Optical measurement of atmospheric carbon dioxide - Revision history

Caoyuan: /* Possible measurement mechanisms */

2025-04-29T09:20:24Z

Possible measurement mechanisms

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	#Interferometry. Carbon dioxide has a slightly different refraction index for all wavelengths. By observing the change in interference patterns, we can tell if there is a change in carbon dioxide concentration due to a change in effective path length.		#Interferometry. Carbon dioxide has a slightly different refraction index for all wavelengths. By observing the change in interference patterns, we can tell if there is a change in carbon dioxide concentration due to a change in effective path length.

	In the end we chose single-wavelength spectroscopy, i.e. absorbance measurement to measure the CO<sub>2</sub> content.		In the end we chose single-wavelength spectroscopy, i.e. '''absorbance measurement''' to measure the CO<sub>2</sub> content.

	==Experiment Preparation==		==Experiment Preparation==

Caoyuan: /* Key objectives= */

2025-04-29T09:20:02Z

Key objectives=

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	As the IR beam passes through the sample gas chamber, CO₂ molecules absorb a fraction of the light at this wavelength, and the thermopile detector (sensitive in the mid-IR range) measures the transmitted IR intensity. The use of a thermopile provides a cost-effective and robust means of converting infrared energy to an electrical signal, but it also necessitates strategies to enhance the detection of small absorption-induced changes. Therefore, a lock-in amplifier technique will be integrated into the detection electronics to improve the signal-to-noise ratio. By modulating the IR source (for instance, with a chopper or by driving it with a sinusoidal waveform) and synchronously demodulating the detector output, the system can extract the CO₂ absorption signal from background noise with high fidelity.[4] This approach effectively amplifies the desired signal and filters out low-frequency drift or random noise, as demonstrated in prior CO₂ sensor research.[4] Overall, the purpose of the project is to realize an IR-based CO₂ sensing device that combines selectivity, sensitivity, and portability – using inexpensive components and innovative signal processing – to facilitate accurate CO₂ monitoring outside the laboratory setting.		As the IR beam passes through the sample gas chamber, CO₂ molecules absorb a fraction of the light at this wavelength, and the thermopile detector (sensitive in the mid-IR range) measures the transmitted IR intensity. The use of a thermopile provides a cost-effective and robust means of converting infrared energy to an electrical signal, but it also necessitates strategies to enhance the detection of small absorption-induced changes. Therefore, a lock-in amplifier technique will be integrated into the detection electronics to improve the signal-to-noise ratio. By modulating the IR source (for instance, with a chopper or by driving it with a sinusoidal waveform) and synchronously demodulating the detector output, the system can extract the CO₂ absorption signal from background noise with high fidelity.[4] This approach effectively amplifies the desired signal and filters out low-frequency drift or random noise, as demonstrated in prior CO₂ sensor research.[4] Overall, the purpose of the project is to realize an IR-based CO₂ sensing device that combines selectivity, sensitivity, and portability – using inexpensive components and innovative signal processing – to facilitate accurate CO₂ monitoring outside the laboratory setting.

	==Key objectives===		===Key objectives===
	*Accurate quantification of CO₂ via IR absorption: Develop the device to reliably measure carbon dioxide concentrations, ensuring that the IR absorption at 4.3 μm can be translated into an accurate quantitative reading of CO₂ levels. This entails calibrating the sensor and optimizing its design so that the CO₂ concentration is determined with high precision and accuracy.		*Accurate quantification of CO₂ via IR absorption: Develop the device to reliably measure carbon dioxide concentrations, ensuring that the IR absorption at 4.3 μm can be translated into an accurate quantitative reading of CO₂ levels. This entails calibrating the sensor and optimizing its design so that the CO₂ concentration is determined with high precision and accuracy.

