WO1994021980A1

WO1994021980A1 - Firing a composition with a microwave generator________________

Info

Publication number: WO1994021980A1
Application number: PCT/FR1994/000291
Authority: WO
Inventors: Jacques David; Yvon Jacquelin
Original assignee: Etienne Lacroix Tous Artifices S.A.
Priority date: 1993-03-16
Filing date: 1994-03-16
Publication date: 1994-09-29
Also published as: DE69409951T2; DE69409951D1; FR2702832B1; FR2702832A1; CA2158280A1; CA2158280C; EP0689661A1; EP0689661B1; ES2115221T3

Abstract

A method for firing a pyrotechnic composition (102) by coupling a microwave generator (111) to a block of the pyrotechnic composition (102) including microwave-sensitive fillers with resistive and/or magnetic electrical losses. The method is characterised in that it comprises controlling the microwave generator (111) to synthetise a detonator-like shock wave. A firing device is also disclosed.

Description

COMPOSITION INITIATION USING A MICROWAVE GENERATOR

The present invention relates to the field of devices for initiating pyrotechnic compositions. Many pyrotechnic igniters have already been proposed.

As shown diagrammatically in the appended FIG. 1, the known igniters generally comprise a housing 10 which contains a pyrotechnic and electrically conductive composition 12 and which carries two electrodes 14, 16. As a variant, a filament placed in the composition can connect the two electrodes. The electrodes 14, 16 are accessible outside the housing 10 and immerse in the composition 12. Thus the application of adequate electrical energy between the electrodes 14, 1 6 allows the composition 12 to be ignited.

Pyrotechnic igniters of the type shown in Figure 1 have been widely used.

However, these known inflammers are not entirely satisfactory.

In particular, untimely ignitions of such igniters have been observed on numerous occasions, in particular by remote influence by electromagnetic waves. It is understood that such untimely firing of devices for initiating pyrotechnic compositions can have serious consequences, in particular in ammunition storage areas.

As indicated for example in the magazine AIR ET COSMOS / AVIATION MAGAZINE n ^s 1402-6 December 1992, there is today a strong demand for ammunition known as attenuated risk.

Current attempts to improve existing initiation devices of the aforementioned type have not been successful.

In addition, pyrotechnic systems with microwave initiation have been proposed on various occasions (see for example documents US-A-3601054, GB-A-2241563, D & A-3131332, EP-A-235010).

However, such systems have not hitherto given rise to large-scale operation.

The object of the present invention is to propose improved means for initiating pyrotechnic compositions. According to a first aspect of the present invention, the above object is achieved by an initiation process comprising the step which consists in coupling a microwave generator and a pyrotechnic composition block comprising charges with resistive electrical losses and / or magnetic, sensitive to microwaves, and to control the microwave generator in a suitable way to synthesize a shock wave equivalent to a detonator.

It is known that detonators are devices designed to apply shock waves to pyrotechnic compositions, while igniters have the function of transmitting a thermal effect.

According to a first advantageous characteristic of the invention, the above-mentioned method is implemented using a single microwave applicator.

According to a second advantageous characteristic of the invention, the aforementioned method is implemented using several applicators controlled successively in a controlled sequence. This controlled sequence is preferably such that the ratio between the distance separating the different applicators and the time interval between the application of microwave energy to these applicators is substantially equal to the speed of mechanical propagation in the pyrotechnic material, in detonating regime.

According to a third advantageous characteristic of the invention, the aforementioned method is implemented using electrically conductive lines, generally divergent in proximity to the coupling on the generator, and placed in the mass of the pyrotechnic composition.

According to a second aspect of the present invention, the above object is achieved by means of an initiation device of the type comprising:

- a microwave generator, and

a block of pyrotechnic composition comprising charges with resistive and / or magnetic electrical losses, sensitive to microwaves, adapted to be coupled to the microwave generator, in which there is further provided a directional coupler coupled to the line of preferably at the output of the microwave generator, and sensitive to the wave reflected on the end thereof, means for controlling the low power microwave generator and means for controlling the wave reflected at the end of the line.

