EP0702350A2 - Driving circuit for a soundpulse source - Google Patents

Abstract

The control circuit has a charging stage for charging a capacitor (2) and a discharge stage in parallel with the latter, containing at least one HV switch (4) and the pulsed sound source (1). The discharge stage has a limiting circuit, for limiting the time duration of the electrical oscillation exhibited by the pulsed sound source, in response to the stored charge transferred from the capacitor upon closure of the switch. Pref. the limiting circuit is provided by a short-circuit loop (7, 8, 9) in parallel with the capacitor and the pulsed sound source, containing a second HV switch (7), with a trigger circuit for the switch operated after the limited time duration.

Description

The invention relates to a control circuit for a pulse sound source, in particular a high-power pulse sound source according to the preamble of claim 1. Such a control circuit is e.g. known from DE-A-39 37 904.

Pulse sound sources have been used in medicine to smash concretions inside the body for several years. New applications for the acoustic irradiation of parts of the body through pulse-shaped sound waves are being developed in the fields of osteotherapy, tumor therapy and the treatment of soft tissue pain. That is why sound sources with a high power reserve and at the same time the longest possible service life are required for efficient and successful treatment. In general, pulse sound sources with piezoelectric, electromagnetic, electro-hydraulic and magnetostrictive transducers or transducer elements are known.

1 shows a basic circuit for controlling electro-acoustic pulse sound sources 1. To control a high-voltage surge capacitor 2 is charged via a charging resistor 3. The pulse-like excitation of the sound source 1 takes place by closing a high-voltage switch 4. A resistor 6 essentially serves to dampen the vibrations that occur due to unavoidable supply inductances and at the same time limits the maximum discharge current that can flow through the pulse sound source 1. As high-voltage switch 4, trigger switching spark gaps, overvoltage switching spark gaps, vacuum relays, switching tubes (e.g. thyratrons), transistor and thyristor switches are used, for example.

Apart from a trigger circuit 5 for triggering the high-voltage switch 4, which is also shown in FIG. 1, the circuit shown in FIG. 1 largely corresponds to the control circuit known from DE-A-39 37 904 mentioned above. As a pulsed sound source, this document shows a spark gap, and in order to improve the ignition behavior of the spark gap, a voltage is applied between the electrodes of the spark gap that is much smaller than the breakdown voltage and that allows a small electrical current to flow between the electrodes, causing local heating in the Area of the tips of the electrodes is effected. This current also leads to hydrolysis, whereby small gas bubbles form on the electrode surfaces, which promote the formation of leaders.

2a, 2b, 2c, 2d each represent in the form of a simplified electrical equivalent circuit diagram the above-mentioned electro-acoustic pulse sound sources which are used in principle.

FIG. 2a shows a piezoelectric pulse sound source 1a as a capacitive load with a discharge resistor 12 connected in parallel. The damping resistor 6 shown in FIG. 1 is dimensioned such that the transducer voltage reaches its maximum within the simple transit time T of the sound in the ceramic (measured in the direction of sound emission) reached. In order to take advantage of the high electroacoustic efficiency of the piezoelectric pulsed sound source, the value of the discharge resistor 12 is chosen so that the discharge time constant given by it reaches at least ten times, more preferably twenty to thirty times the simple transit time T of the sound in the ceramic.

2b shows an electromagnetic pulse sound source 1b, which represents an inductive load and is shown in simplified form as a transformer with a short-circuited secondary winding. 2c shows an electro-hydraulic sound source 1c with a liquid spark gap, which is essentially an ohmic load. Fig. 2d shows a magnetostrictive impulse sound source 1d, which consists of at least one excitation coil, the magnetic field of which e.g. cylindrical magnetostrictive material deflects.

It is an object of the present invention to improve the generic control circuit for pulsed sound sources so that the mechanical load on the sound-emitting components of the pulsed sound sources is reduced, thereby increasing the lifespan of the sound source and improving the uniformity of the pulse power generated during its lifespan. One of the sound sources shown in FIGS. 2a-2d should be usable as the pulse sound source.

The above object is achieved in a control circuit for a pulse sound source, in particular high-power pulse sound source a charging circuit for charging a surge capacitor and a discharge circuit connected in parallel with the surge capacitor, which contains at least a first, electrically controllable high-voltage switch and the pulsed sound source, according to the invention solved in that the discharge circuit has a limiter circuit which follows the duration of the charge stored in the surge capacitor the closing of the first high-voltage switch at the pulse sound source excited electrical vibration limited to a predetermined value.

The control circuit according to the invention enables a longer service life with the same power or a higher power with an unchanged service life of the pulse sound source. The mechanical load on the sound-emitting components of the pulsed sound sources is minimized in that the duration of the electrical excitation is reduced to the minimum required to emit the desired pressure pulse by the limiter circuit.

Advantageous developments of the control circuit for pulse sound sources according to the invention, as characterized in claim 1, are specified in the subclaims.

