Patent Description:
Gas detection based on a non-dispersive infrared (NDIR) technique, in particular those operating in the mid-wavelength IR (MWIR) (<NUM>-<NUM>), generally lack efficient optical sources. And, in applications where a high signal to noise ratio is desired, optical power must be raised. This can result in high power consumption which can pose serious limitations on portable and/or wireless form factor operations, in some applications.

Alternatively, a more sensitive and lower noise detector can be used in some implementations to attain high performance without raising power consumption. However, commercially available MWIR detectors can be expensive, and some detectors require cooling which can add components to the system, among other possible issues, in such implementations.

<CIT> discloses a photoacoustic detector, comprising at least a first chamber (VO) suppliable with a gas to be analyzed, a window for letting modulated and/or pulsed infrared radiation and/or light in the first chamber (VO), a second chamber (V), which constitutes a measuring space with a volume V and which is in communication with the first chamber by way of an aperture provided in a wall of the first chamber, at least one sensor, which is arranged in the wall aperture of the first chamber and arranged to be movable in response to pressure variations produced in the first chamber by absorbed infrared radiation and/or light, and means for measuring the sensor movement.

The present invention is directed to a gas detecting system comprising a gas detector device with a Golay cell as defined by the appended independent claim <NUM>. Particular embodiments of the invention are defined in the appended dependent claims.

A gas detecting system comprising a gas detector device with a Golay cell is described herein. The Golay cell includes a microphone having a front surface with a sound collecting aperture for receiving sound, a substrate, a gas cavity formed in the substrate such that the gas cavity is in gas communication with the sound collecting aperture and the front surface forms a side surface of the gas cavity, and a window abutting the substrate to form a side surface of the gas cavity. The substrate that provides the structural basis for the gas cavity is a printed circuit board (PCB) containing electronic components electrically interconnected with the microphone or with the microphone and other components of a device into which the gas detector is provided.

This disclosure describes creating and utilizing a gas detector using a Golay cell that can, for example, be used as a low cost light detector capable, for example, of detecting a very low level of MWIR radiation and its implementation in an NDIR detector. The detector embodiments of the present disclosure are based on the principle of a Golay cell which is used in infrared and terahertz radiation detections. The Golay cell design of embodiments of the present disclosure can take advantage of the availability of low-cost, high sensitivity microelectromechanical system (MEMS) microphones proliferated by the mobile phone industry. The Golay cell in some embodiments, integrates the microphone with a gas cell of comparable volume, while using the gas or the microphone as an optical absorber. That is, the absorbing material can be the gas and/or the microphone.

In embodiments of the present disclosure, the pressure sensing element, (e.g., the diaphragm, in a conventional Golay cell) is part of the MEMS microphone and can provide sensitive detection of pressure fluctuation in a gas cavity due to absorption of electromagnetic radiation. As discussed above, this functionality would otherwise take a much more expensive and/or complex instrumentation to accomplish. In some embodiments of the present disclosure the microphone structure itself can be used as a heat sensor.

These embodiments are described in sufficient detail to enable those of ordinary skill in the art to practice one or more embodiments of this disclosure. It is to be understood that other embodiments may be utilized and that process changes may be made without departing from the scope of the present disclosure.

As will be appreciated, within the scope defined by the appended claims, elements shown in the various embodiments herein can be added, exchanged, combined, and/or eliminated so as to provide a number of additional embodiments of the present disclosure. The proportion and the relative scale of the elements provided in the figures are intended to illustrate the embodiments of the present disclosure, and should not be taken in a limiting sense.

Directional terms such as "horizontal" and "vertical" "above" and "below" are used with reference to the component orientation depicted in <FIG>. These terms are used for example purposes only and are not intended to limit the scope of the appended claims.

For example, <NUM> may reference element "<NUM>" in <FIG>, and a similar element may be reference as <NUM> in <FIG>.

As used herein, "a" or "a number of' something can refer to one or more such things. For example, "a number of apertures" can refer to one or more apertures.

