CH667931A5 - METHOD AND DEVICE FOR PROTECTING PREMISES FROM INTRUSION. - Google Patents

Description

DESCRIPTION The present invention relates to a method of protecting premises against intrusion, according to which an acoustic signal is emitted inside a room to be monitored and the variations of the reflected acoustic signals are analyzed to detect an intrusion into the local.

The invention also relates to a device for protecting premises against intrusion, comprising at least one transmitter of acoustic signals and at least one detector of reflected acoustic signals, arranged in the room to be protected, as well as a processing assembly. of signals to which are applied, on the one hand, the signals emitted by the transmitter and, on the other hand, the reflected signals picked up by the detector (s).

Numerous methods are known for protecting premises against intrusion using various types of detection and, in particular, so-called volumetric types of detection, that is to say

say intended, not simply to form a protective barrier, but to monitor an entire volume, for example the entire space inside a room.

The known volumetric protection methods are generally based on the use of microwave radiation or sonic or ultrasonic acoustic waves.

The use of microwave radiation makes it possible, using the Doppler effect, to detect movements and to measure the speeds of movement of objects or people in the field of the monitored area. However, microwave radiation passes through the walls of the premises, which makes this type of detection unreliable in many circumstances where disturbing phenomena outside the premises to be protected risk being taken into account by the detection system.

The protection carried out using ultrasonic waves allows, by the same principle of the Doppler effect, to highlight movements within a space to be monitored. However, as in the case of microwave protection methods, movements made at certain speeds that are too fast or, on the contrary, too slow, may not be detected, given the limits specific to the use of detection. based on the Doppler effect. In addition, an ultrasonic detection system is sensitive to acoustic phenomena caused, for example, by fluids circulating in pipes. Finally, the ultrasonic waves have a short wavelength which promotes the triggering of false alarms by movements of small objects or animals.

It has also been proposed to use an acoustic field with frequencies situated in the infrasound range, for example of the order of a few hertz. However, this type of protection also has drawbacks and, in particular, does not lend itself to rapid signal processing, given the frequency range used. This type of protection thus proves to be ill-suited to the creation of an effective protection system capable of reacting quickly, while limiting the risks of false alarms.

The present invention thus aims to remedy the drawbacks of the aforementioned systems and, in particular, to allow rapid detection of intruders entering a room, while limiting the risk of false alarms due, for example, to the presence of small animals or extraneous noise.

These aims are achieved by means of a premises protection method characterized in that an acoustic wave is emitted consisting of trains of pulses modulated linearly in frequency in a band comprised between 500 Hz and 5 kHz for a limited duration comprised between 5 and 20 milliseconds with a recurrence period at least of the order of the reverberation time of the room to be protected, in that the acoustic signal reflected by the room at the detection is detected using at least one detector continuation of the emession of each train of pulses, in that the intercorrelation of the reflected signal and the acoustic signal emitted is performed for each train of pulses, in that the intercorrelation signals produced for count and identify the different echoes they contain, in that each anlysed intercorrelation signal is compared with a pre-recorded reference signal corresponding to an intercorrelation carried out, under reference conditions a with the empty room, without the presence of an intruder and in that an alarm or monitoring device is triggered in the event of a change in the echoes of an intercorrelation signal compared to the pre-recorded reference signal .

Preferably, the acoustic waves emitted comprise pulse trains modulated linearly in frequency in a band comprised between approximately 1 kHz and 3 kHz for a duration comprised between approximately 10 and 15 milliseconds.

The detection of echoes of the reflected signal has, due to the intercorrelation with the transmitted signal, excellent immunity

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compared to outside noise and a high signal-to-noise ratio.

The use of a transmission signal, constituted by a train of pulses linearly modulated in frequency, ensures a high spectral energy density and a short analysis time.

The frequency band used for the pulse train corresponds to wavelengths on the order of dimensions of the human body, which reduces false alarms due to small objects or animals and increases the chances of detection of 'an intruder.

In addition, the frequency band adopted has a good detection selectivity and the duration of the train of pulses which has been retained makes it possible to obtain good temporal compression of the signal.

Advantageously, the period of recurrence of the emission of the pulse trains is of the order of 1 to 3 seconds, that is to say is greater than the usual reverberation time of the premises to be protected, while allowing an analysis complete signals emitted and reflected between two successive emissions of pulse trains.

According to a particular implementation mode of the method according to the invention, the theoretical primary and secondary echoes to be reflected by the walls of the room to be protected are determined beforehand, as a function of the location of the transmitter of the acoustic signal and of the acoustic signal detector (s) reflected by the room and the recognized echoes corresponding to theoretical echoes are identified on the pre-recorded reference signal.

In order to increase the reliability of the process, when the comparison between the analyzed correlation signal and the reference signal reveals a new echo, it is suspended on the triggering of an alarm until the appearance of a predetermined number greater than 2, of detections of echoes representative of faults with respect to the reference signal, for a predetermined number greater than 2 of acquisition of intercorrelation signals analyzed.

Likewise, when the comparison between the intercorrelation signal analyzed and the reference signal reveals the disappearance or attenuation of an unrecognized echo that does not correspond to a theoretical echo, it is suspended when an alarm is triggered until 'taking into account a predetermined number, greater than two, of disappearances or attenuations of echoes not recognized with respect to the reference signal, for a predetermined number greater than two, of acquisitions of intercorrelation signals analyzed.

On the other hand, when the comparison between the analyzed correlation signal and the reference signal highlights the disappearance or attenuation of a recognized echo corresponding to a theoretical echo, an alarm is triggered as soon as d 'a second disappearance or attenuation of echo recognized identical or' close to a predetermined number greater than two of acquisitions of intercorrelation signals analyzed.

Advantageously, one proceeds, periodically, at time intervals much greater than the recurrence frequency, to the acquisition and recording of a new reference signal.

According to a particular method of implementing the method, during the comparison between the intercorrelation signal analyzed and the reference signal, the faults due for the echoes at a difference in value less than a predetermined threshold, corresponding to a determined percentage of the amplitude of the considered echo of the reference signal, are not taken into account for the triggering of an alarm.

According to a particular application of the method according to the invention, applicable, in particular, to fire protection, when the comparison between the analyzed correlation signal and the reference signal reveals both a disappearance of echo and a appearance of echo corresponding to a time offset, a time offset measurement of each echo is carried out between two or more successive analyzes and, in the event of an offset remaining substantially stable, information corresponding to a change in the physical characteristics of the atmosphere of the room to be protected.

In order to prevent failures of the protection system or attempts to destroy it, a specific non-functioning alarm is triggered in the event of the disappearance or appearance of echoes in numbers greater than a predetermined value, for one or more acquisitions of intercorrelation signals analyzed.

The invention also relates to a protection device of the type defined at the head of the description for the implementation of the mentioned method, characterized in that the acoustic signal transmitter comprises a generator of pulse trains modulated linearly in frequency and an omnidirectional loudspeaker for broadcasting said pulse trains in the room, in that the acoustic signal detector comprises at least one microphone and means for conditioning the signals received by the microphone and in that the processing unit signals comprises means for intercorrelation of the acoustic signals emitted by the transmitter and received by the detector to supply an intercorrelation signal, means for analyzing the envelope of the intercorrelation signal and for recognizing echoes, means for comparing the intercorrelation signal and a reference signal having a predetermined number of echoes characteristic of the room to be protected and means for c counting and tracking of echoes that have appeared or disappeared in the intercorrelation signal and in that means for triggering an alarm are controlled by said counting and tracking means of echoes that have disappeared or have appeared, according to a programmed decision logic strategy.

According to a particular embodiment, the signal processing assembly comprises means for sampling the acoustic signals emitted by the transmitter and received by the detector and means for intercorrelation of the acoustic signals emitted and received sampled to supply said signal intercorrelation.

Advantageously, pre-alarm means are interposed between the means for counting and locating missing or appeared echoes so as to control the triggering means only in the event of repeated recognition of disappearances or appearances of echoes according to a programmed sequential logic.

According to one possible embodiment, the protection device comprises several acoustic signal detectors distributed in the room to be protected and each connected to the signal processing assembly which includes means for summing the signals received by the different detectors, means for sampling acoustic signals emitted by the transmitter and summed signals received by the different detectors, means for intercorrelation of the sampled transmitted signals and summed and sampled reception signals corresponding to all of the different detectors to provide for the set of detectors an intercorrelation signal, means for analyzing the envelope of the intercorrelation signal and recognizing echoes, means for comparing the intercorrelation signal of all the various detectors and a reference signal also corresponding to all of the various detectors and having a predetermined number of characteristic echoes ics of the room to be protected and of means for counting the location of echoes that have appeared or disappeared in the intercorrelation signal corresponding to all the detectors.

In general, the transmitter and the detectors are arranged in such a way that at least the acoustic rays linked to the theoretical primary and secondary echoes reflected by the walls of the room to be protected constitute a well distributed beam.

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according to the directions that an intruder is likely to intercept. These rays must, in particular, have an angle between them greater than about 15 °.

Advantageously, several transmitters excited in parallel by the same signal are used concurrently at various points in the same large room and / or of complex shape, or of simple shape but filled with objects constituting obstacles giving rise to the empty space a form which is itself complex, so as to simultaneously insonate all the volumes in which an intruder can move.

The characteristics and advantages of the invention will emerge from the following description of a particular embodiment, with reference to the attached drawings in which:

- fig. 1 represents a perspective view of a room in which a transmitter and two receivers of an intrusion protection device according to the invention have been installed,

- figs. 2 to 4 represent, respectively, views from above, from the front and from the side of the room in FIG. 1, with the indication of the rays emitted by the transmitter and received by a receiver after reflection on the walls of the room,

- fig. 5 shows the form of a signal sent by the transmitter,

- fig. 6 shows the form of a signal received by a receiver,

- fig. 7 shows the form of an intercorrelation signal between a transmitted signal and a received signal,

- figs. 8a and 8b show, according to a time diagram, the different theoretical echoes likely to be received by each of the receivers of FIG. 1 after transmission of a signal by the transmitter,

- fig. 9 shows a reference signal, constituted by the envelope of the intercorrelation function of a signal emitted by the transmitter and a signal received by a receiver, under normal conditions without the presence of intruders,

- fig. 10 shows an intrusion identification signal, constituted by the envelope of the intercorrelation function of a signal emitted by the transmitter and a signal received by a receiver in the presence of an intruder,

- fig. 11 shows the block diagram of a protection device according to the invention and

- fig. 12 shows the block diagram of the signal processing carried out in the protection device according to the invention.

In order to facilitate the description of the process and the device for protecting premises according to the invention, FIG. 1 an example of a room having the shape of a six-sided parallelepiped: a front face 1, a rear face 3, two lateral faces 2 and 4, a lower face 6 and an upper face 5.

Inside the room 7, an acoustic signal transmitter 10 was arranged, constituted for example by an omnidirectional loudspeaker and two acoustic signal receivers Di, D2 constituted by microphones.

