Professor Che Ting Chan

Physics Department

Hong Kong University of Science and Technology (HKUST)

Clear Water Bay, Hong Kong, China

Email: phchan@ust.hk

 

 

Professor Che Ting Chan received his Ph.D. degree from the University of California at Berkeley in 1985. He is currently serving as the Associate Vice-President for Research & Development at HKUST. He is also concurrently the Daniel C. K. Yu Professor of Science, Chair Professor of Physics, and the Director of the Research Office of HKUST. He has been elected a Fellow of the American Physical Society and the Physical Society of Hong Kong and a member of the Hong Kong Academy of Sciences. His primary research interest is the theory and simulation of material properties, including theoretical and computational physics; photonic crystals; acoustic metamaterials; material simulations, etc. He has published over 600 papers with more than 54,000 citations. More detailed publications can be found at https://scholar.google.com/citations?user=qGQ9UX4AAAAJ&hl=en.

Presentation Summary

Topological phenomena in acoustic systems

Che Ting Chan

Physics Department, Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Hong Kong, China.

Abstract. Acoustic systems are relatively simple to design, implement and characterize. As such, they are good platforms to demonstrate new topological concepts and the associated phenomena. However, acoustic waves do not have spin and they do not respond to magnetic fields and hence many external parameters that can be tuned to obtain non-trivial topology in material physics do work for acoustics. We will use some examples to illustrate the realization of topological physics in acoustic systems. We will first use some examples to illustrate how acoustic crystals can exhibit nontrivial topology as characterized by integer topological invariants.

We then use some phononic systems to illustrate that we can have topological phenomena that are not characterized by integers. In the usual description, the topological characterizations are "Abelian" in the sense that the bulk topological invariants are integers which obey commutative algebra. We will see how non-Abelian topological charges (that behave like matrices) can be realized in some acoustic systems in which the bulk topological invariants are matrix-like entities such as quaternions that characterize rotations and are hence non-Abelian in 3D or higher dimensions. The quaternions describe the rotation of the frame in momentum space defined by orthogonal eigenvectors of multiple bands considered together at the same time. Such an approach is different from the usual viewpoint which focuses on a single band or a single band gap. Here, the topology is considered from a multiple band perspective. We will describe the physical consequences that will arise, including the constraints on degeneracy features in the bulk in such systems.

In another example, we will see that some simple phononic crystals which do not have bulk integer topological invariants behave like a valley-Hall topological crystal when specific boundary conditions are applied. Although the transport phenomena are almost indistinguishable from the valley-locked transport in valley-Hall crystals, the underlying principle is based on a boundary-condition induced bulk chiral anomaly, which cannot be classified using the usual topological invariants.

We demonstrate the realization of the non-Abelian braiding of multiple degenerate acoustic waveguide modes. Non-Abelian braiding is regarded as an essential process for realizing logic gates. The cyclic evolution of degenerate states induces a non-Abelian geometric phase, manifesting as the exchange of states. The non-Abelian characteristics are revealed by switching the order of two distinct braiding processes involving three modes. Our work demonstrates wave manipulations based on non-Abelian braiding and logic operations.

 

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 Professor Vitalyi E. Gusev

 

Laboratoire d’Acoustique de l’Université du Mans (LAUM): UMR 
CNRS 6613, Faculté des Sciences et Techniques, av. O. Messiaen, 
72085 Le Mans

E-mail: vitali.goussev@univ-lemans.fr

 

 