Caoyuan: /* Objectives */

2025-04-29T09:19:53Z

Objectives

← Older revision		Revision as of 17:19, 29 April 2025
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	As the IR beam passes through the sample gas chamber, CO₂ molecules absorb a fraction of the light at this wavelength, and the thermopile detector (sensitive in the mid-IR range) measures the transmitted IR intensity. The use of a thermopile provides a cost-effective and robust means of converting infrared energy to an electrical signal, but it also necessitates strategies to enhance the detection of small absorption-induced changes. Therefore, a lock-in amplifier technique will be integrated into the detection electronics to improve the signal-to-noise ratio. By modulating the IR source (for instance, with a chopper or by driving it with a sinusoidal waveform) and synchronously demodulating the detector output, the system can extract the CO₂ absorption signal from background noise with high fidelity.[4] This approach effectively amplifies the desired signal and filters out low-frequency drift or random noise, as demonstrated in prior CO₂ sensor research.[4] Overall, the purpose of the project is to realize an IR-based CO₂ sensing device that combines selectivity, sensitivity, and portability – using inexpensive components and innovative signal processing – to facilitate accurate CO₂ monitoring outside the laboratory setting.		As the IR beam passes through the sample gas chamber, CO₂ molecules absorb a fraction of the light at this wavelength, and the thermopile detector (sensitive in the mid-IR range) measures the transmitted IR intensity. The use of a thermopile provides a cost-effective and robust means of converting infrared energy to an electrical signal, but it also necessitates strategies to enhance the detection of small absorption-induced changes. Therefore, a lock-in amplifier technique will be integrated into the detection electronics to improve the signal-to-noise ratio. By modulating the IR source (for instance, with a chopper or by driving it with a sinusoidal waveform) and synchronously demodulating the detector output, the system can extract the CO₂ absorption signal from background noise with high fidelity.[4] This approach effectively amplifies the desired signal and filters out low-frequency drift or random noise, as demonstrated in prior CO₂ sensor research.[4] Overall, the purpose of the project is to realize an IR-based CO₂ sensing device that combines selectivity, sensitivity, and portability – using inexpensive components and innovative signal processing – to facilitate accurate CO₂ monitoring outside the laboratory setting.

	==~~=Objectives~~===		==Key objectives===
	*Accurate quantification of CO₂ via IR absorption: Develop the device to reliably measure carbon dioxide concentrations, ensuring that the IR absorption at 4.3 μm can be translated into an accurate quantitative reading of CO₂ levels. This entails calibrating the sensor and optimizing its design so that the CO₂ concentration is determined with high precision and accuracy.		*Accurate quantification of CO₂ via IR absorption: Develop the device to reliably measure carbon dioxide concentrations, ensuring that the IR absorption at 4.3 μm can be translated into an accurate quantitative reading of CO₂ levels. This entails calibrating the sensor and optimizing its design so that the CO₂ concentration is determined with high precision and accuracy.

Caoyuan: /* Purpose */

2025-04-29T09:19:15Z

Purpose

← Older revision		Revision as of 17:19, 29 April 2025
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	This project’s purpose is to develop a portable, low-cost CO₂ concentration measurement device based on infrared absorption spectroscopy. The aim is to design and construct an instrument capable of accurately quantifying CO₂ levels in ambient air by detecting the attenuation of IR radiation at the 4.3 μm absorption band of CO₂. By leveraging the selectivity of this mid-IR spectral feature, the device will provide reliable measurements of CO₂ while remaining compact and energy-efficient, making it suitable for field use or continuous environmental monitoring.		This project’s purpose is to develop a portable, low-cost CO₂ concentration measurement device based on infrared absorption spectroscopy. The aim is to design and construct an instrument capable of accurately quantifying CO₂ levels in ambient air by detecting the attenuation of IR radiation at the 4.3 μm absorption band of CO₂. By leveraging the selectivity of this mid-IR spectral feature, the device will provide reliable measurements of CO₂ while remaining compact and energy-efficient, making it suitable for field use or continuous environmental monitoring.

