Per Lunde | University of Bergen (original) (raw)

Papers by Per Lunde

Ultrasonics, 1987

Transit-time ultrasonic gas flowmeters offer several advantages compared to other current flowmet... more Transit-time ultrasonic gas flowmeters offer several advantages compared to other current flowmeter technology, and they have the potential of being developed into cost-effective and reliable flowmeters. One important step towards implementing more fully the advantages of ultrasonic flowmeter technology is to apply flowmeter simulation models in the design process. A simulation model which describes the signal transmission for a single acoustic beam in an ultrasonic transit-time flowmeter, is described here. Some of the capabilities of the model in predicting several important effects in the functioning of a flowmeter signal transmission channel are demonstrated for a given simplified set of design parameters.

Proceedings, Oct 1, 2007

When fluid flow approaches zero, the measurement uncertainty of ultrasonic flow meters (USMs) inc... more When fluid flow approaches zero, the measurement uncertainty of ultrasonic flow meters (USMs) increases, unless specific precautions are made. At zero flow, the measured transit times of upstream and downstream propagation are not necessarily equal, resulting in a zero flow timing offset, which becomes highly important in the low-velocity flow range, and provides false flow detection and degraded accuracy of the USM in this range. Possible precautions may be (a) "zero flow adjustment" or (b) exploitation of reciprocal operation of the USM. In the present paper, reciprocal operation of USMs is discussed on basis of general electro-acoustical principles. The paper extends earlier literature by (a) taking into account the finite electrical impedances of the electronics and transducers, (b) deriving design criteria for reciprocal operation of USMs, and (c) demonstrating reciprocal operation and validity of the theoretical results, also for transducers not being equal in performance. Laboratory measurements are made over a range of pressures, temperatures and signal excitation levels, for a USM custody transfer meter for natural gas. Consequences for USMs are significant, such as (a) simplified "zero flow adjustment" procedures, (b) cost reduction, and (c) improved accuracy, linearity and robustness at low flow velocities in relation to changes in temperature and pressure, ageing drift, etc. The results show the significance and potentials of utilizing reciprocity in USM technology, as well as improvements already achieved by realizing reciprocal operation in high precision flow meters for custody transfer metering of natural gas and petroleum liquids.

Acoustic beam diffraction phenomena for normal beam incidence to a viscoelastic plate, such as re... more Acoustic beam diffraction phenomena for normal beam incidence to a viscoelastic plate, such as resonance frequency downshift, beam narrowing, and axial signal enhancement near certain leaky Lamb modes, have been demonstrated in recent years, as compared to plane-wave analyses. A close correlation between these phenomena and apparantly different guided-wave dispersion phenomena, including negative group velocity, has been shown by [Aanes et al., Proc. IEEE Int. Ultras. Symp., Taipei, Taiwan, 2015]. It was proposed that the beam diffraction phenomena depend on the size of the mode's NGV region being excited. In the present work, such possible connection between the mentioned beam diffraction phenomena in the frequency region of the S1 leaky Lamb mode, and the gradual excitation of this mode's NGV region, is investigated. A detailed study shows a close correlation between these beam diffraction phenomena and the portion of the S1 leaky mode's NGV region being excited.

In a comparison of theoretical models and experimental results, the traditional MMOT and Mason mo... more In a comparison of theoretical models and experimental results, the traditional MMOT and Mason models for isolated R and TE modes in thin circular piezoceramic disks, have been found to yield a reasonable agreement with FEM and experimental results in their expected ranges of validity, i.e. for D/T≫ηn, and D/T≫1, respectively. (Here, ηn is root No. N of the R mode resonance frequency equation.) However, deviations have been observed between the results using Brissaud's model for coupled R and TE modes, and both the experimental results and the other theoretical model results, even for large D/T ratios. Reasons for such deviations are suggested and discussed

arXiv (Cornell University), Apr 30, 2019

A system model is used, describing the voltage-to-voltage transfer function for an ultrasonic tra... more A system model is used, describing the voltage-to-voltage transfer function for an ultrasonic transmit-receive transducer pair based on simulations using a finite element model for piezoelectric transducers (FEMP). The piezoelectric ceramic elements used in this work are cylindrical Pz27 disks vibrating radially in air at room temperature and 1 atm, over a frequency range up to 300 kHz. Comparisons are made between measurements and simulations. Effects of uncertainties in alignment are examined, together with comparisons with prior work.

