Lee A J Davis | University of Warwick (original) (raw)
Papers by Lee A J Davis
AIP Advances, 2016
An acoustic metamaterial has been constructed using 3D printing. It contained an array of air-fil... more An acoustic metamaterial has been constructed using 3D printing. It contained an array of air-filled channels, whose size and shape could be varied within the design and manufacture process. In this paper we analyze both numerically and experimentally the properties of this polymer metamaterial structure, and demonstrate its use for the imaging of a sample with sub-wavelength dimensions in the audible frequency range.
Physical review. E, 2016
The propagation of broad bandwidth solitary wave impulses, generated within granular chains by na... more The propagation of broad bandwidth solitary wave impulses, generated within granular chains by narrow bandwidth ultrasonic excitation, is studied in detail. Theoretical predictions are compared to experimental results. It is demonstrated that the observed effects result from a sum of a solitary wave traveling out from the source with a wave that reflects from the far end of the chain. It is shown that this combination, when used with an excitation in the form of a long-duration tone burst, encourages the generation of multiple impulses with a characteristic periodicity. This study shows that the properties of the chain structure and the excitation can be adjusted so as to generate ultrasonic solitary wave impulses with a high amplitude and known frequency content, which are of interest in applications such as biomedical ultrasound.
Ultrasonics, 2018
A pulse compression technique has been developed for the non-destructive testing of concrete samp... more A pulse compression technique has been developed for the non-destructive testing of concrete samples. Scattering of signals from aggregate has historically been a problem in such measurements. Here, it is shown that a combination of piezocomposite transducers, pulse compression and post processing can lead to good images of a reinforcement bar at a cover depth of 55 mm. This has been achieved using a combination of wide bandwidth operation over the 150-450 kHz range, and processing based on measuring the cumulative energy scattered back to the receiver. Results are presented in the form of images of a 20 mm rebar embedded within a sample containing 10 mm aggregate.
Nondestructive Testing and Evaluation, 2016
Ultrasonic signals at frequencies below 1 MHz have been used for the NDE of thick polymer samples... more Ultrasonic signals at frequencies below 1 MHz have been used for the NDE of thick polymer samples. Coded signals such as chirps and bipolar Golay codes, together with pulse compression and signal processing, have been used to penetrate into thick sections of attenuating polypropylene riser stiffener material, using piezocomposite transducers to provide the required bandwidth. It is shown that this approach can be used to detect manufacturing defects such as air bubbles in flexible riser stiffeners, which might compromise their performance in the offshore oil and gas environments.
2014 IEEE International Ultrasonics Symposium, 2014
Different approaches have been investigated for the transmission of signals through highly attenu... more Different approaches have been investigated for the transmission of signals through highly attenuating and scattering materials. Chirp signals are sent through the material, and then processed using either time-multiplication or cross-correlation with a template to obtain information concerning the sample. The use of both narrow bandwidth piezoelectric transducers and wide bandwidth piezocomposites is also discussed.
Ultrasonic Nondestructive Evaluation Systems, 2014
In many application environments, it is not possible to practice nondestructive evaluation (NDE) ... more In many application environments, it is not possible to practice nondestructive evaluation (NDE) by physically contacting the material under test with probes. Examples include the evaluation of objects that are moving (e.g., on an assembly line), hot materials, materials that cannot risk contamination, and more. Lack of contact means that, typically, the coupling material is air. This poses specific requirements, due to the acoustic impedance mismatch that an air layer can provoke and the consequent energy losses. In this chapter, some examples of setups, transducer arrangements, and signal processing strategies capable of addressing such requirements are illustrated, showing how concepts presented in the previous chapters can be deployed in this particular context. Furthermore, some typical achievable results are illustrated, with respect to a few different testing scenarios, such as the testing of composite materials, the inspection of concrete, imaging of surfaces or thin materials, and food inspection.