	To achieve this, ~~the sensor system will employ~~ a broadband thermal infrared source together with an optical band-pass filter and a thermopile detector, following the classic NDIR configuration. The broadband IR emitter (for example, a heated filament) will produce radiation encompassing the 4.3 μm wavelength, and a narrow band-pass filter centered at ~4.3 μm will isolate the specific CO₂ absorption band.[4]		To achieve this, a broadband thermal infrared source together with an optical band-pass filter and a thermopile detector are employed as the sensor system, following the classic NDIR configuration. The broadband IR emitter (for example, a heated filament) will produce radiation encompassing the 4.3 μm wavelength, and a narrow band-pass filter centered at ~4.3 μm will isolate the specific CO₂ absorption band.[4]

	As the IR beam passes through the sample gas chamber, CO₂ molecules absorb a fraction of the light at this wavelength, and the thermopile detector (sensitive in the mid-IR range) measures the transmitted IR intensity. The use of a thermopile provides a cost-effective and robust means of converting infrared energy to an electrical signal, but it also necessitates strategies to enhance the detection of small absorption-induced changes. Therefore, a lock-in amplifier technique will be integrated into the detection electronics to improve the signal-to-noise ratio. By modulating the IR source (for instance, with a chopper or by driving it with a sinusoidal waveform) and synchronously demodulating the detector output, the system can extract the CO₂ absorption signal from background noise with high fidelity.[4] This approach effectively amplifies the desired signal and filters out low-frequency drift or random noise, as demonstrated in prior CO₂ sensor research.[4] Overall, the purpose of the project is to realize an IR-based CO₂ sensing device that combines selectivity, sensitivity, and portability – using inexpensive components and innovative signal processing – to facilitate accurate CO₂ monitoring outside the laboratory setting.		As the IR beam passes through the sample gas chamber, CO₂ molecules absorb a fraction of the light at this wavelength, and the thermopile detector (sensitive in the mid-IR range) measures the transmitted IR intensity. The use of a thermopile provides a cost-effective and robust means of converting infrared energy to an electrical signal, but it also necessitates strategies to enhance the detection of small absorption-induced changes. Therefore, a lock-in amplifier technique will be integrated into the detection electronics to improve the signal-to-noise ratio. By modulating the IR source (for instance, with a chopper or by driving it with a sinusoidal waveform) and synchronously demodulating the detector output, the system can extract the CO₂ absorption signal from background noise with high fidelity.[4] This approach effectively amplifies the desired signal and filters out low-frequency drift or random noise, as demonstrated in prior CO₂ sensor research.[4] Overall, the purpose of the project is to realize an IR-based CO₂ sensing device that combines selectivity, sensitivity, and portability – using inexpensive components and innovative signal processing – to facilitate accurate CO₂ monitoring outside the laboratory setting.

Tana: /* Team members */

2025-04-28T17:29:06Z

Team members

← Older revision		Revision as of 01:29, 29 April 2025
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	==Team members==		==Team members==
	Ta Na: Responsible for proposing and refining ideas, coordinating experimental records, documenting the experimental process, generating graphs, analyzing experimental data, drawing conclusions, making comparisons, preparing appendices, and formatting.		Ta Na: Responsible for proposing and refining ideas, coordinating experimental records, documenting the experimental process, generating graphs, analyzing experimental data, drawing conclusions, experimental advantages and improvements, making comparisons, preparing appendices, and formatting.

	Cao Yuan: Responsible for refining ideas, leading experimental operations, deriving the experimental principles and related formulas and experiment setup section, and formatting.		Cao Yuan: Responsible for refining ideas, leading experimental operations, deriving the experimental principles and related formulas and experiment setup section, and formatting.

