Multipath spectroscopic absorption cell and gas sensor including the same

Abstract

The present invention relates to a multi-path spectroscopic absorption cell (200), and in particular to a white-type cell operating as a non-dispersive near-infrared gas sensor. The present invention also relates to a gas sensor (300) and an alcohol sensor. The component reflector unit (245; 445) of the multi-path spectroscopic absorption cell (200) includes a first detector (250), a second detector (260), and a light source (210), the light source (210) being arranged to emit a first portion of light that is first reflected in a first concave mirror (220; 420) and forms a first optical path that terminates in the first detector (250), and to emit a second portion of light that is first reflected in a second concave mirror (230; 430) and forms a second optical path that terminates in the second detector (260).

Description

[Technical Field]

[0001] The present invention relates to a multi-path spectroscopic absorption cell operating as a non-dispersive near-infrared gas sensor.The present invention further relates to an alcohol sensor and sensor system. [Background technology]

[0002] Multipass spectroscopic absorption cells are commonly used in various types of gas sensors, particularly non-dispersive near-infrared gas sensors (NDIR sensors). The term "multipass" refers to the optical path and thus the reflection of electromagnetic radiation, preferably multiple times, within the measurement cell, which is part of the sensor, to increase the sensitivity of the sensor or measurement system. A particularly useful implementation of a multipass cell is the so-called White cell, proposed by John U. White as early as 1942 and used ever since (Journal of the Optical Society of America, 1942). A prior art White cell is illustrated schematically in FIG. 1a. The prior art White cell structure 100 comprises three concave mirrors with the same radius of curvature, a light source 110, and a detector 150. First and second reflectors 120 and 130 are positioned side by side on the opposite side of the light source 110, and a third reflector 140 is positioned opposite the first and second reflectors 120 and 130. The light source 110 projects infrared light 115 at a predetermined angle onto a point on the side of the third reflector 140. The infrared light 115 is then reflected by the first reflector 120, repeatedly reflected between the third reflector 140 and the first and second reflectors 120 and 130, and then incident on the detector 150. The gas to be analyzed is maintained within the cavity, and as the infrared light 150 passes through the gas, the output voltage of the detector 150 provides a measure of the concentration of a specific substance present in the gas. The separation of the centers of curvature of the first and second reflectors 120 and 130, and the angle between the incident optical axis and the longitudinal plane, determine the number of reflections of the incident light and, therefore, the effective optical path length of the device. The White cell according to FIG. 1 produces eight reflections. However, White cells producing a substantially greater number of reflections are known in the art. One way to increase the number of reflections known in the art is to position the light source 110 laterally offset from the longitudinal optical plane of the measurement cell to provide a 3D White cell geometry that results in two rows of reflections, top 146 and bottom 147 rows of light spots on the component reflector unit 140 and 16, as illustrated in Figure 1b.

[0003] One limitation of gas sensors based on White cells and used for NDIR applications is that they are suitable for one wavelength or a somewhat limited wavelength range, corresponding to only a limited number of substances that can be detected with one setup. This poses a problem for certain applications, such as in breath analysis to detect and determine the breath concentration of illicit or harmful substances, such as alcohol, with the help of a tracer substance, e.g., carbon dioxide, since simultaneous detection is not possible with the same mirror / detector combination.

[0004] US Patent No. 9,823,237 discloses an integrated breath alcohol sensor system that provides simultaneous measurement of alcohol concentration and tracer substance concentration, typically CO2. The measurement chamber according to US Patent No. 9,823,237 comprises two detector / mirror setups, one suitable for alcohol determination and one for CO2. The optical axes of the two setups are perpendicular to each other and are arranged with their radii of curvature centered in the same plane. Disadvantages include a complex manufacturing process and overlapping mirrors, which increases production costs.

[0005] WO 0181901 discloses a White cell with a more complex geometry compared to the original White cell. The disclosed cell is a 2D cell and can be equipped with multiple detectors associated with different beam paths within the cell. Disadvantages include a very complex geometry with crucial parts spread throughout the cell, which makes it difficult and expensive to mechanically and thermally stabilize the cell. Summary of the Invention

[0006] The object of the present invention is to overcome the drawbacks associated with prior art locking devices. This is achieved by a multi-path spectroscopic absorption cell, a gas sensor and an alcohol meter as defined by the independent claims.

[0007] According to one aspect of the present invention, there is provided a multi-pass spectroscopic absorption cell, the multi-pass spectroscopic absorption cell comprising: a measurement cavity provided with at least one gas inlet and at least one gas outlet, a main reflector unit comprising a first concave mirror and a second concave mirror; a component reflector unit comprising a third mirror 240 facing the first and second concave mirrors, a component reflector unit, wherein the first concave mirror and the second concave mirror are spherical mirrors, have the same concave radius of curvature, and are arranged with their centers of curvature radii aligned in the same longitudinal optical plane A; a light source provided adjacent to or within the component reflector unit and positioned to direct emitted light towards the main reflector unit, the light source being positioned laterally offset to the longitudinal optical plane A; a first detector provided adjacent to or within the component reflector unit; a second detector provided adjacent to or within the component reflector unit, the light source being arranged to emit a first portion of light that is first reflected off the first concave mirror to form a first optical path that terminates at the first detector, and to emit a second portion of light that is first reflected off the second concave mirror to form a second optical path that terminates at the second detector.

