In order to ensure that small diameter steel pipes with thick wall have high intensity and high quality, ultrasonic immersion method with focusing probe was used to detect the flaw of the small-diameter steel pipes with thick wall. In practice, the echoes are often corrupted with external noise or internal noise, therefore, it is necessary to reduce the noise and to enhance the SNR of ultrasonic signals. A technique for improving the SNR of ultrasonic signals using wavelet transform is presented. In this method, WT, consider as one band-pass filter, is used to remove the noises. The performance of this technique has been verified by experimental, which is done by using a series of flaw ultrasonic echoes obtained from a specimen of the small-diameter steel pipes with thick wall. In particular we have found the processing of the ultrasonic signals using wavelet transform extremely useful for noise reduction. After processing, the SNR of ultrasonic signals are enhanced substantially. All experimental results show that this technique is effective for removing the white noise from the ultrasonic signals.

In this paper ,We present a theoretical model which treats one-dimensional target heating and vaporization as well as energy absorption and collision reactions in the melting metal vapor. The coupling effects have been calculated for 0. 3O8-im XeCl laser radiation to Aluminium. The mcident laser intensity and the pulsed duration are 107-109W/cm2 and 80-ns respectively. The time relations of thermal and impulse coupling coefficients are obtained by solving non-linear heat conduction and rate equations about the temperature and density. These results are compared with the experiment measurements and the agreement is fairly good. I . INTRODUCTIONA lot of studies on interaction of pulse laser with metal targets in vaccum have been carried out experimentally and theoritically. Most of these were often limited to the coupling of infrared laser to the metal targets. With the occurrence of high power pulse UV laser and the important roles of UV laser in application,the valuable investigation results in this aspect were given over the past ten years'6. The large absorptivty of metals in the ultraviolet makes excimer lasers appear particularly attractive in the processing of mteals. Rosen"2investigated the coupling proccesses of pulse XeF laser to aluminium and titanium alloys. They obtained interesting pressure parameters by means of the rate equation in uniform vapor layer. Newstein5 developed the theory presented by Harrach7 ,considered the effect of convective flow ,and gave the distribution property in vapor layer by solving the rate equations of density and temperature.The response of a metal surface to irradiation by a high intensity pulse laser consists of several stages. The heated surface first reaches the melting temperature and forms a melt layer. The temperature rises continuously until evaporation commences. Part of the absorbed laser then goes into the latent heat of vaporization kinetic energy of the removed mass and heating of the expelled vapor while the remainder of the energy is conducted into the solid or liquid. Ultimately, under the condition where the intensity is not so high that the expelled vapor becomes strongly absorbing, the system asymptotically approaches a steady state,in which all of the absorbed laser goes into va-Porization at the surface,and the temperature profile within the tatget remains constant. 0-8194-1