Interleaved CRDS Data Acquisition for Interference Mitigation

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Solution Overview

Problem

Optical absorption spectroscopy methods like CRDS face systematic errors due to fluctuating unstructured or structured interference from molecules other than the analyte, especially in high gas flow systems, leading to distorted spectra and erratic results.

Innovation Solution

A new data acquisition method that intersperses measurements of cavity loss at optical frequencies with loss measurements at a reference frequency, allowing for the interpolation of interference levels over time and subsequent subtraction from the frequency-scanned data to correct for interference, thereby improving the accuracy of analyte concentration determination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If CRDS acquires loss vs. frequency spectra point-by-point sequentially, then complete spectral data can be obtained, but time-varying interference is mapped into spectral variation causing distorted measurements

Engineering Contradiction:

Improvespectral measurement accuracyVSAvoidmeasurement reliability under time-varying interference

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent implements periodic reference frequency measurements interleaved with the frequency sweep measurements. A reference frequency is probed periodically throughout the spectral acquisition sequence, creating a time-series of reference measurements that captures the temporal behavior of interference. This periodic sampling of the reference frequency allows the system to track and correct for time-varying interference effects in the spectral data.

Inventive Principle:

Principle #19Periodic action

2Reliability

If spectral measurement interval is decreased to mitigate fluctuating interference, then interference effects are reduced, but the spectrum becomes sparse with poor measurement quality

Engineering Contradiction:

Improveresistance to fluctuating interferenceVSAvoidspectral measurement quality

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent introduces a reference frequency measurement as an intermediary that indirectly characterizes the interference conditions affecting the spectral measurements. By measuring at a reference frequency that is not absorbed by the analyte but is affected by the same interference mechanisms, the system obtains a mediator signal that represents the interference state. This intermediary measurement enables correction of the spectral data without requiring increased measurement density.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Speed

If high gas flow is used to measure fast fluctuations in analyte concentration, then response speed is improved, but rapidly fluctuating contaminant concentrations distort the spectra

Engineering Contradiction:

Improveresponse speed to analyte concentration changesVSAvoidspectral accuracy under high gas flow

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where reference frequency measurements are used to monitor and characterize time-varying interference conditions. The reference measurements provide real-time feedback about the interference state, which is then used to correct the spectral measurements. This feedback loop enables accurate analyte concentration measurements even under high gas flow conditions where both analyte and interferent concentrations are rapidly fluctuating.

Inventive Principle:

Principle #23Feedback

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 significantly reduces the impact of time-varying interference, providing more accurate and reliable measurements of analyte concentrations even in heavily contaminated samples with rapidly fluctuating solvent concentrations.

Implementation Method 1

In the optical absorption technique a light source, commonly a laser, is tuned to an absorption feature of the analyte to be detected and the absorption coefficient of the sample is a quantitative measure of the amount of analyte present

Methodology Applied

Scientific EffectOptical absorption: Absorption (EM radiation)

Implementation Method 2

CRDS (cavity ring-down spectroscopy) measures the total loss of an optical cavity containing the sample

Methodology Applied

Scientific EffectCavity ring-down spectroscopy: Absorption (EM radiation)

Data Source

PatentUS11035728B2Cavity ring-down spectroscopy having interleaved data acquisition for interference mitigation

Publication Date: 2021.06.15 PICARRO INC

AI summary

Interleaved data acquisition in optical spectroscopy is used to provide interference correction for time-varying interference. Measurements at a reference frequency are used to provide an estimate of the interference. These reference measurements are interleaved with the remaining measurements in order to provide estimates of the interference vs. time at relevant times. The interference being corrected can be spectrally structured or unstructured.