Measurement of characteristic parameters of ultrasonic flaw detectors
In order to guarantee the liability and accuracy of ultrasonic flaw detectors, a system is developed for measuring the characteristics of ultrasonic flaw detectors. The parameters which evaluate the characteristics of the pulse excitation circuit include pulse amplitude voltage, pulse rise time, pulse duration, pulse repetition frequency, peak frequency, bandwidth and output impedance. The parameters which evaluate the characteristics of the amplifier circuit include cut-off frequency, pass band, dynamic range, input impedance and equivalent input noise. The parameters which evaluate the coupling characteristics of these two circuits include crosstalk and blocking time during transmission.
Wavelet Filtering of Signals from Ultrasonic Flaw Detector
The paper considers basic principles of the algorithm of wavelet filtering of signals from an ultrasonic aw detector with the help of the fast wavelet transform. Criteria for selection of the type and order of a wavelet are formulated, and the number of decomposition levels required for the needed accuracy and reproducibility of results of ultrasonic tests are determined.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.