A direct wavepath-based element localization algorithm to enable flexible ultrasound array imaging.

An algorithm is developed for determining the element locations of a flexible ultrasonic array when applied to a surface of unknown geometry. The algorithm forms a dataset of traveltimes from the direct wavepaths (i.e. rays) between transmitters and receivers, which serves as the input to an optimization scheme that iterates on the array element locations until an objective function is minimized. Once, the relative array locations have been determined, they are used as an input to a phased array ultrasound imaging algorithm. In this study, the total focusing method with full matrix capture is used as a testbed code to demonstrate the benefits of the relative array element localization algorithm. The algorithm is verified by simulation and experimentation.

Analysis of geometric defects in square locally resonant phononic crystals: A comparative study of modeling approachesa).

Phononic crystals can develop defects during manufacturing that alter the desired dynamic response and bandgap behavior. This frequency behavior change can enable successful defect inspection if the characteristic defect response is known. In this study, the behavior of a defective square unit cell comprising a freed and shortened leg is studied using a wave finite element method and an approximate continuous-lumped model to elucidate the defect induced qualitative dynamical features. These metrics are a computationally inexpensive alternative to modeling a defective unit cell within a large pristine array entirely in finite elements. The accuracy of these models is validated by comparing the result to a full finite element model. The impact of a shortened unit cell leg on the behaviors of an infinite array of defective cells and a finite array with a single defect are successfully predicted through dispersion curves and frequency response functions, respectively. These methods reveal defect-induced modes that split the local resonance bandgap of the pristine cell, as well as new anti-resonances resulting from the shortened leg. The study uses both approaches to evaluate the effect of defects in complex phononic crystal geometries and provides a comparative evaluation of the results of each model.