Lee A J Davis - Profile on Academia.edu (original) (raw)

Papers by Lee A J Davis

Ultrasonics, Apr 1, 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.

NDT & E international, Mar 1, 2019

Near infrared signals have been used to generate images of the internal structure of fibre-reinfo... more Near infrared signals have been used to generate images of the internal structure of fibre-reinforced polymer and foam-filled honeycomb samples. Several different measurement configurations have been investigated, including the use of both modulated light-emitting diodes at discrete wavelengths and broad bandwidth illumination. It is shown that transmission through the samples is wavelengthdependent, and that artificial defects can be detected within polymer composite materials. In addition, wavelength-dependent properties have been used to detect changes due to water ingress into both composite materials and a solar panel structure, leading to a non-contact NDE technique.

AIP Advances, Nov 23, 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.

2015 IEEE International Ultrasonics Symposium (IUS), 2015

There has been recent interest in the transmission of acoustic signals along a chain of spheres t... more There has been recent interest in the transmission of acoustic signals along a chain of spheres to produce waveforms of relevance to biomedical ultrasound applications. Effects which arise as a result of Hertzian contact between adjacent spheres can potentially change the nature of the signal as it propagates down the chain. The possibility thus exists of generating signals with a different harmonic content to the signal input into one end of the chain. This transduction mechanism has the potential to be of use in both diagnostic and therapeutic ultrasound applications, and is the object of the study presented here. The nonlinear dynamics of granular chains can be treated using discrete mechanics models. However, in cases where the underlying assumptions of these models no longer hold, and where geometries are more complex, a more comprehensive numerical solution must be sought. Contact mechanics problems can efficiently be treated using the finite element method. The latter was used to investigate the dynamics of a pre-stressed chain of six, 1 mm diameter stainless steel spheres excited at one end using a tone burst displacement signal with a fundamental frequency of 73 kHz. The final sphere of the chain was assumed to be in contact with a cylindrical matching layer radiating into a half-space of fluid with the properties of water. After addition of the fluid loading, radiated acoustic pressures in the medium were predicted. Comparison with experimental results suggests that finite element analysis is a suitable tool for investigating the design and performance of contact mechanics based transducers. Nevertheless, a better handle on the model input parameters as well as an improved experimental protocol are required to fully validate the model.

Journal of Textile Science & Engineering, 2013

NDT & E International, 2019

Near infrared signals have been used to generate images of the internal structure of fibre-reinfo... more Near infrared signals have been used to generate images of the internal structure of fibre-reinforced polymer and foam-filled honeycomb samples. Several different measurement configurations have been investigated, including the use of both modulated light-emitting diodes at discrete wavelengths and broad bandwidth illumination. It is shown that transmission through the samples is wavelengthdependent, and that artificial defects can be detected within polymer composite materials. In addition, wavelength-dependent properties have been used to detect changes due to water ingress into both composite materials and a solar panel structure, leading to a non-contact NDE technique.

Journal of Physics: Conference Series, 2016

There has been recent interest in the transmission of acoustic signals along granular chains of s... more There has been recent interest in the transmission of acoustic signals along granular chains of spherical beads to produce waveforms of relevance to biomedical ultrasound applications. Hertzian contact between adjacent beads can introduce different harmonic content into the signal as it propagates. This transduction mechanism has the potential to be of use in both diagnostic and therapeutic ultrasound applications, and is the object of the study presented here. Although discrete dynamics models of this behaviour exist, a more comprehensive solution must be sought if changes in shape and deformation of individual beads are to be considered. Thus, the finite element method was used to investigate the dynamics of a granular chain of six, 1 mm diameter chrome steel spherical beads excited at one end using a sinusoidal displacement signal at 73 kHz. Output from this model was compared with the solution provided by the discrete dynamics model, and good overall agreement obtained. In addit...

Low frequency coded waveform for the inspection of concrete structures

2015 IEEE International Ultrasonics Symposium (IUS), 2015

Low frequency piezocomposite transducers have been used in combination with pulse compression met... more Low frequency piezocomposite transducers have been used in combination with pulse compression methods to penetrate 35 cm into concrete-type materials. A chirp signal with a frequency range 100 - 200 kHz and of 10 ms duration was used to excite a pair of 54 mm diameter piezocomposite transducers in patch-catch mode. The centre frequency of the transducers was 170 kHz. Using this arrangement, good signals could be obtained, but there was a problem with variability due to the high degree of scattering - even small changes in transducer location changed the measurement. Thus, an additional signal processing method was introduced, whereby the total energy reaching the receiver was calculated as a function of time from the cross-correlation outputs.