[0008] The distance between the main reflector unit and the component reflector units can be 95% to 105% of the radius of curvature of the first and second mirrors. If the input beam is focused in the plane of the component reflector unit, then each round trip, i.e., after reflection within the main reflector unit, it is refocused in the plane of the component reflector unit.

[0009] The third mirror may also be a concave mirror, but may also comprise several facets arranged in an overall concave configuration, each facet being a plane mirror. Such a configuration of the third mirror provides good results when the distance between the main reflector unit and the component reflector units is approximately the same as the radius of curvature of the first and second mirrors, and can also provide acceptable results for slightly different distances between the main reflector unit and the component reflector units.

[0010] Depending on the configuration of the absorption cell and the number of reflections in the third mirror, the area of ​​the third mirror may be so small that it can be configured as a single flat mirror. The third mirror may be a spherical mirror and may have the same radius of curvature as the first and second mirrors. The first, second, and third mirrors may be arranged with their centers of curvature aligned in the same longitudinal optical plane A.

[0011] The primary reflector unit and the component reflector units may be positioned at a distance from each other that is essentially the same as the radius of curvature of the first, second, and third mirrors. Such a multi-pass spectral absorption cell is commonly referred to as a White cell.

[0012] According to one embodiment of the invention, the first detector is provided in a first detector opening in the third mirror and / or the second detector is provided in a second detector opening in the third mirror. By providing the first detector and / or the second detector in openings in the third mirror, a more rigid mounting of the detectors and light source to each other and to the third mirror is enabled.

[0013] Preferably, a first detector is provided within the component reflector unit and a second detector is provided within the component reflector unit. Preferably, the first detector is fixed relative to the third mirror. Preferably, the second detector is fixed relative to the third mirror. Fixing the first and second detectors to the third mirror can be achieved in many different ways. The first and second detectors can be directly attached to the third mirror. The first and second detectors can be fixed to an intermediate element, such as a printed circuit board, which is attached to the third mirror. Fixation to the intermediate element can be in addition to directly attaching the first and second detectors to the third mirror. By fixing the detectors relative to the third mirror, stable imaging of the light source on the detector is achieved. In this way, the amount of light on the detector does not change due to vibrations or the like. This becomes increasingly important as the number of reflections increases, as this requires a longer third mirror and a longer distance between the light source and the detector.

[0014] The light source may be provided within a light source opening in the third concave mirror. The light source may be fixed relative to the third mirror. The light source may be directly mounted and fixed to the third mirror. The light source may be mounted and fixed to the third mirror using an intermediate element, such as a printed circuit board. Mounting and fixing the light source using an intermediate element may be in addition to directly mounting the light source to the third mirror. Fixing the light source to the third mirror minimizes vibrational movement of the light source relative to the third mirror.

[0015] According to one embodiment of the present invention, the second optical path includes a second detector opening located in the third mirror corresponding to a position where there is only one reflection in the main reflector unit and where the emitted light is reflected only once by the second concave mirror.

[0016] According to one embodiment of the present invention, a light source is provided in a first half, a first detector is provided in a second half of the component reflector unit, and a second detector is provided in the same half of the component reflector unit as the first detector.

[0017] According to one embodiment of the present invention, a first portion of the light that is arranged to initially reflect off a first concave mirror and follows a first optical path comprises a majority of the light emitted by the light source. According to one embodiment of the invention, the first optical path includes a predetermined number of reflections between the main reflector unit and the component reflector unit, and may be arranged to be longer, preferably at least twice as long, and even more preferably at least four times as long, as the second optical path.

[0018] According to one embodiment of the present invention, the majority of the light beam that is directed to reflection in the first mirror accounts for at least 75% of the emitted light, preferably at least 85% of the emitted light, and even more preferably at least 95% of the emitted light.

[0019] The desired percentage of the light beam to be reflected within the first mirror can be achieved by collimating, directing, and / or blocking the light from the light source. Blocking the light can be achieved by shielding the light source so that the desired percentage of light is incident on the first mirror. When the light source is positioned within a light source opening in the third concave mirror, shielding can be provided by the light source opening. Mirrors and / or lenses can be used to direct the light to achieve the desired percentage of light in the first optical path. Placing the light source and detector within the opening in the third mirror facilitates the alignment necessary to achieve the desired percentage of light in the first and second optical paths.

[0020] According to one embodiment of the present invention, a first detector is arranged to measure light intensity in a first wavelength range and a second detector is arranged to measure light intensity in a second wavelength range, the second wavelength range being separate from the first wavelength range.

[0021] According to one embodiment of the present invention, the first concave mirror and the second concave mirror are provided as a continuous structure contained in the main reflector unit, forming a continuous mirror surface with two distinct curvatures.

[0022] According to one embodiment of the present invention, a multi-pass spectroscopic absorption cell comprises: a main reflector unit comprising a first concave mirror and a second concave mirror arranged such that the main reflector unit back surface B is the common symmetrical back surface of the first concave mirror and the second concave mirror; a component reflector unit comprising a third mirror facing the first and second concave mirrors, the component reflector unit having a back surface C symmetrical to the third mirror; the first concave mirror and the second concave mirror are spherical mirrors, have the same concave radius of curvature, and are arranged with their centers of curvature aligned in the same longitudinal optical plane A; The component reflector unit back surface C is positioned transverse to a common longitudinal optical plane A, and the main reflector unit back surface B and the component reflector unit back surface C are positioned relative to each other such that the normal to the main reflector unit back surface B forms an angle α with the normal to the component reflector unit back surface C in the longitudinal optical plane A.

