Physical Acoustics
Faculty: Labuda, Mobley, Zhang
Research Faculty: Lu, Waxler, Prather Emeritus Faculty: Sabatier
The physical acoustics research program at the University is one of the largest in the United States. The program is housed in the state-of-the-art laboratories of the Jamie Whitten National Center for Physical Acoustics (NCPA) on the UM campus. The research involves the study of physical phenomena associated with acoustic waves over a wide frequency range starting from infrasound frequencies all the way up to ultrasound frequency, and the use of acoustics as a tool to investigate other phenomena. In addition to the core study of physical acoustics, the Center’s many research groups are involved in a great variety of other acoustics fields.
Faculty (Labuda, Mobley, Zhang)
Acoustic Metamaterials (Mobley, Zhang)Acoustic metamaterials are designed to manipulate sound waves through controlling material properties at subwavelength scales, offering a large degree of applications. Our work is involved in using principles of physical acoustics to develop state-of-the-art metamaterials of useful acoustic properties, e.g., Phononic Metamaterials, Acoustic Metasurfaces, Metascreen-based Passive Phased Array, Acoustic Purcell effect, etc.
Sound propagation through oceans is a unique method for underwater communication and imaging, e.g., using sonar to probe the sea floor and locate fish, to communicate between ships and submarines, and to probe ocean currents, eddies, and fronts. The propagation is strongly affected by spatial-temporal fluctuations introduced by various ocean processes, particularly ocean gravity waves that oscillate within the ocean (internal waves) and on the surface of the ocean (surface waves). These oceanic waves are generated by tidal flow over bottom topography and by wind on the ocean surface. The fluctuations impose a limit to underwater sound communication. Conversely, measurements on propagating sound waves provide a probe for the fluctuation. Our work is involved in combining laboratory, computational and theoretical approaches to model sound propagation in a continuously stratified ocean containing ocean gravity waves, aiming to understand the dynamics of oceanic waves and their effects on underwater sound propagation.
Rapid growth of oil production in the Gulf of Mexico increases the risk of oil spills. A monitoring system is essential to improve safety and reduce the risk of environmental damage. The leaked oil creates underwater sounds and can be recorded by acoustic sensors (hydrophones). The National Center for Physical Acoustics, the Department of Physics, and the Department of Electrical Engineering at the University of Mississippi are developing a hydrophone network-based real-time passive monitoring system for detecting, locating, and characterizing hydrocarbon leakages undersea. This project directly addresses the purpose of reducing the systemic risks leading to uncontrolled hydrocarbon release set by the Gulf Research Program.
For more details see the project page.
Labuda, Mobley (Ultrasonics Group page)
Understanding the mechanisms of interaction of ultrasonic waves with human is essential for the development of advanced therapeutic and diagnostic applications in biomedicine. Ultrasound is also used to study the fundamental mechanical properties of biologically evolved materials to discover the way nature has solved many of the structural and functional challenges faced by living organisms.
High Intensity Focused Ultrasound (HIFU) for Biomedical Therapeutics. Ultrasound waves in the MHz frequency range can be brought to a tight focus in soft mammalian tissues. The focus occurs remotely on the order of 2 – 20 centimeters from the source. When a focused source is driven at high power, this concentrated sonic energy can be used to therapeutic benefit. The therapeutic effect is delivered without impacting overlying tissues. High temperatures can be generated within the focal region, with surrounding areas remaining largely unaffected. It has been shown that focal peak intensities of 1500 W/cm2 held for 1–2 s can produce temperatures in excess of 56 C (133 F) which leads to instantaneous cell death and coagulative necrosis within the focal zone. Our work is concerned with the deposition of energy via HIFU in regions of large thermal conductivity, such as major vessels.
Tissue Characterization. As a non-invasive probe into the human body, ultrasound is used to acquire diagnostic information non-invasively without inducing significant cellular effects. Interaction of ultrasound with tissues results in scattering, absorption and dispersion, all of which can be linked to tissue microstructure. Determining the fundamental physical and mechanical properties of tissue provides knowledge that is essential for development of advanced diagnostic techniques as well as for understanding the physics of propagation in biological composite materials. Our group is involved in measuring the fundamental ultrasonic properties of various mammalian tissues and finding methods to measure such properties in vivo.
For more details see the Ultrasonics Group page.
Research Faculty / NCPA (Prather, Waxler)
Atmospheric Acoustics (Waxler)The propagation of acoustic waves outdoors involves a wide range of complex phenomena. These include microscopic absorption and dispersion, viscous and seismic interaction with the ground, and scattering from turbulence.
The past decade has seen remarkable advances in our ability to theoretically model sound propagation in the real atmosphere. Several state-of-the-art models are currently being developed and used to predict propagation of audible sound over horizontal distances of several kilometers in the lower atmosphere.
Similar work is ongoing for global infrasound propagation, which involves frequencies down to 0.02 Hz and horizontal distances of several thousand kilometers. Infrasound is proving useful in atmospheric and oceanographic research, as well as for the detection of surreptitious nuclear testing. These problems, as well as diffraction due to barriers and refraction due to velocity of sound gradients, are actively investigated.
The Applied Acoustics group studies what some would call “traditional” acoustics research: the propagation of audible sound in the atmosphere. Because the atmosphere is a striated and dynamic medium, sound waves do not travel in a simple straight line – they may bounce off boundary layers and reflect back down to the earth’s surface far from the source or be diverted by wind patterns. This group studies methods for locating sources of sound in a variety of scenarios: both source and sensors stationary or mobile sensors and stationary targets. Understanding the propagation path is crucial, but also important are methods for reducing wind noise so these systems are more sensitive to the signals of interest. This is accomplished using a sensor array and signal processing of the raw acoustic data. The Applied Acoustics group also has an interest in designing portable airborne acoustic arrays.
In association with engineering faculty
Aeroacoustics is devoted to the study of aerodynamically generated sound. One important area involves the prediction and reduction of sound generated by commercial aircraft. However, the field is quite broad and also involves study of acoustics associated with complex fluid structure interactions of hypersonic vehicles, like that associated with reusable launch vehicles for satellite repair and space station re-supply.
The field involves theoretical, numerical, and experimental efforts to better understand the physics for relating flow field pressures fluctuations to the turbulent dynamics of high speed flows that often contain aero-thermal chemical reactions. Contributions from this field often lead to development of aerospace vehicle systems that meet environmental standards and ones that can be optimized for system performance and reliability.