Huang Songling

Magnetic field properties caused by stress concentration

Measurements of the effects of tensile stress on magnetic field properties, infrared thermography and acoustic emission of a cuboid sample with an elliptical hole in its center were presented. The tensile stress was applied perpendicularly to the sample by electro-tension machine according to a step-loading curve. The changes of the sample temperature was recorded by an infrared thermography system and the noise of domain reversal was inspected by two acoustic probes, which were placed on each end of the sample near the collets of the electro-tension machine, when the sample was in loading process. The magnetic fields on the surface of the sample were inspected with 8 mm lift-off when the loads were held. Valuable information about the changes of domains was obtained from analysis of acoustic emission signals in loading process. Infrared images of the sample provided complementary information about the state of the sample. The results show that stress concentration in ferromagnetic material affects the direction and structure of domain and generates net magnetic moment on its surface. The distribution and magnitude of the net magnetic moment are correlative with those of stress.

Improved immunity to lift-off effect in pulsed eddy current testing with two-stage differential probes

Pulse eddy current (PEC) testing is broadly used as an effective nondestructive testing technique especially for the defect detection of multiple layer and irregular surface objects. PEC testing’s adoption of repeated pulses as excitation provides for the penetration of many frequency components into the piece being tested and returns more information from various depths. As the lift-off height will inevitably change during detection, the lift-off effect serves as a significant obstacle to implement effective nondestructive testing and further evaluations. This paper concentrates on improving the probe’s immunity to the lift-off effect and proposes two-stage PEC differential probes. Physical experiments are addressed in this paper. Experimental results demonstrate that two-stage differential PEC probes are able to suppress lift-off effects.

Progress on accurate measurement of the Planck constant: Watt balance and counting atoms *

The Planck constant h is one of the most significant constants in quantum physics. Recently, the precision measurement of the numeral value of h has been a hot issue due to its important role in establishment for both a new SI and a revised fundamen tal physical constant system. Up to date, two approaches, the watt balance and counting atoms, h ave been employed to determine the Planck constant at a level of several parts in 10. In this paper, the principle and progress on precision measurement of the Planck constant using watt balance and co unting atoms at national metrology institutes are reviewed. Further improvements for the Plan ck constant determination and possible developments of a revised physical constant system in futur e are discussed. PACS numbers: 06.20.-f, 06.20.Jr, 07.05.Fb, 07.10.Pz Submitted to:Chinese Physics BThe Planck constant h is one of the most significant constants in quantum physics. Recently, the precision measurement of the value of h has been a hot issue due to its important role for the establishment of both a new SI and a revised fundamental physical constant system. Up to date, two approaches, the watt balance and counting atoms, have been employed to determine the Planck constant at a level of several parts in 108. In this paper, the principle and progress on precision measurement of the Planck constant using watt balance and counting atoms at national metrology institutes are reviewed. Further improvement in determining the Planck constant and possible developments of a revised physical constant system in future are discussed.

Novel Error Prediction Method of Dynamic Measurement Lacking Information

Predicting for dynamic measurement error is becoming a hot issue in measurement field. The paper deals with the error prediction of dynamic measurement lacking information. Firstly, according to grey system theory and the bootstrap method, the prediction and transfer coefficients of all error sources have been taken into account. Then, the error prediction of dynamic measurement lacking information, are obtained starting from each error sources’ absolute accuracy in terms of the error combination principle. Finally, in a general dynamic measurement, the predicting measurement errors obtained by means of this novel proposed method are compared with the ones obtained from Monte Carlo method. The results are in good agreement with each other.

Optimization of the magnetic circuit in the MFL inspection system for storage-tank floors

Magnetization is the key to inspection of a tank floor via the magnetic-flux-leakage (MFL) technique. In order to optimize the magnetic circuit of the MFL detector and obtain the best detection effects, the influences of the magnet size on the floor magnetization condition, the gap magnetic flux density, and the magnetic force were studied with the help of the finite element method (FEM) and the effects of some other parameters, such as the magnet pole spacing and pole-piece thickness, on the signal-to-noise ratio were analyzed. The simulation results indicate that variation of the magnet width affects the magnetization much more than variation of the magnet thickness and that the detector can reach a trade-off between the magnetization effects and the driving force when the magnet is about 30 mm thick and 40 mm wide. On condition that the floor has reached its magnetizing saturation, an increase in the magnet-pole spacing and the pole-piece thickness can improve the testing sensitivity and the signal-to-noise ratio.Magnetization is the key to inspection of a tank floor via the magnetic-flux-leakage (MFL) technique. In order to optimize the magnetic circuit of the MFL detector and obtain the best detection effects, the influences of the magnet size on the floor magnetization condition, the gap magnetic flux density, and the magnetic force were studied with the help of the finite element method (FEM) and the effects of some other parameters, such as the magnet pole spacing and pole-piece thickness, on the signal-to-noise ratio were analyzed. The simulation results indicate that variation of the magnet width affects the magnetization much more than variation of the magnet thickness and that the detector can reach a trade-off between the magnetization effects and the driving force when the magnet is about 30 mm thick and 40 mm wide. On condition that the floor has reached its magnetizing saturation, an increase in the magnet-pole spacing and the pole-piece thickness can improve the testing sensitivity and the signal-to-noise ratio.

