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DESCRIPTION JPS58165828

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DESCRIPTION JPS58165828
[0001]
The present invention relates to an ultrasonic probe used in a so-called pulse echo method
ultrasonic diagnostic apparatus which irradiates an ultrasonic pulse to a test object such as a
human body and displays a reflected pulse from the inside of the object on a Braun tube. It
relates to a manufacturing method. (1) FIG. 1 shows a general configuration of an ultrasonic
probe used in an ultrasonic diagnostic apparatus i of pulse echo method. In FIG. 1, 1 is a
piezoelectric body such as a piezoelectric ceramic or a piezoelectric crystal. An electrode 2 is
formed on the surface of the piezoelectric body 1 by plating, vapor deposition, coating or the like.
The acoustic matching layer 4 in direct contact with the subject 3 such as a human body is made
of a material such as glass, resin, or a mixture of resin and inorganic substance, and a material
having an acoustic impedance density between the piezoelectric body 1 and the subject 3 is
selected. Be Further, the rear load layer 5 is provided on the opposite side of the acoustic
matching layer via the piezoelectric body 1. In the pulse echo method, sending and receiving
short and strong ultrasonic pulses is important for improving resolution and sensitivity.
Therefore, as the performance of the probe, characteristics such as wide band low loss excellent
in pulse response and linear phase property are desired. In order to realize this characteristic, it
is important to configure the acoustic matching layer 4 of FIG. 1 to a suitable thickness.
Generally, the acoustic matching layer 4 is made of a flat plate of glass or solidified resin bonded
to the piezoelectric body 1 (2) or a resin, a mixture of resin and inorganic substance, etc. is
coated on the piezoelectric body 1 and cured. It is formed in the way. In both cases, the thickness
of the acoustic matching layer 4 is from the speed of sound ν of the material used for the
matching layer, and the frequency f used. The wavelength λ = ν / fo at is calculated and
adjusted to a quarter of this wavelength. However, when a flat plate such as glass or solidified
resin is adhered to a piezoelectric body to form an acoustic matching layer, the substantial
acoustic matching layer consists of two layers of an adhesive layer and a flat plate such as glass
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1
or solidified resin. As a result, even if glass or solidified resin is processed to a thickness of [1⁄4
wavelength, there is a problem that the thickness of the substantial acoustic matching layer
deviates from 1⁄4 wavelength. When the acoustic matching layer is formed by a method of
coating and curing a resin, a mixture of a resin and an inorganic material, or the like on the
piezoelectric body, the influence of the adhesive layer can be avoided. However, in this case, the
thickness of the quarter wavelength can not be accurately determined because the speed of
sound varies depending on the curing conditions of the resin. In addition, when inorganic matter
is mixed in resin, it becomes impossible to determine the speed of sound because it becomes
nonuniform substance due to the precipitation of inorganic matter (3), and the thickness of
quarter wavelength is determined. I can not do anything.
In any case, the method of determining the thickness of the acoustic matching layer from the
conventional speed of sound of the material has failed to form an acoustic matching layer of
exactly 1⁄4 wavelength thickness. For this reason, an ultrasonic probe having a conventional
acoustic matching layer has a disadvantage that the pulse response is poor. The object of the
present invention is to eliminate these drawbacks of the prior art, to form an acoustic matching 1
曽 of exactly 1⁄4 wavelength thick, and to produce an ultrasonic probe which suffers from pulse
response. It is to provide. According to the present invention, the resonant frequencies of the
fundamental mode and the secondary mode of the composite vibrator comprising the
piezoelectric body and the acoustic matching layer are measured, and the difference between
these respective values and the value of the fundamental mode resonant frequency of the
piezoelectric body To make an acoustic matching layer of exactly 1⁄4 wavelength by black
adjusting the thickness of the acoustic matching layer so that absolute values become equal, and
to manufacture an ultrasonic probe with excellent pulse response. Can. (4) The principle of noninvention will be described below. In general, when a layer of a material having a smaller
acoustic impedance than the piezoelectric is provided on the piezoelectric, the piezoelectric and
the provided layer become a composite & facet, having a resonant frequency close to the
resonant frequency of the fundamental mode of the piezoelectric alone. Produce two modes. FIG.