[0023] The third mirror may be configured as described above. The third mirror may be a concave mirror. The first concave mirror, the second concave mirror, and the third concave mirror may be spherical mirrors having the same concave radius of curvature and arranged with their centers of curvature aligned in the same longitudinal optical plane A.

[0024] According to one embodiment of the invention, the multi-pass spectral absorption cell is positioned to provide an upper row of light spots and a lower row of light spots on the component reflector unit, and the angle α is selected to cause a shift of the light spots in the lower row such that at least a majority of the light spots in the lower row are at the same longitudinal position as the light spots in the upper row. The terms "upper" and "lower" are used only with reference to the geometry of embodiments of the invention as shown in the drawings and / or during normal operation or device installation and are not intended to limit the invention in any way.

[0025] According to one aspect of the present invention, there is provided a gas sensor comprising the multi-pass spectroscopic absorption cell as described above, wherein the first wavelength range may relate to a first material and the second wavelength range may relate to a second material.

[0026] According to one embodiment of the invention relating to a gas sensor, a first detector is arranged to provide measures relating to the concentrations of a first and a second substance, wherein the signal related to the concentration of the first substance provided by the first detector relates to a target substance and the signal related to the concentration of the second substance provided by the second detector relates to a tracer substance, the concentration of the target substance being expected to be substantially lower than the concentration of the tracer substance under normal measurement conditions.

[0027] According to one aspect of the present invention, there is provided an alcohol meter comprising the gas sensor described above, wherein the first substance is alcohol and the second substance is carbon dioxide or water. Thanks to the present invention, a miniature multi-path spectroscopic absorption cell, and thus a gas sensor and alcohol meter, can be provided that simultaneously measures two different wavelength ranges and thereby detects two different substances.

[0028] One advantage offered by the present invention is that the design is robust and relatively simple to manufacture. One advantage provided by embodiments of the present invention is that a second detector may be integrated into the component reflector unit without substantially increasing the size of the component reflector unit.

[0029] Numerous additional benefits and advantages of the present invention will become readily apparent to those skilled in the art upon consideration of the following detailed description and accompanying drawings. The invention will now be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0030] [Figure 1a] FIG. 1 is a diagram illustrating a prior art multi-pass spectral absorption cell of the white type; [Figure 1b] FIG. 1 is a diagram illustrating a prior art multi-pass spectral absorption cell of the white type; [Figure 2a] FIG. 1 illustrates schematically a multi-pass spectroscopic absorption cell according to the present invention. [Figure 2b] FIG. 1 illustrates schematically a multi-pass spectroscopic absorption cell according to the present invention. [Figure 2c] FIG. 1 illustrates schematically a multi-pass spectroscopic absorption cell according to the present invention. [Figure 2d] FIG. 1 illustrates schematically a multi-pass spectroscopic absorption cell according to the present invention. [Figure 2e] FIG. 1 illustrates schematically a multi-pass spectroscopic absorption cell according to the present invention. [Figure 2f] FIG. 1 illustrates schematically a multi-pass spectroscopic absorption cell according to the present invention. [Figure 2g] FIG. 1 illustrates schematically a multi-pass spectroscopic absorption cell according to the present invention. [Figure 3] 1A and 1B illustrate schematically a gas sensor device according to the present invention; [Figure 4a] FIG. 1 is a diagram illustrating schematically one embodiment of a multi-pass spectroscopic absorption cell according to the present invention. [Figure 4b] FIG. 1 is a diagram illustrating schematically one embodiment of a multi-pass spectroscopic absorption cell according to the present invention. [Figure 4c] FIG. 1 is a diagram illustrating schematically one embodiment of a multi-pass spectroscopic absorption cell according to the present invention. [Figure 4d] FIG. 1 is a diagram illustrating schematically one embodiment of a multi-pass spectroscopic absorption cell according to the present invention. [Figure 4e] FIG. 1 is a diagram illustrating schematically one embodiment of a multi-pass spectroscopic absorption cell according to the present invention. [Figure 4f] FIG. 1 is a diagram illustrating schematically one embodiment of a multi-pass spectroscopic absorption cell according to the present invention. [Figure 4g] FIG. 1 is a diagram illustrating schematically one embodiment of a multi-pass spectroscopic absorption cell according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] All figures are schematic and not necessarily to scale, generally showing only those parts necessary to elucidate the respective embodiment; other parts may be omitted or merely suggested. Any reference numeral appearing in more than one figure refers to the same object or feature throughout the figures unless otherwise specified.

[0032] Terms such as "top," "bottom," "upper," "lower," "below," "above," and the like are used only with reference to the geometry of embodiments of the invention as shown in the drawings and / or during normal operation or installation of the device, and are not intended to limit the invention in any way.