Ultrasonics, 2014
Please refer to published version for the most recent bibliographic citation information. If a pu... more Please refer to published version for the most recent bibliographic citation information. If a published version is known of, the repository item page linked to above, will contain details on accessing it.
Sensors, 2020
Experiments have been performed to demonstrate that ultrasound in the 100–400 kHz frequency range... more Experiments have been performed to demonstrate that ultrasound in the 100–400 kHz frequency range can be used to propagate signals through various types of industrial insulation. This is despite the fact that they are highly attenuating to ultrasonic signals due to scattering and viscoelastic effects. The experiments used a combination of piezocomposite transducers and pulse compression processing. This combination allowed signal-to-noise levels to be enhanced so that signals reflected from the surface of an insulated and cladded steel pipe could be obtained.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, Nov 7, 2016
The response of a resonant chain of spheres to changes in holder material and pre-compression is ... more The response of a resonant chain of spheres to changes in holder material and pre-compression is studied at ultrasonic frequencies. The system is found to be very sensitive to these parameters, with the creation of impulsive waveforms from a narrow bandwidth input seen only for certain chain lengths and holder materials. In addition, careful experiments were performed using known amounts of pre-compression force, using a calibrated stylus arrangement. At negligible pre-compression levels, impulses were generated within the chain, which were then suppressed by increased pre-compression. This was accompanied by large changes in propagation velocity as the system gradually changes from being strongly nonlinear to being more linear. Simulations using a discrete model for the motion of each sphere agree well with experimental data.
2013 18th International Conference on Digital Signal Processing (DSP), 2013
Acoustical Society of …, 2008
ABSTRACT Ultrasonic anemometers are often used for studies of 3-D atmospheric turbulence on Earth... more ABSTRACT Ultrasonic anemometers are often used for studies of 3-D atmospheric turbulence on Earth, due to their robust calibration and fast operation (>10 Hz). The same qualities make ultrasonic anemometry attractive for use on Mars, where similar atmospheric turbulence is found. The low density of Martian atmosphere - a hundredth that of the Earth's - is problematic, because of the large acoustic impedance mismatch between the atmosphere and piezoelectric transducers. One solution to this problem is to use piezoelectric transducers with a hornlike resonator bonded to their front surface. Another solution is to use a capacitive membrane transducer instead. We report on performance of various ultrasonic transducers in carbon dioxide Martian pressures, and present an instrument design capable of meeting the stringent mass, power, and environmental requirements of the European ExoMars lander.
Loudspeakers are required whenever there is a need to reproduce sound. Utilising the technology b... more Loudspeakers are required whenever there is a need to reproduce sound. Utilising the technology behind ultrasonic capacitance transducers, a radically new loudspeaker concept has been developed, which has resulted in the creation of an ultra-thin loudspeaker. This speaker design, which is less than 1mm thick, is also flexible, being comprised of several thin sheets. Such a device would render it suitable to a wide range of applications, including those where space is at a premium, for example mobile telephones and notebook computers. An accurate mathematical model relating the material properties of the speaker to the expected resonant frequency has been developed, by analysing the fundamental characteristics and operation of the speaker. This has been used to improve the acoustical characteristics of the speaker. By utilising different loudspeaker geometries, there is a possibility of increasing the sound pressure level and bandwidth of the speaker such that a relatively flat response across the audible range can be achieved. This paper will report the work towards achieving this aim, and will discuss the need to fully understand the fundamental characteristics of the device.
This paper describes the use of near infrared techniques for both spectroscopy and imaging. The a... more This paper describes the use of near infrared techniques for both spectroscopy and imaging. The approach uses both techniques on the same sample, so that spectral information can be used in conjunction with an image to identify materials and objects. It is shown that the technique has applications to security screening, food quality inspection and biomedical measurements, using the ability of near infrared to penetrate through barriers.