2 shows this situation, and calculated the relationship between the thickness of the layer
provided on the piezoelectric body (hereinafter referred to as an acoustic matching layer) and the
resonance frequency of the fundamental mode and the secondary mode of the composite
vibrator. It is a thing. Here, as a piezoelectric body, an acoustic impedance field of 35 × 106 kg
7 讐 -sec electromechanical coupling system 50.0% of piezoelectric ceramic as an acoustic
matching layer has an acoustic impedance density of 6.6 X, 10 ′ 絢 V, sec I assumed the
material. Further, in FIG. 2, the thickness of the acoustic matching layer is a thickness of a
quarter wavelength at the resonance frequency of the piezoelectric ceramic, and the frequency is
normalized by the resonance frequency of the piezoelectric ceramic. From FIG. 2, when the
thickness of the acoustic matching layer is a quarter wavelength, the absolute values of the
difference (5) between the resonant frequency of the fundamental mode and the secondary mode
and the fundamental resonant frequency of the piezoelectric ceramic alone become equal to each
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2
other . Conversely, in order to manufacture an ultrasonic probe having a matching layer with a
thickness of a quarter wavelength by utilizing this matter, the resonant frequency is measured
when adjusting the thickness of the matching layer, and the fundamental mode and The absolute
value of the difference between the resonant frequency of the second mode and the resonant
frequency of the fundamental mode of the single piezoelectric ceramic before providing the
matching layer may be equal. EXAMPLES The present invention will be described below by way
of examples. The present embodiment has the same configuration as that of the ultrasonic probe
of FIG.
As a piezoelectric material, a zircon-lead titanate piezoelectric ceramic is 17.0 mm in diameter
and 1. thick. What was processed into the disk shape of Qmln was used. A silver electrode having
a thickness of 10 μm was applied and baked on both sides of this, and polarization processing
was carried out by applying a voltage of 1 to 4 in silicon oil at 100 ° C. for 1 hour. A mixture of
epoxy resin and powder glass was applied to one side of the above-mentioned piezoelectric
ceramic, and was heated and cured. After leaving this at room temperature for 1 day, the resin
layer is polished while measuring the resonance frequency, and the absolute difference between
the resonance frequency of the fundamental mode and the second mode and the fundamental
resonance frequency of the piezoelectric single (6) The values were adjusted to be equal to each
other. It was adhered to the back load layer made of epoxy resin. FIG. 3 shows the insertion gain
of the ultrasonic probe of this example, which was measured using reflection from an aluminum
plate placed firmly in water 20. From this figure, it can be seen that a broadband low-loss
ultrasonic probe is realized. This is because the thickness of the acoustic matching layer is
precisely adjusted to a quarter wavelength. When the thickness of the acoustic matching layer is
a little thicker than this, the loss on the low frequency side, and in the case of a thin layer, the
loss on the high frequency side is actually increased by m =. In addition, it was confirmed that the
method according to the present invention is an effective means capable of eliminating the
influence of the adhesive layer also in the case of bonding the acoustic matching layer on the
piezoelectric body in addition to the present embodiment. Also, in the case of an ultrasonic probe
provided with two or more acoustic matching layers, as in the method of the present invention, a
composite vibrator in which two or more sound l # matching layers are formed on the
fundamental resonance frequency of the piezoelectric body and the piezoelectric body An
optimal acoustic matching layer can be formed by adjusting the resonance frequency of a
specific mode to a fixed relationship. (7)
[0002]
Brief description of the drawings
[0003]
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FIG. 1 is a block diagram of a conventional ultrasonic probe and an embodiment of the present
invention.
In FIG. 1, 1 · · piezoelectric body, 2 · · · electrode · 3 · · broken sample, 4 · · acoustic matching
layer, 5 · back load layer. FIG. 2 is a diagram showing the relationship between the thickness of
the acoustic matching layer and the resonant frequency. In Fig. 2, 1 · basic mode, 2 · · · secondary
mode, Fig. 3 is a diagram showing the frequency characteristics of the insertion loss of the
ultrasonic probe according to one embodiment of the present invention. Agent Attorney Minoru
Uchihara (8)
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4
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