FR2527814A1 - Intruder alarm less prone to false alarms - activated IR emissions and ultrasonic reflection pref. includes polymer etc. components - Google Patents

Abstract

An intruder alarm consists of a detector contg. polarised material with both piezoelectric and pyroelectric properties for sewing acoustic vibrations and electromagnetic waves in the infra-red range. A significant variation of either of these emissions in the area surveyed by the detector causes an electric signal in at least one separate circuit. Signals occurring simultaneously in circuits corresponding to acoustic and i.r. waves trigger an alarm. The material used in the detector is pref. an inorganic oxide, esp. BaTiO3 or LiNbO3 type structures, e.g. titanium lead zirconate ceramics or LiTaO3 or a vinylidene fluoride (co)-polymer. These materials are treated in an intense electric field to acquire piezoelectric and pyroelectric properties.

Description

 INTRUDER DETECTION ALARM DEVICE.

 The present invention relates to an intruder detector alarm device, for example a detector intended for the protection of property or for monitoring dangerous sites.

 Many types of detectors are known. Usually an intruder detector implements either the DOPPLER effect by emission and detection of an electromagnetic wave in the UHF range or a beam of ultrasonic vibrations, either passive or active detection of infrared radiation or even the simple detection of sound vibrations.

 When these devices are used alone, the probability of triggering false alarms is quite high, this in direct proportion to the increase in the sensitivity of these devices. The nuisance trips are due to parasitic phenomena such as the rise in temperature or the simple movement of air mass depending on the effect used. it is therefore generally necessary to combine several of these detectors, possibly in association with the detectors. passage, with galvanic contact for example, whose signals are transmitted to a central processing system for these different signals according to preprogrammed criteria so that the reliability of the alarm triggered is improved. These techniques require that the different sensors must be in connection with these central systems, whether these connections are made by wires, by infrared beams or by radio waves. This increase in crossings correlatively results in a reduction in the overall reliability of the system and, paradoxically, an increase in the probability of triggering a false alarm.

 The invention proposes to overcome the difficulties of the known art.

 The subject of the invention is therefore an alarm device for detecting the passage of an intruder in at least one predetermined region of the monitored space, comprising a sensor detecting significant variations in physical parameters characteristic of the monitored regions caused by said passage. and converting these variations into electrical signals, circuits for selective processing of these signals delivering an electrical alarm control signal and an alarm member actuated by this signal device, characterized in that the sensor comprises at least one active detector element in polarized material having simultaneously piezoelectric and pyroelectric properties so as to be made sensitive to electromagnetic waves in the infrared range and to acoustic waves and delivering in response to the detection of these waves, at the terminals of at least one pair of electrodes , said electrical signals and in that the first circuits constituting a selective processing sensitive to the detected signals due to variations in amplitude of electromagnetic waves in the significant infrared range of temperature variations in said monitored region, and delivering in response a first alarm signal, second circuits constituting at least one channel for selective processing of the signals delivered by the sensor when detecting acoustic waves and delivering in response at least a second alarm signal and a circuit for detecting the simultaneous occurrence of alarm signals delivered by the two processing channels selective and delivering an alarm control signal conditioned by said simultaneous occurrence.

The invention will be better understood and other characteristics will appear with the aid of the description which follows with reference to the appended figures among which:
- Figure 1 schematically shows the configuration of a device according to the invention.

 - Figures 2 to 8 are- optical elements of transmission imaging and / or transmission associated with the sensor used in the device of the invention.

 - Figure 9 is an example of a dual sensor.

 - Figures 10 to 12 are electrical diagrams allowing the association of the sensors used by the device of the invention in several configurations.

 - Figure 13 illustrates schematically an arrangement allowing discrimination of the direction of passage of an intruder.

 - Figures 14 and 15 illustrate imaging elements composed of infrared electromagnetic waves and acoustic vibrations.

 - Figures 16 and 17 are additional electrical diagrams allowing the association of several sensors.

 - Figures 18 to 20 show several concrete embodiments of a sensor used in the device of the invention.

 - Figure 21 is an electrical diagram for the electrical operation of a sensor in an alarm device implementing the emission of ultrasonic vibrations and the detection of these vibrations.

 - Figure 22 is an explanatory diagram of the operation of.

circuit of figure 21.

 - Figure 23 shows in more detail the configuration of an intruder detector alarm device according to the invention.

 FIG. 24 is a diagram explaining the operation of the device in FIG. 23.

 - Figure 25 is the diagram of one of the circuits of the device of Figure 23 allowing the differentiation of echoes due to ultrasonic vibrations.

 The main characteristic of the intruder detector alarm device according to the invention is to use a sensor using at least one active element having simultaneously a piezoelectric effect and a pyroelectric effect. This sensor is associated with imaging elements, in transmission or in reflection, in particular making it possible to focus the infrared rays.

 The general configuration of a device according to the invention is represented schematically in FIG. 1. It comprises a sensor 1, comprising at least one element exhibiting the piezoelectric and pyroelectric effects associated with imaging elements 2 for detection of an intruder 3. The DV output signals from the sensor are transmitted to at least two channels 4 and 5, respectively for the processing of signals corresponding to the detection of acoustic vibrations and the processing of signals corresponding to the detection of electromagnetic waves in the infrared range.

