Richard L Weaver

Professor

Ph.D. Astrophysics Cornell University 1977

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 Hetényi 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.

Other Activities

Ultrasonic Analog for a Random Laser (with colleagues Oleg Lobkis, UIUC, and Alexey Yamilov, U Missouri) — We report measurements on ultrasonic systems analogous to random lasers. An auto-oscillating, and spontaneously emitting, piezoelectric device is found to emit more energetically when stimulated by an incident wave field. The emission is at the same frequency as the stimulating field, and with a phase relation corresponding to super radiance.  Over a wide range of parameters we observe narrow single emission lines, sensitivity to linear cavity properties, complex multi-mode emissions, and line narrowing.  Line widths are more narrow than we can measure. Theory suggests they have Schawlow–Townes widths as low as 10^-9 Hz. Systems of several such oscillators are observed to self-organize into a coherent state with power emission that rises faster than the first power of the number of oscillators.

Statistical Elastodynamics of Large Structures and Quantum Chaos (with Oleg Lobkis, UIUC, and Thomas Seligman, Centro de Ciencias Fisicas, UNAM) — 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, based on information in ray optics or direct numerical simulations over short times.

Seismic Noise Correlations (with M Campillo, B van Tiggelen and E Larose, U Joseph Fourier, and O Lobkis UIUC and X Song UIUC Geology) — Recent attention to diffuse fields in seismology, inspired in part by laboratory experiments done at UIUC, is leading to new methods for probing the interior of the earth. We observe and exploit mesoscopic residual correlations in nominally incoherent multiply scattered elastic wave fields, on the moon, in the seismic coda, in local geophone noise, and in long period world-wide background seismicity. 

Determination of Thin-Film Interfacial Properties by Laser Generated Stress Waves (with N Sottos UIUC MatSE) — We investigate, both theoretically and experimentally, the generation of high-amplitude compression waves due to the sudden deposition of heat from a YAG laser pulse in a thin metallic film between two solids. The resulting pulse, with a duration of 10 nsec and a strain amplitude of the order of 1%, is measured using laser interferometry. Particular issues of concern include the effects of nonlinearity in the wave propagation and the corresponding development of shocks, and mode conversion at oblique interfaces with consequent generation of high-amplitude shear waves. Each of these effects is critical in ultimate application to the testing, by high-speed stress loading, of thin-film coatings.

Additional Information

I have had a long-time interest in developing mesoscopic models for transport in structures whose classical transport has arbitrary diffuse character. This program recently accomplished a break-through ( cf "Unitarization of the classical statistical s matrix for systems with localization," Phys. Rev. E 76, 051122 (2007) ) in which localization behavior is derived for arbitrary structures ( as opposed to the better known simple cases of an unbounded and statistically homogeneous multiply scattering system, or of a chain of rooms ) We have extended our earlier work on quantum fidelity in elastic wave systems, and made more detailed comparisons with predictions of random matrix theory. ( ms under review ) With colleagues at U Nebraska, I have successfully formulated a unified picture for diffuse multiple ultrasonic scattering in random media. The theory incorporates the features of the transducers ( critically essential as it transpires) , and distinguishes clearly between single and multiple backscattering. This has been a long standing challenge in the field of ultrasonic testing, and this work has made some significant progress on it. We have successfully applied our theory for generic diffuse classical transport to a new model structure consisting of coupled elastic plates. Geophysics colleagues and I have confirmed my suggestion that there is a further subtle and possibly useful correlation to be found in ambient seismic waves (ms under review) beyond that which I proposed (with stunning success at least as measured by citations) a few years ago. My undergraduate research assistants and I have successfully demonstrated synchronization and 'uasing' of unbalanced DC motors on a flexible elastic plate.

For more information:

Weaver Research Group

Honors and awards:

• Society of Experimental Mechanics, Hetenyi Award
• Fellow, Acoustical Society of America

Selected Publications:

• Richard L Weaver, Oleg I Lobkis, and Alexey Yamilov "Entrainment and stimulated emission of ultrasonic piezoelectric auto-oscillators," J Acoust Soc Am, 122, 3409-18 (2007)
• Richard L Weaver Wave Diffusion and Mesoscopic Dynamics, towards a universal time dependent scattering matrix, New J. Phys. 9 /234059/PAP/103557 (2007)
• Eric Larose, Oleg I. Lobkis, and Richard L. Weaver "Passive correlation imaging of a buried scatterer," J. Acoust. Soc. Am. 119, 3549 (2006)
• Weaver, R. L. and Lobkis, O. I. On the line width of the ultrasonic Larsen effect in a reverberant body. Journal of the Acoustical Society of America, 120:1, 102-109 (Jul. 2006).
• Gorin, T., Seligman, T. H. and Weaver, Richard L. Scattering fidelity in elastodynamics. Phys Rev E 73 015202 (2006)
• Weaver, Richard L. Transport and localization amongst coupled substructures. Phys Rev E 73 036610-1-8 (2006)
• Weaver, Richard L. and Lobkis, O. I. Diffuse fields in ultrasonics and seismology, invited for special issue of Geophysics 71 (4): SI5-SI9 (2006).
• Kuhl, U., Stockmann, H.-J. and Weaver, Richard L. Classical wave experiments on chaotic scattering. J. Phys. A: Math. Gen. 38 10433-10463 (2005).
• Wolff, Nicholas and Weaver, Richard L. Towards a generalized diffusion model for energy flow in complex structures. Journal of the Acoustical Society of America 118 222-231 (2005).
• Weaver, Richard L. Perspectives Geophysics "Information from Seismic Noise," invited, Science 11 March (2005).