Ultrasonic microscopy using low frequency transducers

Ultrasonic microscopy that mainly concerns itself with depth profiling and characterizing thin layers relies on not only the resolution of the transducer impulse response but also the frequency characterization of propagation paths. The frequency dependent absorption and scattering limits the use of high frequency transducers for improved resolution, detection, and characterization. The information obtained from low frequency transducers is significantly concealed, and not readily resolvable but can be improved by deconvolving the transducer impulse echo from the backscattered echoes. In this study, we adaptively estimate the echo wavelets and their arrival times directly from the experimental measurement using echo models. The estimation of model parameters is addressed using the SAGE algorithm. The model order selection is carried out using the Minimum Description Length (MDL) principle. We have observed that the model-based estimation significantly improves the accuracy and resolution of echo location and amplitude when compared to conventional techniques such as the Wiener Filter and Pseudoinverse solution.