The signals from the piezoelectric effect can also be processed according to two different methods, either by passive detection of sound vibrations in the audio-frequency domain by circuits 40, or by active detection in the range of ultrasound. In the context of the invention, the active term indicates that there is emission of at least one beam of ultrasound and detection after reflection; and processing the signals thus detected. This treatment can be carried out by echo analysis or by taking advantage of the effect
DOPPLER.- The processing is carried out by circuits 41 which will be detailed later. According to the invention, the detection device implements at least one of the acoustic treatments and, in a preferred variant, the device implements both treatments.

 There is therefore a simultaneous presence of signals included in at least two if not three different frequency bands. These signals are marked VA1 to VA3. According to another advantageous aspect of the invention, these different signals are transmitted to circuits 6 verifying the coincidence, weighted or not, of two signals or in a preferred variant of three signals. The circuits 6 emit an output signal VA transmitted to an alarm device 7 when the coincidence is achieved. Contrary to the known art, there is therefore no need for multiple links between different types of devices implementing different effects. The processing of signals due to different effects as well as the detection of their coincidence is carried out. locally without the need for multiple connections between sensors of different types.

 The active element used in the sensor used in the device of the invention can be produced from certain ferroelectric materials which simultaneously exhibit pyroelectric and piezoelectric effects.

These elements can be used simultaneously as a passive infrared detector and as a microphone in the audiofrequency and ultrasound ranges. Finally, it can be used as a transducer for the emission of ultrasonic waves.

 The first types of materials that can be used are certain inorganic materials with oxygen octahedra, in particular the families of barium titanate (Ba Ti 03) and lithium niobate (Li Nb 03). The first family includes PZT (lead titanium zirconate) ceramics with piezoelectric and pyroelectric properties. - In the second family, lithium tantalate (Li Ta 03) has the highest pyroelectric properties.

 Second types of materials that can be used are certain polymers, mainly polyvinylidene fluoride (P-V F2), its copolymers with in particular polytetrafluoride ethylene (PTE), Ihexaflloropropene (HFP) and polytrifluoroethylene (P Tr FE), as well as its alloys, for example with polymethylmethacrylate (PMMA).

 These materials acquire piezoelectric and pyroelectric properties after specific treatments comprising at least one phase of polarization under intense electric field.

 These treatments are well known to those skilled in the art. An example of processing is described in European patent application EP-A-0 002161.

 The devices according to the invention having for main applications the so-called "general public" applications, this latter type of material will be preferred because of its low cost. In addition, since the polymers can be polarized over large areas before being cut to the dimensions required by the sensor used in the device, they are also preferable to ceramic polarized piece by piece and in particular to single crystals.

 Before describing in detail the device of the invention, it is useful to specify the imaging elements associated with the sensor as well as to recall the operation of the detection in the three wave ranges: infrared, audio-frequency and ultrasound.

 The active detector element must be sensitive to both sound waves and infrared rays, it follows that the imaging elements associated with sensor 1 must be compatible with these two types of effect.

The imaging elements can be front elements, for example elements for focusing infrared radiation and / or acoustic vibrations towards the sensitive element, that is to say elements operating in transmission. These elements can consist of elements of reflective types or elements of both types.

 In the first case, it may be prisms or lenses for optical focusing or more generally the delimitation of the optical field of observation which can be made from materials transparent to infrared radiation, for example polyethylene. In - - cases, these front optical elements must include a zone transparent to sound waves: channel, grid, tuned tubular cavity etc ...

 Two examples of this type of element are illustrated in FIGS. 2 and 3. In FIG. 2, the sensor 1, represented in the form of a flat sensor, emits or receives sound and infrared waves in a direction parallel to un- axis A orthogonal to the plane of the sensor. A triple prism 20 is placed in front of the sensor 1. This prism is made of infrared transparent material have a frontal zone parallel to the sensor and two wings intended to focus the infrared radiation towards the sensor. The frontal area of the prism 20 is pierced with a channel 200 of axis coincident with the privileged axis A of transmission and reception.

In FIG. 3, the imaging element 2 is a conventional focusing lens 21 made of infrared transparent material. As in the previous case, this lens has a channel 210 coincident with the Q axis. AT
In other variants, illustrated by FIGS. 4 and 5, the imaging elements may consist of acoustic wave screens made of transparent material in the infrared range.

In FIG. 4, the screen consists of a series of prisms whose edges are arranged parallel to itself on the face of a cylinder of axis of symmetry A passing through the plane of the sensor defined by the face of
c this next to the prisms and dividing it into two equal parts. The prisms are distributed in space so as to define between two adjacent prisms of the direction corridors. means parallel to axes, A to Q6 in Figure 4, these axes converging at a point O located on the axis A c
Preferably, the radial distribution of the prisms is uniform and the directions parallel to the axes A1 and Q6 define as many preferred directions of emission and / or reception of the acoustic waves.

 Figure 5- illustrates another variant of this type of imaging element.

Element 2 comprises two portions of cylinders 23 and 24 drilled with the same number of channels, respectively 230 and 240, aligned, in the example of FIG. 5, on the axis A on the one hand and on axes A 1 to A 4 converging at a point O on the face of the sensor 1 facing the walls 23 and 24. As previously, these axes define as many preferred directions of emission and / or reception of acoustic waves. The material constituting these walls is also a material transparent to infrared.

 A second family of imaging elements is constituted by reflectors.

 In a first example of this family, illustrated in FIG. 6, the reflector consists of a faceted mirror 25 focusing the infrared radiation as well as the acoustic waves towards a point O on the face opposite the sensor 1 located on the axis A. The material must be chosen to be a good reflector of infrared radiation as well as acoustic waves.