Tana: /* Appendix */

2025-04-28T17:22:21Z

Appendix

← Older revision		Revision as of 01:22, 29 April 2025
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	<center>[[File:1.3.png\|800px]]</center>		<center>[[File:1.3.png\|800px]]</center>
	<center>[[File:1.4.png\|800px]]</center>		<center>[[File:1.4.png\|800px]]</center>
	<center>[[File:1.6.png\|400px]][[File:6.png\|~~350px~~]]</center>		<center>[[File:1.6.png\|400px]][[File:6.png\|310px]]</center>

	<center>''Figures The above are respectively: the original data, the surrounding noise environment displayed by the oscilloscope, and the air pressure and speed when CO2 is passed through.''</center>		<center>''Figures The above are respectively: the original data, the surrounding noise environment displayed by the oscilloscope, and the air pressure and speed when CO2 is passed through.''</center>

Tana: /* Appendix */

2025-04-28T17:22:11Z

Appendix

← Older revision		Revision as of 01:22, 29 April 2025
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	<center>[[File:1.3.png\|800px]]</center>		<center>[[File:1.3.png\|800px]]</center>
	<center>[[File:1.4.png\|800px]]</center>		<center>[[File:1.4.png\|800px]]</center>
	<center>[[File:1.6.png\|400px]][[File:6.png\|~~300px~~]]</center>		<center>[[File:1.6.png\|400px]][[File:6.png\|350px]]</center>

	<center>''Figures The above are respectively: the original data, the surrounding noise environment displayed by the oscilloscope, and the air pressure and speed when CO2 is passed through.''</center>		<center>''Figures The above are respectively: the original data, the surrounding noise environment displayed by the oscilloscope, and the air pressure and speed when CO2 is passed through.''</center>

Tana: /* Appendix */

2025-04-28T17:21:46Z

Appendix

← Older revision		Revision as of 01:21, 29 April 2025
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	==Appendix==		==Appendix==
	<center>[[File:1.1.png\|~~400px~~]][[File:1.2.png\|~~200px~~]]</center>		<center>[[File:1.1.png\|800px]]</center>
	<center>[[File:1.3.png\|~~400px~~]][[File:1.4.png\|~~200px~~]]</center>		<center>[[File:1.2.png\|800px]]</center>
			<center>[[File:1.3.png\|800px]]</center>
			<center>[[File:1.4.png\|800px]]</center>
	<center>[[File:1.6.png\|400px]][[File:6.png\|300px]]</center>		<center>[[File:1.6.png\|400px]][[File:6.png\|300px]]</center>

	<center>''Figures The above are respectively: the original data, the surrounding noise environment displayed by the oscilloscope, and the air pressure and speed when CO2 is passed through.''</center>		<center>''Figures The above are respectively: the original data, the surrounding noise environment displayed by the oscilloscope, and the air pressure and speed when CO2 is passed through.''</center>

Tana: /* Purpose */

2025-04-28T17:19:42Z

Purpose

← Older revision		Revision as of 01:19, 29 April 2025
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	This project’s purpose is to develop a portable, low-cost CO₂ concentration measurement device based on infrared absorption spectroscopy. The aim is to design and construct an instrument capable of accurately quantifying CO₂ levels in ambient air by detecting the attenuation of IR radiation at the 4.3 μm absorption band of CO₂. By leveraging the selectivity of this mid-IR spectral feature, the device will provide reliable measurements of CO₂ while remaining compact and energy-efficient, making it suitable for field use or continuous environmental monitoring.		This project’s purpose is to develop a portable, low-cost CO₂ concentration measurement device based on infrared absorption spectroscopy. The aim is to design and construct an instrument capable of accurately quantifying CO₂ levels in ambient air by detecting the attenuation of IR radiation at the 4.3 μm absorption band of CO₂. By leveraging the selectivity of this mid-IR spectral feature, the device will provide reliable measurements of CO₂ while remaining compact and energy-efficient, making it suitable for field use or continuous environmental monitoring.

