Abstract:
A wearable ballistic impact protection system detects impacts to a body. The system includes multiple sensors  10 L,  10 R for detecting vibration. The sensed vibrations are converted to electrical signals which are filtered. Electronic components  15  are provided to determine whether the filtered signal have frequency and amplitude characteristics of impact that cause injury to a body. Preferably, the sensors  10 L,  10 R are Piezo-electric film sensing elements. Information regarding the extent of the impact and injuries to the body may be transmitted to a remote location so that medics or other personnel may be informed to the extent of injuries to the body so that they may provide medical assistance.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention is generally directed to ballistic impact detection systems. More particularly, the invention is directed to a wearable ballistic impact detection system for detecting impacts to a body and especially impacts which might cause injury.  
         [0003]     2. Discussion of the Art  
         [0004]     The future battlefield is projected to be asymmetric, noncontiguous and nonlinear. To meet the challenge of future conflicts, the U.S. Army is changing its paradigm from linear and sequential operations to simultaneous and distributed operations. Sophisticated and adaptive adversaries are making unconventional tactics, such as guerrilla warfare and terrorist attacks, commonplace. In the future, as today, ground forces will continue to be counted on to win, hold the ground and rebuild the peace. The centerpiece enabler of the Army&#39;s transformation is the Future Force Warrior (FFW). FFW is a revolutionary redesign of the individual warfighter platform from the skin out. FFW is a system wherein data from sensors on the individual soldier are fused with similar information from other soldiers in the unit of action. As the data is integrated and sent back, the warfighter becomes a sensor node in a bigger network mesh which ultimately allows battlefield commanders to quickly react to critical information. Elements of the individual warfighters health status will be incorporated into the data stream from physiological monitoring devices worn by each soldier. The Warfighter Physiological Status Monitor (WPSM) is the medical system that will deliver pertinent information that will keep the soldier in the fight and, in the event of becoming a combat casualty, aid medics in rescue and recovery operations.  
         [0005]     The central tenet to the Army&#39;s transformation to FFW is the ability to “see first, understand first, act first and finish decisively.” The underlying foundation for achieving this detect-decide-deliver goal of battlefield tactics will be information technology. Acquiring critical information and delivering it rapidly and correctly will have a profound effect on the tactical, operational and strategic success of future combat missions. In the future, the Army unit of action will conduct operations over larger spaces. This translates into small, disparate fighting groups covering far more territory with a single medic in support. It is quite likely that FFW warfighters will be out of sight and hailing distance of medics and will rely on a medical information sub-network to achieve adequate levels of medical support. Early notification of a soldier&#39;s need for medical attention can reduce the time to initial treatment and thus may reduce the morbidity and mortality of wounded soldiers.  
         [0006]     Data from a study of causes of death from the Vietnam War shows that while 66% of combat casualties die within the first 5 minutes of being wounded, there is an opportunity to save lives if a medic can get to a soldier quickly.  FIG. 1  shows the percentage of all combat deaths as a function of the time from the wounding event. A therapeutic window of opportunity exists for those soldiers killed in action (KIA) in the timeframes encompassing 5 minutes to 6 hours. Given findings during Operation Desert Storm that the predominant cause of deaths in Corps hospitals was exsanguinations from extremity wounds, it is likely that with advances in body armor, extremity wounds will become a large percentage of potentially salvageable casualties on the battlefield. Knowing when a wounding event occurs and the ability to engage other physiological apparatus on the soldier to determine the extent of the casualty will play an important role in the required remote triage capability needed to change battlefield casualty statistics.  
         [0007]     One known way to detect penetrating impacts is to use a mesh fabric incorporating fiber optics. When a fiber is broken, it is assumed to be caused by a penetrating impact. However, such a system is fragile and cannot accurately determine a ballistic impact from a rip or tear in the fabric caused by other sources.  
         [0008]     Regardless of potential solutions, there exists a need in the art for a wearable ballistic impact detection system for detecting impacts to a body and especially impacts which might cause injury. The over-arching goal of the Ballistic Impact Detection System (BIDS) and WPSM program is to increase survivability of the soldier on the battlefield and facilitate more rapid triage for the combat medic. The BIDS has the following advantages: it is less expensive to manufacture; it detects impacts in extremities; is not prone to false positives from rips and tears; and is able to detect non-penetrating, but injurious blast overpressure.  
       SUMMARY OF THE INVENTION  
       [0009]     The Ballistic Impact Detection System (BIDS) comprises a means to detect when a human body is impacted by a potentially injurious impact, such as a bullet, shrapnel or a significant blast wave. Piezo-film sensor elements detect the acoustic vibration patterns caused by an impact and convert them to a voltage. The voltage is passed through a circuit which determines if the impact has the frequency and amplitude characteristics of impacts that cause injuries. BIDS will be integrated into the Warfighter Physiological Status Monitor (WPSM) being developed for the Future Force Warrior (FFW) program. The WPSM represents the first attempt to place physiological monitoring equipment on individual soldiers. While the overall purpose of the WPSM is to provide information as to the health of the soldier, it has two distinct modes: operational and combat casualty. The BIDS will be used as the trigger mechanism to automatically detect a potentially injurious impact. This will enable the WPSM to begin monitoring physiological signals at faster rates in order to provide the medic with information enabling remote triage. This information is also of value to command and control elements.  
         [0010]     Two sound sensors are positioned on a combatant&#39;s body to register high-energy acoustic signatures produced by ballistic impacts. The voltage output from these sensors feeds a small battery-powered analog and/or digital circuit also carried by the combatant. The circuitry isolates these signatures according to their voltage amplitudes and frequencies and discerns the approximate impact locations on the body within right, center and left general regions. The circuitry outputs “off” or “on” signals corresponding to each of these three general locations. The “on” outputs, signifying a ballistic impact, can ultimately be interfaced to a wireless link with a medical receiver in order to provide notification that the soldier has experienced one or more wounding events in these respective locations.  
