EP2265913A1

EP2265913A1 - Sensor arrangement

Info

Publication number: EP2265913A1
Application number: EP09729347A
Authority: EP
Inventors: Herbert Bousack; Andreas Offenhäusser; Helmut Schmitz
Original assignee: Forschungszentrum Juelich GmbH; Rheinische Friedrich Wilhelms Universitaet Bonn
Current assignee: Forschungszentrum Juelich GmbH; Rheinische Friedrich Wilhelms Universitaet Bonn
Priority date: 2008-04-10
Filing date: 2009-03-19
Publication date: 2010-12-29
Also published as: DE102008018504A1; WO2009124644A1

Abstract

The invention relates to a sensor arrangement for detecting electromagnetic radiation, the wavelengths thereof being in or close to the infrared range. Said system comprises at least one measuring chamber (2) that can be filled with a fluid that selectively absorbs the radiation that is to be measured. Said measuring chamber (2) comprises an inlet for the radiation, said inlet being closed by a window (3) and one part of the measuring chamber wall is made as a flexible membrane (M) such that it deforms when the volume of the fluid contained in measurement chamber (2) changes, said change being based on the absorption of the ingoing radiation. A measuring device is associated with the membrane (M) in order to detect the deformation. Said sensor system is characterised in that one pressure relief chamber (7) that is fluidically connected to the measurement chamber (2) is embodied at least on the side of the membrane (M) opposite the measurement chamber (2).

Description

DESCRIPTION

sensor arrangement

The present invention relates to an infrared sensor arrangement for detecting electromagnetic radiation whose wavelength is in or near the infrared range, comprising at least one measuring chamber which can be filled with a fluid selectively absorbing the radiation to be measured, the measuring chamber having an inlet opening closed by a window for the radiation and a part of the measuring chamber wall is designed as a flexible membrane such that it is deformed in a volume change of the fluid contained in the measuring chamber due to the absorption of the incoming radiation, and wherein the membrane is associated with a measuring device to detect the deformation.

The larvae of the black pine beetle of the genus Melanophila acuminata, of which there are about a dozen species worldwide, can only develop in the wood of fresh burnt trees. The parent generation is therefore dependent on locating forest fires as quickly as possible to lay their eggs under the bark of freshly burned trees. To locate the forest fires, the beetle has two right and left on each side of the body arranged pit organs in which are densely packed about 70 infrared (IR) Sensillien very sensitive IR radiation in the wavelength range between 2 and 4 microns can detect. As part of the development of bionic infrared sensors, efforts are being made to develop prototypes that make use of the beetle's photomechanical operating principle for the detection of IR radiation.

The basis for such biological IR sensors form so-called Golay sensors whose function has been known for a long time. These sensors have a measuring chamber (cell), which is filled with a particular gaseous fluid which absorbs IR radiation. The front of the gas-filled cell forms a closed IR radiation inlet opening and the back side of the cell is closed by a flexible membrane. In operation, the IR radiation entering the cell is absorbed by the gas present there and heated thereby, so that the gas expands and the membrane is arched. The curvature is then detected optically or alternatively capacitively or with a tunnel contact and evaluated.

Previously known microstructured Golay sensors, which operate on a capacitive basis, are continuously manufactured on the basis of a silicon wafer, in which the measuring chamber is produced as a cavity by etching methods such as an anisotropic, wet-chemical etching with KOH and the bottom of the cell, for example by gold coating forms a plate of the capacitor. The other plate of the capacitor is replaced by a formed with aluminum coated or correspondingly structured glass substrate, which is connected to the silicon wafer by anodic bonding. A further bonding process then closes the measuring chamber in the silicon wafer through a window with the lowest possible IR absorption.

Essential for the good functioning of the Golay sensors is that the temperature in the measuring chamber increases as much as possible due to the incoming IR radiation. In this respect, the measuring sensitivity of the Golay sensors depends directly on the absorption coefficient of cell filling. The greater this absorption coefficient, the more actively the incident IR radiation is converted into an increase in temperature of the cell filling and thus to an increase in pressure and an associated change in the capacitance of the capacitor. With a cell depth of 0.5 mm and a gas filling only a few percent of the IR radiation is absorbed. For this reason, various measures are taken in the prior art to improve the absorption. On the one hand, it is known to integrate an IR-absorbing foil made of metal or plastic into the cell, which then passes on the absorbed energy by conduction of heat to the gas. Similarly, the cell walls are provided with IR radiation absorbing layers. Alternatively, highly reflective cell walls are used, which cause a multiple IR reflection and thus an improved absorption in the gas. These measures However, in microstructured IR sensors are very expensive, which is why looking for alternatives.

