Gas Detection Modulation Using Orthogonal Zero-Padded Codes
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Solution Overview
Problem
Existing gas detection methods using laser-based optical devices face challenges in achieving fast spatial scanning and distinguishing backscattered radiation from noise, particularly in single photon detection systems where signal-to-noise ratio is low.
Innovation Solution
The method involves modulating radiation of different wavelengths using orthogonal modulation codes with gaps, known as 'zero padded codes,' to differentiate backscattered radiation from noise by interleaving codes and reducing the duration required for analysis, allowing for faster scanning and improved signal differentiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional modulation schemes are used for multi-wavelength gas detection, then the system can detect multiple gases, but the scanning speed is limited and signal differentiation from noise becomes difficult
Solution Approach 1:
The patent divides the modulation signal into multiple orthogonal codes, each assigned to a specific wavelength. This segmentation allows independent detection and analysis of each wavelength component, improving both scanning speed and signal differentiation capability simultaneously
Solution Approach 2:
The patent introduces zero-padding as an intermediary technique between modulation codes. This padding acts as a temporal separator that reduces inter-symbol interference and enhances the distinguishability of backscattered signals from noise, thereby improving measurement precision without sacrificing scanning speed
2Productivity
If multiple wavelengths are transmitted simultaneously for parallel detection, then detection efficiency improves, but code interleaving and analysis time increase
Solution Approach 1:
The patent employs periodic orthogonal modulation codes with structured zero-padding intervals. This periodic structure enables efficient correlation-based detection algorithms that can process multiple wavelengths in parallel while maintaining minimal analysis time, thus improving productivity without increasing time loss
3Measurement precision
If orthogonal modulation codes are used for multiple wavelengths, then signal differentiation improves, but the complexity of modulation and demodulation increases
Solution Approach 1:
The patent utilizes parameter changes in the temporal domain through zero-padding, transforming the modulation structure to simplify differentiation. By adjusting the padding duration parameter, the system achieves optimal signal separation with minimal increase in implementation complexity
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 high-sensitivity, low-power remote gas detection and imaging, enhancing the speed of spatial scanning and reducing noise interference, thereby improving the accuracy and efficiency of gas detection and imaging systems.
Implementation Method 1
emitting radiation of different wavelengths across the absorption spectrum of a gas towards a target area
Implementation Method 2
The radiation is modulated using respective orthogonal modulation codes for the different wavelengths
Implementation Method 3
analysing the spectrum of returned laser light from the target area to identify the gas in the target area
Data Source
AI summary
A method of gas detection comprises emitting radiation of different wavelengths across the absorption spectrum of a gas towards a target area; and analysing the spectrum of returned laser light from the target area to identify the gas in the target area using the time correlation of the emitted radiation and the returning radiation. The radiation is modulated using respective orthogonal modulation codes for the different wavelengths and the modulation codes are modified by the insertion of a gap between each bit of the modulation code, the gap having a duration of at least n-1 bits where n is the number of different wavelengths.