Particle Impedance Measurement Electrode Configuration
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Solution Overview
Problem
Existing apparatus for electrically measuring individual particles in a liquid suffer from high measured impedance variability due to particle position, leading to large coefficients of variation in measured properties, as particles passing close to electrodes distort the electric field and cause uneven current flow between electrode arrangements.
Innovation Solution
Incorporating a signal conditioning electrode between the measurement electrodes of the first and second electrode arrangements, held at the same voltage as the measurement electrodes, to prevent current flow and reduce noise, allowing for differential mode operation and improved accuracy by maintaining a non-uniform electric field, and using a signal processing algorithm to estimate particle position and compensate for off-centre particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If particles pass close to the electrodes, then the measured impedance increases, but the measurement accuracy deteriorates due to electric field distortion and uneven current flow
Solution Approach 1:
A signal conditioning electrode is introduced as an intermediary element between the measurement electrode and the fluidic channel. This electrode is held at the same potential as the measurement electrode and serves to condition the electric field, preventing direct interaction between particles and the measurement electrode that causes field distortion. The signal conditioning electrode mediates the measurement process by maintaining a controlled potential distribution that reduces positional dependence of particle measurements.
2Measurement precision
If differential mode operation is used, then noise and artefacts are reduced, but device complexity increases due to additional electrode arrangements
Solution Approach 1:
The signal conditioning electrode is integrated into the existing electrode structure by fabricating it on the same substrate as the measurement electrode. Both electrodes are positioned on the top and bottom surfaces of the fluidic channel, merging multiple functions into a compact integrated design. This combining approach enables differential mode operation for noise reduction while avoiding the complexity of separate, distributed electrode systems.
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 measurement errors for particles not centered in the channel, enhancing measurement accuracy and reducing particle positional dependence, resulting in more precise impedance signals and improved coefficient of variation.
Implementation Method 1
the electrical potential of the signal conditioning electrode is controlled to substantially prevent current flow between the first electrode arrangement and the other electrode arrangement
Implementation Method 2
the individual particles cause a change in electrical current and this change in electrical current is measured and recorded as an impedance signal
Data Source
AI summary
Apparatus (3) for electrically measuring individual particles (4) flowing in a liquid (6), which apparatus (3) comprises: (i) a fluidic channel (5) for receiving a liquid (6) having the individual particles (4) in suspension in the liquid (6); (ii) a first electrode arrangement (8) having at least one measurement electrode (16) and at least one signal electrode (11); (iii) at least one other electrode arrangement (9) having at least one measurement electrode and at least one signal electrode (13); (iv) at least one signal conditioning electrode (10, 12, 14, 15, 17, 19) positioned adjacent to at least one of the measurement electrodes (16, 18) or at least one of the signal electrode (9); and (v) measuring means (20, 21) for measuring electrical signal changes; and the apparatus (3) being such that: (vi) the first and the other electrode arrangements (8, 9) are connected to the measuring means (20, 21) whereby individual particles passing between the first and other electrode arrangements (8, 9) cause a change in electrical signal which is measured; and (vii) the electrical potential of the signal conditioning electrode (10, 12, 14, 15, 17, 19) is controlled to substantially prevent current flow between the first electrode arrangement (8) and the other electrode arrangement (9).