The location of the transmitter 10 and of the receivers Di, D2, as well as their number, depend on the particular characteristics of the room to be protected. Knowing the geometrical configuration of the room to be protected, it is possible to determine by calculation the different theoretical paths of the sound waves from the transmitter to the different receivers, after primary and secondary reflections on the different walls of the room.

By way of example, for a parallelepipedal room, such as that of FIG. 1, we have shown in FIGS. 2 to 4 different theoretical paths of sound waves from a sound source 10 to a receiver Di, taking into account primary and secondary reflections on the different walls of the room.

In this case, we note that there are six theoretical primary reflections and among the theoretical secondary reflections we have retained the twelve reflections with the shortest paths. Generally, in the case of a rectangular parallelepiped volume, there are 6 primary reflections, 15 secondary reflections, 20 tertiary reflections, etc. Among the secondary reflections, one does not take into account those which correspond to rays which are not presumed to cut an intruder and those which present the longest paths, if the length, width, height of the volume are not too different.

The sound wave paths, in the case of figs. 2 to 4, were established by way of example for a room of length 8.38 m, width 3.93 m and height 2.70 m, with, for the sound source, the first sensor Di and the second sensor D2, the following coordinates in the reference frame Ox, y, z, shown in fig. 1:

- sound source 4.19 m, 1.97 m and 1.70 m

- Di sensor 3.10 m, 2.60 m, 1.20 m

- D2 sensor 5.70 m, 1.10 m, 0.80 m

In the following description, an echo corresponding to a theoretical echo will be identified by its reflection plans. Thus, a primary echo on side 4 will be designated by 4-4 and a secondary echo on sides 5 and 1 will be designated by 5-1.

According to the invention, the method of protecting premises against intrusion is essentially based on the analysis of the modifications of the sound echoes recorded by the detectors Di, D2 for the same emission signal. This is the reason why the transmitter 10 and the detectors Di, D2, must be positioned, inside the room, in such a way that there is a minimum of overlapping echoes, i.e. -to say that there is a minimum of sound waves whose path has a similar length. Furthermore, it is advantageous for the paths of the emitted and reflected acoustic waves to have an angle of between approximately 15 and 30 °. The number of detectors must also be adapted to the room, so that there is a minimum of gray areas in which an intruder would not cut the path of a sound wave. With a number of detectors between two and four, it is possible to envisage good detection security in most cases.

According to the invention, the detection of the presence of an intruder in a room is thus done by analysis of the echoes of an acoustic signal. From a sound wave sent into a room by a transmitter 10, we control the echoes returned by the walls 1 to 6 and received by detectors Di, D2. These echoes are modified if there is an intruder. Thanks to the recognition of a certain number of echoes, corresponding to theoretical echoes, due to primary and secondary reflections on the walls of the room, it is possible to locate an intruder and follow its movement inside the room . The analysis of the echoes returned by the walls can, in fact, be done fairly quickly compared to the normal speed of progression of an individual in an unknown place, that is to say in a time that can range from around 1 to 3 seconds. There is thus, at the end of each analysis, that is to say for example every second, the result of the diagnosis characterizing the state of the room.

An important characteristic of the present invention resides in the fact that the acoustic wave emitted by the transmitter 10 is constituted by trains of pulses modulated linearly in frequency in a band B between, approximately, 500 Hz and 5 kHz, during a limited duration T of between approximately 5 and 20 ms, with a recurrence period at least of the order of the reverberation time of the room to be protected. The frequency band B of the pulse train is preferably between approximately 1 and 3 kHz, to achieve the desired resolution linked to the temporal separation of the echoes, and the duration T of the pulse train is preferably between 10 and 15 ms. In any event, it is indeed important that the BxT product is much greater than 1, in order to achieve, by treatment, a satisfactory signal / noise ratio in realistic acoustic atmospheres.

There is shown in FIG. 5, the form of the signal S transmitted. This

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signal has a high energy spectral density and allows a short analysis time, given its limited duration. The frequency band chosen is adapted, by the acoustic wavelength corresponding to the detection of human intruders, while avoiding false alarms which would be due to intruders of small dimensions, such as small animals.

The form of the signal received by a detector Di or D2 is shown in fig. 6. It can be seen that this signal S 'is naturally delayed in time with respect to the transmitted signal S and comprises a certain number of points corresponding to echoes on the various faces of the room. The echoes are more or less attenuated and offset in time, depending on the length of the sound wave path. The duration of the received signal S ′ is taken into account voluntarily, for example to a duration of the order of 40 to 100 ms and, preferably, close to 50 ms, in order to eliminate the echoes too delayed in time and too muted corresponding, for example, to tertiary or higher order reflections in the room.

The period of recurrence of the pulse trains of signal S is advantageously of the order of 1 to 3 s. Such a value is, in general, greater than the reverberation time of the room and reserves sufficient time for the analysis of the signals transmitted S and received S '.

As indicated previously, the detection of echoes in the received signal is done by intercorrelation of the received signal with the transmitted signal. There is shown in FIG. 7, the form of an intercorrelation signal Gss ', produced by intercorrelation of the signals S and S' and highlighting the echoes Ei.

