EP1517757B1 - Switching circuit for an electromagnetic source for the generation of acoustic waves - Google Patents

Description

The invention relates to a circuit for an electromagnetic source for generating acoustic waves, comprising a coil of the electromagnetic source and at least one first capacitor, which is connected in parallel to at least one series circuit of a second capacitor and a first valve.

For example, from DE 198 14 331 A1, such a circuit for an electromagnetic pressure wave source is known. It has two LC resonant circuits connected in series. Of these, the first resonant circuit has a first capacitor and, in parallel thereto, a semiconductor power switch comprising a triggerable thyristor and a freewheeling diode connected in antiparallel thereto, as well as a subsequent inductance. Part of this first resonant circuit and in series with the semiconductor power switch and the inductor and in parallel with the first capacitor, a second capacitor is connected, which also belongs to the second resonant circuit. Parallel to it, a saturable inductor and designed as an inductive load electromagnetic pressure wave source is arranged. Once the thyristor of the semiconductor power switch has been triggered into the conducting state, the first capacitor charged with a capacitor charger is switched to the first non-charged second capacitor so that its charge is transferred to it. The inductor and the two capacitors are dimensioned so that only at the time when practically all the charge has been transferred from the first capacitor to the second capacitor saturates the saturable inductor and thus becomes low-inductance. At this moment, a high discharge current flows only due to the discharge voltage of the second capacitor with a predetermined by the second resonant circuit Time constant through the inductive load of the electromagnetic pressure wave source, where an acoustic pulse is generated.

The SU 17 47 188 A1 removable circuit for the inductance of an electrodynamic radiator has a common voltage source to which a plurality of parallel branches each having a diode at the input, a grounded storage capacitor and an output side commutator, i. Switch are connected. The diodes are poled in such a way that the storage capacitors of the individual parallel branches always separate with respect to their charging voltages from each other, i. stay separated so that Umlade- or balancing operations of these charging voltages are mutually avoided. For common discharge of the storage capacitors, the commutators of all parallel branches are collectively, i. closed at the same time. During this discharging process, the storage capacitor of the respective branch is connected in parallel with the input-side diode thereof.

Another circuit according to the prior art is shown in FIG. The circuit comprises a DC voltage source 1, a switching means 2, which is usually designed as a spark gap, a capacitor C and a coil L, which is part of a sound generating unit of the electromagnetic source. The sound generating unit of the electromagnetic source has, in addition to the coil L a coil carrier, not shown, on which the coil is arranged, and a likewise not shown, arranged on the coil L insulating membrane. Upon discharge of the capacitor C via the coil L, a current i (t) flows through the coil L, thereby generating an electromagnetic field which interacts with the membrane. The membrane is thereby repelled into an acoustic propagation medium, whereby source pressure waves in the acoustic propagation medium as a carrier medium between the sound generating unit of the electromagnetic source and an object to be irradiated to be sent out. Nonlinear effects in the carrier medium can, for example, result in shockwaves from the acoustic source pressure waves. The structure of an electromagnetic source, in particular an electromagnetic shock wave source, is described for example in EP 0 133 665 B1.

Shock waves are used, for example, for the non-invasive destruction of concrements in the interior of the body of a patient, e.g. used to destroy a kidney stone. The kidney stone shock waves cause cracks to form in the kidney stone. The kidney stone eventually breaks apart and can be excreted naturally.

If the circuit for generating acoustic waves shown in FIG. 1 is operated, the result is during the discharging process of the capacitor C via the coil L, for which purpose a short circuit is generated by means of the switching means 2, which in FIG. 2 shows curves of the voltage u (t ) (Curve 3) across the coil L and the current i (t) (curve 4) through the coil L. The evanescent current i (t) flowing through the coil 4 is, as already mentioned, the cause of the generation of acoustic Waves.

The square of the current i (t), curve 5 in FIG. 2, is proportional to the acoustic waves generated by the electromagnetic shock wave source. Accordingly, a first acoustic source pressure wave from the first acoustic source pressure pulse (1st maximum) and further acoustic source pressure waves from the decaying sequence of positive acoustic source pressure pulses emerge from a discharging process of the capacitor C. The first source pressure wave and the subsequent source pressure waves can, as already mentioned, by non-linear effects in the carrier medium and a non-linear focusing, which is usually done with a conventional acoustic focusing lens, in shock waves forming short upright positive portions and subsequent elongated so-called vacuum pans.

