GB2133615A - Pyroelectric infra-red radiation detector - Google Patents
Pyroelectric infra-red radiation detector Download PDFInfo
- Publication number
- GB2133615A GB2133615A GB08235758A GB8235758A GB2133615A GB 2133615 A GB2133615 A GB 2133615A GB 08235758 A GB08235758 A GB 08235758A GB 8235758 A GB8235758 A GB 8235758A GB 2133615 A GB2133615 A GB 2133615A
- Authority
- GB
- United Kingdom
- Prior art keywords
- detector
- infra
- radiation
- red radiation
- detector element
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000005855 radiation Effects 0.000 title claims abstract description 58
- 238000010521 absorption reaction Methods 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 5
- 229910052729 chemical element Inorganic materials 0.000 claims 4
- 238000002955 isolation Methods 0.000 abstract description 4
- 239000000853 adhesive Substances 0.000 description 6
- 230000001070 adhesive effect Effects 0.000 description 6
- 239000000758 substrate Substances 0.000 description 6
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 230000000903 blocking effect Effects 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 238000012216 screening Methods 0.000 description 2
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229920006332 epoxy adhesive Polymers 0.000 description 1
- 230000005669 field effect Effects 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- 229910052451 lead zirconate titanate Inorganic materials 0.000 description 1
- HFGPZNIAWCZYJU-UHFFFAOYSA-N lead zirconate titanate Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ti+4].[Zr+4].[Pb+2] HFGPZNIAWCZYJU-UHFFFAOYSA-N 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 239000011572 manganese Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910001120 nichrome Inorganic materials 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
- G01J5/34—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using capacitors, e.g. pyroelectric capacitors
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
Abstract
An infra-red radiation detector has two pyroelectric detector elements (1,2) arranged one above the other with a space between them providing mutual thermal isolation. The upper element (1) receives the infra-red radiation (10) to be detected but blocks the radiation from impinging on the lower element (2). The two elements are electrically connected so that signals generated in the upper element (1) by ambient temperature changes tend to be cancelled out by equal and opposite signals generated in the lower element (2). <IMAGE>
Description
SPECIFICATION
Infra-red radiation detector
This invention relates to an infra-red radiation detector and, more particularly, to an infra-red radiation detector comprising a first pyroelectric detector element arranged for receiving radiation to be detected, and a second pyroelectric detector element screened by said first detector element, which second detector element is separated from the first detector element by intermediate supporting means and which is electrically connected to said first detector element so as to compensate for electrical signals generated in the first detector element by ambient temperature fluctuations.
Infra-red radiation detectors comprising pyroelectric detector elements can be used in movement sensors and as such they have applications in, for example, remote switching systems and intruder alarms. A human being provides a moving source of infra-red radiation and his presence can be detected because the radiation he emits is converted by the detector into an electric signal which can be used, for example, to switch lights on or off or to actuate an alarm.
However, because pyroelectric detectors respond to temperature changes, ambient temperature fluctuations generate undesired signals which can give rise to undesired switching and false alarms. To overcome this problem itis known to use two pyroelectric detector elements in a side-by-side arrangement.
One of the elements, referred to here as the 'sensing' element, is exposed to the radiation to be detected and the other, the 'compensating' element, is shielded therefrom, but both elements are equally susceptible to ambient temperature fluctuations. The compensating element is electrically connected to the sensing element so as to cancel out electrical signals generated in the sensing element by ambient temperature changes.
When the two detector elements are arranged side-by-side, as described above, a separate screening member is used to shield the compensating element. However, in U.K. Patent Application
GB 2,021,864A a pyroelectric infra-red radiation detector is disclosed in which the sensing element is located intermediate the radiation source and the compensating element and thus the compensating element is screened by the sensing element. The two detector elements are separated by a relatively thick substrate which may be made of, for example, a ceramics material and which supports the relatively thin detector elements on opposite major surfaces to suppress bending and thereby to minimize the undesired generation of piezoelectric signals. The radiation is blocked from impinging on the compensating element partly by the sensing element but mainly by the intermediate substrate.In contrast with an arrangement where the elements are side-by-side this detector has a symmetrical field of view and avoids the need for a separate screening member.