         [0011]     The BIDS is designed to detect ballistic impacts to the soldier&#39;s body. In future Army battle scenarios, soldiers will be spread over a much larger battle zone. It is quite likely that the solder will be out of direct contact with medical personnel. BIDS will act as a trigger for other on-body systems to collect physiological data at a faster rate. This data will then be radioed to the medic to allow remote triage.  
         [0012]     Some of the novel features of this invention include the application of Piezo-film sensors on the body that pick up skin vibrations, detection and determination of frequencies associated with a ballistic impact, determination of the location of ballistic impacts on the body, determination of wound severity and detection of blast overpressure.  
         [0013]     Ballistic impact detection could also prove valuable to police units, firefighters and other personnel working in hazardous environments for wound detection. The BIDS can also be used to detect impact for machinery, buildings and equipment and to sense vibrations for machinery. The BIDS can be built into body armor, battle fatigue, uniforms or other garments/articles worn by an individual providing for an automatic call for help.  
         [0014]     Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of a preferred embodiment when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a graph showing the percentage of total combat deaths as a function of time from a wounding event during the Vietnam war;  
         [0016]      FIG. 2  is a diagram showing sensors placed on a human body in accordance with the invention;  
         [0017]      FIG. 3  is a schematic view of the overall arrangement of the ballistic impact detection system according to a preferred embodiment of the invention;  
         [0018]      FIG. 4  is a cross-sectional view of a sensor used in the ballistic impact detection system;  
         [0019]      FIG. 5  is a side view of the sensor shown in  FIG. 4 ;  
         [0020]      FIG. 6  is a schematic circuit diagram of the impact detection system according to another preferred embodiment of the invention;  
         [0021]      FIG. 7  is a schematic circuit diagram of another preferred embodiment of the impact detection system;  
         [0022]      FIGS. 8A-8C  are circuit diagrams of the impact detection system;  
         [0023]      FIG. 9  is an enlarged diagrammatic view of the low pass filter of  FIG. 8A ;  
         [0024]      FIG. 10  is an enlarged diagrammatic view of the band pass filter of  FIG. 8A ;  
         [0025]      FIG. 11  shows one channel of the embodiment shown in  FIGS. 8A-8C ;  
         [0026]      FIGS. 12A-12H ,  13 A- 13 D and  14  show a more detailed circuit diagram of the ballistic impact detection system of  FIG. 3 ;  
         [0027]      FIG. 15  shows an impact of a left lateral chest area;  
         [0028]      FIGS. 16   a  and  16   b  show a shock wave amplitude of a left sensor being greater than the amplitude of a right sensor confirming that an impact site was in the left lateral chest;  
         [0029]      FIG. 17  shows the Fast Fourier Transform performed on an initial 7.5 milliseconds of a shock wave of an impact;  
         [0030]      FIG. 18  shows a lateral chest hit with body armor signature;  
         [0031]      FIG. 19  shows a response for a sensor registering shot locations in the abdomen, sternum and hind limb;  
         [0032]      FIG. 20  shows a Fast Fourier Transform for the shock wave portion of the signal shown in  FIG. 18 ;  
         [0033]      FIG. 21  shows the location of sensors placed on the back of a subject;  
         [0034]      FIG. 22  shows a representative left lateral chest impact with body armor from signal sensor  2  as shown in  FIG. 21 ;  
         [0035]      FIG. 23  shows the FFT performed on the impact shown in  FIG. 22 ;  
         [0036]      FIGS. 24 and 25  show typical impact signatures;  
         [0037]      FIGS. 26 and 27  show the frequency spectrum of the impact signatures of  FIGS. 24 and 25 ;  
         [0038]      FIG. 28  shows a signal produced from a 200 gram land-mine blast on channel  1 ;  
         [0039]      FIG. 29  shows the Fast Fourier Transform of the blast shown in  FIG. 28 ;  
         [0040]      FIG. 30  shows the resulting signal from a 30-inch jump;  
         [0041]      FIG. 31  shows a frequency domain spectrum produced by a Fast Fourier Transform of the 30-inch jump; and  
         [0042]      FIG. 32  shows a comparison of two signals filtered with a 3-pole 5,000 Hertz high pass filter.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]     The BIDS design centers on reducing false-positive indications to near zero. It would be approaching impossibility to completely rule out false-positive indications due to the number of ‘normal’ tests on all body types necessary. Because the BIDS is soldier-born, there are always requirements of near-zero cube, weight and power. An analog based system was designed based on the proof-of-concept data. Testing from the proof-of-concept phase indicates that discrimination is achieved by isolating frequencies in the 400-1000 Hertz band. If these frequencies meet a threshold voltage requirement, an impact criterion is met. While high velocity swine tests corroborate the earlier proof-of-concept tests in terms of the frequency range of interest, preferably a high-pass filter is employed for the circuit.  
         [0044]     The circuitry for BIDS is either purely digital in nature or an analog-digital hybrid. In a preferred embodiment, the circuitry is primarily analog with a digital output that is compatible with computing devices. The BIDS includes two sensors that couple to the body in such a way as to sense the vibrations of the skin. The sensors are Piezo-film mounted on a flexible substrate of Mylar plastic. The vibrations produce voltages commensurate to the frequency and amplitude of the vibrations. Each sensor signal is processed in similar circuit sections. All sensor signals are ultimately fed into logic circuitry that makes a determination as to the location of the impact.  
         [0045]     Turning now to  FIG. 2 , there is shown the placement of sensors  10 L and  10 R on a human body connected to the various group of electronics  15  which make up the Ballistic Impact Detection System. Of course, in this case, the body is shown from the rear so that  10 L represents the left sensor and  10 R represents the right sensor. It should be noted that, although two sensors are shown here, numerous different types and numbers of sensors could be used. The sensors  10 L or the electronics  15  may be mounted on a bullet proof vest, body armor, battle fatigues, a uniform or other garments/articles designed for the body. The electronics  15  may include a transmitter to transmit information to a remote location. Such a transmitter is disclosed in U.S. Pat. No. 6,349,201 which is incorporated herein by reference.  
