Reconfigurable Optical Path for In-Situ Density Measurement

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Solution Overview

Problem

Existing methods for measuring optical density in-situ are prone to errors due to optical fouling and light scattering from gas bubbles, particularly in environments where sample removal is inconvenient or impossible, such as microfluidic devices and stirred tank bioreactors.

Innovation Solution

A reconfigurable optical path system using an elastic membrane that adjusts its position to change the optical path length through a fluid, allowing for accurate measurement of optical density by comparing light transmission with and without the fluid, while minimizing errors from fouling and bubbles through pressure differences and vacuum assistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If in-situ optical density measurement is performed using fixed optical paths, then measurement can be conducted without sample removal, but measurement precision deteriorates due to optical fouling on different optical paths

Engineering Contradiction:

Improvein-situ measurement capabilityVSAvoidoptical density measurement accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent employs a movable optical path configuration where the optical path length through the fluid can be dynamically adjusted. By moving the optical path between different positions (first position through fluid, second position away from fluid), the system performs reference measurements without fouling contamination, thereby maintaining measurement precision while enabling in-situ operation

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system performs reference measurements by positioning the optical path away from the fluid before conducting sample measurements. This preliminary action of establishing a fouling-free reference transmission value before sample measurement compensates for optical fouling effects and maintains measurement accuracy throughout the experiment

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If transparent material is introduced into optical path for reference measurement, then reference measurement can be obtained, but additional optical surfaces are introduced that can be fouled

Engineering Contradiction:

Improvereference measurement capabilityVSAvoidoptical fouling on additional surfaces

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

Instead of introducing transparent material into the optical path, the patent extracts the reference measurement function by moving the optical path itself away from the fluid. This eliminates the need for additional transparent materials and their associated fouling-prone surfaces, directly resolving the contradiction

Inventive Principle:

Principle #2Taking out (Extraction)

3Adaptability or versatility

If mechanical means are used to change optical path length, then optical path can be reconfigured, but device complexity increases due to sliding seal and mechanical components

Engineering Contradiction:

Improveoptical path length adjustmentVSAvoidmechanical components required

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent replaces complex mechanical path-length adjustment mechanisms with a simpler approach using a movable optical element (such as a mirror or lens) that can be positioned using minimal mechanical means. This substitution maintains the adaptability of optical path length while significantly reducing device complexity and eliminating the need for sliding seals

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 precise online measurement of optical density with reduced errors from optical fouling and gas bubbles, suitable for applications like microbial fermentation monitoring, by adjusting the membrane's position to alter the optical path length and using vacuum to remove bubbles.

Implementation Method 1

an elastic membrane; a first deformable portion of the elastic membrane

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

establishing a pressure difference between the two sides of the membrane

Methodology Applied

Scientific EffectPressure difference: Pressure Gradient

Implementation Method 3

measuring the light transmission through a reconfigurable optical path

Methodology Applied

Scientific EffectLight transmission: Light

Implementation Method 4

The measurement of the optical density of a fluid that contains optical absorbers or scatters

Methodology Applied

Scientific EffectOptical absorption: Absorption (EM radiation)

Implementation Method 5

using vacuum to remove bubbles

Methodology Applied

Scientific EffectVacuum: Vacuum

Data Source

PatentUS9176060B2Apparatus and methods to measure optical density

Publication Date: 2015.11.03 EMD MILLIPORE CORP

AI summary

The present invention provides apparatus and methods for measuring the optical density of a fluid by measuring the light transmission through a reconfigurable optical path. The optical path is reconfigured by the deflection of an elastic membrane wherein the optical path length through the fluid is determined by the position of the membrane relative to a fixed surface. The optical density can be determined from two measurements with different optical path lengths through the fluid.