Professor Vitalyi E. Gusev received his Ph.D. degree in physics and mathematics in 1982 from M. V. Lomonosov Moscow State University, Russia. He received Habilitations from Moscow State University in 1992 and from Le Mans University, France, in 1997. He is currently a Professor at Le Mans University. His research includes the development of the theoretical foundations of nonlinear acoustic, optoacoustic, photothermal, and thermoacoustic phenomena. His most recent research has focused on applications of picosecond laser ultrasonics for imaging, nonlinear laser ultrasonics, the acoustics of granular media, and non-destructive testing and evaluation of nanomaterials and nanostructures. Prof. Vitalyi E. Gusev is the author of more than 350 publications in international journals and a book “Laser Optoacoustic” published in Russia (1991) and in the USA (1993). He was awarded the Lenin Komsomol Prize in Science and Technology, Physics (Nonlinear Acoustics) in 1987: the highest award for young researchers in the former Soviet Union. He became a Senior Prize Winner of the International Photoacoustic and Photothermal Association (2003) and a Senior Member of the Institute of French Universities (2006). In 2007, he was awarded the French Medal of the French Acoustical Society and, in 2010, the Gay-Lussac Humboldt Research Award. In 2013 and 2016, he became the Fellow of the Acoustical Society of America and of the American Physical Society, respectively.

 

Presentation Summary

Recent Advances in Applications of Picosecond Acoustic Interferometry for Imaging of Polycrystalline Materials and Material Modifications

Vitalyi E. Gusev, Samuel Raetz, Nikolay Chigarev and Sandeep Sathyan

Laboratoire d'Acoustique de l'Université du Mans (LAUM), Institut d'Acoustique - Graduate School(IA-GS), CNRS, Le Mans Université, 72085 Le Mans, France

Abstract. Picosecond acoustic interferometry (PAI) is an experimental technique that uses ultrafast lasers to generate and detect coherent acoustic pulses (CAPs) of nanometers length and picoseconds duration. The detection involves the interferences of two probe light pulses: a weak one, scattered by the CAP propagating in a transparent material, and a strong one, reflected by various stationary interfaces of the sample. The transient optical reflectivity recorded by a photodetector, as the CAP propagates, contains information about the material's local acoustic, optic, and acoustic-optic parameters. PAI imaging is based on Brillouin light scattering and is therefore also known as time domain Brillouin scattering. It can be seen as a potential extension of the traditional frequency domain Brillouin microscopy in science, where depth resolution at the nanoscale is required. Since the first demonstration of PAI for depth profiling nearly fifteen years ago ^[1,2], it has already been applied for imaging nanoporous films, ion-implanted semiconductors/dielectrics, plant and animal cells, texture in polycrystalline materials, temperature distributions in liquids, and for monitoring the transformation of CAPs caused by absorption, diffraction, nonlinearity and focusing ^[3] .

Here we report on recent experimental advances made at the Laboratoire d’Acoustique del’Université du Mans (LAUM) on applications of PAI to 3D imaging of polycrystalline microstructure and 3D characterization of individual grains of coexisting H2O ice phases at high pressure ^[4,5], both with improvements coming from the first applications of shear CAPs in PAI-based imaging. A single-crystal fracture induced by a non-hydrostatic load has been followed in 3D, further expanding the horizons of investigation of solids and their evolution under extreme conditions. We present the results of experimental and theoretical progress in the evaluation by PAI of the inclinations of the interfaces between different grains or materials. We also describe the first application of PAI to imaging the mechanical interface of epoxy with metals and in-situ imaging of the dynamics of a photo induced structural phase transition at high pressures ^[6], of a light-induced modification of organosilica nanoporous films ^[7], and of epoxy curing. Finally, we discuss the perspectives for the further development of PAI-based imaging suggested by experiment and theory.

Acknowledgments

This research was supported by the project <ANR-18-CE42-I2T2M>, the Acoustic Hub® program and the LMAc project NANOSHEAR. The authors thank the colleagues who significantly contributed to our research: Théo Thréard, Nicolas Pajusco, Elton de Lima Savi, Maju Kuriakose, Vincent Tournat, Alain Bulou, and Erwan Nicol (Le Mans Université, France), Andreas Zerr (LSPM, UPR CNRS 3407, France), Mathieu Ducousso (SAFRAN Tech, France), Mikhail R. Baklanov (EUROTEX, Belgium), and David H.Hurley (INL, USA).