Ultrasonic Nondestructive Evaluation Systems, 2014
Optics and Photonics for Counterterrorism, Crime Fighting, and Defence VIII, 2012
ABSTRACT
2013 IEEE International Ultrasonics Symposium (IUS), 2013
ABSTRACT
AIP Advances, 2016
An acoustic metamaterial has been constructed using 3D printing. It contained an array of air-fil... more An acoustic metamaterial has been constructed using 3D printing. It contained an array of air-filled channels, whose size and shape could be varied within the design and manufacture process. In this paper we analyze both numerically and experimentally the properties of this polymer metamaterial structure, and demonstrate its use for the imaging of a sample with sub-wavelength dimensions in the audible frequency range.
Physical review. E, 2016
The propagation of broad bandwidth solitary wave impulses, generated within granular chains by na... more The propagation of broad bandwidth solitary wave impulses, generated within granular chains by narrow bandwidth ultrasonic excitation, is studied in detail. Theoretical predictions are compared to experimental results. It is demonstrated that the observed effects result from a sum of a solitary wave traveling out from the source with a wave that reflects from the far end of the chain. It is shown that this combination, when used with an excitation in the form of a long-duration tone burst, encourages the generation of multiple impulses with a characteristic periodicity. This study shows that the properties of the chain structure and the excitation can be adjusted so as to generate ultrasonic solitary wave impulses with a high amplitude and known frequency content, which are of interest in applications such as biomedical ultrasound.
Ultrasonics, 2018
A pulse compression technique has been developed for the non-destructive testing of concrete samp... more A pulse compression technique has been developed for the non-destructive testing of concrete samples. Scattering of signals from aggregate has historically been a problem in such measurements. Here, it is shown that a combination of piezocomposite transducers, pulse compression and post processing can lead to good images of a reinforcement bar at a cover depth of 55 mm. This has been achieved using a combination of wide bandwidth operation over the 150-450 kHz range, and processing based on measuring the cumulative energy scattered back to the receiver. Results are presented in the form of images of a 20 mm rebar embedded within a sample containing 10 mm aggregate.
Nondestructive Testing and Evaluation, 2016
Ultrasonic signals at frequencies below 1 MHz have been used for the NDE of thick polymer samples... more Ultrasonic signals at frequencies below 1 MHz have been used for the NDE of thick polymer samples. Coded signals such as chirps and bipolar Golay codes, together with pulse compression and signal processing, have been used to penetrate into thick sections of attenuating polypropylene riser stiffener material, using piezocomposite transducers to provide the required bandwidth. It is shown that this approach can be used to detect manufacturing defects such as air bubbles in flexible riser stiffeners, which might compromise their performance in the offshore oil and gas environments.
2014 IEEE International Ultrasonics Symposium, 2014
Different approaches have been investigated for the transmission of signals through highly attenu... more Different approaches have been investigated for the transmission of signals through highly attenuating and scattering materials. Chirp signals are sent through the material, and then processed using either time-multiplication or cross-correlation with a template to obtain information concerning the sample. The use of both narrow bandwidth piezoelectric transducers and wide bandwidth piezocomposites is also discussed.
Ultrasonic Nondestructive Evaluation Systems, 2014
In many application environments, it is not possible to practice nondestructive evaluation (NDE) ... more In many application environments, it is not possible to practice nondestructive evaluation (NDE) by physically contacting the material under test with probes. Examples include the evaluation of objects that are moving (e.g., on an assembly line), hot materials, materials that cannot risk contamination, and more. Lack of contact means that, typically, the coupling material is air. This poses specific requirements, due to the acoustic impedance mismatch that an air layer can provoke and the consequent energy losses. In this chapter, some examples of setups, transducer arrangements, and signal processing strategies capable of addressing such requirements are illustrated, showing how concepts presented in the previous chapters can be deployed in this particular context. Furthermore, some typical achievable results are illustrated, with respect to a few different testing scenarios, such as the testing of composite materials, the inspection of concrete, imaging of surfaces or thin materials, and food inspection.
Ultrasonics, 2014
Please refer to published version for the most recent bibliographic citation information. If a pu... more Please refer to published version for the most recent bibliographic citation information. If a published version is known of, the repository item page linked to above, will contain details on accessing it.