By the frequency of the current i (t) flowing through the coil L, characteristics of the shock wave, e.g. whose focus diameter, be changed. With a variable current frequency and thus a variable frequency of the shock wave, for example, the size of the active focus can be changed and, depending on the application, adjusted to the object to be treated. For example, in a lithotripter, the effective focus can be selected according to the particular stone size, so that the acoustic energy is better utilized for the disintegration of the stone and the surrounding tissue is less stressed.

Because of the relatively high short-circuit power up to the 100 MW range, a variable capacitance of the capacitor C and a variable inductance of the coil L are expensive. Therefore, in order to vary the shock wave, generally only the charging voltage of the capacitor C is varied, whereby the maximums of the current i (t) through the coil L and the voltage u (t) on the coil L change. However, the waveforms of the current i (t) and the voltage u (t) remain substantially the same.

The invention is therefore based on the object, a circuit of the type mentioned in such a way that the generation of acoustic waves is improved.

According to the invention, this object is achieved by a circuit of the type mentioned, which is characterized in that the first valve is connected such that it blocks after charging both capacitors during discharge of the first capacitor, as long as the first capacitor with a larger Voltage as the second capacitor is charged, and becomes conductive, as soon as the charging voltage of the first discharging first capacitor at least substantially the charging voltage of the second capacitor which causes the second capacitor to discharge and the two discharging capacitors energize the coil of the electromagnetic source.

The invention further relates to an electromagnetic source with a circuit according to the invention and a lithotripter with such an electromagnetic source.

The first valve, which according to a preferred embodiment of the invention is a first diode or a first diode module, is connected in such a way that it blocks after charging both capacitors, thus preventing compensation processes between the two capacitors. As a result, as is provided according to a preferred variant of the invention, the first capacitor can be charged with a larger charging voltage than the second capacitor before the discharge of both capacitors. For the generation of the acoustic wave through the circuit is first started with the discharge of the first capacitor, that is with the capacitor with the larger charging voltage, via the coil of the electromagnetic source. As soon as the charging voltage of the first capacitor is at least substantially equal to the charging voltage of the second capacitor, the first valve becomes conductive, so that both capacitors discharge and both capacitors feed the coil of the electromagnetic source with current. Consequently, the circuit has the capacitance of the first capacitor before the second capacitor starts to discharge. As both capacitors discharge, the circuit has a capacitance equal to the sum of the capacitances of both capacitors. Thus, a time-varying capacitance of the circuit adjusts, whereby the waveform of the current flowing through the coil of the electromagnetic source current can be influenced. By varying the charging voltages of both capacitors, the waveform of the current through the coil can thus be changed, which in turn changes the characteristics of the shock wave from the electromagnetic source can be varied. The waveform of the discharge current may be further varied if the circuit has a plurality of series-connected valve / capacitor pairs connected in parallel with the first capacitor and charged with different charging voltages.

Incidentally, the first diode module includes, for example, a series and / or parallel connection of a plurality of diodes.

According to one embodiment of the invention, the first capacitor may be charged with a first DC voltage source and the second capacitor with a second DC voltage source prior to discharge. According to a preferred embodiment of the invention, it is also provided to charge the first capacitor and the second capacitor with exactly one DC voltage source and to switch off the DC voltage source from the second capacitor with a switching means as soon as the second capacitor has reached its charging voltage. The switching means according to one embodiment of the invention comprises at least one semiconductor element.

According to a particularly preferred variant of the invention it is provided that the parallel connection of the second capacitor / first valve and the first capacitor, a second valve is connected in parallel. The second valve is according to an embodiment of the invention, a second diode or a second diode module. By the parallel connection of the second valve to the capacitors can be reached during the discharge the capacitors a time extension of the first source pressure pulse. In addition, the subsequent decaying source pressure pulses are heavily attenuated depending on the impedance of the second valve. The damping can be so great that the subsequent swelling pressure pulses disappear completely. By the time extension of the first source pressure pulse, a stronger first acoustic wave, for example in the generation of shock waves, ie a stronger first shock wave generated, resulting in an increase in the volume of the integrating effect for the destruction of concrements. In addition, since only a few weak or no source pressure pulses following the first source pressure pulse occur, the tissue-damaging cavitation caused by the shock waves following the first shock wave and resulting from the subsequent source pressure pulses is also reduced. As a result, the reduced polarity reversal voltage caused by the second valve increases the service life of the first and second capacitors. In addition, with such a generation of shock waves less audible sound waves are generated, so that there is a noise reduction. The decisive factor in the generation of audible sound waves in the generation of shock waves is namely the total area under the curve of the square of the current. In the case of the present invention, this is reduced overall by the omission of the source pressure pulse normally following the first source pressure pulse.

