Particle Characterisation Apparatus with Adjustable Detection Region
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Solution Overview
Problem
Photon correlation spectroscopy (DLS) is hindered by multiple scattering at high particle concentrations and signal-to-noise ratio issues at low concentrations, where static scattering from the cell wall and number fluctuations affect measurement accuracy.
Innovation Solution
A particle characterisation apparatus that allows adjustable positioning and volume of the detection region within the sample cell, using a beam expander and moveable lenses to optimise the light beam width and focussing, combined with a single mode fibre for improved signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the detection region is placed near the cell wall to reduce multiple scattering, then multiple scattering is reduced, but static scattering from the wall increases noise for low concentration samples
Solution Approach 1:
The patent applies the dynamics principle by making the detection region movable within the sample cell. The detection region can be dynamically repositioned between near the cell wall (to reduce multiple scattering in high concentration samples) and away from the cell wall (to reduce static scattering noise in low concentration samples). This dynamic adjustment resolves the contradiction by allowing the system to adapt its detection position based on sample concentration conditions.
2Measurement precision
If the detection region size is expanded to accommodate more particles, then number fluctuations are reduced, but the beam size exceeds a single coherence area reducing signal to noise
Solution Approach 1:
The patent applies parameter changes by using a single mode fibre to select a specific spatial frequency from the speckle field image. This changes the detection parameter from collecting all scattered light to selectively detecting light within a single coherence area. The single mode fibre acts as a spatial filter that maintains optimal signal-to-noise ratio by ensuring measurements are taken from within a single coherence area while still accommodating sufficient particles through the adjustable detection region positioning.
3Ease of operation
If a moving lens is used to position the detection region, then detection region positioning is improved, but device complexity increases
Solution Approach 1:
The patent applies the intermediary principle by introducing a beam expander as a mediating optical component between the light source and the sample cell. The beam expander, which includes a moving lens, serves as an intermediary device that enables detection region positioning and volume adjustment without requiring complex reconfiguration of the entire optical path. This intermediary component simplifies the overall system architecture while achieving the desired detection region control.
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 configuration enhances the signal-to-noise ratio for both high and low particle concentrations, enabling more accurate particle sizing by reducing multiple scattering and noise contributions.
Implementation Method 1
using a beam expander and moveable lenses to optimise the light beam width and focussing
Implementation Method 2
Photon correlation spectroscopy (or dynamic light scattering, DLS) measures the time resolved signal scattered from particle suspensions
Implementation Method 3
a single mode fibre may be used in the detection optical path, to select out a single spatial frequency from the 'image' of the speckle field
Implementation Method 4
The relaxation time of the sample is determined from the correlation function of the scattered signal from which the particle size distribution can be estimated
Data Source
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AI summary
A particle characterisation apparatus (300) is disclosed comprising: a sample cell (110) for holding a sample (150), a light source (302) for producing a light beam (106) for illuminating the sample (150) in the sample cell (110), thereby producing scattered light by the interaction of the light beam (106) with the sample (150); a focussing lens (130) for focussing the light beam (106) within the sample (150); and a detector (306) for detecting the backscattered light along a detection optical path (108) that intersects the focussed light beam (106) within the sample (150). The intersection of the light beam (106) and the detection optical path (108) in the sample define a detection region (120). The apparatus comprises an optical arrangement for varying the volume of the detection region (120).