[0033] A multi-pass spectroscopic absorption cell 200 according to the present invention is schematically depicted in FIGS. 2a-2h. As depicted in FIG. 2a, in a top view, the multi-pass spectroscopic absorption cell 200 comprises a measurement cavity 211 provided with at least one gas inlet 212 and at least one gas outlet 213. Arranged within the measurement cavity 211 are a primary reflector unit 235 comprising a first concave mirror 220 and a second concave mirror 230, and a component reflector unit 245 comprising a third concave mirror 240 facing the first concave mirror 220 and the second concave mirror 230. The first concave mirror 220, the second concave mirror 230, and the third concave mirror 240 are spherical mirrors with the same concave radius of curvature. The radius of curvature is typically about 2-15 cm, which determines the minimum physical length of the system and the achievable optical path length. First concave mirror 220, second concave mirror 230, and third concave mirror 240 are positioned with their centers of curvature radii aligned in the same longitudinal optical plane A, as shown schematically in the side view of FIG. 2b and the elevation view of component reflector unit 245 in FIG. 2c. Second concave mirror 230 and second concave mirror 230 are positioned essentially adjacent to one another and side-by-side within main reflector unit 235. This can be viewed as first concave mirror 220 and second concave mirror 230 having a common back surface transverse to the longitudinal optical plane, main reflector unit back surface B, which runs around the periphery of the spherical surfaces associated with first concave mirror 220 and second concave mirror 230, respectively. Similarly, a component reflector unit back surface C, also transverse to the longitudinal optical plane C, can be defined that includes the periphery of the spherical surface associated with third concave mirror 240 and is symmetrical about third concave mirror 240. The main reflector unit back surface B and the component reflector unit back surface C are perpendicular to the longitudinal optical plane A, and the main reflector unit back surface B is parallel to the component reflector unit back surface C.

[0034] The distance between the main reflector unit back surface B and the component reflector unit back surface C is close to the radius of curvature of the first concave mirror 220, the second concave mirror 230 and the third concave mirror 240 according to the White Cell geometry.

[0035] Alternatively, the third mirror may comprise several facets arranged in an overall concave configuration, each facet being a flat mirror. Such a configuration of the third mirror produces good results when the distance between the main reflector unit and the component reflector unit is approximately the same as the radii of curvature of the first and second mirrors. Hereinafter, the third mirror will be referred to as a concave mirror.

[0036] Both the component reflector unit 245 and the main reflector unit 235 are typically rectangular in shape, extending further longitudinally than laterally. The optimal minimum shape of the active area of ​​the main reflector unit 235 depends on the actual active emitter area, which is ideally magnified onto the main reflector unit 235 by the concentrator. Typically, this image is 10 to 40 times larger than the emitter source. The third concave mirror 240 may have dimensions of 10 x 35 mm, and the first concave mirror 220 and second concave mirror 230 may each have dimensions of approximately 10 x 15 mm.

[0037] It should be understood that the first concave mirror 220 provided adjacent to the second concave mirror 230 may abut the first concave mirror 220. However, they may also be positioned with a small distance between them. According to one embodiment, the first concave mirror 220 and the first concave mirror 220 are provided as a continuous structure contained in the main reflector unit 235, essentially forming a mirror unit with two distinct curvatures. Such a monolithic dual-mirror design may be advantageous because it firmly fixes the relative positions of the centers of the two radii of curvature, a highly sensitive parameter for the propagation of light rays within the multipass cell. Any small change in this parameter value, d, will result in a large change in the d, with consequent transmission signal loss at the beam exit. * Move the final output position by N (N = number of single paths in the cell).

[0038] Light source 210 is positioned adjacent to or within component reflector unit 245 and is oriented such that emitted light is directed essentially towards primary reflector unit 235. Light source 210 is positioned laterally offset to longitudinal optical plane A, providing a 3D White cell geometry that results in at least two rows of light spots, top row 246 and bottom row 247, on component reflector unit 245 as illustrated in Figure 2c.

[0039] According to one embodiment of the present invention, the light source 210 is positioned with its light emitting portion coinciding with an imaginary sphere associated with the third concave mirror 240. According to one embodiment, the light source 210 is provided outside the third concave mirror 240, but is preferably integrated within the component reflector unit 245. According to one embodiment, the light source 210 is provided within a light source opening 221 in the third concave mirror 240. Typically and preferably, the light source 210 is provided closer to one end of the third concave mirror 240 in the extension direction than to the center.

[0040] In the multi-pass spectroscopic absorption cell 200 according to the present invention, the component reflector unit 245 is provided with a first detector 250 and a second detector 260 adapted to measure the intensity of incoming light. According to one embodiment, at least one of the first detector 250 and the second detector 260 is provided in an opening in the third concave mirror 240. According to one embodiment, the first detector 250 is provided in the first detector opening 251 and the second detector 260 is provided in the second detector opening 261. Preferably, the first detector 250 and the second detector 260 are aligned with an imaginary spherical surface associated with the third concave mirror 240.

[0041] In a multi-pass spectroscopic absorption cell 200 according to the present invention, a light source 210 is arranged to emit a first portion of light that is initially reflected by a first concave mirror 220 and a second portion of light that is initially reflected by a second concave mirror 230, as shown schematically in top view (e) and elevation view (f) in Figures 2e-2f. The light that initially reflects in the first concave mirror 220 is arranged to form a first optical path 222 that includes multiple reflections between a main reflector unit 235 and a component reflector unit 245, and this first optical path 222 terminates in a first detector 250. For simplicity, only the first reflection is illustrated in the figures. The multiple reflections are typically and preferably a predetermined number of reflections, such as 16 reflections, resulting in an optical path length of about 1 meter. Light that first reflects in the second concave mirror 230 is arranged to form a second optical path 223 that terminates in the second detector 260, as illustrated schematically in top view (g) and elevation view (h) in Figures 2g-2h.