         [0046]     Turning now to  FIG. 3 , there is shown left and right channels of electronics which lead to a logic circuit. The left channel starting with sensor  10 L is shown in parallel with the right channel beginning with sensor  10 R. Since both channels are correspondingly constructed, only one channel needs to be discussed below. The voltage signal from sensor  10 L is conducted to an input buffer amplifier  20 L. The signal then passes through a high pass filter  30 L. The current embodiment uses a 3-pole Bessel with a cutoff frequency of 5000 Hertz. While much of the work to date indicates that telltale frequencies exist in to 400-1000 Hertz range, it is impossible to create an analog filter with such a narrow band pass. The 5000 Hertz filter is 42 dB down at 1000 Hertz and 60 dB down at 500 Hertz. It has been found that there is enough frequency information passed by this filter to adequately discriminate the impact signals collected. The signal is then conducted to a full-wave rectifier  40 L which converts the voltage from bipolar to only positive. The signal then passes through a 3-pole 1000 Hertz low pass filter  50 L which widens the voltage peaks of interest. The signal is then conducted into a logarithmic amplifier  60 L. The output of amplifier  60 L is a voltage equal to the log of the input voltage. This stage at amplifier  60 L prevents a large signal from saturating the next stages. Saturation would cause loss of frequency information that could lead to false-positive impact determinations. The next stage is a peak hold circuit  70 L which determines and conducts the peak voltage in the signal to the threshold circuit stage  80 L. Threshold circuit stage  80 L compares the peak voltage of the signal to a threshold voltage. If the signal voltage is higher than the threshold, then an impact has occurred. The original signal voltage is passed to logic  90  that determines location. This location logic  90  compares the amplitudes of all the sensors to make a location determination.  
         [0047]     Turning now to  FIGS. 4 and 5 , there is shown a sensor  10  which could be either of sensors  10 L or  10 R described above. This particular sensor is a Piezoelectric-film type sensor generally formed of a Piezoelectric-polymer such as polyvinylidene-floride (PVDF). Such a sensor has a base layer  110  preferably formed of approximately 14 mil thick Mylar and a top layer  120  formed of approximately 7 mil thick Mylar. Between the two outer Mylar layers  110  and  120 , there are formed, in order: a layer  130  of approximately 1/16″ thick foam, which is located below Mylar layer  120 ; a metal silver ink layer  140  forming the negative terminal of sensor  10 ; a PVDF layer  150 ; and a positive silver ink layer  160 . Although not shown, each sensor  10 L,  10 R preferably incorporates FET circuitry.  
         [0048]     The negative silver ink layer  140  and the positive silver ink layer  160  are connected to output wires  170  and  180  by means of eyelet connectors  175  and  185 , respectively. All of the layers mentioned above are preferably laminated together, such as with an approximately 1 mil acrylic adhesive. The overall capacitance for such a sensor is preferably 550 Pico-farads, with a dissipation factor of less than 0.025. Sensors  10 L and  10 R could be constructed in other ways, such as those shown in U.S. Pat. Nos. 4,413,202 and 4,761,005 which are incorporated herein by reference.  
         [0049]     Turning now to  FIG. 6 , there is shown a more detailed diagram of the two channels shown in  FIG. 3 . However, there are modifications and detailed below. In this case, with reference to the left sensor  10 L, the signal is passed to a low pass filter  230 L with a 20 kHz cutoff. Likewise, right sensor  10 R is connected to a low pass 20 kHz filter  230 R. At this point, it should be noted that low pass filters  230 L and  230 R are not crucial to the invention and need not be present. If provided, both left and right filters  230 L and  230 R would be input to an analog to digital converter circuit  234  as shown. With reference to the left channel, the signal passes through 500-1000 Hz band pass filter  236 L then to a root mean squared DC converter  240 L and next to comparators  280 L and  281 L which checks the signal versus a reference voltage. Finally, a search logic  290  determines whether a hit is a left side hit, a center hit or a right side hit. The right channel has similar circuitry which will not be described separately.  
         [0050]     Turning now to  FIG. 7 , there is shown a more detailed circuit diagram similar to that shown in  FIG. 6 . However, this diagram includes both 1 kHz and 3 kHz band pass filters  336 L,  336 R,  338 L,  338 R for each channel. These filters pass 500-100 Hz for the kHz filters  336 L and  336 R and pass 2000-4000 Hz for the 3 Hz filters  338 L and  338 R. The relative strength of the signal from each type of filter provides additional information regarding the impact.  
         [0051]     Turning now to  FIGS. 8A-8C , there is shown again left and right channels coming from left and right sensors  10 L and  10 R. The channels correspond to those shown in  FIG. 6 . In this case, the low pass filters  230 L and  230 R (again optionally shown) are specified as UAF  42  microchips and their pin configurations are shown with each pin connected to an appropriate electrical element to set each filter at the 20 kHz level. Next, in each channel is shown another UAF  42  microchip, this time set to be a respective band pass filter  236 L,  236 R. Again, low pass filter  230 L and  230 R are optionally shown. If not provided, the output from a respective sensor  10 L,  10 R would be sent to pin  2  of a respective band pass filter  236 L,  236 R as represented by the dotted lines in  FIG. 8A . Next shown in each channel are AD  637  microchips which act as rectifiers  240 L and  240 R of the block diagram shown in  FIG. 6 . Furthermore, the pin configuration of four different comparators  280 L,  281 L,  280 R and  281 R are shown in  FIG. 8B . These comparators  290  are equivalent to those shown in  FIG. 6 . Finally, the details of the logic gates shown in  FIG. 6  are shown in much more detail in  FIG. 8C .  
         [0052]      FIG. 9  is simply a close-up of a UAF  42  chip shown in a low pass filter mode set at 20 kHz and is a more detailed view of one of the UAF  45  chips  230 L,  230 R shown in  FIG. 8A . Again, it should be noted that low pass filters  230 L and  230 R are optional as discussed above with particular reference to  FIG. 8A . Likewise,  FIG. 10  shows another UAF  45  chip  236 , this time set up to be one of the band pass filters  236 L or  236 R as shown in  FIG. 8A .  