Design and characterization of 3D-printed phononic crystals for sub-MHz ultrasound manipulation

2015 IEEE International Ultrasonics Symposium (IUS), 2015

Additive manufacturing (3D printing) has been used to construct phononic crystals that operate in... more Additive manufacturing (3D printing) has been used to construct phononic crystals that operate in the 100 kHz - 1MHz frequency range. These were in the form of regular arrays and columns of steel spheres, embedded within a polymer matrix. Experimental measurements using coded waveforms in a water tank were able to demonstrate that focusing effects were present at certain frequencies, as expected from a phononic crystal structure.

2015 IEEE International Ultrasonics Symposium (IUS), 2015

Discrete dynamic equations of spheres in granular chains have been developed so as to simulate th... more Discrete dynamic equations of spheres in granular chains have been developed so as to simulate the evolution of acoustic signals in these media. The model was built based on Hertzian laws as well as the dissipation effect within the system, and the contact dynamics involving both compression and separation between spheres was also modelled. A molecular dynamics simulation method using the Velocity Verlet algorithm was developed to solve the equations. The strongly nonlinear solitary wave impulses are predicted by the numerical calculations and match the experimental results well. The simulation system has been used as a design tool to determine the optimal chain structure in term of the bandwidth and frequencies which are required within the output impulses. The results exhibit great potential in biomedical applications.

EPL (Europhysics Letters), 2015

PACS 43.35.+d -Acoustics: Ultrasonics, quantum acoustics, and physical effects of sound PACS 46.4... more PACS 43.35.+d -Acoustics: Ultrasonics, quantum acoustics, and physical effects of sound PACS 46.40.-f -Vibrations and mechanical waves PACS 45.50.-j -Dynamics and kinematics of a particle and a system of particles Abstract -It is demonstrated that broad-bandwidth ultrasonic signals containing frequency components in excess of 200 kHz can be created in spherical chains using harmonic excitation at 73 kHz. Multiple reflections created a periodic waveform containing both harmonics and subharmonics of the original forcing frequency, due to non-linear Hertzian contact. These discrete frequencies represented some of the many allowed non-linear normal modes of vibration of the whole chain. Excitation at a single fixed frequency could thus be used to produce wide-bandwidth impulses for different lengths of spherical chains. Experimental results were in good agreement with theoretical predictions.

Physics Procedia, 2015

This paper investigates the use of chains of spheres to produce impulses. An ultrasonic horn is u... more This paper investigates the use of chains of spheres to produce impulses. An ultrasonic horn is used to generate high amplitude sinusoidal signals. These are then input into chains of spheres, held together using a minimal force. The result is a non-linear, dispersive system, within which solitary waves can exist. The authors have discovered that resonances can be created, caused by the multiple reflection of solitary waves within the chain. The multiply-reflecting impulses can have a wide bandwidth, due to the inherent nonlinearity of the contact between spheres. It is found that the effect only occurs for certain numbers of spheres in the chain for a given input frequency, a result of the creation of a nonlinear normal mode of resonance.The resulting impulses have many applications, potentially creating high amplitude impulses with adjustable properties, depending on both the nature and number of spheres in the chain, and the frequency and amplitude of excitation.

Ultrasonics, 2016

A narrowband ultrasound source has been used to generate solitary wave impulses in finite-length ... more A narrowband ultrasound source has been used to generate solitary wave impulses in finite-length chains of spheres. Once the input signal is of sufficient amplitude, both harmonics and sub-harmonics of the input frequency can be generated as non-linear normal modes of the system, allowing a train of impulses to be established from a sinusoidal input. The characteristics of the response have been studied as a function of the physical properties of the chain, the input waveform and the level of static pre-compression. The results agree with the predictions of a theoretical model, based on a set of discrete dynamic equations for the spheres for finite-length chains. Impulses are only created for very small pre-compression forces of the order of 0.01 N, where strongly non-linear behaviour is expected.