Furthermore, efforts are being made to increase the sensitivity of the uncooled IR sensors. This is essentially influenced by the temperature noise and the photon noise, which can only be reduced by cooling the sensor. In addition, there is the noise of the readout method, which in the case of a capacitive evaluation can be of the same order of magnitude as the temperature noise. Countermeasures are not known in the prior art.

Finally, a problem with the Golay sensors is that, in contrast to semiconductor sensors, they are sensitive to changes in ambient temperature and therefore have to be operated at a constant temperature. Specifically, the temperature increase in the measuring chamber is a few mK to about 100 mK and is thus always significantly lower than the temperature changes of the environment. The suppression of disturbances from the ambient temperature change is achieved in the prior art by artificial leaks from the measuring chamber into the environment. In this case, the leak opening is dimensioned so that its time constant is substantially greater than the time constant during the heating of the cell, for example a few minutes compared to a few milliseconds, and thus the mass flow flowing out through the leak during the heating process is negligible. The object of the invention is therefore to develop a sensor arrangement of the type mentioned in such a way that they have a high sensitivity and are suitable for microstructured arrangements.

This object is achieved in that at least on the opposite side of the measuring chamber of the membrane, a pressure relief chamber is formed, which is in fluid communication with the measuring chamber. By this measure, a pressure equalization between the pressure relief chamber and the measuring chamber is made and thus ensures that slow pressure changes in the measuring chamber, for example due to changes in ambient temperature does not lead to deformation of the membrane. However, it must be ensured that rapid temperature changes due to the absorption of IR radiation nevertheless lead to a pressure build-up in the measuring chamber and thus to a measurable deformation of the membrane.

When the measuring chamber is filled with a gaseous fluid, the measuring chamber with the pressure relief chamber can be realized through perforation openings in the plate of the capacitor and the membrane adjacent to the membrane. However, the geometry of the perforation, ie the number of holes and the hole diameter, must ensure that the time constant τ _gas or ^τ _{water of} the pressure compensation is much greater than the time constant. constant τ _cell of pressure build-up in the cell due to IR radiation.

The time constant for pressure equalization in the case of gas filling results from negligible density changes (Δp / p = 0) from the equation

and for a water filling, where now also the dielectric in the condenser is water, from the equation

w ^asd 77 vT

with η: viscosity of the fluid, L _L : length of a perforation hole, here equal thickness of the capacitor plate, V _z : cell volume, V _R : unloading volume, ß: compressibility coefficient water, N _L : number of perforation holes, R _L : radius of the perforation holes, P ₀ : gas pressure in the cell. The time constant for the heating of a circular cell by an IR radiation can be approximately determined for a very good heat conducting material such as silicon

2

** λ 2.404δ ²

with p: density fluid, c _p : heat capacity fluid, λ: thermal conductivity fluid, R ₂ : cell radius.

For a cell filled with xenon with a diameter of 0.75 mm results in a time constant of τ _cell = 3.6 ms. The time constant of the pressure compensation τ _gas should be about 100 times greater than τ _cell , so that the measurement of the IR signal is not distorted by a noticeable loss of gas until reaching the stationary temperature in the cell.

With a perforation of 25 holes with a diameter D _L of 0.6 microns (thickness of the condenser plate L _L = 1.5 microns) only to the volume V _R between the capacitor plates results only a time constant τ _Gas = 1.9 ms, ie the Pressure equalization takes place immediately during heating and there is no more measuring effect. An increase in the time constant through fewer holes is impractical, otherwise the Effect of reducing the condenser noise is lost. A reduction in the diameter of the perforation holes is also problematic, since an aspect ratio L _L / D _L = 2.5 is already achieved and the production of holes with larger aspect ratios becomes increasingly difficult. The only realistic measure remains only the increase in the volume V _R. At V _R = V ₂ , a τ _gas = 480 ms results, with a maximum τ _gas = 950 ms being achievable in this example with V _R >> V ₂ . In this way, the requirement τ _gas >> τ _cell can be achieved. The reduction of the condenser noise for this perforation improves the specific detectivity D * by about 45% compared to the capacitor without perforation. The most effective way to improve this result is to produce perforation holes with a larger aspect ratio.