[0042] According to one embodiment, the second optical path 223 includes only one reflection within the main reflector unit 235 and the second detector opening 261, corresponding to the emitted light being reflected only once by the second concave mirror 230, and the second detector 260 is positioned at a position within the third concave mirror 240.

[0043] According to one embodiment, second optical path 223 includes a predetermined number of reflections between main reflector unit 235 and component reflector unit 245. Accordingly, second detector aperture 261 and second detector 260 are positioned at positions associated with the predetermined number of reflections.

[0044] The curvature of a concave mirror, although described as spherical, may have a slightly elliptical form to correct for anastigmatic imperfections. Such corrections are well known in the art, and the term spherical mirror, as used herein, encompasses such variations and corrections.

[0045] According to one embodiment, illustrated schematically in Figure 2c, light source 210 is provided in first half 246 and first detector 250 is provided in second half 247 of component reflector unit 245. Second detector 260 is provided in the same half of component reflector unit 245 as light source 210.

[0046] According to one embodiment, a first portion of the light, which is arranged to first reflect off the first concave mirror 220 and follows the first optical path 222, represents a majority of the light emitted by the light source 210. Consequently, a second portion of the light, which is arranged to first reflect off the second concave mirror 230 and follows the second optical path 222, represents a minority of the light emitted by the light source 210. The relationship between the majority and minority light should be selected in relation to the desired S / N requirements for the two detectors. The majority of the emitted light, i.e., the light in the first optical path, represents, for example, at least 75% of the emitted light, for example, at least 85% of the emitted light, or for example, at least 95% of the emitted light. The desired proportion of the emitted light in the first optical path can be controlled by the positioning of the light source 210 relative to the light source opening 221 and the size and shape of the light source opening 221.

[0047] According to one embodiment, the first detector 250 is configured to measure light intensity in a first wavelength range, and the second detector 260 is configured to measure light intensity in a second wavelength range, the second wavelength range being distinct from the first wavelength range. The first wavelength range may relate to a first substance, and the second wavelength range may relate to a second substance. The first detector 250 may be configured to provide a signal related to the target substance, and the second detector 260 may be configured to provide a signal related to the tracer substance. The term "target substance" refers to a substance whose concentration is of primary interest. The term "tracer substance" refers to a substance whose concentration is of primary interest to facilitate measurement of the target substance concentration, e.g., to eliminate the effects of confounding factors or to relate the measurement to a specific condition. Typically, the concentration of the target substance is expected to be substantially lower than the concentration of the tracer substance. When the multi-path spectroscopic absorption cell 200 is utilized in a breath alcohol sensor system, the first substance / target substance is alcohol and the second substance / tracer substance is carbon dioxide or water.

[0048] According to one embodiment, the first detector 250 and the second detector 260 are arranged to measure light intensity within the same wavelength range, thereby providing a measure of the concentration of the same substance. In such a case, an arrangement using two separate light paths and two detectors can be utilized to extend the sensitivity range of the multi-path spectroscopic absorption cell 200, with the first light path 222 (longer light path) providing accurate measurement of a lower concentration range and the second light path (shorter light path) providing accurate measurement of a higher concentration range of the measured substance. Alternatively, or in combination, a setup using the first detector 250 and the second detector 260 arranged to measure light intensity within the same wavelength range can be utilized primarily to provide redundancy and / or facilitate functional control or calibration.

[0049] The multi-path spectroscopic absorption cell 200 can be incorporated into a wide variety of gas sensor devices. A gas sensor device 300 according to the present invention is illustrated schematically in FIG. 3. The gas sensor device 300 is suitable for use as a breath analysis device, particularly, but not exclusively, for measuring alcohol content in breath samples with the aid of tracer substances such as water vapor or carbon dioxide. In the following, breath analysis devices are described as non-limiting examples. Other gas sensor devices in which the multi-path spectroscopic absorption cell 200 is a central part include, but are not limited to, devices configured for measurements in which there is overlap between the target substance and the water vapor absorber. Examples of such devices are gas sensors for measuring nitrous oxide, methane, and carbon dioxide.

[0050] The gas sensor device 300 includes a multipath spectroscopic absorption cell 200 with a measurement cavity 211, a gas inlet 212, and a gas outlet 213 contained within a housing 301. The gas inlet 212 and gas outlet 213 of the measurement cavity 211 are connected to an inlet 302 and an outlet 303 of the housing 301. During use, a gas sample 304, e.g., a breath sample, is drawn into the measurement cavity 211 for analysis of the content of tracer substances and other substances, e.g., toxic substances. The inlet 302 may include a heater 311 arranged to heat the gas sample. Heating the gas sample may be important due to the temperature dependence of the measurement and also to avoid condensation in parts of the measurement cavity 211. A fan 312 is typically provided to provide a uniform airflow through the measurement cavity 211. The fan 312 may be provided at the outlet 304 of the housing 301.