Other characteristics, aims and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the appended drawings given by way of nonlimiting examples and in which:

FIG. 1 previously described represents a schematic view of an igniter according to the state of the art,

FIG. 2 represents a schematic view of an initiation device according to the present invention with a single applicator,

FIGS. 3 and 4 respectively represent two alternative layouts of a microwave application line on a block of pyrotechnic composition,

FIG. 5 schematically illustrates the production of an assembly bringing together different initiation devices in accordance with the present invention for the sequential firing of a plurality of munitions,

- Figure 6 shows an alternative embodiment of a device according to the present invention for the design of a detonator, using multiple applicators, - Figures 7 and 8 show two implementation variants with lines electric integrated in the composition 102, and

- Figure 9 shows a variant with multiple applicators spread evenly around the composition.

There is shown in Figure 2 attached, schematically, an embodiment of an initiation device according to the present invention.

This device comprises a block of suitable pyrotechnic composition 102, sensitive to microwaves, placed in a box 100. The box

100 can be the subject of numerous embodiments. It will therefore not be described in detail below. It will simply be noted that the housing 100 must be locally transparent to the microwave.

The pyrotechnic composition block 102 can also be formed from any suitable conventional pyrotechnic composition provided that this composition 102 is sensitive to microwaves and includes resistive and / or magnetic electrical loss charges. The aforementioned fillers can be formed for example of graphite, ferrite or metallic oxides or even of any equivalent material.

The device shown in FIG. 2 is completed by a control circuit 1 10 comprising a microwave generator 1 1 1 selectively coupled, by a line 120, to the block 102 of pyrotechnic composition.

Selective coupling of generator 1 1 1 to block 102 can be obtained by directly connecting the output of generator 1 1 1 to a microwave application line on block 102 and by controlling generator 1 1 1 in all or nothing or by modulating the power output thereof.

More specifically, according to the embodiment shown in Figure 2, the microwave generator 11 1 is coupled to line 120 by means of a switch 130 consisting of a PIN diode. The PIN diode 130 thus constitutes a microwave switch. However, the invention is of course not limited to the use of such a particular switch.

More precisely, the output 1 12 of the microwave generator is connected to the anode of the PIN diode 130 by means of a coupling capacitor C1 13. The cathode of the PIN diode 130 is coupled to the line 120.

Line 120 is itself coupled to composition 102 by capacitive coupling.

The control circuit shown in Figure 2 also includes a controller module 140 whose function is to apply a bias voltage on the PIN diode to make it selectively conductive and allow the passage of microwaves, generator 1 11, on block 102 in order to initiate it.

More specifically, the output 141 of the controller 140 is connected to the anode of the PIN diode 10 by means of an inductor L142. In addition, the cathode of the PIN diode 130 is connected to ground via a second inductor L143 allowing the closure of the bias circuit.

The operation of the initiator device shown in Figure 2 is essentially as follows. As long as the controller 140 does not apply the adequate bias voltage to the anode of the PIN diode 130, the latter is blocked in the non-conducting state. The microwaves from the generator 1 1 1 cannot therefore be applied to line 120 and therefore cannot therefore be applied to pyrotechnic composition 102. In this state, the device has great immunity to untimely initiations.

When the controller 140, on the other hand, applies the correct bias voltage to the anode of the PIN diode 130 via the inductor L142, this PIN diode 130 is turned on. The microwaves from the HF generator 111 are then applied via the PIN diode 130 on the line 120, and from there on the pyrotechnic composition block 102. This application of microwaves causes a rise in temperature in the area of resistive and / or magnetic loss charges of block 102. This area can typically be of the order of lmm ² . Once this rise in temperature is obtained, the propagation throughout the block 102 occurs rapidly.

More precisely within the framework of the invention, the controller 140 applies on line 141 a sequence of polarization pulses adapted to generate in composition 102 a shock wave of speed substantially equal to the speed of mechanical propagation in the material in detonating regime in order to synthesize a shock wave equivalent to a detonator.

In the context of the invention, it is not necessary to provide screens, in the mass of the pyrotechnic composition 102, to confine the microwaves coming from the line 120. In fact, the confinement of the microwaves is obtained by locating resistive and / or magnetic loss charges near line 120.