References

1. C. Mechri, et al., Appl. Phys. Lett. 95, 091907 (2009).

2. A. Steigerwald, et al., Appl. Phys. Lett. 94, 111910 (2009).

3. V. E. Gusev and P. Ruello, Appl. Phys. Rev. 5, 031101 (2018).

4. T. Thréard, et al., Photoacoustics, 23, 100286 (2021).

5. S. Sandeep, et al., J. Appl. Phys. 130, 053104 (2021).

6. M. Kuriakose, et al., New J. Phys. 19, 053206 (2017).

7. S. Sandeep, et al., Nanomaterials 12, 1600 (2022)

 

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 Professor Hairong Zheng

Shenzhen Institutes of Advanced Technology

Chinese Academy of Sciences

Shenzhen, Guangdong, China

Email:  hr.zheng@siat.ac.cn

 

 

Professor Hairong Zheng obtained his B.S. and M.S. degrees from the Harbin Institute of Technology (HIT). He earned his Ph.D. degree at the University of Colorado at Boulder in 2006 with partial support from American Heart Association (AHA) Predoctoral Fellowship. He did his postdoctoral training at the University of California, Davis in 2007. In the same year, he joined Shenzhen Institutes of Advanced Technology (SIAT), Chinese Academy of Sciences (CAS), where he is presently Deputy Director and a Professor. He leads the Paul C. Lauterbur Research Center for Biomedical Imaging at SIAT. He is the Director of the National Innovation Center for Advanced Medical Devices. Prof. Zheng currently conducts research primarily in biomedical imaging technology. Its thrust is to develop multifunctional ultrasonic imaging systems that can be used for elastography, molecular imaging, neuromodulation, and fast high-field MRI imaging technologies and systems Prof. Zheng has published 160 peer-reviewed journal articles and held more than 100 issued patents based on his research, some of which have been translated into commercial products for clinical use. He served as the editorial board member for Physics in Medicine and Biology. He was also the associate editor of the IEEE Transactions on UFFC.

 

Presentation Summary

Acoustic Tweezers: Design and Bio-Application

Hairong Zheng

Shenzhen Institutes of Advanced Technology in Chinese Academy of Sciences Shenzhen, Guangdong, China

Abstract. Noncontact trapping and transportation of microparticles, cells, bacteria, and nanoparticles as well as exosomes is of crucial importance in investigating the microscopic world. Particle manipulation at the microscale is a highly topical field, and has been gaining increasing attention in the scientific literature of the past few years. In 1986, Arthur Ashkin first used a tightly focused light beam to realize microparticle manipulation, termed optical tweezers, and was awarded the 2018 Nobel Prize in Physics ‘for the optical tweezers and their application to biological systems’. Acoustic tweezers are gaining increasing attention as a noncontact method that is capable of handling microparticles and nanoparticles in a controllable manner. Owing to objects absorbing, scattering, and reflecting an acoustic wave, an exchange of momentum and energy between the particles and the acoustic wave will occur, resulting in the generation of an acoustic radiation force on the objects. By designing the acoustic field, objects, such as cells, bacteria, exosomes, and even worms, could be precisely and flexibly manipulated by the acoustic radiation force. In this talk, we will demonstrate the historical development and the current state of the theory of the acoustic radiation force. Moreover, we introduce the recent advancements of our work in acoustic tweezers based on the complex and arbitrary wave fields. With an arbitrary field, desired patterning and transportation of particles could be achieved by switching the excited elements or adjusting the relative phase among excited elements. Arbitrary acoustic fields based on artificial structures open new avenues for acoustic manipulation and are anticipated to facilitate application development using flexible acoustic fields. Some biomedical applications, such as cell separation, cell sonoporation, cell fusion, referring to the acoustic tweezers are also presented. Interestingly, acoustic tweezers can activate the neuronalion channel, resulting in the modulation of neuronal discharges, which has proven to be a powerful tool in brain science. With the advantages of non-invasiveness, label-free operation, and low power consumption, acoustic tweezers have been proven to be crucially important for a diverse range of applications, particularly in the biomedical domain.