[0051] In one embodiment of the present invention, the sensor signal is generated by non-dispersive infrared (NDIR) spectroscopy, where the light source 210 is an IR source and the first and second detectors 250 are IR-sensitive detectors. Suitable light sources and detectors are commercially available. In one embodiment, the first detector 250 is tuned to the absorption spectrum of an intoxicant, typically ethyl alcohol, and the second detector 260 is tuned to the absorption spectrum of CO2 or water. CO2 has a strong absorption peak at a wavelength of 4.26 μm, while H2O has relatively broad peaks at 2.5-2.8 and 5.3-7.6 μm. Ethyl alcohol has a specific peak at 9.5 μm that is not shared by any of the most common interfering substances but has little cross-sensitivity to CO2.

[0052] The IR source, light source 210, and first and second detectors 250, 260 are preferably operated synchronously using repetition and sampling rates exceeding the frequency bandwidth required for analyzing the breath signal. Synchronous operation using phase-locking techniques is preferred from the standpoint of noise and interference suppression. A repetition and sampling rate of 5 Hz is considered the lower limit compatible with the response time of MEMS-based (microelectromechanical systems) IR emitters and photovoltaic or thermopile IR detectors.

[0053] Interface electronics 321, 322, 323, 324, 325 respectively control the heater 311, light source 210, first detector 250, second detector 260, and fan 312. Each of these subsystems contains electronic drive and power control devices that accommodate different functions manageable by a general-purpose digital microcontroller, central processing unit (CPU) 310. Also included in the gas sensor device 300 are memory devices 332, 333 for permanent and temporary storage of information.

[0054] The CPU 310 and memory devices 332 and 333 are arranged to control the transfer and storage of data, including the sensor signals, during the analysis described below, as well as to control the method steps and perform the mechanical operations described below in real time. As will be appreciated by those skilled in the art, other configurations are possible to provide the control and calculation functions shown here, and the above should be considered an illustrative example and one embodiment. One alternative embodiment is for the breath analysis system to be integrated with other measurement and / or control systems in the vehicle, with the functions of CPU 331 being provided by a main CPU in the vehicle that also handles other tasks, and the detectors and other units of the gas sensor device 300 communicating via a vehicle bus system or the like.

[0055] The gas sensor device 300 may include or be connected to a human / machine interface (HMI) unit 334 for audiovisual communication between the system and the user. The HMI unit 334 typically includes a microphone / loudspeaker, a touchscreen, or other input / output devices for communication. It is capable of visual, verbal, or symbolic communication of specific requests and classification results to a subject. Alternatively, the gas sensor device 300 may be connected to or utilize an existing infotainment system in a vehicle for human / machine interfacing.

[0056] In automotive applications, the system may include a vehicle drivability control unit 335 connected directly to the vehicle control system, which provides the "Alcolock" functionality. In fossil fuel-powered vehicles, unit 335 may control the ignition; in other types of vehicles, it controls other basic drive mechanisms.

[0057] A communication unit 336 may be provided for wireless information exchange between the gas sensor device 300 and other external units, preferably via the Internet, which is useful in a wide range of applications.

[0058] In one embodiment of the present invention, the above-described dual-wavelength setup is provided without significantly increasing the size of the White cell, particularly without increasing the size of the mirrors. One implementation of a White-type multi-pass spectral absorption cell 200 according to such an embodiment is schematically depicted in FIGS. 4a-4g. As depicted in a top view in FIG. 4a, the multi-pass spectral absorption cell 200 includes a measurement cavity 211 provided with at least one gas inlet 212 and at least one gas outlet 213. Disposed within the measurement cavity 211 are a primary reflector unit 435 including a first concave mirror 420 and a second concave mirror 430, and a component reflector unit 445 including a third concave mirror 440 facing the first concave mirror 420 and the second concave mirror 430. The first concave mirror 420, the second concave mirror 430, and the third concave mirror 440 are spherical mirrors with the same concave radius of curvature. The radius of curvature, typically on the order of 2-15 cm, determines the minimum physical length of the system as well as the achievable optical path length. First concave mirror 420, second concave mirror 430, and third concave mirror 440 are arranged with their centers of curvature aligned within a common longitudinal optical plane A, as illustrated schematically in the side view of FIG. 4b, the elevation view of component reflector unit 445 in FIG. 4c, and the elevation view of main reflector unit 435 in FIG. 4d. Second concave mirror 430 and third concave mirror 440 are positioned essentially adjacent to each other and side-by-side within main reflector unit 435. This can be viewed as first concave mirror 420 and second concave mirror 430 having a common back surface, main reflector unit back surface B, which runs around the periphery of the sphere associated with first concave mirror 420 and second concave mirror 430, respectively. Similarly, a component reflector unit back surface C may be defined that includes the periphery of the sphere associated with third concave mirror 440 and is symmetrical about third concave mirror 440. Component reflector unit back surface C is positioned transverse to a common longitudinal optical plane A. Primary reflector unit back surface B and component reflector unit back surface C are positioned at an angle α relative to one another such that the normal to primary reflector unit back surface B forms angle α with the normal to component reflector unit back surface C only in longitudinal optical plane A.This tilt of main reflector unit 435 relative to component reflector unit 445 is illustrated in FIG. 4a, where main reflector unit back surface B forms angle α with the component reflector unit back surface C plane when viewed from above, with imaginary plane C' shown near plane B. In the side view, FIG. 4b, the projections of planes B and C are parallel and both are perpendicular to longitudinal optical plane A. In FIG. 4c, the normals to main reflector unit back surface B and component reflector unit back surface C and angle α are shown. The effect of tilted main reflector unit 435 is further illustrated in FIGS. 4d-4e, which illustrate the relationship of the optical axes of first concave mirror 420, second concave mirror 430, and third concave mirror 440, where d) is a prior art mirror arrangement without tilt and b) is a tilted optical arrangement according to this embodiment.