It should be noted that preferably, apart from the presence of charges with resistive and / or magnetic electrical losses in the microwave application area, the entire pyrotechnic composition 102 is homogeneous. As a result, the propagation of the initiation takes place in a homogeneous material of the same nature as the zone initiated by the microwaves. Thanks to this arrangement, an excellent communicability of the initiation and a rapidity of the transfer thereof are obtained. Current microwave components allow powers much higher than lkW / mm ² . It is understood that the use of a microwave initiator therefore makes it possible to obtain a strong immunity with regard to external aggressions. Indeed, in the current state of the art, it is completely unthinkable to generate such a power density at a distance.

The PIN diodes currently available on the market allow ultra-fast switching on the order of nano-seconds, while pyrotechnic compositions have response times on the order of microseconds.

However, the invention is not limited to the use of a semiconductor switch of the PIN diode type. Thus, for example, in the context of the present invention, it is possible to envisage using a mechanical type switch interposed between the HF generator 1 1 1 and the line 120.

FIG. 3 illustrates an example of installation of the application line 120 on the housing 100. As can be seen in FIG. 3, preferably the application line 120 is placed in the center of the face 104 of the base of the housing 100. More specifically, an electrically insulating sheet 106 is interposed between the application line 120 coming from the PIN diode 130 and the pyrotechnic composition block 102.

More precisely still, to improve the coupling between the line 120 and the composition block 102, there is preferably provided therein a first plate 107 of electrically conductive material, central, placed opposite the line 120, and an electrode electrically conductive annular ground 108. The electrode 108 surrounds the electrode 107.

The coupling defined through the insulating sheet 106 between the line 120 and the central electrode 107 is a coupling of the capacitive type. The guard ring 108 can be connected to ground by any suitable conventional means, for example by capacitive coupling with an external electrode 105 to ground.

Preferably the resistive and / or magnetic electrical loss charges placed between the central electrode 107 and the ground electrode 108 has an impedance tuned on line 120, for example from a few ohms to a few tens of ohms typically of the order of 50Ω. Of course, one can consider placing the line 120 from the PIN diode 130 in a different location from the center of the base 104 of the housing 100. Furthermore, the end 121 of the line 120 adjacent to the housing 100, as well as the face opposite 104 of the base of the housing 100 can be the subject of numerous geometries.

As shown in Figure 4, one can for example provide an end 121 of line 120 and a base 104 of housing 100 of generally complementary shape. More specifically, preferably the base 104 of the housing 100 has at its center a concave blind housing 109, for example frustoconical and the end 121 of the line 120 is formed of a generally complementary protuberance.

This arrangement guarantees better confinement of the microwaves in the pyrotechnic composition block 102. Furthermore, this arrangement makes it easier to center the block 100 on the applicator line 120. This last characteristic is particularly advantageous when the munitions equipped with the composition 102 are placed in removable chargers. It is indeed appropriate in this case to place with precision the block of pyrotechnic composition 102 relative to the applicator line 120 which is generally placed in a fixed and reusable base.

FIG. 5 shows the structure of an assembly comprising different blocks of pyrotechnic composition 102 associated with respective switches 130 for firing in sequence a plurality of munitions.

Such an assembly can be used for example for the sequential launch of lures in the field of countermeasures.

We find in FIG. 5, for each block of pyrotechnic composition 102, a line 120 connected to the output of the microwave generator 111 by means of a PIN diode 130. Each PIN diode 130 is connected by a capacitor of coupling 1 13 on the output of the microwave generator 1 11. Furthermore, each PIN diode 130 has its anode connected to a respective output of the controller 140 via an inductor L142 and to its cathode connected to ground by a self L143. It is understood that within the framework of the embodiment represented in FIG. 5, the microwave generator 1 1 1 emits microwaves continuously during the firing period, and the controller 140 generates successively and in a controlled sequence, the appropriate bias voltages on its outputs to make the various PIN diodes 130 passably successive and consequently successively initiate the different compositions 102.

To allow a test function, that is to say to control the installation and / or the initiation of the pyrotechnic composition 102 following the generation of an adequate bias voltage at the output of the controller 140, provision is made for preferably, in the context of the present invention, to associate with the output 1 12 of the generator 1 1 1, a proximity directional coupler 150 sensitive to the reflected wave.