Ultrasonic gas flow meters for volumetric flow rate fiscal metering of natural gas (USMs) may pos... more Ultrasonic gas flow meters for volumetric flow rate fiscal metering of natural gas (USMs) may possibly also be used for mass and energy flow rate measurement, partially based on velocity of sound (VOS) measurement. To establish the accuracy of the VOS measurements given by the USM, and for traceability purposes, an independent and high-accuracy VOS measurement cell may be used as reference. To include relevant effects of dispersion, the cell should preferably work in the operational frequency range of USMs, e.g. 100-200 kHz, with natural gas under high pressure. Three different transient methods are investigated, aiming to realize a VOS measurement cell, and they are seen to have several common experimental uncertainty sources. In the present work, a two-distance method is discussed in more detail as an example, and some results from measurements in an insulated chamber with air at 1 atm and ca. 25 ◦ C are presented. The relative expanded measurement uncertainty was estimated according to ISO guidelines to 282 ppm (95 % conf. level). One major source of measurement uncertainty was experienced to be small convection currents in the chamber. Without these, the expanded uncertainty would have been about 162 ppm. Such convection effects are expected to be strongly reduced in a properly designed measurement cell. The VOS measurement results were compared with predictions from a VOS model for standard air, including dispersion (J. Acoust. Soc. Amer. 93 (5), pp. 2510-2516, 1993), resulting in a mean deviation of -18 ppm with a two standard deviation spread in the data of 190 ppm over the temperature range.

arXiv (Cornell University), Apr 8, 2016

The interaction of ultrasonic waves with fluid-embedded viscoelastic plates, pipes, and shells, h... more The interaction of ultrasonic waves with fluid-embedded viscoelastic plates, pipes, and shells, have been subject to extensive theoretical and experimental studies over several decades. In normal-incidence through-transmission measurements of a water-embedded solid plate using ultrasonic piezoelectric transducer sound fields, significant deviations from plane wave theory have recently been observed. To quantitatively describe such measured phenomena, finite element modeling (FEM), also combined with an angular spectrum method (ASM), have been used for three-dimensional (3D) simulation of the voltage-to-sound-pressure signal propagation through the electro-acoustic measurement system consisting of the piezoelectric transducer, the waterembedded steel plate, and the fluid regions at both sides of the plate. The observed phenomena of frequency downshift of the plate resonance, increased sound pressure level through the plate, and beam narrowing / widening, are ascribed to the finite angular spectrum of the beam, that excites a region of negative and zero group velocity for the leaky Lamb mode in question.

Journal of the Acoustical Society of America, May 1, 2017

Accurate knowledge of the sound field generated by an ultrasonic transducer is important in certa... more Accurate knowledge of the sound field generated by an ultrasonic transducer is important in certain applications, such as custody transfer oil and gas flow measurement. Near- and farfield diffraction effects may influence on the measurement result, demanding a need for control of magnitude and phase influences. In many situations, the simplified model of a planar and uniformly vibrating baffled piston is used to approximate the transducer’s sound field. The Rayleigh distance of the piston model is often used as a measure of the near- and farfield transition range. Real transducers typically exhibit a non-uniform vibration distribution at the front, with significant side and rear vibration. It is of interest to investigate the accuracy of the traditional piston and Rayleigh distance approaches for real transducer sound fields. A circular and baffled Pz27 piezoelectric ceramic disk with diameter 12.7 mm and thickness 2.0 mm is studied, operating in air. Finite-element modeling, supported by analytical and numerical modeling, is used to investigate the near- and farfield sound pressure field over the 0-500 kHz range, including radiation at the two lowest radial modes of the piezoelectric disk. Significant nearfield effects are observed well beyond the Rayleigh distance, both on and off the acoustic axis.

IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, Oct 1, 2017

Plane-wave theory for fluid-embedded isotropic plates is often used in ultrasonic guided-wave app... more Plane-wave theory for fluid-embedded isotropic plates is often used in ultrasonic guided-wave applications, and to estimate wall thickness, corrosion, or sound velocities in plates and pipes. In such structures, measured ultrasonic transmission through the solid material is affected by acoustic beam diffraction effects, and the results may deviate from plane-wave descriptions, which are insufficient to describe the complex effects that occur. When exciting a fluid-embedded steel plate with a pulsed ultrasonic beam at normal incidence, resonance frequency downshift, axial sound pressure level (SPL) increase, and beam narrowing have been observed, for measured resonance peaks in the frequency regions of certain leaky Lamb mode branches of the plate. In the ranges of other leaky Lamb mode branches, the effects observed are different. Measurements, finite element and angular spectrum modeling are used to indicate a close connection between these beam diffraction phenomena and the backward wave characteristics of certain leaky Lamb mode pairs, in the frequency and Poisson's ratio regions around coincidence of two Lamb mode cutoff frequencies of similar symmetry. In particular, such observations made for the steel plate's fundamental thickness-extensional (TE) mode appear to be caused by acoustic beam excitation of the backward wave regions of the − and leaky Lamb modes. Index Terms-Finite transducer aperture effects, guided waves, negative group velocity, zero group velocity, complex dispersion spectrum, backward wave, fluid-embedded plate.

2015 IEEE International Ultrasonics Symposium (IUS), 2015

The plane wave theory of fluid-embedded viscoelastic plates is often used in waveguide applicatio... more The plane wave theory of fluid-embedded viscoelastic plates is often used in waveguide applications, and to estimate wall thickness and sound velocities in plates and pipe walls. In normal-incidence through-transmission measurements, downward frequency shift, signal amplification, and distorted beam patterns, as compared to plane-wave theory, have been observed for resonant peaks in frequency bands near certain Lamb modes. These phenomena are here studied using three models, accounting for 3D description of the transducer's sound field. Finite element modelling, angular spectrum modelling, and a combination of these, are used to simulate the signal propagation through a system consisting of a piezoelectric transducer and a water-embedded steel plate. This includes description of the transducer (its electro-acoustical coupling, vibration, and radiation in water), excitation of viscoelastic leaky Lamb modes in the plate, and the subsequent transmitted sound field in water. The models, capable of accurately describing the measured sound field phenomena, are used to investigate the observed deviations between measurements and plane-wave theory, by varying Poisson's ratio for the plate over the range 0.01 - 0.49.

1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)

Piezoceramic disks with a front layer of varying thickness have been investigated using the FE me... more Piezoceramic disks with a front layer of varying thickness have been investigated using the FE method. Emphasis is laid on the frequency bands around the fundamental thickness extensional mode (TE1) and the first radial mode (R1) of the disks. The influence of varying the density and the compressional and shear velocity of the front layer material has been investigated using electrical input conductance, average displacement and mode shapes. For the frequency band around the TE1 mode, agreement with 1D transmission line model simulations has been found, and further interpretation has been possible. For the frequency band around the R1 mode, similar effects to the ones for the frequency band around the TE1 mode are seen for a front layer material with low characteristic impedance. For higher-impedance front layer materials, the situation changes significantly

Acta Acustica united with Acustica

Several authors have presented resonance frequency spectra of piezoceramic disks calculated using... more Several authors have presented resonance frequency spectra of piezoceramic disks calculated using the Finite Element (FE) method, but the accuracy in these frequency spectra has often not been very high, with relative errors of up to several percent in the calculated resonance frequencies. In the present work, frequency spectra with a maximum relative error of 150 ppm in all calculated resonance frequencies are presented for some of the materials which have been subjected to similar analyses in earlier works; PZT-5A, PZT-5H, PbTiO3, BaTiO3 and Pb(ZrTi)O3. The bound for the relative error is found using an a priori error estimator for the calculation of resonance frequencies of piezoceramic disks using the FE method. The error estimator is found based on convergence tests for disks of different piezoceramic materials with varying diameter over thickness ratios. Some work on a corresponding error estimator for electrical and mechanical response functions is also presented.

