Papers by Keyword: Time-of-Flight (TOF)

Abstract: The traditional power station boiler temperature field reconstruction algorithm is sensitive to the time of flight. In the boiler movement, the temperature field has symmetric distribution feature within the boiler. On the basis of the boiler temperature field reconstruction fundamental by using the acoustic method, the paper presents a new two dimension temperature field reconstruction algorithm, which combines the single path method and genetic algorithm. Firstly, the algorithm makes sure the temperature distribution by using single path function. It uses the points denote the temperatures on each path, and plots the mesh, which can represent the temperature preliminary distribution, by using the Bezier spline principle and linear multistep integration. Finally, the surface mesh is Interpolated and fitted by using genetic algorithm. The experimental result proved that, compared to the least square method, the new reconstruction algorithm has the feature of higher accuracy and higher reconstruction speed.

Abstract: The acoustic pyrometer system uses physical properties of the gas and registers the perceivable temperature without the effects of radiation, and the measuring accuracy of acoustic wave flight time is the major factor in its application. The traditional correlation algorithm could not overcome convolution interference and calculate the time delay of acoustic signals accurately, under the low SNR (Signal Noise Ratio) and complex reverberation noise conditions. This paper presents a generalized cross power spectrum algorithm to filter the product and convolution interferences, and improves the performances of anti-noise and anti-convolution by whitening the sample signals and adjusting the weighted value of cross power spectrum algorithm with the variation of SNR. The experimental result and theoretical analysis showed that the new generalized cross power spectrum algorithm compared to the traditional correlation function analytical algorithm, can overcome the convolution interferences from reverberation noise, and sharpen peak value, thereby estimate the time delays of signals accurately.

Abstract: We are presenting the work progress and recent results in a development and construction of new technologies for submillimeter laser ranging and picosecond accuracy laser time transfer. The key hardware components: the Start detector and discriminator, the echo signal detector, the timing device and signal cablings were studied in detail. The new devices have been designed, built and tested in our lab. To minimize the systematic errors the photon counting approach has been selected. The ranging chain has been designed and optimized with a goal of single shot resolution of several millimeters and sub-millimeter normal points and overall system stability. The Start detector and discriminator are constructed as a single device to optimize their matching and maintain stability. The NPET timing system based on surface acoustic wave interpolator has a resolution of 800 fs and 4 fs long term stability. The echo detector is based on innovated SPAD detector optimized for high repetition Gate rate and minimal dark count rate. Both the detectors output signals have ultrafast slew rates < 200 ps / 1 V. In connection to the 6 GHz bandwidth of the timing system inputs these fast slew rates improves the timing and temperature stability along with the RF interference immunity. The new low temperature drift signal cables have been selected, tested and used. The new hardware was tested in indoor calibration experiments. We have achieved the single shot resolution of 3 mm rms. The temperature and temporal stability of the individual components is excellent. The drift is typically below 200 fs/K for each contributor. The overall temperature drift of the entire laser ranging chain is below 500 fs/ K. The long term stability of the ground target calibration is better than ± 800 fs within 3 days. During this period the environment temperature changed by more than 4°C. In the sense of time deviation Tdev the stability of 300 fs was achieved. The presented components will enable to carry out laser ranging with submillimeter normal points stability and reproducibility. The accuracy of the “ranging machine” based on these devices will reach sub-mm values, as well. The concept and construction will be presented along with the achieved devices parameters.

Abstract: The growth of thin films by laser ablation involves very complex physical processes. The quality of the layer and stoechiometry of the deposits depend on key parameters like the ion energy and their angular distribution. The evolution of ions number and energy, and the angular distributions in regards to the incident laser energy, have been studied by the mean of a charges collector. We present the polar diagrams of energy and number of ions collected by irradiating a silicon target using an excimer laser at different energies.

Abstract: Shock waves are indispensable tools for medical applications, and hence their interactions with human tissue become one of the most important basic research topics. In this paper, the determination of shock Hugoniot curves for liquids that can model human tissue, namely water, castor oil, and aqueous solutions of sodium chloride, sucrose and gelatin, at 10 and 20 weight percent are presented. Underwater shock waves were generated by ignition of 10 mg silver azide pellets and time variations of over-pressures were measured and simultaneously the shock speed was measured by the time of flight technique. Then shock Hugoniot curves were obtained, by assuming the Tait type equation of state, to relate the estimated density and measured pressure values. Results show in the cases of aqueous solutions that increasing amount of additives into water causes only a very minute decrease in the compressibility of the solution. This difference was more pronounced in the case of sodium chloride, less for gelatin, and almost none for sucrose aqueous solution.

Abstract: A series of digital frequency filters (DFFs) were designed to screen diverse noises and the spectrographic analysis was conducted to isolate complex boundary reflection, which obscures the damage-induced signals. The scale-averaged wavelet power (SAP) technique was applied to enhance the measurement accuracy of Time of Flight (TOF). As an example, the propagation characteristics of elastic wave in a structural beam of square cross-section were analyzed using such an approach and verified experimentally and numerically, with the consideration of the complicated wave scatter caused by the non-ignorable section dimensions.

Abstract: Neutron imaging using a pulsed neutron time-of-flight method can give an energy dependent transmission image, namely, spectroscopic image. This image includes the structure information if the sample is coherent scatterer. Here, two examples are introduced. First, we obtained the transmission image of a welded sample of SS304 and 308. Change of the crystal structure depending on the position was observed. Furthermore, we measured spatial dependent transmission of SS samples treated in different ways, surface treatment and whole body treatment. There were almost no spatial dependent change, but the cross section change was found between surface and whole body treatment samples. It was suggested that this might be due to the difference of a grain size. These results demonstrated that the spectroscopic imaging using a pulsed neutron source is a useful tool for material characterization.

Abstract: High-tension bolts have been used widely for the clamping of many kinds of large structures. In these bolts, the estimation of clamping force has been regarded as the main issue in the evaluation of clamping condition. This paper proposes a method using ultrasonic wave, which is based on the dependency of sound speed on the stress. In order to verify the usefulness of the proposed method, two kinds of experiments are carried out. The first one involves the measurement of sound speed when the bolt is stressed by the tension tester, and here, the relationship between the exact axial force and sound speed is calibrated. The result shows good agreement with the expected linear relationship between sound speed and axial stress. The second experiment involves the measurement of axial stress by the proposed method when the bolt is stressed by the torque wrench. The results are coincident to the strain gage measurement. From these results, we can conclude that the proposed method is indeed useful in evaluating clamping force in high-tension bolts.

Abstract: Plastic anisotropy can affect the strains measured by neutron diffraction. If this is not properly accounted for significant errors can result in the calculated stresses. This paper illustrates addresses this issue using measurements of the residual strain field around a 60 mm long single weld bead deposited on the surface of a 17 mm thick stainless steel plate. Measurements were made on ENGIN-X, the engineering spectrometer at the ISIS facility of the Rutherford Appleton Laboratory (UK). Diffraction spectra from these measurements have been fitted using both single and multi-peak fitting approaches. Both residual strain and stress results have been presented for (111) and (200) single peak fits and compared to a multi-peak fit (Rietveld) analysis. Results from these analyses have revealed significant anisotropy in the response of the individual lattice planes. This effect is most severe in measurements carried out in the normal direction and is shown to be predicted using an elasto-plastic self-consistent model.