System and method to detect and deactivate or detonate explosive devices

Abstract

System to detect and deactivate or detonate explosive devices, which includes: - an electronic oscillator (5) configured to generate a strong high-frequency alternating magnetic field through a resonant circuit (6) formed by a capacitor (9) in parallel with a metal coil (10), preferably with an external diameter greater than 50 mm; - a power and control device (2), connected by cable (4) to the electronic oscillator (5), which comprises: a battery (14), a power converter (15) to, when activated, feed the electronic oscillator (5) with the amplified battery voltage, at least one switch (16,29) configured to activate the power converter (15) or deactivate it and feed the electronic oscillator (5) with the battery voltage (14), and an explosive detection unit (17) to detect changes in the resonance frequency (feq) of the electronic oscillator (5) when the power converter (15) is deactivated.

Description

Field of invention

[0001] The present invention is included in the field of electromagnetic systems for the detection, destruction or detonation of improvised explosive devices (IED), mines, bombs and other explosive devices.Background of the invention

[0002] Currently there are portable systems by an operator to detect explosive devices, such as mines. However, there are no known portable systems that allow, in addition to the detection, deactivation or detonation of explosive devices.Description of the invention

[0003] The invention relates to a system and method for detecting and deactivating or detonating explosive devices.

[0004] The system for detecting and defusing or detonating explosive devices comprises a magnetic head and a power and control device. Both elements are connected by a long cable (e.g. 50 meters), preferably reelable on a drum.

[0005] The magnetic head is configured to generate an alternating magnetic field and includes an electronic oscillator comprising a resonant circuit, a feedback circuit, and an amplifier circuit. The resonant circuit includes a condenser in parallel with a metal coil responsible for generating the alternating magnetic field when an alternating current at a certain resonance frequency flows through the coil. The feedback circuit comprises a transformer with a first winding in parallel with the capacitor of the resonant circuit. The feedback circuit is configured to provide the amplifier circuit, via a second transformer winding, with a positive feedback current from the resonant circuit. The amplifier circuit, which comprises at least one power transistor, is configured to amplify the feedback current coming from the resonant circuit. The frequency range of the electronic oscillator is preferably between 40 kHz and 1MHz, although ISM (industrial, scientific and medical) radio bands can also be used, especially the low frequency bands, centered on 6.75MHz, 13.56MHz or 27.12MHz.

[0006] The power and control device comprises a battery, a power converter, at least one switch and an explosive detection unit. The power converter is configured to, when activated, supply the electronic oscillator with a higher DC voltage (e.g. 8 times higher) than that supplied by the battery. The at least one switch (which can be part of the power converter or be a separate element) is configured to toggle between at least two states including: - A first state in which the power converter is activated. - A second state in which the power converter is deactivated, so that the electronic oscillator is supplied with a direct voltage equal to or less than that supplied by the battery.

[0007] The explosive detection unit is configured to detect changes in the resonant frequency of the electronic oscillator when the power converter is turned off.

[0008] On the one hand, the system allows the detection of explosive devices, for which the power converter must be deactivated and the electronic oscillator fed with battery voltage (i.e. without amplifying its voltage), and use the explosive detection unit. On the other hand, the system also allows deactivating or detonating explosive devices by activating the power converter. Preferably, a certain activation and deactivation pattern of the power converter is used to perform the deactivation or detonation of the explosive devices.

[0009] With respect to the function of deactivation or detonation of explosive devices, the system of the present invention aims to generate a product w· B ( w= 6.28 f, where f is the frequency and B is the magnetic flux density) as as large as possible in order to destroy any electrical circuits to neutralize the explosive device, or heat the metallic parts of the explosive device to (i) change the state of the secondary explosive from solid to liquid (e.g. TNT, around 90°C) to deactivate the explosive device, (ii) change the state of the secondary explosive from liquid to gas (e.g. evaporate TNT, around 220°C) to defuse the explosive device, or (iii) detonate the explosive device.

[0010] The method for detecting and defusing or detonating explosive devices employs the system described above. The method comprises the following stages: Perform a sweep of the magnetic head in a search area. Detect, by means of the explosive detection unit, changes in the resonance frequency of the electronic oscillator during the scan. Determine a position of the coil of the magnetic head that produces a greater change in the resonant frequency of the electronic oscillator. Activate and deactivate, through at least one switch, the power converter according to the following activation patterns: • Activate the power converter in a series of short activation pulses with a duration less than a first activation threshold. • If there has been no detonation of the explosive device, activate the power converter in a series of long activation pulses with a duration greater than a second activation threshold, with the second activation threshold being greater than the first activation threshold. Brief description of the drawings

[0011] Next, a series of drawings that help to better understand the invention and that are expressly related to an embodiment of said invention that is presented as a non-limiting example thereof, is briefly described. Figure 1 shows the elements of a system for detecting and defusing or detonating an explosive device according to the present invention. Figure 2 illustrates components of a system of the present invention according to one embodiment. Figure 3 represents an embodiment example of the system. Figure 4 shows an example of a magnetic head. Figures 5A and 5B show the extension of the cable in the deactivation or detonation stage of an explosive device. Figure 6 is a flowchart of a method for detecting and defusing or detonating explosive devices using the above-described system. Figure 7A represents the scanning of the magnetic head in a search area. Figure 7B shows the placement of the coil in a certain position in which the greatest change in the resonant frequency of the electronic oscillator occurs during the sweep. Figure 8A shows an example of a circuit used as an electronic oscillator. Figures 8B and 8C illustrate several simulations carried out in said circuit. Figure 9A represents an example of an electrical circuit that includes the electronic oscillator and the power converter. Figure 9B illustrates a simulation carried out in said circuit. Figure 10 shows a scan of the coil to estimate the distance to a buried explosive device and, optionally, the mass of iron contained therein. Detailed description of the invention

[0012] Figure 1 illustrates in a simplified manner the components of a system 1 for detecting and deactivating or detonating an explosive device 10, such as a mine, bomb or an improvised explosive device (IED).

[0013] System 1 comprises a power and control device 2 and a magnetic head 3. Both elements are connected by at least one cable 4. Figure 2 illustrates the internal components of system 1 in more detail.

[0014] The magnetic head 3 is a unit configured to generate an alternating magnetic field. The magnetic head 3 includes a magnetic dipole formed by a circular coil that conducts high amplitude alternating current to generate a strong alternating magnetic field around the coil. The magnetic head 3 incorporates an electronic oscillator 5, which comprises a resonant circuit 6, a feedback circuit 7 and an amplifier circuit 8.

[0015] The resonant circuit 6 comprises a capacitor 9, of capacitance C, in parallel with a metallic coil 10, of inductance L, which determine a first resonant frequency f0 of the oscillator: f 0 = 1 2 π LC

[0016] The capacitor 9 is a low loss capacitor capable of working with at least 100 A, for example 500 A, 1 KV AC (thus 500 kVAR at high frequency, typically between 40 kHz and 1 MHz). Coil 10 is responsible for generating the alternating magnetic field when an alternating current circulates through the coil at a certain resonance frequency f of the oscillator.

[0017] In one embodiment, coil 10 has an outer diameter D greater than 50mm, preferably between 100mm and 600mm.

[0018] In one embodiment, the coil 10 is made of a hollow metal tube, with one or more turns (for example, a tube of copper or aluminium and with a section of 12 mm in diameter). The coil 10 can be implemented in other different ways; for example, by aluminium strips or sheets, by braided wire, etc. Stranded wire coils have lower high-frequency losses (due to lower resistance), but are difficult to cool and expensive to manufacture. Aluminium sheets are light, but provide less mechanical stability. Hollow copper or aluminium tube coils can be cooled by circulating air inside them.

[0019] Under normal use conditions, when there are no external elements close to the coil that interact with the magnetic field generated by it, the alternating current generated by system 1 in coil 10 has a resonance frequency feq equal to f0 (feq= f0). However, when the coil 10 is brought close to an explosive device 11 containing metal parts, the metal near the coil 10 changes the equivalent resonant frequency f eq of the electronic oscillator 5, by modifying the equivalent inductance Leq of the coil 10 in the resonant circuit 6. f eq = 1 2 π L eq C

[0020] For example, aluminum and other metals (gold, silver, copper) near coil 10 reduce the equivalent inductance Leq of coil 10 and increase the resonant frequency f eq , while iron increases the equivalent inductance L eq of coil 10 and reduces the resonant frequency f eq . There is normally iron in an explosive device 11, which causes a decrease in the resonant frequency f eq .

