# US 2012/0075618 A1 · Photoacoustic sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2012/0075618 A1 - Document ID: US20120075618A1 - Status: Published application - Kind: A1 - Application number: 13/312,368 - Filed: 2011-12-06 - Published: 2012-03-29 - Earliest claimed: 2008-08-21 - Assignees: Honeywell International Inc. - Inventors: Bernard S. Fritz; Matthew S. Marcus - Web page: https://patentgrep.com/patent/US20120075618A1 ## CPC - G01N 21/1702: {with opto-acoustic detection, e.g. for gases or analysing solids} - G01N 2021/1704: {in gases} - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract Embodiments of the apparatus, systems, and methods relate to a photoacoustic sensor includes an excitation source, a modulator, a quantum dot filter, an interferometer, a gas chamber, and a microphone. The excitation source generates a monochromatic light. The modulator intensity modulates the monochromatic light at a first modulation frequency. The quantum dot filter down converts the modulated monochromatic light into a broadband spectrum of infrared light. The interferometer further intensity modulates the broadband spectrum such that the at least one wavelength component of the broadband spectrum is further intensity modulated at a second modulation frequency. The gas chamber stores a sample gas and receives the plurality of modulated wavelength components. The microphone detects pressure changes within the gas chamber to produce an acoustic signal, which can be used to analyze properties of the sample gas. ## Claims ### Claim 1 A photoacoustic sensor comprising: a quantum dot filter to down convert an input monochromatic light into a broadband spectrum of infrared light, which includes a plurality of wavelength components with distinct wavelengths; and an interferometer to intensity modulate the broadband spectrum, wherein at least one of the plurality of wavelength components is intensity modulated at a modulation frequency related to a scanning speed of the interferometer and a distinct wavelength of the wavelength component to produce an output resultant broadband spectrum of infrared light. ### Claim 2 (depends on 1) The photoacoustic sensor of claim 1, further comprising: a gas chamber to store a sample gas and to receive the output resultant broadband spectrum of infrared light. ### Claim 3 (depends on 2) The photoacoustic sensor of claim 2, further comprising: a microphone coupled to the gas chamber to detect pressure changes within the gas chamber to produce an acoustic signal representative of properties of the sample gas. ### Claim 4 (depends on 2) The photoacoustic sensor of claim 2, wherein the gas chamber comprises at least one gas permeable wall through which a sample gas may be introduced. ### Claim 5 (depends on 1) The photoacoustic sensor of claim 1, wherein the modulation frequency is directly proportional to the interferometer scanning speed and is inversely proportional to the distinct wavelength of the at least one wavelength component. ### Claim 6 (depends on 1) The photoacoustic sensor of claim 1, further comprising: an excitation source to generate a monochromatic light; a modulator to intensity modulate the monochromatic light at a pre-modulation frequency into the input monochromatic light. ### Claim 7 (depends on 6) The photoacoustic sensor of claim 6, wherein the output resultant broadband spectrum of infrared light is modulated at a resultant frequency of the pre-modulation frequency and the modulation frequency. ### Claim 8 A method of detecting gas by a photoacoustic sensor, comprising: down-converting an input monochromatic light to emit a broadband spectrum of infrared light, which includes a plurality of wavelength components with distinct wavelengths; and intensity modulating the broadband spectrum of infrared light by an interferometer, wherein at least one of the plurality of wavelength components is intensity modulated at a modulation frequency, which is related to a scanning speed of the interferometer and a distinct wavelength of that wavelength component, to produce an output broadband spectrum. ### Claim 9 (depends on 8) The method of claim 8, further comprising: receiving the output broadband spectrum within a gas chamber; and detecting pressure changes within the gas chamber to produce one or more acoustic signals corresponding to one or more energy absorption of one or more gases within in the gas chamber. ### Claim 10 (depends on 8) The method of claim 8, wherein the modulation frequency is directly proportional to the interferometer scanning speed and is inversely proportional to the distinct wavelength of the at least one wavelength component. ### Claim 11 (depends on 8) The method of claim 8, further comprising: generating a monochromatic light from an excitation source; intensity modulating the monochromatic light at a pre-modulation frequency to produce the input monochromatic light. ### Claim 12 (depends on 11) The method of claim 11, wherein the pre-modulation frequency is in a range of 0-10 kilohertz. ### Claim 13 (depends on 11) The method of claim 11, wherein the output broadband spectrum of infrared light is modulated at a resultant frequency of the pre-modulation frequency and the modulation frequency. ### Claim 14 (depends on 8) The method of claim 8, further comprising: selecting the quantum dot filter such that the distinct wavelength of the at least one wavelength component of the broadband spectrum of infrared light emitted by the quantum dot filter corresponds to an energy absorption band of one of a plurality of target sample gases. ### Claim 15 A photoacoustic gas sensing system comprising: an interferometer to intensity modulate a broadband spectrum, wherein each wavelength component is intensity modulated at a modulation frequency, which is a function of a scanning speed of the interferometer and a distinct wavelength of each wavelength component, to produce a resultant broadband spectrum of infrared light; and a gas chamber to store a sample gas and to receive the resultant broadband spectrum of infrared light. ### Claim 16 (depends on 15) The photoacoustic gas sensing system of claim 15, wherein the modulation frequency is directly proportional to the interferometer scanning speed and is inversely proportional to the distinct wavelength of the at least one wavelength component. ### Claim 17 (depends on 15) The photoacoustic gas sensing system of claim 15, further comprising: an intensity modulated excitation source to produce the broadband infrared spectrum. ### Claim 18 (depends on 15) The photoacoustic gas sensing system of claim 15, further comprising: a microphone positioned onto the gas chamber to detect pressure changes within the gas chamber to produce an acoustic signal representative of properties of the sample gas. ### Claim 19 (depends on 18) The photoacoustic gas sensing system of claim 18, further comprising: a processor electrically coupled to the microphone to receive the acoustic signal. ### Claim 20 (depends on 19) The photoacoustic gas sensing system of claim 19, wherein the processor performs calculations on the acoustic signal to identify one or more gases contained in the gas chamber and a concentration related to the one or more gases.