Fig. 1

die bereits erläuterte gattungsgemäße Ansteuerschaltung;

Fig. 2a, 2b, 2c und 2d

bereits erläuterte Ersatzschaltbilder der piezoelektrischen, elektromagnetischen, elektrohydraulischen und magnetostriktiven Impulsschallquellen;

Fig. 3

eine erste Variante einer erfindungsgemäßen Ansteuerschaltung, bei der die Begrenzerschaltung in Form eines Kurzschlußkreises ausgeführt ist;

Fig. 4

eine zweite Variante der vorgeschlagenen Ansteuerschaltung, ebenfalls mit einer als Kurzschlußkreis realisierten Begrenzerschaltung;

Fig. 5

eine dritte Variante einer Ansteuerschaltung, ebenfalls mit einer als Kurzschlußkreis realisierten Begrenzerschaltung;

Fig. 6a

eine vierte Variante einer erfindungsgemäßen Ansteuerschaltung für eine elektromagnetische Impulsschallquelle, bei der die Begrenzerschaltung Teil einer Triggerschaltung für den ersten elektrisch steuerbaren Hochspannungschalter ist;

Fig. 6b

eine der vierten Variante gemäß Fig. 6a ähnliche Ausführung einer elektrohydraulischen Impulsschallquelle, bei der die Begrenzerschaltung ebenfalls ein Teil einer Triggerschaltung für den ersten Hochspannungsschalter ist;

Fig. 6c

eine den Varianten gemäß Fig. 6a und 6b ähnliche Ansteuerschaltung für eine magnetostriktive Impulsschallquelle, wobei auch hier die Begrenzerschaltung Teil einer Triggerschaltung für den ersten elektrisch steuerbaren Hochspannungsschalter ist;

Fig. 7a, 7b, 7c

jeweils Schwingungskurven der eine piezoelektrische Impulsschallquelle erregenden elektrischen Spannung und die daraus resultierenden Pulsformen des von der piezoelektrischen Impulsschallquelle erzeugten Schalldrucks jeweils ohne Kurzschluß (Fig. 7a), bei vollständigem Kurzschluß (Fig. 7b) und bei teilweisem Kurzschluß (Fig. 7c);

Fig. 8a und 8b

jeweils Kurvenformen des elektrischen Erregerstroms an einer elektromagnetischen Impulsschallquelle und die daraus resultierenden Kurven des erzeugten Schalldrucks jeweils ohne und mit Kurzschluß- bzw. Begrenzerfunktion;

Fig. 9a, 9b und 9c

jeweils Schwingungsformen des elektrischen Erregerstroms einer elektrohydraulischen Impulsschallquelle und die daraus resultierenden Druckimpulsverläufe jeweils ohne Begrenzungs- bzw. Kurzschlußwirkung und beim Kurzschluß zu zwei unterschiedlichen Zeitpunkten;

Fig. 10a

eine erfindungsgemäße Ansteuerschaltung mit einem Kurzschlußkreis für eine piezoelektrische Impulsschallquelle mit Überspannungsfunkenstrecke;

Fig. 10b

ein Beispiel eines RC-Netzwerkes zur Verzögerung der Überspannungsfunkenstrecke;

Fig. 10c

ein Beispiel RLC-Netzwerks zur Verzögerung der Überspannungsfunkenstrecke;

Fig. 11

die Realisierung eines Kurzschlußkreises durch entsprechende Dimensionierung des Entladewiderstandes;

Fig. 12

eine erste Ausführungsform einer Ansteuerschaltung mit Kurzschlußkreis für eine piezoelektrische Impulsschallquelle;

Fig. 13

eine zweite Ausführungsform einer erfindungsgemäßen Ansteuerschaltung mit einem Kurzschlußkreis für eine piezoelektrische Impulsschallquelle, bei der der Kurzschlußkreis lediglich aus passiven Bauelementen besteht; und

Fig. 14

ein Schaltungsbeispiel einer Ansteuerschaltung für eine piezoelektrische Impulsschallquelle, die einen Kurzschlußkreis für eine partielle Kurzschlußentladung aufweist.

The invention is described in more detail below in several principal and some preferred embodiments with reference to the accompanying drawing. Show it:

Fig. 1

the generic control circuit already explained;

2a, 2b, 2c and 2d

already explained equivalent circuit diagrams of the piezoelectric, electromagnetic, electrohydraulic and magnetostrictive pulse sound sources;

Fig. 3

a first variant of a control circuit according to the invention, in which the limiter circuit is designed in the form of a short circuit;

Fig. 4

a second variant of the proposed control circuit, also with a limiter circuit implemented as a short circuit;

Fig. 5

a third variant of a control circuit, also with a limiter circuit implemented as a short circuit;

Fig. 6a

a fourth variant of a drive circuit according to the invention for an electromagnetic pulse sound source, in which the limiter circuit is part of a trigger circuit for the first electrically controllable high-voltage switch;

Fig. 6b

an embodiment of an electrohydraulic pulse sound source similar to the fourth variant according to FIG. 6a, in which the limiter circuit is also part of a trigger circuit for the first high-voltage switch;

Fig. 6c

a control circuit for a magnetostrictive pulse sound source similar to the variants according to FIGS. 6a and 6b, the limiter circuit also being part of a trigger circuit for the first electrically controllable high-voltage switch;

