Xiong Wan

An online emission spectral tomography system with digital signal processor.

Emission spectral tomography (EST) has been adopted to test the three-dimensional distribution parameters of fluid fields, such as burning gas, flame and plasma etc. In most cases, emission spectral data received by the video cameras are enormous so that the emission spectral tomography calculation is often time-consuming. Hence, accelerating calculation becomes the chief factor that one must consider for the practical application of EST. To solve the problem, a hardware implementation method was proposed in this paper, which adopted a digital signal processor (DSP) DM642 in an emission spectral tomography test system. The EST algorithm was fulfilled in the DSP, then calculation results were transmitted to the main computer via the user datagram protocol. Compared with purely VC++ software implementations, this new approach can decrease the calculation time significantly.

Lagrange interpolation reprojection-revising reconstruction with incomplete data in optical computed tomography

In the case of optical computed tomography (OpCT) reconstructions for the field comprising obstacle objects, parts of the projection data are lost; hence, the image reconstruction would be always imprecise with conventional OpCT algorithms if no other preprocessing or interpolation approaches are adopted. To solve the problem of the reconstruction with incomplete data, a Lagrange interpolation reprojection-revising (LIRR) algorithm is proposed. First a Lagrange interpolation polynomial is adopted to preestimate the lost projection data. By comparing to the reprojection of the rough reconstructed image in the iteration, the unbiased Lagrange interpolation estimations are retained; otherwise, the biased estimations are revised, ray by ray, with the weighed superposition of the interpolation and the reprojection data. These steps are repeated until all estimations for lost data are acceptable. Reconstruction results of some known algorithms and the LIRR algorithm for two typical tested images, including a circle round opaque object, were compared. Additionally, an emission spectral tomography experiment was also designed to evaluate the LIRR. The simulation and experiment results show the LIRR makes a great improvement in reconstruction precision over the traditional OpCT algorithms and hence has potential application of OpCT reconstructions with incomplete data.

Three dimensional measurements of engine plumes with four-channel single spectral tomography

The design and improvement of an aeroengine rely on the analysis of the combustion process in the combustion chamber to a certain extent. It is difficult to investigate the combustion inside the chamber directly due to its obturation and invisibility, however, the physical distribution of exhaust plumes outside the chamber can be measured by various means and provide the information to deduce the combustion condition inside the chamber. Most traditional measurementations such as thermography can only measure the plane temperature distribution of the plumes, hence its applications are restrained. In this paper, a three dimensional (3D) measurement approach is proposed, which is based on a multichannel single spectral tomography (SST) and the radiation theory of blackbody. Furthermore, an SST real-time testing system was built to measure the 3D temperature distribution of the plumes of a pulse detonation engine. To improve the precision of the testing system, an emission projection matrix was proposed and t...

Emission Spectral Tomography Reconstruction Based on Maximum Entropy Interpolation

To improve the performance of optical computed tomography (OpCT) reconstruction in the case of limited projection views, maximum entropy (ME) algorithms were proposed and can achieve better results than traditional ones. However, in the discrete iterative process of ME, the variables of the iterative function are continuous. Hence, interpolation methods ought to be used to improve the precision of the iterative function values. Here, a sinc function interpolation approach was adopted in ME algorithm (SINCME) and its reconstruction results for OpCT with limited views were studied using four typical phantoms. Compared results with ME without interpolation, traditional medical CT back-projection algorithm (BP), and iterative algorithm algebraic reconstruction technique (ART) showed that the SINCME algorithm achieved the best reconstruction results. In an experiment of emission spectral tomography reconstruction, SINCME was also adopted to calculate the three-dimensional distribution of physical parameters of a candle flame. The studies of both algorithm and experiment demonstrated that SINCME met the demand of limited-view OpCT reconstruction.

Detection and compensation of basis deviation in satellite-to-ground quantum communications

Basis deviation is the reference-frame deviation between a sender and receiver caused by satellite motion in satellite-to-ground quantum communications. It increases the quantum-bit error ratio of the system and must be compensated for to guarantee reliable quantum communications. We present a new scheme for compensating for basis deviation that employs a BB84 decoding module to detect basis deviation and half-wave plate to provide compensation. Based on this detection scheme, we design a basis-deviation compensation approach and test its feasibility in a voyage experiment. Unlike other polarization-correction schemes, this compensation scheme is simple, convenient, and can be easily implemented in satellite-to-ground quantum communications without increased burden to the satellite.