It follows from the above that the signal S transmitted is of the type:

S (t) = A.cos [27tv0t + (J> (t)]

(1)

or:

- A is a constant,

- v0 represents the minimum frequency of the pulses (for example, v0 = 1 kHz),

- <t> (t) represents the instantaneous phase corresponding to the instantaneous frequency Vj (t) such that:

1 d <]) B

Vj (t) = v0 + - • _ £ = v0 + —t 27t dt T

(2)

with:

- B = width of the frequency modulation band (for example, B = 2 kHz),

- T = duration of signal S (t) (for example T = 10 ms). The intercorrelation of this signal S with the acoustic signal S '

received by a Di or D2 detector is of the form:

NOT

Gss- (t) = Z a; i = 1

sinftB (x — xi) B (T-Ti)

COS 271 Ve (t — Ti)

with:

- N = number of echoes detected,

- at; = echo attenuation,

- Tj = delay of echo i,

g

- v = v0 H— = central frequency of the signal S (t).

2

The intercorrelation signal Gss- thus corresponds, for the different echoes Ei spread over time, to a series of autocorrelation functions of width ± ì which defines the spatial resolution of the detection. In the example considered where B = 2 kHz,

Ì = 0.5 ms and the spatial resolution is then approximately 17 cm. B

To recognize and analyze the echoes Ej, the intercorrelation signal is sampled. The signal Gss' can thus be scanned on, for example, 512 points sampled at 10 kHz. This corresponds to a sequence of echoes with a duration of 51.2 ms and makes it possible to monitor a sphere of 9 m radius centered on the emitter of sound signals 10. Naturally, other numerical values can be chosen, in order to adapt the protection to the dimensions of the room to be monitored.

5 In order to avoid false alarms and to be able to locate the position of an intruder inside the room, each intercorrelation signal obtained is compared with a reference signal which has itself been formed by an intercorrelation "at empty ”, that is to say in the room without the presence of the intruder and results from the intercorrelation carried out under the reference conditions between a basic transmitted signal S and a signal received S 'by the one or more detectors Di, D2. The reference signal is processed in such a way that each echo it contains is recognized and, for some, that the rays which carry them are identified. The result of this processing, which consists of a time sequence, is stored in memory and will be used later for comparison with the intercorrelation signals produced when the monitoring device is in action.

As indicated above, even before the setting of a reference signal, the sequences of theoretical echoes to be received by each of the different sensors Di, D2 placed in the room were recorded. to protect.

Figs. 8a and 8b represent, for the sensors Di and D2 of FIG. 1, the distribution over time of the different theoretical echoes that each of these sensors must receive for a predetermined period after primary and secondary reflections on the various faces of the room to be protected. In fig. 8a and 8b, the different theoretical echoes Ei, some of which capsize, 30 have been identified by the numbers of the planes on which the reflections leading to the formation of an echo have occurred.

We will now refer to fig. 9 which represents the envelope b of the intercorrelation function developed from the signal emitted by the transmitter 10 and the signal received by a detector Di in the reference conditions, without the presence of an intruder. This envelope b, in combination with the information relating to the theoretical echoes Ei of a sequence c of theoretical echoes, corresponding to a location of the detector Di which causes a minimum of overlap of the various theoretical echoes 40 Ei, makes it possible to develop a sequence of reference Sr which implies the counting and identification of all the echoes whose energy exceeds a predetermined energy threshold a and the recognition among these echoes of those whose position in the time scale is ie the delay, corresponds to a theoretical echo 45 of the series c. The reference signal Sr of FIG. 9 thus includes, by way of example, 9 recognized theoretical echoes Eìr identified by the numbers of the reflective planes 5-5, 1-1, 6-6, 5-1, 1-2, 6-3, 2-3 , 4-4, 5-4. In addition to these 9 recognized theoretical echoes Eìr, the reference signal includes ten other non-recognized echoes 50, that is to say exceeding the predetermined energy threshold a, but whose delays do not correspond exactly to those of theoretical echoes. These echoes, present in the reference signal Sr, but not identifiable by a theoretical echo, are simply designated by the indices 0-0. It will be noted that the echoes 55 present in the reference signal, but not corresponding to predetermined theoretical echoes, may correspond, for example, to reflections on furniture or other objects present in the room to be monitored and which are therefore possibly subject to change over time, when, for example, an object is moved, while the theoretical echoes identified, which are due to reflections on the walls of the room, must, in principle, remain immutable.

Once determined, the reference signal is recorded in a memory, in order to be able to be used as a basis for a comparison 65 with the intercorrelation signals which will then be produced periodically.

The characteristics of the reference signal Sr put in memory, we pass to the active surveillance phase of the room where the

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frequency-modulated pulse trains are emitted periodically and with each pulse train emitted, an intercorrelation is performed between the emitted signal and the signal received by a detector and the envelope of the intercorrelation function between signal is determined transmitted and signal received. Fig. 10 shows such a cross-correlation function envelope of a transmitted signal and a received signal which manifests the presence of an intruder. As in the case of determining the reference signal Sr, the envelope of the intercorrelation function d of FIG. 10 is treated in combination with the sequence c of theoretical echoes E ;. Thus, on the envelope d of the signal of FIG. 10, the various echoes, the amplitude of which is greater than a predetermined energy threshold a, are counted and the echoes corresponding to theoretical echoes Ei are recognized and identified. We thus see, in fig. 10, six echoes Eìr, which correspond to recognized theoretical echoes and seven echoes which are simply identified by the indices 0-0 insofar as they do not correspond to theoretical echoes Ei of the series c. The different characteristics of the signal in fig. 10, i.e. the different recognized theoretical echoes Eìr and the different unrecognized echoes Eio, are compared with those of the reference signal Sr, in order to determine whether recognized or unrecognized echoes have disappeared or, on the contrary, appeared. The research is done in fact, preferably, from the most energetic echoes, that is to say from the echoes least delayed in time.

Furthermore, in order to avoid detection errors, an echo is considered to have disappeared if its attenuation relative to the corresponding echo of the reference signal is greater in percentage than a predetermined value compared to the echo of the signal of reference.

Considering figs. 9 and 10, it can be seen that, in the case of FIG. 10, there are 4 less recognized theoretical echoes than in the case of FIG. 9, namely the recognized theoretical echoes identified in FIG. 9 with references 6-6, 6-3, 4-4 and 5-4. There is, also, in fig. 10, 4 unrecognized Eîo echoes which disappeared and two recognized theoretical echoes 5-2 and 5-3 appeared. The comparison between the signals of fig. 10 and 9 clearly illustrate the resolution capacity between the various echoes of the signal processing principle adopted.

In order to ensure good reliability in the detection of intrusion, it is advantageous not to trigger an alarm as soon as the comparison of an envelope of intercorrelation function, such as that of FIG. 10, with a reference signal, such as that of FIG. 9, reveals a non-coincidence between echoes. We thus establish, preferably, a hierarchy in the echoes and we first examine the recognized theoretical echoes Eìr. It is only if there is no disappearance or appearance of recognized theoretical echoes E; r with respect to the reference signal, that one examines whether unrecognized echoes Eio have disappeared or appeared by relative to the reference signal Sr. Furthermore, it is advantageous to carry out monitoring sequences taking into account a series of data corresponding to successive pulse trains of the signal emitted by the transmitter 10. Thus, from a pre-established reference signal Sr and for a set of M acquisitions, that is to say M signals of envelopes of intercorrelation function corresponding to trains of pulses emitted by the transmitter 10, comparisons are made successive for detecting the appearance or disappearance of echoes in the various signals acquired with respect to the reference signal Sr. Preferably, an alarm is avoided as soon as a fault is detected for the first time. On the contrary, the appearance of a fault, that is to say the disappearance or the appearance of an echo in relation to the echoes of the reference signal, triggers a prealarm which corresponds to the incrementation of a counter . A distinction is however made according to whether the faults correspond to recognized or unrecognized echoes. Thus, if it is a question of erasing recognized echoes Eìr, the alarm is triggered very quickly, for example after two faults appearing in M acquisitions, provided that the echoes corresponding to these faults are indeed echoes recognized Eìr identical or located in the same detection zone. In the event that the faults correspond to the appearance of echoes or to the disappearance of non-recognized Eio echoes, the alarm is triggered only after N faults appearing in M acquisitions, the number N being greater to 2.

In order to detect a type of system operating anomaly, during comparisons made with the reference signal Sr, a test is also carried out, with the aim of determining whether the number of echoes or disappeared is not greater than one predetermined value corresponding, for example, to more than half of the echoes present in the reference signal Sr.

Changes in physical parameters, affecting the transmission of sound in the room to be monitored, for example temperature changes, can lead to relatively continuous changes in the time scale of the distribution of echoes compared to the echoes of the reference signal. To adapt to these variations, periodic intervals are made which are much higher than the frequency of repetition of the emission of pulse trains, for example every quarter of an hour, the acquisitions and the recording of a refreshed reference signal Sr. In this case, the protection system remains sensitive to rapid changes in the conditions of sound transmission in the room to be monitored, and this can help to ensure monitoring that is complementary to that of the intrusion, for example monitoring aimed at detecting a sudden rise in temperature and, by that, which could make it possible to issue an alarm in the event of a fire.

We will describe below, with reference to FIG. 11, an example of a device for protecting premises against intrusion which implements the intrusion detection method which has just been mentioned. The protection device essentially comprises a transmitter 10 of acoustic signals and an assembly 20 for detecting reflected acoustic signals. The signal transmitter 10 comprises one or more loudspeakers 11, suitably placed to insonate all the areas to be protected, taking into account the shape of the premises and of the objects, furniture, equipment, storage placed there. The detection device 20 comprises a sensor assembly 21 made up of one or more microphones distributed according to the various paths of direct and reflected acoustic rays which one chooses to consider, using the mentioned mobilization, to ensure the density desired surveillance according to the described procedure for comparing the sequences of echoes collected. A signal processing assembly 30 receives the signals transmitted by the transmitter (s) 10 (line

33), as well as the signals delivered by the detectors 21 (line

34). It will be noted that the various signals delivered by several sensors 21, in response to the emission of an acoustic signal by the loudspeakers 11, can be processed globally by the processing assembly 30. In this case, the reference signal is itself established by taking into account the analog sum of the signals delivered by the various microphones 21.

The signal processing assembly 30 furthermore controls, via line 35, the timing of the transmission of the various pulse trains by the transmitter 10. An alarm device 40 is triggered by the assembly 30 signal processing via line 36. The signal processing assembly 30 comprises a stage 31 which constitutes an interface for acquiring data and digitizing the information received by lines 33 and 34. The signals delivered by the sensors 21 are applied to the interface 31 after amplification in amplifiers 22 and sounding in a buzzer 23. Line 33 provides the reference signal of the transmitter.

The digital signals from the interface 31 are processed by a microprocessor 32. At the end of each processing sequence, the microprocessor 32 transmits on line 35 a signal

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resetting a binary counter 121, the output of which is connected to a digital analog converter 122 which transforms the digital information coming from the binary counter 121 into a voltage which increases linearly as a function of time. A voltage-frequency converter 123 is mounted at the output of the digital-analog converter 122 to transform the voltage signal into a sinusoidal signal of linearly variable frequency, like the input voltage, as a function of time. An analog switch 124 is interposed between the voltage-frequency converter 123 and the amplifier 125. The analog switch 124 cuts the signal emitted by the voltage-frequency converter after a predetermined duration T defined by a time-out circuit 126 connected to the binary counter 121. The circuit 126 in fact ensures the adjustment of the duration of the pulse train T and of the recurrence period Tr of the different pulse trains. The analog switch 124 is thus closed as soon as the counter 121 is reset to zero then is opened after a predetermined duration T and, finally, is closed again after the recurrence time Tr corresponding to a new reset of the counter 121. The binary counter 121 is controlled by a pilot clock 127, itself connected to a circuit 128 for adjusting the frequency band B. The circuit 128 regulates the frequency band B by its action on the pilot clock 127 and therefore on the counting speed of the binary counter 121. The frequency modulated pulse trains present at the output of the analog switch 124 are applied, on the one hand, to the processing circuit 30 by the line 33 and, on the other hand , to the loudspeaker 11 via an amplifier 125.

It will be noted that, in the example of device shown in FIG. 11, the microprocessor 32 ensures by the line 35 the piloting of the recurrence frequency Tr between the different pulse trains emitted by the circuit 12 for developing frequency modulated pulse trains. This allows a relatively short recurrence time, for example of the order of 1 second. However, with recurrence periods corresponding to longer time intervals between two trains of consecutive pulses, one could also, conversely, provide for control of the signal processing assembly 30 by the circuit 12 of pulse train emission.

We will now note, with reference to FIG. 12, an example of an algorithm for processing the signals by the processing unit 30 in the case where the operation of cross-correlation of the transmitted signals and of the received signals is carried out after analog-digital conversion of these signals. This intercorrelation of the signals delivered on lines 33, 34 of the device of FIG. 11 could also be produced in a hybrid manner within the unit 31 which then delivers the cross-correlation function in digital form.

According to the block diagram of FIG. 12, there is a first acquisition phase comprising modules 201 and 202. The module 201 corresponds to a waiting phase during which the acquisition, in synchronism with the operation of the transmitter, of information relating to a train of transmission signals transmitted on line 33 and to the echo signals received on line 34. The module 202 corresponds to the reading of the digital tables of the signals transmitted and received after the phase of conversion into digital form carried out by l 'interface 31.

The module 203 corresponds to the phase of intercorrelation of the digital signals transmitted and received for each pulse train transmitted by the transmitter 10. This intercorrelation can be carried out in the frequency domain, by FOURIER transform, then by return to the time domain.

The module 204 corresponds to the initialization of the phases of intrusion detection. Variables and simulated data are taken into account which correspond, in particular, to the recording of theoretical echoes Ei specific to the room to be monitored.

During an initialization of the intrusion detection phase or when a sufficiently long time has already elapsed during which an intrusion detection has continued, a first phase is carried out in module 205 for determining or refreshing a reference signal Sr. As indicated above, there is a procedure, starting from a no-load cross-correlation signal, that is to say coming from a transmitted signal and from received signals corresponding to a room, considered to be under reference conditions, to the detection of the different echoes, to the recognition of the Ejr echoes corresponding to recognized theoretical echoes and to the recording in memory of this information. The module 206 corresponds to a control phase by viewing the reference signal and comparing it with the envelope of the intercorrelation signal developed during an active monitoring phase. This phase is useful for pre-setting and checking the operation of the system.

The module 207 corresponds to an active monitoring phase during which a comparison of the intercorrelation signal and the reference signal recorded in memory is carried out. The counting and the tracking of the echoes appeared and disappeared is carried out automatically during this phase. The echoes are divided into Eìr recognized theoretical echoes and Eio unrecognized echoes.

The modules 208 and 209 correspond to a pre-alarm phase. The module 208 corresponds to a test making it possible to determine for each acquisition of a new cross-correlation signal if anomalies have been detected with respect to the reference signal. In the case where no anomaly is detected, a return is made to the initial phase of acquisition of new signals at the level of the module 201. In the case where an anomaly is detected at the level of the test 208, a prealarm in module 209, then return to an acquisition phase.

The modules 210 to 217 correspond to additional tests leading to alarms after a pre-mined number of pre-alarms recorded at the level of module 209. The module 210 corresponds to a test to determine whether recognized echoes Eìr have disappeared or not . If this test indicates that recognized echoes have not disappeared, this means that the previous prealarm corresponds to an unrecognized echo. A test is then carried out on the unrecognized echoes at the level of the module 216 which counts the various recorded pre-alarms, relating to the appearance or disappearance of unrecognized echoes. The module 217 triggers an alarm after a predetermined number N of pre-alarms counted by the module 216.

When the module 210 test indicates that the pre-alarm recorded is due to the disappearance of a recognized echo, it is proceeded, at the level of the module 211, to the identification of the recognized echoes which have disappeared and an activation is carried out memory of the result at the level of module 211. The tests carried out at the level of module 211 make it possible to carry out topological monitoring of the intruder and thus to operate a logical confirmation of the diagnosis. Thus, if during the next sequence at the level of the module 211 it is noted the disappearance of the same recognized echo or of a echo recognized topologically close, it can be triggered at the level of the module 213 an alarm from this sequence which constitutes a confirmation of the diagnosis of presence of an intruder and continuity of its trajectory in the room. If, on the contrary, during the following sequence, at the level of test 211, no disappearance of the same recognized echo or of a neighboring recognized echo is observed, but simply, for example, of an echo distant topologically from the first echo whose disappearance had been noted, a pre-alarm message and an alarm are recorded at the level of the module 212

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can then be triggered upon detection of at least a third prealarm at the level of the module 209. The logical structure for developing the alarm signal is thus programmable in the microprocessor according to a logic mode adapted to the topology of the local and the general surveillance strategy applied to it.

The modules 214 and 215 correspond to specific tests on the number of different echoes that have disappeared. Thus, at the level of the module 214, the detection of a disappearance of at least more than half of the echoes is interpreted as a malfunction of the monitoring system and an alarm is automatically triggered immediately. At module 215, a test is carried out to determine whether the disappeared echoes are systematically offset on the time scale by a value greater than a predetermined value. The observation of systematic offset in time of the different echoes with respect to the echoes of the reference signal, which can be made by comparison between the number of echoes that have disappeared and that of the echoes that have appeared, provides specific information on the evolution sound propagation conditions in room 20 and in all cases causes a refresh sequence of the reference signal Sr by the module 205.

In summary, the decision process for triggering an alarm is as follows: for each pulse train emitted by the sound source 10, a feedback signal is received which reflects the configuration of the room to be monitored. Due to the intercorrelation carried out on the transmitted signal and the received signals, there is a very strong elimination of the spurious signals and therefore a self-recognition of the received signals which always constitute echoes of the transmitted signal. A simple comparison of the different intercorrelation signals produced successively from the different pulse trains transmitted and the different echo signals received makes it possible to detect a modification of the echoes and therefore to induce a presumption of intrusion. However, to minimize the risk of false alarms, a strategy for confirming this presumption is implemented in the system as follows. Starting from the positions of the sound source and the various sensors and the geometrical characteristics of the room to be protected, a simulation is used to determine the sound paths of the least attenuated echoes due to primary and secondary reflections. on the different walls and fixed obstacles of the room. Such a simulation of the echo sound paths makes it possible then to establish, taking into account the length of the sound paths, a series of theoretical echoes distributed over the time scale and which can be identified each by the reflective plane or planes to which they are due. The recognition of the planes and of the sound rays defining the conditions of spatial and temporal reception of the echoes (fig. 2 to 4 and fig. 8a, 8b) makes it possible to define a comparison matrix gathering the information relating to the determined theoretical echoes.

In the developed reference signal, a distinction is made between recognized echoes, which correspond to previously determined theoretical echoes, and unrecognized echoes. Each time an intercorrelation signal is analyzed, this signal is compared with the reference signal and any modification detected on an intercorrelation signal triggers the recording of a prealarm. If this pre-alarm is due to a fault corresponding to an unrecognized Eio echo, it will only be confirmed as an alarm if a defined number of such faults is counted against a predetermined number of signal acquisitions. Thus, an alarm will, for example, be triggered after the fourth detection of a fault due to the disappearance of an unrecognized echo for a dozen acquisitions.

On the other hand, in the case where the fault is due to the disappearance of a recognized echo, that is to say corresponding to an identifiable theoretical echo, the alarm may be triggered as soon as the second finding of the same fault or of a fault due to an echo recognized topologically close to the echo which caused the detection of a first fault. It will be noted that the use of identifiable echoes, because corresponding to theoretical echoes, makes it possible to trace the route followed by an intruder within the premises and therefore to confirm the diagnosis of intrusion, which greatly increases the safety of the system.

The invention is not limited to the examples described and shown, since various modifications can be made thereto without departing from its scope.

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Claims (19)