FIG. 7 illustrates a second example of a reflective element constituted by a portion of a conventional spherical mirror 26 making the infrared radiation and the acoustic waves converge towards a point O on the face of the sensor 1 opposite the reflector located on the axis A
The operation of the device in the infrared range will now be described in more detail. In the context of the present invention, the detection in the infrared range is of the passive type, that is to say that the sensor detects the ambient infrared radiation. When an intruder is present, the characteristics of the detected radiation will be changed. It is this change which will trigger the emission of a signal VA3 by the channel 5 for processing the signals due to the pyroelectric effect.

 The optical elements of the type which have just been described define observation windows delimited by a simple cone of privileged reception axis A i. This cone can itself be subdivided into different solid angles. For example if we refer again to the imaging element of the spherical mirror type 26 of FIG. 7 and if a grid 260 has been added between the detector 1 and this mirror 26 as illustrated in FIG. 8 holes 261, with regular distribution in a preferred embodiment, these holes 261 define as many preferred directions of reception. It follows that the emission diagram is of the multilobe type, the distribution and the shape of these lobes depending on the distribution and the shape of the holes 261. The material constituting the screen 260 must be opaque to infrared radiation. red.

 The creation of several lobes can also be obtained using a sensor made up of several active elements. Such a configuration is illustrated in FIG. 9. The sensor 1 having the shape of a circular patch of center O comprises a first active element in the form of a disc 10 with the same center and a second active element in the form of a peripheral ring. he.

This sensor can consist of a plate of active material covered on its lower face with a single metal area and on its upper face with two areas having the configuration of zones 10 and 11. Such a sensor has an emission diagram with two lobes, the first being
a central lobe in the shape of a cone with a medium axis and a second lobe
peripheral surrounding the first-as well as a region of blind space
between the two lobes. Such a configuration is particularly interesting.
health for signal processing due to the pyroelectric effect.
as is known, a pyroelectric effect sensor can - detect -
temperature variations of the order of 10-6 to 10-3 C, corresponding to
temperature variations of a few degrees in the observed area. Such
sensor is completely blinded, by saturation of the associated amplifier,
if its own temperature changes a few degrees as a result of the change
ambient temperature To overcome this drawback, it is known
to use two paroelectric detectors associated with a different amplifier
profitable, both undergoing the same temperature variations
ambient, but only one of which is exposed to the thermal rays to be detected.

Such a configuration is illustrated by 9a FIG. 10. The sensors
comprise a first detector element 12 and a second element 13
mounted in opposition and connected to the differential inputs of an amplifier
A10. These two sensors are mounted in an enclosure. common thermal
100. It follows that the variations in output signals of these two sensors due to the temperature variations of these compensate each other. In what
relates to external infrared radiation, only infrared radiation
red IR1 will reach element B2, the part of IR2 radiation being
blocked by a screen 27. In the context of the present invention
preferential, - these two elements are elements 10 and 11 of the sensor
single 1 according to the configuration illustrated in FIG. 9.

Figures 11 and 12 illustrate two more advantageous variants of this
mounting. In these two variants a single input amplifier is
used. The active detector elements 12 and 13 are mounted either in series
either in parallel and only one is subjected to infrared radiation IR1
before hitting element 13 and blocking as before by a screen
27. It is then necessary that the polarizations of these detectors are
reversed for the compensation effect to occur.

Amplifiers A10 and A11 deliver the VD signals transmitted to
selective treatment channels 4 and 5.

 In another variant, while retaining this compensation for variation in ambient temperature, each of the elements can be arranged in space so as to observe a different region and then plays an active role. This operating mode can be deduced simply from FIG. 12 by removing the screen 27. In this case the infrared radiation IR1 and 1R2 come from different regions.

 A sensor with a multi-lobe reception diagram can also be associated with imaging elements which are themselves multi-lobe, for example the element illustrated in FIG. 8 by the reflector 26 and grid 260 assembly.

 The existence of a multilobe diagram can be used with profit in an application which will be described in relation to FIG. 13. In this example, the sensor I is supposed to have a reception diagram with two lobes L1 and L2 distributed in part. and other symmetrically with respect to an axis A orthogonal to the plane of the sensor. It is assumed that the sensor 1 is of the type illustrated in FIG. 12, that is to say comprising two elements 12 and 13 connected in parallel on the amplifier A11, the assembly not comprising the screen 27. The two radiations 1R1 and IR2 corresponding in the case of FIG. 13 to the lobes L1 and L2. An intruder 3 moving from left to right in FIG. 13, that is to say crossing the region covered by the reception lobe L1 then the region covered by the reception lobe L2, will cause the generation by the amplifier A11 of an output signal whose characteristics are plotted on the upper diagram of FIG. 13 giving the voltage VD1 at the output of the amplifier A11 as a function of time. I1 is assumed on this diagram that, when the intruder 3 will cross the region covered by the reception lobe L1, the detected signal is negative with respect to the reference zero: electrical ground, this for a period of time equal to T1. Then, the intruder will cross a blind zone, then the region covered by the lobe L2.The output signal of the amplifier A1 I will become positive, this for a period of time equal to T2. If the geometric characteristics of the two lobes are identical, these two signals will have the same amplitude and the same duration.

Otherwise, when the intruder 3 'crosses the regions in opposite directions, the resulting signal is illustrated by the lower diagram of the
FIG. 13, that is to say a signal comprising first a positive pulse during a time interval T'1, followed by a negative pulse during a time interval T'2.

 Simple logic circuits can be associated with the sensors to determine the direction of passage by understanding the respective polarities of the first and second pulses.

