Measuring and testing – Vibration – Sensing apparatus
Patent
1994-10-03
1997-01-07
Williams, Hezron E.
Measuring and testing
Vibration
Sensing apparatus
73579, 3404255, 340438, G01N 2904, G08B 2100
Patent
active
055919162
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns equipment for detecting a device, such as a car bomb, attached to a panel of a vehicle or the like.
BACKGROUND OF THE INVENTION
Car bombs are the most efficient way which terrorists have devised to kill or maim their victims. It is a method which is used frequently in Northern Ireland. Except on relatively rare occasions these devices have been attached to the vehicle by quite powerful permanent magnets. Several systems relying on the detection of the magnetic fields emitted by the magnets have been devised to detect these bombs. Clearly, these systems can only detect those devices which have been attached magnetically and are thus extremely limited in scope.
SUMMARY OF THE INVENTION
The present invention seeks to overcome the disadvantages of current detecting systems. This invention senses the change in the mechanical properties of the car panel to which the bomb is attached. It does not depend on the magnetic properties of the explosive device.
In accordance with the invention there is provided equipment for detecting the attachment of a device to a panel of a vehicle or the like, comprising means for exciting vibrations in the panel, means for detecting the vibrations, control and analysis means for controlling the exciting and detecting means, for recording a normal vibration pattern, and for detecting departures from that pattern resulting from the attachment of a device, and an alarm triggered by the control and analysis means when the presence of a device is detected.
When a membrane such as a metal plate is caused to vibrate certain frequencies will predominate. The amplitude and frequency of the displacements depend on the tension in, and the mass per unit area of the membrane.
If an extra mass is attached to the membrane both these quantities will change. If, on the other hand, an external force is applied to the membrane, caused perhaps by an object being pressed against it, the tension in the membrane will change, also the vibrations will be differently damped. The vibrational pattern will be altered as a result.
The invention utilises these principles by considering the floor pan of the vehicle as a membrane under tension. The floor-pan is forced into vibration. The pattern of vibrations is detected, analyzed and stored in microprocessor memory. This process is repeated at certain predetermined intervals and the vibration patterns correlated with one another. A sudden change in this correlation indicates a change in the mass, the tension, or vibrational damping of the vehicle's floor-pan. This is interpreted and a warning given if suitable criteria are met.
BRIEF DESCRIPTION OF THE DRAWING
An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which
FIG. 1 is a block diagram of the electronic circuitry of a car-bomb detector.
FIG. 1A is a block diagram of the partial contents of the random access memory of this invention and
FIG. 2 is a flow chart of the operations performed by the circuitry.
DETAILED DESCRIPTION
The structure of the vehicle can be set into vibration either mechanically or by piezo-electric crystals 27. A set of receiving piezo-electric crystals detect the resulting frequency pattern. This signal is amplified by a variable gain amplifier and filtered to remove unwanted frequencies. It is then routed to an analogue to digital converter and thence to a microprocessor and other digital hardware as shown in the block diagram of FIG. 1.
The block diagram shows the equipment for one channel with a single piezo-electric detector 9 which is connected by way of pre-amplifier 10, filter 11, amplifier 12, and analog to digital converter 13 to the digital electronic circutry. Normally a separate detector 9 is required for each panel and has its own amplifiers 10, 12 and filters 11. The analog to digital converter 13 and the remainder of the circuit, in particular a micro-processor 14, RAM 15, EPROM 16 and associated digital integrated circuits, are common t
REFERENCES:
patent: 4553137 (1985-11-01), Marxer et al.
patent: 4607520 (1986-08-01), Dam
patent: 4685326 (1987-08-01), Peterson
patent: 4941356 (1990-07-01), Pallaske
patent: 5144838 (1992-09-01), Tsuboi
patent: 5404128 (1995-04-01), Ogino et al.
Patent Abstracts of Japan vol. 8, No. 113 (P-276) (1550) 26 May 1984 & JP,A,59 20 819 (Hitachi Seisakusho KK).
Kwok Helen C.
Williams Hezron E.
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