Unfortunately, however, the presence of the intermediate substrate which supports the detector element promotes thermal conduction from the sensing element to the substrate and this heat loss from the sensing element can seriously impair the performance ofthe detector particularly at low frequencies, typically 0.2-3.0 Hertz, involved in intruder alarm applications. Moreover, at such low frequencies heat can be conducted right through the substrate to the compensating element thereby further impairing the low frequency performance of the detector because the compensating element then provides an undesired signal which tends to cancel out the pertinent signal from the sensing element.
A further disadvantage of this known detector is that there is inevitably a mismatch between the thermal expansion properties of the pyroelectric detector elements and the intermediate substrate which presents manufacturing difficulties and can lead to reliability problems.
According to the present invention an infra-red radiation detector having the features mentioned in the opening paragraph is characterized in that the supporting means determine a space between the two detector elements, and in that the first detector element (the sensing element) blocks a major part of the radiation incident thereon from impinging on the second detector element (the compensating element).
The Applicants were surprised to find that an infrared radiation detector in accordance with the invention can have an unexpectedly high performance particularly at low frequencies. This is attributable not only to the effective radiation blocking, i.e. shielding, by the sensing detector element, but also to the space between the elements which not only substantially reduces the thermal loading on the sensing element and minimizes the transfer of thermal energy by conduction betweenthetwo elements but also avoids the problem of mismatch in thermal expansion associated with the prior art detector mentioned above.
For optimum performance the infra-red radiation should not be able to impinge on the compensating element and so it is preferable that the sensing element blocks substantially all the incident radiation.
For optimum shielding the detector elements preferably are spaced close together but not so close as to impair the thermal isolation of the compensating element.
Certain measures may be taken to optimise the shielding effect provided by the sensing element. For example the sensing element may have a larger surface area than the compensating element so that it is more difficult for radiation to reach the compensating element by passing round the edges of the sensing element. Furthermore, the sensing element may be blackened to enhance the absorption of radiation incident thereon. Also, it may be desirable to provide the compensating element with a reflective layer in order to minimize absorption of any radiation which might still reach the compensating element.
The two detector elements may be present in an envelope which is opaque to the radiation to be detected and which has a windowfortransmitting the radiation to the sensing element. The envelope may be evacuated or it may contain an inert atmosphere such as dry nitrogen which fills the space between the two detector elements without impairing the thermal isolation of the compensating element.
An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing, in which the single Figure is a partly schematic cross-section of an infra-red radiation detector in accordance with the invention.
It should be noted that, for the sake of clarity, the
Figure is not drawn to scale.
The infra-red radiation detector shown in the Figure comprises two pyroelectric detector elements each formed from a body 1,2 of pyroelectric ceramic material such as lanthanum and manganese doped lead zirconate titanate. (For more information about this material reference is invited to United Kingdom
Patent Specification G B 1,504,283). The pyroelectric body 1,2 of each element-which may be 2 mm long, 1 mm wide, and 150 micrometres thick is sandwiched between two nichrome electrodes 3a, 3b and 4a, 4b respectively which are substantially transparentto infra-red radiation of a wavelength atwhichthe detector is responsive. The detector elements are mounted one above the other so that the upper detector element 1 screens the lower detector element from the incident infra-red radiation to be detected.
The two elements are arranged with opposed polarity as represented by the arrows 6 in the Figure so that when the elements are connected electrically in series with the facing electrodes 3b and 4a connected electrically together the lower detector element 2 compensates for electrical signals generated in the upper detector element 1 by ambient temperature changes. Thus the upper detector element 1 constitutes the sensing element and the lower detector element 2 constitutes the compensating element.
The sensing element 1 is supported at opposite ends above the compensating element 2 by a respective wire 5 thus determining a space 24 between the two elements. The wires 5, which may have a diameter of 150 micrometres and run the full width of the detector elements, are secured using a conductive adhesive 25. The facing electrodes 3b, 4a of the detector elements are therefore connected electrically by the wires 5.