 

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 Professor Leonard J. Bond

Department of Aerospace Engineering

Iowa State University, Ames

Iowa, 50011, USA

Email:  bondlj@iastate.edu

 

 

Professor Leonard J. Bond received his Ph.D. in Physics from The City University, London. After a long career in industry, national laboratories, and academia he is now a Professor Emeritus at Iowa State University and an Honorary Professor, at Beijing University of Technology (BJUT). From 2012-2018, he was the Director of the Centre for NDE and then Coordinator for the Minor in NDE at Iowa State University. He has throughout his career worked on aspects of both high and low-power ultrasonics, particularly focused on measurements in harsh and novel environments for nuclear, defense, and process industries problems. He continues activities with research into various aspects of nondestructive evaluation, nonlinear ultrasonics, acoustic microscopy, and advanced x-ray imaging. Professor Bond is the author of more than 350 papers in journals and conference proceedings. He has been the author or co-author for 18 book chapters, working party reports, and editor for sixteen books and proceedings. He is co-author of the book “Ultrasonics” – Ensminger and Bond and is currently finishing the manuscript for the 4th Edition. He has 10 patents. He started his academic career as a faculty member, at University College London, becoming a Reader in Ultrasonics. Midcareer he took a sabbatical at the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder, which became a move to the USA. His subsequent activities included positions with the University of Denver, Denver Research Institute, Pacific Northwest National Laboratory (PNNL), where he was a Laboratory Fellow, and the Idaho National Laboratory (INL), where he was the founding Director of CASE (Center for Advanced Energy Studies). He has held positions with various technical societies including as a Region Director and Director of IEEE. He is a Fellow American Association for the Advancement of Science (AAAS) and the UK Institute of Physics.

 

Presentation Summary

A novel cryogenic acoustic microscope to evaluate electronic components.

L.J. Bond^1,2, N.Poonthottathil^3,4, S. Doran³ , A.Weinstein³ , D. Barnard² , and F.Krennrich³

1. Department of Aerospace Engineering, Iowa State University, Iowa, USA

2. Center for Nondestructive Evaluation, Iowa State University, Iowa, USA

3. Department of Physics and Astronomy, Iowa State University, Iowa, ISA.

4. Physics Department, Indian Institute of Technology, IIT Kanpur, India.

Abstract. Cold electronics is a key technology in many areas of science and technology including space exploration programs and particle physics. A major particle physics experiment with a very large number of analog and digital electronics signal processing channels to be operated at cryogenic temperatures is the next-generation neutrino experiment, the Deep Underground Neutrino Experiment (DUNE). DUNE uses liquid Argon at ~ 87 K as a target material for neutrinos and as a medium to track charged particles resulting from interactions in the detector volume. The DUNE electronics will consist of about 24,000 custom-designed ASIC (Application Specific Integrated Circuits) chips based on low-power 180 nm-CMOS technology. A major risk for this technology is failures in the electronics components which will be immersed in liquid argon for 20-30 years, without opportunity for access or replacement. One challenge is that the ASICs which are being developed can be tested (electrically) at room temperature, and yet still fail when cooled to cryogenic temperatures. There is therefore a need is to provide a capability that can assess chips at cryogenic temperatures, including identifying anomalies with the potential to develop to cause defects and failure, due to thermal cycling to cryogenic temperatures. Various inspection technologies, including both x-ray and ultrasound, are being considered to ensure chip QA/QC. One activity is the design, use, and data analysis for a novel low-cost cryogenic acoustic microscope (CryoSAM) which has been developed and used to evaluate reliability issues of ASICs that may arise from thermal stress, packaging, and manufacturing-related defects. Cryogenic acoustic microscopy in itself is not new: a GHz frequency unit was reported by a Stanford University group in the 1980s. The current CryoSAM is intended to be an engineering capability that can operate to frequencies of about 50 MHz. The paper will report on the design and testing of the CryoSAM, the differences in response seen due to using a liquid gas as the complaint, including differences in resolution and sensitivity between water and the liquid gas, the challenges faced in the development and use of the instrument, including thermal issues and management of bubbles. It will also present a sophisticated correlation analysis technique, applied to the acoustic microscope images and digitized 4-D (xyz and time) data records, that is capable of finding even subtle changes that occur inside the ASICs, including during those which develop during multiple thermo-cycles. The cryogenic acoustic microscopy and this powerful data analysis technique is demonstrating that it will allow screening of DUNE ASIC and potentially significantly reduce the risk of sensor failure during DUNE operation.

