Self-Mixing Laser Sensor for Particle Size Detection
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Solution Overview
Problem
Existing particle size detection systems are complex and expensive, making them unsuitable for cost-effective and efficient use in applications such as air quality monitoring in mobile devices.
Innovation Solution
A simpler and cheaper laser sensor module that uses self-mixing interference signals from a laser cavity to determine particle size by analyzing the relative distance and amplitude information from reflected laser light, allowing for accurate particle size measurement even when particles are out of focus, and incorporates features like modulated drive currents and multiple laser wavelengths for enhanced accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional light analysis systems are used for particle size detection, then measurement capability is achieved, but system complexity and cost increase significantly
Solution Approach 1:
The patent extracts only the essential measurement function from complex conventional systems by using a single laser source and detecting only the intensity modulation caused by self-mixing interference, eliminating unnecessary optical components and signal processing systems while maintaining particle size detection capability
Solution Approach 2:
The laser cavity serves itself as both the light source and the interference detection system. The reflected light from particles re-enters the laser cavity and creates self-mixing interference that modulates the laser output intensity, eliminating the need for separate reference beams, beam splitters, and interferometric detection systems
2Measurement precision
If conventional light analysis systems are used for particle size detection, then measurement capability is achieved, but system cost increases significantly
Solution Approach 1:
The patent uses inexpensive VCSEL lasers and simple photodetectors instead of expensive conventional optical systems. The system accepts reduced component lifespan and performance margins in exchange for dramatically lower cost, making particle size detection economically viable for mass-market applications like mobile devices
Solution Approach 2:
The patent removes expensive optical components such as beam splitters, mirrors, and complex interferometric setups, retaining only the essential laser source and photodetector to perform measurement, thereby dramatically reducing system cost while maintaining functional capability
3Reliability
If focus is optimized for maximum signal strength, then signal amplitude increases, but particles out of focus range cannot be detected
Solution Approach 1:
The patent changes the detection parameter from spatial position (focus) to signal characteristic analysis (zero-crossing count). By counting the number of zero-crossings in the self-mixing interference signal, the system can determine particle size regardless of whether the particle is in focus, thereby extending detection range without sacrificing signal strength reliability
Solution Approach 2:
Instead of adjusting focus to detect particles, the patent inverts the approach by keeping focus fixed and using signal analysis to determine both particle size and effective detection range. The system determines particle properties from the temporal characteristics of the interference signal rather than from spatial positioning
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 solution provides a cost-effective and efficient method for particle size detection, enabling accurate measurement of particle size in air quality monitoring applications, particularly in mobile devices, with improved signal-to-noise ratio and reduced complexity.
Implementation Method 1
The at least one first detector is adapted to determine a first self-mixing interference signal of an optical wave within a first laser cavity of the first laser. The first self-mixing interference signal is caused by first reflected laser light reentering the first laser cavity.
Implementation Method 2
The first reflected laser light is reflected by a particle receiving at least a part of the first laser light.
Data Source
AI summary
The invention describes a laser sensor module (100) for particle size detection. The laser sensor module (100) comprises at least one first laser (110), at least one first detector (120), at least one electrical driver (130) and at least one evaluator (140). The first laser (110) is adapted to emit first laser light in reaction to signals provided by the at least one driver (130). The at least one first detector (120) is adapted to determine a first self-mixing interference signal (30) of an optical wave within a first laser cavity of the first laser (110). The first self-mixing interference signal (30) is caused by first reflected laser light reentering the first laser cavity, the first reflected laser light being reflected by a particle receiving at least a part of the first laser light. The evaluator (140) is adapted to determine a size of the particle by determining a first relative distance between the particle and the first laser (110) by means of the first self-mixing interference signal (30) and by determining a first amplitude information by means of the first self-mixing interference signal (30). The invention is further related to a corresponding method of determining a particle size.