FR2512591A1 - RADIATION DETECTOR, IN PARTICULAR INFRARED RADIATION - Google Patents

Abstract

THE INVENTION RELATES TO RADIATION DETECTORS. THE DETECTOR ACCORDING TO THE INVENTION INCLUDES A BOX 10 WITH A WINDOW 16 TRANSPARENT TO THE RADIATION TO BE DETECTED. TWO DETECTORS 12, 14 CONNECTED IN OPPOSITION ARE MOUNTED IN BOX 10. A BLOCK COVER 18 ON WINDOW 16 PREVENTS RADIATION TRANSMISSION TO ONE DETECTOR 12 BUT NOT TO THE OTHER, IN ORDER TO AVOID THE EFFECTS OF VARIATIONS D 'EXTERNAL ENVIRONMENT. THE DETECTOR IS PARTICULARLY SUITABLE FOR DETECTING INFRARED RADIATION.

Description

The present invention relates to detections

  radiation, for example detectors for

  to detect infrared radiation.

  Infrared radiation detectors are already known, in the form of pyroelectric elements,

  for example in pyroelectric ceramic material, in particular

  Pyroelectric plastic material or crystalline material, for example lithium tantalate, or in the form of thermocouples or thermistors, reacting

  infrared radiation by producing an electrical signal

  output, for example an electrical voltage.

  These detectors can be used for different purposes; for example, they can be used to detect intrusion, by detecting infrared radiation or a change in infrared radiation resulting from an intrusion A problem posed by these infrared detectors is that they

  are sensitive to variations in environmental parameters.

  such as ambient temperature, pressure, humidity,

  and others and that these variations in

  may be such that the device produces a spurious output signal or a spurious change

the output signal.

  It is known to arrange these elements in such a way that they operate in pairs, electrically connected in opposition so that the variations of environmental parameters also affect the two elements of the environment.

  so that the output signals and signal variations

  The resulting output levels cancel each other out

  remain able to detect the infra-

  red (resulting for example from an intruder) because the

  tion is such that this radiation does not fall simultaneously

  on both elements, but first on one and

  on the other hand, there is a disadvantage

  is that it has been shown to have a

  weakly to the infrared radiation to be detected, particularly because of the geometric layout of the detectors. For example, if an intruder is

  the "field" of the two detectors at the same time, the

  The output levels of these detectors cancel each other

  and his presence is not detected.

  The invention thus relates to a radiation detection device comprising two sensing elements

  radiation each producing an electrical signal

  output pole of a predetermined polarity in response

  upon reception of the radiation to be detected, the two elements

  radiation-sensitive elements being connected electrically

  in opposition; this device is characterized in that the radiation-sensitive elements are mounted so that one of them can freely receive the radiation to be detected while the other can not receive this radiation while the two can freely react to variations of other external parameters

  environment, the electrical connection of the sen-

  the radiation being such that it produces a sign

  electrical output in response to the receipt of

  radiation to be detected but without producing an electrical

  sensitive output under the effect of variations in

environment settings.

  The invention also relates to a device

  infrared-sensitive, consisting of two pyrotechnic elements

  electric infrared sensitive electric connected-

  in opposition, a window of transmitting material

  infrared radiation on both elements; this provision

  It is characterized in that it further comprises a blocking device which is substantially opaque to infrared radiation, placed on the window in such a way as to block the transmission of the infrared radiation towards one of the elements but not towards the other, so as to when the other element receives infrared radiation through the window, the assembly produces an electrical signal of

  resulting output, although the variations of the other para-

  meters of outdoor environment affect together the

  elements so that they produce electrical signals

  exit issues that are opposed and tend to cancel each other out.

12591

  Other features and advantages of the invention will be better understood when reading the

  following description of an exemplary embodiment

  and with reference to the attached drawing on L. La Figure unique represents an example of

  the use of a device according to the invention.

  The device 8 comprises a box 10 which

  holds two elements 12 and 14 of substantially identical infrared detection Each element 12, 14 may have

  1 an area of about 2 x 1 mm and these elements are separated

  res, for example, of one; distance of one millimeter In the present example, each element consists of a pyroelectric ceramic material with two electrodes connected to it. Each element reacts to the variations of

  infrared radiation by producing an electrical voltage

  of a predetermined polarity, when the variation

  radiation is complete, the output voltage de-

believe to zero.

  Above elements 12 and 14 is a

  "window" 16, for example made of germanium or silicon

  cium, made opaque to visible light but transparent to infrared radiation Miais part of the window

  16 above the detector 12 is rendered opaque to the radiation

  infra-red by a cover or coating 18

  propriety, for example a band which is placed in good

thermal tact with the window.

  Each element 12, 14 can be considered as a voltage source and the two elements 12 and 14 are electrically connected in opposition (by connections not shown) so that the output voltages they produce in response to infrared radiation are in opposition The device has terminals

output 20, 22.

  In operation, the device 8 is posi-

  in such a way that the window 16 is turned towards the

  region in which there may be an infra-red radiation

  red to detect This infrared radiation passes through the unblocked portion of the window 16 to fall on

  the element 14 The cover 18 prevents this radiation

  As a result, element 14 produces an electrical output signal in response to any variation in received radiation and since element 12 does not produce an output signal.

  corresponding in the opposite direction, the result is

  signal output between terminals 20, 22.

