EP0268082A1 - Shock wave generator with a short initial pulse - Google Patents

Abstract

The shock wave source (1) comprises a coil carrier (3), a flat or concave flat coil (5), a membrane (9) and a film (11). The membrane (9) is loosely arranged between the flat coil (5) and the film (11). The membrane (9) consists of electrically highly conductive material, while the film (11) consists of electrically non-conductive material. When a capacitor (21) is discharged into the flat coil (5), the membrane (9) is suddenly moved away, only the mechanical forces of the membrane (9) acting on the film (11) and no electromagnetic forces from the flat coil (5). The acoustic pulse (P) generated is divided into a shock wave pulse in a transmission medium adjacent to the film (11). The advantage of this configuration of the shock wave source (1) is a short duration of the output pulse (P) with the resulting advantages of a short lead distance, a small focus zone, a high focusing factor, a low electrical and thermal load on the shock wave source (1) and a low in A patient's body emitted acoustic energy.

Description

The invention relates to a shock wave source with an electromagnetic flat coil, in front of which a membrane consisting of an electrically conductive material is arranged.

Such a shock wave source ("shock wave tube") is known for example from DE-OS 3,502,751. According to recent studies, e.g. specified in DE-OS 3,312,014, used in medical technology for crushing concrements in the body of a patient. Due to the high pressure pulse, e.g. The materials of such a shock wave tube are subjected to heavy loads of 100 bar with repeated discharges and shock wave emissions. The membrane in particular is exposed to high electromagnetic and mechanical forces, which can lead to early material fatigue.

In the electromagnetic shock wave sources that have become known so far, this membrane is compact and preferably consists of a material with high electrical conductivity and at the same time high mechanical strength. As a whole, it is firmly clamped at the edge, as described, for example, in DE-OS 35 02 751. This membrane can be homogeneous. It can consist of a metal, such as copper or an alloy with high conductivity, for example a bronze such as silver bronze. However, it can also consist of a carrier, for example beryllium bronze or a polymer, with an applied coating, for example a galvanic layer of silver or copper.

The duration of the initial acoustic pressure pulse is important for various factors. A shortening of the duration of the pressure pulse would result in:

- a shortening of the lead distance until the formation of a shock wave;
- a smaller focus zone (-6dB zone);
a higher focus factor, ie a higher peak pressure in focus at a given initial pressure;
- A lower electrical and thermal load on the shock wave source and a relatively small amount of the acoustic energy emitted into the patient's body to achieve a certain peak pressure; such as
- A change in the predominantly effective mechanism of stone destruction, in the direction of a "removal" of the concrement, instead of a "shattering" with a relatively long pressure pulse.

Shortening the duration of the initial acoustic pulse compared to the conventional technique would bring with it a wealth of advantages.

The duration of the initial pressure pulse is determined by the duration of the discharge current of a capacitor connected to the coil and thus by the electrical properties of the discharge circuit and by the mass of the conductive membrane. If, when using a metallic membrane, the impedance of the discharge circuit is reduced by using a capacitor with a smaller capacitance (e.g. 0.25 µF instead of 1 µF), it can be observed that the discharge current is significantly shorter, but the membrane is lagging behind due to its inertia the movement to be expected from the current can no longer be carried out completely, so that a pressure pulse of longer duration and lower amplitude than in the ideal case results. When using a coated membrane, on the other hand, it should be noted that the highly conductive layer with a thickness of about 30 to 50 μm is not strong enough to allow the eddy currents induced by the coil to develop in full strength, which likewise results in a lower efficiency. The production of a significantly thicker galvanic layer with the good conductivity of the compact metal is complex. Connection techniques other than electroplating between the carrier material and the conductive material (layer) are less mechanically resilient. As a rule, advantages on the electrical side are offset by certain weighty disadvantages with regard to the mechanical function, and vice versa.

The invention is based on the consideration that the disadvantages can be avoided if a separation - also material - of the electrical and mechanical function of the conventional membrane into an induction membrane (hereinafter referred to as "membrane") and a "free" is made.

The object of the invention is to design a shock wave source of the type mentioned at the outset, avoiding any significant disadvantages, in such a way that its initial electrical pulse is relatively short.

This object is achieved in that the membrane is loosely but closely arranged between the coil and an edge-attached film made of electrically poorly conductive material.

The membrane is in the form of an electrically highly conductive layer (sheet, disc).

If a current flows through the flat coil, the membrane is accelerated away from the flat coil due to the induction, due to its loose arrangement practically no radial forces that would promote wear act on it. The film is only deflected by the membrane, but not by electromagnetic forces, since no current is induced in it. The greatest mechanical stress on the film occurs at its edge; due to the flexibility and elastic stretchability of the film, it can be absorbed without damage. If necessary, the film can be reinforced at the edge.

