Research On Theory And Application Of Ultrasonic Resonance Spectrum Measurement

If the frequency of ultrasonic propagation in a finite length material measured is equal to the natural frequency of material, the resonance phenomenon occurs. In this paper, the theory of ultrasonic resonance spectrum measurement and its application are studied.First, the resonance frequency formula of the finite length material is derived with the physical properties of one-dimensional bar and mechanical vibration, which gives the relation between resonance frequency, acoustic velocity, length of material and vibration mode. It shows that resonance frequency decreases with the increase of length, the higher the order number corresponding with vibration mode, the larger the resonance frequency is. The velocity of aluminum and steel rods are measured using this formula. Establish three layer media model of water-steel-water, to analyses the influence of resonance frequency on transmission coefficient and reflection coefficient. And discuss the transmission and reflection characteristics of ultrasonic at resonance frequency. At resonance frequency, transmission coefficient reaches a maximum value while reflection coefficient has minimum. But frequency range corresponding to maximum or minimum is very small meanwhile transmission and reflection curves change more serve at resonance frequency. Second, transmitted and reflected wave spectrum of ultrasonic is obtained by the spectrum of probe and the relation between transmission as well as reflection coefficients with frequency, and analyze the differences between transmitted and reflected wave with the incident one. At resonance frequency, the shape of transmitted wave is close to incident wave; but at non-resonance frequency, the shape of reflected wave is close to the incident wave. Then establish one mode to reflect the cemented circumstances about I interface of cased well with the spectral differences when resonance occurs. Using this method of ultrasonic resonance spectrum to analyze this mode and judging various defects or cracks in solid materials and cement judge by means of this kind of difference is possible. Finally, the reasons that blind spots occurs when measuring with ultrasonic resonance spectrum measurement are discussed.