[0021] Figure 1 represents the magnetic field B p generated by the alternating current I p circulating through the coil 10 itself. Resonance is necessary to have a very high current I p in coil 10 and thus a very strong magnetic field Bp. Due to the fact that the current I p that circulates through the coil 10 is alternating, the magnetic field B p generated is variable in time. The magnitude of the magnetic field B p on the explosive device 11, located below the coil 10, also depends on its distance from the coil 10.

[0022] The variation in time of the magnetic field Bp generates, according to Faraday's law of electromagnetic induction, an induced current I s in the metallic part of the explosive device 11, which in turn generates a magnetic field Bs that impacts the coil, 10, changing the value of the equivalent inductance L eq of the coil 10 and, with it, the equivalent resonance frequency f eq of the electronic oscillator 5.

[0023] The amplifier circuit 8 provides the alternating current Ip in the coil 10, at the resonant frequency feq. The amplifier circuit 8 comprises at least one power transistor and is configured to amplify the feedback current coming from the resonant circuit 6.

[0024] The amplifier circuit 8 receives a positive feedback from the resonant circuit 6 through the feedback circuit 7, which comprises a transformer 12 with a first winding 12a (main winding) in parallel with the capacitor 9 of the resonant circuit 6. The feedback circuit 7 is configured to provide amplifier circuit 8, through a second winding 12b (a secondary winding) of transformer 12, a positive feedback current from resonant circuit 6.

[0025] During the operation of the system 1, high powers are used, which can excessively heat the metallic coil 10. Said overheating can be transmitted to the other components of the electronic oscillator 5. In order to maintain the temperature of the electronic components (e.g. semiconductors) below a maximum operating temperature (e.g. 100°C) during the transfer of high power to the device explosive 11, the metal coil 10 can be cooled by means of a cooling circuit, preferably by air. In one embodiment, the refrigeration circuit of the coil 10, integrated in the magnetic head 3, includes a compressor 13 or a fan (powered by the power and control device 2 from the voltage supplied by the cable 4) configured to force air to circulate inside the metal coil 10 formed by a hollow metal tube, as illustrated in the example of Figure 2.

[0026] The power and control device 2 is connected by cable 4 to the electronic oscillator 5 and comprises a battery 14 that provides power to the system, a power converter 15, a first switch 16 and an explosives detection unit 17. The power device and control 2 is used by an operator to detect explosive devices 11 and, once detected, defuse them by high voltage induction or detonate them by induction heating.

[0027] The deactivation or neutralization of the explosive device 11 can be produced by the heating produced in the metallic elements due to the alternating magnetic field in the coil 10, which induces Eddy currents in the metal of the explosive device 11. The induction can destroy the electronics of the explosive device 11, inducing over voltages and over currents. So, for example, in a bomb (which is usually a metallic hole with TNT or another secondary explosive), induction heats the metal, which then heats the TNT, which changes from a solid to a liquid state when heated above about 90°C. If the bomb hole has an exit, the TNT can come out as a liquid and the bomb is neutralized. If not, the liquid TNT cannot escape, prolonged and continuous induction can greatly heat the metal, reaching an explosion temperature (e.g. about 200°C) of the primary charge or changing the state of the secondary explosive from liquid to gas. Therefore, the system 1 is capable of deactivating explosive devices 11 or detonating them, depending on the type of explosive device and the heating profile used.

[0028] Battery 14 can be any portable power supply source including a battery, battery bank, and one or more supercapacitors, among other power sources. The battery can be, for example, 36 V and 150 A.

[0029] The power converter 15 is configured to supply the electronic oscillator 5 with a DC voltage greater than that supplied by the battery 14. In one embodiment, the power converter 15 supplies at least 8 times the voltage of the battery 14; for example, it transforms the 36 volts of the battery into 288 volts (8 times the voltage of the battery 14) of direct voltage that is supplied through the cable 4 to the electronic oscillator 5. The power converter can be, for example, of 5kW output. The power converter 15 may be a DC / DC converter (e.g. a DC / DC boost converter).

[0030] The first switch 16 is responsible for turning on or off (i.e. activate or deactivate) the power converter 15. When the power converter 15 is on (active or activated), it supplies the electronic oscillator 5 with a certain power (which can be regulated). at a DC voltage greater than that of the battery. When the power converter 15 is turned off (inactive or deactivated), the battery voltage is not increased; instead, the voltage of the battery 14 supplies the electronic oscillator 5 directly. The first switch 16 thus alternates between at least two states, a first state in which the power converter 15 is active, providing the electronic oscillator with a voltage greater continuous greater than the battery 14, and a second state in which the power converter 15 is inactive, so that it is the battery 14 that directly feeds the electronic oscillator 5.

[0031] The first switch 16 can be controlled manually, for example by means of a selector that allows an operator to select the power converter 15 on or off.

[0032] Alternatively, the first switch 16 can be controlled by a control unit, such as a microcontroller, based on an input received through an input means. For example, an operator can select on a control panel to turn the power converter 15 on or off, or even a certain output power of the power converter 15, and the control unit receives said input command and controls the first switch 16 according to the command received. The input means may include, but is not limited to, a control panel, a touch screen, a selector, a wireless communication module for receiving remote commands, etc.

[0033] The first switch 16 can be implemented in different ways to fulfill the functions described for turning power converter 15 on and off; for example, by means of a manually controlled rotary selector, by means of one or more transistors governed by a control unit, by means of a circuit with a combination of semiconductors (e.g. one or several transistors and resistors), etc.

[0034] The explosive detection unit 17 is configured to detect (or monitor) changes in the resonance frequency of the electronic oscillator 5, which occur when the magnetic head 3 is brought closer to the metal of an explosive device 11. To detect such changes the explosives detection unit 17 continuously receives from the magnetic head 3 a signal Sf eq representative of the resonance frequency f eq of the electronic oscillator 5, that is, an alternating signal at the resonance frequency f eq of the electronic oscillator 5 (for example, the current flowing through a secondary winding of the transformer 12). Said signal can be sent through the cable 4 or wirelessly by means of a radio signal.

[0035] The detection of changes in the frequency of a signal can be carried out by any of the methods known in the state of the art. For example, it can be done acoustically or by means of a frequency counter. The detection of explosive devices 11 using the magnetic head 3 works in a similar way to a metal detector device.

[0036] An exemplary embodiment of the system in which the detection of the frequency deviation of the heterodyne is used is shown in Figure 3. In this embodiment the explosives detection unit 16 comprises a mixer 20, a local oscillator 21 tuneable via input E, an audio amplifier 22 and a loudspeaker 23 or earphone. The mixer 20 receives a signal Sf eq (in this case, the Sf eq signal is provided by a second secondary winding 12c of the transformer 12) of frequency f eq , the resonant frequency f eq of the electronic oscillator 5, and mixes it with the signal S fs coming from the local oscillator, at a tuneable frequency fs through input E. The mixer 20 provides an output signal with the difference in frequencies (i.e. at a frequency f=f eq -f s ) to an amplifier 22, which amplifies the signal to play it on a speaker 23 or a headset.

[0037] An operator can tune the frequency of the local oscillator 21 so that the pitch of the frequency difference is maintained in an audible audio frequency range, from 16 Hz to 20000 Hz. The frequency of the local oscillator 21 can be adjusted so that the difference of frequencies is located in a comfortable audio tone, between 200Hz and 5 kHz, preferably close to 500 Hz. When scanning for explosive devices 11, by scanning the magnetic head 3 over a certain area or terrain, the presence of metal in the explosive device 11 (e.g. a mine buried in the scanned terrain) will cause the audio tone reproduced by the speaker 23 to change due to the change in frequency f eq of the signal S feq coming from the electronic oscillator 5. In the sweep of the magnetic head 3, performed by an operator or by a vehicle / drone that carries the magnetic head 3, the point where the maximum frequency change is obtained is sought and, once found, the magnetic head 3 is left motionless in said position to proceed with the deactivation or destruction of the explosive device 11.

[0038] The explosive detection unit 17 can detect a change in the resonant frequency of the electronic oscillator 5 using other methods, such as by means of a frequency counter, through which the frequency of the signal at the output of the mixer 20 can be measured or directly measure the frequency of the S feq signal coming from the electronic oscillator 5, which can be represented on a screen. An operator scanning with the magnetic head 3 can detect the maximum frequency change by reading the frequency measurement.

[0039] When the magnetic head 3 moves over a metal, such as a small detonator, there is an increase in the power consumption of the battery and a variation in the resonance frequency, which will depend on the type of metal. The explosive detection unit 17 can be configured to measure the power variation Δp supplied by the battery (using for example a current sensor) and the resonance frequency variation Δf during the sweep of the magnetic head 3 to, based on to the so said variations, estimate an amount of metal that produces said variation and / or determine (e.g. by comparison with reference values) if it corresponds to an explosive device 11.

