FIG. 6 is a received waveform diagram showing the pulse width obtained by the probe of the present invention.

FIG. 7 is a frequency characteristic diagram showing wideband characteristics obtained with the probe of the present invention.

FIG. 8 is a configuration diagram of an embodiment showing another embodiment of the present invention.

FIG. 9 is an explanatory view of a conventional water immersion type ultrasonic probe.

FIG. 10 is an explanatory diagram of a conventional Langevin oscillator.

FIG. 11 is a received waveform diagram showing the pulse width obtained by the conventional Langevin oscillator.

FIG. 12 is a frequency characteristic diagram showing a narrow band characteristic obtained by a conventional Langevin oscillator.

[Explanation of symbols]

1a, 1b: Piezoelectric vibrator 10a, 10b: Resonance block 13: Transmission circuit 14: constant voltage source 16: Transmitter 17: Water 18: Receiver oscillator 19: Receiver circuit

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[Procedure amendment]

[Submission date] November 28, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

Further, as shown in FIG. 8 , the pair of piezoelectric vibrators 1a and 1b may be a single piezoelectric vibrator 1a only.

Claims (2)

[Claims] 1. A broadband ultrasonic probe having a Langevin oscillator structure in which resonant blocks are symmetrically provided on both sides of a pair of piezoelectric oscillators, wherein the resonant block is made of plastic. Broadband ultrasonic probe. 2. The wideband ultrasonic probe according to claim 1, wherein the pair of piezoelectric vibrators are a single piezoelectric vibrator.