667,931 1. A method of protecting premises against intrusion, according to which an acoustic signal is emitted inside the room to be monitored, the acoustic signals reflected by the room to be monitored are detected and the variations of the reflected acoustic signals are analyzed to detect an intrusion into the room, characterized in that an acoustic wave is emitted consisting of pulse trains linearly modulated in frequency in a band (B) between 500 Hz and 5 kHz for a limited period (T) between 5 and 20 milliseconds with a recurrence period at least of the order of the reverberation time of the room to be protected, in that the acoustic signal reflected by the room at the detection is detected using at least one detector continuation of the emission of each pulse train, in that one carries out for each pulse train transmitted the intercorrelation of the reflected signal and the acoustic signal emitted, in that one analyzes the intercorrelation signals products for d enumerate and identify the different echoes they contain, in that each intercorrelation signal analyzed is compared with a pre-recorded reference signal corresponding to an intercorrelation carried out under reference conditions with the empty room, without the presence of intruder and in that an alarm or monitoring device is triggered in the event of a change in the echoes of an intercorrelation signal compared to the pre-recorded reference signal. 2. Protection method according to claim 1, characterized in that the acoustic waves emitted comprise trains of pulses modulated linearly in frequency in a band (B) between approximately 1 kHz and 3 kHz for a duration (T) between about 10 and 15 milliseconds. 2 3 667,931 characterized in that the signal processing assembly (30) comprises means for sampling the acoustic signals emitted by the transmitter (10) and received by the detector (20) and means for intercorrelating the acoustic signals emitted and sampled receipts to provide said cross-correlation signal. 3. Protection method according to claim 1 or 2, characterized in that the frequency of recurrence of the emission of the pulse trains is of the order of 1 to 3 seconds. 4. Protection method according to any one of claims 1 to 3, characterized in that the duration of the reflected acoustic signals taken into account is between approximately 40 and 100 milliseconds, depending on the dimensions of the room to be monitored. 5 5. Protection method according to any one of claims 1 to 4, characterized in that, in order to analyze the intercorrelation signal and compare it to a reference signal, sampling of the signal is carried out. reference and the cross-correlation signal to be analyzed. 6. Protection method according to any one of claims 1 to 5, characterized in that one determines beforehand the theoretical primary and secondary echoes to be reflected by the walls of the room to be protected, depending on the location of the or acoustic signal transmitters and acoustic detector (s) reflected by the room and in that the recognized echoes corresponding to theoretical echoes are identified on the pre-recorded reference signal. 7. A protection method according to any one of claims 1 to 6, characterized in that, when the comparison between the analyzed intercorrelation signal and the reference signal reveals a new echo, it is suspended when a alarm until the appearance of a predetermined shadow (N), greater than 2, of detection of echoes representative of faults with respect to the reference signal, for a predetermined number (M) greater than 2 of signal acquisitions of intercorrelation analyzed. 8. Protection method according to claim 6, characterized in that, when the comparison between the analyzed correlation signal and the reference signal brings out the disappearance or the attenuation of a recognized echo corresponding to a theoretical echo, it an alarm is triggered as soon as a second disappearance or attenuation of echo recognized as identical or similar is noted for a predetermined number (M) greater than 2 of acquisitions of intercorrelation signals analyzed. 9. A protection method according to claim 8, characterized in that, when the comparison between the analyzed correlation signal and the reference signal brings out the disappearance or the attenuation of an unrecognized echo not corresponding to an echo theoretical, it is suspended when an alarm is triggered until a predetermined number (N), greater than two, of disappearances or attenuation of unrecognized echoes relative to the reference signal is taken into account for a number predetermined (M) greater than two, for acquisition of analyzed intercorrelation signals. 10 10. Protection method according to any one of claims 1 to 9, characterized in that one proceeds, periodically, at time intervals much greater than the frequency of recurrence, the acquisition and the recording of a new reference signal. 11. Protection method according to any one of claims 1 to 10, characterized in that, during the comparison, between the analyzed correlation signal and the reference signal, the faults due for the echoes to a difference in value lower than a predetermined threshold, corresponding to a determined percentage of the amplitude of the considered echo of the reference signal, are not taken into account for the triggering of an alarm. 12. Protection method according to any one of claims 1 to 11, characterized in that, when the comparison between the analyzed intercorrelation signal and the reference signal reveals both a disappearance of echo and an appearance of echo corresponding to a time offset, the time offset of each echo is measured between two or more successive analyzes and in that, in the event of an offset remaining substantially stable, information corresponding to a change in physical characteristics is delivered the atmosphere of the room to be protected. 13. Protection method according to any one of claims 1 to 12, characterized in that a specific non-operation alarm is triggered in the event of the disappearance or appearance of echoes in numbers greater than a predetermined value (Ni ), for one or more acquisitions of intercorrelation signals analyzed. 14. Device for protecting premises against intrusion for implementing the method according to any one of claims 1 to 13, comprising at least one transmitter (10) of acoustic signals and at least one detector (20) of signals reflected acoustics, arranged in the room to be protected, as well as a set (30) of signal processing to which are applied, on the one hand, the signals emitted by the transmitter (10) and, on the other hand, the reflected signals picked up by the detector (s) (20), characterized in that the transmitter (10) of acoustic signals comprises a generator (12) of trains of pulses linearly modulated in frequency and a loudspeaker omnidirec-tional speaker (11) for broadcasting said pulse trains in the room, in that the acoustic signal detector (20) comprises at least one microphone (21) and means (22) for conditioning the signals received by the microphone and in that the signal processing assembly (30) comprises means for intercorrelating the acoustic signals emitted by the transmitter and received by the detector to provide an intercorrelation signal, means for analyzing the envelope of the intercorrelation and echo recognition signal, means for comparing the intercorrelation signal and a reference signal having a predetermined number of echoes characteristic of the room to be protected, and means for counting the location of the echoes appeared s or disappeared in the cross-correlation signal and in that means (40) for triggering an alarm are controlled by said means for counting the detection of missing or appeared echoes, according to a programmed decision logic strategy. 15 20 25 30 35 40 45 50 55 60 65 15. Protection device according to claim 14, 16. Protective device according to claim 14 or claim 15, characterized in that pre-alarm means are interposed between the counting and tracking means of echoes that have disappeared or appeared so as to control the means (40) for triggering only cases of repeated recognition of disappearances or echoes, according to a programmed sequential logic. 17. Protection device according to any one of claims 14 to 16, characterized in that it comprises several detectors (Di, D2) of acoustic signals distributed in the room to be protected and each connected to the signal processing assembly (30) which comprises means for summing signals received by the different detectors (Di, D2), means for sampling the acoustic signals emitted by the transmitter (10) and summed signals received by the different detectors (Di, D2), means for intercorrelating the sampled transmitted signals and summed and sampled reception signals corresponding to all of the different detectors (Di, D2) to provide for all the detectors an intercorrelation signal, means d analysis of the envelope of the intercorrelation and echo recognition signal, means of comparison of the intercorrelation signal of all the various detectors and of a reference signal also corresponding to th nsemble various detectors and having a predetermined number of echoes characteristic of the room to be protected, and means for counting and locating echoes that have appeared or disappeared in the intercorrelation signal corresponding to all the detectors. 18. Protection device according to any one of claims 14 to 17, characterized in that the transmitter (10) and the detectors (20) are arranged so that at least the theoretical primary and secondary echoes reflected by the walls of the premises to be protected have a minimum of overlap and correspond to reflected acoustic rays having an angle between them greater than about 15 °. 19. Protection device according to one of claims 14 to 18, characterized in that several transmitters excited in parallel by the same signal are concurrently used at various points in the same room of large dimensions and / or of complex shape , or simple in shape but filled with objects constituting obstacles giving the empty space a form which is itself complex, so as to simultaneously insonate all the volumes in which an intruder can move.