In practice, the coupler 150 can be placed at any point between the output 112 of the generator 111 and the end 121 of the line. However, the coupler 150 is preferably connected to the output of the generator 1 1 1. This arrangement makes it possible to avoid multiplying the couplers 150 when the generator 111 attacks several loads.

The signal from this directional coupler 150 is applied to the control module 152 comprising the microwave generator 1 1 1 and the controller 140. To process the signal from the coupler 150, the module 152 controls the microwave generator to reduced power. In this configuration, the power generated by the microwave generator 1 1 1 must be insufficient to cause the untimely initiation of block 102. When the microwave generator 11 1 thus works at reduced power and the PIN diode 130 is enabled by the generation of an appropriate bias voltage at the output of the controller 140, the presence of a reflection detected by the coupler 150 signals the absence of charge 102. On the other hand, the absence of such reflection detected by the coupler 150 signals the presence of a load 102 opposite the end of the line 120. In fact, as indicated previously, the load 102 being adapted to the terminal impedance of the line 120, it absorbs microwaves, when present, and thus avoid any reflection on the end of line 120. This test function can be used, on the one hand to check the correct positioning of an ammunition loader on a base housing the control module 152 and the application lines 120. This test function can also be used to control the effect of an initiation by the controller 140 and reiterate the command sequence in the event of failure.

The signal from the coupler 150 can also be applied in feedback to the HF generator 11 11 in order to tune it on the line and guarantee a maximum amplitude of the microwaves applied to the load 102.

In practice, the microwave generator 11 1 can be formed of a self-oscillator or of a voltage-controlled oscillator associated with a power amplifier.

It should be noted that in the context of the present invention, taking into account the powers involved, it is possible to place the charges with resistive and / or magnetic electrical losses, not in the primary, but in the secondary, or even directly in the main charge of the ammunition concerned. Thus, the present invention makes it possible to reinforce security by eliminating the use of primary, even secondary, which we know to be very sensitive to temperature. According to the above-mentioned embodiments, the invention synthesizes a detonator using a single microwave applicator.

The present invention also proposes to produce a detonator using an initiation device with multiple applicators. To this end, as shown in FIG. 6, it is proposed in the context of the present invention, to associate different applicators 120 with the same block of pyrotechnic composition 102, which applicators 120 receive successively, via diodes PIN 1 30 respectively, the microwaves coming from the microwave generator 111.

By a suitable sequencing of microwave applications, that is to say by a suitable sequencing of the control of the various PIN diodes 130, the controller 140 can synthesize waves equivalent to those of a conventional detonator. More precisely, for this, in the context of the present invention, the controller 140 applies to the various PIN diodes 130 a sequence of respective control pulses separated from each other by a time Δt such that the ratio between the distance separating the different applicators 120 and this time difference Δt is substantially equal to the mechanical propagation speed in the composition 102, in detonating regime.

By way of nonlimiting example, the Applicant has obtained satisfactory results with a composition 102 formed from a tolite type explosive whose propagation speed in detonating regime is of the order of 4 km / s, and applicators 120 spaced between 10 mm and powered by lkW pulses sequenced at 0.6 μs.

In addition, the initiation device according to the present invention can be used to directly attack a conventional primer, as shown in FIG. 1. More specifically, it is possible to envisage placing an applicator

120 directly against the housing 10 of a conventional primer, if the latter comprises charges adapted to resistive electrical losses or to magnetic losses. If the conventional primer does not include such charges with resistive and / or magnetic electrical losses, the initiation of a conventional primer can be obtained by juxtaposing therewith an adequate composition block 102 provided with such charges, associated with an applicator 120.

It is understood that the advantage of initiating a conventional primer is to allow the use of existing ammunition stocks with an initiator in accordance with the present invention.

The control circuit comprising the microwave generator 111, the controller 140 and the switch formed by the PIN diode 130 can be designed as a consumable or reusable product.

