GB2117948A - Initiation of devices by high- frequency sound waves - Google Patents

Abstract

In order to initiate operation of a device (27, 28, 29), such as an explosive device, an electrical signal from a source (17) is fed to a transmitter transducer (14, 15, 16) which emits high-frequency ultrasonic waves into a solid member (2) which preferably forms part of an existing structure, such as the framework of an aircraft. The ultrasonic waves are received by a receiver transducer (23, 24, 25) which is rigidly fixed to the structure, and the resultant transducer output is fed to the device which is to be initiated. The electrical signal may be modulated (18) so that the ultrasonic waves carry encoded information. This information may be used at the receiving end to select a particular device for initiation and/or to provide a security check before operation of a device is initiated. The receiver transducer may comprise two back-to-back transducer units which are so coupled as to cancel out signals produced therein due to spurious vibrations in the structure. A plurality of transmitter transducers and a plurality of receiver transducers, operating at mutually different frequencies, may be used, so that a respective device may be operated by each frequency. <IMAGE>

Description

SPECIFICATION Initiation of devices by high-frequency sound waves This invention relates to the initiation and switching of signal-responsive devices, such as electrically-excited ordnance devices, by means of ultra-high-frequency sound waves which are transmitted through substantially solid material interfaces.

The majority of explosive and ordnance devices and the units associated with their initiation, both in the commercial and military fields, are controlled either by electrical induction or by the direct application of an electrical supply. Work has also been done on initiation systems using optical signals transmitted through fibre optic light-guide systems.

It is an object of the present invention to provide apparatus whereby devices, such as explosive devices, ordnance devices, and/or electrical or electronic units which control such items or devices may be initiated, fused, or selected, either singly or in combination, using ultra-high-frequency sound waves.

According to the invention, apparatus for initiating operation of a device, such as an explosive device, comprises a transmitter transducer; means to feed electrical signals to the transmitter transducer to cause it to emit ultrahigh-frequency sound waves; at least one receiver transducer; a member along which sound waves emitted by the transmitter transducer travel for reception by the receiver transducer; and means responsive to the received sound waves to initiate said operation.

Preferably, the member along which the sound waves travel comprises the mechanical structure of an assembly or sub-assembly to which the transducers are fitted.

The receiver transducer is preferably embedded in the structure or incorporated in the interior of the ordnance, explosive, or control device.

In addition to their use as a direct initiation input, the ultra-high-frequency sound waves may be used to provide uniquely-coded release order and fuzing signals.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of one form of initiation apparatus according to the invention, Fig. 2 is a schematic diagram of another form of initiation apparatus, in which operation of an explosive device is initiated by heat generated in a receiving transducer, Fig. 3 is a schematic diagram of a further form of initiation apparatus, in which the effect of mechanical shocks is cancelled out, Fig. 4 is a schematic diagram of another form of initiation apparatus whereby a plurality of devices may be initiated independently, Fig. 5 is a schematic sectional view of a cartridge incorporating a receiving transducer, and a breech provided with a transmitting transducer, Fig. 6 is a schematic sectional view through a casing incorporating back-to-back mounted transducer crystals, Figs. 7 (a) and 7(b) illustrate the mode of operation of the back-to-back crystals, Fig. 8 is a pictorial view of a transducer crystal, Fig. 9 is a sectional view through a crystal mounted in the end of a cartridge case.

Referring to Fig. 1 of the drawings, an ultrasonic transmitting transducer 1 is rigidly attached to a member 2 which forms part of a structure, such as an aircraft frame. The transducer 1 may be located close to the cockpit of the aircraft. A receiving transducer 3 is rigidly attached to the member 2, or to another part of the structure which is in sound-transmitting contact with the member 2.

The transducer 1 is connected to a source 4 of high-frequency electrical signals, the frequency being, for example, in the range 1 OOKHz to 500KHz, via a screened cable 5. The transducer 3 is connected via a screened cable 6 to a device 7 which is to be initiated.

In use of the apparatus, when the device 7 is to be initiated, a signal is fed over the line 5 from the source 4 to the transducer 1, causing the transdeucer to emit an ultrasonic wave into the member 2. The wave travels along the member 2, and any other intermediate structure, and impinges upon the transducer 3. The transducer 3 produces a corresponding electrical output, which is fed over the line 6 to initiate the device 7. The device 7 may be, for example, a cartridge which fires an ejector seat.

