Remote Absorption Spectroscopy Coded Transmission
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Solution Overview
Problem
Conventional active source absorption spectroscopy systems face errors due to partial path scattered returns and transmission power losses when measuring gases over long distances, especially with diffuse reflectors, limiting their range and accuracy.
Innovation Solution
The system employs spatially isolated transmitter and receiver subsystems with multispectral electromagnetic radiation, where spectral components in an absorption band and an off-line band are modulated to maintain a temporally constant relationship, allowing for line-of-sight propagation and analysis of spectral content deviations to determine absorption without noise from backscattered radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional collocated transmitter and receiver components are used with short path length, then the system can detect absorbed radiation, but transmission power losses increase and range is limited over long distances
Solution Approach 1:
The system segments the measurement function by using spatially isolated transmitter and receiver subsystems, allowing the transmitter to emit radiation through the medium while the receiver collects transmitted radiation at a remote location, eliminating the need for collocated components and enabling long path lengths without excessive power loss
Solution Approach 2:
The patent introduces an intermediary relationship where the medium itself serves as the transmission path between spatially separated transmitter and receiver, eliminating the need for reflectors or mirrors that cause scattering losses, and allowing direct measurement of transmitted radiation after passing through the medium
2Length of stationary object
If reflected signals are used to return transmitted signals to the source location, then long distance measurement is enabled, but scattered returns from aerosol constituents or particles give rise to additive error from backscattered radiation
Solution Approach 1:
The system extracts the receiver from the transmitter location and places it at a remote position to directly receive transmitted radiation, taking out the problematic backscattered radiation that would otherwise return to the source location and contaminate the measurement with additive errors
Solution Approach 2:
The patent converts the harmful effect of backscattered radiation into a beneficial measurement approach by having the receiver specifically collect only the forward-transmitted radiation that has passed through the medium, using the scattering events as a natural filter to separate transmitted from backscattered radiation through spatial positioning
3Length of stationary object
If diffuse reflectors are used to reflect transmitted radiation, then long range implementation is possible, but large range-squared losses result in the system
Solution Approach 1:
Instead of using reflectors to bounce radiation back to the source, the system inverts the approach by having the receiver positioned in the forward transmission path to directly collect transmitted radiation, eliminating range-squared losses associated with diffuse reflection while enabling long-range measurement
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate absorption measurements over long distances by isolating scattered returns and reducing transmission power losses, providing precise absorption profiles without noise contamination from backscattering, thus enhancing the system's range and accuracy.
Implementation Method 1
Multispectral electromagnetic radiation may be generated to have spectral content coinciding with both an absorption band of a medium and an off-line band
Implementation Method 2
Deviation of the spectral content of the received radiation from the relationship defined by the transmitter may be attributable to absorption by the medium of the spectral component inside the absorption band
Implementation Method 3
The receiver accepts the transmitted radiation through line-of-sight propagation through the medium
Data Source
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Figure 1B
Figure 1C
AI summary
Remote absorption spectroscopy uses coded electromagnetic transmission (240) directed through a medium under investigation to one or more remote receivers (262). The coded transmission includes at least one wavelength (242) coincident with an absorption band of interest and one wavelength (244) in an off-line band and a predefined relationship between spectral components in and outside the absorption band is controlled. The relationship between spectral components may be evaluated at the receiver to determine whether deviation thereof from the controlled relationship at the transmitter exists at the receiver. The deviation of the received optical signal from the prescribed relationship is processed to indicate the absorption of the radiation in the absorption band.