         [0053]      FIG. 11  shows a single channel of the embodiment shown in  FIGS. 8A and 8B . First shown is the UAF microchip  236  set to act as a band pass filter. Next shown is the AD  637  microchip  240  which is acting as a rectifier. Next is shown a comparator  280  labeled MAX  931 , which is one of the comparators shown in  FIG. 8B . Finally, a 4043 microchip  290  is shown which sends a signal on for further processing.  
         [0054]     Although considered to be shown in sufficient detail in reference to the figures discussed above, for the sake of completeness a further detailing of preferred circuitry will be briefly discussed with reference to  FIGS. 12A-13D  and certain test results below. However, at this point, is should be understood that the particular circuitry employed could take various forms, while still achieving the desired results.  FIGS. 12A-12H  show the left channel of the BIDS circuit represented in  FIG. 3 . Note, once again, sensor  10 L is connected to an input amplifier  20 L which then sends a signal to high pass filter  30 L, which, in turn, sends a signal to full wave rectifier  40 L. Next in the sequence is low pass filter  50 L which connects to logarithmic unit  60 L and next to peak hold circuit  70 L. Likewise,  FIGS. 12E-12H  show the right hand channel of the BIDS circuit represented from  FIG. 3 . Sensor  10 R is connected to input amp  20 L which then sends a signal to high pass filter  30 R, which in turn, sends a signal to full wave rectifier  40 R. Next in the sequence is low pass filter  50 R which connects to logarithmic unit  60 R and next to peak hold circuit  70 R.  FIGS. 13A-13D  show the end of the channel  5  shown beginning with  13 A showing left and right threshold circuits  80 L and  80 R, while  13 B- 13 D show the logic circuitry  90 . Finally,  FIG. 14  presents a detailed view of the preferred circuitry for threshold circuit  80 R.  
         [0055]     Regardless of the particular circuitry employed, the current two sensor embodiment, if the amplitude signals from sensors  10 L and  10 R are less than a 2:1 ratio and at least one sensor signal meets the threshold voltage requirement, the impact is deemed to have occurred between the sensors or in a center location. If the ratio of the signals is greater than 2:1 and the greater signal also meets the threshold voltage requirement, the location is deemed to be distal to the sensor with the greater amplitude signal. Thus, in the two sensor embodiment, three locations are possible: center; right and left. The voltage signals for these location outputs are latched and then available to be read or transmitted to a computer. Once read, the BIDS accepts a reset voltage signal which returns the location outputs to ground. In its current embodiment, the BIDS circuitry can distinguish one impact in each location until a reset is received. The current analog BIDS circuit measures 1.5 square inches and requires approximately 600 microamperes of current at 3 volts.  
         [0056]     A further aspect of BIDS is linking the impact detection with the wounding severity to provide the medic with as much triage information as possible. At this point, it should be noted that the BIDS can be based on a digital signal processor which would sample the incoming analog voltage from the sensors, establish Fast Fourier Transforms and perform power analysis on the signals to determine impacts and locations. Sophisticated algorithms could be established to tell from frequency analysis whether a bone has been struck and from power analysis whether an exit wound exists. In this digital embodiment, BIDS would track multiple impacts in the same general location, as well as potentially providing an indication of wounding severity.  
         [0057]     In connection with the creation and testing of the Ballistic Impact Detection System (BIDS) of the invention, hypothesis outlined that acoustic vibrations on the skin created by penetrating ballistic missiles could be sensed and analyzed to determine severity of the wounding event. A proof-of-concept phase was conducted with the acquisition of impact signatures from a swine model used in a non-lethal wounding protocol. During this protocol, a single ‘plastic bullet’ (a 12 mm steel bearing ball with a thin plastic coating weighing approximately 16 grams) was fired from a gas gun at an anesthetized pig (referenced as Test ID 65-4) from a distance of 8 feet. Three impact locations were used—lateral chest, sternum, and abdomen. Velocities ranged from 239 to 298 feet/second. Two Piezo-film sensor elements were attached using duct tape to the back of the animal, symmetrically about the spine just below the scapulas or symmetrically about the sternum. The voltage response from the sensor elements were digitized at 20,000 samples per second and digitally recorded.  FIG. 15  illustrates an impact to the left lateral chest for one test (Test ID 65-4). Analysis of the impact signatures showed consistent characteristics. Each waveform was made up of two distinct frequency patterns. The first pattern was a low-amplitude, high-frequency section lasting on the order of 20 milliseconds. The second pattern was a high-amplitude, low-frequency section.  FIGS. 16A and 16B  show exemplary voltage recordings.  
         [0058]     For purposes of this disclosure, we will refer to the high frequency section as the shock wave and the lower frequency section as the tissue displacement wave.  FIG. 15  shows the two frequency sections, the shock wave as a fast moving slight rippling  300  effect that moves outward from the impact site and the slower developing tissue displacement wave  310  radiating outward tantamount to ripples in a pool. Examination of  FIGS. 16A and 16B  show that the shock wave amplitude of the left sensor  10 L is greater than the amplitude of the right sensor  10 R, confirming that the impact site was the left lateral chest. Examination of the tissue displacement waves also confirms a left side hit. They also show that, once formed, they move rapidly as witnessed by the imperceptible delay of the tissue displacement waves between the sensors. Frequency analysis in the form of Fast Fourier Transforms (FFT) was performed on the waveforms.  FIG. 17  shows the FFT performed on the initial 7.5 milliseconds of the shock wave for Test ID 65-4. Peak frequencies in the range from 500 to 1000 Hertz were typical in all shots. The peak frequencies (frequencies with the highest power) in this range from this analysis are tabulated in Table 2. FFTs were also performed on the tissue displacement section of the waveform. In every case the predominant frequency of the tissue displacement wave was 98 Hz±19 Hz.  
