Measurement of Attenuation Using a Normalized Amplitude Spectrum

摘要

In conventional material evaluation and attenuation measurement, methods employing multiple ultrasonic echoes in the thickness direction of the samples are often used to calculate the reflection and attenuation coefficients. The successive echoes must be well resolved, and there is consequently a minimum thickness of material which can be tested for a given frequency transducer. For thin specimens, a high frequency probe may be used, but this may be problematic for composite laminates since the reflections from the individual plies can cause interference. In this paper, an alternative method based on the amplitude spectrum of the reflections from the specimen is presented. The technique deduces the attenuation coefficients by using the spectral amplitudes at the anti-resonance (or resonance) frequencies of the normalized amplitude spectrum, and has the advantage that it does not require that the successive echoes be separated in time. Measurements made on glass, epoxy, and composite laminate specimens are used to compare our attenuation measurement technique with the standard method.