In this paper, a visualization system was proposed based on ultrasound excitation from a Q-switched pulsed YAG laser. The ultrasonic wave was received by a piezoelectric transducer. The electrical time-domain signal was analyzed in the Fourier-domain in order to detect a hole-like reflector in an austenitic stainless steel specimen. At a given receiver position, a piezoelectric transducer received the ultrasonic wave signal. The electrical time-domain signal was analyzed in the Fourier-domain. The experimental research on the influence of the relative position distance between the laser excitation spot and the defect of the test specimen was conducted. The experimental results showed a significant geometrical imaging of the reflector shape with the scanned data. Therefore, a quantitative laser ultrasound visualization system was realized along with the spectral analysis. It will provide a new method of defects detection and sizing.
An enhanced magneto-optic (MO) imaging system is presented to detect the invisible and buried subsurface flaws in
metallic specimens. The choice of the MO thin films, the design of the magnetic excitation device and the development
of the image processing approaches are presented in this paper and the quality improvement in MO imaging has been
demonstrated due to the proposed methods. Experimental results have been provided and verify the reliability and
accuracy of the enhanced MO imaging system.
Corrosion under coating has a serious effect on the metal conductivity and corrosion layer permittivity. A high frequency (13.56 MHz) Radio Frequency Identification (RFID) based system has been developed to measure corrosion under coating. The corrosion behaviour of coated steel has been investigated from a very fundamental understanding of permittivity using a Vector Network Analyser (VNA). This paper will first review corrosion and dielectric property measurement methods and investigate RFID tag antenna responses under different material properties of corrosion samples with atmospheric exposure times using VNA. The purpose of this study was to examine the RFID system for corrosion detection. The RFID tag’s coil and VNA are employed to measure the impedance change to determine the conductivity and relative permittivity variance with different atmospheric exposure times (1 month, 3 months, 6 months, 10 months and 12 months). Different spectrum distributions under different corrosion samples are investigated. Based on the studies, VNA based system testing, phase responses from the mild steel samples with different coating thickness are measured. The experimental results show that these two introduced techniques are able to distinguish between different exposure times with coating. Based on the results, corrosion detection under coating using equivalent permittivity and conductivity are developed and evaluated. Preliminary results show that the high frequency (HF) RFID method can be extended to a new application for detection of corrosion under coating and development of HF RFID systems for corrosion monitoring. Dielectric probe is applied to measure the permittivity variance with different paint thickness. With the paint thickness increasing, the dielectric is getting close to the paint’s properties. Waveguide is using here to measure the paint thickness effect for further UHF RFID study.
Pulsed electromagnetic Non-destructive Evaluation (NDE) techniques can be used for defect detection and stress assessment. Currently there is no single technique which would have the capability to provide a comprehensive picture of these material changes, therefore the fusion of data from a number of different sensors is required for early failure prediction. In contrast to fusion techniques, signal feature separation can be applied for defect as well as lift-off measurement. Eddy current sensors can be applied for displacement (proximity) measurement as well as NDE for defect detection and material characterisation. For displacement measurement, one of research aims is to overcome measurement uncertainties due to material variation and in-homogeneity. After the introduction of pulsed eddy current (PEC) NDE, this work reports the separation of pulsed eddy current responses for surface profile and defect inspection. Experimental studies of pulsed eddy current for defects and surface profile measurement are reported.
It briefly introduces the international development status of the high resolution for air-to-ground remote sensing satellite.
High resolution for the air-to-ground observation is also the civil and martial pursuing target. Because of the rising cost
along with the large-diameter telescope, the weight, cubage will also become large. Nowadays, how to get high
resolution with light weight, small cubage launch and large diameter is one of the important research directions in many
countries. We raise a method of large field-of-view and high resolution optical synthesis telescope which can solve this
problem. It is a co-phased segment mirrors which synthetic aperture diameter is about 1 m. Four 50cm diameter segment
mirrors can fulfill the requirement. It is folded during its launch and is spread after it reaches to its working spot. In this
way, it can reach the requirement of low launch weight, small launch cubage and can get high resolution observation.
This method contains the key technologies of real-time UV coverage, optics design optimization, co-phase measurement
and adjustment, micro-displacement sensor technology, the optics design and structure design. We explore the
technology which can fulfill field-of-view of 1.86° and the resolution of 0.4m. We will discuss the UV-coverage method
which includes the aperture arrangement, the relationship between the aperture number and the synthetic aperture
diameter. There are much more detail calculation and analysis to it. Something is discussed about its structure design and
optics design in the paper.
Guns and knives have become a significant threat to public safety. Recently, a variety of techniques based on Electromagnetics (EM) have been used for their detection. For example, walk-through metal detection has been used in airports; X-ray and THz detection systems have been used for luggage screening. Different EM frequencies for metallic object detection have demonstrated different merits. This paper reports on a 1-14 GHz swept-frequency radar system for metallic object detection using reflection configuration. The swept frequency response and resonant frequency behaviour of a number of metallic objects, in terms of position, object shape, rotation and multiple objects have been tested and analysed. The system working from 1 to 14 GHz has been set up to implement sensing of metal items at a standoff distance of more than 1 meter. Through a series of experimental investigations, it can be found that the optical depths derived from the Fourier Transform of the power spectrum profile is in close relation with the relative location of the metallic object. The cross correlation between coherence-polarisation and cross-polarisation RF returns can be used to distinguish different objects. Therefore the optical depth and the cross correlation can be used as useful features for metallic object detection and characterisation in this portion of the microwave frequency spectrum.
Colors recorded in an image depend on the color of the capture illuminant. As such image colors are not stable features for object recognition but we wish they were stable since perceived colors (the colors we see) are illuminant independent and do correlate with object identity. Color constancy algorithms attempt to infer and remove the illuminant color through image analysis. Over the last two decades, various models for color constancy have been developed. Unfortunately, color constancy algorithms are still not good enough to support object recognition. In this paper, we evaluate optimal color constancy procedures against color normalization. Two perfect color constancy algorithms are described. One is perfect color constancy by the scene, which arrives at an estimate of the illuminant not through algorithmic inference, but through measurement: the light source is measured using a spectraradiometer, assuming the reflectances of object surface are known. The other is perfect color color constancy by the illuminant, which arrives at an estimate of the illuminant through measurement, assuming the reflectances of object surface are unknown. Instead of color constancy, color normalization normalizes color images in terms of the context to remove illumination. To remove dependency due to illumination, images in a calibrated dataset are preprocessed using either the color constancy or color invariant normalization. Two experiments are reported in the paper. In the first experiment, the optimal algorithms of perfect color constancy based on measurement were tested using a calibrated image dataset. In the second experiment, the performances of the optimal color constancy algorithms are compared with color invariant normalization. Unfortunately, measurement driven color constancy by the illuminant does not support perfect recognition. However, color constancy preprocessing based on a scene dependent 'effective illuminant' facilitates near-perfect recognition. In comparison the color invariant normalization also deliver near-perfect recognition. The failure of color constancy by the illuminant is understandable because the measured illuminant doesn't correspond to the actual effective illuminant. Rather, we found illumination to depend both on the light source and characteristics of the scene.
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