The upper electrode 3a of sensing element 1 is electrically connected by a wire bond 7 to the surface 8 of the base 9 of a three lead header which may for example have a conventional TO-5 outline. Two ofthe leads 11 a,1 1 b extend through the base 9 to form terminals (not shown in the Figure) which protrude above surface 8, while the third lead 1 ic is conductively connected to surface 8 and hence also to the upper electrode 3a of sensing element 1.
The two detector elements are maintained in spaced relation above the base 9 of the header by two equally tall supporting pillars 12,13. The pillar 12, which is electrically insulating, may be made of a ceramic such as high density alumina and fastened between the compensating element 2 and the surface 8 of base 9 using an insulating adhesive 1 4a, 14b. The pillar 13, which is electrically conductive, may be made of an electrically conductive material or, alternatively of an insulating material such as alumina but with a conductive coating of, for example, gold. The upper end of pillar 13 is fastened and electrically connected to the lower electrode 4b of sensing element 2 by a conductive adhesive 15a and the lower end is fastened to the surface 8 of base 9 by an insulating adhesive 15b.The conducive adhesive used here may be Ablebond 36/2 (Trade Mark) available from
Ablestick Laboratories, U.S.A., and the nonconductive adhesive may be a conventional epoxy adhesive.
As shown schematically in the Figure the lower electrode 4b of compensating element 2 is connected elelctricallyvia the pillar 13 to the gate of a field effect transistor T. Two diodes D1 and D2 in parallel opposition are connected between the gate ofthe transistor
T and the lead 11c (via surface 8) to provide a gate leakage path for the Transistor T. The source and drain ofthe transistorT are connected to the leads 11 a and 11 bvia the terminals (not shown) which protrude above the surface 8 as mentioned earlier. The circuit arrangement comprising the transistor T and diodes
D1,D2 may be contained in an encapsulating package 16 such as a plastic encapsulated microminiature package.Moreover, instead of using pillars 12,13, the terminal leads extending from such a microminiature package may be used to support the pyroelectric elements above the base 9 as described in greater detail in our British patent application GB 2,102,200 (to be published on 26th January 1983) and in copending British patent application number 8220816 (at present unpublished), to which reference is invited,
It is noted here that in an alternative arrangement the two pyroelectric detector elements may be connected electrically in parallel rather than in series as described above. In this case both elements 1,2 are arranged with the same polarity orientation. In contrast with the arrangement shown in the accompany ing drawing,therefo re. the arrows 6 would now point in the same direction.The facing electrodes 3b,4a are electrically connected by the supporting wires as before, but now the top electrode 3a of the sensing element 1 is connected electrically to the bottom electrode 4b of the compensating element 2. Either the top electrode 3a or the bottom electrode 4b is connected electrically, for example by a wire bond, to the surface 8 and so to lead 11 a ofthe header 9 and either ofthe facing electrodes 3b,4a is connected to the gate of a FET which forms part of the same circuit arrangement comprising two diodes in parallel opposition as described above.
The detector shown in the accompanying drawing also includes a conventional envelope cover member 17 secured to the rim of the base 9 in known manner.
The envelope may be evacuated or it may be filled with a gas such as dry nitrogen which is relatively inert with respect to the component parts of the detector contained within the envelope. The atmosphere in the envelope, of course, fills the space between the two detector elements without impairing the good thermal isolation therebetween.
The cover member 17 has a window 18 which is transparent to the radiation 10 to be detected and which is in line with the detector elements 1 and 2.
Thus the transmitted radiation can impinge on the sensing element 1, but is blocked by the sensing element 1 from impinging on the compensating element 2. The pyroelectric signal generated in the sensing element 1 as a result of receiving infra-:ed radiation from a source such as an intruder can be detected as an output signal from the circuit arrangement described. On the other hand signals generated by ambient temperature fluctuations tend to be cancelled out bythe generation of a substantially equal, but opposite signal in the compensating element 2.