                                                         TABLE 2                                       Primary Right   Primary Left               Test ID   Frequency   Frequency   Impact Area                                        11-5   645.8   508.8   Stomach           12-11   763.2   547.9   Chest           12-9   665.4   743.6   Stomach           13-11   684.9   665.4   Chest           22-9   724.1   489.2   Abdomen           24-10   547.9   782.8   Chest           26-12   508.8   626.2   Sternum           65-1   606.6   645.8   Chest           65-2   821.9   645.8   Sternum           65-3   673.2   665.4   Chest           65-4   782.8   743.6   Chest           65-5   743.6   567.5   Abdomen           65-6   645.8   802.3   Abdomen            9-3   626.2   508.8   Chest           Average   674.30   638.79           Standard   88.07   104.01           Deviation                      
 
         [0059]     The similarity of the primary frequencies provided a proof-of-concept for ballistic impact detection. The primary frequency range (489-822 Hz) of the impact signature is much higher than what is typically generated in the body during routine activity. Running, jumping and even blunt thumps to the body elicit only a typical 100 Hertz tissue displacement frequency that was also seen in the ballistic signature analysis.  
         [0060]     A multi-protocol research plan was developed to compare impact signatures across models with those from humans. For this purpose, a commercial paintball rifle was chosen to deliver standardized impacts. Paintballs offered a socially acceptable method of delivering an impact to human volunteers for comparison to similar swine and human cadaver impacts. It was thought that similarity of low velocity impact signatures with that of humans would build a strong case for the necessary high velocity impacts in that model. Four swine weighing from 48 to 75 kg were impacted in four locations each (sternum, lateral chest, abdomen and hind leg), with and without body armor while under anesthesia. Five paintballs were fired at each location for a total of forty shots per pig (4 locations×5 shots with body armor plus 4 locations×5 shots without body armor). Eight Piezo-film sensors were attached to the pig&#39;s back in two columns of four, symmetrical about the spine. The armor/non-armor portions of the testing were randomized, as was the shot order in each portion. However, all 20 shots were fired before changing into or out of the body armor. Similarly, all five shots per position were fired before changing to a different impact location. The animals were fitted with older versions of aviation flak jackets for these tests. A total of 1280 impacts recordings were acquired (4 pigs×4 locations×2 body armor×5 shots×8 sensors). Analysis revealed that, while impacts were discernable for almost every sensor and every shot, many of the impact recordings were too low in amplitude and not similar to the non-lethal impacts seen in the proof-of-concept work. Load cell analyses of the paintball impacts show forces that are 25 times less than the solid steel balls used in the non-lethal phase. Calculated values for the non-lethal projectiles range from 46 to 66 Joules, at the velocities (250-300 ft/sec) used in the protocol. Paintball impacts can be calculated at 8 Joules (using 3 grams and 250 ft/sec). However, this calculation does not consider the work expended as the paintball breaks upon impact. Paintball impacts were measured using a load cell at 2 Joules. It is suspected that the difference in the force of the impacts does not cause the characteristic impact signatures of the non-lethal wounding studies. A typical lateral chest with armor signature is shown in  FIG. 18 . The signature in  FIG. 18  can be broken into three separate sections: the pre-impact section from 0 to 9 milliseconds; the impact section from 9 to 12 milliseconds; and the tissue displacement section from 12 milliseconds on. With no way of determining the actual time of impact of these recordings, the pre-impact section of the signatures is considered to represent the response from the air blast of the paintball rifle when fired. The impact section corresponds to the shock wave section in the non-lethal wounding signatures. Due to the diminished force of impact of the paintball, the impact section duration is shorter than the non-lethal signatures. The diminished force of impact also causes the amplitudes of the tissue displacement wave to be much lower than the non-lethal recordings. It should be noted that a plywood baffle was used in the non-lethal wounding protocol to dissipate the air blast from the gun to prevent the chronographs from prematurely actuating. No indication of the air blast is evident in those recordings.  
         [0061]      FIG. 19  shows a typical response for all but the closest sensors for shot locations in the abdomen, sternum and hind limb. The tissue displacement phase of the signal is present albeit very low in amplitude, but no discernable shock component of the signal is present. It is not surprising that the high frequency ‘shock’ components are lost over time and distance as the body&#39;s elastic and dampening nature acts to filter higher frequencies faster.  
         [0062]     Signals from all sensors were digitally recorded at 50,000 samples per second on each channel with a 10,000 hertz anti-aliasing filter. Analysis of the lateral chest shots of the pig (both armor and non-armor) revealed that the predominant shock frequencies occurred in the range of 300 to 700 Hz. Fast Fourier Transforms were performed on the shock section of each signature. The first 120 points of the shock section was zero-padded to 1024 points. The FFT returned 512 frequency coefficients over 25,000 Hertz range for a resolution of 48.8 Hertz per coefficient. The top two frequencies were recorded based on amplitude for each FFT.  FIG. 20  shows the FFT for the shock wave portion of the signal shown in  FIG. 18 . It was quite common to see the double peaks shown in  FIG. 20 . These peaks are considered to be harmonics.  
         [0063]     Table 3 shows average sensor reading for five shots at a lateral chest location while wearing body armor. In the cases where there was no top frequency in the 300-1000 Hertz range, the most significant peak in that range was selected and the amplitude noted.  