Figur 1

einen bekannten Schaltkreis zur Erzeugung akustischer Wellen,

Figur 2

Den Verlauf der Spannung u(t), des Stromes i(t) und des Quadrates des Stromes i²(t) über der Zeit während der Entladung des Kondensators des Schaltkreises aus Figur 1,

Figur 3

eine elektromagnetische Stoßwellenquelle,

Figur 4

einen erfindungsgemäßen Schaltkreis zur Erzeugung akustischer Wellen,

Figur 5

den Verlauf des Stromes i'(t) über der Zeit während der Entladung eines erfindungsgemäßen Schaltkreises und

Figur 6 bis 8

weitere erfindungsgemäße Schaltkreise.

Embodiments of the invention are illustrated by way of example in the accompanying schematic drawings. Show it:

FIG. 1

a known circuit for generating acoustic waves,

FIG. 2

The course of the voltage u (t), the current i (t) and the square of the current i ² (t) over the Time during the discharge of the capacitor of the circuit of Figure 1,

FIG. 3

an electromagnetic shock wave source,

FIG. 4

a circuit according to the invention for generating acoustic waves,

FIG. 5

the course of the current i '(t) over time during the discharge of a circuit according to the invention and

FIGS. 6 to 8

further circuits according to the invention.

FIG. 3 shows, in the form of a partially sectioned and partially block diagram-like illustration, an electromagnetic shockwave source in the form of a therapy head 10, which in the case of the present exemplary embodiment is part of a lithotripter not shown in more detail. The therapy head 10 has a known per se 11, known per se sound generating unit, which operates on the electromagnetic principle. The sound generating unit 11 has, in a manner not shown in FIG. 3, a coil carrier, a flat coil arranged thereon, and a metallic membrane insulated from the flat coil. To generate shockwaves, the membrane is repelled by electromagnetic interaction with the pancake coil into an acoustic propagation medium denoted by 12, whereby a source pressure wave is emitted into the acoustic propagation medium 12. The source pressure wave of the acoustic lens 13 is focused on a focus zone F, with the source pressure wave splitting into a shock wave as it propagates in the acoustic propagation medium 12 and into the body of a patient P. In the case of the embodiment shown in FIG. 3, the shock wave serves to break up a stone ST in the kidney N of the patient P.

The therapy head 10 is associated with an operating and supply unit 14 which, except for the flat coil, comprises the circuit according to the invention for generating acoustic waves shown in FIG. The control and supply unit 14 is electrically connected via a connecting line 15 shown in FIG. 3 to the sound generating unit 11 comprising the flat coil.

The acoustic shock wave source circuit according to the invention shown in FIG. 4 has DC power sources DC0, DC1 and DC2, a switching means S, capacitors C0, C1 and C2, and the flat coil 23 of the electromagnetic sound generating unit 11 of the therapy head 10. With the capacitor C1 is in the case of the present embodiment, a diode D1 and the capacitor C2, a diode D2 is connected in series. The series circuits of capacitor C1 / diode D1 and capacitor C2 / diode D2 are also connected in parallel with the capacitor C0.

For a charging of the capacitors C0 to C2, the switching means S is opened. The capacitor C0 is therefore charged with the DC voltage U _{0 of} the DC voltage source DC0 and the polarity shown in FIG. The capacitor C1 is charged with the DC voltage U _{1 of} the DC voltage source DC1 and the polarity shown in FIG. The voltage U _{1 of} the DC voltage source DC1 is smaller than the voltage U _{0 of} the DC voltage source DC0 in the case of the present embodiment. The diode D1 is switched so that it blocks as long as the capacitor C0 is charged with a larger voltage u ₀ (t) than the capacitor C1. The diode D1 thus prevents a compensation process between the charged with the voltages U ₀ and U ₁ capacitors C0 and C1, which is why the capacitor C0 is charged at the end of the charging with the higher voltage U ₀ than the capacitor C1, which at the end of the charging charged with the voltage U ₁ . The capacitor C2 becomes the Further charged with the DC voltage U _{2 of} the DC voltage source DC2 and the polarity shown in Figure 4. The DC voltage U ₂ is smaller than the DC voltage U ₁ in the case of the present embodiment. The diode D2 is also connected to turn off as long as the voltage u ₂ (t) of the capacitor C2 is lower than the voltage u ₀ (t) of the capacitor C0. Thus, it is possible to charge the capacitors C0 to C2 with different voltages.