A membrane made of aluminum, which has only about 30% the mass of an equally thick copper or bronze membrane, but is still at least 60% of the conductivity of silver, is particularly favorable with regard to a short pressure pulse and high efficiency. Thus, a particularly advantageous embodiment of the invention is characterized in that the disc or membrane consists of pure aluminum.

An important advantage is seen in the fact that the duration of the electrical initial pulse can be varied with little effort. This can be done by replacing the membrane.

• Fig. 1 eine ebene Stoßwellenquelle mit lose angeordneter Membran in aufgeschnittener Querschnittsdarstellung,
• Fig. 2 eine konkave Stoßwellenquelle mit lose angeordneter Membran in seitlicher Schnittdarstellung und
• Fig. 3 eine Stoßwellenquelle mit zentraler Aussparung in Spule und Membran in aufgeschnittener Querschnittsdarstellung.

Further advantages and refinements of the invention result from the description of exemplary embodiments with reference to the figures. The same reference numerals are used for identical or equivalent components. Show it:

• 1 is a flat shock wave source with loosely arranged membrane in a cut cross-sectional view,
• Fig. 2 shows a concave shock wave source with loosely arranged membrane in a side sectional view and
• Fig. 3 shows a shock wave source with a central recess in the coil and membrane in a cut cross-sectional view.

In Fig. 1, a shock wave source 1 is shown, which comprises a coil carrier 3, on one end of which a flat coil 5 is attached. The flat coil 5 is cast, for example, with a casting resin 7 and then face-ground on the end face. The turns are spiral.

In front of the flat coil 5, a membrane 9 is loosely arranged, which preferably consists of a metal with a small mass and high electrical conductivity, such as preferably aluminum. The membrane 9 has a thickness of approximately between 50 and 500 μm. The diameter is such that the membrane 9 is not significantly influenced in its movement on the edge side by existing housing parts. In the direction of propagation of the shock waves P of the membrane 9, a film 11 made of an electrically poorly conductive material is arranged, in particular clamped on the edge. The film 11 consists for example of a polymeric plastic, such as polyimide or polyethylene, which has a certain elasticity. Their thickness can be up to approx. 200 µm. The diameter of the membrane 9 is smaller than the diameter of the film 11 and also smaller than the diameter of the socket 12 which clamps or holds the film 11 on the edge.

1, components 5, 9 and 11 are shown in the form of an exploded drawing. The elements of the flat coil 5, membrane 9 and film 11 are sealed at the edge (as will be explained in FIG. 2) by means of the holder 12 (for example in the form of a union nut) such that a closed space 13 is formed in which the membrane 9 is movably introduced. The membrane 9 lies loosely but closely between the flat coil 5 and the film 11.

A supply line 15 leads from the outside into the closed space 13 in order to be able to apply a negative pressure to it. In the present case, the feed line 15 opens from above through the casting resin 7 into the outer region of the room 13.

In FIG. 2, the same parts are provided with the same reference numerals as in FIG. 1. The shock wave source 1 here comprises a coil carrier 3, which is cylindrical and whose one end face is concavely curved. A single-layer flat coil 5 is placed on the concavely curved end face and is cast, for example, with an insulating casting resin 7. When a shock wave is triggered, the curved flat coil 5 is connected to a capacitor 21 by means of an electrical line 17 via a spark gap 19.

The coil carrier 3 is designed as a first housing part 23, which is provided with a plurality of bores 25 on the edge.

A metallic membrane 9 is placed in front of the flat coil 5 and has the same properties as described in FIG. 1. The membrane 9 is also spherically curved so that it adapts well to the shape of the flat coil 5. A flexible non-metallic film 11 is placed over the membrane 9, the properties of which are the same as described in FIG. 1. The film 11 is chosen so large that its edge protrudes up to the flat edge 24 of the first housing part 23. Here, too, the membrane 9 lies loosely, but closely between the film 11 and the insulation of the flat coil 5. Here, too, it is important to separate the electrical and mechanical function.

A second, annular housing part 27 is arranged opposite the first housing part 23. The edge of the film 11 is located between the flat edge 24 of the first and the flat edge 28 of the second housing part 23 and 27. The second housing part 27 has further bores 25a, which are opposite the bores 25 to match. The bores 25a are provided with threads so that screws 29 pull the second housing part 27 against the first housing part 23 and thus clamp the film 11 firmly on the edge.

The membrane 9 is also here in a closed space 13, which is formed by the outside of the flat coil 5 together with casting resin 7, the inside of the film 11 and an edge-side inner portion 23i of the first housing part 23. To the space 13, in particular to the portion 23i or to the end face of the coil 5, leads a supply line 15 to which a vacuum pump can be connected.

In the exemplary embodiment shown in FIGS. 1 and 2, the space 13 is evacuated, so that the flat coil 5, the membrane 9 and the film 11 lie closely against one another. This is the initial state before the triggering of a shock wave P. To trigger the shock wave P, the discharge current of the capacitor 21 accelerates the membrane 9 away from the flat coil 5, with virtually no radial forces promoting wear due to the lack of clamping of the membrane 9 would attack her. The film 11 is deflected only by touching the membrane 9, but not by electromagnetic forces. The greatest load on the film 9 occurs at the edge and is absorbed without damage due to the flexibility and stretchability of the film 11. After triggering the shock wave P, the membrane 9 and the film 11 are pulled back into the described starting position due to the vacuum generated in the space 13.