                                                                                                                                                     TABLE 3                                       Pig ID   Totals                P337   P377   P378   P379   Average   Average                Frequency   Amplitude   Frequency   Amplitude   Frequency   Amplitude   Frequency   Amplitude   Frequency   Amplitude                        Sensor 1                                               Avg   434.26   141.50   454.02   4.70   600.48   272.13   400.08   254.96   472.21   168.32       SD   47.10   34.12   139.89   1.38   47.69   12.58   47.70   31.39   108.21   111.95       Sensor 2       Avg   649.28   75.10   512.62   89.04   419.76   531.20   458.64   236.97   510.08   233.08       SD   180.79   5.42   48.70   12.54   20.51   22.36   60.76   17.56   127.24   188.76       Sensor 3       Avg   429.32   126.24   497.88   151.94   473.38   259.58   331.88   163.10   433.12   175.22       SD   47.48   26.64   264.22   35.99   95.37   43.07   13.58   37.38   146.14   61.58       Sensor 4       Avg   458.64   6.09   419.58   23.52   590.56   15.99   493.10   50.43   490.47   24.01       SD   95.31   2.08   43.84   7.42   179.16   3.18   55.52   3.34   118.11   17.38       Sensor 5       Avg           385.64   44.08       SD           36.25   21.90       Sensor 6       Avg           522.22   175.26       SD           27.75   60.16                  
 
         [0064]     The location of all lateral chest shots was on the right side approximately equal distance from two sensors. The snug fit of the body armor stabilizes the sensors and their response. To this end, data recorded in connection with armored protection were more consistent than the unarmored data. Table 4 shows the results of the lateral chest shots with body armor, comparable to the live animal impacts summarized in Table 3. Immediately noticeable in the cadaver impacts was the lack of analyzable signatures in channels  2  and  4  in some of the animals. These are the sensors on the far side (non-shot side). However, overall the top frequencies are very comparable those of the live impacts. While the frequencies are remarkably similar, the amplitude of the cadaver signals is dramatically lower across all four sensors. Signal strength in the live animals ranged from 160 to 230 (except for sensor  4 ) while signals in the cadavers were markedly lower; the closest sensor registering an average of 65 and sensors  2  and  3  registering 26 and 24, respectively. Sensor  4  is again understandable lower than the other sensors as it is the farthest from the shot in both scenarios.  
                                                                                                                                                     TABLE 4                                       Pig ID   Totals                P337   P377   P378   P379   Average   Average                Frequency   Amplitude   Frequency   Amplitude   Frequency   Amplitude   Frequency   Amplitude   Frequency   Amplitude                        Sensor 1                                               Avg   390.46   63.14   527.0   71.7   429.7   94.2   424.6   31.7   442.9   65.2       SD   71.0   24.0   47.7   4.9   21.9   8.4   50.7   11.0   70.0   26.4       Sensor 2       Avg   468.4   51.6   615.1   9.1   473.4   17.0           519.0   25.9       SD   85.2   35.4   86.9   2.3   27.8   4.1           97.0   27.0       Sensor 3       Avg   541.8   2.0   444.3   42.8   400.2   10.0   624.7   42.1   502.7   24.3       SD   263.6   0.8   10.7   22.4   50.6   7.5   58.9   29.9   154.6   25.8       Sensor 4       Avg           546.7   4.0   395.3   3.1   748.4   3.5   535.0   3.5       SD           27.9   0.2   52.9   0.9   13.9   0.2   144.2   0.7                  
 
         [0065]     Three human test subjects volunteered for the paintball impact testing. Each subject received eight impacts, four with body armor and four without body armor. Subjects received impacts in the abdomen, lateral chest with and without the armor and received two extremity shots (one arm and one thigh) wearing armor and then two more extremity shots (opposite arm and opposite thigh) while not wearing the armor. Sensors were placed on the back of the subjects and fixed with adhesive tape similar to the pigs as shown in  FIG. 21 . Subjects wore jacket-style NATO body armor for this test.  
         [0066]     In general, numerous human impact locations were analyzed and FFT data from eight, impact locations were computed.  FIG. 22  shows a representative left lateral chest impact with body armor signal from sensor  2 . It should be noted that the small pre-impact waves that were visible on the swine recordings are not visible in the human recordings. As previously stated, these small waves are believed to be artifact from the air blast of the gun. Since the human subjects stand behind protective plywood, it seems logical that the air blast is dissipated. The human impact signature in  FIG. 22  prevents shock and tissue deformation components corresponding to the swine recordings.  FIG. 23  shows the FFT performed on the impact shown in  FIG. 22 . FFT analysis on the shock portion of the recordings similar to those performed on the swine impact recordings for the lateral chest impacts are summarized in Table 5.  
                                                                                                               TABLE 5                                       Subject 1   Subject 2   Subject 3   Average            Sensor   Frequency   Amplitude   Frequency   Amplitude   Frequency   Amplitude   Frequency   Amplitude                    1   341.8   3.6   537.1   6.3   341.8   7    406.90   5.63       2   390.6   501.5   488.3   323.3   —   —   439.45   412.40       3   390.6   22.2   488.3   60.9   609.9   12.1   496.27   31.73       4   439.4   70.5   512.3   273.7   —   —   475.85   172.10       5   439.5   29.2   365.8   114.2   365.8   12.2   390.37   51.87       6   365.8   57.5   585.9   321.4   488.3   11.6   480.00   130.17       7   488.3   173.7   414.6   163.9   341.8   40.2   414.90   125.93       8   439.4   215.4   390.6   259.7   390.6   10.5   406.87   161.87                  
 
         [0067]     The frequencies noted in Table 5 represent the top frequency peaks. Overall to this point, the peak frequencies of the human subject correlate well with the swine frequencies. The average frequency for the human lateral chest shots with body armor is 437.1 Hertz with a standard deviation of 78.6 (n=22). The average frequency for the swine lateral chest shots with body armor is 471.1 Hertz with a standard deviation of 122.0 (n=90).  
         [0068]     Similarities between the low impact swine and low impact human signatures provided the needed impetus to perform high velocity swine impacts. A protocol was written to perform a limited number of shots using two caliber bullets (7.62 M80 ball and 5.56 M855 ball), four locations (sternum, lateral chest, abdomen and hind limb) and three velocities (2800 ft/sec, 2300 ft/sec and 1300 ft/sec). The impact schedule is shown in Table 6. It was important to test a combination of threats facing the soldier today. Given that resources were limited, certain tradeoffs were made. The velocities were chosen to reflect an AK47 muzzle velocity (2800 ft/sec), an approximate 200 yard rifle engagement (2300 ft/sec) and handgun velocity (1300 ft/sec).  