Theoretical studies of the local structures and electron paramagnetic resonance parameters for Cu2+ center in Zn(C3H3O4)2(H2O)2 single crystal

The electron paramagnetic resonance (EPR) parameters (g factors gxx, gyy, gzz and hyperfine structure constants Axx, Ayy, Azz) are interpreted by taking account of the admixture of d-orbitals in the ground state wave function of the Cu2+ ion in a Zn(C3H3O4)2(H2O)2 (DABMZ) single crystal. Based on the calculation, local structural parameters of the impurity Cu2+ center were obtained (i.e. Ra≈1.92 Å, Rb≈1.96 Å, Rc≈1.99 Å). The theoretical EPR parameters based on the above Cu2+−O2− bond lengths in the DABMZ crystal show good agreement with the observed values and some improvements have been made as compared with those in the previous studies.

Remote Quantitative Analysis of Minerals Based on Multispectral Line-Calibrated Laser-Induced Breakdown Spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS) is a feasible remote sensing technique used for mineral analysis in some unapproachable places where in situ probing is needed, such as analysis of radioactive elements in a nuclear leak or the detection of elemental compositions and contents of minerals on planetary and lunar surfaces. Here a compact custom 15 m focus optical component, combining a six times beam expander with a telescope, has been built, with which the laser beam of a 1064 nm Nd; YAG laser is focused on remote minerals. The excited LIBS signals that reveal the elemental compositions of minerals are collected by another compact single lens-based signal acquisition system. In our remote LIBS investigations, the LIBS spectra of an unknown ore have been detected, from which the metal compositions are obtained. In addition, a multi-spectral line calibration (MSLC) method is proposed for the quantitative analysis of elements. The feasibility of the MSLC and its superiority over a single-wavelength determination have been confirmed by comparison with traditional chemical analysis of the copper content in the ore.

Diagnostics of Three-Dimensional Temperature Distribution of Ar Arc Plasma by Spectrum Tomography Technique

In this paper, a new technology which can be used to diagnose 3-D temperature distribution of argon arc plasma is proposed. Compared with current technologies, two aspects have been improved. First, a new hybrid reconstruction technique [max-entropy, least square, and flatness reconstruction technique (MLFRT)] is presented as an algorithm system, where the numerical simulation of the MLFRT has been realized. The results show that the MLFRT has good convergence, stability, and efficiency. Second, two orthographic double-wavelength light paths have been designed in the experimental setup, which can collect intensity data in real time. Based on these data, we reconstruct the emission coefficient using the MLFRT. Then, a spectral line relative intensity method was chosen to calculate the 3-D temperature distribution, where the spectral analysis of argon arc plasma was introduced. This new technology can acquire good result by just two orthographic intensity data sets. Therefore, the experimental system is simple, and the experimental cost is low. The result is beneficial to understand the working principle of argon arc plasma, improving the level of craftsmanship. It also has good application advantages over other 3-D flow field testing, such as density field, pressure field, velocity field, etc. It shows great academic and economic value.

Thermal computed tomography for biological tissue reconstruction based on radiation balance

In this paper, a thermal computed tomography (TCT) for structural reconstruction of optical-thin biological tissues is proposed, which is based on a radiation balance between adjacent infinitesimals. A theoretical analysis has been carried out and several influential factors have been analyzed for the reconstructions of a physical model in numerical simulations. The simulation results give a criterion of how to choose an appropriate set of parameters to reconstruct biological tissues with the TCT. Besides, a TCT system was established and a validation experiment was carried out. The studies of both numerical simulations and experiments have verified the feasibility of the proposed TCT and give a valuable reference for the future applications of TCT in biology.

Three-dimensional radiation thermometer combining near-infrared passband thermometry with optical fiber bundle tomography

We report an implementation of a three-dimensional (3D) middle-temperature (500?1500 kelvin) radiation thermometer, which combines a near-infrared passband (1?3 micron) thermometry with an optical fiber bundle tomography (OFBT). To improve the probe precision, we calibrate the digital output of each OFB unit?vs. the passband radiant intensity of the blackbody. Furthermore a digital signal processor (DSP) based system is built to accomplish the emission signal processing and the tomographic computation with which the calculation speed can be improved. A temperature probe experiment of the flame of a candle has testified the feasibility of the OFBT-based 3D thermometer.