By using a membrane 9, especially made of aluminum, a very good conductivity is achieved with a low weight of the membrane 9. In comparison to a membrane 9 made of silver or a bronze alloy, a shorter initial acoustic pulse is generated due to the different masses (under otherwise identical conditions for the shock wave source 1). This shortening has the advantages mentioned at the beginning of a smaller lead section (in the case of a flat shock wave source with a lens) up to the formation of a shock wave, a smaller focus zone, a higher focusing factor, a Smaller electrical and thermal stress on the shock wave source 1, a reduction in the acoustic energy emitted into the patient's body and a change in the destruction mechanism of a concrement from "smashing" to "ablation". In addition to these advantages, which are directly connected to the shortening of the initial pulse, there is the possibility, by changing the properties of the generated shock wave, of replacing the flat coil 5 and / or, above all, the membrane 9, by disassembling the body or coil carrier 3 from the To carry out this exchange back without emptying water in the leading section 30 adjoining the film 11 and without having to dismantle the entire shock wave source 1. The mechanical design for this is not shown in detail in the figures.

In addition, starting from a short pulse duration when using a capacitor 21 of e.g. 0.25 µF if there is a corresponding clinical need by changing to a capacitor 21 with a larger capacitance, e.g. of 1.0 µF, a longer initial pressure pulse with a correspondingly larger focus zone and acoustic energy are generated.

3 shows the shock wave source 1 according to FIG. 1, but additionally with a central recess 31 in the coil carrier 3 together with casting resin 7 and a central recess 31a in the membrane 9. Through the openings or recesses 31, 31a, the transmission / Receiving head 33 of an ultrasound locator pushed. This device, for example a sector scanner, can be used to determine the concretion along the center axis Z of the shock wave source 1. This is considered a particularly interesting embodiment of the invention. The feed line 15 opens into the opening 31 here.

Even without using an ultrasound locating device, it can be expedient (only) to provide the membrane 9 made of a highly conductive material with a central, preferably round opening 31a. It has been shown in experiments that if the membrane 9 is provided with a central recess 31a of approximately 10 to 30% of its diameter, the possibility of voltage flashovers between the coil 5 and the membrane 9 is considerably reduced. This is a particularly important aspect. A central recess 31a in the membrane 9 has also proven to be advantageous in connection with a concave flat coil 5 (as shown for example in FIG. 2). The membrane 9 and the film 11 are then - also due to their flexibility - particularly well adaptable to the profile of the coil 5 together with the insulating cast resin layer 7.

It should also be mentioned that the film 11 on the circumference, on which it is clamped, can be made stronger than its central region. This can contribute to an extended lifespan.

Claims (13)

1. Shock wave source with an electromagnetic flat coil, in front of which a membrane made of electrically conductive material is arranged, characterized in that the membrane (9) is loose, but closely between the coil (5) and a circumferentially attached film (11) made of electrical poorly conductive material is arranged. 2. Shock wave source according to claim 1, characterized in that the membrane (9) consists of aluminum. 3. Shock wave source according to claim 1 or 2, characterized in that the membrane (9) is between 50 microns and 500 microns thick. 4. Shock wave source e according to one of claims 1 to 3, characterized in that the film (11) consists of a polymeric plastic, such as polyimide or polyethylene. 5. Shock wave source according to one of claims 1 to 4 with a cylindrical housing, characterized in that the film (11) is clamped on the edge side in the housing (23, 27). 6. Shock wave source according to claim 5, characterized in that the housing has two partial housings (23, 27), between which the film (11) is clamped (Fig. 2). 7. Shock wave source according to one of claims 1 to 6, characterized in that the coil (5), the membrane (9) and the film (11) are concave (Fig. 2). 8. Shock wave source according to one of claims 5 to 7, characterized in that the diameter of the membrane (9) is less than the inner diameter of the housing (23, 27). 9. Shock wave source according to one of claims 1 to 8, characterized in that the membrane (9) has a central opening (31 a). 10. Shock wave source according to claim 9, characterized in that the diameter of the central opening (31 a) is about 10 to 20% of the diameter of the membrane (9). 11. Shock wave source according to one of claims 8 or 9, characterized in that the electromagnetic coil (5) and the membrane (9) each have a central opening (31, 31a) into which the scanning head (33) of an ultrasound locating device can be inserted ( Fig. 3). 12. Shock wave source according to one of claims 1 to 11, characterized in that the membrane (9) is housed in a space (13) in which a negative pressure can be generated. 13. Shock wave source according to one of claims 1 to 12, characterized in that the film (11) is reinforced on the circumference to which it is attached.

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