Capacitive transducer development for ultrasonic anemometry on Mars

ABSTRACT

The study of broadband acoustic metamaterials in air

2014 IEEE International Ultrasonics Symposium, 2014

Acoustic metamaterials have been attracting huge research efforts in the last years due to the ex... more Acoustic metamaterials have been attracting huge research efforts in the last years due to the exotic properties they exhibit that can be exploited to realize innovative tools such as hyperlenses, acoustic cloacking, etc. In this paper we analyze both numerically and experimentally some basic structures that can constitute the building blocks of a broadband acoustic metamaterial for imaging applications.

2014 IEEE International Ultrasonics Symposium, 2014

Wave propagation in chain-like materials has been studied previously at low frequencies. The pres... more Wave propagation in chain-like materials has been studied previously at low frequencies. The present study has generated these waves at higher frequencies with components >200 kHz, using chains of 1 mm diameter spheres. Resonant ultrasonic horns at 73 kHz have been used as sources of narrowband excitation, which transform into a train of broadband impulses that have the characteristics of solitary waves. These have potential applications in biomedical ultrasound as high amplitude, wide bandwidth impulses.

2014 IEEE International Ultrasonics Symposium, 2014

This is a repository copy of Time-delay estimation and correlation analysis of acoustic signals i... more This is a repository copy of Time-delay estimation and correlation analysis of acoustic signals in granular media using wavelet decomposition.

Journal of Nondestructive Evaluation, 2020

Mid-infrared signals in the 2–5 μm wavelength range have been transmitted through samples of poly... more Mid-infrared signals in the 2–5 μm wavelength range have been transmitted through samples of polymer pipes, as commonly used in the water supply industry. It is shown that simple through-transmission images can be obtained using a broad spectrum source and a suitable camera. This leads to the possibility of tomography, where images are obtained as the measurement system is rotated with respect to the axis of the pipe. The unusual 3D geometry created by a source of finite size and the imaging plane of a camera, plus the fact that refraction at the pipe wall would cause significant ray bending, meant that the reconstruction of tomographic images had to be considered with some care. A result is shown for a thinning defect on the inner wall of a polymer water pipe, demonstrating that such changes can be reconstructed successfully.

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, Apr 1, 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.

NDT & E international, Mar 1, 2019

Near infrared signals have been used to generate images of the internal structure of fibre-reinfo... more Near infrared signals have been used to generate images of the internal structure of fibre-reinforced polymer and foam-filled honeycomb samples. Several different measurement configurations have been investigated, including the use of both modulated light-emitting diodes at discrete wavelengths and broad bandwidth illumination. It is shown that transmission through the samples is wavelengthdependent, and that artificial defects can be detected within polymer composite materials. In addition, wavelength-dependent properties have been used to detect changes due to water ingress into both composite materials and a solar panel structure, leading to a non-contact NDE technique.

AIP Advances, Nov 23, 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.

2015 IEEE International Ultrasonics Symposium (IUS), 2015

There has been recent interest in the transmission of acoustic signals along a chain of spheres t... more There has been recent interest in the transmission of acoustic signals along a chain of spheres to produce waveforms of relevance to biomedical ultrasound applications. Effects which arise as a result of Hertzian contact between adjacent spheres can potentially change the nature of the signal as it propagates down the chain. The possibility thus exists of generating signals with a different harmonic content to the signal input into one end of the chain. This transduction mechanism has the potential to be of use in both diagnostic and therapeutic ultrasound applications, and is the object of the study presented here. The nonlinear dynamics of granular chains can be treated using discrete mechanics models. However, in cases where the underlying assumptions of these models no longer hold, and where geometries are more complex, a more comprehensive numerical solution must be sought. Contact mechanics problems can efficiently be treated using the finite element method. The latter was used to investigate the dynamics of a pre-stressed chain of six, 1 mm diameter stainless steel spheres excited at one end using a tone burst displacement signal with a fundamental frequency of 73 kHz. The final sphere of the chain was assumed to be in contact with a cylindrical matching layer radiating into a half-space of fluid with the properties of water. After addition of the fluid loading, radiated acoustic pressures in the medium were predicted. Comparison with experimental results suggests that finite element analysis is a suitable tool for investigating the design and performance of contact mechanics based transducers. Nevertheless, a better handle on the model input parameters as well as an improved experimental protocol are required to fully validate the model.