 

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 Professor Wen Wang

Institutes of Acoustics in the Chinese Academy of Sciences

No.21 4th North Ring Road

Beijing 100190, China

Email:  wangwenwq@mail.ioa.ac.cn

 

Professor Wen Wang obtained his B.S. and M.S. degrees from Central South University (CST). He earned his Ph.D. from the Institute of Acoustics in the Chinese Academy of Sciences (IACAS) in 2005, during which he worked at Chia University as a visiting scholar supported by the Japan Society for the Promotion of Science. From 2005 to 2009, he worked at Ajou University (S. Korea) as a postdoctoral researcher and assistant professor. Subsequently, he was funded by the Humboldt Foundation of Germany to work at Freiburg University as a visiting professor, and awarded the "Experienced Researcher". In 2011, he joined IACAS as a full-time professor. He also holds a professorship at the University of the Chinese Academy of Sciences (UCAS) since 2020. Prof. Wang is currently engaged in the research of micro-acoustic sensing technology. Its thrust is to study multi-physical field coupling based surface acoustic wave sensing effect and mechanism, and develop multi-parameter sensing devices and systems. Professor Wang has published 190 peer-reviewed journal articles and holds more than 40 issued patents based on his research. Some of his achievements have been industrialized successfully and have produced significant economic and social benefits. He served on the editorial board of “Sensors” and “Applied Sciences”.

 

Presentation Summary

Surface acoustic wave and sensing applications

Wen Wang

Institutes of Acoustics in the Chinese Academy of Sciences, Beijing,  China

 

Abstract. Micro-Acoustics is a branch of acoustics that studies acoustic phenomena with characteristic scales ranging from microns to nanometers. Surface acoustic wave (SAW) technology is one of the representative research directions. Since the invention of the interdigital transducer by White et. al. in the 1970s, SAW technology has achieved rapid development. Its powerful signal processing capability has made it an indispensable functional component in the field of mobile communication. Additionally, the SAW was confined to the piezoelectric substrate surface at a depth of one or two wavelengths and hence was very sensitive towards the external perturbations. So, the SAW devices were explored to build many sensors for sensing chemical or physical measurements. Common features of SAW sensors are micro-nano scale, high sensitivity, fast response, and excellent reliability. Another outstanding advantage is that they can work without a battery and wireless interrogation, as they are connected only by a radio frequency link to a transceiver. This feature makes it very promising in extreme or harsh or unattended scenarios. In this talk, we will demonstrate the historical development and the current state of SAW technology. Moreover, we introduce the recent advancements in our work in SAW sensors. A micro-scale sensor was constructed for sensing toxic and harmful gases by depositing a specific sensitive film along the propagation path of SAW. Sub-second ultra-fast hydrogen detection capability was realized for the first time. Environmental temperature and mechanical effects will lead to significant changes in the SAW velocity. Using this character and referring to the RF radar technology, a series of wireless and passive SAW sensors were developed for sensing temperature, pressure, and strain. Some of them have been applied successfully to the health monitoring of power equipment. The magnetic sensor was built by preparing the magnetic sensitive material on the surface of the SAW device, which is expected to solve the anti-interference problem of the existing technology. Interestingly, we also found that the ice layer formed on the SAW device surface will lead to transient acoustic attenuation because of the porous structure. Using this feature, a new ice detector with high sensitivity, sub-second fast response, and ability of ice type discrimination was developed. In addition, we explored the SAW devices for sensing physical measurements at ultra-high temperature environments (›1000°C), which will hopefully solve the problem of information acquisition in an extreme environment in aerospace and other fields.