The diagram according to FIG. 13 shows the influence of the perforation of a capacitor plate on the noise in the case of a gas-filled cell. From this diagram, it is clear that by a suitable choice of the number of perforation holes and the hole diameter, the noise of a capacitor can be significantly reduced.

If the measuring chamber is filled with a liquid fluid such as water, the design is more problematic because the same cell geometry, the time constant for water filling is significantly greater compared to the gas filling, which is why to reduce the time constant ^τ _ze ii _e the cell radius should be reduced. For a cell diameter of, for example, 0.5 mm, a time constant of τ _cell = 74 ms results. Even with only one perforation hole with the geometry as above and V _R >> V ₂ results in τ _water = 21 ms, ie for a water filling there is no solution because of τ _cell > τ _water .

In order to achieve a pressure relief for slow pressure changes in the case of a water filling, the channel length must be increased significantly. For this purpose, it is provided that the pressure relief chamber is connected to the measuring chamber in the case of using a liquid fluid through a channel which surrounds the pressure chamber and opens at its one end into the pressure chamber and at its other end into the pressure relief chamber. In this embodiment, the pressure relief chamber and the measuring chamber are thus not connected by perforation in the capacitor plate, but by a discharge channel, which is guided around the measuring chamber. Due to this extended channel length, acceptable time constants ^{τ of} _water can be achieved. With a channel diameter of 2 μm, for example, even with a channel length of 4 mm, an acceptable time constant τ _water of 460 ms results. The measuring device can work capacitively, optically or piezoelectrically in the usual way. In the case of a capacitive measuring device, the pressure relief chamber is formed at least in the region between the capacitor plates. These can be used as coatings on the side facing away from the measuring chamber side of the membrane and be formed, for example, a base plate. The channel may be formed, for example, spiral or meandering.

In a further development of the invention it is provided that the pressure relief chamber has a pressure relief opening to the environment, which is covered by a flexible film in the case of using a liquid fluid. This can additionally take place a pressure equalization to the environment.

If a plurality of measuring chambers are provided, according to one embodiment of the invention, the pressure relief chamber for each measuring chamber is a closed volume. Thus, the sensor arrangements are independent of each other and can be evaluated separately from each other.

In a manner known per se, the at least one measuring chamber may be formed by a cavity introduced into a substrate, in particular into a silicon wafer, which is covered on one side by a window plate on the active side having the inlet opening. In this case, the membrane can form the bottom of the recess.

If a plurality of measuring chambers are formed in the substrate, it is provided according to a preferred embodiment of the invention that in the wall regions between the measuring chambers additionally isolation recesses are provided. This design, which incidentally also is dependent on a fluid connection between the measuring chamber and a pressure relief chamber can be realized, is based on the consideration that the improvement of the thermal insulation of the cell in a silicon wafer can be achieved by an exemption of the cell walls.

Due to the improved isolation of the cells, the average temperature level increases with an IR absorption compared to a less isolated cell. The higher temperature causes a higher pressure in the cell and thus a higher capacity change.

The influence of the cell geometry and the material values on the average temperature level in the cell can be described under the assumption of a negligible heat conduction in the axial direction for the stationary state by the equation

where T ₀ : ambient temperature, q ''': absorbed IR

Radiation per unit volume, X ₁ , X ₁ : thermal conductivity of the gas in the cell and wall material; α: Thermal coefficient on the outside wall. The temperatures can be seen from Figure 14, which shows a diagram representing the temperature profile in an isolated cell.

Without insulation by exemption of the turn, the following average temperature level for X ₁ << X ₂ results, as in a silicon wafer

The temperature profile is shown in FIG.