                               TABLE 6                       Shot ID.   Location   Round   Armor   Velocity                   PHV-1   Lat Chest   M80 Ball   Soft Armor   High       PHV-2   Lat Chest   M80 Ball   Soft Armor   High       PHV-3   Lat Chest   M80 Ball   Soft Armor   High       PHV-4   Lat Chest   M80 Ball   Soft Armor   High       PHV-5   Lat Chest   M80 Ball   Soft Armor   High       PHV-6   Sternum   M80 Ball   Plate   High       PHV-7   Sternum   M80 Ball   Plate   High       PHV-8   Sternum   M80 Ball   Plate   High       PHV-9   Sternum   M80 Ball   Plate   High       PHV-10   Sternum   M80 Ball   Plate   High       PHV-11   Abdomen   M80 Ball   Soft Armor   High       PHV-12   Abdomen   M80 Ball   Soft Armor   High       PHV-13   Abdomen   M80 Ball   Soft Armor   High       PHV-14   Abdomen   M80 Ball   Soft Armor   High       PHV-15   Abdomen   M80 Ball   Soft Armor   High       PHV-16   Limb   M80 Ball   No Armor   High       PHV-17   Limb   M80 Ball   No Armor   High       PHV-18   Limb   M80 Ball   No Armor   High       PHV-19   Limb   M80 Ball   No Armor   High       PHV-20   Limb   M80 Ball   No Armor   High       PHV-21   Lat Chest   M80 Ball   Soft Armor   Medium       PHV-22   Lat Chest   M80 Ball   Soft Armor   Medium       PHV-23   Lat Chest   M80 Ball   Soft Armor   Medium       PHV-24   Lat Chest   M80 Ball   Soft Armor   Medium       PHV-25   Lat Chest   M80 Ball   Soft Armor   Medium       PHV-26   Sternum   M80 Ball   Plate   Medium       PHV-27   Sternum   M80 Ball   Plate   Medium       PHV-28   Sternum   M80 Ball   Plate   Medium       PHV-29   Sternum   M80 Ball   Plate   Medium       PHV-30   Sternum   M80 Ball   Plate   Medium       PHV-31   Abdomen   M80 Ball   Soft Armor   Medium       PHV-32   Abdomen   M80 Ball   Soft Armor   Medium       PHV-33   Abdomen   M80 Ball   Soft Armor   Medium       PHV-34   Abdomen   M80 Ball   Soft Armor   Medium       PHV-35   Abdomen   M80 Ball   Soft Armor   Medium       PHV-36   Limb   M80 Ball   No Armor   Medium       PHV-37   Limb   M80 Ball   No Armor   Medium       PHV-38   Limb   M80 Ball   No Armor   Medium       PHV-39   Limb   M80 Ball   No Armor   Medium       PHV-40   Limb   M80 Ball   No Armor   Medium       PHV-41   Lat Chest   M80 Ball   Soft Armor   Low       PHV-42   Lat Chest   M80 Ball   Soft Armor   Low       PHV-43   Lat Chest   M80 Ball   Soft Armor   Low       PHV-44   Lat Chest   M80 Ball   Soft Armor   Low       PHV-45   Lat Chest   M80 Ball   Soft Armor   Low       PHV-46   Sternum   M80 Ball   Plate   Low       PHV-47   Sternum   M80 Ball   Plate   Low       PHV-48   Sternum   M80 Ball   Plate   Low       PHV-49   Sternum   M80 Ball   Plate   Low       PHV-50   Sternum   M80 Ball   Plate   Low       PHV-51   Abdomen   M80 Ball   Soft Armor   Low       PHV-52   Abdomen   M80 Ball   Soft Armor   Low       PHV-53   Abdomen   M80 Ball   Soft Armor   Low       PHV-54   Abdomen   M80 Ball   Soft Armor   Low       PHV-55   Abdomen   M80 Ball   Soft Armor   Low       PHV-56   Limb   M80 Ball   No Armor   Low       PHV-57   Limb   M80 Ball   No Armor   Low       PHV-58   Limb   M80 Ball   No Armor   Low       PHV-59   Limb   M80 Ball   No Armor   Low       PHV-60   Limb   M80 Ball   No Armor   Low       PHV-61   Lat Chest   M855   Soft Armor   Medium       PHV-62   Lat Chest   M855   Soft Armor   Medium       PHV-63   Lat Chest   M855   Soft Armor   Medium       PHV-64   Lat Chest   M855   Soft Armor   Medium       PHV-65   Lat Chest   M855   Soft Armor   Medium       PHV-66   Limb   M855   No Armor   Medium       PHV-67   Limb   M855   No Armor   Medium       PHV-68   Limb   M855   No Armor   Medium       PHV-69   Limb   M855   No Armor   Medium       PHV-70   Limb   M855   No Armor   Medium       PHV-71   Lat Chest   M855   Soft Armor   Low       PHV-72   Lat Chest   M855   Soft Armor   Low       PHV-73   Lat Chest   M855   Soft Armor   Low       PHV-74   Lat Chest   M855   Soft Armor   Low       PHV-75   Lat Chest   M855   Soft Armor   Low       PHV-76   Limb   M855   No Armor   Low       PHV-77   Limb   M855   No Armor   Low       PHV-78   Limb   M855   No Armor   Low       PHV-79   Limb   M855   No Armor   Low       PHV-80   Limb   M855   No Armor   Low                  
 
         [0069]     7.62 rounds are currently the most common small arms threat to US soldiers on the battlefield and are fired by various Soviet Block style weapons (e.g. AK-47, RPK, RPD, etc.). The M855 round (5.56 mm) is a standard NATO round and represents the trend of reducing the bullet caliber and total round weight to gain higher velocity and decrease soldier basic ammunition load weight. This smaller caliber provides information about smaller high-velocity fragmentation munitions impacts (e.g. howitzers, mortars, grenades, etc). The chosen locations reflect the desire to maintain consistency with the low velocity protocols. However, in this study, body armor was used for all impacts. The targeted population for the BIDS is the frontline combat soldier. Projected warfighter designs call for body armor. It was important in the low velocity impact study to relate back to the proof-of-concept work originally done without body armor. Therefore, low impact tests were conducted wearing body armor and without body armor. The high impact tests do not need to relate back to previous low impact tests since results from these high impact tests alone will be the basis for the BIDS circuitry. Interceptor body armor from Point Blank with SAPI and Gamma Plus ceramic plates were used for this study. Sternum shots were fired into the ceramic plates of the vest, abdomen shots were fired into the Kevlar outer tactical vest just below the ceramic plates, lateral chest shots were fired into the Kevlar outer tactical vest and hind limb shots were fired into the unprotected thigh of the animal. The ceramic plates, which are rated to protect against 7.62 rounds at 2800 ft/sec, defeated all rounds at all velocities, although permanent backface deformations of approximately 1 cm were created at the high velocities. The Kevlar outer tactical vest is rated to defeat handgun rounds; however, the high ogive of the rifle rounds allowed all rounds to penetrate the Kevlar. A pilot study was performed to determine if freshly euthanized animals could be used instead of live anesthetized animals. Lateral chest shots using 7.62 rounds at 2800 ft/sec from six live anesthetized animals were compared to animals that were euthanized minutes before the impact. As in previous experiments, eight sensors were placed equidistant about the spine in two columns of four. Unlike other experiments, these tests employed six newly design Piezo-film sensors as well as two of the older style bone conducting sensors. Unfortunately, the new sensors were not as responsive as the older bone conducting ones and have been left out of the analysis. The results from these tests will be from signatures recorded from the two bone conducting sensors.  