CAPACITIVE SENSOR FOR PHOTOACOUSTIC SPECTROSCOPY, DEVICE AND METHOD USING SUCH A SENSOR

Abstract

A sensor for photoacoustic spectroscopy including a support and a mechanical resonator fastened to the support, including at least one sensor element designed to be vibrated by an acoustic wave, and at least one first capacitive electrode mechanically coupled to the sensor element so as to be moved by the sensor element when it is vibrated; and at least one second capacitive electrode forming with the at least one first electrode, a capacitive sensor; the support facing the sensor element, an apertured part formed by one or more through-openings. Also provided is a detection and/or measurement device and method, for photoacoustic spectroscopy, using such a sensor.

Claims

1. A sensor for photoacoustic spectroscopy comprising: a support; a mechanical resonator, fastened to said support, and including: at least one sensor element intended to be vibrated by an acoustic wave, and at least one first capacitive electrode, mechanically coupled to said sensor element, so as to be moved by said sensor element when it is vibrated; at least one second capacitive electrode forming, with said at least one first electrode, a capacitive sensor; and said support has, opposite said sensor element, a perforated part formed by one or more through holes.

2. The sensor according to claim 1, characterized in that the resonator comprises several first electrodes mechanically coupled to the sensor element and moved by said sensor element.

3. The sensor according to claim 1, characterized in that the resonator comprises four first capacitive electrodes aligned in pairs with the sensor element so as to form a cross centered on the sensor element.

4. The sensor according to claim 1, characterized in that the resonator is fastened to the support at the level of at least one mechanical vibration node.

5. The sensor according to claim 1, characterized in that, for at least one first capacitive electrode, the resonator is fastened to the support at a fastening position located between the sensor element and said first capacitive electrode.

6. The sensor according to claim 5, characterized in that, for at least one first capacitive electrode, the fastening position is closer to the sensor element than said first capacitive electrode.

7. The sensor according to claim 1, characterized in that the resonator is produced in a single piece.

8. The sensor according to claim 1, characterized in that at least one first capacitive electrode is integral with the sensor element through at least one linking arm having a width that is smaller than that of the sensor element.

9. The sensor according to claim 1, characterized in that at least one first capacitive electrode is formed by several branches, having a negligible width, at a distance from one another.

10. The sensor according to claim 1, characterized in that at least one, in particular each, second electrode is arranged on/in the support, opposite the, or a, first capacitive electrode.

11. The sensor according to claim 1, characterized in that it is produced from a structure constituted by a stack of layers of a conductive material and insulating material.

12. A detection and/or measurement device for photoacoustic spectroscopy comprising: at least one light source emitting a modulated light radiation; and at least one sensor according to claim 1.

13. The device according to claim 12, characterized in that it comprises several modulated light sources.

14. The device according to claim 12, characterized in that the modulation frequency of at least one light source is adjustable.

15. A method for detecting a gas, and/or measuring the concentration of a gas, using: a sensor according to claim 1.

16. A method for detecting a gas, and/or measuring the concentration of a gas, using a device according to claim 12.

Description

DESCRIPTION OF THE FIGURES AND EMBODIMENTS

[0108] Other advantages and characteristics will become apparent on examination of the detailed description of an embodiment which is in no way limitative, and the attached drawings, in which:

[0109] FIGS. 1 and 2 are diagrammatic representations of a first non-limitative embodiment example of a sensor according to the invention;

[0110] FIGS. 3 and 4 are diagrammatic representations of a second embodiment example of a sensor according to the invention;

[0111] FIG. 5 is a diagrammatic representation of a third embodiment example of a sensor according to the invention; and

[0112] FIG. 6 is a diagrammatic representation of the device according to the invention.

[0113] It is of course understood that the embodiments that will be described hereinafter are in no way limitative. In particular, variants of the invention can be imagined comprising only a selection of the characteristics described hereinafter, in isolation from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of the prior art. This selection comprises at least one, preferably functional, characteristic without structural details, or with only a part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of the prior art.

[0114] In the figures, elements common to several figures keep the same reference.

[0115] FIG. 1 is a diagrammatic representation of a first non-limitative embodiment example of a sensor according to the invention.

[0116] The sensor 100, shown in FIG. 1, comprises a support 102.

[0117] The sensor 100 comprises a mechanical resonator 104, intended to enter into mechanical resonance at its resonant frequency, under the effect of a sound wave.

