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JPH01111476

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DESCRIPTION JPH01111476
[0001]
FIELD OF THE INVENTION The present invention relates primarily to piezoelectric devices with
reduced negative waves, and the destruction of extracorporeal crushed stones or specific tissues
to which this device is applied. In the prior art in general, a piezoelectric oscillator is mainly
constituted by one, several or very many piezoelectric elements. The piezoelectric element is
preferably disposed on a spherical dome member capable of focusing all the minute sound waves
generated by each of the basic particles constituting one or more transducers (for example, the
document "Ultrasonic (Ultrasonics) J, Vol. 5, April 1967, pp. 105-112, P, P, P (P, P). L (see ELE)).
Also other devices are known which generate ultrasound waves which converge to a point. This
device comprises a plurality of transducer elements of the piezoelectric type arranged outside the
spherical dome member. This device is also used for therapeutic purposes, for example to control
the generation of eye blemishes. (See the article published by COLEMAN in the Journal of
American Journal of Ophta 1 mo 1 ogy 86: 185-192 (1978)). Coleman also describes that the
diagnostic transducer is located paraxially. As a result of experiments, it has been found that the
quality of convergence, i.e. the volume of the focal point, becomes smaller as the filling factor is
closer to 1 and as the openness determined by the angle of the spherical dome member is larger.
Furthermore, the shape of the wave at the focal point is equal to or very similar to the shape of
the emitted wave at the location of the piezoelectric transducer and in any case closely related. If
one face is in contact with water and the second face is in contact with air (the simplest and most
common configuration), the wave emitted after the electrical pulse will be in the form of a
decaying sine curve . This wave therefore contains positive and negative waves. Negative waves
are dangerous for tissues to induce cavitation effects (eg Coleman et al. In RUltrasound in Med, &
Biol, Vol, 13. ??? 2, pp. 69 "76, see the article published in 1987 J). It has previously been
proposed to generate so-called unipolar waves (DE-OS 34 25 992). The transducer emits a series
of pulses when a very short pulse is applied. The front of the transducer emits a wave of positive
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polarity and the back emits a wave of opposite polarity. The resulting radiation wave is of course
a superposition of these waves and is therefore either positive or negative.
The solution proposed in the German patent DE 34 25 992 A1 aims to "separate" such positive
and negative waves. To this end, the back side is cut irregularly so that the waves reflected on the
back side do not converge or converge very poorly. As a result, the ratio of positive to negative
waves increases as the focus is approached. Note that in this solution the second positive wave
also does not converge well. Because this second positive wave is generated due to the reflection
of the first wave on the back of the transducer. Also, by placing a material on the front of the
piezoelectric transducer, the impedance is a value between the impedance of this transducer and
the impedance of the water that is the medium that transmits the ultrasound to the target located
at the focal point. It is known to fit (Physical acoustics, Volume 1 by Parson, par) A, see Academic
Press). For this reason, the duration of the signal is very short, and from the comparison between
FIG. 1 a (ultrasound emitted from the non-conforming transducer) and FIG. 1 b (ultrasound
emitted from the conforming transducer) Thus, it can be confirmed that the maximum value of
the ultimate pressure is much larger. Accordingly, in a monopolar system as described in the
above-mentioned German patent FR 34 25 992, only the first wave converges, and unfortunately
this first wave is the second wave. The ratio of the convergent wave between the adapting
converter and the non-adapting converter is about 10, since it is always weaker than the first and
third waves. However, in the case of a non-conforming transducer where the back side is not
randomly cut, this system produces a negative wave whose amplitude is equal to that of the
positive wave (see FIG. 1C). Another explanation is that despite adopting this solution, negative
waves still exist and their strength is a cavitation effect that is dangerous to the nearby
gemstones and specific tissues to be destroyed. Large enough to induce. Therefore, the present
invention has the above-mentioned new technical problems by finding a method of reducing or
nulling the amplitude of the negative wave inherently existing in the sine wave radiated from any
piezoelectric transducer. To solve the problem. The invention further not only reduces or
eliminates the amplitude of the negative wave inherently present in the sine wave radiated from
the piezoelectric transducer, but also the height of the peak of the radiation wave, and so on It is
an object of the present invention to solve the above-mentioned new technical problems by
finding a method of maintaining at least a constant pressure peak value in the proposed prior art,
in particular, a technique for reducing the amplitude of negative waves.
The above new technical problems are solved for the first time with the present invention in a
satisfactory manner and can be used on an industrial scale. Means for Solving the Problem For
the purpose described above, according to the present invention, a support means for focusing
on one focal point, for example a plurality of piezoelectric transducers arranged outside the
spherical dome-like member An apparatus for generating an ultrasonic wave having few negative
waves and converging to a focal point, wherein the conversion elements are divided into at least
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two groups of conversion elements having different resonance frequencies, and emitted from
each conversion element group An apparatus is provided, characterized in that the main positive
ultrasound waves are added together and the secondary negative ultrasound waves are at least
partially extinguished. According to a particularly preferred embodiment of the present
invention, the resonant frequencies of the second group of conversion elements, ie the
conversion elements of the groups other than the first group, coincide with a multiple or
submultiple of the resonant frequency of the first group of conversion elements, Or it almost
matches. According to a particular embodiment, the resonance frequency of the second group of
conversion elements is equal to or approximately equal to twice the resonance frequency of the
first group of conversion elements. According to a particularly preferred alternative embodiment,
the conversion elements of each group are arranged alternately such that the total surface area
covered by the conversion elements of each group is approximately equal to one another.
According to another particular embodiment of the invention, all the conversion elements of each
conversion element group are equally spaced from the focus by a distance called the focal length.
When the support means is a stadium dome member, the focal length is preferably equal to the
radius of curvature of the dome member. In the simplest case where the focal length is the same
for all transducer elements of each group, each pulse is sent by sending a delayed or advanced
pulse or voltage to the reference group depending on the driven group. The transducer element
groups are electronically driven at a predetermined frequency to match the peaks of maximum
pressure between the different groups of resonant frequencies. At this time, the (delay or phase
advance) time difference is expressed by the following equation:% equation% (where, .box-solid.
Is the velocity of ultrasonic waves in a medium (generally water) filling the interior of the domelike member) Of the drive group). If the support means are flat, it is possible to realize the
electrical convergence as described in DE-A 3 119 295. According to yet another particular
embodiment of the invention, when the support means is a spherical dome member, the set
distance between the front face and the focal point of a given group of conversion elements is the
conversion of another group of different resonance frequencies. Different from the set distance
between the front of the element and the focal point, the electrical drive of all the conversion
elements is performed simultaneously to bring the peak of the maximum pressure into
agreement.
For example, the difference in focal length between the first group and the second group is about
1?4 of the wavelength. It can be seen that when the focal length is constant, this correction
difference corresponds to the time correction difference (?t). Furthermore, when the resonant
frequency of the predetermined group of transducers is less than the resonant frequency of the
first group of transducers, referred to as the reference group, the distance between the
transducer of this predetermined group and the focal point is the transducer of the reference
group and Greater than the distance between the focal points. This means that the conversion
elements of this predetermined group are arranged behind the conversion elements of the
reference group. Similarly, when the resonance frequency of a given group is greater, the
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distance between the focal point and the conversion elements of this predetermined group is
smaller than the distance between the focus and the conversion elements of the reference group.
That is, the conversion elements of the predetermined group having a higher resonance
frequency are arranged in front of the conversion elements of the reference group. According to
a particularly preferred further embodiment, a third group of conversion elements is provided,
the resonance frequency of which is equal to or approximately four times the resonance
frequency of the first group of conversion elements. equal. As is apparent to those skilled in the
art, superposition of waves emitted from transducer groups having different resonant
frequencies results in a composite wave with a reduced percentage of negative waves. This is
because, by means of this superposition, the main positive waves are added together, while the
negative waves are maximally canceled, in particular by the secondary positive waves. The
superposition of all of the major positive waves produces a pressure peak equal to the pressure
peak that occurs in the conventional case with a single resonant frequency for all conversion
elements. In this way, to obtain an effect which is completely unexpected and not obvious to the
person skilled in the art of breaking down a calculus (kidney calculus) or a specific tissue
(surgery), or a person skilled in the art of ultrasound technology. Can. Other objects, features and
advantages of the present invention will become better understood by those skilled in the art
from the description taken in conjunction with the accompanying drawings. Embodiments FIGS.
2, 2A and 2B illustrate an apparatus according to the invention for generating ultrasound waves
which are focused on one focal point with few negative waves. The ultrasonic generator 1 is of
the type known in the field of ultrasonic generators. A brief summary of the ultrasound generator
is provided in the beginning of the Detailed Description of the Invention herein. The illustrated
ultrasound generator 1 comprises a plurality of transducer elements 2.4.6 of the piezoelectric
type arranged outside the support means 8 for focusing on the focal point 10.
This support means 8 is here constituted, for example, by a spherical dome member. This
structure and the means capable of pulsing the transducer element are well known to those
skilled in the art and will not be described further. According to the invention, in the ultrasound
generator 1 the transducer elements are at least two groups of transducer elements with
different resonant frequencies, ie here for example the first group of transducer elements 2 and
the second group of transducer elements 4 And the third group of conversion elements 6. As a
result, the main positive ultrasound waves emitted from each group are added together, and the
secondary ultrasound waves (positive or negative waves) are at least partially canceled.
According to a particularly preferred embodiment of the invention, the second group of
conversion elements 4 or the second and third groups of conversion elements 4.6 have a
resonant frequency that is the resonant frequency of the conversion elements of the first group
of conversion elements 2. Values that are equal to or close to multiples or divisors of, especially
multiples. According to another preferred embodiment, the resonance frequency of the
conversion elements 4 of the second group is equal to or close to twice the resonance frequency
Fo of the conversion elements 2 of the first group. According to the particular embodiment
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shown, the conversion elements of each group are arranged alternately, such that the total
surface area covered by the conversion elements of each group is approximately the same. This
can be clearly seen in FIGS. 2, 2A and 2B. For example, FIG. 2A shows an embodiment in which
three groups of conversion elements having different resonance frequencies, ie, the first group of
conversion elements 2, the second group of conversion elements 4, and the third group of
conversion elements 6 are arranged alternately. It is shown. When the conversion element 6 of
the third group is present, the resonance frequency of the conversion element 6 is equal to or
close to four times the resonance frequency of the conversion element 2 of the first group. For
example, the resonance frequency F of the conversion element 2 of the first group. ?
?????????? Furthermore, in another embodiment shown in FIG. 2B, which comprises
two groups of transducer elements of different resonant frequencies, the central position is
occupied by the first group of transducer elements 2 but its periphery is alternately It is occupied
by one group of conversion elements 2 and a second group of conversion elements 4.
Furthermore, in order to obtain different resonance frequencies, the thickness of the conversion
elements 2 of the first group is set to a value twice or near that of the thickness of the conversion
elements 4 of the second group. When the conversion element 6 of the third group is present,
the thickness of the conversion element 2 of the first group is set to a value four times the
thickness of the conversion element 6 of the third group or a value close thereto.
According to the simplest embodiment, all conversion elements 2.4.6 of each group are at equal
distances from the focal point 10, called focal length. When the support means is a spherical
dome as shown in FIG. 2, the focal length is preferably equal to the radius of curvature of the
dome. In the simplest case, where the focal length is equal to all conversion elements 2.4.6 in
each group, the rising edge delays or advances the pulse or voltage relative to the reference
group depending on the driven group. By sending each transducer element group electronically
at a predetermined frequency, the peak of the maximum pressure between each group having
different resonance frequency is matched. At this time, the (delay or phase advance) time
difference is expressed by the following equation:% equation% (where ? represents the velocity
of ultrasonic waves in a medium (generally water) filling the interior of the dome-like member)
Of the drive group). Those skilled in the art will readily know how to implement electronic drive
of each group to match the peak of the maximum pressure between each group of different
resonant frequencies at the focal point 10. For example, the resonance frequency F of the
piezoelectric conversion element 2 of the first group. Is 0.5 MHz and the resonant frequency of
the second group of piezoelectric transducers 4 is twice that of the other, ie, I MHz, the electronic
drive of the second group of piezoelectric transducers has a period of about 1 Execute with a
delay of / 4, ie, 250 nanoseconds. According to another aspect possible according to the
invention, as shown in FIG. 2, in particular when the support means are constituted by spherical
dome members, it is set between the front face of each conversion element of the predetermined
group and the focal point 10 The distance taken is different from the set distance between each
transducer element of another group of different resonant frequencies and the focal point. As a
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result, electrical or electronic actuation can be performed simultaneously for all groups so that
the peaks of maximum pressure coincide. For example, the difference in focal length between the
first group and the second group is about 1?4 of the wavelength. It can be seen that if the focal
length is constant, this correction difference corresponds to the time correction difference ?t.