Sensors, 2020
Experiments have been performed to demonstrate that ultrasound in the 100–400 kHz frequency range... more Experiments have been performed to demonstrate that ultrasound in the 100–400 kHz frequency range can be used to propagate signals through various types of industrial insulation. This is despite the fact that they are highly attenuating to ultrasonic signals due to scattering and viscoelastic effects. The experiments used a combination of piezocomposite transducers and pulse compression processing. This combination allowed signal-to-noise levels to be enhanced so that signals reflected from the surface of an insulated and cladded steel pipe could be obtained.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, Nov 7, 2016
The response of a resonant chain of spheres to changes in holder material and pre-compression is ... more The response of a resonant chain of spheres to changes in holder material and pre-compression is studied at ultrasonic frequencies. The system is found to be very sensitive to these parameters, with the creation of impulsive waveforms from a narrow bandwidth input seen only for certain chain lengths and holder materials. In addition, careful experiments were performed using known amounts of pre-compression force, using a calibrated stylus arrangement. At negligible pre-compression levels, impulses were generated within the chain, which were then suppressed by increased pre-compression. This was accompanied by large changes in propagation velocity as the system gradually changes from being strongly nonlinear to being more linear. Simulations using a discrete model for the motion of each sphere agree well with experimental data.
2013 18th International Conference on Digital Signal Processing (DSP), 2013
Acoustical Society of …, 2008
ABSTRACT Ultrasonic anemometers are often used for studies of 3-D atmospheric turbulence on Earth... more ABSTRACT Ultrasonic anemometers are often used for studies of 3-D atmospheric turbulence on Earth, due to their robust calibration and fast operation (>10 Hz). The same qualities make ultrasonic anemometry attractive for use on Mars, where similar atmospheric turbulence is found. The low density of Martian atmosphere - a hundredth that of the Earth's - is problematic, because of the large acoustic impedance mismatch between the atmosphere and piezoelectric transducers. One solution to this problem is to use piezoelectric transducers with a hornlike resonator bonded to their front surface. Another solution is to use a capacitive membrane transducer instead. We report on performance of various ultrasonic transducers in carbon dioxide Martian pressures, and present an instrument design capable of meeting the stringent mass, power, and environmental requirements of the European ExoMars lander.
Loudspeakers are required whenever there is a need to reproduce sound. Utilising the technology b... more Loudspeakers are required whenever there is a need to reproduce sound. Utilising the technology behind ultrasonic capacitance transducers, a radically new loudspeaker concept has been developed, which has resulted in the creation of an ultra-thin loudspeaker. This speaker design, which is less than 1mm thick, is also flexible, being comprised of several thin sheets. Such a device would render it suitable to a wide range of applications, including those where space is at a premium, for example mobile telephones and notebook computers. An accurate mathematical model relating the material properties of the speaker to the expected resonant frequency has been developed, by analysing the fundamental characteristics and operation of the speaker. This has been used to improve the acoustical characteristics of the speaker. By utilising different loudspeaker geometries, there is a possibility of increasing the sound pressure level and bandwidth of the speaker such that a relatively flat response across the audible range can be achieved. This paper will report the work towards achieving this aim, and will discuss the need to fully understand the fundamental characteristics of the device.
This paper describes the use of near infrared techniques for both spectroscopy and imaging. The a... more This paper describes the use of near infrared techniques for both spectroscopy and imaging. The approach uses both techniques on the same sample, so that spectral information can be used in conjunction with an image to identify materials and objects. It is shown that the technique has applications to security screening, food quality inspection and biomedical measurements, using the ability of near infrared to penetrate through barriers.
Ultrasonic Nondestructive Evaluation Systems, 2014
Optics and Photonics for Counterterrorism, Crime Fighting, and Defence VIII, 2012
ABSTRACT
2013 IEEE International Ultrasonics Symposium (IUS), 2013
ABSTRACT