Richard L Weaver

Professor Emeritus

Contact

Richard L Weaver

Primary Research Area

  • Cross-cutting Physics
4115 Engineering Sciences Building
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Biography

Professor Richard Weaver received an A.B. degree in physics from Washington University in St Louis in 1971 and a Ph.D in astrophysics from Cornell University in 1977. He came to Illinois in 1981 after a research associateship in theoretical elastic wave propagation and ultrasonics at Cornell. He was elected a fellow of the Acoustical Society of America in 1996 and received the Hetenyi Award from the Society for Experimental Mechanics in 2004. He is associate editor of the Journal of the Acoustical Society of America. Formerly a professor in the Department of Theoretical and Applied Mechanics at Illinois, he joined the Department of Physics in 2006.

Research Statement

Theory, experiments, and numerical simulations of stochastic wave propagation, with a view towards applications in material science, quantum chaos, and seismology.

Experiments in Slow Dynamic Nonlinear Elasticity.  -- with J Y Yoritomo, J Popovics and K Dahmen (UIUC). We use reverberant ultrasound to probe a universal but perplexingly peculiar non-equilibrium phenomenon originating at the internal surfaces of heterogeneous solids and manifesting in large scale behavior. These structures will exhibit an apparent loss of stiffness after even modest applied strains, as if the strain did damage. Yet the stiffness is seen to then recover, like log(t), quickly at first and then steadily slower, on times from msec to years. The phenomenon is observed widely, from natural rocks to cements to cracked glass, and from the laboratory scale to the seismic. Neither the loss of stiffness nor the universal recovery is understood. In a search for the microphysical basis, we employ MHz reverberant ultrasound to monitor the changing stiffness while controlling external parameters.

Mechanical Analog for a Random Laser with J P Coleman (UIUC) Numerical simulations of phase transitions among nonlinear auto-oscillators coupled through a wave bearing substrate show most of the features of optical lasing, including spectral purity and greatly enhanced luminescence.

Statistical Elastodynamics of Large Structures and Quantum Chaos Numerical simulations, analytic theory and laboratory measurements are used to study the statistics of linear waves in complex systems. Particular attention is paid to wave energy density (or probability for quantum waves), and its mean flow and fluctuations. We seek methods to predict mean flow and fluctuations over long times.

Seismic Noise Correlations (with M Campillo, University Grenoble-Alpes, and X Song UIUC Geology) Recent attention to diffuse fields in seismology, inspired by (scaled by a factor of 10^-6) laboratory experiments done here is leading to new methods for probing the interior of the earth in which the seismic Green function is retrieved from noise. We observe and exploit mesoscopic residual correlations in nominally incoherent multiply scattered elastic wave fields, on the moon, in the seismic coda after earthquakes, in local geophone noise, and in long period world-wide background seismicity.

Graduate Research Opportunities

We have an opening for a student in an experimental/theoretical PhD research project funded by the DOE. The new student would build on previous work in the group using novel methods with reverberant ultrasound to probe a universal but perplexingly peculiar phenomenon originating at the internal surfaces of heterogeneous solids. The project is mostly experimental, but includes theory for the modeling of the multiply scattered ultrasound, and theory for the phenomenon itself. Laboratory techniques include design of the experiments and digital RF signal processing.

Students with interest in complex classical waves and/or nonlinear material properties, are encouraged to contact Prof. Weaver for more information.

Research Honors

  • Eotvos Award of the European Association of Geoscientists and Engineers (2009)
  • Society of Experimental Mechanics, Hetenyi Award (2004)
  • Fellow, Acoustical Society of America (1996)

Semesters Ranked Excellent Teacher by Students

SemesterCourseOutstanding
Spring 2019PHYS 325
Spring 2015PHYS 325
Fall 2014PHYS 326
Spring 2014PHYS 325
Fall 2013PHYS 326
Spring 2013PHYS 325
Fall 2010PHYS 211

Selected Articles in Journals

Related news

  • Research
  • Astrophysics/Cosmology

In its search for extrasolar planets, the Kepler space telescope looks for stars whose light flux periodically dims, signaling the passing of an orbiting planet in front of the star. But the timing and duration of diminished light flux episodes Kepler detected coming from KIC 846852, known as Tabby’s star, are a mystery. These dimming events vary in magnitude and don’t occur at regular intervals, making an orbiting planet an unlikely explanation. The source of these unusual dimming events is the subject of intense speculation. Suggestions from astronomers, astrophysicists, and amateur stargazers have ranged from asteroid belts to alien activity.  

Now a team of scientists at the University of Illinois at Urbana-Champaign—physics graduate student Mohammed Sheikh, working with Professors Karin Dahmen and Richard Weaver—proffer an entirely novel solution to the Tabby’s star puzzle. They suggest the luminosity variations may be intrinsic to the star itself.