Huanqin Wang

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.

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 5u2009µA with 2.6u2009kV 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 20–1000u2009nm), respectively. The intrinsic and extrinsic charging efficiency increased with the particle diameter. The intrinsic efficiency is practically 100% for particle diameters above 50u2009nm. 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.

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.

Comparative study of cylindrical and parallel-plate electrophoretic separations for the removal of ions and sub-23 nm particles

Cylindrical and parallel-plate electrophoretic separations for the removal of ions and sub-23xa0nm particles were compared in this study. First, COMSOL Multiphysics® software was utilized to simulate the ion and particle trajectories inside both electrophoretic separations. The results show that ions and sub-23xa0nm particles are removed simultaneously and that all particles can pass through both electrophoretic separations smoothly at a trap voltage of 25xa0V. The experimental results show that ion losses become smaller with increasing ion flow rates, and ion losses of the cylindrical and parallel-plate electrophoretic separations range from 56.2 to 71.6% and from 43.8 to 59.6%, respectively, at ion flow rates ranging from 1-3xa0L/min. For the removal of ions and sub-23xa0nm particles, the collection efficiency of both electrophoretic separations can reach 100%, but the parallel-plate electrophoretic separation requires a lower trap voltage. The particle loss of the parallel-plate electrophoretic separation is under approximately 10%, which is lower than that of the cylindrical electrophoretic separation. In particular, for large particles (800-2500xa0nm), the particle losses inside the cylindrical electrophoretic separation are approximately two times higher than those inside the parallel-plate electrophoretic separation. The parallel-plate electrophoretic separation is beneficial for the removal of ions and sub-23xa0nm particles.

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.

Optimal design of optical length in low turbidity measurement system with wavelength 1310 nm and 1550 nm

To meet the need of long distance transmission in low turbidity measurement system for low-loss, a new optical structure with wavelength 1310nm and 1550nm as the incident light is employed. In this research, experiments have been done for different optical length of the two wavelength light sources. The results show that: first, the transmitted light intensity has big difference under the circumstance of same concentration and optical length, though the loss has no remarkable difference transmitted in optical fiber between 1310nm and 1550nm. Second, the optimized optical length for better absorbance has been determined for 1310nm and 1550nm and it is irrelevant to the incident intensity. Third, the intensity of the two transmitted light decreases exponentially with the increase of optical length. For example, when the range of the optical length of 1310nm is 0.5mm-2mm, the transmitted intensity is about 60%-79% and the absorbance is 0.12-0.42. The transmitted intensity is about 5%-44%. When the range of the optical length of 1550nm is 0.5mm-2mm and the absorbance is still 0.12-0.42. Our experimental data provides the basis both for the optical length selection of these two light sources in water and the near-infrared spectral wavelength selection.

Optimized design of a TOF laser range finder based on time-correlated single-photon counting

A time-of-flight (TOF) laser range finder based on time-correlated single photon counting (TCSPC) has been developed. By using a Geiger-mode avalanche photodiode (G-APD) with the ability of detecting single-photon events and Time-to-Digital Converter (TDC) with picosecond resolution, a good linearity with 4.5 cm range precision can be achieved in the range of 1-10 m. This paper highlights a significant advance in improving the key parameters of this system, including the range precision and measurement dynamic range. In our experiments, it was found that both of the precision and the measurement dynamic range were limited by the signal to noise rate (SNR) and the inherent jitter of system. The range precision can be improved by enhancing the SNR of system. However, when the SNR is high enough, the main factors affecting the range precision will turn into the inherent jitter, which makes the range precision can not be improved infinitely. Moreover, the inherent jitter generated by pulsed laser and the signal processing module has been measured, and its influence on the system performance has also been discussed. Taking all of these factors into account, some optimized designs have been proposed to improve range precision and dynamic range simultaneously. The final experiment results show that, after all of these optimization designs, the range precision of system is better than 1.2 cm and the measurement dynamic range is enlarged to 54 m when the sampling time is as short as 1 ms, which is sufficient for many applications of 3D object recognition, computer vision, reverse engineering and virtual reality.

A high resolution laser ranging system based on time-correlated single-photon counting technology

Laser ranging has become an important method for both distance measurements and acquisition of threedimensional (3D) images. In this paper, a laser ranging system based on Time-Correlated Single-Photon Counting technology (TCSPC) is developed. A Geiger-mode avalanche photodiode (G-APD), which has the ability of detecting single-photon events, is used to capture the weak light scattered from the long-range target. In order to improve the ranging resolution of TCSPC based measurement system, a high repetition frequency of subnanosecond narrow pulse generator circuit based on the avalanche effect of RF-BJT is designed and applied as the light source. Moreover, some optimized optical light designs have been done to improve the system signal to noise rate (SNR), including using a special aspherical lens as projecting lens, adopting a telephoto camera lens with small view angle and short depth of field before detector. Experimental tests for evaluation of the laser raging system performance are described. As a means of echo signal analysis, three different algorithms have been introduced, in which the cross-correlation algorithm was demonstrated to be the most effective algorithm to determining the round trip time to a target, even based on histograms with a significant amount of background noise photons. It was found that centimeter ranging resolution can be achieved thanks to the use of Time-to-Digital Converter (TDC) with picosecond resolution and the Cross-Correlation algorithm. The proposed laser ranging system has advantages of high range resolution, short response time and simple structure, which was potential applications for 3D object recognition, computer vision, reverse engineering and virtual reality.