Huaqiao Gui

Instrument for Real-Time Measurement of Low Turbidity by Using Time-Correlated Single Photon Counting Technique

A real-time turbidimeter based on time-correlated single photon counting (TCSPC) was developed to measure the low-level turbidity for drinking water. To improve measurement accuracy, we use a single-photon avalanche diode (SPAD) with high sensitivity to accurately detect the intensity of weak scattering light. A novel statistics principle-based TCSPC technique was applied in this system to reduce the fluctuation of measurement and improve the stability of turbidity measurement. Thanks to the SPAD with short response time and the digital output of single-photon detecting module, the real-time and steady measurement of low turbidity is finally implemented. Experimental tests for the turbidimeters performance were described and the results showed that 0.1 Nephelometric Turbidity Units (NTU) can be measured stably in the range of 0-400 NTU within 1 s. On the basis of the theoretical analysis, a turbidity measurement model was proposed. It was found that a tradeoff between the high measurement resolution and wide linearity range should be considered adequately depending on the practical applications. By adjusting the system parameters, we demonstrated that the linear range of measurement could be expanded in the regime of low turbidity, while maintaining high resolution of this system. The proposed turbidimeter has advantages of high resolution, wide linear range, and short response time, which is sufficient for many applications, including the real-time online turbidity or particle concentration monitoring.

Identification of long-range transport pathways and potential sources of PM 2.5 and PM 10 in Beijing from 2014 to 2015

Trajectory clustering, potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) methods were applied to investigate the transport pathways and identify potential sources of PM2.5 and PM10 in different seasons from June 2014 to May 2015 in Beijing. The cluster analyses showed that Beijing was affected by trajectories from the south and southeast in summer and autumn. In winter and spring, Beijing was not only affected by the trajectories from the south and southeast, but was also affected by trajectories from the north and northwest. In addition, the analyses of the pressure profile of backward trajectories showed that backward trajectories, which have important influence on Beijing, were mainly distributed above 970hPa in summer and autumn and below 950hPa in spring and winter. This indicates that PM2.5 and PM10 were strongly affected by the near surface air masses in summer and autumn and by high altitude air masses in winter and spring. Results of PSCF and CWT analyses showed that the largest potential source areas were identified in spring, followed by winter and autumn, then summer. In addition, potential source regions of PM10 were similar to those of PM2.5. There were a clear seasonal and spatial variation of the potential source areas of Beijing and the airflow in the horizontal and vertical directions. Therefore, more effective regional emission reduction measures in Beijings surrounding provinces should be implemented to reduce emissions of regional sources in different seasons.

High-accuracy fiber optical microphone in a DBR fiber laser based on a nanothick silver diaphragm by self-mixing technique

A high-accuracy fiber optical microphone (FOM) is first applied by self-mixing technique in a DBR fiber laser based on a nanothick silver diaphragm. The nanothick silver diaphragm fabricated by the convenient and low cost electroless plating method is functioned as sensing diaphragm due to critically susceptible to the air vibration. Simultaneously, micro-vibration theory model of self-mixing interference fiber optical microphone is deduced based on quasi-analytical method. The dynamic property to frequencies and amplitudes are experimentally carried out to characterize the fabricated FOM and also the reproduced sound of news and music can clearly meet the ear of the people which shows the technique proposed in this paper guarantee steady, high signal-noise ratio operation and outstanding accuracy in the DBR fiber laser which is potential to medical and security applications such as real-time voice reproduction for throat and voiceprint verification.

Design and evaluation of a unipolar aerosol particle charger with built-in electrostatic precipitator

ABSTRACT A new unipolar charger of aerosol particle has been designed and evaluated. The free ion and particle trajectories have been simulated. Four parameters, including electrical characteristics, particle loss, charging efficiency and the average charges, were varied to evaluate the charger. The experimental results show that the average discharge current was stable at 5 µA with 2.6 kV applied on the needle. The standard deviation is 0.0016 when clean air is entered in the discharging zone, as compared to the deviation of 0.024 with unfiltered ambient air which indicates that discharge current is more stable when clean air is entered. The electrostatic loss, diffusion loss and total particle loss were below about 4, 7 and 9% for all particles (sizes of 20–1000 nm), respectively. The intrinsic and extrinsic charging efficiency increased with the particle diameter. The intrinsic efficiency is practically 100% for particle diameters above 50 nm. Compared to the intrinsic efficiency, the extrinsic charging efficiency decreased by 5% given the fact that some of particles may be deposited inside the charger. As for the average particle charge number, the maximum relative error between the results of experiment and theory was less than 15%.

All-Fiber Configuration Laser Self-Mixing Doppler Velocimeter Based on Distributed Feedback Fiber Laser

In this paper, a novel velocimeter based on laser self-mixing Doppler technology has been developed for speed measurement. The laser employed in our experiment is a distributed feedback (DFB) fiber laser, which is an all-fiber structure using only one Fiber Bragg Grating to realize optical feedback and wavelength selection. Self-mixing interference for optical velocity sensing is experimentally investigated in this novel system, and the experimental results show that the Doppler frequency is linearly proportional to the velocity of a moving target, which agrees with the theoretical analysis commendably. In our experimental system, the velocity measurement can be achieved in the range of 3.58 mm/s–2216 mm/s with a relative error under one percent, demonstrating that our novel all-fiber configuration velocimeter can implement wide-range velocity measurements with high accuracy.

Design and Evaluation of an Aerosol Electrometer with Low Noise and a Wide Dynamic Range

A low-noise aerosol electrometer with a wide dynamic range has been designed for measuring the total net charge on high concentration aerosol particles within the range of −500 pA to +500 pA. The performance of the aerosol electrometer was evaluated by a series of experiments to determine linearity, sensitivity and noise. The relative errors were controlled within 5.0%, 1.0% and 0.3% at the range of −40 pA to +40 pA, ±40 pA to ±100 pA, and ±100 pA to ±500 pA respectively. The stability of the designed aerosol electrometer was found to be highly sensitive to temperature variations, but under temperature control, the root mean square noise and the peak-to-peak noise were 1.040 fA and 5.2 fA respectively, which are very close to the calculated theoretical limit of the current noise. The excellent correlation and the advantage of a wide dynamic range have been demonstrated by comparing with the designed aerosol electrometer to a commercial aerosol electrometer. A 99.7% (R2) statistical correlation was obtained; meanwhile, the designed aerosol electrometer operated well even when an overrange phenomenon appeared in the commercial aerosol electrometer.

Regional Air Pollution Distribution and Transportation Monitoring by Spectroscopic Remote Sensing

The regional air pollution distribution and transportation monitoring system was develpoed by spectroscopic remote sensing techniques. With the demonstration, spectroscopic techniques were proved to be critical in regional air quality monitoring.

Development of a new Portable Ultrafine Particle Sizer for Indoor Aerosol Monitoring

A new portable Ultrafine Particle Sizer based on unipolar charger and mini-plate DMA has been developed to monitor indoor aerosol. The performance of the Ultrafine Particle Sizer is discussed in detail.

Instrument for all-fiber structure measurement of ultra-low turbidity by using single photon detection technique

An all-fiber structure detection system based on single photon detection technique(SPDT) has been developed to measure the ultra-low turbidity ofliquids. To assure the measurement accuracy,the total intensity of transmission light has been detected and quantified as number of photons by avalanche photodiode (APD) which has the advantage of high sensitivity.A fresh all-fiber structure optical fiber probe based on SPDT is applied in the system to reduce the volume and fluctuation of traditional transmission-light measurement system,in which the all-fiber structure probe is used to delivery and collection of transmission light.On the basis of Beer-Lambert (B-L) transmission law,a test system has been established and carried out a series of experiments.By combining B-Llaw with the principle of SPDT,a novel model for detecting turbidity has been proposed to explain the experimental results.The results have shown a well exponential relationship over the range of 0.01–1NTU (Nephelometric Turbidity Units).It also has showna good linear relationship with a resolution as high as 0.01NTUin the range of 0.01-0.09 NTU.When it is 1 secondofthe sampling time,the mean error of measurement result can be controlled within 5% of full scale.In addition,the new detection structure proposed in this paper, which makes the system more compact and more suitable in the small special space.

Accurate Time-of-flight Measurement of Particle Based on ECL-TTL Timer

Because of its aerodynamic diameter of the aerosol particles are stranded in different parts of different human respiratory system, thus affecting human health. Therefore, how to continue to effectively monitor the aerosol particles become increasingly concerned about. Use flight time of aerosol particle beam spectroscopy of atmospheric aerosol particle size distribution is the typical method for monitoring atmospheric aerosol particle size and particle concentration measurement , and it is the key point to accurate measurement of aerosol particle size spectra that measurement of aerosol particle flight time. In order to achieve accurate measurements of aerosol particles in time-of-flight, this paper design an ECL-TTL high-speed timer with ECL counter and TTL counter. The high-speed timer includes a clock generation, high-speed timer and the control module. Clock Generation Module using a crystal plus multiplier design ideas, take advantage of the stability of the crystal to provide a stable 500MHz clock signal is high counter. High count module design using ECL and TTL counter mix design, timing accuracy while effectively maintaining , expanding the timing range, and simplifies circuit design . High-speed counter control module controls high-speed counter start, stop and reset timely based on aerosol particles time-of-flight, is a key part of the high-speed counting. The high-speed counting resolution of 4ns, the full scale of 4096ns, has been successfully applied Aerodynamic Particle Sizer, to meet the precise measurement of aerosol particles time-of-flight.