Page 14 - CEGE Magazine - Fall 2016

ON THE CREST OF WAVES RESEARCH
BOJAN GUZINA: WAVE-BASED SENSING
The study of acoustic and elastic
waves is one of the pillars of modern engineering mechanics. Recent technological advances have turbocharged various new developments in this rich eld and opened
exciting possibilities for engineering breakthroughs and new collaborations with the physical sciences.
Guzina’s research goal is to develop innovative ways in which waves can be used to non-invasively probe, image, and diagnose earth’s subsurface, civil infrastructure, engineered materials, and even human bodies.
Guzina’s research addresses issues at the interface of engineering and applied mathematics. His engineering expertise gives him insight into physical processes and mechanics that make things work. He also understands mathematical theories and computational tools that can make engineering tasks easier. His multidisciplinary knowledge helps him see new pathways for progress, leading to new theories and new solutions.
CEGE houses a unique nexus of expertise in waves. CEGE faculty members pursue several avenues of waves research, the tentacles of which reach into wide-ranging areas including subsurface monitoring, web-based sensing, medical imaging, non- destructive testing, innovative materials design, seismic control, and more.
The work of three CEGE researchers illustrates the breadth of waves research being done in CEGE and how these research approaches and results are addressing some of today’s toughest enduring and emerging engineering challenges.
“WAVES AND VIBRATIONS ARE UBIQUITOUS. WITH PROPER UNDERSTANDING WE CAN USE THEM, WITH VIRTUALLY NO ADVERSE EFFECTS, TO ‘SEE THROUGH’ AND INTERROGATE BODIES AS LARGE AS OUR PLANET OR AS SMALL AS TINY LESIONS IN OUR BODY.”
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Vibration and waves have long been lynchpins of remote sensing. Wave- form sensing capabilities have greatly expanded over the past decade, due in part to breakthroughs in wireless communication, signal processing, and design of microelectromechanical sys- tems. These technological advances, however, have yet to provide real-time 3D “scans” of solid bodies, which could be used to maintain dams or nuclear power plants, or to ensure safe mining operations and ef cient energy production (e.g., hydraulic fracturing).
To help bridge the gap, Guzina’s research group is developing new theories and techniques to make 3D imaging and diagnosis of solids and structures by way of waveform tomography (which normally requires the use of supercomputers) possible for everyday engineering appli- cations. See examples in Figure 1.
Materials including rock, concrete, or human tissue, are rarely homogeneous as presumed by classical theories of wave-based sensing. Instead, they
Figure 1. 3D seismic reconstruction of an S-shaped tunnel (left) and cylindrical fracture (right) by non-iterative waveform tomography.
contain small features (mineral grains, aggregate, vasculature) that cumulatively affect the propagation of waves through the matter. One impact is that “short” (seismic or ultrasonic) waves repeatedly bounce off small-scale heterogeneities, thus restricting wave-based interrogation of real materials to “long” (low frequency) waves. Unfortunately, the use of only long waves as an imaging tool is limiting because the resulting tomographic images are coarsely pixelated.
Guzina strives to propel the use of sub-wavelength imaging by looking at long-wavelength data and identifying the “ ngerprints” of sustained, small-scale heterogeneities inside a material. He
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