<FIG> illustrates a gas detector device of a gas detecting system in accordance with one or more embodiments of the present disclosure. In the embodiment illustrated in <FIG>, the device <NUM> includes a microphone <NUM> having a front surface <NUM> and a sound collecting aperture <NUM>, a gas cavity <NUM> formed in substrate <NUM> such that the gas cavity <NUM> is in gas communication with the aperture <NUM> and wherein the front surface forms a side surface of the gas cavity <NUM>, and a <NUM> window abutting the substrate <NUM> to form a side surface of the gas cavity <NUM>. In some embodiments, the substrate may have electronic components <NUM> mounted on one or both side of its surfaces. These components can be related to the functioning of the gas detector or can be components not related to the function of the gas detector, but located proximate to the gas detector.

In some embodiments, the window can include optical characteristics that change the characteristics of the light passing through the window. For example, the window can have a diffusing or collimating characteristic designed into the window. In some embodiments, the window could also be a lens or waveguide.

These optical characteristics can be accomplished based on the formation of the interior of the window, the formation and/or preparation (e.g., polishing) of one or more sides of the window, and/or through the use of coatings applied to the window on one or more sides. The window can also be coated with optical films to enhance or retard the transmission of light at certain wavelengths. This may be beneficial in some embodiments to isolate or focus certain wavelengths for purposes of improving detection. For example, certain wavelengths that can be isolated or enhanced can be <NUM> and/or <NUM> micrometers for hydrocarbons, <NUM> micrometers for CO<NUM>, or <NUM> micrometers for ammonia, among others.

In the embodiments of the present disclosure, the gas cavity (formed by other elements of the device, such as the one or more substrates, the window, and the microphone) is a closed cell that does not allow interaction with the ambient surroundings. Accordingly, the gas within the closed cell can be selected to enhance the sensitivity for the presence of a particular gas or a particular set of gases.

In accordance with the present invention, the substrate <NUM> is a printed circuit board.

(PCB) and the microphone <NUM> is electrically connected with the substrate <NUM>. Additionally, in some embodiments, the structure comprising the substrate can be of multiple layers rather than a single substrate layer, as shown in <FIG>. In various embodiments, the microphone and/or the window can be attached to the substrate <NUM> such that the gas cavity <NUM> is hermetically sealed. Such embodiments allow for formation of a gas filled cavity which is fluidly connected to the microphone inlet port (i.e., aperture <NUM>) but insulated from the ambient conditions.

When radiative power (e.g., light from a light source) <NUM> enters the gas cavity <NUM> through the window <NUM> and is absorbed by the gas and/or microphone surfaces, a small amount of heat can be generated. The heat causes a pressure rise which can be sensed by the microphone.

The fill gas in the cavity <NUM> can be selected to optimize the sensitivity and/or temperature range of the detector, based on parameters such as specific heat, thermal conductivity, permeability, triple point, and/or chemical stability, among other parameters that can be utilized based upon the operating conditions of the detector.

The fill gas is at least one of nitrogen, hydrogen, argon, krypton, xenon, hydrocarbons, fluorocarbons, or a mixture of above gases. In various embodiments, the pressure of the fill gas can be less or larger than the ambient pressure.

For example, the fill gas pressure can range from 10kPa to 1000kPA (<NUM> bar to <NUM> bar), insome embodiments. An advantage of the detector is the isolation of the microphone from the ambient surroundings, thus eliminating interferences and instabilities due to environmental variables such as acoustic noise, pressure, density, moisture, chemicals, and particulates that are in the ambient surroundings around the device.

One benefit of using a PCB is to make electrical interconnects to the microphone (e.g., through surface mount soldering pads) thus the detector can be an integral part of a PCB and connected to other components on the same board. In some applications, a user could have several of these devices (e.g., on the same substrate, such as a PCB) each having different gases in their respective gas cavity and they could be inserted into a larger system, to accomplish gas detection. Additionally, in some embodiments" a single device (e.g., the structure of <FIG> or a similar structure) could be used in a system (e.g., a structure like that of <FIG> or another suitable structure) and that device could be removed and replaced with another that could sense one or more other gases. In other embodiments, multiple devices could be used at the same time (e.g., either on the same substrate or on different substrates) to sense multiple gases or could have the same gas in the gas cavity and could provide redundancy, which could be beneficial as it would provide increased certainty that the gas detection was correct.

<FIG> illustrates a gas detector system in accordance with one or more embodiments of the present disclosure. <FIG> shows a gas detector design which can be compact and have low power consumption in many implementations.

