Design Of Particle Concentration Detection Device Based On Laser Forward Scattering Method

As fine particulate matter pollution has become a significant public health issue in China,directly affecting the atmospheric environment,air visibility,and human health,the government has issued a series of relevant documents to improve the ecological environment.In November 2021,China set a target in the"Opinions on Deepening the Fight against Pollution"to reduce the concentration of fine particulate matter in cities at or above the prefecture level by 10%by 2025.To achieve this national target,it is necessary for local cities to monitor the concentration of particulate matter in the atmosphere in real-time.However,currently most domestic monitoring devices are large in size and high in cost,making them unsuitable for grid-based monitoring of ambient air quality.Moreover,when the particle concentration is low,scattered light signals are easily interfered by noise and cause systematic errors.Therefore,this project aims to design a miniaturized particulate matter concentration detection device that can control costs while ensuring accuracy.The main tasks of this project are as follows:(1)Based on Mie scattering theory,mathematical models for the relationship between scattering light intensity and particle parameters,as well as theoretical models for measuring particle concentration using group particle scattering method,are established.Through Matlab simulation analysis of the scattering light intensity of different wavelengths of light source,particle diameter,and refractive index at different scattering angles,the optimal light source wavelength around 650 nm and the detection optical signal structure with the optimal forward scattering angle of 45°were determined.(2)Aiming at the problem that the optical system of the detection device does not meet the miniaturization requirements and poor uniformity of the laser beam,an aspheric lens group is designed to collimate the laser beam on the fast and slow axes,and the parameters of the lens group are determined through Zemax optimization simulation.The optimized beam divergence angles are all less than 0.2°,and a collimated spot less than10 mm is formed in the detection cavity 50 mm away from the light source.Finally,the structural design of the entrance aperture,inlet/outlet ports,and light trap for the detection chamber was carried out.(3)Design hardware circuits and software systems to address the errors caused by weak signals being susceptible to noise interference and environmental relative humidity.The data acquisition and control module is designed with STM32 microcontroller as the core,and a PWM-modulated laser driving circuit is designed to achieve constant power for the laser diode.After the photodiode collects the signal,a transimpedance amplifier circuit and a low-pass filter circuit are designed for signal processing using MCP6022operational amplifier.An alarm circuit is designed to automatically trigger an alarm when the particle concentration exceeds the threshold or the relative humidity of the environment exceeds 60%.The programming of the firmware for the microcontroller and the software for the PC interface is completed using C language and C#.(4)Finally,conduct a complete experimental test of the particle concentration detection device,including zero input noise,upper computer function,and particle concentration detection experiments.The particulate matter concentration detection experiment was conducted using a prototype and the filter membrane weighing method for comparison.The particulate matter concentrations of two types of dust with different characteristics were analyzed at sampling concentrations of 10 mg/m~3 and 5 mg/m~3 were both less than 10%,and the fitting coefficients were all greater than 0.97.The experimental results indicate that this miniaturized device can achieve real-time monitoring of particulate matter with high accuracy.