[0059] The distance between the main reflector unit back surface B and the component reflector unit back surface C is close to the radius of curvature of first concave mirror 420, second concave mirror 430, and third concave mirror 440 according to the White Cell geometry.

[0060] Both the component reflector unit 445 and the main reflector unit 435 are typically rectangular in shape, extending further longitudinally than laterally. The optimal minimum shape of the active area of ​​the main reflector unit 435 depends on the actual active emitter area, which is ideally magnified onto the main reflector unit 435 by the concentrator. Typically, this image is 10 to 40 times larger than the emitter source. The third concave mirror 440 may have dimensions of 10 x 35 mm, and the first concave mirror 420 and second concave mirror 430 may each have dimensions of approximately 10 x 15 mm.

[0061] It should be understood that the first concave mirror 420 provided adjacent to the second concave mirror 430 can abut. However, they can also be positioned with a small distance between them. According to one embodiment, the first concave mirror 420 and the first concave mirror 420 are provided as a continuous structure contained in the main reflector unit 435, essentially forming a mirror unit with two distinct curvatures. Such a monolithic dual-mirror design can be advantageous because it firmly fixes the relative positions of the centers of the two radii of curvature, a highly sensitive parameter for ray propagation within a multipass cell. Any small change d in this parameter value shifts the final output position by d*N (N = the number of single passes in the cell), with a resulting transmission signal loss at the beam exit.

[0062] Light source 410 is positioned adjacent to or within component reflector unit 445 and is oriented such that emitted light is directed essentially toward main reflector unit 435. Light source 410 is positioned laterally offset to longitudinal optical plane A, providing a 3D White cell geometry that, during use, results in at least two rows of light spots on component reflector unit 445: top row 446 and bottom row 447, as illustrated in FIG. 4d. As a result of angle α between main reflector unit 435 and component reflector unit 445 in accordance with the present invention, the positions in the longitudinal distance between the light spots in bottom row 447 are shifted, while the light spots in top row 446 are not shifted compared to an equivalent White cell with main reflector unit back face B parallel to component reflector unit back face C, as illustrated in FIG. 1b. The shift of the light spots in bottom row 447 depends on angle α as well as the dimensions of the mirrors and the number of passes (optical path length) between the mirrors by simple trigonometry. Those skilled in the art, with knowledge of the geometry of the White cell and insight into this description, will readily calculate the angle α corresponding to a particular shift. For a multi-pass spectroscopic absorption cell 200 in which the third concave mirror 440 has dimensions of 10×35 mm, the first concave mirror 420 and the second concave mirror 430 each have dimensions of approximately 10×15 mm, and with an optical path length of 100 mm and 2 to 5 passes, suitable angles range from 2° to 15°.

[0063] According to one embodiment of the present invention, angle α is selected to cause a shift in the position of the light spots in the lower row 447, as shown schematically in FIG. 4g, so that their longitudinal positions are essentially the same as those of the light spots in the upper row 446. Thus, second detector 460 and corresponding second detector opening 261 can be positioned below first detector 450 and corresponding first detector opening 251, and a component reflector unit 445 with two detectors can be provided without any increase in size or with a very limited increase in size. This corresponds to a cell angle α of 6° according to the example described above. As shown in FIGS. 4a and 4c, light source 410, first detector 450, and second detector 460 are arranged on a common printed circuit board 415. Printed circuit board 415 is attached to component reflector unit 445.

[0064] According to one embodiment of the present invention, the light source 410 is positioned with its light emitting portion coinciding with an imaginary sphere associated with the third concave mirror 440. According to one embodiment, the light source 410 is provided outside the third concave mirror 440, but is preferably integrated within the component reflector unit 445. According to one embodiment, the light source 410 is provided within the light source opening 221 in the third concave mirror 440. Typically and preferably, the light source 410 is provided closer to one end of the third concave mirror 440 in the extension direction than to the center.

[0065] The curvature of a concave mirror, although described as spherical, may have a slightly elliptical form to correct for anastigmatic imperfections. Such corrections are well known in the art, and the term spherical mirror, as used herein, encompasses such variations and corrections.

[0066] The embodiment described with reference to FIGS. 4a-4g is readily implemented in the gas sensor device 300 described with reference to FIG. The above-described embodiments are to be understood as illustrative examples of the system and method of the present invention. It will be understood by those skilled in the art that various modifications, combinations, and changes can be made to the embodiments. In particular, different part solutions in different embodiments can be combined in other configurations, where technically possible.