FIGS. 24 and 25  show typical impact signatures from form the pilot study. The graph on the left is a 2800 ft/sec 7.62 round left lateral chest impact from a live anesthetized animal. The graph on the right is the same parameters from a freshly euthanized animal.  
         [0070]     Similarly,  FIGS. 26 and 27  show the frequency spectrum of the above impact signatures: live in  FIG. 26  and freshly euthanized in  FIG. 27 . The FFTs below are 1024 point FFTs using 75 data points and zero-padding. The Y-axis is always in arbitrary units which can be compared between graphs in which similar processing has been performed. After completing the pilot study, the remaining animals were impacted directly after euthanasia. It should be noted that the sensor used in these recordings has a particular resonance at 17,000 Hz explaining the large frequency response in that area on the graphs in  FIGS. 26 and 27 . While there was some signal present in that frequency region, care must be used in characterizing the frequency response of the sensors as it affects the analysis of the impact signatures.  
         [0071]     Mine surrogates containing surrogates containing 100 and 200 grams of C4 explosive were used against cadavers with and without a blast suit. Sensors were affixed to the cadavers using superglue in the same configuration as  FIG. 21 . Signals were recorded at 50,000 samples per second on each channel.  FIG. 28  shows the impact signal from a 200-gram blast with a blast suit. The subject&#39;s nose was 55 centimeters (measured radially) from the center of the mine surrogate. The response from the sensor seems to be that of a second-order system in response to a step function. A second order system consists of a mass, a spring and a dashpot (shock absorber).  FIG. 28  shows a longer duration event lasting well beyond 600 milliseconds. Examination of the recording indicates higher frequency components for the first 150 milliseconds and slower frequencies after 150 milliseconds. It is likely that part of the slower frequency waves are made up of the tissue deformation waves. An FFT on the first 170 milliseconds of the blast is shown in  FIG. 29 . Much of the response to this type of blast is in the lower frequencies, less than 200 Hertz. This seems to indicate that the surface of the body couples with the primary low frequency blast wave.  
         [0072]     Data was also acquired for simulated normal activity to determine key characteristics of signals from running, hopping and a significant jolt. Human data was collected while the subject ran and hopped in place. The jolt signature resulted in a jump off a 30 inch table.  FIG. 30  is the resultant signal from the 30 inch jump.  FIG. 31  is the frequency domain spectrum produced by the FFT. The frequency spectrum shows that this jolt to the body produces two significant frequencies: a larger amplitude component at 293 Hertz and a smaller but significant frequency at 586 Hertz. This latter frequency is in the range produced by the bullet impacts. Of the three ‘normal’ recordings, only the big jump proved to contain frequencies in the range of those produced by the bullet impacts.  
         [0073]     Bench testing of the BIDS circuit included converting the digital impact signatures in analog voltages and feeding them through the circuit. The impact threshold settings were set so as to discriminate between the swine impacts and the normal human movement signatures. Setting the threshold is somewhat arbitrary since the voltage at that point is dependent upon the initial amplification from the input amplifier. More important is the relative voltage levels between the smallest detectable impact and the largest normal movement signal.  FIG. 32  shows a comparison of two signals that have been filtered using the 3 pole 5000 Hertz high pass filter in the BIDS circuit. The first trace 400 is the time domain signal from a hind limb, 5.56 caliber impact at 1300 ft/sec; the second trace  450  is the time domain signal from the big jump in  FIG. 30 .  FIG. 32  shows the ability to easily discriminate the weakest bullet impact recorded from the strongest ‘normal’ activity recording.  
         [0074]     Although described with reference to preferred embodiments of and tests conducted in connection with the invention, it should be readily understood that various changes and/or modifications could be made to the invention without departing from the spirit thereof. For example, different types of signal processing circuitry for determining location of impacts or a target are shown in U.S. Pat. No. 4,349,728 which is incorporated herein by reference. Certainly, other logic elements could be used in the BIDS system without departing from the scope of the invention. In general, it is important that the sensor system of the invention can be used to detect, verify and locate a ballistic impact on a body, particularly an impact which causes an injury to the body. Detection and location information can be transmitted to a remote location, with this information being potentially used to enhance the ability to appropriately respond to counter the injury. In any case, the invention is only intended to be limited by the scope of the following claims.