With the infra-red radiation detector described above it may be possible for incident radiation to reach the compensating element 2 by passing round the edges of the overlying sensing element 1. To avoid this problem the sensing element 1 can have a larger surface area than the compensating element 2 and, although this may introduce a degree of mismatch between the detector elements, the disadvantage tends to be outweighed by the improved shielding of the compensating element. However, the mismatch problem can be avoided if the pyroelectric body ofthe sensing element has a largersurface area than the compensating element, but the electrodes of the sensing element have the same dimensions as the electrodes of the compensating element. Also, other measures may be taken to enhance the radiation blocking effect of the sensing element 1 without introducing mismatch. For example, the upper electrode 3a of the sensing element may be provided with a layer of, for example, a gold blackwhich enhances the absorption of the radiation incident on the sensing element 1. Moreover, in order to minimize absorption of any radiation which might still reach the compensating element 2 it may be desirable to provide a layer of reflective material which may, for example, be a relatively thick top electrode 4a, on the compensating element 2.
Of course,the particular embodiment and the mod- ifications described here are merely illustrative and it will be appreciated that various other modifications can be made within the scope of the present invention.
Claims (11)
1. An infra-red radiation detector comprising a first pyroelectric detector element arranged for receiving radiation to be detected, and a second pyroelectric detector element screened by said first detector element, which second detector element is separated from the first detector element by intermediate supporting means and which is electrically connected to said first detector element so as to compensate for electrical signals generated in the first dectector element by ambient temperature fluctuations, characterized in that the supporting means determine a space between the two detector elements, and in that the first detector element blocks a major part ofthe radiation incident thereon from impinging on the second detector element.
2. An infra-red radiation detector as claimed in
Claim 1, characterized in that the first detector element blocks substantially all the radition to be detected from impinging on the second detector element.
3. An infra-red radiation detector as claimed in any ofthe preceding Claims, characterized in that the thickness of each detector element and the distance separating the two detector elements is between approximately 150 and 200 micrometres.
4. An infra-red radiation detector as claimed in any of the preceding Claims, characterized in that the space between the two detector elements is filled with an inert atmosphere.
5. An infra-red radiation detector as claimed in any of the preceding Claims, characterized in that the first detector element comprises a layer of material which enhances the absorption of the radiation incident thereon.
6. An infra-red radiation detector as claimed in any of the preceding Claims, characterized in that the second detector element comprises a layer of material which reflects the radiation to be detected.
7. An infra-red radiation detector as claimed in any of the preceding Claims, characterized in that the first detector element comprises a pyroelectric body which is larger in surface area than the second detector element.
8. An infra-red radiation detector as claimed in any of the preceding Claims, characterized in that the first and second detector elements comprise electrodes having substantially the same surface area.
9. An infra-red radiation detector as claimed in any of the preceding Claims, characterized in that the detector elements are present in an envelope which is opaque to the radiation to be detected, the envelope having a window fortransmitting said radiation to be detected to the first detector element.
10. An infra-red radiation detector as claimed in any of the preceding Claims, characterized in that the detector elements have facing electrodes which are electrically connected by the supporting means.
