Laser Sensor Module Suppressing False Self-Mixing Interference
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Solution Overview
Problem
Existing laser sensor modules face challenges in accurately detecting particle density due to false positive signals caused by reflections from optical elements and surface irregularities, leading to disturbances in the optical path.
Innovation Solution
The method involves suppressing false self-mixing interference signals through periodic mirror movement, adaptive filtering using techniques like Adaptive Line Enhancer (ALE) or Fast Fourier Transformation (FFT), and frequency filtering to distinguish and discard signals based on specific characteristics and thresholds, ensuring accurate particle detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser beam is scanned through cover glass or optical imaging device, then particle detection capability is enabled, but false positive signals are generated due to reflections
Solution Approach 1:
The patent applies periodic action by oscillating the mirror at a specific frequency (e.g., 400 Hz) to modulate the laser beam path. This periodic movement creates a characteristic frequency signature for true particle signals, allowing differentiation from false positive signals caused by optical path disturbances. The evaluation device uses this frequency information to filter and suppress false positives while maintaining detection accuracy.
Solution Approach 2:
The patent implements feedback by using the mirror's periodic movement as a reference signal in the evaluation device. The system continuously monitors the detected self-mixing interference signals against the known mirror oscillation pattern, providing feedback to distinguish genuine particle detection signals from false positives generated by optical element reflections or surface irregularities.
2Measurement precision
If optical elements are added for beam focusing, then detection sensitivity is improved, but disturbance in optical path increases causing false signals
Solution Approach 1:
The patent introduces the oscillating mirror as an intermediary element that mediates between the laser source and the optical imaging device. This intermediary provides a controllable, periodic modulation to the beam path that enables signal differentiation without requiring complex optical arrangements. The mirror acts as a simple yet effective mediator that adds temporal information to the detection process.
Solution Approach 2:
The patent applies dynamics by transforming the static optical path into a dynamic one through mirror oscillation. Instead of using complex static optical arrangements to differentiate signals, the system introduces controlled temporal dynamics through the oscillating mirror, creating time-varying signal characteristics that enable false positive suppression while maintaining optical path simplicity.
3Measurement precision
If surface irregularities or dirt particles are present on optical elements, then false self mixing interference signals are generated, but particle detection remains necessary
Solution Approach 1:
The patent uses periodic action by oscillating the mirror to create a time-varying detection scheme. True particle signals exhibit the characteristic oscillation frequency, while false signals from surface irregularities or dirt particles do not. This periodic modulation enables the system to reliably distinguish between genuine particle detection events and artifacts caused by optical element contamination.
Solution Approach 2:
The evaluation device uses feedback by continuously comparing detected signals against the reference oscillation pattern from the mirror. This feedback mechanism allows the system to identify and suppress signals that do not match the expected temporal characteristics, thereby maintaining high signal reliability even in the presence of surface irregularities or dirt particles on optical elements.
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 improves detection accuracy and sensitivity by effectively filtering out false signals, allowing for precise measurement of particle density, especially for particles smaller than 20 µm in a fluid.
Implementation Method 1
determination of a self mixing interference signal of laser light reflected by particles
Implementation Method 2
laser light reflected by particles
Implementation Method 3
filter characteristics for filtering such disturbing self mixing interference signals are adapted in accordance with the periodical movement
Data Source
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Figure 3~4
AI summary
The invention relates to a method of measuring a particle density of particles (10) with a size of less than 20 µm, preferably less than 10 µm in a fluid, the method comprising the steps of: emitting a laser beam (112) to a mirror (160), dynamically redirecting the laser beam (112) by means of the mirror (160) with a predetermined periodical movement, imaging the laser beam (112) to a detection volume, by means of an optical imaging device (171), allowing determination of a self mixing interference signal of an optical wave within a laser cavity of the laser if the self mixing interference signal is generated by laser light of the laser beam (112) reflected by at least one of the particles (10), suppressing of a false self mixing interference signal if the self mixing interference signal is caused by a disturbance in an optical path of the laser beam (112). The invention further relates to a laser sensor module (100), a particle detector (200) and a device (190) comprising such a laser sensor module (100). The invention finally relates to a corresponding computer program product.