7a, 7b, 7c

in each case vibration curves of the electrical voltage exciting a piezoelectric pulsed sound source and the resulting pulse shapes of the sound pressure generated by the piezoelectric pulsed sound source in each case without a short circuit (FIG. 7a), with a complete short circuit (FIG. 7b) and with a partial short circuit (FIG. 7c);

8a and 8b

in each case waveforms of the electrical excitation current at an electromagnetic pulse sound source and the resulting curves of the sound pressure generated in each case without and with short-circuit or limiter function;

9a, 9b and 9c

each waveforms of the electrical excitation current of an electrohydraulic pulse sound source and the resulting pressure pulse curves each without limitation or short-circuit effect and in the event of a short circuit at two different times;

Fig. 10a

a drive circuit according to the invention with a short circuit for a piezoelectric pulsed sound source with overvoltage spark gap;

Fig. 10b

an example of an RC network for delaying the overvoltage spark gap;

Fig. 10c

an example RLC network for delaying the overvoltage spark gap;

Fig. 11

the realization of a short circuit by appropriate dimensioning of the discharge resistance;

Fig. 12

a first embodiment of a drive circuit with a short circuit for a piezoelectric pulsed sound source;

Fig. 13

a second embodiment of a control circuit according to the invention with a short circuit for a piezoelectric pulsed sound source, in which the short circuit consists only of passive components; and

Fig. 14

a circuit example of a drive circuit for a piezoelectric pulsed sound source, which has a short circuit for a partial short circuit discharge.

The variants of the basic circuit of the control circuit according to the invention shown in FIGS. 3 to 5 have, in addition to the control circuit already shown in FIG 9 exists. The high-voltage switch 7 is actuated by a trigger circuit 8. The delayed switch-on of the second high-voltage switch 7 compared to the switch-on of the first high-voltage switch 4 determines the duration of the electrical excitation.

In the first basic circuit variant shown in FIG. 3, the short circuit is located directly parallel to the pulse sound source 1. In the second basic circuit variant shown in FIG. 4, the short circuit is parallel to the series circuit comprising the pulse sound source 1 and the resistor 6, which is used for current limitation and for vibration damping. In the third basic circuit variant shown in FIG. 5, the short circuit is directly parallel to the surge capacitor 2.

Based on the voltage-time, current-time and the pressure-time diagrams, which are shown in FIGS. 7a, 7b, 7c, 8a, 8b, 9a, 9b and 9c, the functions of the drive circuit according to the invention provided with the short-circuit are now in accordance with the basic circuits of FIGS. 3 to 5 when using the various electro-acoustic pulse sound sources explained:

1. Piezoelectric pulse sound source

The time course of the electrical voltage U _PE at a piezoelectric pulsed sound source 1a is determined by the oscillation of the electrical charge between the surge capacitor 2 and the pulsed sound source 1a and by the mechanical settling of the pulsed sound source (see curve 70 in FIG. 7a). For the radiation of the unipolar pressure pulse represented by curve 71 in FIG. 7a, the voltage curve U _PE in the time interval 0 ≦ t ≦ τ is decisive. τ is the sum of the simple propagation time T of the sound in the piezoelectric material illustrated in FIG. 7a and the rise time T 'of the electrical excitation, where, as was explained in relation to FIG. 2a, T'<T applies.

wird die Erregung der Impulsschallquelle 1a abgebrochen, ohne daß sich der Verlauf des im Zeitintervall 0 ≦ t ≦ τ abgestrahlten, unipolaren Druckpulses wesentlich verändert. Hierdurch wird eine schnelle Rückkehr des piezoelektrischen Materials in seine Ausgangslage eingeleitet. Dies ist, wie die Kurve 73 in Fig. 7b zeigt, mit der Abstrahlung eines an sich unerwünschten Zugwellenanteils verbunden, der durch den Verlauf der Kurve 73 im negativen Bereich der P-Ordinate dargestellt ist. Wählt man den Wert des Dämpfungswiderstands 9 jedoch so, daß die Spannung U_PE in einem Zeitintervall Δt' mit τ ≦ Δt' < 10 T abklingt, so bleibt der durch das Kurzschließen verursachte Zugwellenanteil klein gegenüber dem Zugwellenanteil, der durch den in der Praxis meist realisierten schallweichen rückseitigen Abschluß des piezoelektrischen Materials gegeben ist. Durch das Kurzschließen der Schallquelle zum Zeitpunkt t ≧ τ wird die Auslenkung des Piezomaterials auf das zeitlich erforderliche Mindestmaß begrenzt. Somit wird die mechanische Belastung von Anpaß-, Verguß- und Klebeschichten sowie des Piezomaterials vermindert und dadurch eine höhere Lebensdauer erzielt.By short-circuiting the electrical excitation at times t ≧ τ, preferably to $\text{t = τ}$

the excitation of the pulse sound source 1a is stopped without the course of the unipolar pressure pulse emitted in the time interval 0 ≦ t ≦ τ changing significantly. This initiates a quick return of the piezoelectric material to its original position. As curve 73 in FIG. 7b shows, this is associated with the radiation of an inherently undesirable tensile wave component, which is represented by the curve 73 in the negative region of the P-ordinate. However, if the value of the damping resistor 9 is chosen so that the voltage U _PE decays in a time interval Δt 'with τ mit Δt'<10 T, the remains due to the short-circuiting, the draw wave component is small compared to the draw wave component, which is given by the sound-proof rear closure of the piezoelectric material, which is usually implemented in practice. By short-circuiting the sound source at time t ≧ τ, the deflection of the piezo material is limited to the minimum time required. This reduces the mechanical load on the matching, potting and adhesive layers as well as the piezo material, thereby achieving a longer service life.

