A conventional VMI (velocity map imaging)-TOF (time-of-flight) spectrometer is modified by adding an extra electrode. By this small modification, the longitudinal focus can be realized for TOF mass resolution while maintaining the lateral focus for optimal VMI energy resolution simultaneously. The mass-resolving power by four-electrode ion optics is greatly enhanced. Our design is especially useful in experiment with a non-focused laser beam.
Physical properties, such as density, refractive index and morphology of the aerosol particles will be changed when the relative humidity of the environment is relatively high, which leads to a significant variation of the scattered light signal collected by the single particle light scattering measurement system. If the calibration parameters in the condition of low humidity are applied to inverse aerosol mass concentration, the measurement accuracy will certainly be degraded. Therefore, the calibration parameters of the system must be corrected. In this case, the monotonic relationship between the particle size and the scattered light signal collected by the system should be considered carefully. Combining the Mie scattering theory with the humidity growth model of the particle size and the refractive index, the influence of relative humidity on the scattered light signals of spherical particles has been investigated in this paper. The results indicate that the diameters of spherical particles grow exponentially and the refractive index decreases linearly when the relative humidity is increased between 60% and 95%. Consequently, a significant change of the angular distribution of the scattering intensity occurs. The forward-scattered light is getting stronger, while the back-scattered light becomes weaker. Meanwhile, the scattered light flux of the particle within a solid angle displays exponential growth with increasing the relative humidity. Thus, the monotonous relationship between the particle size and the scattered light flux has changed significantly in the case of the high humidity, and their quadratic coefficient decreases clearly assuming the particle density invariant, which causes an obvious increase of the calibrated proportional coefficient. The results of this work provide an important theoretical guidance for the humidity correction of calibration parameters for the inversion of aerosol mass concentration by the single particle light scattering method.
Optical computerized tomography (OCT), as a branch of computerized tomography (CT) techniques, has been widely used to display and diagnose a variety of complex flow fields, due to its characteristics of real-time, stable, non-contact and can supply 3-D distributions. In practical applications, we found some different phenomenon when they are adopted in clod and hot complex flow fields. In this paper, the cold and hot flow field’s OCT diagnosis is analyzed and compared. The results show that 1) OCT can directly reflect the spatial distribution of the measured flow field’s refractive index, for both the cold and the hot complex flow fields; 2) OCT can reflect the boundary or structure of the cold flow fields, but could not well done for the hot flow fields. The involved results will help us to make better use of OCT methods to diagnose various cold or hot complex flow fields.
In order to accurately measure counting efficiency of laser airborne particle counter, the characteristics and shortages of
the signal amplitude response functions of domestic instruments were analyzed firstly. Then the design of performance
optimization for optical sensors was developed through using sheath air inlets to replace the original inlets, which can
cause the signal amplitude response functions to be described by the normal distribution. Base on these, a new method
for calculating counting efficiency was presented. Through analyzing the relation between signal amplitude response
function and coordinate origin, the counting efficiency for mono-disperse particles can be confirmed. If the signal
amplitude response function intersected with the coordinate axis, fitting the incomplete curve into the complete curve
using non-linear Least Square Method, then the counting efficiency can be defined as the ratio of the included area of the
incomplete curve to the complete curve. If the whole signal amplitude response function totally diverged from the
coordinate origin, it proved that the counting efficiency of mono-disperse particles was up to 100%. The theory and
experiments prove that this method is simple, useful and practical. It also offers the clear guidance direction for
appraising performance of the instrument.
The light scattering signal amplitude distribution of aerosols, which was measured by the single particle counting
technique, was applied to calculate aerosol mass concentration using an inversion algorithm. Therefore, how to
accurately extract the information of the signal amplitude distribution is a crucial problem for aerosol mass concentration
inversion. In view of mass concentration inversion accuracy and stability are related to information extraction methods,
the linear and non-linear segmentation methods were presented. Experimental results indicate the information entropy of
the signal amplitude distribution obtained by the non-linear segmentation method is clearly larger in the same number of
signal subsets, and when inversion accuracy achieves stability, the ratio of information entropy to the number of signal
subsets is also larger than that of the linear segmentation method, leading to rapid stability of inversion accuracy. The
study of the information entropy characteristic of the signal amplitude distribution of aerosol provides theoretical
guidance for the circuit design of an optical particle counter.