[0118] The mechanical resonator 104 comprises a sensor element 106 on which a sound wave is exerted to set the whole of the resonator 104 in resonance.

[0119] The mechanical resonator 104 also comprises at least one first capacitive electrode that is offset and separated from the sensor element, and mechanically coupled to the sensor element so that it is moved by the sensor element 106 when it is made to move. In the example shown in FIG. 1, the mechanical resonator 104 comprises two first electrodes 108.sub.1 and 108.sub.2, mechanically coupled to the sensor element 106, positioned on either side of the sensor element, and aligned with the sensor element 104.

[0120] The sensor 100 comprises a second capacitive electrode 110, common to the two first capacitive electrodes 108.sub.1 and 108.sub.2, and forming a capacitive sensor with each of said first capacitive electrodes 108.sub.1-108.sub.2. In the example shown in FIG. 1, the second capacitive electrode 110 is formed by the whole of the support 102. To this end, the support 102 is made of an electrically conductive material.

[0121] The sensor 100 comprises fastening blocks 112.sub.1-112.sub.4, to make the resonator 104 integral with the support 102 at the level of the two oscillation nodes of said resonator 104.

[0122] The support 102 has an entirely perforated part 114 at the level of, and opposite, the sensor element 106. This perforated part 112 allows air to circulate so as to avoid the formation of a layer of air between the sensor element 106 and the support 102, which could damp the movement of the sensor element during its oscillation under the effect of the sound wave.

[0123] The sensor element 106 is linked to the first capacitive electrode 108.sub.1 by two parallel linking arms 116.sub.1 and 118.sub.1, having a very narrow width compared with that of the sensor element 106 and being at a distance from one another. Similarly, the sensor element 106 is linked to the second capacitive electrode 108.sub.2 by two parallel linking arms 116.sub.2 and 118.sub.2, having a very narrow width compared with that of the sensor element 106 and being at a distance from one another.

[0124] Thus, the link between the sensor element 104 and the first capacitive electrodes 108.sub.1-108.sub.2 is not affected by a damping effect during the mechanical oscillation of the resonator 104.

[0125] In addition, the resonator 104 comprises a first branch 120.sub.1, called fastening branch, making it possible to fasten the resonator 104 to the fastening blocks 112.sub.1-112.sub.2. This fastening branch 120.sub.1 creates a fastening line located at the level of an oscillation node between the sensor element 106 and the first capacitive electrode 108.sub.1. This fastening branch 120.sub.1 is held in a mobile manner, on either side, in the blocks 112.sub.1-112.sub.2.

[0126] Similarly, the resonator 104 comprises a second branch 120.sub.2, called fastening branch, making it possible to fasten the resonator 104 to the fastening blocks 112.sub.3-112.sub.4. This fastening branch 120.sub.2 creates a fastening line located at the level of an oscillation node between the sensor element 106 and the first capacitive electrode 108.sub.2. This fastening branch 120.sub.2 is held in a mobile manner, on either side, in the blocks 112.sub.3-112.sub.4.

[0127] In the sensor 100 in FIG. 1, the first capacitive electrodes 108.sub.1-108.sub.2 are identical.

[0128] In the example shown in FIG. 1, each first capacitive electrode 108.sub.1-108.sub.2, has two branches, perpendicular to one another so as to form a cross or a “+”.

[0129] Such an architecture makes it possible to limit the damping effect at the level of each of these electrodes, while bringing each of the first capacitive electrodes 108.sub.1-108.sub.2 as close as possible to the second capacitive electrode 110.

[0130] In addition, each first capacitive electrode 108.sub.1-108.sub.2 is polarized to a non-zero electrical potential by electrical contacts (not shown) at the level of the fastening blocks 112.sub.1-112.sub.4. The electrical potential is propagated in the whole of the resonator, and in particular in the first capacitive electrodes 108.sub.1-108.sub.2 due to the fastening branches 120.sub.1-120.sub.2 held in the fastening blocks 112.sub.1-112.sub.4.

[0131] In the example shown, the sensor element 106 and the first capacitive electrodes 108.sub.1-108.sub.2 are produced in a single piece/layer. More generally, the whole of the resonator is produced in a single piece/layer.

[0132] As can be seen in FIG. 1, the sensor 100 defines a general plane.

[0133] The sensor element 106 is intended to capture a sound wave in the direction perpendicular to the principal plane of the sensor 100. The sensor element 106, and more generally the resonator 104, is intended to be deformed in the direction perpendicular to the principal plane.