	To achieve this, the sensor system will employ a broadband thermal infrared source together with an optical band-pass filter and a thermopile detector, following the classic NDIR configuration. The broadband IR emitter (for example, a heated filament) will produce radiation encompassing the 4.3 μm wavelength, and a narrow band-pass filter centered at ~4.3 μm will isolate the specific CO₂ absorption band[4].		To achieve this, the sensor system will employ a broadband thermal infrared source together with an optical band-pass filter and a thermopile detector, following the classic NDIR configuration. The broadband IR emitter (for example, a heated filament) will produce radiation encompassing the 4.3 μm wavelength, and a narrow band-pass filter centered at ~4.3 μm will isolate the specific CO₂ absorption band.[4]

	As the IR beam passes through the sample gas chamber, CO₂ molecules absorb a fraction of the light at this wavelength, and the thermopile detector (sensitive in the mid-IR range) measures the transmitted IR intensity. The use of a thermopile provides a cost-effective and robust means of converting infrared energy to an electrical signal, but it also necessitates strategies to enhance the detection of small absorption-induced changes. Therefore, a lock-in amplifier technique will be integrated into the detection electronics to improve the signal-to-noise ratio. By modulating the IR source (for instance, with a chopper or by driving it with a sinusoidal waveform) and synchronously demodulating the detector output, the system can extract the CO₂ absorption signal from background noise with high fidelity [4]. This approach effectively amplifies the desired signal and filters out low-frequency drift or random noise, as demonstrated in prior CO₂ sensor research[4]. Overall, the purpose of the project is to realize an IR-based CO₂ sensing device that combines selectivity, sensitivity, and portability – using inexpensive components and innovative signal processing – to facilitate accurate CO₂ monitoring outside the laboratory setting.		As the IR beam passes through the sample gas chamber, CO₂ molecules absorb a fraction of the light at this wavelength, and the thermopile detector (sensitive in the mid-IR range) measures the transmitted IR intensity. The use of a thermopile provides a cost-effective and robust means of converting infrared energy to an electrical signal, but it also necessitates strategies to enhance the detection of small absorption-induced changes. Therefore, a lock-in amplifier technique will be integrated into the detection electronics to improve the signal-to-noise ratio. By modulating the IR source (for instance, with a chopper or by driving it with a sinusoidal waveform) and synchronously demodulating the detector output, the system can extract the CO₂ absorption signal from background noise with high fidelity.[4] This approach effectively amplifies the desired signal and filters out low-frequency drift or random noise, as demonstrated in prior CO₂ sensor research.[4] Overall, the purpose of the project is to realize an IR-based CO₂ sensing device that combines selectivity, sensitivity, and portability – using inexpensive components and innovative signal processing – to facilitate accurate CO₂ monitoring outside the laboratory setting.

	===Objectives===		===Objectives===

Tana: /* Background */

2025-04-28T17:18:17Z

Background

← Older revision		Revision as of 01:18, 29 April 2025
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	==Background==		==Background==
	Carbon dioxide (CO₂) is a prominent greenhouse gas whose rising concentration plays a critical role in climate change. In the atmosphere, CO₂ molecules absorb Earth’s outgoing infrared radiation in specific wavelength bands, notably around 15, 4.3, 2.7, and 2 μm, which causes heat to be trapped and contributes to atmospheric warming[1]. Indeed, empirical climate analyses have identified increasing CO₂ levels as a primary driver of recent global warming[2]. This dual significance of CO₂—as both an essential climate variable and a gas requiring careful monitoring—motivates the development of accurate sensing technologies.		Carbon dioxide (CO₂) is a prominent greenhouse gas whose rising concentration plays a critical role in climate change. In the atmosphere, CO₂ molecules absorb Earth’s outgoing infrared radiation in specific wavelength bands, notably around 15, 4.3, 2.7, and 2 μm, which causes heat to be trapped and contributes to atmospheric warming.[1] Indeed, empirical climate analyses have identified increasing CO₂ levels as a primary driver of recent global warming.[2] This dual significance of CO₂—as both an essential climate variable and a gas requiring careful monitoring—motivates the development of accurate sensing technologies.