Finally, see Figure 16. This graph shows a comparison of a radial temperature profile and the transmitted temperature profile in the cell between a cell with insulating gap (top) and a cell without insulating gap for the stationary state (bottom), wherein the cell is provided with a carbon dioxide absorbing gas as IR radiation , Edge data can be mentioned:

R ₁ = 0.5mm, R ₂ = 2mm; X ₁ (CO ₂ ) = 0.0164 W / mK, X ₂

(Silicon) = 148 W / mK, α = 40 W / m ² K, q '''= 20 KW / m ³ corresponding to IR power density of 10 W / m ² and a cell depth of 0.5 mm with complete absorption.

In the production of the measuring chambers or cell volumes with a Bosch process or other Äzprozessen can For example, at the same time radial annular gaps are made around the cell, so that freestanding cell walls arise. As an alternative to the annular gap, all the material between the walls can also be removed. For ease of preparation in silicon by Äzprozesse the width of the annular gap should correspond approximately to the annular gap depth. With the total clearance of the cell walls, the minimum distance of the cell walls can be reduced because of the improved removal of the reaction products.

The thickness of the cell walls should be as small as possible in order to reduce the heat flow to the remaining silicon floor. The minimum cell wall thickness results from the stability of the cell walls and the area needed to bond the IR-transmissive window.

The high thermal conductivity of silicon with 148 W / mK leads to a low insulating effect of the wall itself. By a material with poor thermal conductivity, the wall can contribute to the isolation in addition to the insulating effect of the gap itself. Accordingly, the measuring chamber may be formed of tubes of a heat-insulating material such as glass (Pyrex) having a thermal conductivity of 1.13 W / mK and polymethyl acrylate (PMMA) having a thermal conductivity of 0.19 W / mK applied to a silicon wafer , in which the membranes are formed, are fixed for example by bonding or gluing. In this case, the IR radiation permeable windows are also glued to the tubes.

Also in this case, the tubes may be spaced apart from one another to form isolation spaces that may be filled with a heat insulating material such as an adhesive to enhance stability.

Figure 17 shows a comparison of the radial temperature profile in the averaged temperature profile in an insulating gap cell for the various wall materials when the cells are filled with carbon dioxide, and Figure 18 shows the comparison when the cells are filled with water. The diagrams show, for example, the improved insulating effect of the wall for the materials glass and polymethyl acrylate.

The tubes may also be formed circular and arranged in line contact with each other. In this case, they form a tube bundle which has a high stability. If its spaces are also filled with an adhesive, the glass bundle can be glued at the same time in this casting process. The arrangement of the tubes as a contacting bundle has the advantage that the tubes can be handled together and adhered to the carrier substrate, ie the silicon wafer, the bundle being positioned in only two places. needs to be tioned to get an accurate alignment.

In all the above-described embodiments, the isolation spaces may also be filled with an IR radiation absorbing material. As this heats up when IR radiation impinges, it is essentially prevented that heat can be dissipated from the cells in an undesired manner.

According to a further measure of the present invention, which may be provided independently of the claimed connection of the pressure relief chamber and the measuring chamber and the claimed isolation of the measuring chambers by corresponding isolation recesses between the measuring chambers and / or the formation of the measuring chambers in tubes made of a heat-insulating material consists It is also to introduce at least one infrared radiation absorbing material in the at least one measuring chamber.

The invention is therefore based on the idea to increase the absorption coefficient of the cell for infrared radiation by the additional IR-absorbing material with the result that a higher level of IR radiation is absorbed and thus takes place a strong increase in temperature. Suitable materials include plastics such as polymers that have very high absorption coefficients. If one of one Starting wavelength of 3 microns of IR radiation, resulting absorption coefficients of various polymers between 20 and 240 1 / cm. For absorption of 99% of the IR radiation of this wavelength, the thickness of the polymer would have to be about 0.2 to 2 mm.

In order to achieve a large surface area, the polymers may be introduced into the cell as individual particles or, in particular, as spongy structures. According to a preferred embodiment, it is provided that thin polymer threads or polymer fibers are provided, which may for example have a length of 10 to 15 microns. These polymer strands can be loosely wound into cylindrical or spherical absorbent bodies which, when cut to the appropriate length, can be automatically inserted into the cells. By varying the polymer material, the thread diameter and the winding density, it is possible to produce absorbent bodies which are adapted with regard to absorption and heat capacity. Often referred to as angel hair polymer threads arise as an undesirable by-product in granule production and therefore need not be prepared separately.