 All these circuits can be incorporated into circuits 5 of the detection channel assigned to the pyroelectric effect. These circuits will be detailed later.

 According to the invention, the device of FIG. 1 comprises at least a second channel 4 detecting acoustic waves.

 A first type of detection which will be described in the following is the passive detection of acoustic waves generated Hz Hz by the intruder.

 The active element of the sensor 1 according to the invention has two effects, piezoelectric and pyroelectric. To detect acoustic waves, the piezoelectric effect is used and the active element is used as a microphone. However, in the materials used, the piezoelectric and pyroelectric effects are both proportional to the polarization, so that the active element is deaf: compensation for variation in ambient temperature also causing compensation for piezoelectric effects. To overcome this difficulty, we can as for the pyroelectric effect, arrange the two active elements so that they cover the different solid angles so as to bring out only differences in noise, due to the displacement of the intruder from one supervised area to another.

 A first example of a device enabling this function is illustrated in FIG. 14. The sensor 1 comprises two active elements 12 and 13 electrically connected in the manner described in relation, for example, to FIG. 12. These two elements 12 and 13 are associated each to a receiver, respectively 28 and 28 ', which can be a spherical mirror, reflecting in the infrared range and also in the range of acoustic waves. The imaging assembly is completed by acoustic lenses 280 and 280 'made up of deflecting fins focusing the acoustic waves towards the active elements 12 and 13. The material.

constituting these fins must be transparent to infrared radiation.

This set defines two receiving lobes of medium axis A and A 'orthogonal, respectively, to the active elements 12 and 13. Therefore the composite sensor observes regions of space in the directions parallel to the axes A and AT'.

 In practice, the solution which has just been described in relation to FIG. 14 is difficult to implement, because of the long wavelengths corresponding to the low sound frequencies, wavelengths which require large focusing devices. dimensions.

 Another family of solutions consists in listening to two active elements in the same region of space and in performing frequency discrimination. The simplest solution is to associate these active elements with acoustic devices of resonant type, at different frequencies: cavities, vibrating plates, etc.

 A first exemplary embodiment is illustrated in FIG. 15. The sensor 1 comprises two active elements 12 and 13 associated respectively with a first resonant cavity 29 and with a second resonant cavity 29 ′ as well as with two infrared imaging elements 2 and 2 ′ which can be of any type among those described by example in FIGS. 2 to 5. The reception diagram associated with each active element 12 and 13 is a single lobe with respective mean axis d and ′. If these two sets are arranged so that the axes A and A 'intersect at a point C, the composite sensor thus formed will monitor a region surrounding this point C.

Frequency discrimination can be carried out by using electrical circuits tuned to different frequencies, each of these circuits being associated with one of the elements 12 and 13. FIG. 16 illustrates one such arrangement. The element 12 is associated with a series resonant circuit of the LC type comprising a choke L1 and a capacitor C1. Element 13 is also associated with a circuit of the same type comprising a choke L'1 and a capacitor C'1. The voltages at the terminals of elements 12 and 13 are transmitted via adaptation resistors, respectively R1 and R'1, to the inputs of an amplifier A12. A resistor R can also be arranged in parallel on the inputs of the amplifier A12 and defines with the resistors R1 and R'1 a porit and according to the respective values of these resistors the voltages appearing at the terminals of the elements 12 and 13 can be weighted. It should be understood that the directions of polarizations
elements 12 and 13 are those described in relation to FIG. 12 of
so as to compensate for the pyroelectric effect.

Finally, it is possible to add the information due to the accous effect
tick and information due to the thermal effect, using an assembly
electronics shown in Figure 17. Indeed, the sum: V1 + V2 of
output voltages from two detectors after amplification by the
amplifiers A13 and A14 contain the information due to the acoustic effect
whereas the differentiation of these same voltages V1 - V2 only contains the information due to the thermal effect. Summation and differentiation
are carried out respectively by amplifiers A16 and A15 delivering
the voltages V'D and VD representative of said summations and differentiations
tions.

Instead of having two separate elements 12 and 13, 'the sensor which
has just been described can be achieved in a preferred variant of the invention by an element 'active .composite single. Such an element will be described in
relationship to Figures 18-20.

FIG. 18 represents a first possible embodiment of a composite element with a circular configuration. This element is a bimorph plate
comprising, as is known, a first sheet of polarized polymer
stuck on a second sheet, not polarized. The element, in the form of a pellet
is therefore intended to be embedded by a flange 123, for example, in a
rigid frame. The deformation of this embedded plate comprises at least one
line of inflection, delimiting zones of reverse flexions. In the case of
circular configuration illustrated in figure 18, this line is a circle
with the same center as the patch and radius-r, the useful area of the patch
having a radius R. The ratio r / R obeys the following relation: r / R ~ 'Ç2.

 FIG. 19 illustrates the case of an active element of rectangular type.

As before, it is composed of a bimorph comprising two
polymer sheets joined together, one polarized, the other not. If this plate
bimorph is embedded in regions close to the short sides. 123 and 123 '- from the rectangle, the line of inflection is located on either side of an axis of
symmetry of the rectangle at the distance d from this axis. If D is half length
the relationship between these two lengths follows the following relationship:
d / D = 1 /.

 Under the effect of a difference in sound pressure between the two faces of such a circular or rectangular bimorph piezoelectric plate, carrying disjoint electrodes in the vicinity of the lines of inflection, the voltages corresponding to the zones of reverse bending are opposite. FIG. 20 illustrates in section the phenomena which have just been recalled in the case of a plate of rectangular shape.