[0134] The first electrodes 108.sub.1-108.sub.2 are separated/shifted from the sensor element 106 in the principal plane of the sensor, or at least in a direction perpendicular to the direction in which the sensor element moves under the effect of an acoustic wave.

[0135] FIG. 2 is a representation of the sensor in FIG. 1, without the support 102.

[0136] In FIG. 2, the resonator 104 is shown in a rest state, and in a state of deformation under the effect of a sound wave.

[0137] As explained above, the sensor element, and more generally the resonator, is made to move in the direction indicated by the double arrow 202, perpendicular to the plane of the sensor, which is also the plane of the resonator 104 when it is at rest.

[0138] FIG. 2 clearly shows the sensor element 106 the movement of which moves each of the first capacitive electrodes 108.sub.1-108.sub.2. The direction of movement of the sensor element 106 is opposite to that of the first capacitive electrodes 108.sub.1-108.sub.2.

[0139] In addition, the resonator has a displacement that is zero, or almost zero, at the level of the fastening branches 120.sub.1-120.sub.2, which correspond to oscillation nodes.

[0140] FIG. 3 is a diagrammatic representation of a second non-limitative embodiment example of a sensor according to the invention.

[0141] The sensor 300, shown in FIG. 3, comprises all of the elements of the sensor 100 in FIG. 1.

[0142] The sensor 300 comprises a resonator 302 which comprises all of the elements of the resonator 104 of the sensor 100 in FIG. 1.

[0143] The resonator 302 comprises, in addition to the elements of the resonator 104, two other first electrodes 108.sub.3-108.sub.4, positioned on either side of the sensor element 106.

[0144] The first electrodes 108.sub.3-108.sub.4 are aligned with the sensor element 106 in a direction different from that formed by the first electrodes 108.sub.1-108.sub.2 with the sensor element 106. Thus, the first electrodes 108.sub.1-108.sub.2 and the first electrodes 108.sub.3-108.sub.4 form a cross at the center of which the sensor element 106 is located. In particular, the branches of the cross thus formed are perpendicular to one another.

[0145] The first capacitive electrodes 108.sub.3 and 108.sub.4 are identical to the first electrodes 108.sub.1 and 108.sub.2.

[0146] The sensor element 106 is linked to the first capacitive electrode 108.sub.3 by two parallel linking arms 116.sub.3 and 118.sub.3, having a very narrow width compared with that of the sensor element 106 and being at a distance from one another. Similarly, the sensor element 106 is linked to the first capacitive electrode 108.sub.4 by two parallel linking arms 116.sub.4 and 118.sub.4, having a very narrow width compared with that of the sensor element 106 and being at a distance from one another.

[0147] In addition, the resonator 104 comprises a third branch 120.sub.3, called fastening branch, making it possible to fasten the resonator 104 to the fastening blocks 112.sub.2-112.sub.3. This fastening branch 120.sub.3 creates a fastening line located at the level of an oscillation node between the sensor element 106 and the first capacitive electrode 108.sub.3. This fastening branch 120.sub.3 is held in a mobile manner, on either side, in the blocks 112.sub.2-112.sub.3.

[0148] Similarly, the resonator 104 comprises a fourth branch 120.sub.4, called fastening branch, making it possible to fasten the resonator 104 to the fastening blocks 112.sub.4-112.sub.1. This fastening branch 120.sub.4 creates a fastening line located at the level of an oscillation node between the sensor element 106 and the first capacitive electrode 108.sub.4. This fastening branch 120.sub.4 is held in a mobile manner, on either side, in the blocks 112.sub.4-112.sub.1.

[0149] Thus, the resonator 302 comprises four identical first capacitive electrodes 108.sub.1-108.sub.4.

[0150] FIG. 4 is a representation of the sensor in FIG. 3, without the support 102.

[0151] In FIG. 4, the resonator 302 is shown in a rest state, and in a state of deformation under the effect of a sound wave.

[0152] As explained above, the sensor element 106, and more generally the resonator 302 is made to move in the direction indicated by the double arrow 402, perpendicular to the plane of the sensor 300, which is also the plane of the resonator 302 when it is at rest.

[0153] FIG. 4 clearly shows the sensor element 106 the movement of which moves each of the first capacitive electrodes 108.sub.1-108.sub.4. The direction of movement of the sensor element 106 is opposite to that of the first capacitive electrodes 108.sub.1-108.sub.4.