11. An infra-red radiation detector substantially as herein described with reference to the accompany- ing drawing.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08235758A GB2133615B (en) | 1982-12-15 | 1982-12-15 | Pyroelectric infra-red radiation detector |
| DE19838335469U DE8335469U1 (en) | 1982-12-15 | 1983-12-10 | INFRARED RADIATION DETECTOR |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08235758A GB2133615B (en) | 1982-12-15 | 1982-12-15 | Pyroelectric infra-red radiation detector |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2133615A true GB2133615A (en) | 1984-07-25 |
| GB2133615B GB2133615B (en) | 1986-03-19 |
Family
ID=10535004
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08235758A Expired GB2133615B (en) | 1982-12-15 | 1982-12-15 | Pyroelectric infra-red radiation detector |
Country Status (2)
| Country | Link |
|---|---|
| DE (1) | DE8335469U1 (en) |
| GB (1) | GB2133615B (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0172594A2 (en) * | 1984-08-24 | 1986-02-26 | Koninklijke Philips Electronics N.V. | Infra-red radiation detector |
| EP0175418A2 (en) * | 1984-09-19 | 1986-03-26 | Philips Electronics Uk Limited | Infra-red radiation detector |
| GB2278016A (en) * | 1993-05-12 | 1994-11-16 | Optex Co Ltd | Pyroelectric infared detector |
| EP0775895A1 (en) * | 1995-11-27 | 1997-05-28 | Everspring Industry Co. Ltd. | Thermal-isolation frequency transferable pyroelectric infrared radiation detector and manufacturing process thereof |
| EP0913675A1 (en) * | 1997-10-28 | 1999-05-06 | Matsushita Electric Works, Ltd. | Infrared sensor |
| DE102007062688B3 (en) * | 2007-12-17 | 2009-02-05 | Pyreos Ltd. | Device with a shielded sandwich structure for the detection of heat radiation and use of the device |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1464555A (en) * | 1974-01-22 | 1977-02-16 | Marconi Co Ltd | Pyro-electric detector arrangements |
| GB1542877A (en) * | 1975-02-18 | 1979-03-28 | Minnesota Mining & Mfg | Electret sensing medium having plural sensing units |
| GB2021864A (en) * | 1978-05-30 | 1979-12-05 | Kureha Chemical Ind Co Ltd | Pyroelectric infrared detector |
-
1982
- 1982-12-15 GB GB08235758A patent/GB2133615B/en not_active Expired
-
1983
- 1983-12-10 DE DE19838335469U patent/DE8335469U1/en not_active Expired
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1464555A (en) * | 1974-01-22 | 1977-02-16 | Marconi Co Ltd | Pyro-electric detector arrangements |
| GB1542877A (en) * | 1975-02-18 | 1979-03-28 | Minnesota Mining & Mfg | Electret sensing medium having plural sensing units |
| GB2021864A (en) * | 1978-05-30 | 1979-12-05 | Kureha Chemical Ind Co Ltd | Pyroelectric infrared detector |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0172594A2 (en) * | 1984-08-24 | 1986-02-26 | Koninklijke Philips Electronics N.V. | Infra-red radiation detector |
| EP0172594A3 (en) * | 1984-08-24 | 1986-07-23 | Philips Electronic And Associated Industries Limited | Infra-red radiation detector |
| EP0175418A2 (en) * | 1984-09-19 | 1986-03-26 | Philips Electronics Uk Limited | Infra-red radiation detector |
| EP0175418A3 (en) * | 1984-09-19 | 1987-05-13 | Philips Electronic And Associated Industries Limited | Infra-red radiation detector |
| US4803360A (en) * | 1984-09-19 | 1989-02-07 | U.S. Philips Corp. | Infrared radiation detector with flanged semiconductor window |
| GB2278016A (en) * | 1993-05-12 | 1994-11-16 | Optex Co Ltd | Pyroelectric infared detector |
| US5468960A (en) * | 1993-05-12 | 1995-11-21 | Optex Co., Ltd. | Pyroelectric infrared detector |
| GB2278016B (en) * | 1993-05-12 | 1997-06-25 | Optex Co Ltd | Pyroelectric infrared detector |
| EP0775895A1 (en) * | 1995-11-27 | 1997-05-28 | Everspring Industry Co. Ltd. | Thermal-isolation frequency transferable pyroelectric infrared radiation detector and manufacturing process thereof |
| EP0913675A1 (en) * | 1997-10-28 | 1999-05-06 | Matsushita Electric Works, Ltd. | Infrared sensor |
| DE102007062688B3 (en) * | 2007-12-17 | 2009-02-05 | Pyreos Ltd. | Device with a shielded sandwich structure for the detection of heat radiation and use of the device |
| US8575550B2 (en) | 2007-12-17 | 2013-11-05 | Pyreos Ltd. | Apparatus having a screened structure for detecting thermal radiation |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2133615B (en) | 1986-03-19 |
| DE8335469U1 (en) | 1984-07-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |