Final Report Summary - VECTRA (HIGH-RESOLUTION AND ROBUST TIME REVERSAL ACOUSTICS USING VECTOR SENSOR ARRAYS)
Focusing waves at a point in space (both in time and space) with a high-precision through a complex medium is of great interest in a variety of science and engineering disciplines such as astronomy, medicine, wireless communications, electromagnetics, and geophysics, to name a few. In recent years, time reversal focusing has emerged as the most promising method for this purpose and offers several important advantages over conventional methods. However, time reversal has its own drawbacks which have limited its success, mainly due to the lack of desired spatial resolution of the focus.
The project ‘High Resolution and Robust Time Reversal Acoustics Based on Vector Sensor Arrays’ (acronym VecTRA), funded by the EC FP 7 Marie Curie People Programme (FP7-MC-IRG), aims to improve time reversal processing by using vector sensors capable of not only measuring the acoustic pressure, but also the induced acoustic particle velocity. A propagating acoustic wave is fully described with two separate variables: a scalar pressure variable and a vectorial particle velocity variable. The pressure variable is simpler to measure, and hence, conventional acoustic systems (such as microphones, sonar systems, ultrasonic imaging devices and conventional time reversal systems) have relied only on pressure measurements. The particle velocity, despite providing more detailed information regarding the acoustic field, has typically been overlooked due to the lack sensors capable of reliable measurements. However, the demand for higher performance acoustic systems, coupled with recent advancements in sensor technology, has resulted in a surge in particle velocity based acoustics research in the past decade. The researchers affiliated with the project have investigated advanced, array processing, localization and signal processing algorithms that utilize the additional information provided by the acoustic particle velocity field for improving the performance of time reversal methods.
The research has been implemented in several phases. In the first phase of the research, the existing mathematical framework for modeling time reversal problems was expanded to incorporate particle velocity fields as well. This was accomplished by reformulating time reversal physics in terms of the scalar variable particle velocity potential, from which both the acoustic pressure and particle velocity can be derived from. Thus, a unifying framework was developed for modeling both conventional pressure based and particle velocity based time reversal problems.
In the second phase of the research, equipped the unifying theoretical framework developed under phase, the researchers developed several novel algorithms and techniques for improving time reversal performance using acoustic vector sensors instead of pressure sensors. Three key performance metrics were identified and utilized to measure the improvements. These metrics were the temporal and spatial resolution of the time reversal focus (measuring the sharpness of the focus), signal-to-noise ratio (the relative strength compared to background noise) of the focus, and the convergence (how quickly a focus can be achieved). A simulation software was developed as a part of phase 3 for testing the algorithms and techniques developed in phase 2. Using these algorithms and techniques, researchers were able to improve the signal-to-noise ratio up to ~25 dB (15 fold improvement) and the convergence rate up to 10 times. Furthermore, a signal processing method was developed for acoustic vector sensor arrays used in the time-reversal setup, resulting in a reduction in the array sizes of up to 75%-80% without sacrificing performance. In the final phase of the project, the algorithms and techniques developed and tested through numerical simulations were validated through experiments. The results obtained from experiments were in accordance to those predicted by numerical simulations. In conclusion, the initial hypothesis put forward that time reversal performance can be improved through the incorporation of acoustic vector sensors was proven.
Through in-depth theoretical knowledge accumulated and experience gained from this research, two key applications that can potentially benefit from the project results were identified. The first new application area is related to high resolution biomedical imaging. The expertise acquired though this project has enabled the MC fellow to secure additional funding for investigating high-resolution biomedical imaging techniques for screening breast cancer. If successful, the proposed approach will eventually lead to the development of a mobile medical imaging device that will improve accessibility to and reduce costs associated with advanced cancer screening techniques. The second research frontier that is currently being pursued by the research group is personal audio-home entertainment applications. Based on results obtained from the project, the MC fellow is collaborating with researchers from the audio engineering and sound technologies fields in applying particle velocity based time reversal techniques for room acoustic characterization, target localization, and the delivery of personal audio in unstructured indoor environments.
The project played a pivotal role in the reintegration of the researcher to the European scientific community. Through the Programme grant, the principle investigator was able to establish an acoustics research lab at the host institution and acquire additional funding to continue pursuing his research agenda and establish a sustained research program. The results of the project were disseminated in the form of six scientific publications and the project website (In addition, the MC fellow was able to open up new collaborations and research frontiers within the European scientific community.