 The lower face in FIG. 20 is uniformly covered with a metal pad forming an electrode E2 with zero potential or electrical ground. The upper face has three distinct metal areas, a central area forming the electrode E10 and two peripheral areas E11 and E12 electrically isolated from the central area E10 and located beyond the aforementioned lines of inflections.

Under these conditions, the potential differences due to the piezoelectric effect V1 (between the electrodes Ell and E2) and V'1 (between the electrodes
E12 and E2), on the one hand, and V2 (between the electrodes E10 and E2), on the other hand, corresponding to zones of reverse inflections are opposite. The following relationships are checked
Vla V2, AO (l)
V'la - V2a ss (2) in which the index "a" is associated with the piezoelectric effect. In the case of a circular element of the type illustrated in FIG. 18, the voltages Vla and V 'are combined.

On the other hand, if this plate which also has pyroelectric properties, is subjected to a uniform temperature variation, the metallized areas on either side of the inflection lines being equal the potential differences due to the pyroelectric effect are equal and obey the following relations VIT T V2T 0 (3)
V 1T V2T (4) in which the index "T" is associated with the thermal effect.

 The sensor comprising an active element of one of the types described in relation to FIGS. 18 to 20, is therefore a composite sensor having pyroelectric properties compensated for variations in ambient temperature and capable of functioning as a microphone, since the phase inversion necessary for the acoustic voltages is obtained mechanically.

 Finally, the acoustic detection channel can also include circuits sensitive to ultrasound. In the context of the invention, the detection is done dynamically. That is, it requires the emission of ultrasonic pulses followed by the detection of the reflected waves. In case of intrusion, this has an additional echo compared to those due to the fixed scene observed by the sensor. We then proceed to highlight this additional echo by differentiating with those due to the fixed scene and previously stored in memory. One can also detect the movement of the intruder by DOPPLER effect.

 Transmission and reception can be carried out by separate transducers or, in a preferred variant of the invention, by the same active piezoelectric element. In this case, a composite element of one of the types illustrated in FIGS. 18 to 20 is preferably chosen.

However, for correct operation, certain special provisions must be retained. First of all, the amplifier connected to the active elements must be decoupled from the generator of electrical signals at ultrasonic frequency supplying the active element. FIG. 21 schematically represents an electrical circuit making it possible to carry out this function. The sensor 1 is connected to a generator of electrical signals at ultrasonic frequency by a switch C1. I1 is also connected to the input of an amplifier A16 via a second switch
C2. For safety, the input of the amplifier can be earthed electrically using a third switch C3 during the transmission period. Logic circuits 8 control the closing and opening of these three switches.

 Secondly, during the ultrasonic emission, there is heating by dielectric losses of the piezoelectric element. It is then necessary to avoid carrying out the pyroelectric measurement during the relaxation period of the detector element, that is to say the period necessary for a return to its initial temperature, so as not to saturate the signal amplification chain. due to the pyroelectric effect, and especially not to introduce an additional noise source due to a thermodynamic non-equilibrium.

Therefore, pyroelectric measurement should only start after
the emission of the ultrasonic pulse, only at the end of a period equivalent to
several thermal time constants, a constant which depends on the type of
the active element of the sensor 1. This therefore limits the rate of exploration.

However, in most applications of the device of the invention, the
low rates possible are fully compatible with long
observation times.

Figure 22 is a diagram explaining the chronology adopted. The switches C1 and C3 are closed, closing represented by the state
logic "1", during a period of time equal to TE, that is to say the duration of the ultrasonic emission, and open during the period of time equal to TR which is itself equal to several thermal time constants. Switch C2 is on the contrary open during the first period and
closed the rest of the time. To do this, the control circuit 8 delivers two signals, respectively for controlling the switches C1 and C3,
on the one hand, and C2 on the other. I1 can be achieved simply from a
bistable element delivering pulses whose cyclic ratio is equal to the TE / TR ratio.

 It should be understood that the pyroelectric detection being different such, it is necessary in reality to have two active elements, for example the elements 12 and 13 of FIG. 10, and in this case a differential amplifier is used in place of amplifier A16. The circuit shown in Figure 21 is split in reality.

 Finally, whatever the solution adopted, the dimensions of the active elements, and more generally their configuration, are chosen so that there is resonance at the chosen ultrasonic frequency so that there is an increase in efficiency at 'transmission' and reception sensitivity.

A more detailed concrete embodiment of the circuits associated with the sensor of the device according to the invention will now be described in relation to FIG. 23. After amplification at high input impedance, by amplifiers of the type of those described above, the signals
VD due to the piezoelectric and pyroelectric effects are separated into two channels, respectively 4 and 5. In a preferred variant of the invention, the device actually comprises three different channels corresponding to the range of infrared waves and the acoustic ranges audio- frequency and ultrasound.

 The signals due to the pyroelectric effect are very low frequency signals. The circuits 5 therefore comprise a first circuit 50 consisting of a low-pass filter limited to approximately 20 Hz or less followed by a switch 51 which switches off the amplifier 52 which detects these signals for a time equal to at least twice the thermal time constant of the active element of the sensor 1. This time constant is typically equal to a few tens of seconds.