The initiation device according to the present invention can be used for any type of ammunition such as missile, bomb, shell, etc. The initiation device according to the present invention offers the advantage of being insensitive to attack external, in particular to thermal shock such as fire, to mechanical shock, such as bullet impacts or detonations, and insensitive to external electromagnetic influences. According to another variant of implementation shown diagrammatically in FIGS. 7 and 8, it is possible to synthesize a shock wave equivalent to a detonator by placing in composition 102 electrically conductive lines 160, 162 generally divergent in approximation of the coupling on the generator. 11 1, and placed in the mass of the pyrotechnic composition 102. In this case the generator 1 1 1 can permanently supply the lines 160, 162 and no longer impulse as indicated above.

According to Figure 7, these lines 160, 162 are rectilinear. According to Figure 8, these lines 160, 162 are broken, not straight.

The arc generated between lines 160, 162 during the commissioning of generator 111 starts on the ends of lines 160, 162 furthest from generator 1 1 1, that is to say the most close to these lines. Then the arc gradually approaches generator 111, by ionization of composition 102, with a speed v = c / (ε _r μ _r ) ^1/2 , relationship in which ε _r represents the dielectric constant and μ _r represents the permeability magnetic composition

102.

It suffices to adapt ε _r and μ _r so that the speed of propagation of the arc is substantially equal to the speed of mechanical propagation in composition 102, in detonating regime, to synthesize there again a detonator.

It is necessary to protect the generator 1 1 1 from the destructive effect of the ascent of this arc. The introduction of an optical sensor for example between the generator 1 1 1 and the lines 160, 162 can give satisfaction for this purpose.

Of course the present invention is not limited to the particular embodiments which have just been described but extends to any variant in accordance with its spirit. Thus, the present invention can be used to ignite the initiation device by passing it in front of an applicator 120, thanks to the capacitive coupling then obtained between the applicator 120 and the pyrotechnic composition 102. In other terms, we can provide a dynamic arrangement between applicator 120 and composition 102, and not only static. The present invention also applies to an arrangement of applicators 120 distributed evenly around composition 102, for example but not limitatively of circular or semi-circular contour.

Claims

1. A method of initiating a pyrotechnic composition (102) of the type comprising the step which consists in coupling a microwave generator (11) and a block of pyrotechnic composition (102) comprising charges with resistive electrical losses and / or magnetic sensitive to microwaves, characterized in that it consists in controlling the microwave generator (11 1) in a manner adapted to synthesize a shock wave equivalent to a detonator.

2. Method according to claim 1, characterized in that it is implemented using a single microwave applicator (120).

3. Method according to claim 2, characterized in that the microwave applicator (120) is supplied with a sequence of pulses adapted to generate a shock wave traveling at a speed substantially equal to the propagation speed mechanical in detonating regime in the composition (102).

4. Method according to claim 1, characterized in that it is implemented using multiple applicators (120) of microwaves.

5. Method according to claim 4, characterized in that the applicators (120) are successively supplied in a controlled sequence such that the ratio between the distance separating the different applicators (120) and the time interval between the application d microwave energy to these applicators, ie substantially equal to the speed of mechanical propagation in the pyrotechnic composition, in detonating regime.

6. Method according to claim 1, characterized in that it is implemented using electrically conductive lines (160, 162), generally divergent in approach of the coupling on the generator (1 1 1) and placed in the mass of the pyrotechnic composition (102).

7. Method according to claim 6, characterized in that the dielectric constant ε _r and the magnetic permeability μ _r of the pyrotechnic composition (102) are adapted to obtain a speed v = c / (ε _r μ _r ) ^{1 2} in the composition, substantially equal to the speed of mechanical propagation in detonating regime.

8. Method according to one of claims 1 to 7, characterized in that it further consists in coupling a directional coupler (150) to the microwave applicator line (120), preferably at the output of the generator (111), to control the microwave generator (11 1) at reduced power and to control the wave reflected on the end of the line, using the directional counter (150).

9. Method according to one of claims 1 to 8, characterized in that it consists in connecting a PIN diode (130) to the microwave generator (1 1 1) via a coupling capacitor (Cl 13) and applying a controlled bias voltage to this PIN diode (130) to make it passable, by means of an inductor (L142).