 

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 Professor Hoon Sohn

Professor in Civil and Environmental Engineering Department

Korea Advanced Institute of Science and Technology

Republic of Korea (South Korea)

Email:  hoonsohn@kaist.ac.kr

 

Professor Hoon Sohn received his B.S. and M.S. (1994) degrees from Seoul National University, Seoul Korea and Ph.D. (1999) from Stanford University, California, USA, all in Civil Engineering. He worked at Los Alamos National Laboratory (LANL) from 1999 to 2004 as a Technical Staff Member and in the Civil and Environmental Engineering Department at Carnegie Mellon University for 2004-2006 as an Assistant Professor. He is now a Professor at KAIST (Korea Advanced Institute of Science and Technology), and the Director of the 3D Printing Nondestructive Center sponsored by the Ministry of Land, Infrastructure and Transport in Korea. Over the last twenty-five years, his research interest has been in the areas of structural health monitoring, nondestructive testing, sensing technologies, and data analytics. His research interests include guided waves, noncontact laser ultrasonics, structural health monitoring, nondestructive testing, smart materials and sensing, and statistical pattern recognition to name a few. He has published over 190 refereed journal articles, over 370 conference proceedings, and 11 book & book chapters. He is holding 27 domestic and 13 international patents, and his developed technologies are licensed and commercialized by private companies, resulting in over 1 Million USD in licensing agreements. He is currently a SPIE Fellow, a Member of the National Academy of Engineering of Korea (NAEK), and a Member of the Korean Academy of Science and Technology (KAST). He was selected as one of the 100 most promising individuals in Korea in 2012 by Donga Daily Newspaper, which is one of the three major newspapers in Korea. He was also the recipient of the SHM Person-of-Year Award at the 2011 International Workshop on SHM, the 2008 Young Scientists Award from KAST, and 2017 Young Engineers Award from NAEK, 2017 KAIST Best Research Award in Korea. His work has been funded by the Boeing Company, Samsung Electronics, Samsung Display, US Air Force Research Laboratory, US Air Force Office of Scientific Research (US AFOSR), US National Science Foundation, National Research Foundation of Korea, Korea Agency for Defense Development, Hyundai & KIA Motors, Hyundai Heavy Industries, Bombardier, POSCO, Daewoo Construction, and Foongsan FNS.

 

Presentation Summary

Online laser ultrasonic testing and process control during metal additive manufacturing

Hoon Sohn^a,b, Kiyoon Yi^a,b, Peipei Liu^a,b, Ikgeun Jeon^a, Seong-Hyun Park^b,c, Liu Yang^a,d 

^a Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea

^b Center for 3D Printing Nondestructive Testing, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea

^c School of Mechanical Engineering, Hanyang University, Seoul, 04763, Republic of Korea

^d Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong

 

Abstract. Additive manufacturing (AM), also known as 3D printing, is revolutionizing how various structural components are manufactured. Directed energy deposition (DED, which is one time of metal AM, utilizes a concentrated laser source and metal powers to achieve layer-by-layer deposition of materials. Although significant progress has been made in the development of DED processes and materials, little work has been done for online nondestructive testing and quality control. In this study, a suit of online nondestructive testing (NDT) and process control techniques based on laser ultrasonics are developed, including (1) porosity inspection based on transient thermoreflectance measurement using a femtosecond laser, (2) mechanical properties estimation based on noncontact ultrafast ultrasonic measurement, and (3) porosity reduction and microstructure improvement using an Nd: YAG pulse laser.