The signal produced by the source 4 may be modulated by a signal from a modulator 8 to provide uniquely-coded release and/or fuzing commands, which are decoded by the device 7, thereby ensuring that it responds only to correct commands.

The operating frequency of the transducer 1 is chosen to be higher than any frequency which exists in the structure forming the ultrasonic transmission path, under all expected and abnormal operational conditions.

Referring to Fig. 2, in which the same reference numerals indicate the same parts as in Fig. 1 , the transducer 3 is attached directly to, or is contained integrally within, a device 9. This device may be a cartridge which is filled with an explosive powder or mixture of powders of a type which is fired by a device operating at a relatively low temperature, so that energisation of the transducer 3 by the received ultra-sonic wave produces sufficient heat to fire the explosive.

Referring to Fig. 3, a receiver transducer assembly 10 preferably comprises two transducing units 11 and 12 of identical cut, mounted back-to-back. They are electrically interconnected in order that mechanical shocks will not cause generation of spurious electrical outputs which will fire the device 7. The outputs of the transducing units 11 and 12 are fed to a summer 13, so that intentionally-generated signals of the correct frequency result in the summing of the outputs from the two units. The separation of the two transducing units is chosen to be sympathetic with the operating frequency and sensitivity of the units.

In the embodiment shown in Fig. 4, a plurality of transmitting transducers 14, 1 5 and 1 6 are connected to a source 1 7 which provides signals on lines 20-22, respectively, for feeding the transducers. The signals are of mutually different frequencies, so that three ultrasonic waves of different frequencies are emitted along the member 2.

Three receiver transducer back-to-back pairs 23-25 are arranged to receive the ultrasonic waves. The receiver transducers are designed to resonate at a respective one of the ultrasonic frequencies, and so respond fully to only the respective one of the transmissions. The transmitted waves can be modulated by a modulator 18, and a decoder 26 is connected to the receiver transducer outputs to decode the modulation signals. For security purposes, the decoded signals may be effective to fire respective devices 27-29 only when the code content of the signals has been verified by the decoder 26.

Instead of using a plurality of transmitter and receiver transducers and a plurality of transmitted frequencies, a single frequency may be used, and seiection between a plurality of devices may be made by encoding the modulation to represent a particular device which is to be initiated, and steering the initiation signal to that device by decoding the received modulation.

The position of attachment of the transducers to the framework is appropriate to, and dependent upon, the size and shape of the framework; the construction of the framework; the size, shape and power of the transducers; and the sensitivity of the device it is required to initiate.

Although the above embodiments have been described in relation to transmission of ultrasonic waves through the framework of an aircraft, the invention may be used in other situations in which ultrasonic waves can be transmitted through a solid member or structure to which both the transmitter and receiver transducers are rigidly attached. For example, the member may be a container in which the device to be initiated is housed.

Such an arrangement is illustrated in Fig. 5.

which shows an aluminium cartridge case 30 within a steel breech 31. A piezo-ceramic crystal transducer 32 having electrodes 33 is bonded to the inner surface of the base of the case 30. A fuze gap 34 is provided between the ends of the electrodes. The case is packed with an explosive compound 35 which is electrically-conductive, so that current passed through the compound by energisation, of the transducer 32 will cause heating, and hence firing, of the compound.

A transmitting piezo-ceramic crystal transducer 36 is bonded to the outer surface of the breech 31 and, when energised by application of a highfrequency signal to input leads 37, transmits an ultrasound beam 38 through the breech 31 and the cartridge base, the beam being refracted at the steel/aluminium interface 39 between the breech and the case.

One particular form of receiving transducer is shown in Fig. 6. The transducer 40 comprises two back-to-back crystals 41 and 42 mounted within a casing 43 and insulated therefrom by a sleeve 44 of insulating material. A double-sided printed circuit board 45 is mounted between the transducer 40 and an annular flange 46 within the casing, so that conductors on the board make contact with output conductors of the transducer and provide a fuze gap. The remainder of the casing is filled with conductive explosive compound 47, which is retained in the casing by a diaphragm 48. The transducer 40 has a threaded boss 49 by which it is retained in a threaded aperture 50 in a case 51.

The crystals 41 and 42 are aligned such that the boundary between them is perpendicular to the direction 52 of the ultrasonic energy which is transmitted to them. Referring to Fig. 7(a), it will be seen that any mechanical shock applied to the crystal will cause electrical outputs of the same polarity to be produced at the outer ends of the crystal assembly, so that virtually no voltage is produced at a fuze gap 53. On the other hand, it will be seen from Fig. 7(b) that each of the crystals has a thickness of half a wavelength of the ultrasound signal, so that the voltages produced by the crystals due to the ultrasound signal impinging thereon are additive, and a relatively large voltage is produced at the gap 53.

