[0001] Field of the Invention (Technical Field)

[0002] The invention is in the field of detecting significant electromagnetic events, locating and discriminating between EMP events, such as lightning strikes, nuclear events, large explosions, and muzzle flash.

[0003] Background

[0004] An EMP (Electromagnetic Pulse) can be a source of failure to many electronic devices. Human themselves are fairly unaffected by an EMP. An EMP can damage electronics. The time history of the electrical pulse can be a source of diagnostic information to tell us what has happened. See, e.g., E. F. Vance and M.A. Uman, IEEE Trans. On EM Compatibility, vol. 30, No. 1, Feb. 1988, 'Differences between Lightning and Nuclear Electromagnetic Pulse Interactions'; J.E. Fine and S.J. Vinci, Adelphi, MD 20783- 1197, ARL report ARL-TR-1690, 1998, 'Causes of Electromagneic Radiation from Detonation of Conventional Explosives: A Literature Survey'; J. Sweeney, LLNL, "Low Frequency Electromagnetic Pulse and Explosions, Jan., 2011; each of which is incorporated herein by reference. Primary sources of EMPs include lightning, solar flares, chemical explosions (such as a fuel tanker or chlorine tank), firearms or explosives and nuclear devices such as a bomb or radiation dispersive device (RDD). These EMP events are functionally the result of a plasma burst. Equivalent to sheets of charge and the time dependent charge sheets create large electromagnetic fields, which can be discriminated based on their time dependent features to tell us what physics gave rise to the pulse. Unfortunately, electronics currently in use can be strongly affected by EMP and accordingly be unable to provide knowledge of the source of the EMP. The present invention provides methods to capture the trace, analyze it and key features of hardware that can survive in order to capture the trace, keep it or send it out to be used.

[0005] Simple handheld devices are currently available to measure the distance to and identify lightning strikes; examples include devices such as those sold by SKYSCAN and ACURITE (trademarks of their respective owners). Such devices can provide estimates of distance but not direction. They cannot discriminate between different types of EMP. The data they capture, as well as the devices themselves might not function after an intense EMP burst. They are designed as safety devices in order to know when to shut down equipment or to protect against moderate intensity lightning events.

[0006] There are lightning maps available on the web (e.g. Iightingmaps.org, geology.com/lightning-map and others); the data can be acquired by tools such as the Tropical Rainfall Measuring Missing satellite LDAR array (Lightning Detection and Ranging system developed by NASA). There are a few papers describing the phenomenon in chemical explosions. None use the features as a diagnostic. Technologies such as LIDAR, b-dots arrays, and optical burst measurements can also be made to image and diagnose the plasma sheet which characterizes lightning and EMP. Wide area fielding of any of these assumes a presetup device and a known type of situation. [0007] Summary of the Invention

[0008] The present invention provides methods and apparatuses that can detect EMP events and distinguish among several different types of EMP event causes. Embodiments provide a plurality of timedependent sensing circuits, each responsive to electromagnetic signals with a different time-dependent response. Embodiments combine the signals from the plurality of sensing circuits to allow the type of EMP source to be determined. These circuits can be analogue or digital. The circuit can contain sample and hold, either active or passive (e.g., resistor/capacitor, or RC, circuit, analogue or digital signal processing) elements to maintain the signal until after the portion of the incoming signal which might destroy the electronics has passed in order to wake the storage circuit so that data can be exfiltrated to a user. With multiple sensors location, distance and size of explosion can be estimated.

[0009] Embodiments of the present invention provide an apparatus for sensing of an electromagnetic pulse (EMP), comprising: (a) a receiver configured to produce an electrical signal responsive to the EMP;

(b) a plurality of time-dependent voltage sensing circuits, each in electrical communication with the receiver, where each sensing circuit has a time dependent relationship between input voltage and sensed voltage, and there the relationship of each sensing circuit is different from that of other sensing circuits; and (c) a determination system configured to determine a source of the EMP from the sensed voltages of the plurality of sensing circuits.

[0010] In some embodiments, the apparatus of claim 1, wherein the receiver is an antenna or multiple antennae. In some embodiments, the sensing circuits comprises a resistor and a capacitor connected in series between the receiver and ground, and wherein the voltage between the resistor and the capacitor is used as the sensed voltage.

