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DESCRIPTION JPS56138399

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DESCRIPTION JPS56138399
Description 1, title of the invention
Ultrasound probe
3. Detailed Description of the Invention The present invention transmits and receives ultrasonic
waves with the same probe, and transmits and receives 9% of ultrasonic probes suitable for use
in ultrasonic temporary devices. The present invention relates to an ultrasonic probe that can
expand the frequency band of Medium 0 A tomographic image of, for example, a human body or
a gold layer is sent out with ultrasonic pulses from a predetermined probe, and the transmission
pause period · by reproducing the reflected wave from the medium received and input to the
probe The so-called ultrasonic pulse echo procedure to be obtained is generally known. 1)
Conventionally, PZT is used as a pressure IF element that constitutes such a probe. It is also
practiced to use a material having a large coupling coefficient such as LiNbO3 11. However,
although the piezoelectric EndPage: 1 e constant used conventionally is large, the g constant
indicating the acousto-electrical conversion efficiency and the efficiency at the time of reception
is small. Furthermore, it has the disadvantage that matching with the medium is difficult because
the acoustic impedance is large. Although it is common practice to achieve a wide band by the
acoustic matching layer, it is considered that there is a limit to it. On the other hand, piezoelectric
materials such as quartz, sulfuric acid sulfate and PVF 鵞 have smaller e-constants but larger gconstants and smaller acoustic impedances and easier matching as compared with PZT and
LiNbO5. The present invention provides a probe that compensates for the disadvantages of these
piezoelectric materials, enhances transmission / reception efficiency, and realizes a wider band.
In the present invention 0 to achieve the above object. A plurality of piezoelectric elements are
laminated to form a probe. A piezoelectric element for transmission with a large e constant and a
piezoelectric element for reception with a large 1 g constant are arranged 11 □ in the mosquito
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probe. That is, the e constant of the piezoelectric element can be defined by the following
equation according to the applied strength E of the magnetic field and the generated stress T. e =
−Knee or 會 g constant is defined by a ninth equation using input sound pressure T and output
environment strength E. The piezoelectric constant eeg of the g = -valley piezoelectric element is
described in the table together with the acoustic impedance 2. In the same case, it can be seen
that PZT and LiNbO5Fie constants are large, and that quartz and lithium sulfate * PvF2 have at
least a g constant greater than that of PZT or LINbOs. Focusing on this point, the present
invention is constructed by laminating 28 or more efficient piezoelectric elements, and the
transmission and reception characteristics of the probe itself and the probe itself are improved. I
will explain in detail. FIG. 1 is a perspective cross-sectional view of one embodiment of the
present invention. In the figure, an IFi transmitting element, 2 is a receiving element, and 3 is a
matching layer.
4 is a medium, 5 is a backing, 6.7.8 Fi electrode layer. In this example, PZT 'e having a large e
constant is used as the transmitting element 1, and lithium sulfate having a large g constant is
used as the receiving element 2. When the medium 5 is a human body 1. The acoustic impedance
of the human body is approximately 1.5 × 10 ′ (Kg / m 鵞 S). Therefore, the acoustic
impedance is e3 × 10 ′ (m3) to match the impedance of lithium sulfate as the receiving
element. A matching layer 3 made of an epoxy resin of Kg / m 鵞 S) is provided. Furthermore, on
the side of the transmission element 1 opposite to the medium 4, the ultrasonic wave output
from the back surface of the transmission element 1 is attenuated. For example, as a damping
material 9, a damping material such as epoxy resin in which powder or foil such as tungsten or
alumina is dispersed is used to disperse and attenuate the ultrasonic signal from the back surface
of the receiving element by the dispersion. Configured Furthermore, in this example, each
element is in the order of closeness to the impedance of the medium 4, that is, medium (1, 5xx
'Kg / rn'S)-matching layer (3xlO' Kg / m "S), receiver element (15X10 Kg) / M's) and transmitting
elements (33 × 10′Kg / m 鵞 S) are arranged in this order. Therefore, the impedance mismatch
between the element provided on the medium side and the medium can be reduced. At the time
of transmission, the ultrasonic signal from the transmitting element 1 can be reduced due to
impedance difference or the like at the interface with the receiving element, the interface of the
matching layer, or the interface between the medium 4 and the probe side. The operation of the
probe is as follows. At the time of transmission, a predetermined signal voltage is applied
between the terminals 10.11 to cause the transmitting element 1 to oscillate. The generated
ultrasonic signal is received by the receiving element 2. It is transmitted to the medium 4
through the matching layer 3. EndPage in the medium 4: The receiving element 2 is vibrated
through the two layers 3. As a result, a signal voltage is generated between the electrodes 6 and
7 at both ends of the receiving element 20 and is output between the terminals 9.11. FIG. 2 is a
perspective sectional view of another embodiment of the present invention. The same
components as those used in FIG. 1 are denoted by the same reference numerals, and 7m and 7b
are electrodes. This example. The figure shows one using PVF * as the receiving element 2 and
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using PZT as the transmitting element 1. In this case, since the acoustic impedance of the PVF
obtained by the receiving element 2 is close to the acoustic impedance of the medium, the
receiving element 2. Instead of providing the matching layer between the media 4, since the
impedance difference between the acoustic impedance of the PZT used as the transmitting
element 1 and the receiving element 2 is large, the matching layer 3 of fused silica is provided
therebetween .
Note that various combinations of such piezoelectric elements can be used. It goes without saying
that the matching layer is arranged at an arbitrary position according to the difference in
impedance. FIG. 3 is a perspective view of a further different embodiment of the present
invention. The figure shows a unit probe 9. 9n shows a two-way probe in which n backings 5 are
shared. Each of the unit probes 91 to 9 n is the same as the structure of the probe shown in FIG.