Journal of Textile Science & Engineering, 2013

NDT & E International, 2019

Near infrared signals have been used to generate images of the internal structure of fibre-reinfo... more Near infrared signals have been used to generate images of the internal structure of fibre-reinforced polymer and foam-filled honeycomb samples. Several different measurement configurations have been investigated, including the use of both modulated light-emitting diodes at discrete wavelengths and broad bandwidth illumination. It is shown that transmission through the samples is wavelengthdependent, and that artificial defects can be detected within polymer composite materials. In addition, wavelength-dependent properties have been used to detect changes due to water ingress into both composite materials and a solar panel structure, leading to a non-contact NDE technique.

Journal of Physics: Conference Series, 2016

There has been recent interest in the transmission of acoustic signals along granular chains of s... more There has been recent interest in the transmission of acoustic signals along granular chains of spherical beads to produce waveforms of relevance to biomedical ultrasound applications. Hertzian contact between adjacent beads can introduce different harmonic content into the signal as it propagates. This transduction mechanism has the potential to be of use in both diagnostic and therapeutic ultrasound applications, and is the object of the study presented here. Although discrete dynamics models of this behaviour exist, a more comprehensive solution must be sought if changes in shape and deformation of individual beads are to be considered. Thus, the finite element method was used to investigate the dynamics of a granular chain of six, 1 mm diameter chrome steel spherical beads excited at one end using a sinusoidal displacement signal at 73 kHz. Output from this model was compared with the solution provided by the discrete dynamics model, and good overall agreement obtained. In addit...

Low frequency coded waveform for the inspection of concrete structures

2015 IEEE International Ultrasonics Symposium (IUS), 2015

Low frequency piezocomposite transducers have been used in combination with pulse compression met... more Low frequency piezocomposite transducers have been used in combination with pulse compression methods to penetrate 35 cm into concrete-type materials. A chirp signal with a frequency range 100 - 200 kHz and of 10 ms duration was used to excite a pair of 54 mm diameter piezocomposite transducers in patch-catch mode. The centre frequency of the transducers was 170 kHz. Using this arrangement, good signals could be obtained, but there was a problem with variability due to the high degree of scattering - even small changes in transducer location changed the measurement. Thus, an additional signal processing method was introduced, whereby the total energy reaching the receiver was calculated as a function of time from the cross-correlation outputs.

Design and characterization of 3D-printed phononic crystals for sub-MHz ultrasound manipulation

2015 IEEE International Ultrasonics Symposium (IUS), 2015

Additive manufacturing (3D printing) has been used to construct phononic crystals that operate in... more Additive manufacturing (3D printing) has been used to construct phononic crystals that operate in the 100 kHz - 1MHz frequency range. These were in the form of regular arrays and columns of steel spheres, embedded within a polymer matrix. Experimental measurements using coded waveforms in a water tank were able to demonstrate that focusing effects were present at certain frequencies, as expected from a phononic crystal structure.

2015 IEEE International Ultrasonics Symposium (IUS), 2015

Discrete dynamic equations of spheres in granular chains have been developed so as to simulate th... more Discrete dynamic equations of spheres in granular chains have been developed so as to simulate the evolution of acoustic signals in these media. The model was built based on Hertzian laws as well as the dissipation effect within the system, and the contact dynamics involving both compression and separation between spheres was also modelled. A molecular dynamics simulation method using the Velocity Verlet algorithm was developed to solve the equations. The strongly nonlinear solitary wave impulses are predicted by the numerical calculations and match the experimental results well. The simulation system has been used as a design tool to determine the optimal chain structure in term of the bandwidth and frequencies which are required within the output impulses. The results exhibit great potential in biomedical applications.

EPL (Europhysics Letters), 2015

PACS 43.35.+d -Acoustics: Ultrasonics, quantum acoustics, and physical effects of sound PACS 46.4... more PACS 43.35.+d -Acoustics: Ultrasonics, quantum acoustics, and physical effects of sound PACS 46.40.-f -Vibrations and mechanical waves PACS 45.50.-j -Dynamics and kinematics of a particle and a system of particles Abstract -It is demonstrated that broad-bandwidth ultrasonic signals containing frequency components in excess of 200 kHz can be created in spherical chains using harmonic excitation at 73 kHz. Multiple reflections created a periodic waveform containing both harmonics and subharmonics of the original forcing frequency, due to non-linear Hertzian contact. These discrete frequencies represented some of the many allowed non-linear normal modes of vibration of the whole chain. Excitation at a single fixed frequency could thus be used to produce wide-bandwidth impulses for different lengths of spherical chains. Experimental results were in good agreement with theoretical predictions.