For more information, please send an email to the primary investigator (berke.gur@eng.bahcesehir.edu.tr) or visit the project website at:
http://akademik.bahcesehir.edu.tr/vectra/
The project ‘High Resolution and Robust Time Reversal Acoustics Based on Vector Sensor Arrays’ (acronym VecTRA), funded by the EC FP 7 Marie Curie People Programme (FP7-MC-IRG), aims to improve time reversal processing by using vector sensors capable of not only measuring the acoustic pressure, but also the induced acoustic particle velocity. A propagating acoustic wave is fully described with two separate variables: a scalar pressure variable and a vectorial particle velocity variable. The pressure variable is simpler to measure, and hence, conventional acoustic systems (such as microphones, sonar systems, ultrasonic imaging devices and conventional time reversal systems) have relied only on pressure measurements. The particle velocity, despite providing more detailed information regarding the acoustic field, has typically been overlooked due to the lack sensors capable of reliable measurements. However, the demand for higher performance acoustic systems, coupled with recent advancements in sensor technology, has resulted in a surge in particle velocity based acoustics research in the past decade. The researchers affiliated with the project have investigated advanced, array processing, localization and signal processing algorithms that utilize the additional information provided by the acoustic particle velocity field for improving the performance of time reversal methods.
The research has been implemented in several phases. In the first phase of the research, the existing mathematical framework for modeling time reversal problems was expanded to incorporate particle velocity fields as well. This was accomplished by reformulating time reversal physics in terms of the scalar variable particle velocity potential, from which both the acoustic pressure and particle velocity can be derived from. Thus, a unifying framework was developed for modeling both conventional pressure based and particle velocity based time reversal problems.
In the second phase of the research, equipped the unifying theoretical framework developed under phase, the researchers developed several novel algorithms and techniques for improving time reversal performance using acoustic vector sensors instead of pressure sensors. Three key performance metrics were identified and utilized to measure the improvements. These metrics were the temporal and spatial resolution of the time reversal focus (measuring the sharpness of the focus), signal-to-noise ratio (the relative strength compared to background noise) of the focus, and the convergence (how quickly a focus can be achieved). A simulation software was developed as a part of phase 3 for testing the algorithms and techniques developed in phase 2. Using these algorithms and techniques, researchers were able to improve the signal-to-noise ratio up to ~25 dB (15 fold improvement) and the convergence rate up to 10 times. Furthermore, a signal processing method was developed for acoustic vector sensor arrays used in the time-reversal setup, resulting in a reduction in the array sizes of up to 75%-80% without sacrificing performance. In the final phase of the project, the algorithms and techniques developed and tested through numerical simulations were validated through experiments. The results obtained from experiments were in accordance to those predicted by numerical simulations. In conclusion, the initial hypothesis put forward that time reversal performance can be improved through the incorporation of acoustic vector sensors was proven.
Through in-depth theoretical knowledge accumulated and experience gained from this research, two key applications that can potentially benefit from the project results were identified. The first new application area is related to high resolution biomedical imaging. The expertise acquired though this project has enabled the MC fellow to secure additional funding for investigating high-resolution biomedical imaging techniques for screening breast cancer. If successful, the proposed approach will eventually lead to the development of a mobile medical imaging device that will improve accessibility to and reduce costs associated with advanced cancer screening techniques. The second research frontier that is currently being pursued by the research group is personal audio-home entertainment applications. Based on results obtained from the project, the MC fellow is collaborating with researchers from the audio engineering and sound technologies fields in applying particle velocity based time reversal techniques for room acoustic characterization, target localization, and the delivery of personal audio in unstructured indoor environments.
The project played a pivotal role in the reintegration of the researcher to the European scientific community. Through the Programme grant, the principle investigator was able to establish an acoustics research lab at the host institution and acquire additional funding to continue pursuing his research agenda and establish a sustained research program. The results of the project were disseminated in the form of six scientific publications and the project website (In addition, the MC fellow was able to open up new collaborations and research frontiers within the European scientific community.
For more information, please send an email to the primary investigator (berke.gur@eng.bahcesehir.edu.tr) or visit the project website at:
http://akademik.bahcesehir.edu.tr/vectra/