[0011] In some embodiments, the determination system uses the sensed voltages of the plurality of sensing circuits at a single time. In some embodiments, the determination system uses the sensed voltages of the plurality of sensing circuits at a plurality of times. In some embodiments, the determination system uses digital signal processing instead of analogue circuits to determine amplitude of the event, angle and distance from the sensed voltages of the plurality of sensing circuits at a plurality of times. In some embodiments, the determination system uses digital signal processing and artificial intelligence methods to discern the characteristics of the source instead of analogue circuits to determine amplitude of the event, angle and distance from the sensed voltages of the plurality of sensing circuits at a plurality of times. In some embodiments, the determination system determines the source of the EMP from ratios of the sensed voltages. In some embodiments, the determination system is connected to the sensing circuits with an optical connection.

[0012] In some embodiments, a first sensing circuit comprises a IkOhm resistor and a 10-8 F capacitor; a second sensing circuit comprises a IkOhm resistor and a 10-6 F capacitor; and a third sensing circuit comprises a IkOhm resistor and a 10-2 F capacitor. In some embodiments, adjustable RC circuits are used to identify the source of an event. [0013] Some embodiments are coupled with a radiation sensor to provide early warning of a nuclear event with a directional radiation sensor to contribute to reducing the consequences and assist in evacuating the fallout area. Some embodiments are coupled with one or more electromagnetic sensors or piezoelectric switches to provide early identification of events creating a plasma (from nuclear weapon scale to a simple cap gun). This includes most firearms. The processing of such signals can provide amplitude, distance and angle. Some embodiments are coupled with a directional radiation sensor to contribute to reducing the consequences and assist in evacuating the fallout area. Some embodiments are coupled with a directional and distance inferring EMP sensor and circuit to contribute to reducing the consequences from a nuclear, lightning, chemical, accidental or weapon induced event resulting in a discernable EMP source. Some embodiments are coupled with an infrared camera or visible camera in order to assist emergency responders by understanding better the hazards associated with a nearby plasma cloud.

[0014] Brief Description of Drawings

The accompanying drawings show aspects of the specification and practice of example embodiments of the invention. They are meant to illustrate embodiments and serve as examples. They are not meant to limit the invention.

[0001] FIG. 1A is an illustration of the time-dependent characteristics of a high-altitude electromagnetic pulse (HEMP). FIG. IB presents experimental data of a cap gun and piezoelectric switch (a triggered firestarter). The traces show the large differences in pulse shape and the ability to measure from a large pulse as well as a small one. There is little information in the cap and piezo device at time less than 1 us, where the nuclear is highest. The nuclear event is dominated by signal between 1 nanosecond and 1 microsecond. The traces of the piezo device and the small explosive are also pronounced in terms of both high and low frequencies of the output signatures. Because the rise time is always clear and risetimes can be used for location the locations determined can be very accurate with these techniques.

[0002] FIG. 2 is a simplified schematic illustration of an example analogue circuit embodiment of the present invention. The voltages measured at the tops of the resistors. The figure shows a simple type of analogue filter. Other embodiments can use a digital frequency filter and other numerical techniques to discriminate types of EMP sources as well as distance and angle. The analogue circuit shown is an embodiment that is easy and low cost to implement. The ratios of the peaks can be used to determine the type of EMP or other source and the timing can be used to determine location. Amplitudes can be used to determine magnitude once the location is determined.

[0003] FIG. 3 is an illustration of an example embodiment of the present invention.

[0004] Fig. 4 is schematic illustration of an example embodiment having optical communication to shielded electronics. This protects the unit from being damaged by the EMP as the electronics is in a shielded cage and the sensor is electrically isolated. [0005] Detailed Description of the Invention

[0006] Often time-of-flight techniques, for instance radar, can be used to image almost anything. In this context that means find an object or localize it. Radar which has a source of electromagnetic waves and the return signal is analyzed. The present invention provides methods to do something similar, except that the ElectroMagnetic (EM) radiation is produced by the source. It is asynchronous, not repetitive and almost any plasma will do. A single sensor or antenna can provide amplitude and time. Multiple antennae can provide location, distance and size. The equations to unfold and determine these plasma parameters are essentially point-in-time transforms of the radiated EM spectrum. Basically, the time-of-flight, at the speed of light, is used to triangulate in order to determine the location of an event. These time-of-flight (TOF) techniques involve multiple sensors in a spatial array to obtain event location.

[0007] A tool to identify the source mechanism and potentially a diagnostic for source location can be useful. The present invention provides a simple and direct way to provide useful diagnostic signature measurements and interpretation of the time dependent and spatial features of EMP. In addition to the simple analogue method for processing more complex digital means can improve resolution.