Physics Procedia, 2015

This paper investigates the use of chains of spheres to produce impulses. An ultrasonic horn is u... more This paper investigates the use of chains of spheres to produce impulses. An ultrasonic horn is used to generate high amplitude sinusoidal signals. These are then input into chains of spheres, held together using a minimal force. The result is a non-linear, dispersive system, within which solitary waves can exist. The authors have discovered that resonances can be created, caused by the multiple reflection of solitary waves within the chain. The multiply-reflecting impulses can have a wide bandwidth, due to the inherent nonlinearity of the contact between spheres. It is found that the effect only occurs for certain numbers of spheres in the chain for a given input frequency, a result of the creation of a nonlinear normal mode of resonance.The resulting impulses have many applications, potentially creating high amplitude impulses with adjustable properties, depending on both the nature and number of spheres in the chain, and the frequency and amplitude of excitation.

Ultrasonics, 2016

A narrowband ultrasound source has been used to generate solitary wave impulses in finite-length ... more A narrowband ultrasound source has been used to generate solitary wave impulses in finite-length chains of spheres. Once the input signal is of sufficient amplitude, both harmonics and sub-harmonics of the input frequency can be generated as non-linear normal modes of the system, allowing a train of impulses to be established from a sinusoidal input. The characteristics of the response have been studied as a function of the physical properties of the chain, the input waveform and the level of static pre-compression. The results agree with the predictions of a theoretical model, based on a set of discrete dynamic equations for the spheres for finite-length chains. Impulses are only created for very small pre-compression forces of the order of 0.01 N, where strongly non-linear behaviour is expected.

Capacitive transducer development for ultrasonic anemometry on Mars

ABSTRACT

The study of broadband acoustic metamaterials in air

2014 IEEE International Ultrasonics Symposium, 2014

Acoustic metamaterials have been attracting huge research efforts in the last years due to the ex... more Acoustic metamaterials have been attracting huge research efforts in the last years due to the exotic properties they exhibit that can be exploited to realize innovative tools such as hyperlenses, acoustic cloacking, etc. In this paper we analyze both numerically and experimentally some basic structures that can constitute the building blocks of a broadband acoustic metamaterial for imaging applications.

2014 IEEE International Ultrasonics Symposium, 2014

Wave propagation in chain-like materials has been studied previously at low frequencies. The pres... more Wave propagation in chain-like materials has been studied previously at low frequencies. The present study has generated these waves at higher frequencies with components >200 kHz, using chains of 1 mm diameter spheres. Resonant ultrasonic horns at 73 kHz have been used as sources of narrowband excitation, which transform into a train of broadband impulses that have the characteristics of solitary waves. These have potential applications in biomedical ultrasound as high amplitude, wide bandwidth impulses.

2014 IEEE International Ultrasonics Symposium, 2014

This is a repository copy of Time-delay estimation and correlation analysis of acoustic signals i... more This is a repository copy of Time-delay estimation and correlation analysis of acoustic signals in granular media using wavelet decomposition.

Journal of Nondestructive Evaluation, 2020

Mid-infrared signals in the 2–5 μm wavelength range have been transmitted through samples of poly... more Mid-infrared signals in the 2–5 μm wavelength range have been transmitted through samples of polymer pipes, as commonly used in the water supply industry. It is shown that simple through-transmission images can be obtained using a broad spectrum source and a suitable camera. This leads to the possibility of tomography, where images are obtained as the measurement system is rotated with respect to the axis of the pipe. The unusual 3D geometry created by a source of finite size and the imaging plane of a camera, plus the fact that refraction at the pipe wall would cause significant ray bending, meant that the reconstruction of tomographic images had to be considered with some care. A result is shown for a thinning defect on the inner wall of a polymer water pipe, demonstrating that such changes can be reconstructed successfully.

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.