For generating the shock waves, the switching means S is closed. As a result, the capacitor C0 begins to discharge via the coil 23, whereby the voltage u ₀ (t) of the capacitor C0 decreases and a current i '(t) flows through the flat coil 23. The voltage applied to the flat coil 23 is denoted by u '(t). When the voltage u ₀ (t) of the capacitor C0 reaches the value of the voltage U _{1 of} the charged capacitor C1, the diode D1 becomes conductive and the current i '(t) through the flat coil 23 is fed by both capacitors C0 and C1. When the voltage u ₀ (t) of the capacitor C0 and the voltage u ₁ (t) of the capacitor C1 reach the voltage U _{2 of} the charged capacitor C2, the diode D2 becomes conductive and the current i '(t) through the flat coil 23 becomes of the three capacitors C0 to C2 fed. Thus, a time-variable capacitance of the circuit adjusts, whereby the waveform of the current flowing through the flat coil 23 current i '(t) can be influenced. By not further shown in Figure 4, parallel to the capacitor C0 switched capacitor / diode combinations whose capacitors are charged with different high voltages smaller than the voltage U _{0 of} the DC voltage source DC0, the waveform of the current i '(t) through the flat coil 23 are further influenced during unloading.

FIG. 5 shows, as an example, curves of currents i '(t) through the flat coil 23 during discharging, when the circuit shown in FIG. 4 only shows the capacitors C0 and C1 includes. By a suitable choice of the voltages U ₀ and U _{1 of} the DC voltage sources DC0 and DC1, the current maxima have the same values.

FIG. 6 shows a further embodiment of a circuit according to the invention. The circuit shown in FIG. 6 comprises, in the case of the present exemplary embodiment, capacitors C0 'to C2', switching means S ', S1 and S2, diodes D1' and D2 ', a DC voltage source DC0' and the flat coil 23.

The diode D1 'and the capacitor C1' and the diode D2 'and the capacitor C2' are connected in series. The series circuits of capacitor C1 '/ diode D1' and capacitor C2 '/ diode D2' are connected in parallel with the capacitor C0 '. The diodes D1 'and D2' are poled in such a way that they block as long as the capacitor C0 'is charged with a voltage u ₀ ' (t) according to the polarity shown in FIG. 6 which is greater than the voltage u ₁ '(t ) of the capacitor C1 'and the voltage u ₂ ' (t) of the capacitor C2 'according to the marked polarity.

During charging of the capacitors C0 'to C2', the switching means S 'is opened. At the beginning of charging, the scarfs S1 and S2 are closed. Since the capacitors C1 'and C2' are to be charged with charging voltages U ₁ 'and U ₂ ' which are smaller than the voltage U ₀ 'of the DC voltage source DC0', the switches S1 and S2 are then opened when the capacitors C1 'and C2 'are charged with the desired voltages U ₁ ' and U ₂ '. Since the capacitors in the case of the present embodiment are charged with relatively low currents of less than 1 ampere, switching accuracies of the switches S1 and S2 in the millisecond range are sufficient to charge the capacitors C1 'and C2' with sufficient accuracy. The voltages u ₁ '(t) and u ₂ ' (t) of the capacitors C1 'and C2' are monitored during charging with measuring devices not shown in FIG.

At the end of the charging, therefore, the switching means S1 and S2 are opened, the capacitor C0 'with the voltage U ₀ ' of the DC voltage source DC0 'and the capacitors C1' and C2 'with the voltages U ₁ ' and U ₂ 'loaded. In addition, in the case of the present embodiment, the voltage U ₂ 'of the charged capacitor C2 is smaller than the voltage U ₁ ' of the charged capacitor C1.

For the discharge of the capacitors C0 'to C2', the switching means S 'is closed and the capacitor C0' begins to discharge via the flat coil 23, whereby a current i '(t) flows through the flat coil 23. As long as the voltage u ₀ '(t) of the capacitor C0' is greater than the voltage U ₁ 'of the charged capacitor C1', the diodes D1 'and D2' lock. When the voltage u ₀ '(t) of the capacitor C0' reaches the value of the voltage U ₁ 'of the charged capacitor C1', the diode D1 'becomes conductive and the current i' (t) through the flat coil 23 is discharged from the capacitors C0 '. and C1 'fed. If the voltages u ₀ '(t) and u ₁ ' (t) of the capacitors C0 'and C1' reach the value of the voltage U ₂ 'of the charged capacitor C2', the diode D2 'becomes conductive and the current i' (t ) through the flat coil 23 is fed by the capacitors C0 'to C2'.

FIG. 7 shows a further circuit according to the invention which has an additional diode D3 in comparison to the circuit shown in FIG. The diode D3 is connected in parallel and in the reverse direction to the charging voltage U _{0 of} the capacitor C0.

FIG. 8 shows yet another circuit according to the invention, which has an additional diode D3 'in comparison to the circuit shown in FIG. The diode D3 'is connected in parallel and in the reverse direction to the charging voltage U' _{0 of} the capacitor C0 '.

Instead of the diodes D1 to D3 and D1 'to D3' in particular diode modules having a series connection and / or parallel connection of a plurality of diodes can be used. In particular, the switching means S, S ', S1 and S2 may be a series connection of thyristors known per se, e.g. from the company BEHLKE ELECTRONIC GmbH, Am Auerberg 4, 61476 Kronberg in their catalog "Fast High Voltage Solid-State Switches" from June 2001 are offered.

Claims (10)

1. Switching circuit for an electromagnetic source (10) for generating acoustic waves, comprising a coil (23) of the electromagnetic source (10) and at least one first capacitor (C0), which is connected in parallel with at least one series circuit composed of a second capacitor (C1) and a first valve (D1)
   characterised in that
   the first valve (D1) is connected such that it blocks after charging both capacitors (C0,C1) during discharge of the first capacitor (C0) as long as the first capacitor (C0) is charged with a larger voltage (u ₀(t)) than the second capacitor (C1) and it is conductive as soon as the charging voltage (u ₀(t)) of the first capacitor, during discharge thereof, reaches at least substantially the charging voltage (u ₁(t)) of the second capacitor (C1), whereupon the second capacitor (C1) begins to discharge and the two discharging capacitors (C0, C1) feed the coil (23) of the electromagnetic source (10) with current (i'(t).
2. Switching circuit according to claim 1,
   characterised in that
   the first valve is a first diode (D1, D2, D1', D2') or a first diode module.
3. Switching circuit according to claim 1 or 2,
   characterised in that
   the first capacitor (C0, C0') can be charged with a greater charging voltage (U ₀.U ₀') than said second capacitor (C1, C2, C1', C2'), before discharge of the first capacitor (C0, C0') and of the second capacitor (C1, C2, C1', C2').
4. Switching circuit according to one of claims 1 to 3,
   characterised in that
   before discharge, the first capacitor (C0) can be charged with a first direct voltage source (CD0) and the second capacitor (C1, C2) can be charged with a second direct voltage source (DC1, DC2).
5. Switching circuit according to one of claims 1 to 3,
   characterised in that
   the first capacitor (CO') and the second capacitor (C1', C2') can be charged with precisely one direct voltage source (DC) and the direct voltage source (DC) can be disconnected from the second capacitor using a switching means (S1, S2) when said second capacitor has reached its charging voltage.
6. Switching circuit according to claim 5,
   characterised in that
   the switching means (S1, S2) comprises at least one semiconductor element.
7. Switching circuit according to claims 1 to 6,
   characterised in that
   the parallel circuit composed of the second capacitor (C1, C2, C1', C2')/first valve (D1, D2, D1', D2') and a first capacitor (C0, C0') is connected in parallel with a second valve (D3, D3').
8. Switching circuit according to claim 7
   characterised in that
   the second valve is a second diode (D3, D3') or a second diode module.
9. Electromagnetic source (10) with a switching circuit according to one of the preceding claims.
10. Lithotripter with an electromagnetic source (10) according to claim 9.

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