 

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 Dr. Tobias M. Müller

Department of Seismology

Ensenada Center for Scientific Research and Higher Education Baja California, Mexico

Visiting Professor of the School of Geosciences University of Petroleum (Eastern China) Qingdao, China
Email:  tobias@cicese.mx

 

Dr. Tobias Müller is a senior research scientist affiliated with the Center for Scientific Research and Higher Education in Ensenada (CICESE), Mexico, and is currently a visiting professor at the School of Geosciences, University of Petroleum (Eastern China). From 2008 to 2018, he was a principal senior research scientist with the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Perth, Australia. Previously, he was at Karlsruhe University (2005-2008) and Curtin University (2002-2005). He obtained his Ph.D. in 2001 from the Freie Universität Berlin and a Diploma from Karlsruhe University, both in geophysics. His research interests include the theory of elastic waves in random media, poromechanics, seismic modeling, and rock physics. He has made significant contributions to the understanding of acoustic wave attenuation phenomena in elastic and poroelastic solids. In this research area, he published more than 100 peer-reviewed papers. He is a member of the European Association of Geoscientists and Engineers (EAGE) and the Society of Exploration Geophysicists (SEG); he also serves on the editorial boards of Geophysical Prospecting and the Journal of Geophysical Research-Solid Earth. Dr. Müller is an Emmy-Noether fellow of the German Research Foundation, received the ‘Young Researcher of the Year award from Curtin University in Australia, and is a three-time recipient of the Herbette fellowship from the University of Lausanne. Together with colleagues from CSIRO and Curtin University of Australia, he received the Laric Hawkins Award from the Australian Society of Exploration Geophysicists in 2009.

 

Presentation Summary

Ultrasonic waves in porous media: Challenges and recent advances

Prof. Tobias M. Müller^a,b 

^a School of Geosciences, University of Petroleum (Eastern China), Qingdao, China.

^b Department of Seismology, Ensenada Center for Scientific Research and Higher Education,Baja California, Mexico.

 

Origins of the theory of acoustic waves in porous media date back to the mid-20th century pioneering works of Maurice Biot. This theoretical framework is a rich source for modeling and predicting elastic wave phenomena in natural porous media such as rocks. Despite great efforts from the acoustical, civil engineering, and geophysical research communities, challenges remain when it comes to a unified theoretical description of high-frequency elastic waves. This is no surprise since shorter wavelengths mean that progressively more pore-scale phenomena come into play, which, in the macroscopic poroelasticity theory, can only be captured in an averaged sense. So, an important challenge is to achieve proper upscaling, even if a clear separation of scales is no longer guaranteed. In this presentation, we review progress made on the basis of the volume averaging theory of poroelasticity initiated by de la Cruz and Spanos in the 1980s. The key concept is the change of porosity as a macroscopic signature of pore interface deformation. This enables us to clarify the somewhat vague notion of micro-inhomogeneity in laboratory experiments involving porous rocks. Further ramifications of the change-of-porosity concept include (i) the description of nonreciprocal fluid-solid interactions, allowing us to quantify incompressible flow in a deformable porous frame, and (ii) a new take on porosity–permeability relations in the presence of porosity gradients. Specifically relevant to ultrasonic wave propagation, we highlight the importance of the out-of-phase shear motion, manifested as a so-called slow shear wave, within viscous boundary layers and its interaction with fast compressional and shear waves. The interaction takes place through conversion scattering, which we quantify analytically by the method of statistical smoothing for randomly inhomogeneous porous media and semi-analytically for stacks of porous layers with arbitrarily high impedance contrasts. Our results lend support to the joint use of remote-sensing technologies for improved permeability determination and cross-fertilization of laboratory and in-field techniques. As a new development, we discuss the possibility of peeking into pore-scale relative fluid-solid motion triggered by moving pore interfaces under the action of ultrasound.