	Infrared (IR) absorption spectroscopy provides a robust physical principle for detecting gases like CO₂ by exploiting their unique vibrational absorption fingerprints. When IR light at certain wavelengths passes through a gas, molecules that have vibrational modes resonant with those wavelengths will absorb energy, reducing the transmitted light intensity. Polyatomic gases such as CO₂ exhibit strong vibrational-rotational absorption features in the mid-IR region (e.g., near 4.3 μm) that can be measured for quantification [1]. The relationship between absorbed light and gas concentration is governed by the Beer–Lambert law, which states that the intensity of transmitted light decays exponentially with the path length and concentration of the absorbing species[3]. In practice, this means the amount of IR attenuation at a characteristic wavelength is directly related to the CO₂ concentration along the optical path, enabling concentration measurements via absorbance. Non-dispersive infrared (NDIR) sensors are built on this principle by using a broadband IR source and a detector with an optical filter to isolate the wavelength of interest, yielding a selective and linear response to the target gas under most conditions[4].		Infrared (IR) absorption spectroscopy provides a robust physical principle for detecting gases like CO₂ by exploiting their unique vibrational absorption fingerprints. When IR light at certain wavelengths passes through a gas, molecules that have vibrational modes resonant with those wavelengths will absorb energy, reducing the transmitted light intensity. Polyatomic gases such as CO₂ exhibit strong vibrational-rotational absorption features in the mid-IR region (e.g., near 4.3 μm) that can be measured for quantification.[1] The relationship between absorbed light and gas concentration is governed by the Beer–Lambert law, which states that the intensity of transmitted light decays exponentially with the path length and concentration of the absorbing species.[3] In practice, this means the amount of IR attenuation at a characteristic wavelength is directly related to the CO₂ concentration along the optical path, enabling concentration measurements via absorbance. Non-dispersive infrared (NDIR) sensors are built on this principle by using a broadband IR source and a detector with an optical filter to isolate the wavelength of interest, yielding a selective and linear response to the target gas under most conditions.[4]

	Among the infrared bands of CO₂, the asymmetric-stretch fundamental near 4.3 µm is particularly suited to sensing. At this wavelength the transition dipole moment is large, so even trace-level concentrations yield a measurable attenuation of the incident beam[4]. Spectroscopic surveys show that the integrated absorption at 4.3 µm exceeds that of the next-strongest fundamental band at 15 µm by roughly one order of magnitude, and is about two orders of magnitude stronger than the overtone combination band around 2.7 µm[5]. Independent modelling of atmospheric spectra confirms that the 4.3 µm and 15 µm bands are, respectively, the first- and second-most intense mid-IR features of CO₂[1]. This exceptionally high line strength translates into superior signal-to-noise performance for compact non-dispersive infrared (NDIR) sensors: by isolating a narrow window centered on approximately 4.3 µm, the detector can quantify CO₂ selectively with minimal cross-interference from other gases[4]. The pronounced absorption at this line therefore underpins our decision to base the instrument’s optical filter on the 4.3 µm peak.		Among the infrared bands of CO₂, the asymmetric-stretch fundamental near 4.3 µm is particularly suited to sensing. At this wavelength the transition dipole moment is large, so even trace-level concentrations yield a measurable attenuation of the incident beam.[4] Spectroscopic surveys show that the integrated absorption at 4.3 µm exceeds that of the next-strongest fundamental band at 15 µm by roughly one order of magnitude, and is about two orders of magnitude stronger than the overtone combination band around 2.7 µm.[5] Independent modelling of atmospheric spectra confirms that the 4.3 µm and 15 µm bands are, respectively, the first- and second-most intense mid-IR features of CO₂.[1] This exceptionally high line strength translates into superior signal-to-noise performance for compact non-dispersive infrared (NDIR) sensors: by isolating a narrow window centered on approximately 4.3 µm, the detector can quantify CO₂ selectively with minimal cross-interference from other gases.[4] The pronounced absorption at this line therefore underpins our decision to base the instrument’s optical filter on the 4.3 µm peak.

	==Purpose==		==Purpose==