Alternatively, it is possible to apply thin polymer threads or polymer fibers on a polymer film. If the production of the film and the fibers in the required dimensions is possible, Wrap this film also be made cylindrical absorbent body.

Alternatively or additionally, absorption bodies may be provided in the form of hollow bodies with a shell of plastic, wherein the cavity of the absorption body is filled with gas. This embodiment is based on the idea to create a polymer body which acts as an absorbent body and at the same time still takes over the compensation of slow temperature or pressure changes.

Thermoplastics such as polyethylene show above the glass transition temperature (transition from the brittle to the elastic region) a viscoelastic behavior in which the reversible deformation behavior is represented by a time-dependent and a time-independent component. This behavior is described in the rheology by the Kelvin-Voigt model, in which a spring element and a viscous damping element are connected in parallel. In a sudden load, the spring element can not be compressed, so that damping element initially shows no deformation. With increasing time, however, the damping element is deformed and the spring tensioned, so that a stationary deformation state is achieved. After relieving the spring is relaxed, again the attenuator delays the deformation time-dependent. After a sufficient time, the initial state is reached again. This gives you a model with a rever- sensitive, time-dependent deformation. With the right choice of parameters, the element does not deform during a momentary impact load, but can compensate for slow loads reversibly.

An example ball-shaped structure in which the shell is made of eg polyethylene and the cavity is filled with gas, would be an example of a Kelvin-Voigt model, since the shell is the attenuator and the gas space is the spring. The requirement that the operating temperature must be above the glass transition temperature of the polyethylene sheath can be adjusted by selecting the chlorine content in the polyethylene in a sufficiently large temperature range, for example, a glass transition temperature of less than ^{0 0} C can be achieved. Possible embodiments would be, for example, gas-filled polymer microspheres (diameter about 10-100 μm) or a body made of polymer foam. The choice of damping properties could be adjusted to the application by the polymer material, the wall thickness of the sheaths and other geometric features.

With regard to further advantageous embodiments of the invention, reference is made to the dependent claims and the following description of exemplary embodiments with reference to the present drawings. In the drawing shows

Figure 1 in longitudinal section through an embodiment of a sensor arrangement for the detection of electromagnetic Radiation according to the present invention for the use of a liquid absorption fluid,

FIG. 2 shows the sensor arrangement in section A-A from FIG. 1,

3 shows a further embodiment of a sensor arrangement according to the invention for use with a gaseous absorption fluid in longitudinal section, FIG.

FIG. 4 shows the sensor arrangement in section A-A from FIG. 3,

5 shows a longitudinal section of a second embodiment of a sensor arrangement for the use of a gaseous absorption fluid,

FIG. 6 shows the sensor arrangement in section A-A from FIG. 5,

7 shows a third embodiment of a sensor arrangement according to the invention for use with a gaseous absorption fluid in longitudinal section, FIG.

8 shows a sensor arrangement for the detection of electromagnetic radiation with measuring chambers or cells isolated from each other in longitudinal section, FIG.

9 shows the sensor arrangement in section AA from FIG. 8, FIG. 10 shows a second embodiment of a sensor arrangement with spaced-apart measuring chambers in longitudinal section,

11 shows the sensor arrangement from FIG. 10 with filled gaps, FIG.

FIG. 12 shows a tube bundle for use in a sensor arrangement according to the present invention,

FIG. 13 is a graph showing the influence of the perforation of a capacitor plate on the noise of a gas-filled cell.

FIG. 14 is a diagram showing the temperature profile in an isolated cell.

Figure 15 is a diagram showing the temperature profile in a non-isolated cell.

Figure 16 is a graph showing the comparison of a radial temperature profile and the averaged temperature profile in a cell between a cell with insulating gap and a cell without insulating gap for the steady state,

17 is a diagram showing the comparison of a radial temperature profile and the averaged temperature profile in the cell with insulating gap for the wall material SiIi. zium, glass (pyrex) and plastic (PMMA) for the stationary state at cell filling shows carbon dioxide and

Figure 18 is a graph showing the comparison of a radial temperature profile and the averaged temperature profile in a cell with insulating gap for the wall materials silicon, glass (Pyrex) and plastic (PMMA) for the stationary state in cell filling water.

