Patent No. 5530429 Electronic surveillance system

 

Patent No. 5530429

Electronic surveillance system (Hablov, et al., Jun 25, 1996)

Abstract

An electronic surveillance system for detecting unauthorized persons within a building. The system comprising a microwave transmitting/receiving device which transmits a microwave signal into the area under surveillance and receives microwave signals reflected from the area. The microwave signal having frequencies corresponding to the life functions of any living beings present in the area. The transmitting/receiving device comprising a signal conditioning device, a memory device, and a comparator unit. The signal conditioning device adjusts the amplitude and phase of a portion of the outgoing microwave signal and adds it to the incoming microwave signal, eliminating the carrier wave. The resultant actual signal is transmitted to the comparator unit which also receives a signal from the memory device comprising characteristic frequencies representing authorized occupants. If the results of the comparison are above a predetermined threshold, an alarm is generated.

Notes:

SUMMARY OF THE INVENTION

The invention is based on the object of providing an electronic surveillance system of the generic type mentioned at the beginning by which the presence of unknown persons in an area under surveillance--in particular a building--which is also used by authorized persons and/or animals can be established.

An advantageous area of application is that of increasing accuracy in the detection of living beings, preferably persons, present without authorization in buildings which are under the control of a mobile security service.

This object is achieved by an electronic surveillance system for sensing living beings behind a wall or in a building on the basis of a reflection of a wave field radiated into the spatial area to be subjected to surveillance, having a microwave transmitting/receiving device for generating and radiating the wave field, and for receiving and conditioning a signal reflected from the living being, and a device for outputting a signal indicating presence, characterized by

a first signal-conditioning device, provided in the microwave transmitting/receiving device, for elimination in the received signal of the unmodulated component corresponding to the transmitted signal already contained in the latter,

a second signal-conditioning device, which is arranged downstream of the microwave transmitting/receiving device and further conditions the microwave signal reflected from the area under surveillance, modulated by the body oscillations of any living being present in the area, and conditioned by the first signal-conditioning device, with a frequency and/or correlation analysis being executed to supply an actual signal quantity,

a first memory device for storing and outputting at least one model signal quantity, which describes a normal (model) state of the area to be subjected to surveillance and/or comprises characteristic oscillation spectra registered in advance, and

a first comparator unit for comparison of the actual signal quantity, supplied by the second signal-conditioning device, with the at least one model signal quantity, output from the first memory device, which comparator unit outputs an output value quantity characterizing the result of the comparison, the output of the comparator unit being connected to the input of the signal device, which outputs a signal dependent on the degree of matching.

The invention embraces a recognition of the idea that intruders can be detected in principle by means of an electronic surveillance system of the generic type once the detection principle used can distinguish between different living beings present in the area in question.

The invention makes it possible furthermore, in an advantageous way, that an alarm can be set off in a surveillance operation if there is no match in a comparison of the sensed signals with predetermined comparison values which correspond to the signals to be sensed in a case where there is no disturbance, that is to say if there are no or only authorized persons present in the premises to be protected.

Furthermore, it is favourable if every human or every sizeable animal in an area to be subjected to surveillance--in particular buildings which cannot be (completely) seen into--has due to its breathing and heart function and further body functions a characteristic mechanical oscillation spectrum which characterizes the said human or animal--assuming sufficiently accurate analysis--in the manner of a fingerprint. Consequently, the distinguishing mentioned above is possible on the basis of this oscillation spectrum.

A selectively operating electronic surveillance system (in particular for protecting buildings against unauthorized use) can thus be realised if a signal pattern produced at an earlier time by means of microwaves of the buildings to be subjected to surveillance, which represents the normal (or model) state of the building with regard to the presence of persons or other living beings, is compared with a signal pattern determined by security staff or recorded in some other way. A measure of the deviation between the two signal patterns, to be suitably defined in advance, on the basis of the presence of additional persons in the building, unauthorized at the time of surveillance, is a criterion for setting off an alarm or for the initiation of corresponding security measures.

The execution of such a comparison is facilitated or, under unfavourable conditions, made possible in the first place if the receiving circuit is designed such that it permits a measurement even in the case of very small signal-to-noise ratios and without overdriving, in order to ensure an unfalsified sensing of the modulation frequencies (i.e. consequently of the body oscillation frequencies). For this purpose, an automatic sensitivity control is advantageously provided.

For carrying out the data comparison, it is of particular advantage if the signals determined, sensed in the time domain, are subjected to a frequency analysis, in particular in the form of a fast Fourier transformation (FFT). The FFT-conditioned signals in this case respectively represent a frequency spectrum.

The accuracy of detection is increased in an advantageous way by the scanning of a building to be subjected to surveillance being performed by scanning in the sense of a spatial scanning with a highly concentrated microwave beam by means of a correspondingly designed directional aerial with variable alignment. The changing of the alignment of the aerial is in this case preferably performed electronically.

According to a preferred configuration of the invention, the electronic surveillance system for the mobile surveillance of a plurality of buildings for the purpose of establishing persons who have entered one or more of these buildings without authorization has first and second memory devices, the memory addresses Z.sub.1 to Z.sub.n of which are assigned to the individual buildings to be subjected to surveillance and the memory content of which comprises signal quantities relating to building-specific features for the reference or normal situation, premises-related security measures for the event of unauthorized use of a building, time-variable occupancy and use criteria, positional data of the buildings in a respective area of land and of the location of a vehicle for carrying out the mobile surveillance and building-specific additional information.

After compensation of their unmodulated component and automatic level setting, the microwaves reflected from the building and picked up by the mobile detector of the surveillance system are subjected to a fast Fourier transformation and then compared with the signal quantities available in the memory device and assigned to the same building or section of building or land.

In the signal processing unit, a device is provided for the optional accumulation of a plurality of measuring signals, which is put into operation if the signal-to-noise ratio of an individual measurement is not adequate for obtaining a Fourier transform which is comparable with respect to noise with the one which is stored.

The memory devices are designed such that they can be cyclically driven by a multiplexer. Putting the sending and receiving devices into operation and reading out the building-specific signal quantities from the memory devices of the surveillance system is always performed whenever the vehicle used for mobile surveillance has taken up a location which is defined and can be checked by a separate control system.

For setting off an alarm owing to persons present in the building without authorization, it is necessary that the deviation of the stored (model) signal quantities from the detected (actual) signal quantities satisfies predetermined criteria or--more simply--exceeds a certain amount. A comparator unit, operating in an advantageous way by a correlation method, and a suitably dimensioned threshold stage bring about the required setting off of the alarm, for instance on an indicating device, when there is a corresponding signal-quantity deviation. For the reading out of the signal data, in particular of the positional data for the individual buildings, from the second memory device there is provided a multiplexer, which is driven by a random generator. As a result, in an advantageous way, a manipulation of the sequence of surveillance of the individual premises--and consequently of the constitution of a control journey--is avoidable and results in an increase in the effectiveness of the surveillance measures.

Other advantageous further developments of the invention are characterized in subclaims and/or are presented in more detail below together with the description of the preferred configuration of the invention with reference to the figures.

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The invention is not restricted in its execution to the preferred exemplary embodiment specified above. Rather, a number of variants which make use of the solution presented are conceivable, even in the case of configurations of a fundamentally different type. In particular, it is also possible in such cases to dispense with a directional aerial and its control and to radiate and record the measuring signal by means of simple metal surfaces.