[0008] Explosions, inherently a burst of activity can have explicit signatures as well. See, e.g., J.E. Fine and S.J. Vinci, Adelphi, MD 20783-1197, ARL report ARL-TR-1690, 1998, 'Causes of Electromagneic Radiation from Detonation of Conventional Explosives: A Literature Survey', incorporated herein by reference. Time history of the burst and amplitude are key signatures. There were no commercial devices found for when looking for gunshot locators based on EM signatures or for the ability to look and identify different kinds of burst plasmas or explosions. It is not clear at this point if differences between caliber of weapon, or gun manufacturer will be resolved. However, whatever the plasma, source this information will be useful to law enforcement, military and others to diagnose mundane and emergency situations and saving lives.

[0009] A typical prior art device does not discriminate between types of events such as nuclear, chemical or lightning. However, both time-of-flight and pulse shape analysis, including phase of a given pulse can be used in the present invention to discriminate between the source of a given EMP, angle, distance and magnitude. Consider the pulse shape issues. If the timing indicates that the event happened at many locations around the earth at the same time in a ring it is a solar flare. If it is large and propagates from a point it is likely nuclear. If the effect is local (e.g., a few tens of miles), it might be lightning, a chemical explosion or a small nuclear one. Based on the pulse shape from these smaller events one can likely discriminate between the events and first responder, society or individuals can determine the best response in order to minimize consequences. This can be done by reducing the time to appropriately respond.

[0010] For example, a solar flare will irradiate the surface of the earth at nominally the same time and locations; a constant distance from the sun (e.g., a ring) will see the event at exactly the same time since all light moves at the speed of light in a vacuum. A nuclear event exo-atmospheric will leave a telltale footprint, closer to the earth there will be a fire ball and surface effect will affect the time history of the pulse. With lightning there is a usually a linear feature (the bolt) and its physical shape affects the time history and the plasma can have a larger extent than a simple explosive or other large chemical explosion. For each of these an array of sensor can diagnose the type of an event from the differences in signals at different points.

[0011] The time-of-flight (TOF) offers a means of diagnosing the location and method of creation of the charge sheet associated with the creation of the EMP. Usually two or more sense elements are needed to obtain distance. Embodiments of the present invention consider the pulse shapes as they are less hardware intensive and analysis comes from a single pulse on a single electric field sensor. For example, the time history of events can be characterized in phases. If multiple sensors or antennae are used then the distance to the event can be estimated as well as the amount of energy behind the plasma.

[0012] FIG. 2 is an illustration of an example embodiment of the present invention. An antenna is configured to be exposed to electromagnetic events of interest, for example outside of any electromagnetic shielding. The antenna is electrically connected to first and second electrodes of each of multiple bandpass filters (for example three as configured in FIG. 2). The concept can be extended to more bandpass filters for greater discrimination.

[0013] The resistors and capacitors in the bandpass filters can be chosen so that each bandpass filter provides filter output distinguished from that of the other bandpass filters. Important characteristics are the cutoff time or frequencies. These sets of filter frequencies (~l/times) will allow discrimination between plasma types (e.g. the types of events we wish to discriminate between). Voltages can be sampled at the output of each of the bandpass filters, e.g., El(t), E2(t), and E3(t). Because of the different filter performances, the voltages El(t), E2(t), and E3(t) will have different time-dependent characteristic for a specific input signal from the antenna. The relationships among the voltages can reveal the likely source of the electromagnetic event. The relationships can be determined at several times, in the simplest case at a single time. For the more complicated situation, for instance, where an explosion starts a fire then the initial event tells the source and the longer time features inform us about what is happening (e.g., an explosion starts a fire). Different values of Rl, R2,... R _n , Cl and C2, C _n for different stages will provide different bandpasses for El, E2, E3, ...E _n . Purely passive circuitry can also be suitable.

[0014] FIG. 3 shows a description of a simple system designed to discriminate between lightning and nuclear events by acquiring and discriminating signatures. The time history is in the upper left quadrant. A rough discriminator circuit to the right, comprising simple resistor-capacitor frequency response circuits, each having different time-dependent response than the others. Timing signature circuitry is not shown. A rendering of a device illustrating the location of the optical isolation is shown in the lower left. The rendering shows an EMP module (for sense and discrimination) with optical linkage to a data processing and exfiltration unit.

[0015] FIG. 4 illustrates more detail regarding the device design illustrating how the optical isolation will protect the electronics processor. An EMP module (for sense and discrimination) - will also connect to antennae - not shown. An interface optical linkage to data processing and exfiltration unit comprises a short distance transmit-receiver pair. An electronics module is electrically isolated from the sensor module and in this case the outer surface is a Faraday cage. This can contain storage and processing capability for signals; and can contain hardened wireless transmitter/receiver for networking. Multiple sensors/antennae can be required for distance and location measurements.