  Any variation of environment parameters

  such as ambient temperature, pressure, hhmi-

  and others which are of a type to change the output of the elements 12, 14 also does not affect these two elements It is so because the blockage produced by the band 18 only prevents the transmission of infrared radiation to the element 12 but not the transmission to the latter of the effects of the environmental parameters which could otherwise pass through the window 16 Therefore, the variations of the environmental parameters which affect the output of the elements 12 and 14 result in the production by these elements of the environment. electrical signals of same value but of opposite polarity and the total signal

  output between terminals 20 and 22 is not changed.

  As a result, the device represented on

  Figure 1 has a high sensitivity to infra-

  red to be detected but low susceptibility to

  changes in environmental parameters.

  If only one element was used, the variations of the environmental parameters would not be corrected and would appear immediately at the exit.

  arrangements in which two detectors are

  electrically connected in opposition, arranged to receive the infrared radiation to be detected, have a low sensitivity It is so because, although these devices

  are arranged to operate in such a way that

  only one of the two detectors at a time (first a detector, then the other) normally when the infrared radiation source passes in front of the device, it is inevitable that in practice a

  part of the radiation falling on one of the detec-

  do not fall on the other; and since the

  two elements are connected electrically oppo-

  sition, it appears a reduction of the floor signal

Release.

  It has been found that the benefits achieved by the illustrated provision are not achieved if

  element 12 is closed by interposed locking

  be him and the window 1 U, or by blocking his

  surface A blocking positioned in this way re-

  the effect on this detector of the variations of

  Thus, the assembly becomes sensitive to environmental variations. The blocking must therefore be positioned in such a way that it does not have any effect on the other side of the casing 10. not significantly affect the

  transmission to the element of variations of environ-

  occurring outside and in the vicinity of

  go of the stacker 10 This block can be applied on the

  lower surface of the window 16.

  The device described above comprises detector elements 12 and 14 in the form of pyroelectric ceramics, but it is not necessary that they be of this form. They may be of any other suitable form producing an electrical signal of

  output in response to the radiation to be detected, for example

  ple, they may be pyroelectric plastic films or crystalline form, for example lithium tantalate They may also consist of thermocouples or thermistors They can be electrically connected in opposition by any

  For example, they can be connected to

  opposite inputs of an amplifier or the output of

  of one can be reversed and added to the output

of the other.

  The shutter of the detector 12 may be made in other ways. For example, the window 16 itself may be modified. This window may for example be positioned only above the element 14 to the extent that the material that covers the element 12

  is likely to transmit to him the variations of

  environment-wise, in much the same way as they are transmitted to the detector 14, but

  to transmit to the detector 12 the radiation to be detected.

  b. Of course, various modifications can be made by those skilled in the art to the device described and illustrated by way of non-limiting example without

depart from the scope of the invention.

Claims (8)

  1 Compound radiation detection device   taking two elements sensitive to the radiation produced by   each with an electrical output signal from a polari-   predetermined in response to the reception of the radiation to be detected, the two radiation-sensitive elements being electrically connected in opposition,   characterized in that the radiation sensitive elements   2 (14) are mounted so that one of them (14) can freely receive the radiation to be detected while the other (12) can not receive the radiation.   but both (12, 14) can freely react to   other external environment parameters,   the electrical connection of the radiation-sensitive elements   being such that it produces an electrical signal of   output in response to the reception of the radiation to be detected.   but without producing an electrical output signal   in response to variations in said parameters of ronment.   2 Device according to claim 1, characterized   in that each of said   radiation (12, 14) is a radiation detection element infrared.   3 Device according to claim 2, characterized   in that each element (12, 14) is made of a   pyroelectric ceramic material.   4 Device according to claim 2, characterized   each element (12, 14) is made of lithium tantalate.   Device according to claim 2, characterized in that each element (12, 14) is made of a   film of pyroelectric plastic material.   6 Device according to any one of the   1 to 5, characterized in that L comprises a cover (16) capable of transmitting radiation at 3, detecting, the two radiation-sensitive elements (12a, 14) being mounted on a side of the lid (16) and R a blocking device (18) closing said cover (16) on one of said surfaces, above one (12) of the radiation-sensitive elements but not above the other (14) of whereby said first radiation-sensitive element (12) is rendered incapable of receive radiation.   7 Infrared Sensitive Device, Compatibility   taking two pyroelectric elements sensitive to   infrared which are connected electrically in oppo-   sition, a window of material transmitting radiation   infrared device above the two elements, characterized in that it further comprises a blocking device (18) substantially impermeable to infrared radiation placed on the window (16) so as to block   the transmission of infrared radiation to one of the   said elements (12) but not towards each other (14), thereby   that the reception of infrared radiation through the window (16) by said other element (14) leads to   the production by the device (8) of an electrical signal   the resultant output but that variations in other external environment parameters affecting the two elements (12, 14) result in the production of the resulting output electrical signals which oppose each other and tend to cancel each other out.   8. Device according to claim 7,   in that the material transmitting the radiation infrared is germanium.   Apparatus according to claim 7, characterized   characterized in that the radiation-transmitting material Infrared is silicon.