10. Pyrotechnic composition initiation device, of the type comprising:

- a microwave generator (111), and - a block (102) of pyrotechnic composition comprising charges with resistive and / or magnetic electrical losses sensitive to the microwave, suitable for being coupled to the generator, characterized in that '' It further comprises a directional coupler (150) coupled to the line (1 12) preferably at the output of the generator (1 1 1) of microwave application, and sensitive to the wave reflected on the end thereof, means for controlling the microwave generator (1 1 1) at reduced power and means for controlling the wave reflected on the end of the line (120).

11. Device according to claim 10, characterized in that the fillers are included in the group comprising graphite, ferrites and metal oxides.

12. Device according to one of claims 10 or 1 1, characterized in that a controlled switch (130) is interposed between the microwave generator (111) and a line (120) designed to be placed nearby of the pyrotechnic composition block (102).

13. Device according to claim 12, characterized in that the switch (130) is a mechanical switch.

14. Device according to claim 12, characterized in that the switch (130) is formed by a PIN diode.

15. Device according to claim 14, characterized in that the microwave generator (1 1 1) is connected to the PIN diode via a coupling capacitor (C l 13) and in that the device comprises a controller (140) capable of applying a controlled bias voltage to the PIN diode (130), to make it passable, via an inductor (L142).

16. Device according to one of claims 10 to 15, characterized in that it comprises a line (120) of microwave application connected to the microwave generator (11 1) and adapted to be placed in look from the center of the base (104) of the block (102) of pyrotechnic composition.

17. Device according to one of claims 10 to 16, characterized in that the block (102) of pyrotechnic composition, comprises at its base, an electrically insulating plate (106), and inside its mass , a first plate (107) adapted to be capacitively coupled to the microwave application line (120) through the insulating plate (106), as well as a ground electrode.

18. Device according to one of claims 10 to 17, characterized in that the charges with resistive and / or magnetic electrical losses form an impedance tuned to the line (120), for example from a few ohms to a few tens of ohms , typically of the order of 50Ω.

19. Device according to one of claims 10 to 18, characterized in that the block (102) of pyrotechnic composition comprises a base provided with a concave housing (109), preferably frustoconical, capable of receiving the complementary end of the line (120).

20. Device according to one of claims 10 to 19, characterized in that it comprises a coupler (150) coupled to the line (112) and means for applying the signal from the coupler (150) in feedback on the microwave generator (111).

21. Device according to one of claims 10 to 20, characterized in that it comprises means capable of synthesizing a shock wave equivalent to a detonator.

22. Device according to claim 21, characterized in that it comprises a single microwave applicator (120).

23. Device according to claim 21, characterized in that the applicator (120) is supplied with a sequence of pulses adapted to generate a shock wave traveling at a speed substantially equal to the speed of mechanical propagation in detonating regime in the composition (102).

24. Device according to claim 21, characterized in that it comprises multiple applications of microwaves (120) coupled to a common pyrotechnic composition (102).

25. Device according to claim 24, characterized in that the applicators (120) are successively supplied in a controlled sequence such that the ratio between the distance separating the different applicators (120) and the time interval between the application d microwave energy to these applicators (120) is substantially equal to the speed of mechanical propagation in the pyrotechnic composition, in a detonating system.

26. Device according to claim 21, characterized in that it comprises electrically conductive lines (160, 162) generally divergent in approach of the coupling on the generator (111) and placed in the mass of pyrotechnic composition (102).

27. Device according to claim 26, characterized in that the dielectric constant ε _r and the magnetic permeability μ _r of the pyrotechnic composition (102) are adapted to obtain a speed v = c / (ε _r μ _r ) ^1/2 in the composition, substantially equal to the speed of mechanical propagation in detonating regime.

28. Device according to one of claims 10 to 27, characterized in that the microwave generator is connected directly to the microwave application line on the block (102) of pyrotechnic composition and by the fact that the selective coupling of the generator (1 1 1) to the block (102) is obtained by controlling the generator (111) in all or nothing or by modulating the output power of the latter.

29. Assembly comprising different microwave applicators (120) associated with blocks (102) of respective pyrotechnic composition according to one of claims 10 to 28, and a sequencer (140) adapted to command the initiation, according to a pre-established sequence, of the different blocks (102) in order to ignite respective munitions.