FIG. 1 shows a sensor arrangement according to the present invention for detecting electromagnetic radiation whose wavelength is in or near the infrared range-referred to below as IR radiation. Such a sensor arrangement in microstructure is particularly suitable for use in night vision devices, for example for automobiles or aircraft. They can also be used to monitor industrial production processes, fire service operations, medical and veterinary diagnostics, and mine detection in military and civilian night vision equipment. The sensor arrangement comprises a substrate 1, which is formed here by a silicon wafer. In the substrate 1 are a plurality of measuring chambers

2 or cells are etched, which are etched as through holes in the silicon material.

On the top of the substrate 1 is a window plate

3 attached from an IR radiation-transmissive material such as Pyrex by gluing or bonding, which covers the above-mentioned inlet openings of the cells 2.

On its underside, the cells 2 are closed by a thin silicon wafer 4, which is fastened to the underside of the substrate 2 and forms a removable membrane M. Each cell 2 is associated with a capacitor 5, the upper capacitor plate 5a is provided in the form of a coating on the silicon wafer 4 below the cell 2 and the lower capacitor plate 5b is attached to a base plate 6.

Between the thin silicon wafer 4 and the base plate 6, a continuous space is formed forming a pressure relief chamber 7. The pressure relief chamber 7 is connected to the measuring chambers 2 in each case by a connecting channel 8. This is formed in the silicon wafer 4 and provided between this and the substrate 2 intermediate plate 9 spirally and opens on the one hand in the cell 2 and on the other hand in the pressure relief chamber 7. The connecting channel 8 may be formed, for example, meandering. Through the channels 8 it is achieved that in the pressure relief chamber 7 and the cells 2, a pressure equalization between the chambers 2, 7 can take place. The cross-sectional area and length of the channels 8 are determined so that slow pressure changes in the measuring chamber 2, as they occur for example in changes in the ambient temperature, are compensated, but at fast However, pressure changes, such as occur when IR radiation enters the blades 2, such pressure equalization can not take place, so that the membrane M deformed. Furthermore, in the base plate 6, a pressure relief opening 10 is provided to the environment, so that approximately ambient pressure is established in the measuring chamber 2 and the pressure relief chamber 7. On the underside of the base plate 6, a film 11 is provided, which closes the pressure relief opening, so that no water can escape from the pressure relief chamber 7.

FIGS. 3 and 4 show an alternative embodiment of a sensor arrangement. This consists, like the embodiment shown in Figures 1 and 2, of a substrate 1 in the form of a silicon wafer, in which measuring chambers 2 and cells are formed. As can be seen in FIG. 3, the measuring chambers 2 are formed in the substrate 1 by recesses which are still closed towards the bottom side, wherein the bottom remaining in the production of the recesses forms a thin membrane M.

On the upper side of the substrate 2, a window plate 3 is also provided here, which closes the open upper sides of the measuring chambers 2, and on the underside of the substrate 2, capacitors 5 are provided, wherein in each case the upper plate 5a of the capacitors on the underside of a membrane M and the lower plate 5 b of the capacitor are formed on the base plate 6. As in the embodiment described above, a pressure relief chamber 7 is formed between the base plate 6 and the substrate 1, which is connected through a pressure relief opening 10 in the base plate 6 with the environment. The pressure relief chamber 7 is further connected to the measuring chambers 2, in this case through perforations 12, which pass through the upper plates 5a of the capacitors 5a and the membranes M. Also in this embodiment, the perforation openings 12 are dimensioned so that a pressure equalization between the measuring chambers 2 and the pressure relief chamber 7 takes place at slow pressure changes, but not rapid pressure changes due to incoming IR radiation are compensated.

The embodiment of a sensor arrangement according to the invention shown in FIGS. 5 and 6 corresponds to the embodiment previously described with reference to FIGS. 3 and 4, with the proviso that each measuring chamber 2 is assigned its own pressure relief chamber 7. For this purpose, an intermediate plate 13 is provided between the base plate 6 and the substrate 1, in which the measuring chambers 2 associated, circular cavities are formed. Due to this arrangement, the measuring chambers 2 and associated pressure relief chambers 7 are independent of each other. In addition, the pressure relief chambers 7 are also not open to the environment, so that the measuring represent chambers 2 and associated pressure relief chambers 7 completed systems.