[0154] In addition, the resonator has a displacement that is zero, or almost zero, at the level of the fastening branches 120.sub.1-120.sub.4, which correspond to oscillation nodes.

[0155] In the examples described, the sensor comprises a single second capacitive electrode formed by the support.

[0156] Alternatively, the second capacitive electrode 110 can be formed by a layer, or a track, of conductive material deposited on the support 102, or provided in the thickness of the support 102, or deposited under the support 102.

[0157] Alternatively, or in addition, the sensor 100 can comprise several second capacitive electrodes, in particular a second capacitive electrode that is individual for each first capacitive electrode.

[0158] FIG. 5 is a diagrammatic representation of a third non-limitative embodiment example of a sensor according to the invention.

[0159] The sensor 500, shown in FIG. 5, comprises the support 102 serving as second capacitive electrode 110, and having the perforated part 114.

[0160] The sensor 500 also comprises a resonator 502 comprising the sensor element 106 opposite the perforated part 114. The resonator 502 is fastened to the support 102 with the fastening blocks 112.sub.1-112.sub.4, thanks to the fastening branches 120.sub.1-120.sub.2 held in the fastening blocks 112.sub.1-112.sub.4, and each positioned at the level of a vibration node of the resonator 502.

[0161] The resonator 502 comprises four identical first capacitive electrodes 504.sub.1-504.sub.4, having a shape different from that of the electrodes 108.sub.1-108.sub.4.

[0162] In particular, each first capacitive electrode 504.sub.i, with i=1 . . . 4, is formed by a distal branch 506.sub.i linked to the sensor element 106 by three branches 508.sub.i, 510.sub.i and 512.sub.i, parallel to one another, and perpendicular to the distal branch 506.sub.i. For example, the first capacitive electrode 504.sub.1 is formed by a distal branch 506.sub.1 linked to the sensor element 106 by three branches 508.sub.1, 510.sub.1 and 512.sub.1, parallel to one another, and perpendicular to the distal branch 506.sub.i. The width of each of the branches 506.sub.i, 508.sub.i, 510.sub.i and 512.sub.i is very narrow, of the order of approximately ten micrometers.

[0163] In addition, it should be noted that the fastening branches 120.sub.1-120.sub.2 are each located on a vibration node, in a position closer to the sensor element than distal branches 506.sub.1-506.sub.4 forming part of the first capacitive electrodes 504.sub.1-504.sub.4. This architecture makes it possible to create a lever effect amplifying the mechanical movement of the first capacitive electrodes 504.sub.1-504.sub.4. Thus, the sensitivity of the sensor 500 is improved.

[0164] FIG. 6 is a representation of a non-limitative embodiment example of a detection and/or measurement device according to the invention.

[0165] The device 600 in FIG. 6 comprises a sensor 602, which can be any one of the sensors 100, 300 or 500 in FIGS. 1-5.

[0166] The device 600 also comprises a laser source 604 emitting a laser radiation 606 modulated to a given modulation frequency and a given wavelength in the direction of a gaseous environment 608.

[0167] The modulation frequency can be comprised between 1 and 100 kHz, and in particular between 10 and 50 kHz.

[0168] The modulated laser radiation 606 is absorbed by the gas 608, which in response emits a sound wave 610 which is detected by the sensor 602.

[0169] The device 600 also comprises detection electronics for on the one hand polarizing the capacitive electrodes of the sensor 602 and on the other hand measuring an electrical signal representative of the capacitive detection.

[0170] In the example shown, the detection/measurement device comprises a single modulated laser source.

[0171] Alternatively, the device can comprise several laser sources emitting modulated laser radiations, at one and the same frequency, but having different wavelengths.

[0172] Alternatively or in addition, the device can comprise a light source which is not a laser source. For example, the device can comprise at least one light emitting diode, at least one resonant cavity light emitting diode, and at least one RCLED the emission spectrum of which is much narrower than a traditional infrared LED.

[0173] Advantageously, but non-limitatively, each mechanical resonator 104, 302 and 502 is produced in a single piece from one and the same material. In other words, in each mechanical resonator: [0174] the sensor element 106, [0175] the first capacitive electrodes, and [0176] the linking branches linking the sensor element and each first capacitive electrode; [0177] are produced in a single piece and from one and the same material. As a result, the sensor element and the linking branches also behave like a capacitive sensor linked or connected to each first capacitive electrode.

[0178] Of course, the invention is not limited to the examples detailed above.