Thus, by varying the electrical drive between each group, all transducer elements are equidistant
from focal point 10 but synchronization is done to match the peaks of maximum pressure, or
focal lengths between each group Alternatively, it can be seen that in this case it is possible to
carry out the electrical drive of all the conversion elements of each group simultaneously.
Another possible embodiment of the invention uses the flat support means described in DE-A 3
119 295 described above.
Thus, the focal length is different for each conversion element that may belong to the same
group. In this case, electronic convergence is realized as described above. This is quite obvious to
those skilled in the art of ultrasound. The combination of conversion elements with different
resonant frequencies makes it possible to significantly reduce the emitted negative waves as well
as to significantly increase the main positive wave pressure peak. This is illustrated in FIGS. 3A
and 3B, which correspond to FIGS. 1A and 1B, and will be described below. In order to simplify
the description, in FIG. 3A, the outline of the time change curve of the wave emitted from the
conversion element 2 of the first group and the outline of the time change curve of the wave
emitted from the conversion element 4 of the second group are respectively It is represented
using the same reference number 2.4 as the conversion element. It can be seen that the main
positive wave 2p of the conversion element 2 of the first group and the main positive wave 4p of
the conversion element 4 of the second group coincide in peak. As a result, these waves are
added together to obtain the composite wave shown as 2p + 4p in FIG. 3B. On the other hand, the
secondary positive wave and the secondary negative wave radiated from the conversion element
of the first group of conversion elements 2 or conversion elements of the conversion element
group 4 at least partially cancel each other. This results in the composite curve of FIG. 3B. Thus,
it can be seen that the negative waves are significantly reduced. This effect becomes increasingly
fatter when the third group of conversion elements 6 is present. Unlike a conventional ultrasonic
generator having a single group of transducer elements having a single resonant frequency, the
amplitude of the negative wave is reduced, and this negative wave is a disease tissue including
calculus and cancer. Etc. Make the level lower than the threshold value which induces cavitation
effect which may destroy or damage the fibrotic cells in the vicinity of the target to be destroyed.
Furthermore, the synthetic wave obtained by the present invention has a positive maximum
pressure peak at least equal to the pressure peak obtained conventionally, which is an effect that
is neither predictable nor obvious to the person skilled in the art. This single pressure peak with
few negative waves improves the destruction efficiency of the target located at the focal point.
Thus, all the above-mentioned important technical advantages are obtained. Of course, the
invention includes all technical iso-packs of the above mentioned means. For example, the
piezoelectric conversion element may be of any type, and may be a conventional one having
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zirconate titanate as a main component, or any configuration as long as the required function can
be performed.
Likewise, the size of the individual conversion elements and the radius of the spherical dome can
be varied within wide limits. Furthermore, the conversion element may not necessarily be
disposed on the spherical dome member. The reason is that, for example, as described in the
above-mentioned German Patent Application Publication No. 3119295 mentioned above,
electronic convergence can be realized by changing the moment of electrically driving each
conversion element group. It is.
[0002]
Brief description of the drawings
[0003]
FIG. 1A shows that the resonance frequency is F.
And a graph of a sine wave emitted from the non-conforming piezoelectric transducer. FIG. 1B is
a graph of a sine wave emitted from a piezoelectric transducer that has been adapted by
depositing an epoxide resin layer on the emitting surface of the same piezoelectric transducer.
FIG. 2 is a schematic view of an ultrasonic generator according to the invention comprising a
spherical focusing dome for focusing on one focal point. FIG. 2A is a plan view of the inner
surface of a converging dome according to an embodiment comprising three groups of
transducer elements of different resonant frequencies as shown in FIG. FIG. 2B is a plan view of
the inner surface of a focusing dome according to another embodiment comprising two groups of
transducer elements of different resonant frequencies. FIG. 3A shows that the resonance
frequency is F. And a graph of a sine wave emitted from a second group having a resonance
frequency of 2Fo. FIG. 3B is a graph of a composite wave obtained as a result of superposition of
two waves respectively emitted from the first group and the second group. (Major reference
numbers) 1 иии Ultrasonic generator, 2.4.6 и и и и и и и и и и Means of support, 10 и и и Focus anselm
attorney patent attorney Takashi Koshiba Nd] mouth r- Kui] Mr. Higuchi "Ai Kuri
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