[0040] Figure 3 shows an example of the electronic oscillator 5. In this embodiment, the active elements of the amplifier circuit 8 are two MOSFET power transistors (Q1,Q2) that work in a push-pull configuration, although other topologies could be used. That fulfill the function of amplifying the feedback current coming from the resonant circuit. The feedback circuit 7 can include, as reflected in the example of Figure 3, the transformer 12 and the resistors R1 and R2 as feedback components and gate driver of the transistors. Zener diodes Z1 and Z2 are responsible for holding the gate voltages of transistors Q1 and Q2 to safe values, and fast diodes D1 and D2 are holding the gate voltages of transistors Q1 and Q2, to prevent conduction simultaneous use of said transistors. Resistors R3 and R4 and Zener diode Z3 are responsible for providing bias voltage to transistors Q1 and Q2. Inductances L2 and L3 provide a DC power supply to the drain of switching transistors Q1 and Q2.

[0041] Figure 4 shows an example of a magnetic head 3, where the coil 10 is a metallic tube with two turns or turns and the rest of the oscillator components are integrated inside a casing 25.

[0042] The magnetic head 3 may be carried by an operator or may be mounted on a remotely controlled vehicle (e.g. a ground vehicle or a drone).

[0043] In one embodiment, during the detection of the explosive device 11, the operator carries the power and control device 2 (for example, on the back, in a backpack) and the magnetic head 3 in one hand. The operator moves the magnetic head 3 in a search area until a possible explosive device 11 (mine, bomb, grenade, IED, etc.) is detected. Once detected, the magnetic head 3 is left motionless at the point of maximum change in resonant frequency and the deactivation or detonation phase is passed, for which the operator moves away with the control and power device 3, unwinding the cable 4.

[0044] Figure 5A shows the extension of the cable 4 in a stage of deactivation or detonation of the explosive device 11, where the magnetic head is mounted on a support 26 to be carried by the operator 30 during the search.

[0045] The cable 4 is preferably incorporated in a drum to be able to collect or extend the cable. The cable 4 allows the distance between the magnetic head 3 and the operator 30 controlling the power and control device 2 to be increased to 50 meters or more, depending on the type of explosive device 11 to be deactivated or detonated.

[0046] In another embodiment, during the detection of the explosive device 11 a vehicle, controlled by remote control by the operator or autonomously, carries the magnetic head 3 and moves through a search area until detecting an explosive device 11. Figure 5B shows the operator 30 away from the vehicle 27 carrying the magnetic head 3, during the search phase or during the deactivation / detonation phase.

[0047] A flowchart of a method 100 for detecting and defusing or detonating explosive devices using the previously described system 1 is shown in Figure 6.

[0048] The method 100 comprises performing a scan 110 of the magnetic head 3 in a search area 40. Figure 7A represents the scan in a search area 40 of the magnetic head 3 (the rest of the components of the system 1, that is, the cable 4 and the power and control device 2 are not illustrated). The scanning of the magnetic head 3 includes changes in the positions (x i , y i , z i ) of the coil 10 within said search area, following a certain trajectory 41, and may also include changes in the orientations (e.g. angles of inclination with respect to the ground) of the coil 10. The dashed line illustrates the magnetic head 3 in an initial position (x 0 , y 0 , z 0 ) of the sweep and the solid line illustrates the magnetic head 3 in a final position (x f ,y f ,z f ), once trajectory 41 has been traversed.

[0049] During the sweep 120 (e.g. by acoustic monitoring), using the explosive detection unit 17, changes in the resonant frequency feq of the electronic oscillator 5 are detected. Next, a position (xm,ym,zm) of the coil 10 of the magnetic head 3, and optionally an orientation thereof, which produces the greatest change in the resonant frequency feq of the electronic oscillator 5 during the scan, and the coil 10 is arranged 130 in said position (and orientation), as illustrated in Figure 7B. Additionally, to ensure the presence of metal from a possible explosive device (11) it can be required, as a requirement to continue with method 100, that the resonance frequency variation Δf and / or the power variation Δp supplied by magnetic 3 in a final position (xf,yf,zf), once trajectory 41 has been traversed.

[0050] Once the coil 10 is correctly positioned and the operator 30 of the power and control device 2 is away at a certain safety distance, outside the radius of action of the explosive device 11, the first switch 16 is controlled (e.g. manually by the operator 30) to activate and deactivate the power converter 15 following certain activation patterns. The power converter 15 is first activated 140 in a series of short activation pulses 142 of a duration T ON less than a first activation threshold T i , where T ON is the activation duration of each pulse during which the power converter 15 is activated. During these bursts of short driving pulses 142 of the power converter 15, a high voltage is provided to the electronic oscillator 5 through the cable 4, greatly increasing the magnetic flux density Bp generated by the coil 10. In one embodiment, the pulses activation shorts 142 have a duration T ON less than 3 seconds (that is, Ti=3s). For example, a series of 2-second activation pulses (T ON =2s) repeated every 5 seconds can be used (that is, every 5 seconds the power converter turns on for 2 seconds and remains off for 3 seconds). Repetition of these short activation pulses 142 a certain number of times, using for example 10 or more short pulses, can damage electronic circuits included within an explosive device 11 or destroy the internal electronics, in which case the explosive device 11 It is deactivated or detonated, depending on the explosive device 11 and the destroyed circuit.

[0051] Next, it is checked whether there has been a detonation 150. If the explosive device 11 has exploded, the process is terminated (in this case the magnetic head 3 has possibly also been destroyed and has to be replaced). Otherwise, the power converter 15 is turned on 160 in a series of long turn-on pulses 162 of duration T ON greater than a second turn-on threshold T s , where T s >T i . In one embodiment, the long trigger pulses 162 have a duration (T ON ) greater than 10 seconds (ie, T s =10s); for example, 20s activation pulses (T ON =20s) can be used. In this case, pulses of longer duration are used to heat the metallic part of the explosive device 11. These long activation pulses 162 are repeated a certain number of times (for example, 10 times).

[0052] The application of an alternating current to the coil 10 establishes an alternating magnetic field BP inside and outside the coil 10. By introducing an explosive device with a metallic part inside the magnetic field BP generated by the coil 10, a force is generated electromotive inside the metal that causes an internal electric current that produces heat because metals have electrical resistance. Iron losses include hysteresis losses and losses due to electrical resistance.

[0053] Thus, for example, in an improvised explosive device (IED), the induced currents generated by the short activation pulses 142 can damage the associated electronics, thereby neutralizing the IED. The induction of high voltages in electrical wiring inside and outside an IED can cause it to trip. The short activation pulses 142 are high voltage induction pulses that aim to neutralize the electronics of the explosive device 11 due to overvoltage or overcurrent.

[0054] The long activation pulses 162 are heating pulses that are intended to generate significant induction heating in the explosive device 11, which can cause its deactivation or detonation, depending on the type of explosive device 11. Thus, if the main charge of the explosive device 11 is TNT, when the temperature of the explosive device 11 rises to about 90°C a change in the state of the TNT to liquid occurs. TNT may end up escaping through vent holes in the metal cover surrounding the main charge of the grenade, mine, or bomb, rendering the explosive device deactivated or the final detonation less destructive.

[0055] In other explosive devices 11, induction heating can cause an explosion when the temperature of the detonator is reached. For example, if explosive device 11 is a classic bomb, it gets hot due to the iron and explodes.

[0056] The main function of the magnetic head 3 is to provide a very high magnetic field frequency product to induce destructive currents in the electrical circuits that are part of the explosive device 11. The induced voltage per square meter is V=2πfB.

[0057] The resonance in the electronic oscillator 5 makes it possible to obtain very high currents in the coil 10 and, therefore, a very strong magnetic field B. Furthermore, the resonant circuit is configured to have a high resonant frequency. For example, if the resonant frequency is 500kHz and the magnetic field in the explosive device is B= 0.001T, the induced voltage is 3142 V / m2. These high induced currents, first generated by the short activation pulses 142, can damage the electronic circuitry of the explosive device 11, disabling or exploding it. In addition, the induced currents generate over time, especially when long activation pulses 162 are applied, an induction heating in the explosive device 11, which can also cause its deactivation or denotation.

[0058] In one embodiment, induction heating can be controlled by monitoring the heating temperature, using for example an infrared camera or sensor. In this way it is possible to control the activation of the power converter 15 based on a temperature profile, taking into account the currently monitored temperature and the target temperatures of the temperature profile.

[0059] A circuit used as an electronic oscillator 5 is shown in Figure 8A only by way of example. V4 represents the supply voltage from the power and control device 2 through the cable 4. The metal of the explosive device 11 is represented by L7 and R4. L represents the coil 10 of the resonant circuit 6, and C the capacitor 9 of the resonant circuit 6 that makes the resonance with the coil L and the metal that is nearby (in this case, the metal of the explosive device 11 represented by L7 and R4). M1 and M2 are two power transistors of the amplifier circuit 8.

[0060] A simplified simulation of the circuit of Figure 8A, without non-linear elements, is illustrated in Figures 8B and 8C. In particular, Figure 8B shows the current I(L) in the coil L and I(L7) the induced current in the coil L7, that is, the induced current in the explosive device 11. I(L) has a peak of 170 A, while I(L7) has a peak of about 30 A. For its part, Figure 8C represents the current I(M1) in transistor M1, of about 20.5 A peak.

[0061] An example of an electrical circuit is shown in Figure 9A, representing the components of the electronic oscillator 5 and the power converter 15, connected by cable 4. The metal of the explosive device 11 is also shown, represented by a coil and a resistor, in which current is induced by the proximity of coil 10.

[0062] V1 is a voltage source (for example, a 15V and 100mA source) that powers the transistors of the power converter 15, providing the voltage necessary for its turn-on. The first switch 16, in series with the voltage source V1, controls the on or off of the power converter 15. V represents the voltage provided by the battery 14 (e.g. 36 V). The battery 14 is connected to the electronic oscillator 5 through a diode 28. Optionally, a second switch 29 (e.g. 10A) can be incorporated in series with the diode.

[0063] The activation (connection or disconnection) of the first switch 16 (and, optionally, the second switch 29 if present) defines at least two states in system 1.

[0064] The connection of the first switch 16 defines a first state by which the power converter 15 is activated (V1 supplies voltage to the transistors of the power converter 15) and supplies the electronic oscillator 5 with the voltage of the amplified battery; for example, in the circuit of Figure 9A the 36V battery source is multiplied by 8, providing the oscillator with a voltage of about 288V.

[0065] The disconnection of the first switch 16 defines a second state, by which the power converter 15 is deactivated (since no voltage is supplied to the transistors of the power converter 15) and the electronic oscillator 5 is supplied with a direct voltage equal to or lower than that supplied by the battery. This second state additionally requires that the second switch 29 be connected, if present. In this second state, the power converter 15 is connected to the battery 14, but does not consume current because all the gates of the MOSFET transistors are at 0 volts, and system 1 is in explosive device detection mode, therefore which the battery consumption is low and the battery voltage (or slightly lower, considering the intermediate voltage drop across diode 28) is supplied to the oscillator.

[0066] When the second switch 29 is used, system 1 can go to a third state, for which both switches (16, 29) must be disconnected. In this way, system 1 is off, with no consumption by the electronic oscillator 5 or the power converter 15.

[0067] The system 1 represented in Figure 9A therefore has three modes of operation: Off: This operating mode occurs when the power converter 15 is off (first switch 16 off) and the second switch 29 is off. In this case, the voltage supplied to the electronic oscillator 5 is zero, and the consumption of system 1 is zero. Explosive device detection mode: When the power converter 15 is disabled (first switch 16 off) and the second switch 29 is on. The voltage supplied to the electronic oscillator 5 is approximately the battery voltage (about 36V). In this mode, in which there is a low consumption, the explosive detection unit 17 detects changes in the resonant frequency of the electronic oscillator 5. Explosive devices deactivation or detonation mode: This operating mode occurs when the power converter 15 is activated by operating the first switch 16 in short activation pulses 142 for induction of high voltages and later in long activation pulses 162 for heating the metal of the explosive device 11. In the example of Figure 9A the voltage provided to the electronic oscillator 5 is about 288V and the consumption of the battery 14 is about 5 kW.

[0068] Figure 9B illustrates a simulation of the current I (L) in the coil 10 in a first state 50, when the power converter 15 is activated (90 A peak), and in a second state 52, when the power converter 15 is disabled and only battery voltage (about 30 A peak) is supplied to the oscillator. The first switch 16 is responsible for switching between both states (50, 52).

[0069] The strong alternating magnetic field generated by the coil when the power converter 15 is activated causes heating of the metal in the explosive device 11. In the case that the explosive device 11 includes iron, the most used material, the specific heat of iron It is 450 J / kg*K., that is, it costs 450 joules to heat one kilogram of iron one degree. Thus, assuming that explosive device 11 has 1Kg of iron that is heated with 1kW, the temperature rise will be 2.22 degrees C / second. The rate of heating of the iron will therefore vary depending on the iron content of the explosive device and the intensity of the currents induced in the metal.

[0070] Returning to the flow chart of Figure 6, method 100 may include obtaining an estimate of the distance from the magnetic head 3 to the explosive device 11 and the mass of iron contained in the explosive device 11. Figure 10 shows shows a scan 110 of the coil 10 of the magnetic head 3 in a straight horizontal line (x axis) at a certain height H above the ground 60, trying to locate an explosive device (e.g. a mine 11) buried in the ground 60. Represent three different positions (A, B and C) of coil 10 during scanning. The figure shows the cross section of the coil tube 10 when it is centered in position B. Sweeping can be performed manually (an operator) or automatically (e.g. using a robot).

[0071] While the sweep is being performed, 120 changes in the resonant frequency of the oscillator are detected. Coil 10 is located 130 where there is maximum frequency change, which corresponds to position B centred on lead 11. In this position the distance between coil 10 and lead 11 is d. The frequency deviation is half in positions A and B, corresponding to a distance 1.41d between coil 10 and lead 11. Thus, once the distance AB between positions A and B (or the distance BC between positions B and C), it is possible to estimate the distance d between the coil 10 and the explosive device 11 when the coil 10 is in position B with the greatest frequency deviation.

[0072] The maximum frequency deviation Δf, at position B, is proportional to the mass of the iron in the mine 11. Once the distance d has been estimated and the frequency deviation Δf at position B has been measured, the size of the explosive device can be estimated 11 searching a table of frequency measurements for different relevant mines.

[0073] Obtaining a distance d and an estimated iron mass on the explosive device 11 can be used to determine an appropriate power converter activation pattern, that is, the power converter activation times (the short activation pulses 142 and / or long activation pulses 162) to heat the iron of the explosive device 11.

Examples

Embodiment Construction

[0012]Figure 1 illustrates in a simplified manner the components of a system 1 for detecting and deactivating or detonating an explosive device 10, such as a mine, bomb or an improvised explosive device (IED).

[0013]System 1 comprises a power and control device 2 and a magnetic head 3. Both elements are connected by at least one cable 4. Figure 2 illustrates the internal components of system 1 in more detail.

[0014]The magnetic head 3 is a unit configured to generate an alternating magnetic field. The magnetic head 3 includes a magnetic dipole formed by a circular coil that conducts high amplitude alternating current to generate a strong alternating magnetic field around the coil. The magnetic head 3 incorporates an electronic oscillator 5, which comprises a resonant circuit 6, a feedback circuit 7 and an amplifier circuit 8.

[0015]The resonant circuit 6 comprises a capacitor 9, of capacitance C, in parallel with a metallic coil 10, of inductance L, which determine a first resonant fre...

Field of invention

[0001] The present invention is included in the field of electromagnetic systems for the detection, destruction or detonation of improvised explosive devices (IED), mines, bombs and other explosive devices.Background of the invention

[0002] Currently there are portable systems by an operator to detect explosive devices, such as mines. However, there are no known portable systems that allow, in addition to the detection, deactivation or detonation of explosive devices.Description of the invention

[0003] The invention relates to a system and method for detecting and deactivating or detonating explosive devices.

[0004] The system for detecting and defusing or detonating explosive devices comprises a magnetic head and a power and control device. Both elements are connected by a long cable (e.g. 50 meters), preferably reelable on a drum.

[0005] The magnetic head is configured to generate an alternating magnetic field and includes an electronic oscillator comprising a resonant circuit, a feedback circuit, and an amplifier circuit. The resonant circuit includes a condenser in parallel with a metal coil responsible for generating the alternating magnetic field when an alternating current at a certain resonance frequency flows through the coil. The feedback circuit comprises a transformer with a first winding in parallel with the capacitor of the resonant circuit. The feedback circuit is configured to provide the amplifier circuit, via a second transformer winding, with a positive feedback current from the resonant circuit. The amplifier circuit, which comprises at least one power transistor, is configured to amplify the feedback current coming from the resonant circuit. The frequency range of the electronic oscillator is preferably between 40 kHz and 1MHz, although ISM (industrial, scientific and medical) radio bands can also be used, especially the low frequency bands, centered on 6.75MHz, 13.56MHz or 27.12MHz.

[0006] The power and control device comprises a battery, a power converter, at least one switch and an explosive detection unit. The power converter is configured to, when activated, supply the electronic oscillator with a higher DC voltage (e.g. 8 times higher) than that supplied by the battery. The at least one switch (which can be part of the power converter or be a separate element) is configured to toggle between at least two states including: - A first state in which the power converter is activated. - A second state in which the power converter is deactivated, so that the electronic oscillator is supplied with a direct voltage equal to or less than that supplied by the battery.

[0007] The explosive detection unit is configured to detect changes in the resonant frequency of the electronic oscillator when the power converter is turned off.

[0008] On the one hand, the system allows the detection of explosive devices, for which the power converter must be deactivated and the electronic oscillator fed with battery voltage (i.e. without amplifying its voltage), and use the explosive detection unit. On the other hand, the system also allows deactivating or detonating explosive devices by activating the power converter. Preferably, a certain activation and deactivation pattern of the power converter is used to perform the deactivation or detonation of the explosive devices.

[0009] With respect to the function of deactivation or detonation of explosive devices, the system of the present invention aims to generate a product w· B ( w= 6.28 f, where f is the frequency and B is the magnetic flux density) as as large as possible in order to destroy any electrical circuits to neutralize the explosive device, or heat the metallic parts of the explosive device to (i) change the state of the secondary explosive from solid to liquid (e.g. TNT, around 90°C) to deactivate the explosive device, (ii) change the state of the secondary explosive from liquid to gas (e.g. evaporate TNT, around 220°C) to defuse the explosive device, or (iii) detonate the explosive device.

[0010] The method for detecting and defusing or detonating explosive devices employs the system described above. The method comprises the following stages: Perform a sweep of the magnetic head in a search area. Detect, by means of the explosive detection unit, changes in the resonance frequency of the electronic oscillator during the scan. Determine a position of the coil of the magnetic head that produces a greater change in the resonant frequency of the electronic oscillator. Activate and deactivate, through at least one switch, the power converter according to the following activation patterns: • Activate the power converter in a series of short activation pulses with a duration less than a first activation threshold. • If there has been no detonation of the explosive device, activate the power converter in a series of long activation pulses with a duration greater than a second activation threshold, with the second activation threshold being greater than the first activation threshold. Brief description of the drawings

[0011] Next, a series of drawings that help to better understand the invention and that are expressly related to an embodiment of said invention that is presented as a non-limiting example thereof, is briefly described. Figure 1 shows the elements of a system for detecting and defusing or detonating an explosive device according to the present invention. Figure 2 illustrates components of a system of the present invention according to one embodiment. Figure 3 represents an embodiment example of the system. Figure 4 shows an example of a magnetic head. Figures 5A and 5B show the extension of the cable in the deactivation or detonation stage of an explosive device. Figure 6 is a flowchart of a method for detecting and defusing or detonating explosive devices using the above-described system. Figure 7A represents the scanning of the magnetic head in a search area. Figure 7B shows the placement of the coil in a certain position in which the greatest change in the resonant frequency of the electronic oscillator occurs during the sweep. Figure 8A shows an example of a circuit used as an electronic oscillator. Figures 8B and 8C illustrate several simulations carried out in said circuit. Figure 9A represents an example of an electrical circuit that includes the electronic oscillator and the power converter. Figure 9B illustrates a simulation carried out in said circuit. Figure 10 shows a scan of the coil to estimate the distance to a buried explosive device and, optionally, the mass of iron contained therein. Detailed description of the invention

[0012] Figure 1 illustrates in a simplified manner the components of a system 1 for detecting and deactivating or detonating an explosive device 10, such as a mine, bomb or an improvised explosive device (IED).

[0013] System 1 comprises a power and control device 2 and a magnetic head 3. Both elements are connected by at least one cable 4. Figure 2 illustrates the internal components of system 1 in more detail.

[0014] The magnetic head 3 is a unit configured to generate an alternating magnetic field. The magnetic head 3 includes a magnetic dipole formed by a circular coil that conducts high amplitude alternating current to generate a strong alternating magnetic field around the coil. The magnetic head 3 incorporates an electronic oscillator 5, which comprises a resonant circuit 6, a feedback circuit 7 and an amplifier circuit 8.

[0015] The resonant circuit 6 comprises a capacitor 9, of capacitance C, in parallel with a metallic coil 10, of inductance L, which determine a first resonant frequency f0 of the oscillator: f 0 = 1 2 π LC

[0016] The capacitor 9 is a low loss capacitor capable of working with at least 100 A, for example 500 A, 1 KV AC (thus 500 kVAR at high frequency, typically between 40 kHz and 1 MHz). Coil 10 is responsible for generating the alternating magnetic field when an alternating current circulates through the coil at a certain resonance frequency f of the oscillator.

[0017] In one embodiment, coil 10 has an outer diameter D greater than 50mm, preferably between 100mm and 600mm.

[0018] In one embodiment, the coil 10 is made of a hollow metal tube, with one or more turns (for example, a tube of copper or aluminium and with a section of 12 mm in diameter). The coil 10 can be implemented in other different ways; for example, by aluminium strips or sheets, by braided wire, etc. Stranded wire coils have lower high-frequency losses (due to lower resistance), but are difficult to cool and expensive to manufacture. Aluminium sheets are light, but provide less mechanical stability. Hollow copper or aluminium tube coils can be cooled by circulating air inside them.

[0019] Under normal use conditions, when there are no external elements close to the coil that interact with the magnetic field generated by it, the alternating current generated by system 1 in coil 10 has a resonance frequency feq equal to f0 (feq= f0). However, when the coil 10 is brought close to an explosive device 11 containing metal parts, the metal near the coil 10 changes the equivalent resonant frequency f eq of the electronic oscillator 5, by modifying the equivalent inductance Leq of the coil 10 in the resonant circuit 6. f eq = 1 2 π L eq C

[0020] For example, aluminum and other metals (gold, silver, copper) near coil 10 reduce the equivalent inductance Leq of coil 10 and increase the resonant frequency f eq , while iron increases the equivalent inductance L eq of coil 10 and reduces the resonant frequency f eq . There is normally iron in an explosive device 11, which causes a decrease in the resonant frequency f eq .

[0021] Figure 1 represents the magnetic field B p generated by the alternating current I p circulating through the coil 10 itself. Resonance is necessary to have a very high current I p in coil 10 and thus a very strong magnetic field Bp. Due to the fact that the current I p that circulates through the coil 10 is alternating, the magnetic field B p generated is variable in time. The magnitude of the magnetic field B p on the explosive device 11, located below the coil 10, also depends on its distance from the coil 10.

[0022] The variation in time of the magnetic field Bp generates, according to Faraday's law of electromagnetic induction, an induced current I s in the metallic part of the explosive device 11, which in turn generates a magnetic field Bs that impacts the coil, 10, changing the value of the equivalent inductance L eq of the coil 10 and, with it, the equivalent resonance frequency f eq of the electronic oscillator 5.

[0023] The amplifier circuit 8 provides the alternating current Ip in the coil 10, at the resonant frequency feq. The amplifier circuit 8 comprises at least one power transistor and is configured to amplify the feedback current coming from the resonant circuit 6.

[0024] The amplifier circuit 8 receives a positive feedback from the resonant circuit 6 through the feedback circuit 7, which comprises a transformer 12 with a first winding 12a (main winding) in parallel with the capacitor 9 of the resonant circuit 6. The feedback circuit 7 is configured to provide amplifier circuit 8, through a second winding 12b (a secondary winding) of transformer 12, a positive feedback current from resonant circuit 6.

[0025] During the operation of the system 1, high powers are used, which can excessively heat the metallic coil 10. Said overheating can be transmitted to the other components of the electronic oscillator 5. In order to maintain the temperature of the electronic components (e.g. semiconductors) below a maximum operating temperature (e.g. 100°C) during the transfer of high power to the device explosive 11, the metal coil 10 can be cooled by means of a cooling circuit, preferably by air. In one embodiment, the refrigeration circuit of the coil 10, integrated in the magnetic head 3, includes a compressor 13 or a fan (powered by the power and control device 2 from the voltage supplied by the cable 4) configured to force air to circulate inside the metal coil 10 formed by a hollow metal tube, as illustrated in the example of Figure 2.

[0026] The power and control device 2 is connected by cable 4 to the electronic oscillator 5 and comprises a battery 14 that provides power to the system, a power converter 15, a first switch 16 and an explosives detection unit 17. The power device and control 2 is used by an operator to detect explosive devices 11 and, once detected, defuse them by high voltage induction or detonate them by induction heating.

[0027] The deactivation or neutralization of the explosive device 11 can be produced by the heating produced in the metallic elements due to the alternating magnetic field in the coil 10, which induces Eddy currents in the metal of the explosive device 11. The induction can destroy the electronics of the explosive device 11, inducing over voltages and over currents. So, for example, in a bomb (which is usually a metallic hole with TNT or another secondary explosive), induction heats the metal, which then heats the TNT, which changes from a solid to a liquid state when heated above about 90°C. If the bomb hole has an exit, the TNT can come out as a liquid and the bomb is neutralized. If not, the liquid TNT cannot escape, prolonged and continuous induction can greatly heat the metal, reaching an explosion temperature (e.g. about 200°C) of the primary charge or changing the state of the secondary explosive from liquid to gas. Therefore, the system 1 is capable of deactivating explosive devices 11 or detonating them, depending on the type of explosive device and the heating profile used.

[0028] Battery 14 can be any portable power supply source including a battery, battery bank, and one or more supercapacitors, among other power sources. The battery can be, for example, 36 V and 150 A.

[0029] The power converter 15 is configured to supply the electronic oscillator 5 with a DC voltage greater than that supplied by the battery 14. In one embodiment, the power converter 15 supplies at least 8 times the voltage of the battery 14; for example, it transforms the 36 volts of the battery into 288 volts (8 times the voltage of the battery 14) of direct voltage that is supplied through the cable 4 to the electronic oscillator 5. The power converter can be, for example, of 5kW output. The power converter 15 may be a DC / DC converter (e.g. a DC / DC boost converter).

[0030] The first switch 16 is responsible for turning on or off (i.e. activate or deactivate) the power converter 15. When the power converter 15 is on (active or activated), it supplies the electronic oscillator 5 with a certain power (which can be regulated). at a DC voltage greater than that of the battery. When the power converter 15 is turned off (inactive or deactivated), the battery voltage is not increased; instead, the voltage of the battery 14 supplies the electronic oscillator 5 directly. The first switch 16 thus alternates between at least two states, a first state in which the power converter 15 is active, providing the electronic oscillator with a voltage greater continuous greater than the battery 14, and a second state in which the power converter 15 is inactive, so that it is the battery 14 that directly feeds the electronic oscillator 5.

[0031] The first switch 16 can be controlled manually, for example by means of a selector that allows an operator to select the power converter 15 on or off.

[0032] Alternatively, the first switch 16 can be controlled by a control unit, such as a microcontroller, based on an input received through an input means. For example, an operator can select on a control panel to turn the power converter 15 on or off, or even a certain output power of the power converter 15, and the control unit receives said input command and controls the first switch 16 according to the command received. The input means may include, but is not limited to, a control panel, a touch screen, a selector, a wireless communication module for receiving remote commands, etc.

[0033] The first switch 16 can be implemented in different ways to fulfill the functions described for turning power converter 15 on and off; for example, by means of a manually controlled rotary selector, by means of one or more transistors governed by a control unit, by means of a circuit with a combination of semiconductors (e.g. one or several transistors and resistors), etc.

[0034] The explosive detection unit 17 is configured to detect (or monitor) changes in the resonance frequency of the electronic oscillator 5, which occur when the magnetic head 3 is brought closer to the metal of an explosive device 11. To detect such changes the explosives detection unit 17 continuously receives from the magnetic head 3 a signal Sf eq representative of the resonance frequency f eq of the electronic oscillator 5, that is, an alternating signal at the resonance frequency f eq of the electronic oscillator 5 (for example, the current flowing through a secondary winding of the transformer 12). Said signal can be sent through the cable 4 or wirelessly by means of a radio signal.

[0035] The detection of changes in the frequency of a signal can be carried out by any of the methods known in the state of the art. For example, it can be done acoustically or by means of a frequency counter. The detection of explosive devices 11 using the magnetic head 3 works in a similar way to a metal detector device.

[0036] An exemplary embodiment of the system in which the detection of the frequency deviation of the heterodyne is used is shown in Figure 3. In this embodiment the explosives detection unit 16 comprises a mixer 20, a local oscillator 21 tuneable via input E, an audio amplifier 22 and a loudspeaker 23 or earphone. The mixer 20 receives a signal Sf eq (in this case, the Sf eq signal is provided by a second secondary winding 12c of the transformer 12) of frequency f eq , the resonant frequency f eq of the electronic oscillator 5, and mixes it with the signal S fs coming from the local oscillator, at a tuneable frequency fs through input E. The mixer 20 provides an output signal with the difference in frequencies (i.e. at a frequency f=f eq -f s ) to an amplifier 22, which amplifies the signal to play it on a speaker 23 or a headset.

[0037] An operator can tune the frequency of the local oscillator 21 so that the pitch of the frequency difference is maintained in an audible audio frequency range, from 16 Hz to 20000 Hz. The frequency of the local oscillator 21 can be adjusted so that the difference of frequencies is located in a comfortable audio tone, between 200Hz and 5 kHz, preferably close to 500 Hz. When scanning for explosive devices 11, by scanning the magnetic head 3 over a certain area or terrain, the presence of metal in the explosive device 11 (e.g. a mine buried in the scanned terrain) will cause the audio tone reproduced by the speaker 23 to change due to the change in frequency f eq of the signal S feq coming from the electronic oscillator 5. In the sweep of the magnetic head 3, performed by an operator or by a vehicle / drone that carries the magnetic head 3, the point where the maximum frequency change is obtained is sought and, once found, the magnetic head 3 is left motionless in said position to proceed with the deactivation or destruction of the explosive device 11.

[0038] The explosive detection unit 17 can detect a change in the resonant frequency of the electronic oscillator 5 using other methods, such as by means of a frequency counter, through which the frequency of the signal at the output of the mixer 20 can be measured or directly measure the frequency of the S feq signal coming from the electronic oscillator 5, which can be represented on a screen. An operator scanning with the magnetic head 3 can detect the maximum frequency change by reading the frequency measurement.

[0039] When the magnetic head 3 moves over a metal, such as a small detonator, there is an increase in the power consumption of the battery and a variation in the resonance frequency, which will depend on the type of metal. The explosive detection unit 17 can be configured to measure the power variation Δp supplied by the battery (using for example a current sensor) and the resonance frequency variation Δf during the sweep of the magnetic head 3 to, based on to the so said variations, estimate an amount of metal that produces said variation and / or determine (e.g. by comparison with reference values) if it corresponds to an explosive device 11.

[0040] Figure 3 shows an example of the electronic oscillator 5. In this embodiment, the active elements of the amplifier circuit 8 are two MOSFET power transistors (Q1,Q2) that work in a push-pull configuration, although other topologies could be used. That fulfill the function of amplifying the feedback current coming from the resonant circuit. The feedback circuit 7 can include, as reflected in the example of Figure 3, the transformer 12 and the resistors R1 and R2 as feedback components and gate driver of the transistors. Zener diodes Z1 and Z2 are responsible for holding the gate voltages of transistors Q1 and Q2 to safe values, and fast diodes D1 and D2 are holding the gate voltages of transistors Q1 and Q2, to prevent conduction simultaneous use of said transistors. Resistors R3 and R4 and Zener diode Z3 are responsible for providing bias voltage to transistors Q1 and Q2. Inductances L2 and L3 provide a DC power supply to the drain of switching transistors Q1 and Q2.

[0041] Figure 4 shows an example of a magnetic head 3, where the coil 10 is a metallic tube with two turns or turns and the rest of the oscillator components are integrated inside a casing 25.

[0042] The magnetic head 3 may be carried by an operator or may be mounted on a remotely controlled vehicle (e.g. a ground vehicle or a drone).

[0043] In one embodiment, during the detection of the explosive device 11, the operator carries the power and control device 2 (for example, on the back, in a backpack) and the magnetic head 3 in one hand. The operator moves the magnetic head 3 in a search area until a possible explosive device 11 (mine, bomb, grenade, IED, etc.) is detected. Once detected, the magnetic head 3 is left motionless at the point of maximum change in resonant frequency and the deactivation or detonation phase is passed, for which the operator moves away with the control and power device 3, unwinding the cable 4.

[0044] Figure 5A shows the extension of the cable 4 in a stage of deactivation or detonation of the explosive device 11, where the magnetic head is mounted on a support 26 to be carried by the operator 30 during the search.

[0045] The cable 4 is preferably incorporated in a drum to be able to collect or extend the cable. The cable 4 allows the distance between the magnetic head 3 and the operator 30 controlling the power and control device 2 to be increased to 50 meters or more, depending on the type of explosive device 11 to be deactivated or detonated.

[0046] In another embodiment, during the detection of the explosive device 11 a vehicle, controlled by remote control by the operator or autonomously, carries the magnetic head 3 and moves through a search area until detecting an explosive device 11. Figure 5B shows the operator 30 away from the vehicle 27 carrying the magnetic head 3, during the search phase or during the deactivation / detonation phase.

[0047] A flowchart of a method 100 for detecting and defusing or detonating explosive devices using the previously described system 1 is shown in Figure 6.

[0048] The method 100 comprises performing a scan 110 of the magnetic head 3 in a search area 40. Figure 7A represents the scan in a search area 40 of the magnetic head 3 (the rest of the components of the system 1, that is, the cable 4 and the power and control device 2 are not illustrated). The scanning of the magnetic head 3 includes changes in the positions (x i , y i , z i ) of the coil 10 within said search area, following a certain trajectory 41, and may also include changes in the orientations (e.g. angles of inclination with respect to the ground) of the coil 10. The dashed line illustrates the magnetic head 3 in an initial position (x 0 , y 0 , z 0 ) of the sweep and the solid line illustrates the magnetic head 3 in a final position (x f ,y f ,z f ), once trajectory 41 has been traversed.

[0049] During the sweep 120 (e.g. by acoustic monitoring), using the explosive detection unit 17, changes in the resonant frequency feq of the electronic oscillator 5 are detected. Next, a position (xm,ym,zm) of the coil 10 of the magnetic head 3, and optionally an orientation thereof, which produces the greatest change in the resonant frequency feq of the electronic oscillator 5 during the scan, and the coil 10 is arranged 130 in said position (and orientation), as illustrated in Figure 7B. Additionally, to ensure the presence of metal from a possible explosive device (11) it can be required, as a requirement to continue with method 100, that the resonance frequency variation Δf and / or the power variation Δp supplied by magnetic 3 in a final position (xf,yf,zf), once trajectory 41 has been traversed.

[0050] Once the coil 10 is correctly positioned and the operator 30 of the power and control device 2 is away at a certain safety distance, outside the radius of action of the explosive device 11, the first switch 16 is controlled (e.g. manually by the operator 30) to activate and deactivate the power converter 15 following certain activation patterns. The power converter 15 is first activated 140 in a series of short activation pulses 142 of a duration T ON less than a first activation threshold T i , where T ON is the activation duration of each pulse during which the power converter 15 is activated. During these bursts of short driving pulses 142 of the power converter 15, a high voltage is provided to the electronic oscillator 5 through the cable 4, greatly increasing the magnetic flux density Bp generated by the coil 10. In one embodiment, the pulses activation shorts 142 have a duration T ON less than 3 seconds (that is, Ti=3s). For example, a series of 2-second activation pulses (T ON =2s) repeated every 5 seconds can be used (that is, every 5 seconds the power converter turns on for 2 seconds and remains off for 3 seconds). Repetition of these short activation pulses 142 a certain number of times, using for example 10 or more short pulses, can damage electronic circuits included within an explosive device 11 or destroy the internal electronics, in which case the explosive device 11 It is deactivated or detonated, depending on the explosive device 11 and the destroyed circuit.

[0051] Next, it is checked whether there has been a detonation 150. If the explosive device 11 has exploded, the process is terminated (in this case the magnetic head 3 has possibly also been destroyed and has to be replaced). Otherwise, the power converter 15 is turned on 160 in a series of long turn-on pulses 162 of duration T ON greater than a second turn-on threshold T s , where T s >T i . In one embodiment, the long trigger pulses 162 have a duration (T ON ) greater than 10 seconds (ie, T s =10s); for example, 20s activation pulses (T ON =20s) can be used. In this case, pulses of longer duration are used to heat the metallic part of the explosive device 11. These long activation pulses 162 are repeated a certain number of times (for example, 10 times).

[0052] The application of an alternating current to the coil 10 establishes an alternating magnetic field BP inside and outside the coil 10. By introducing an explosive device with a metallic part inside the magnetic field BP generated by the coil 10, a force is generated electromotive inside the metal that causes an internal electric current that produces heat because metals have electrical resistance. Iron losses include hysteresis losses and losses due to electrical resistance.

[0053] Thus, for example, in an improvised explosive device (IED), the induced currents generated by the short activation pulses 142 can damage the associated electronics, thereby neutralizing the IED. The induction of high voltages in electrical wiring inside and outside an IED can cause it to trip. The short activation pulses 142 are high voltage induction pulses that aim to neutralize the electronics of the explosive device 11 due to overvoltage or overcurrent.

[0054] The long activation pulses 162 are heating pulses that are intended to generate significant induction heating in the explosive device 11, which can cause its deactivation or detonation, depending on the type of explosive device 11. Thus, if the main charge of the explosive device 11 is TNT, when the temperature of the explosive device 11 rises to about 90°C a change in the state of the TNT to liquid occurs. TNT may end up escaping through vent holes in the metal cover surrounding the main charge of the grenade, mine, or bomb, rendering the explosive device deactivated or the final detonation less destructive.

[0055] In other explosive devices 11, induction heating can cause an explosion when the temperature of the detonator is reached. For example, if explosive device 11 is a classic bomb, it gets hot due to the iron and explodes.

[0056] The main function of the magnetic head 3 is to provide a very high magnetic field frequency product to induce destructive currents in the electrical circuits that are part of the explosive device 11. The induced voltage per square meter is V=2πfB.

[0057] The resonance in the electronic oscillator 5 makes it possible to obtain very high currents in the coil 10 and, therefore, a very strong magnetic field B. Furthermore, the resonant circuit is configured to have a high resonant frequency. For example, if the resonant frequency is 500kHz and the magnetic field in the explosive device is B= 0.001T, the induced voltage is 3142 V / m2. These high induced currents, first generated by the short activation pulses 142, can damage the electronic circuitry of the explosive device 11, disabling or exploding it. In addition, the induced currents generate over time, especially when long activation pulses 162 are applied, an induction heating in the explosive device 11, which can also cause its deactivation or denotation.

[0058] In one embodiment, induction heating can be controlled by monitoring the heating temperature, using for example an infrared camera or sensor. In this way it is possible to control the activation of the power converter 15 based on a temperature profile, taking into account the currently monitored temperature and the target temperatures of the temperature profile.

[0059] A circuit used as an electronic oscillator 5 is shown in Figure 8A only by way of example. V4 represents the supply voltage from the power and control device 2 through the cable 4. The metal of the explosive device 11 is represented by L7 and R4. L represents the coil 10 of the resonant circuit 6, and C the capacitor 9 of the resonant circuit 6 that makes the resonance with the coil L and the metal that is nearby (in this case, the metal of the explosive device 11 represented by L7 and R4). M1 and M2 are two power transistors of the amplifier circuit 8.

[0060] A simplified simulation of the circuit of Figure 8A, without non-linear elements, is illustrated in Figures 8B and 8C. In particular, Figure 8B shows the current I(L) in the coil L and I(L7) the induced current in the coil L7, that is, the induced current in the explosive device 11. I(L) has a peak of 170 A, while I(L7) has a peak of about 30 A. For its part, Figure 8C represents the current I(M1) in transistor M1, of about 20.5 A peak.

[0061] An example of an electrical circuit is shown in Figure 9A, representing the components of the electronic oscillator 5 and the power converter 15, connected by cable 4. The metal of the explosive device 11 is also shown, represented by a coil and a resistor, in which current is induced by the proximity of coil 10.

[0062] V1 is a voltage source (for example, a 15V and 100mA source) that powers the transistors of the power converter 15, providing the voltage necessary for its turn-on. The first switch 16, in series with the voltage source V1, controls the on or off of the power converter 15. V represents the voltage provided by the battery 14 (e.g. 36 V). The battery 14 is connected to the electronic oscillator 5 through a diode 28. Optionally, a second switch 29 (e.g. 10A) can be incorporated in series with the diode.

[0063] The activation (connection or disconnection) of the first switch 16 (and, optionally, the second switch 29 if present) defines at least two states in system 1.

[0064] The connection of the first switch 16 defines a first state by which the power converter 15 is activated (V1 supplies voltage to the transistors of the power converter 15) and supplies the electronic oscillator 5 with the voltage of the amplified battery; for example, in the circuit of Figure 9A the 36V battery source is multiplied by 8, providing the oscillator with a voltage of about 288V.

[0065] The disconnection of the first switch 16 defines a second state, by which the power converter 15 is deactivated (since no voltage is supplied to the transistors of the power converter 15) and the electronic oscillator 5 is supplied with a direct voltage equal to or lower than that supplied by the battery. This second state additionally requires that the second switch 29 be connected, if present. In this second state, the power converter 15 is connected to the battery 14, but does not consume current because all the gates of the MOSFET transistors are at 0 volts, and system 1 is in explosive device detection mode, therefore which the battery consumption is low and the battery voltage (or slightly lower, considering the intermediate voltage drop across diode 28) is supplied to the oscillator.

[0066] When the second switch 29 is used, system 1 can go to a third state, for which both switches (16, 29) must be disconnected. In this way, system 1 is off, with no consumption by the electronic oscillator 5 or the power converter 15.

[0067] The system 1 represented in Figure 9A therefore has three modes of operation: Off: This operating mode occurs when the power converter 15 is off (first switch 16 off) and the second switch 29 is off. In this case, the voltage supplied to the electronic oscillator 5 is zero, and the consumption of system 1 is zero. Explosive device detection mode: When the power converter 15 is disabled (first switch 16 off) and the second switch 29 is on. The voltage supplied to the electronic oscillator 5 is approximately the battery voltage (about 36V). In this mode, in which there is a low consumption, the explosive detection unit 17 detects changes in the resonant frequency of the electronic oscillator 5. Explosive devices deactivation or detonation mode: This operating mode occurs when the power converter 15 is activated by operating the first switch 16 in short activation pulses 142 for induction of high voltages and later in long activation pulses 162 for heating the metal of the explosive device 11. In the example of Figure 9A the voltage provided to the electronic oscillator 5 is about 288V and the consumption of the battery 14 is about 5 kW.

[0068] Figure 9B illustrates a simulation of the current I (L) in the coil 10 in a first state 50, when the power converter 15 is activated (90 A peak), and in a second state 52, when the power converter 15 is disabled and only battery voltage (about 30 A peak) is supplied to the oscillator. The first switch 16 is responsible for switching between both states (50, 52).

[0069] The strong alternating magnetic field generated by the coil when the power converter 15 is activated causes heating of the metal in the explosive device 11. In the case that the explosive device 11 includes iron, the most used material, the specific heat of iron It is 450 J / kg*K., that is, it costs 450 joules to heat one kilogram of iron one degree. Thus, assuming that explosive device 11 has 1Kg of iron that is heated with 1kW, the temperature rise will be 2.22 degrees C / second. The rate of heating of the iron will therefore vary depending on the iron content of the explosive device and the intensity of the currents induced in the metal.

[0070] Returning to the flow chart of Figure 6, method 100 may include obtaining an estimate of the distance from the magnetic head 3 to the explosive device 11 and the mass of iron contained in the explosive device 11. Figure 10 shows shows a scan 110 of the coil 10 of the magnetic head 3 in a straight horizontal line (x axis) at a certain height H above the ground 60, trying to locate an explosive device (e.g. a mine 11) buried in the ground 60. Represent three different positions (A, B and C) of coil 10 during scanning. The figure shows the cross section of the coil tube 10 when it is centered in position B. Sweeping can be performed manually (an operator) or automatically (e.g. using a robot).

[0071] While the sweep is being performed, 120 changes in the resonant frequency of the oscillator are detected. Coil 10 is located 130 where there is maximum frequency change, which corresponds to position B centred on lead 11. In this position the distance between coil 10 and lead 11 is d. The frequency deviation is half in positions A and B, corresponding to a distance 1.41d between coil 10 and lead 11. Thus, once the distance AB between positions A and B (or the distance BC between positions B and C), it is possible to estimate the distance d between the coil 10 and the explosive device 11 when the coil 10 is in position B with the greatest frequency deviation.

[0072] The maximum frequency deviation Δf, at position B, is proportional to the mass of the iron in the mine 11. Once the distance d has been estimated and the frequency deviation Δf at position B has been measured, the size of the explosive device can be estimated 11 searching a table of frequency measurements for different relevant mines.

[0073] Obtaining a distance d and an estimated iron mass on the explosive device 11 can be used to determine an appropriate power converter activation pattern, that is, the power converter activation times (the short activation pulses 142 and / or long activation pulses 162) to heat the iron of the explosive device 11.

Examples

Embodiment Construction

[0012]Figure 1 illustrates in a simplified manner the components of a system 1 for detecting and deactivating or detonating an explosive device 10, such as a mine, bomb or an improvised explosive device (IED).

[0013]System 1 comprises a power and control device 2 and a magnetic head 3. Both elements are connected by at least one cable 4. Figure 2 illustrates the internal components of system 1 in more detail.

[0014]The magnetic head 3 is a unit configured to generate an alternating magnetic field. The magnetic head 3 includes a magnetic dipole formed by a circular coil that conducts high amplitude alternating current to generate a strong alternating magnetic field around the coil. The magnetic head 3 incorporates an electronic oscillator 5, which comprises a resonant circuit 6, a feedback circuit 7 and an amplifier circuit 8.

[0015]The resonant circuit 6 comprises a capacitor 9, of capacitance C, in parallel with a metallic coil 10, of inductance L, which determine a first resonant fre...

Claims

1. A system to detect and deactivate or detonate explosive devices, characterized in that the system (1) comprises: - a magnetic head (3) configured to generate an alternating magnetic field and including an electronic oscillator (5) comprising: a resonant circuit (6) comprising a capacitor (9) in parallel with a metal coil (10) responsible for generating the alternating magnetic field when an alternating current at a certain resonant frequency (feq) flows through the coil (10); a feedback circuit (7) comprising a transformer (12) with a first winding (12a) in parallel with the capacitor (9) of the resonant circuit (6), the feedback circuit (7) being configured to provide a circuit amplifier (8), through a second winding (12b) of the transformer (12), a positive feedback current coming from the resonant circuit (6); and the amplifier circuit (8), which comprises at least one power transistor and which is configured to amplify the feedback current coming from the resonant circuit; and - A power and control device (2), connected by a cable (4) to the electronic oscillator (5), and comprising: a battery (14), a power converter (15) configured to, when activated, feed the electronic oscillator (5) with a higher continuous voltage than that supplied by the battery (14), at least one switch (16,29) configured to toggle between at least two states including: a first state (50) in which the power converter (15) is activated; a second state (52) in which the power converter (15) is deactivated and the electronic oscillator (5) is powered with a direct voltage equal to or lower than that supplied by the battery (14); and an explosive detection unit (17) configured to detect changes in the resonance frequency (feq) of the electronic oscillator (5) when the power converter (15) is deactivated.

2. The system according to claim 1, characterized in that the coil (10) is formed by a hollow metal tube arranged in one or more turns.

3. The system according to claim 2, characterized in that the magnetic head (3) comprises a coil cooling circuit that includes a compressor (13) or a fan configured to circulate air inside the coil ( 10).

4. The system according to any of the preceding claims, characterized in that the coil (10) has an outer diameter greater than 50 mm.

5. The system according to any of the preceding claims, characterized in that the power converter (15) is configured to supply the electronic oscillator (5) with a continuous voltage at least four times greater than the battery voltage (14).

6. The system according to any of the previous claims, characterized in that the frequency range of the electronic oscillator (5) is 40 kHz-1MHz.

7. A method for detecting and deactivating or detonating explosive devices using the system (1) according to any of claims 1-7, characterized in that the method (100) comprises: - performing a scan (110) of the magnetic head (3) in a search area (40); - detecting (120), by means of the explosive detection unit (17), changes in the resonant frequency (feq) of the electronic oscillator (5) during the sweep; - determining (130) a position of the coil (10) of the magnetic head (3) that produces a greater change in the resonant frequency (feq) of the electronic oscillator (5); - activate and deactivate the power converter (15) according to the following activation patterns: activating (140) the power converter (15) in a series of short activation pulses (142) of a duration TON less than a first activation threshold Ti; and if there has been no detonation of the explosive device (11), activate (160) the power converter (15) in a series of long activation pulses (162) with a duration of TON greater than one second activation threshold Ts, where Ts> Ti8. The method according to claim 7, characterized in that the short activation pulses (142) have a duration (TON) of more than 3 seconds.

9. The method according to any one of claims 7 to 8, characterized in that the long activation pulses (162) have a duration (TON) of more than 10 seconds.

10. The method according to any of claims 7 to 9, characterized in that it comprises estimating the distance (d) of the coil (10) to the explosive device (11) in the position in which a greatest change in frequency occurs in resonance, based on the sweep (110) carried out and the detection (120) of changes in the resonance frequency produced in said sweep.

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