In the embodiment of <FIG>, the light wavelength detecting element <NUM> and an optical source <NUM> are face-to-face mounted on the opposite ends of a housing <NUM> with an optical cavity <NUM>, which can have a reflective internal surface finish <NUM> to facilitate maximum light entry into the detector <NUM>.

The optical source can, for example, be one or more filament bulbs, microelectromechanical systems (MEMS) hotplates, light emitting diodes (LEDs), and/or lasers. Such components can all potentially be advantageously paired with detector embodiments described herein to provide a gas sensor with good performance.

The reflective surface does not need to be reflective to visible light in all applications, but rather, may be reflective to one or more wavelengths that will be used with respect to detecting the particular one or more gases within the gas cavity.

In some embodiments, the surface of the optical cavity may have a texture. The texture may provide a more homogeneous light pattern that is directed to the detector. Further, in some embodiments, the surface may be non-reflective. At least part of the walls of the housing <NUM> with the optical cavity <NUM> are permeable to ambient gases via permeable material, holes (e.g., openings <NUM>), or porous media (porous at least to the wavelengths of light that will be useful for detection), thus the presence of gases of interest in the ambient surroundings that absorb the radiation could be detected by the detector when a reduction of received radiation at specific wavelengths (e.g., for example, wavelengths such as <NUM> or <NUM> micrometers for hydrocarbons, <NUM> micrometers for CO<NUM>, or <NUM> micrometers for ammonia, among others) is observed.

In order to be sensitive to specific gases, optical band-pass filters may be added as additional components in the optical path or a coating on the interior surface (nearer to the microphone) or the exterior surface <NUM> of the detector window. In some instances, even though the gas cavity has a particular gas therein, there may still be a need for filtering of ambient components that may have similar characteristics as the particular gas in the cavity.

In such situations, one or more filters, such as thin film, applied coatings, filters physically separate from the window, or other types of filters, could be placed in the path of the light from the light source to filter out such ambient noise (characteristics that may be mistaken for the particular gas in the cavity) associated with these ambient components. Such an implementation may also be done in applications having multiple gases within the cavity. Examples of ambient components that can be filtered can, for example, can include CO<NUM>, water vapor, or condensed water, among others.

In some embodiments where modulated or, for example, alternating current (AC) is utilized, since the Golay cell is only sensitive to modulated optical intensity, the optical source must be modulated at a certain frequency, for example, a frequency in the <NUM> to <NUM> range. The gas detector of this configuration can be operated at extremely low power because the Golay cell is able to detect a very low level of radiative power thus the optical source can be energized at correspondingly low levels.

Embodiments of the present disclosure can be constructed as a micro-Golay detector device with an elongate size (width of widest side of the microphone) of the microphone component being <NUM>-<NUM>. With such embodiments, these devices could be used in small and/or portable applications and such devices may have a lower power consumption as opposed to devices on the magnitude of <NUM>-<NUM> width dimension. Another benefit of a micro-Golay device is the reduced ability of contaminants to get into the device.

Claim 1:
A gas detecting system (<NUM>) comprising:
a gas detector device (<NUM>) with a Golay cell, the Golay cell comprising:
a microphone (<NUM>) having a front surface (<NUM>) with a sound collecting aperture (<NUM>) for receiving sound;
a substrate (<NUM>);
a gas cavity (<NUM>) configured to detect a first gas formed in the substrate (<NUM>) such that the gas cavity (<NUM>) is in gas communication with the sound collecting aperture (<NUM>) and the front surface (<NUM>) forms a side surface of the gas cavity (<NUM>);
wherein the gas cavity (<NUM>) includes a fill gas comprising at least one or more of hydrogen, argon, nitrogen, krypton, xenon, hydrocarbons, or fluorocarbons;
wherein the gas cavity (<NUM>) is sealed such that ambient gas cannot enter the gas cavity (<NUM>) once it is sealed;
a window (<NUM>) abutting the substrate (<NUM>) to form a side surface of the gas cavity (<NUM>), characterized in that the substrate (<NUM>) is a printed circuit board, and in that the microphone (<NUM>) is electrically connected with the substrate (<NUM>); and
in that the gas detector device (<NUM>) is replaceable to allow the replacement of the gas detector device (<NUM>) from the gas detecting system (<NUM>).