Acousto-Optic Modulator Electrophoretic Mobility Measurement
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Solution Overview
Problem
Current electrophoretic mobility measurement instruments rely on resolving time-domain beat signals and detecting local oscillators, which are prone to mechanical vibrations and frequency shifts, limiting precision and stability.
Innovation Solution
An apparatus utilizing a long coherence length laser, fiber splitter, polarization maintaining acousto-optic modulator, sample cell, polarization maintaining combiner, photo detector, and in-phase quadrature phase demodulator to measure electrophoretic mobility by analyzing frequency shifts without resolving beat signals or local oscillators, employing RF demodulation and narrow-band filters to enhance precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If time-domain beat signals and local oscillators are used for measurement, then the measurement can be performed with conventional instruments, but mechanical vibrations and frequency shifts occur leading to reduced precision and stability
Solution Approach 1:
The patent replaces mechanical vibration-prone components (moving mirrors, local oscillators) with an acousto-optic modulator that uses acoustic waves to modulate light frequency. This substitution eliminates mechanical vibrations from the optical path while achieving the same frequency shifting function, thereby improving both measurement precision and phase stability
Solution Approach 2:
The patent introduces an acousto-optic modulator as an intermediary device between the laser source and the sample. This modulator acts as a stable frequency reference generator that does not rely on mechanical oscillators, providing a vibration-free reference signal for heterodyne detection and improving overall system reliability
2Measurement precision
If conventional heterodyne detection is used, then electrophoretic mobility can be measured, but mechanical vibrations limit the precision and stability of the measurement
Solution Approach 1:
The patent eliminates mechanical vibration sources by replacing moving mirrors and mechanical oscillators with an acousto-optic modulator that uses sound waves in a stationary medium to achieve frequency modulation. This substitution removes the harmful mechanical vibrations while preserving the heterodyne detection capability
Solution Approach 2:
The patent extracts and removes the mechanical vibration-prone components (local oscillators, moving mirrors) from the measurement system, retaining only the essential heterodyne detection functionality through acoustic-optic interaction, thereby eliminating the harmful mechanical vibrations from the 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
The apparatus achieves precise measurement of electrophoretic mobility by directly detecting Doppler frequency shifts, allowing for the detection of multiple mobility species and particle sizes, and simultaneously measuring electrophoretic and dynamic light scattering, with improved phase stability and reduced noise.
Implementation Method 1
a polarization maintaining acousto-optic modulator (AOM) optically coupled to a sample arm output of the splitter
Implementation Method 2
a photo detector to detect light outputted from the combiner
Implementation Method 3
a long coherence length laser
Implementation Method 4
to be analyzed for shifts in frequency to measure electrophoretic mobility in the sample
Data Source
AI summary
The present disclosure describes an apparatus to measure electrophoretic mobility. In an embodiment, the apparatus includes a laser, a fiber splitter optically coupled to the laser, a polarization maintaining acousto-optic modulator optically coupled to a sample arm output of the splitter, a sample cell to contain a sample and optically coupled to an output of the acousto-optic modulator, a polarization maintaining combiner optically coupled to a reference arm output of the splitter and to an output of the sample cell, a photo detector to detect light outputted from the combiner, a radio frequency source electrically coupled to an input of the acousto-optic modulator, and a demodulator electrically coupled to an output of the photo detector and electrically coupled to an output of the radio frequency source, to output in-phase data and quadrature phase data to be analyzed for shifts in frequency to measure electrophoretic mobility in the sample.