Circuit-field coupled finite element analysis method for an electromagnetic acoustic transducer under pulsed voltage excitation

tation and considers the non-uniform distribution of the biased magnetic fleld. A complete model of EMATs including the non-uniform biased magnetic fleld, a pulsed eddy current fleld and the acoustic fleld is built up. The pulsed voltage excitation is transformed to the frequency domain by fast Fourier transformation (FFT). In terms of the time harmonic fleld equations of the EMAT system, the impedances of the coils under difierent frequencies are calculated according to the circuit-fleld coupling method and Poynting’s theorem. Then the currents under difierent frequencies are calculated according to Ohm’s law and the pulsed current excitation is obtained by inverse fast Fourier transformation (IFFT). Lastly, the sequentially coupled flnite element method (FEM) is used to calculate the Lorentz force in the EMATs under the current excitation. An actual EMAT with a two-layer two-bundle printed circuit board (PCB) coil, a rectangular permanent magnet and an aluminium specimen is analysed. The coil impedances and the pulsed current are calculated and compared with the experimental results. Their agreement verifled the validity of the proposed method. Furthermore, the in∞uences of lift-ofi distances and the non-uniform static magnetic fleld on the Lorentz force under pulsed voltage excitation are studied.

A new frequency-tuned longitudinal wave transducer for nondestructive inspection of pipes based on magnetostrictive effect

Facing the difficulty of carrying out optimum inspection of defects and optimization design of Kwuns magnetostrictive transducer, a new transducer configuration is proposed. The mutilple-belts coils are used as the transmitting coil and receiving coil. This kind of coil is often used in electromagnetic ultrasonic transducer (EMAT), but it is used for magnetostrictive tansducer firstly. To verify the performance of the transducer, several experiments were performed. The results show that the proposed coils not only could tune the center frequency but also could improve the amplitude and signal-to-noise (SNR) of the detected signals.

Automatic inspection of the localizer slope based on improved Hough transform

In light of the present situation of inspecting slope of localizer with less accurate and low efficiency, the novel method of automatic inspection based on computer vision was proposed. This paper introduced the hardware structure for image acquisition in the automatic inspection system, and analyzed the technologies used in image processing. Otsu threshold segmentation, eliminate noise and thinning were used in image pretreatment to enhance image quality and to improve inspecting precision; an improved Hough transformation was brought forward to detect lines and calculate the slope of the localizer. The proposed approach not only has high precision, but also accelerates the compute speed. The experimental result shows that this algorithm is validate.

Analysis of cantilever vibration of gamma radiation system

Cantilever vibration criterion of gamma radiation system was presented on the fundamental of discussing the relationship between vibration and the performance of mobile container inspection system. Static deformation, vibration mode and inherent frequency of the cantilever of gamma radiation system were calculated with ALGOR Finite Element System to verify strength and rigidity of the cantilever. The amplitude of the cantilever vibration will achieve its maximum value at its startup accelerating process. This process was easily simulated by imposing an inertial force on the cantilever. The predictions show good agreement with test results. It indicates that this kind of finite element model of the cantilever structure is capable of capturing the mechanical characteristic.

Design of the feedback type DC electronic load hardware circuit using IPM

Firstly, the paper shows the comparison between the traditional resistance load and the new electronic load. And then it suggests the implementation scheme of the feedback type DC electronic load, which features feeding back energy to the public grid. Furthermore, the structure of the inverter, which is the kernel module of the feedback type electronic load, is introduced. Finally, an excellent functional and reliable single-phase grid-connected inverter is developed, using IPM to constitute its main circuit. The driving circuit, as well as the snubber circuit and protection circuit, is designed. With advantages of energy saving and high efficiency, the feedback type DC electronic load possesses extensive application foreground and pretty well economic benefit.