1 m 2, and the detailed description of the structure will be omitted. The pressure #L element for
transmission of the unit probe 91 of the function of the commercial law stylus 90 and 1 f is
oscillated. The oscillated ultrasonic wave is propagated in the arrow A direction. It is reflected by
the reflective surface in the medium. The reflected ultrasonic waves are all unit probes 9. The
piezoelectric element for reception of ~9 n is vibrated to generate a voltage between its
electrodes. A control unit (not shown) is adapted to obtain a tomographic image tube from the
distance between the nine reflected parts and the like, combining the pressure between the
electrodes, and the like. As a result, since the electric signal by the weak reflected wave is also
synthesized, the transmission and reception gain of the probe itself is improved. Further, in the
configuration as shown in FIG. 3, each of the phases of the ultrasonic waves from each element is
controlled by the control device f (not shown); shifting the activation phase of each element
according to a predetermined rule. A well-known phased array method of matching at any
position can increase the size of one reflected wave to substantially improve the transmission and
reception gain of the probe. Note that if a method is adopted to synchronize each phase at an
arbitrary position in the medium, the receiving elements of all unit probes may be used, or one of
a selected number of unit probes may be used. A receiving element may be used. In addition, in
the predetermined number of unit probes, it is preferable to use one at a position where there
are not 9 selected unit probes between each selected unit probe. Because the vibration of the
selected unit probe is the backing material or the medium between the unit probes (for example,
air). It is because water and the like are adversely affected to the mutual vibration operation.
Furthermore, as shown in FIG. 3, the backing material may not be common. This will be
described in detail using the following examples. Example 1 Acoustic impedance 3 as matching
layer 3 having the structure described in FIG. IX10 '(Kg / m2 · see: L thickness o, using 2 s (mm)
araldite, receiving / m ′ ′-8), 0.544 (mm) thickness, lithium sulfate (L lz SO 4 · H 2 O) Acoustic
impedance 35.3 × 10 ′ ′ (Kg / mw · S) l 0.835 (mm) thick PZT is used as the feed element 1
and acoustic impedance ao, oxxoe is used as the backing material in history. (Xg / m!
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S] A probe having a thickness of 20 mm was obtained. As the electrodes 6, 7.8, a silver electrode
of 2 microns in thickness was used. For the obtained probe, the transmission / reception gain
near 2.5 MHz is determined, and each frequency is normalized at a center frequency of 2.5 MHz,
as shown in FIG. The voltage Vin is applied to the input terminal to be oscillated, and when the
transmitted sound wave is reflected in the 1oos medium, it indicates a value corresponding to the
ratio of the output voltage VUutO generated in the receiving element, and is represented by a
linear equation It is to be expressed. V hundred utG = 201 og Vi. Further, as a comparative
example, PZTEndPage: 3 of the probe of the present invention is indicated by a wavy line.
According to the figure, in the case of 9 invention products, the gain is higher than that of the
prior art. It can be seen that the bandwidth system increases significantly. Incidentally, the ratio
(Δf / f,) of the center frequency f to Δf in the band which is −3 dB below the peak value of the
gain of the 9 invention products. It is 0.75, and is 0.6 in the comparative example. EXAMPLE 2
Silver electrodes of several microns were formed on 9 sides according to the arrangement
sequence shown in FIG. PVFt 0.23 mm thick-0.5 mm thick fused quartz 1 0.84 mm thick PZT
with several micron silver electrodes formed on both sides and acoustic impedance as a backing
30. Each one of 20 mm thick was laminated with OXloa (Kg / m circle 5 ec). I got a probe. As in
the first embodiment, an input voltage Vin of about 2.5 MHz in one frequency is applied to the
electrodes at both ends of the PZT and transmitted, and the output voltage V? jut was extracted,
and the transmission / reception gain 201 og (Vout / Vin) of the said probe was calculated |
required. Similarly, the transmission / reception gain was determined when the frequency was
changed from the center frequency of 2.5 MHz. 7 shows the transmission and reception gain
characteristics of the probe in question. The solid line in the figure is the characteristic of the
probe according to the second embodiment. Further, as a comparative example, transmission and
reception gain characteristics in the case of being used also as a PZT'e receiving element of the
probe prepared in Example 2 are shown by dotted lines. According to this figure, it can be
understood that the probe according to the second embodiment is a probe with a wide range of
gain, as compared with the comparative example. Incidentally, when comparing the ratio (Δf / f,)
between the band Δf lower than the peak value by −3 dB and the center frequency f, the
product of the present invention is 0.9. The comparative example product is 0.6. As described
above, according to the present invention, a probe in which a plurality of types of piezoelectric
elements are stacked is used, and transmission and reception piezoelectric elements are made of
different appropriate materials and transmitted and received. The present invention has an effect
that the range in which the gain is equal to or larger than a predetermined gain is spread, and the
transmission and reception gain itself is larger than that of a single element that is used for
transmission and reception.
4. Brief description of the drawings 2g 1 FIGS. 2 and 3 are perspective views of different
embodiments of the present invention, and FIGS. 4 and 5 show transmission / reception
characteristics for one frequency. In the figure, 1 is a transmitting element, 2 Fi receiving
element, 3 is a matching layer. 411-1t media, 5 is a backing, and 6, 7.8 are electrodes. 祁 1
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Figure EndPage: 4 Figure 2! I% 3 figures # Kaji Okanami 4th depression-wave number Figure 5
EndPage: 5
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