Electroacoustic transducer

Details Electroacoustic transducer Electroacoustic transducer

1998-06-26

2001-05-15

Lateef, Marvin M. (Department: 3737)

Surgery: kinesitherapy

Kinesitherapy

Contact-free comminution of concretion

C600S459000, C367S157000

Reexamination Certificate

active

06231529

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to an electroacoustic transducer with the features specified in the introductory part of claim
1
. Electroacoustic transducers of this type consist of a dome-shaped carrier which on its inner side is furnished with piezoelectric elements which in each case are electrically contacted on a side directed to the carrier as well as a side distant from the carrier and connected to a high voltage impulse generator. On applying a voltage by way of the piezoelectric effect a sound wave in the form of a pressure wave is produced, which on account of the dome-shaped arrangements of the piezoelectric elements is focussed to a point or a region which is dependent on the radius of curvature of the carrier. With such electroacoustic transducers, apparatus for medical treatment, for example lithotripters are equipped whose regions of applications are numerous (from the destruction of stones to the treatment of soft tissue and pain).
An advantage of these piezoelectric transducers with a dome-shaped carriers and piezoelectric elements arranged thereon lies in the high energy intensity in the focus region which can hardly be reached by other systems, by which means a directed and largely pain-free application of shock waves may be effected. The complete irradiated sound power however on account of the limited available irradiation surface may not be increased further beyond certain limits. An enlargement of the irradiating surface can specifically only be achieved by enlarging the radius of the dome or by enlarging the opening angle (aperture). The first is in practise not possible since with this the constructional size of the sound source would increase so much that the application in the field of table apparatus would no longer be possible. An enlargement of the aperture angle can likewise be ruled out since otherwise the penetration depth of the shock waves in the patient itself would become so slight and any increase in power would be compensated by this.
On the other hand one strives rather to reduce in size the constructional shape of the transducer in order to reduce the constructional size of the therapy apparatus and thus to form new fields of application, for example treatment of salival stones or treatment of pain. The acoustic power of the transducer may be increased by electrically precharging the piezoeclectric elements but this increase in power is at the expense of the life expectancy of the transducer dome.
From DE 31 19 295 it is known to arrange several electrical transducers behind one another and to so trigger these in a delayed manner that their pressure waves add. Such an arrangement has been found to be unsuitable with the application of piezoelectric transducer domes, since the focus region in the direction of the treatment depth is heavily extended which is undesirable. Furthermore it has been found out that enormous losses are caused by damping which the sound waves undergo when they must penetrate through a prior-mounted transducer. Finally also these inner friction losses are at the expense of the life expectancy, in particular of the foreward transducer dome directed towards the treatment location.
BRIEF SUMMARY OF THE INVENTION
Against this state of the art it is the object of the present invention to design an electroacoustic transducer of the previously mention constructional type such that the effective sound power irradiated to the therapy loaction is increased without significantly increasing the constructional size or reducing the life expectancy.
According to the invention this object is achieved by those feature specified in claim
1
.
Surprisingly it has been shown that an increase in power may be achieved by comparatively simple measures if a dome-shaped carrier on its inner and outer side is provided with piezoelectric elements. With this the damping effect occuring by way of the connecting behind one another of several electroacoustic transducers practically does not occur since the piezoelectric elements on the outer side as well as on the inner side are seated the same carrier and thus acoustic coupling losses by intermediate layers practically do not occur. Furthermore the constructional size by way of this compact arrangement of elements on the front and rear side of the carrier may be kept relatively small.
Preferably the carrier is designed of metal, for example an aluminium or brass dome so that it may not only assume a carrying function for the piezoelectric elements, but at the same time also an electrical function for these. For this purpose the piezoelectric elements are conductingly connected with the carrier, for example by adhesing by way of a conducting, e.g. silver-containing epoxy adhesive. If the piezoelectric elements, which is useful, are formed essentially in a cylindrical shape, with one end face they may be fastened on the carrier and a multitude of elements may be arranged next to one another.
Amazingly it has been found out that for reasons of manufacturing technology as well as for power reasons it is useful to arrange the piezoelectric elements of the outer and inner side not axially equal in pairs but to arrange them essentially randomly on the carrrier in order to be able thus to mount a higher number of piezoelectric elements and thus to obtain a higher sound power. The arrangement of the piezoelectric elements thus is effected exclusively from the point of view of the highest packing density.
If the metallic carrier is connected to a pole of the piezoelectric elements, then this should be switched to the minus pole and the carrier contacted to earth. Then on the one hand the carrier dome by way of a lateral flange or other projection may serve at the same time the mechanical fixation within the apparatus and the electrical safety against the application of electrical high voltage impulses to the apparatus may be reliably secured in a simple manner by way of earthing the apparatus.
In order to electrically insulate the piezoelectric elements laterally to one another it is useful to arrange these with a lateral distance to one another. An inner connection of these is achieved in that these intermediate spaces are filled with a high voltage stable insulating casting mass, so that an acoustic quasi-homogeneous layer is formed.
In order to further optimize the sound power of the transducer, on the rear side of the transducer, thus on the side of the outer-side piezoelectric elements which is distant to the carrier, a backing as a reflection body may be provided. Such a reflection body may be formed as a metal body, which will achieve a high degree of reflection, but also may be formed of a suitable plastic of compound material. In order to ensure a good acoustic coupling of the reflection body to the piezoelectric elements, the reflection body is preferably connected to the piezoelectric elements of the outer side by a casting mass. It is also conceivable instead of a separate reflection body to form the casting mass itself as such, for this for example metal chips may be added to the casting mass.
Usefully the electrical connection of the piezoelectric elements is effected in two groups in a manner such that the piezoelectric elements located on the inner side can be separately electrically triggered. Then specifically by way of a directed temporal triggering of the impulses, running time differences of the acoustic waves between the outside and inside groups may be compensated for or produced in a directed manner, in order to increase the sound intensity in the focus region or to expand the focus region.
In order to achieve this it is useful to allocate to the electrical transducer two generators, able to be triggered independently of one another, for producing high voltage impulses, more specifically a generator for the inside group and a generator for the outside group of piezoelectric elements. Also when the generators function independently of one another, they should however be tunable with one another in a manner such that the directed superposition of the sound wave

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