 The signals VD are also transmitted simultaneously to two circuits 40 and 41 each comprising a first stage constituted by a filter. To process the ultrasonic signals, this filter is a filter 410 tuned to the transmission frequency of the ultrasonic signals. To passively process the acoustic signals in the audio-frequency range, the circuits 40 include a bandpass filter 400, letting the signals pass typically in a band between 20 Hz and 10 kHz. This last filter is followed by an amplifier 401 delivering an output signal VA1 proportional to the amplitude of the detected sound. Finally the filter tuned to the ultrasonic frequency is followed by an echo differentiator circuit 411 which itself delivers an output signal VA2 when there is detection of additional echoes due to an intrusion. In this figure, the circuits d The emission of the ultrasonic pulses which have been described in connection with FIG. 21 are not repeated. All of the circuits in FIG. 23 are supplemented by control circuits 8 delivering in particular a control signal C2 intended for closing the switch 51 of the pyroelectric path 5 and control signals Vcl, which will be explained in what follows, transmitted to the echo differentiation circuit 411.

The diagram in FIG. 24 explains the chronology of the operation of the main elements of the device shown in FIG. 23. The control circuits 8 include a clock delivering clock pulses H with a recursion period equal to 2. In FIG. 24, five of these pulses are shown, the rising edges of which appear at times t ,, t1, t2, t3 and t4. The control signals Vc2 have a recursion frequency half that of the clock signals H. They can be generated by a bistable latch sensitive to the rising edges of the clock signals H. In FIG. 24 of the rising edges of the signals
VC2 appear at times tl and t3.When the signal VC2 is in 'logic state "1", the switch 51 is closed and the signals at the output of the low-pass filter 50 are transmitted to the amplifier 52 which does not amplify as the variations of the VD signals due to the pyroelectric effect. On this diagram are represented, under the reference C1, the control signals of the switch of the same index of the circuits of FIG. 1 and these signals are in the logic state "1" during a time interval equal to TE starting with the rising edge of pulses H at tempos t0, t2 and t4, in the diagram of FIG. 24. These time intervals TE define the windows for transmitting the ultrasonic signals.

 FIG. 25 represents a possible alternative embodiment of the echo differentiation circuits 411. These circuits receive from the tuned filter 410 a VDE signal transmitted to an interface circuit for shaping the detected echo pulses. These shaped pulses are transmitted simultaneously to two switches 4111 and 4112, the outputs of which supply the inputs of shift registers 4113 and 4114. These switches are actuated in turn by implementing the control signals VCIO and Vcll represented on the diagram of FIG. 24, frequency signals half of the signals C1. The signal VC10 is the logical complement of the signal Vcl1. These two signals can be derived from signal C1 using a flip-flop, scale of two. During the period of time which extends from time t0 to t2 the detected echo pulses are therefore transmitted to the register 4113 and during the following period, extending from time t2 to time t4, to shift register 4114. At the end of these two periods, the contents of these two registers are compared bit by bit with the using a comparator 4115. A comparison authorization signal VC12 is transmitted to this comparator, for example during the rising edge of the signal Vol0, that is to say at times t0 and t4 on the diagram of FIG. 24. The control signals VC10 to VC12 are conveyed by the Vcl links and developed in the control circuits 8 in FIG. 23. The signal Vol2, of frequency half that of the signal C1 can be derived from this using a rocker, scale of two.

 If the contents of the two registers 4113 and 4114 are identical after two periods of emission of ultrasonic pulses, there is no delivery of an intruder detection signal. Otherwise, one of the two registers has recorded at least one additional echo pulse due to the intrusion. In this case, there is detection of non-coincidence of the state of the two registers and transmission of a signal VA2.

The output signals of the different channels VA1 to VA3 are transmitted to an alarm triggering circuit 6. According to one aspect of the invention, this circuit only delivers an alarm triggering signal VA if there has been effective detection of an intrusion by all analysis channels. In the simplest form, this circuit 6 can be constituted by a logic "AND" gate. However in reality the signals VA1 to VA3 appearing at different times, it is necessary to store them until the end of a complete measurement period, period extending from the instant t0 to t4 on the diagram in Figure 24. Storage can be done simply using a flip-flop used as the final stage of the various measurement channels. This flip-flop is reset to zero at time t4, for example using the VCl2 control signal
To illustrate the invention more fully, typical data concerning the sensor 1 are as follows:
- number of active elements: two mounted according to the configuration in FIG. 14.

- structure: disc
- material: polyvinylidene fluoride (PVF2)
- diameter: 12 mm
- thickness: 400 µm
Under these conditions, for use in microphone, the sensitivity is approximately 1 m V Pa 1 in the audio band, this approximately up to the upper limit of approximately 12 kHz, first resonant frequency.

 As receiver and transmitter of ultrasonic pulses, one places oneself at the frequency of second resonance that is approximately 24 kHz.

 As regards the pyroelectric effect, the sensitivity of the sensor is proportional to the pyroelectric coefficient: p = 5 10 9 cm 2 K-1, for the material used in the embodiment.

The output voltage of each active element of pyroelectric origin obeys the relation
vDP = # Q = # Q = S # P
CC #S
#P #T
= # e = p # e; in which .C is the electrical capacity of the active elements of the sensor .S its surface. e its thickness
AAQ the variation of the electric charge in the active elements
P the electrical polarization of the material of the active elements AAT the temperature variation detected. e the dielectric constant of the material of the active elements, ie 10-10F. m-1 for PVF2.

 Under the conditions listed, the amplitude of the potential difference developed across the active elements is VDp = 20 mV.K 1, i.e. for a typical temperature variation detected of the order of 10-3 K due to the passage of an intruder in the field of observation, a potential difference of the order of 20 PV perfectly measurable after amplification using an electronic element with high input impedance of the differential amplifier type commonly available on the market.