Claims

1. A multi-pass spectroscopic absorption cell (200) comprising a measurement cavity (211) provided with at least one gas inlet (212) and at least one gas outlet (213), wherein: a main reflector unit (235; 435) comprising a first concave mirror (220; 420) and a second concave mirror (230; 430), a component reflector unit (245; 445) comprising a third mirror 240 facing the first concave mirror (220; 420) and the second concave mirror (230; 430), the first concave mirror (220; 420) and the second concave mirror (230; 430) being spherical mirrors with the same concave radius of curvature and arranged with their centers of curvature aligned in the same longitudinal optical plane A; a light source (210) provided adjacent to or within said component reflector unit (245; 445) and arranged to direct emitted light towards said main reflector unit (235; 435), said light source (210) being positioned laterally offset to said longitudinal optical plane A; and a first detector (250) provided adjacent to or within said component reflector unit (245; 445); Equipped with The multi-pass spectroscopic absorption cell comprises: a second detector (260) provided adjacent to or within said component reflector unit (245; 445), characterized in that said light source (210) is arranged to emit a first portion of said light, which is first reflected by said first concave mirror (220; 420) to form a first optical path (222) that ends at said first detector (250), and to emit a second portion of said light, which is first reflected by said second concave mirror (230; 430) to form a second optical path (223) that ends at said second detector (260).

2. 2. The multi-pass spectroscopic absorption cell (200) of claim 1, wherein the first detector (250) is provided in a first detector opening (251) in the third mirror (240; 440) and / or the second detector (260) is provided in a second detector opening (261) in the third mirror (240; 440).

3. 3. The multi-path spectroscopic absorption cell (200) of claim 1 or 2, wherein the second optical path (223) includes the second detector opening (261) positioned in the third mirror (240; 440) corresponding to a position where there is only one reflection at the main reflector unit (235; 435) and where the emitted light is reflected only once by the second concave mirror (230; 430).

4. 4. A multi-pass spectroscopic absorption cell (200) according to any one of claims 1 to 3, wherein the light source (210) is provided in a first half (246), the first detector (250) is provided in a second half (247) of the component reflector unit (245; 445), and the second detector (260) is provided in the same half of the component reflector unit (245; 445) as the first detector (250).

5. 5. A multi-pass spectroscopic absorption cell (200) according to claim 1, wherein the first portion of the light that follows the first optical path (212) and is arranged to initially reflect off the first concave mirror (220; 420) constitutes a majority of the light emitted by the light source (210).

6. 6. A multi-pass spectroscopic absorption cell (200) according to any one of claims 1 to 5, wherein the first optical path (212) includes a predetermined number of reflections between the main reflector unit (235; 435) and the component reflector unit (245; 445).

7. 7. The multi-pass spectroscopic absorption cell (200) of claim 6, wherein the first optical path (212) is longer than the second optical path (223), preferably at least twice as long, and even more preferably at least four times as long.

8. 6. The multi-pass spectroscopic absorption cell (200) of claim 5, wherein the majority of the light beam (212) that is directed to reflection in the first mirror (220; 420) accounts for at least 75% of the emitted light, preferably at least 85% of the emitted light, and even more preferably at least 95% of the emitted light.

9. 9. The multi-pass spectroscopic absorption cell (200) of claim 1, wherein the first detector (250) is arranged to measure light intensity in a first wavelength range and the second detector (260) is arranged to measure light intensity in a second wavelength range, the second wavelength range being separate from the first wavelength range.

10. The first concave mirror (220; 420) and the second concave mirror (230; 430) are 10. The multi-pass spectroscopic absorption cell (200) of any one of claims 1 to 9, provided as a continuous structure contained by the main reflector unit (235; 435) to form a continuous mirrored surface with two distinct curvatures.

11. - the first concave mirror (420) and the second concave mirror (430) are arranged such that the main reflector unit back surface B is the common symmetrical back surface of the first concave mirror (420) and the second concave mirror (430); - said third mirror (440) is concave and said component reflector unit has a rear surface C symmetrical to said third concave mirror (440); - the first concave mirror (420), the second concave mirror (430), and the third concave mirror (440) are spherical mirrors, have the same concave radius of curvature, and are arranged with their centers of curvature radii aligned in the same longitudinal optical plane A; 11. A multi-pass spectroscopic absorption cell (200) according to any of claims 1 to 10, wherein the component reflector unit back surface C is arranged transverse to the common longitudinal optical plane A, and the main reflector unit back surface B and the component reflector unit back surface C are arranged relative to each other such that the normal to the main reflector unit back surface B forms an angle α with the normal to the component reflector unit back surface C in the longitudinal optical plane A.

12. 12. The multi-pass spectral absorption cell (200) of claim 11, wherein the multi-pass spectral absorption cell (200) is arranged to provide an upper row of light spots (446) and a lower row of light spots (447) on the component reflector unit (445), and the angle α is selected to cause a shift of the light spots in the lower row (447) so that at least a majority of the light spots in the lower row are at the same longitudinal position as the light spots (446) of the upper row.

13. A gas sensor (300) comprising a multi-pass spectroscopic absorption cell (200) according to any one of claims 1 to 12.

14. 14. The gas sensor (300) of claim 13, wherein the first wavelength range pertains to a first material and the second wavelength range pertains to a second material.

15. 15. The gas sensor of claim 14, wherein the first detector is positioned to provide measures related to the concentrations of the first and second substances, wherein the signal related to the concentration of the first substance provided by the first detector is related to a target substance, and the signal related to the concentration of the second substance provided by the second detector is related to a tracer substance, and wherein the concentration of the target substance is expected to be substantially lower than the concentration of the tracer substance under normal measurement conditions.

16. An alcohol meter comprising a gas sensor (300) according to claim 13, wherein the first substance is alcohol and the second substance is carbon dioxide or water.

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