The embodiment of a sensor arrangement according to the invention shown in FIG. 7 corresponds to the embodiment shown in FIGS. 5 and 6 with the only difference that the pressure relief chambers 7 have a larger volume. For this purpose, a base plate 6 of greater thickness is used, in which annular recesses 14 are formed around the lower capacitor plate 5b.

In all the above-described sensor arrangements, the measuring chambers 2 are filled with a gaseous or liquid fluid which absorbs IR radiation. When IR radiation enters the measuring chambers 2 through the window plate 3, this radiation is correspondingly at least partially absorbed with the result that the temperature of the fluid increases and expands. Due to the expansion, the diaphragm M and thus the upper capacitor plate 5a is deformed, so that the capacitance of the capacitor 5 changes. This change is recorded and evaluated.

The measuring chambers 2 and the pressure relief chamber (s) 7 are connected to each other, so that pressure differences between the chambers 2, 7 due to slow pressure changes in one of the chambers 2, 7 ausgegli- example due to changes in the ambient temperature chen and the upper capacitor plate 5a does not deform due to such slow temperature changes.

FIGS. 8 and 9 show a further embodiment of a sensor arrangement for detecting electromagnetic radiation. This comprises a substrate 1, in which measuring chambers 2 are introduced as recesses open towards the upper side of the substrate and closed towards the underside of the substrate. The bottoms of the measuring chambers 2 are designed as thin-walled membranes M.

Below the substrate 1, a base plate 6 is arranged, which is connected to the substrate bottom by an intermediate plate 15. In the intermediate plate 15 circular recesses are provided so that between the substrate 1 and the base plate 6 in the region of the measuring chambers circular cavities 17 are formed. In these cavities 17 capacitors 5 are housed, wherein the upper capacitor plate 5a is provided as a coating on the underside of the membrane M and the lower capacitor plate 5b is fixed to the base plate 6. The cavities 17 may be formed as pressure relief chambers, which are connected to the measuring chambers 2 in the manner described above, but need not.

The open upper sides of the measuring chambers 2 are protected by a window pane 3 permeable to infrared radiation. closed, which is attached to the top of the substrate 2, in particular glued or bonded.

As FIGS. 8 and 9 clearly show, the cells of the measuring chambers 2 are limited only by thin walls 18, while the surrounding areas are etched away to form the insulation space 19. Through this insulation column 19 heat losses are reduced by heat conduction.

The embodiment shown in FIG. 10 corresponds to the embodiment illustrated in FIGS. 8 and 9, with the proviso that the measuring chambers 2 are formed by tubes 20 made of a heat-insulating material, such as glass (Pyrex), which is placed on the substrate 1, here formed as a thin plate fixed, for example, glued or festgebondet. By using a heat-insulating material, heat losses from the interior of the measuring chambers 2 can be more effectively prevented.

FIG. 11 further shows the sensor arrangement from FIG. 10, wherein the insulation spaces 19 formed between the tubes 20 are filled with an adhesive 22 made of a heat-insulating material. The adhesive gives the arrangement additional support. In addition, at the same time a fixation of the tubes 20 can be achieved on the substrate 2 when pouring the adhesive into the interstices. The adhesive may also be derived from IR radiation. consist of sorbent material. In this case, the adhesive 22 heats up when incident IR radiation, whereby a heat dissipation from the measuring chambers 2 is counteracted.

FIG. 12 also shows an arrangement of the glass tubes 20, which here have a circular cross-section, and contact one another to form line contacts. In this arrangement, the glass tubes 20 are bonded together so that they form a bundle, which can be positioned and fixed together on a substrate 2. The line contact hardly allows any heat transfer from one tube 20 to the other.

Claims

Anspruch [en] A sensor arrangement for detecting electromagnetic radiation whose wavelength is in or near the infrared range, comprising at least one measuring chamber (2) which can be filled with a fluid selectively absorbing the radiation to be measured, and a pressure relief chamber (7) which at least on the measuring chamber

(2) on the opposite side of the membrane (M), and which is in fluid communication with the measuring chamber (2), the measuring chamber (2) passing through a window

(3) has a sealed inlet opening for the radiation and a part of the measuring chamber wall is designed as a flexible membrane (M) such that it is deformed when the volume of the fluid contained in the measuring chamber (2) changes due to the absorption of the incoming radiation, and wherein the Membrane (M) is associated with a measuring device to detect the deformation, characterized in that the fluid is a liquid.