eingeschaltet wird und dann den Kurzschluß bewirkt.In order to take advantage of the high electroacoustic efficiency of the piezoelectric sound source, no electrical charge must flow away for t ≦ τ. On the other hand, in order to keep the mechanical-electrical load low, it should be broken down as quickly as possible for t ≧ τ. For this reason, the best desired effect is achieved if the short circuit at the time $\text{t = τ}$

is turned on and then causes the short circuit.

It should be mentioned that instead of the complete short-circuit discharge described so far to zero potential, the short-circuit discharge can also be carried out only partially, ie to an intermediate potential U _Z. In this way, on the one hand, the peak load relevant to the life of the sound source is reduced as quickly as possible, and on the other hand, the train wave component radiated as a result of the short circuit is reduced. 7b and 7c show the voltage profiles 72 and 74 for a given voltage gradient and the associated pressure and tension wave profiles 73, 75 for the complete and partial short-circuit discharge, respectively. The amplitude and pulse width of the tensile wave component decrease noticeably in the event of partial short-circuit discharge. As shown in FIG. 7c, the pull wave amplitude is preferably reduced by limiting the partial short-circuit discharge to a time interval smaller than T. A subsequent discharge from the intermediate potential U _Z to zero potential occurs with a higher time constant and consequently negligible tensile wave amplitude.

The drive circuit is shown in FIG. 14 as an example of a circuit for the partial short-circuit discharge of a piezoelectric pulsed sound source. The second high-voltage switch 7 located in the short-circuit is actuated with a delay by the time interval Δt ≧ τ compared to the first high-voltage switch 4. As a result, the sound source discharges like a short circuit via the resistor 9 into the capacitor 25, the intermediate potential U _{Z being} established. The resistor 26 is required if the capacitor 25 cannot be discharged via the second high-voltage switch 7 and the discharge resistor 12. This applies in particular when the second high-voltage switch is implemented as a switching spark gap.

Furthermore, it can be advantageous to selectively activate or deactivate the limiter circuit or the short circuit. For a piezoelectric pulsed sound source, it makes sense, for example, to deactivate the limiter circuit for low and medium power in order to emit a pressure pulse that is particularly gentle on the tissue and has a minimal proportion of draft waves (cf. FIG. 7a). With high power and a correspondingly high mechanical load, the limiter circuit must be activated (see FIGS. 7b and 7c) in order to achieve a sufficient service life. The highest service life is achieved in any case with a permanently activated limiter circuit.

2. Electromagnetic pulse sound source

den erwünschten ersten Druckpuls hoher Amplitude, dem für jede weitere Halbwelle weitere Druckpulse mit jeweils abnehmender Amplitude folgen (Fig. 8a). Die Gesamtauslenkung der schwingenden Membran ist, bedingt durch ihre Trägheit, im wesentlichen die Summe der den aufeinanderfolgenden Druckpulsen zugeordneten Einzelauslenkungen.The electrical excitation of the pulsed electromagnetic sound source 1b (FIG. 6a) takes place by discharging the surge capacitor 2 via the inductance of the sound source in the form of a damped oscillation with the period T₁. The course of the electrical current I _EM through the sound source is shown as curve 80 in FIG. 8a. The temporal course of the sound pressure P shown as curve 81 in FIG. 8a is proportional to the square of the electric current I _EM through the sound source. Consequently, the first half-wave of the electrical current I _EM delivers in the time interval ${\text{0 ≦ t ≦ T}}_{\text{1}}\text{/ 2nd}$

the desired first pressure pulse of high amplitude, which is followed by further pressure pulses with a decreasing amplitude for each additional half-wave (FIG. 8a). Due to its inertia, the total deflection of the vibrating membrane is essentially the sum of the individual deflections assigned to the successive pressure pulses.

According to the invention, the damped electrical oscillation is therefore interrupted by short-circuiting the sound source 1b or the surge capacitor 2 immediately after the first half-wave of the discharge current by means of the short-circuit, so that the curves 82 and 83 of the time profile of the current I _EM and the pressure P in FIG. 8b arise. This limits the total deflection of the diaphragm to the required minimum and achieves a longer service life due to the reduced mechanical load.

6a shows an alternative control circuit which can be used for an electromagnetic pulse sound source and which, instead of a short-circuit circuit, contains a limiter circuit which is assigned to a trigger circuit 11 for a high-voltage switch 10 which can be switched on and off. The high-voltage switch 10 is closed by the trigger circuit 11 for controlling the pulse sound source 1b and opened again after the time interval T 1/2. The time interval T 1/2 can be 100 ns to 10 microseconds. According to the current state of the art, extinguishing spark gaps, high-voltage switching tubes (eg tyrathrons), high-voltage transistor switches or thyristors that can be switched on are suitable for this.

3. Electro-hydraulic pulsed sound source

The electrical excitation of the electro-hydraulic pulse sound source 1c (FIG. 6b) takes place by discharging the surge capacitor 2 into a nonlinear, time-dependent electrical resistance of the pulse sound source implemented as a liquid spark gap. Sound is emitted in the form of a shock wave due to the expansion of the plasma generated in the liquid.

der Stromschwingung I_EH(t) gegeben. Die zweite Viertelperiode ${\text{T}}_{\text{2}}\text{/2 ≦ t ≦ T₂}$

beeinflußt die abfallende Flanke der Druckwelle P(t) gemäß Kurve 91. Der sich an die erste Halbperiode T₂ anschließende Stromfluß heizt das Plasma zwar weiter auf, er ist aber für die Amplitude und die Pulsform der zu diesem Zeitpunkt bereits ausgelösten Druckwelle ohne Bedeutung.Due to the inevitable inductance of the spark gap and the feed lines between the surge capacitor and the pulsed sound source, an electrical oscillation of the current I _EH with the half-period T₂ is damped by the resistance of the spark gap (cf. curve 90 in FIG. 9a). The pressure amplitude of the pressure wave radiated into the liquid, as represented by curve 91 in FIG. 9a, is essentially due to the amplitude and the rise time and thus through the first quarter period ${\text{0 ≦ t ≦ T}}_{\text{2nd}}\text{/ 2nd}$

given the current oscillation I _EH (t). The second quarter ${\text{T}}_{\text{2nd}}\text{/ 2 ≦ t ≦ T₂}$

influences the falling edge of the pressure wave P (t) according to curve 91. The current flow following the first half period T₂ continues to heat the plasma, but it is of no importance for the amplitude and pulse shape of the pressure wave already triggered at this point.

(vgl. die Kurven 92 und 93 in Fig. 9b) bzw. nach der ersten Halbperiode t ≧ T₂ (vgl. die Kurven 94 und 95 in Fig. 9c) unterbrochen. Bei dem Druckverlauf P(t) gemäß Kurve 93 in Fig. 9b ist die Druckamplitude unverändert, die Pulsform jedoch anders als in Fig. 9a, während bei dem Druckverlauf P(t) gemäß Kurve 95 in Fig. 9c die Amplitude und Pulsform gegenüber dem Druckverlauf 91 gemäß Fig. 9a unverändert bleiben.In order to minimize the erosion of the electrodes of the liquid spark gap and thus to increase the service life and the uniformity over the time the electrodes function, the damped electrical oscillation according to the invention is achieved by short-circuiting the electrodes either immediately after the first quarter period ${\text{t ≧ T}}_{\text{2nd}}\text{/ 2nd}$

(see curves 92 and 93 in Fig. 9b) or after the first half period t ≧ T₂ (see curves 94 and 95 in Fig. 9c) interrupted. With the pressure curve P (t) according to curve 93 in FIG. 9b the pressure amplitude is unchanged, but the pulse shape is different from that in FIG. 9a, while with the pressure curve P (t) according to curve 95 in FIG. 9c, the amplitude and pulse shape remain unchanged compared to the pressure curve 91 according to FIG. 9a.

Similar to the electromagnetic pulse sound source, instead of using a short circuit, the limiter circuit in the form of a trigger circuit 11 for a high-voltage switch 10 that can be switched on and off can also be implemented in the electrohydraulic pulse sound source, which circuit can be closed and opened again after the time interval T₂ / 2 or T₂ in the order of 100 ns ... 10 µs allowed (see. Fig. 6b).

Electro-hydraulic pulsed sound sources are used in medicine for extracorporeal and intracorporeal stone therapy. In the case of intracorporeal stone therapy, an electrical spark discharge takes place between two electrodes, which are inserted into the patient's body via an endoscope and positioned adjacently to the stone. If the spark discharge is ignited, a plasma bubble forms, which expands at supersonic speed. The pressure wave radiated into the surrounding body fluid strikes the stone and leads to its destruction. Depending on the discharge voltage and the time course of the discharge current, this bubble can reach a diameter of> 1 mm.

An application of electrohydraulic impulse sound sources in the ureter (ureter stone) or also in blood vessels (eg removal of limescale deposits, thrombolysis, thromboization) has hitherto stood in the way that the growth of the plasma bubble can lead to an expansion and, if necessary, to tearing of the sensitive walls. According to the current state of the art, the plasma bubble is kept small by reducing the amplitude of the discharge current I _EH or the frequency of the damped electrical vibration is increased by using surge capacitors with reduced capacitance. Both measures are linked to a basically undesirable decrease in the amplitude or energy of the radiated pressure wave.

aktiviert, so bleibt die Amplitude der abgestrahlten Druckwelle unverändert, und die Energie der Druckwelle und ebenso das Volumen der Plasmablase werden reduziert. Durch Steuerung des Zeitpunktes für die Aktivierung des Kurzschlußkreises im Intervall ${\text{T}}_{\text{2}}\text{/2 ≦ t ≦ T₂}$

bzw. allgemeiner im Intervall 0 ≦ t ≦ T₂ läßt sich die Energie der abgestrahlten Druckwelle bei konstanter Ladespannung U_L regeln.As already described, the discharge current for t> T₂ (see FIG. 9a) heats the plasma further, but it has no influence on the pressure wave already emitted. Thus, the current flow for t> T₂ leads to an unnecessary increase in the plasma bubble. By short-circuiting the electrodes, the current flow according to Fig. 9c is interrupted for t> T₂ and thereby the growth of the plasma bubble, with unchanged amplitude and energy of the radiated pressure wave, is limited to the minimum. If the short circuit of Fig. 9b for ${\text{t> T}}_{\text{2nd}}\text{/ 2nd}$

activated, the amplitude of the radiated pressure wave remains unchanged, and the energy of the pressure wave and also the volume of the plasma bubble are reduced. By controlling the time for activating the short circuit in the interval ${\text{T}}_{\text{2nd}}\text{/ 2 ≦ t ≦ T₂}$

or more generally in the interval 0 ≦ t ≦ T₂, the energy of the radiated pressure wave can be regulated at a constant charging voltage U _L.

4. Magnetostrictive impulse sound source

Magnetostrictive impulse sound sources have so far not been used to generate power sound. However, as soon as suitable magnetostrictive materials are available, it can be expected that the interruption of the electrical excitation described using the example of the piezoelectric, electromagnetic and electrohydraulic pulsed sound sources, as soon as possible after the desired pressure pulse shape has been acoustically emitted, will also be corresponding has a beneficial effect on the lifespan of a magnetostrictive pulse sound source. The sign of the change in length is a parameter of the respective magnetostrictive material. A control circuit according to the invention according to FIGS. 3 to 6 allows, for example, the radiation of a pressure pulse in the case of a material with a positive change in length, while a tensile pulse is emitted in the case of a material with a negative change in length.

FIG. 6c shows a control circuit for a magnetostrictive pulse sound source 1d, in which the short-circuit circuit described with reference to FIGS. 3 to 5 is replaced by a limiter circuit which is implemented in a trigger circuit 11 for a high-voltage switch 10.

10a, 10b, 10c and 11 show circuit variants of a drive circuit for a piezoelectric pulsed sound source 1a, which contains a short circuit using purely passive components.

According to FIG. 10a, the short circuit consists of an overvoltage spark gap 13, which may be supplemented by a resistor 9 to limit the short circuit current. The spark gap is designed in such a way that it responds due to its own delay at the time t ≧ τ (cf. FIGS. 7a to 7c). It is of course also possible, and shown in FIGS. 10b and 10c, to use a network of passive components 14, 15, 16 in a known manner to delay the ignition of the spark gap.

In the circuit variants of the control circuit according to FIGS. 10a, 10b, 10c and 11, the short circuit is directly parallel to the piezoelectric pulsed sound source 1a, which corresponds to the basic circuit described above with reference to FIG. 3.

In FIG. 10b, an RC element consisting of a resistor 14 and a capacitance 15 is connected between the pulse sound source 1a and the overvoltage spark gap 13 for delaying the ignition; in FIG. 10c, an RLC network consisting of a resistor 14, an inductor 16 and a capacitor 15 is connected between the piezoelectric pulsed sound source 1a and the overvoltage spark gap 13 for delaying the ignition.

Fig. 11 shows that it is possible to realize the effect of the short circuit for a piezoelectric pulsed sound source in the simplest way by choosing the discharge resistor 12a as small as possible.

In known control circuits, the discharge resistor 12 (FIG. 2a) assumes at least ten times the value of the damping resistor 6 in order not to unnecessarily reduce the electroacoustic efficiency of the piezoelectric source by its external wiring. In order to emulate the mode of operation of a short circuit, a value less than ten times the resistance value of the damping resistor 6, preferably less than or equal to six times the value of the damping resistor 6, is selected for the discharge resistor 12a. Of course, in order to keep the voltage at the pulsed sound source and thus the acoustically radiated energy constant, the charging voltage of the surge capacitor 2 must increase as the discharge resistance 12a decreases.

FIG. 12 shows an advantageous circuit variant of a drive circuit according to the invention for a piezoelectric pulsed sound source 1a. A triggerable switching spark gap 17 is fired with a time delay in relation to the first high-voltage switch 4. For this purpose, a high voltage pulse is tapped between the first high voltage switch 4 and the damping resistor 6 and Via an LC delay chain 18a, 18b, 18c, 19a, 19b, 19c, a coupling capacitor 20 and a resistor 21 are fed to the trigger electrode of the switching spark gap 17. The amplitude of the trigger pulse applied to the trigger electrode is exaggerated by the runtime chain. The ignition delay of the switching spark gap is given by the LC runtime chain and the intrinsic delay of the switching spark gap. If a switching spark gap with a correspondingly high self-delay is selected, the number of links in the LC runtime chain can be reduced or the runtime chain can even be omitted entirely. In the latter case in particular, the trigger current must be limited via the resistor 21 or the charge flowing off via the coupling capacitor 20. The resistor 22 serves to equalize the potential between the trigger electrode and the adjacent main electrode of the switching spark gap 17.

FIG. 12 also contains a switch 27 which serves to deactivate the short-circuit for low and medium powers of the pulse sound source if, as has already been mentioned in the description of FIG. 7, a particularly tissue-protecting pressure pulse is to be emitted.

The circuit shown in Fig. 12 also makes it clear that it is for the ignition of the second high-voltage switch 7 or the triggerable switching spark gap 17 due to the different ignition delay in the order of magnitude of 100 ns to a few microseconds for a high-voltage switch, in particular for switching spark gaps Defined ignition or short-circuit discharge delay is usually not sufficient to simply delay the drive signals for the first and second high-voltage switches 4 and 7, which each generate the trigger circuits 5 and 8, in relation to one another. Rather, as shown in FIG. 12, it is necessary to switch on the switching time from the first high-voltage switch 4 tapping the linked measurement signal and supplying it accordingly delayed and electronically processed to the second high-voltage switch 7, in particular the triggerable switching spark gap 17, as a trigger signal. Such a measurement signal can be obtained, for example, from the current flow that occurs when the first high-voltage switch 4 closes, the voltage change at the surge capacitor or the pulse sound source 1, and in the case of a switching spark gap as the first high-voltage switch 7, also optically from the flash of light of the plasma discharge.

The delay in the short-circuit discharge caused by the short-circuit can be regulated from the measurement signal for the switching instant of the first high-voltage switch 4 and a second corresponding measurement signal for the switching instant of the second high-voltage switch 7. In this way, for example, a drift of the point in time of the short-circuit discharge can be compensated for as the two high-voltage switches 4 and 7 wear out.

13 shows a particularly simple and inexpensive implementation of a short circuit of a control circuit for a piezoelectric pulsed sound source by means of passive components. The short-circuit takes place via the high-frequency coil 23, the inductance of which determines the course over time and thus the delay and the maximum current in the short-circuit. The diode 24 lying parallel to the high-frequency coil 23 prevents oscillation of the electrical energy between the coil 23 and the capacitance of the pulse sound source 1a. This avoids the undesired activation of the sound source with a negative half-wave in pulse operation.

An additional series resistor 9, the resistance value of which is dimensioned in such a way that, in conjunction with the coil 23, the voltage U _PE decays to the value 1 / e in a time interval Δt 'with Δt'<10 T, the switching behavior of the diode 24 influence favorably. The discharge resistor 12 is unnecessary in the circuit described above and shown in FIG. 13. It should be noted that FIG. 13 represents only one of the possible combinations of resistor 9, coil 23 and diode 24. The equivalent to FIG. 13 would be, for example, a diode 24 arranged in parallel with the series connection of resistor 9 and coil 23 or a series connection of resistor 9, coil 23 and diode 24.

14 shows an example of one of the conceivable circuit variants for the partial short-circuit discharge of a piezoelectric pulsed sound source. In this case, the switch 7 is actuated with a delay by the time interval Δ t ≧ τ compared to the switch 4. As a result, the sound source discharges like a short circuit via the resistor 9 into the capacitor 25. Here, the intermediate potential U _{Z is established} . The resistor 26 is required if the capacitor 25 cannot be discharged via the switch 7 and the discharge resistor 12. This applies in particular when using a switching spark gap.

With the curves in the event of a short circuit in accordance with FIGS. 7, 8 and 9 are each idealized representations of the current and voltage profiles. However, it goes without saying that with components available today and because of the voltage and current conditions present in the sound sources concerned here, no sudden short circuit is possible, but rather periods of time must always be observed until the currents to be switched off have each decreased to zero.

Claims (20)

Control circuit for a pulse sound source (1), in particular high-power pulse sound source, consisting of a charging circuit for charging a surge capacitor (2) and a discharge circuit connected in parallel with the surge capacitor (2), the at least one first, electrically controllable high-voltage switch (4) and the pulse sound source (1) contains, characterized in that the discharge circuit has a limiter circuit, the duration of the electrical oscillation excited by the charge stored in the surge capacitor (2) after closing the first high-voltage switch (4) at the pulse sound source (1) to a predetermined value (Δt) limited. Control circuit according to Claim 1, characterized in that the limiter circuit has a short-circuit (7, 8, 9, 13-16) connected in parallel with the surge capacitor (2) and the pulsed sound source (1) for at least partially short-circuiting the from the surge capacitor (2) to the pulsed sound source (1) flowing discharge current or the voltage across the pulse sound source (1) at a time corresponding to the predetermined time period (Δt) after the time of closing the first high-voltage switch (4). Control circuit according to claim 2, characterized in that the short circuit (7, 8, 9) at least a second, electrical Controllable high-voltage switch (7) and a trigger circuit controlling this for closing the second high-voltage switch (7) at the time corresponding to the time period (Δt) mentioned. Control circuit according to claim 2 or 3, characterized in that the short circuit (7, 8, 9) is directly parallel to the pulse sound source (1) (Fig. 2). Control circuit according to Claim 2 or 3, characterized in that a damping resistor (6) is connected in series with the pulse sound source (1) and the short-circuit circuit (7, 8, 9) is parallel to the series connection of pulse sound source (1) and damping resistor (6) ( Fig. 4). Control circuit according to claim 2 or 3, characterized in that the short circuit (7, 8, 9) is connected directly in parallel to the surge capacitor (2) (Fig. 5). Control circuit according to Claim 1, characterized in that the first high-voltage switch (10) can be switched on and off electrically and its on / off times are determined by trigger electronics (11) which comprise the limiter circuit (FIGS. 6a, 6b, 6c). Control circuit according to one or more of Claims 1 to 6, characterized in that the pulsed sound source is a piezoelectric pulsed sound source (1a) and that the value of the time period (Δt) determined by the limiter circuit is preferred to Δt ≧ τ $\text{Δt = τ}$

is selected, where τ is approximately equal to the sum of the simple propagation time T of the sound in the piezoelectric material and is the rise time T 'of the electrical excitation (U _PE ) of the piezoelectric material (Fig. 7a, 7b, 7c). Control circuit according to Claim 8, characterized in that the limiter circuit is designed such that the voltage U _PE at the pulse sound source is at least partially reduced in a subsequent time interval Δt 'with τ ≦ Δt'<10 T after the predetermined time period Δt has elapsed. Control circuit according to Claim 9, characterized in that the limiter circuit is designed such that the mentioned voltage U _{PE is} reduced to an intermediate potential U _Z in a subsequent time interval Δt '<τ after the predetermined time period Δt has elapsed. Control circuit according to one or more of claims 1 to 7, characterized in that the pulsed sound source is an electromagnetic pulsed sound source (1b) and that the value (Δt) of the time period determined by the limiter circuit increases ${\text{Δt ≦ T}}_{\text{1}}\text{/ 2nd}$

, prefers ${\text{Δt = T}}_{\text{1}}\text{/ 2nd}$

is selected, T₁ is the period of a damped oscillation (I _EM ) caused by the inductance of the electromagnetic pulse sound source (1b) when the surge capacitor (2) is discharged (Fig. 8a, 8b). Control circuit according to Claim 11, characterized in that the limiter circuit is designed such that the current I _EM through the electromagnetic pulse sound source after the predetermined time period Δt has elapsed in a subsequent time interval ${\text{Δt '<T}}_{\text{1}}\text{/ 2nd}$

decreases to almost zero. Control circuit according to one or more of Claims 1 to 7, characterized in that the pulse sound source is a Electro-hydraulic pulse sound source (1c) and that the value .DELTA.t of the time period determined by the limiter circuit ${\text{Δt ≧ T}}_{\text{1}}\text{/ 2nd}$

or selected to be Δt ≧ T₂, where T₂ is the duration of a half period of the damped oscillation (I _EH ) caused by the inductance of the feed lines and the electrohydraulic pulsed sound source (1c) when the surge capacitor (2) is discharged (FIGS. 9a, 9b, 9c ). Control circuit according to Claim 13, characterized in that the limiter circuit is designed such that the current I _EH through the electrohydraulic pulsed sound source decreases to approximately zero in a subsequent time interval Δt '<T₂ after the predetermined time period Δt has elapsed. Control circuit according to one or more of Claims 1 to 7, characterized in that the pulse sound source is a magnetostrictive pulse sound source (1d). Control circuit according to one or more of Claims 2 to 10, characterized in that the short circuit in parallel with the piezoelectric pulsed sound source (1a) has an overvoltage spark gap (13) and a delay network (9; 14, 15; 14, 15, 16) for delayed ignition of the Overvoltage spark gap (13) at a time corresponding to the value Δt of the aforementioned period (Fig. 10a, 10b, 10c). Control circuit according to one or more of Claims 2 to 10, characterized in that the short circuit has a triggerable switching spark gap (17) parallel to the piezoelectric pulsed sound source (1a) and an LC delay chain (18a, 18b) coupled to the trigger input of the switching spark gap (17). 18c, 19a, 19b, 19c, 20, 21), which at their entrance taps a high-voltage pulse generated between the first high-voltage switch (4) and a damping resistor (6) connected in series with the pulse sound source (1a) and generates a delayed trigger pulse for the switching spark gap (17) (FIG. 12). Control circuit according to one or more of Claims 2 to 10, characterized in that the short-circuit circuit has a coil (23) parallel to the piezoelectric pulsed sound source (1), one of the diodes (24) connected to the coil (23) for preventing electrical oscillation between the Coil (23) and the capacitance of the piezoelectric pulsed sound source (1a) is provided, this coil (23) determining the predetermined time period (Δt) and the maximum current in the short-circuit (Fig. 13). Control circuit according to Claim 18, characterized in that a resistor (9) is also connected in series between the pulse sound source (1a) and the coil (23), the resistance of which is dimensioned such that the voltage U _PE in connection with the coil (23) decays within a time interval Δt 'with Δt'<10 T to the value 1 / e. Control circuit according to one or more of claims 1 to 19, characterized in that the limiter can be activated and deactivated.

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