Communications – electrical: acoustic wave systems and devices – Distance or direction finding – By combining or comparing signals
Reexamination Certificate
2000-03-16
2001-02-06
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
By combining or comparing signals
C367S118000, C367S906000
Reexamination Certificate
active
06185153
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to the detection of gunshots fired from weapons and, more particularly, to the use of a detection system for distinguishing from background environmental noise that a weapon has been fired.
BACKGROUND OF THE INVENTION
In urban or city environments as well as rural locations there is a need by various police, military and civilian activities to identify that a gun or weapon has been fired. There are systems and methods for detecting gunshots.
For example, U.S. Pat. Nos. 5,504,717 and 5,703,835 issued to Sharkey, et. al. disclose security systems for detecting and reporting gunshot events in which a variety of individual detection units are positioned on a plurality of remote, separate pole units. Each pole unit includes a microphone for sensing acoustic signals, a signal conditioning and threshold unit coupled to the microphone, a data acquisition and signal processing unit, a communication unit, and a power supply. The outputs from the pole units are transmitted to a central processor at a base station where time domain differencing techniques are employed to fix the location of the gunshot(s). The signal conditioning and thresholding unit includes a signal comparator for detecting when an output signal from the microphone exceeds a predetermined level, and a peak background level averager that receives signals from both an averager rise time constant circuit and an averager decay time circuit. The averager rise time and averager decay time circuits produce output signals that are representative of time factors, as measured for example in milliseconds, of the acoustic signals sensed by the microphones.
Another system for detecting gunshots or gunfire is set forth in a South African patent application (Application No. 935960 dated Aug. 16, 1993) by Robin L. Foxcroft of FoxCraft Controls. Disclosed is a system for detecting and locating the origin of sounds such as gunfire, and means for reporting the occurrence of such gunfire. The system includes at least one microphone to convert sound waveforms into an intermediate electrical signal, processing means for comparing the intermediate signal produced by the microphone against a known signal, and means for producing an output if the intermediate electrical signal is sufficiently similar to the known signal. Other features include a processing means capable of generating a Fourier transform of an intermediate electrical signal and of comparing the transformed intermediate signal against a Fourier transform a known gunshot, and a memory which stores the transforms of various known signals.
Another acoustic detection method and system for locating the source of a gunshot is set forth in U.S. Pat. No. 5,586,086 issued to Permuy, et.al. The system comprises an antenna having at least three microphones that are spaced apart from each other and connected via a microphone conditioning stage to a processing and display unit. The processing and display unit includes means for processing the signals and for determining the location and possible type of projectile being fired.
Acoustic detection circuits are also disclosed in U.S. Pat. Nos. 4,001,771 issued to Amrine; 4,083,031 issued to Pharo; 4,091,366 issued to Lavallee; 4,279,027 issued to Van Sloun; and 5,046,053 issued to Gilchrist.
SUMMARY OF THE INVENTION
The present invention is directed to a self-contained system and method for detecting sounds from various sources and for detecting that a gun has been fired. The system or apparatus comprises an input section which includes a microphone for converting acoustic pulses into electrical output signals and amplifiers coupled to the microphone for producing an amplified output signal that is adjusted to an appropriate level for further processing. A threshold detector section is connected to the input section for comparing the amplified output signal with a threshold level and for providing an output signal when the amplified output signal exceeds the threshold level.
The gunshot detecting system also includes pulse width and pulse count test sections which are connected to the threshold detector and input sections and which become activated when the amplified output signal exceeds the threshold level. The pulse width detection unit determines the pulse width of the initial acoustic signal that exceeds the threshold level. If the pulse width is within a range of acceptable pulse widths, then an appropriate positive output signal is provided. The pulse count detection unit determines the number of times that the amplitudes of the acoustic pulses approach or exceed a predetermined level during the time interval or sampling period. If, for example, the pulse count is less than a predetermined number, then an appropriate positive output signal is provided. The outputs of the threshold detector, the pulse width detector, and the pulse count detector are coupled to an output section. A gunshot event is detected only if output signals are produced by the threshold detector, the pulse width detector, and the pulse count detector. The output section may contain an indicating device such as a light or an audible alarm.
The method for detecting that a weapon has been fired includes the steps of detecting acoustic signals and converting the acoustic signals to electrical signals, and then comparing the electrical signals with a predetermined threshold level. When the threshold level is exceeded, the signals are sampled and analyzed for a predetermined period of time to determine the number of threshold output signals which exceed the threshold level within a predetermined period of time. The signals are also sampled and analyzed to determine the pulse width of the initial signal which exceeds the threshold level during the sampling period. A predicted gunshot event is expected to occur when the pulse width of a signal is within a predetermined range and the number of pulse counts which approach a threshold level within a time period are below a prescribed number.
The above brief description sets forth rather broadly the more important features of the present invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described and which will form the subject matter of the claims appended hereto.
Accordingly, it is one object of the present invention to provide a compact acoustic detection apparatus which is of self-contained, efficient design that is capable of readily detecting gunshots.
Another object of the present invention is to provide a relatively simple gunshot detection system and method which can be readily adapted to a variety of different environments.
It is another object of the present invention to provide a new and improved gunshot detection method and system of reliable design and which may be easily manufactured and marketed.
These together with still other objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention.
REFERENCES:
patent: 5455868 (1995-10-01), Sergent et al.
patent: 5504717 (1996-04-01), Sharkey et al.
patent: 5703835 (1997-12-01), Sharkey et al.
patent: 5917775 (1999-06-01), Salisbury
Cole James Lee
Hynes Mark William
Lobo Ian J.
Medsger William
Randolph William
Stolarum Edward
The United States of America as represented by the Secretary of
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