 The invention is not limited to the exemplary embodiments described for the sole purpose of illustration in relation to the appended figures.

Claims (26)

 1. Alarm device on the detection-of the passage of an intruder (3) in  at least one predetermined region of the monitored space comprising a  sensor (1) detecting significant variations in physical parameters characteristic of the monitored regions caused by said passage and converting these variations into electrical signals (VD), circuits (4,5,6)  selective processing of these signals delivering an electrical signal ('VA) of  alarm control and an alarm member (7) actuated by this signal; device characterized in that the sensor (1) comprises at least one active element (12,13) detector made of polarized material having simultaneously piezoelectric and pyroelectric properties so as to be made sensitive to electromagnetic waves in the infrared range and to waves acoustic and delivering in response to the detection of these waves, at the terminals of at least one pair of electrodes, said electrical signals (VD) and in that the processing circuits comprise first circuits (5) constituting a processing channel selective sensitive to the detected signals due to the amplitude variations of electromagnetic waves in the. significant infrared range of temperature variations in said monitored region and delivering in response a first alarm signal (VA3),  second circuits (4) constituting at least one channel. selective processing of the signals delivered by the sensor during the detection of acoustic waves and delivering in response at least a second alarm signal (VAl, V2) and a detection circuit <6) of the simultaneous occurrence of alarm signals 'delivered by the two selective processing channels and delivering an alarm control signal (VA) conditioned by said simultaneous occurrence.  2. Device according to claim 1, characterized in that the element  active detector (12,13) is a plate of material having  piezoelectric and pyroelectric properties and provided with at least one pair  electrodes (E2, E10-E12) deposited on the main faces of the wafer.  3. Device according to claim 2, characterized in that the mate  riau is chosen from the following: barium titanate, niobate of  lithium, polyvinylidene fluoride polymer, poly copolymers  vinylidene fluoride with polytetrafluoride ethylene, hexatluor'opro-  pene and polytrifluoroethylene and the polyvinylidene fluoride alloy  with polymethylmethacrylate.  4. Device according to any one of claims 2 or 3, charac  terized in that each active detector element (12, 13) is associated with a  frontal optical element (2) focusing the electromagnetic waves of the infrared range towards one of the faces of the active element (12,13), The element  optic (2) being made of transparent refractive material in the range  infrared and pierced with a channel (200,210) orthogonal to the main faces  cipales and of average axis confused with an axis (A) passing through the center of the  plate so as to form a preferred direction of propagation of  acoustic waves parallel to said axis.  5. Device according to claim 4, characterized in that the element  frontal optic in the form of a blade (20) with parallel face extended by  two prism-shaped side wings, the blade being arranged in space  parallel to the main faces of the plate forming the active element  (1) and pierced from said channel (200).  6. Device according to claim 4, characterized in that the element  front optic consists of a converging lens (21) pierced by said  channel (210).  7 Device according to any one of claims 2 or 3, charac-.  all through the center (0) of the main face of the active detector element.  (A, A1- A4) of privileged propagations of the acoustic waves passing  said wall and pierced with orifices (230,240) defining radial directions  with the main face of the active detector element (12,13) opposite  range of infra-grooves in the form of cylinder sections with the same axis  refractive material transparent to electromagnetic waves in the  front optical element (2) consisting of at least one wall (23,24) in  terized in that each active detector element (12, 13) is associated with a  8. Device according to any one of claims-2 or 3, charac  terized in that each active detector element (12, 13) is associated with a  frontal optical element (2) consisting of a series of prisms (22) not  adjoining refractive material transparent to electromagnetic waves  in the infrared range distributed over an arc of a center circle  coinciding with an axis (AC) passing through the center (0) of the main face of the active detector element (1) opposite said front optical element (2) and the edges of which are arranged on a cylinder of axis of symmetry confused with said axis (AC) ;; channels (220) formed by the spaces left free between two adjacent prisms defining directions (A A A 1- a of privileged propagation of the acoustic waves.  9. Device according to any one of claims 2 or 3, characterized in that each active detector element (12,13) is associated with a reflector (25,26) focusing the electromagnetic waves in the infrared range and the acoustic waves on one of the main faces of the active detector element.  10. Device according to claim 9, characterized in that the reflector is a mirror (25) with planar facets whose edges are parallel to the main faces of the active detector element.  11. Device according to claim 9, characterized in that the reflector is a spherical mirror (26).  12. Device according to any one of claims 9 to 11, characterized in that in addition a screen (260) opaque to electromagnetic waves in the infrared range and to acoustic waves is disposed between the reflector (25,26) and the active detector element (12, 13) and in that this screen (260) is pierced with orifices (261) arranged in a configuration determined so as to define a multilobe spatial reception diagram; the number of lobes being equal to the number of orifices.  13. Device according to any one of claims 2 to 12, characterized in that the active detector element (12,13) is a composite element comprising at least two sets of electrodes (E2, E10-E12) consisting of pads metallic insulated from each other arranged on the main faces of the wafer and of configuration determined so as to define a spatial receptivity diagram associated with the element comprising at least two distinct lobes (L1, L2).  14. Device according to claim 13, characterized in that the plate constituting the active detector element (12,13) having the shape of a disc, it comprises on one of the main faces a first metal area (10) of circular configuration concentric with the disc formed by the wafer and a second metal pad (11) having the shape of a metallic ring and in that the second face is uniformly covered with a metallic pad.  15. Device according to any one of claims 2 or 3, characterized in that each active detector element (12,13) is associated with a front acoustic lens consisting of deflector fins made of material transparent to electromagnetic waves in the range below -red and focusing the acoustic waves towards the active detector element and a rear reflector (28fui28 ') constituted by a mirror reflecting the waves in the infrared range and the acoustic waves towards the active detector element (12,13) .  