2. Sensor arrangement according to claim 1, characterized in that the pressure relief chamber (7) with the measuring chamber (2) by a particular spiral channel (8) is connected, which surrounds the measuring chamber (2) and at its one end in the measuring chamber (2 ) and at its other end in the pressure relief chamber (7) opens.

3. Sensor arrangement according to claim 1, characterized in that on the membrane (M) adjacent plate (5a) of the capacitor (5) and the membrane (M) are perforated to the measuring chamber (2) and the pressure relief chamber (7) connect.

4. Sensor arrangement according to one of the preceding claims, characterized in that the pressure relief chamber (7) has a pressure relief opening (10) to the environment.

5. Sensor arrangement according to claim 4, characterized in that the pressure relief opening (10) is covered by a flexible film (11).

6. Sensor arrangement according to one of claims 1 to 3, characterized in that the pressure relief chamber (7) for each measuring chamber (2) represents a closed volume.

7. Sensor arrangement according to one of the preceding claims, characterized in that the measuring device comprises a capacitor (5) and the pressure relief chamber (7) is formed at least in the region between the Kodensatorplatten (5a, 5b).

8. Sensor arrangement according to one of the preceding claims, characterized in that the at least one Messkam- mer (2) of a in a substrate (1), in particular with formation of the membrane (M), introduced cavity is formed on one side of the inlet opening having the active side of a window pane (3) is covered.

9. Sensor arrangement according to claim 8, characterized in that in the substrate (1) a plurality of measuring chambers (2) are formed, wherein in the wall regions between the measuring chambers (2) isolation spaces (19) are provided.

10. Sensor arrangement according to claim 9, characterized in that the insulation spaces (19) are filled with an IR radiation absorbing material or a heat insulating material.

11. Sensor arrangement according to one of claims 8 to 10, characterized in that the substrate (2) is a silicon wafer, glass wafer or plastic wafer.

12. Sensor arrangement according to one of claims 1 to 7, characterized in that the measuring chambers (2) of tubes (20) are formed of a heat-insulating material on a wafer (2) in particular of silicon, glass or plastic, in which Membranes (M) are formed, are fixed.

13. Sensor arrangement according to claim 12, characterized in that the tubes (20) consist of glass.

14. Sensor arrangement according to claim 12 or 13, characterized in that the tubes (20) are arranged at a distance from each other.

15. Sensor arrangement according to one of claims 12 to 14, characterized in that the tubes (20) are formed round and arranged in line contact with each other.

16. Sensor arrangement according to claim 14 or 15, characterized in that the insulation spaces (19) between the tubes (20) are filled with an adhesive (22).

17. Sensor arrangement according to claim 16, characterized in that the adhesive (22) consists of an IR radiation absorbing material.

18. Sensor arrangement according to one of the preceding claims, characterized in that in the at least one measuring chamber (2) additionally at least one infrared radiation absorbing material is introduced.

19. Sensor arrangement according to claim 16, characterized in that the IR radiation absorbing material is a plastic and in particular a polymer.

20. Sensor arrangement according to claim 18 or 19, characterized in that the IR radiation absorbing material is applied in the form of a coating on the side wall of the measuring chamber.

21. Sensor arrangement according to claim 20, characterized in that the absorber layer has a sponge or net-like structure.

22. Sensor arrangement according to claim 18 or 19, characterized in that the IR radiation absorbing material is in the form of thin polymer threads or polymer fibers.

23. Sensor arrangement according to claim 2, characterized in that polymer threads are loosely wound into cylindrical or spherical absorption bodies.

24. Sensor arrangement according to claim 22 or 23, characterized in that thin polymer threads or polymer fibers are applied to a polymer film.

25. Sensor arrangement according to one of claims 18 to 24, characterized in that absorption bodies are provided as a hollow body with a shell made of plastic and the cavity of the absorption body is filled with gas.