[0016] The phase and amplitude of the signal allows determination of plasma type, size, amplitude, distance and angle when triangulated. Use of the ratios as a function of time can reduce the amount of data to be shuttled between sensors and processors. Depending on the electronics used it might not be necessary to save bandwidth. Otherwise Digital Signal Processing (DSP) can give greater detail and resolution in the unfold process to characterize the plasma. The pulses for lightning can show multiple peaks indicative of a lightning strike. A nuclear event, a typical chemical explosion and a longer burning fire will have single peaks and various shaped tails. The three amplitudes (El, E2, E3) present different characteristics depending on the source of the electromagnetic event. More parameters filtered at different frequencies can provide more resolution. With a DSP and wavelet or machine learning algorithms the resolution can be even higher.

[0017] An embodiment of the present invention can determine the likely source of an electromagnetic event from as few as a single time sample of the multiple amplitudes (or voltages). A single time sample of one voltage would not provide enough information to discriminate between sources, since each voltage can assume any voltage value after any source event, depending on the maximum amplitude of the antenna signal and the time since the event. Sensing the maximum amplitude of the event can be problematic, however, because such events can present signals too large (i.e. 10V) for conventional electronics sampling. The present invention can be used with high bandwidth amplifiers and A/D converters to incorporate a wide dynamic range of events. The circuits can be protected against overvoltage to limit damage from nearby or intense events.

[0018] Sampling two or more voltages (three in this example, though other numbers can be used) at even a single time can reveal the likely source event since the different filter outputs (or RC constants) reveal sufficient information about the time characteristics of the electromagnetic event. In FIG. 1 we showed how the electric field as a function of time can expressed in terms of multiple time phases. Currently the literature employs three time phases El, E2 and E3. The limit of three is arbitrary because the intent has only been to separate nuclear events from lightning. In the future we will use more because with these techniques we can resolve finer distinctions in the EMP producing plasma The filters separate the signals by frequency space which we described in terms of RC time or one over frequency. This processing can be done in frequency space or in the time domain. Embodiments can be configured to use the one which uses the least power. In some embodiments and applications, DSP can be best. However, analogue processing can save cost and power in the circuitry, making it more suitable for some embodiments and application. Such processing will happen in the time domain. For example, simple moving averages will capture the derivatives of integral passive circuitry. The ratios of the derivatives can be overlaid on different kinds of events and the derivatives allow discrimination between events based on the time dependent amplitudes. The values of these ratios as a function of time allows for continuous monitoring of EMP pulses and a peak monitored with a threshold can be used to determine the presence of a positive event and if the ratio threshold is not triggered.

[0019] Sampling these moving data sets can be complex. The description herein of the physics of what is happening can be used by one skilled in the art of frequency filtering. We show how one type of event is different from the others in the plot and we discriminate therefore by amplitude in the algorithm. A different kind of processing, using frequency space, is also feasible and can offer improvements in some settings, and will be appreciated by those skilled in the art from the disclosure herein.

[0020] An example embodiment provides a system that reveals time and magnitude relationships that allow determination of a likely source event using only passive components that can survive typical electromagnetic pulse events. FIG. 3 is an illustration of an example embodiment that provides an analog to digital converter. Using this method the pulses can be analyzed as a streaming event, rather than needing download and additional processing. The output (based on amplitude and ratio discriminator circuits) is passed through an optical link directly to another module for storage and further analysis. The full-time course of the event signal can be analyzed by analyzing stored signals.

[0021] Some events able to trigger an event positive can be incompatible with operation of digital electronics, and often can destroy such electronics. To accommodate such events, an optical link can be implemented between the initial acquisition and processing and a more sophisticated processor. The EMP module can be connected through multiple optical fibers to the receiver module in order to protect against high voltages and EMP crosstalk between modules. An example embodiment is shown in FIG. 4. The analog to digital circuits are used to process circuit outputs, passive and/or active sample and holds and be used to maintain processing capability and restore power to normally off circuits (these are used to save power). Once enabled/powered back on the voltage parameters can be stored for later read and store the data. Separate power is used in each module to provide robust operation and prevent damage by the EMP to be measured.

[0022] A low power, power supply can provided with separate batteries and regulation to a Cortex M0 or better processor to analyze the signal in real time and generate a trigger to identify than an event has occurred and both analogue output and/or a processed signal specifying the type of event from the analogue analysis. Memory can be provided (like an oscilloscope or data recorder) to store and exfiltrate the data. Analogue and/or digital optical links can be supplied for data transfer.

[0023] The present invention has been described in connection with various example embodiments. It will be understood that the above descriptions are merely illustrative of the applications of the principles of the present invention, the scope of which is to be determined by the claims viewed considering the specification. Other variants and modifications of the invention will be apparent to those skilled in the art.