A pictorial view of a piezo-ceramic receiving transducer crystal 54 is shown in Fig. 8. The flat ends of the crystal are provided with silver plated electrodes 55 and 56. The lower electrode 56 is linked to a further electrode 57 on the upper side (as viewed in Fig. 8) of the crystal by a silver plated link track 58, which may, if required, be provided with a series spark gap 59. The working gap 60 for firing the explosive is provided between the adjacent edges of the electrodes 55 and 57.

The mounting of such a transducer crystal 54 in a cartridge case 61 is shown in Fig. 9. The crystal is bonded to the base of the case within a chamber 62 formed in an annular boss 63. The upper end (as viewed in Fig. 9) of the crystal is encircled by a silicon rubber acoustic and electrical isolator ring 64, and the space within the chamber above the ring is filled with a conductive explosive compound 65. The compound is retained in the chamber by a closure cap 66 which engages with an enlarged rim 67 of the boss 63. A thin copper disc 68 is bonded to the outside of the case 61, in alignment with the crystal 54, to provide coupling to a transmitting transducer (not shown).

If two receiving crystals as shown in Fig. 8 are to be mounted back-to-back, the electrode 56 of one crystal will be bonded to the cartridge case; the other surface of that crystal will have an allover electrode with which the electrode 56 of the second crystal makes contact, the second crystal will be provided with an electrode arrangement 55, 57 as in Fig. 8; and that electrode 57 will be connected to the electrode 56 of the first crystal by a link electrode.

Advantages of ultra-high-frequency sound initiation control of live ordnance, explosive and other devices are: a) the ability to utilise simple mechanical transmission lines comprising part of existing structures, b) the controlled devices can, with respect to the signal source, be totally enclosed in metal containers of substantial strength, there being no necessity for discontinuities in the containers such as are associated with conventional electrical initiation, c) a metal container, in addition to forming an effective shield against possible RF and EMC hazards, also prevents the ingress of contaminants into the device, d) imperfect filling and forming of explosive devices does not impair the ignition efficiency, e) unique frequency coding, selection, and routing sequences are possible without recourse to complex electronic switching networks, f) piezo-ceramic or magnetostrictive transducers are stable devices which need neither tuning components nor ancillary items, g) the system is impervious to extraneous electrical noise, h) initiation or fuzing signals can be transmitted through solid bulkheads or breeches irrespective of the material.

Claims (8)

1. Apparatus for initiating operation of a device, such as an explosive device, comprising a transmitter transducer; means to feed electrical signals to the transmitter transducer to cause it to emit ultra-high-frequency sound waves; at least one receiver transducer; a member along which sound waves emitted by the transmitter transducer travel for reception by the receiver transducer; and means responsive to the received sound waves to initiate said operation.

2. Apparatus as claimed in Claim 1 , wherein the member along which the sound waves travel comprises the mechanical structure of an assembly or sub-assembly to which the transducers are fitted.

3. Apparatus as claimed in Claim 1 or Claim 2, including means to modulate the electrical signals so that the modulation carries encoded data; and means coupled to the receiver transducer to decode the received modulation and to select a device to be initiated as a result of the decoding.

4. Apparatus as claimed in Claim 1 or Claim 2, wherein the device is an explosive device which can be fired by application of a relatively small amount of heat thereto; and wherein the receiver transducer is in intimate contact with the device so that heat generated within the receiver transducer due to the receipt of the sound waves is sufficient to fire the device.

5. Apparatus as claimed in Claim 1 or Claim 2, wherein the device is an explosive device comprising an electrically-conductive explosive; and wherein the receiver transducer is operative in response to the sound waves to pass an electric current through the explosive to fire it.

6. Apparatus as claimed in any preceding claim, wherein the or each receiver transducer comprises two transducer units mounted back-to-back, whereby signals produced therein due to spurious mechanical vibrations produced in the member are cancelled out.

7. Apparatus as claimed in any preceding claim, including a plurality of transmitter transducers to which electrical signals of respectively mutually different frequencies can be fed; and a corresponding plurality of receiver transducers having mutually different resonance frequencies corresponding respectively to the frequencies of the electrical signals, whereby a respective device is initiated by receipt of sound waves of the respective frequency by a said receiver transducer.

8. Apparatus as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.