16. Device according to any one of claims 2 or-3, characterized in that the sensor comprises two active elements (12,13) and each active detector element is integral with an acoustic cavity (29,29 ') tuned on separate frequencies.  17. Device according to any one of claims 2 to 16, characterized in that the sensor comprises two active detector elements (12, 13) in a common thermal enclosure (100) and an amplifier (Alo, All) with impedance of input higher than the intrinsic impedance of the active detector elements, receiving the electrical signals appearing at the terminals of their electrodes and in that the polarizations of the material constituting the detector elements and the direction of connection of the electrodes are made so that the combination of the amplified signals (VD) due to the appearance by pyroelectric effect of potential differences at the terminals of the electrodes during temperature variations specific to said thermal enclosure compensate each other.  18. Device according to claim 17, characterized in that, in addition, one (13) of the active detector elements is provided with a screen (27) opaque to electromagnetic waves in the range of infrared so that only the second active element (12) detects the erectromagnetic waves in the infrared range emitted by said regions of the space to be monitored.  19. Device according to claim 17, characterized in that the two active detector elements (12, 13) are arranged so as to detect electromagnetic waves in the infrared range emitted by regions  separate space to watch.  20. Device - according to any one of claims 1 to 19, charac  terized in that the sensor comprises two active detector elements  (12,13) arranged so as to monitor two distinct regions of space,  the first and the second element "delivering signals (VDl, VD2) respecti  first and second polarization when passing a  intruder (3.3 ') in the area of the monitored space associated with them and in this  that it further comprises circuits for discriminating the order of occurrence of these polarities - so as to determine the direction of crossing of these regions by said intruder '(3,3').  thermal of the active detector element (18,13).  control circuit (8) deli. providing a binary signal (VC2) for controlling the opening and closing of said switch (51); the duration of the opening period being greater than at least twice the time constant  low-pass filter (50) whose high cut-off frequency is 20 Hz and whose output is connected via an electronically controlled switch (51) to an amplifier (52) delivering a first signal alarm (Y 3) during a determined amplitude variation of said electromagnetic waves in the infrared range and in that it comprises a  of electromagnetic waves in the infrared range include a  - selective processing sensitive to signals due to amplitude variations  21. Device according to any one of claims 1 to 20, characterized in that in addition the first circuits (5) for processing the path  22. Device according to any one of claims 1 to 20, charac  characterized in that the second circuits (4) constituting the processing channel  selective of the signals delivered by the sensor during the detection of waves  acoustics includes circuits (40) having a bandpass filter  (400) for the selection of signals located in the audio frequency range followed by an amplifier (401) delivering a second alarm signal (YA1? When the -  detection. of acoustic waves in the amplitude audio frequency range  higher than a determined threshold and circuits (41) comprising means for periodically transmitting acoustic waves during time intervals  determined at ultrasonic frequency, a tuned filter (410) on this  frequency selecting the signals delivered by the sensor resulting from the detection of echo due to the reflection of said acoustic wave at ultrasonic frequency on obstacles located in regions of the monitored space and a circuit (411) differentiating echoes cpmparant in continues the echoes received during consecutive periods of emission of said wave and delivering a third alarm signal (VA2) when the detected echoes differ from one period to the next.  23. Device according to claim 22, characterized in that the echo differentiation circuits (411) comprise first (4113) and second (4114) registers for recording the signals representing the detected echoes, means (4111,4112 ) routing these signals, alternately from one transmission period to another, to one of these registers and  means (4115) for comparing the content of these registers delivering said third alarm signal (VA2) when the latter is different from one period to another.  24. Device according to claim 22, characterized in that the  means for transmitting acoustic waves at ultrasonic frequency uses as transducer at least one active detector element (12, 13) of the sensor  and in that this element has a bimorph structure comprising a first  sheet of unpolarized material and a second sheet joined in material  polarized having pyroelectric and piezoelectric properties; the the-  is lying. active (12,13) being fixed at the periphery (123) to a chassis, and in that it comprises at least one pair of electrodes each attached to a face  main of the element and connected to a generator (G) delivering during  said emission intervals an electrical frequency excitation signal  ultrasonic.  25. Device according to claim 24, characterized in that, the ele  active detector (1) having the shape of a disk of radius R, it comprises  two sets of electrodes, the first consisting of a metal pad  central unit registered in a circle of radius less than R / V7 arranged on a  first main face of the element and a metal surface covering  the other main face in its entirety, and the second set by a metal pad  in the form of a peripheral crown with an internal radius greater than R / and  the metal area covering the other main face; and in that  the element is fixed to a frame pinching the disc at its periphery (123).  26. Device according to claim 24, characterized in that the element having the shape of a half-length rectangle equal to D, it comprises a first set of electrodes constituted by a central metallic area (E1 inscribed in a rectangle of dimension according to the length of the plate less than two D / # 3 disposed on one of the main faces of the element and a metal area (E2) completely covering the other main face; and second sets of '' electrodes formed by pads  metallic peripherals (E11, E12) at a distance from an axis dividing in two  equal parts the rectangle higher than D / get the metallic range (E2)  covering the second main face; and in that element is fixed by  pinching of two ends (123,123'j to a frame depending on the width of the  rectangle.