2007 IEEE Ultrasonics Symposium Proceedings, 2007

When fluid flow approaches zero, the measurement uncertainty of ultrasonic flow meters (USMs) inc... more When fluid flow approaches zero, the measurement uncertainty of ultrasonic flow meters (USMs) increases, unless specific precautions are made. At zero flow, the measured transit times of upstream and downstream propagation are not necessarily equal, resulting in a zero flow timing offset, which becomes highly important in the low-velocity flow range, and provides false flow detection and degraded accuracy of the USM in this range. Possible precautions may be (a) "zero flow adjustment" or (b) exploitation of reciprocal operation of the USM. In the present paper, reciprocal operation of USMs is discussed on basis of general electro-acoustical principles. The paper extends earlier literature by (a) taking into account the finite electrical impedances of the electronics and transducers, (b) deriving design criteria for reciprocal operation of USMs, and (c) demonstrating reciprocal operation and validity of the theoretical results, also for transducers not being equal in performance. Laboratory measurements are made over a range of pressures, temperatures and signal excitation levels, for a USM custody transfer meter for natural gas. Consequences for USMs are significant, such as (a) simplified "zero flow adjustment" procedures, (b) cost reduction, and (c) improved accuracy, linearity and robustness at low flow velocities in relation to changes in temperature and pressure, ageing drift, etc. The results show the significance and potentials of utilizing reciprocity in USM technology, as well as improvements already achieved by realizing reciprocal operation in high precision flow meters for custody transfer metering of natural gas and petroleum liquids.

IEEE Ultrasonics Symposium, 2005.

Ultrasonic gas flow meters for volumetric flow rate fiscal metering of natural gas (USMs) may pos... more Ultrasonic gas flow meters for volumetric flow rate fiscal metering of natural gas (USMs) may possibly also be used for mass and energy flow rate measurement, partially based on velocity of sound (VOS) measurement. To establish the accuracy of the VOS measurements given by the USM, and for traceability purposes, an independent and high-accuracy VOS measurement cell may be used as reference. To include relevant effects of dispersion, the cell should preferably work in the operational frequency range of USMs, e.g. 100-200 kHz, with natural gas under high pressure. Three different transient methods are investigated, aiming to realize a VOS measurement cell, and they are seen to have several common experimental uncertainty sources. In the present work, a two-distance method is discussed in more detail as an example, and some results from measurements in an insulated chamber with air at 1 atm and ca. 25 ◦ C are presented. The relative expanded measurement uncertainty was estimated according to ISO guidelines to 282 ppm (95 % conf. level). One major source of measurement uncertainty was experienced to be small convection currents in the chamber. Without these, the expanded uncertainty would have been about 162 ppm. Such convection effects are expected to be strongly reduced in a properly designed measurement cell. The VOS measurement results were compared with predictions from a VOS model for standard air, including dispersion (J. Acoust. Soc. Amer. 93 (5), pp. 2510-2516, 1993), resulting in a mean deviation of -18 ppm with a two standard deviation spread in the data of 190 ppm over the temperature range.

A modified free-and far-field three-transducer reciprocity calibration method has been utilized t... more A modified free-and far-field three-transducer reciprocity calibration method has been utilized to determine the receiving voltage sensitivity, M V , of a piezoelectric disc. The measurement results are compared to finite element modelling (FEM). A system model has been employed to give a theoretical description of the measurement system at hand, allowing corrections to be made accounting for laboratory instrumentation, diffraction and attenuation in air. A technique to isolate different noise contributors has been utilised to obtain two different signal-tonoise ratio (SNR) analyses. It is shown that the SNR given coherent noise drops significantly, compared to that of random noise, for a certain frequency range when the piezoelectric discs are moved closer together. All work is performed on piezoelectric discs radiating in air at room temperature at approximately 1 atm, with the first radial mode, R1, at about 100 kHz. The frequency range of interest is 100-300 kHz, though only a subset of this, 50-140 kHz, is investigated in the current work.

arXiv (Cornell University), Apr 30, 2019

Experimental acoustic laboratory measurement methods for hydrate-bearing poroelastic solid media ... more Experimental acoustic laboratory measurement methods for hydrate-bearing poroelastic solid media are biefly reviewed. A measurement example using the Fourier spectrum method is given, for compressional and shear wave velocities in hydrate-bearing Bentheim sandstone.

Ultrasonics, 1987

Transit-time ultrasonic gas flowmeters offer several advantages compared to other current flowmet... more Transit-time ultrasonic gas flowmeters offer several advantages compared to other current flowmeter technology, and they have the potential of being developed into cost-effective and reliable flowmeters. One important step towards implementing more fully the advantages of ultrasonic flowmeter technology is to apply flowmeter simulation models in the design process. A simulation model which describes the signal transmission for a single acoustic beam in an ultrasonic transit-time flowmeter, is described here. Some of the capabilities of the model in predicting several important effects in the functioning of a flowmeter signal transmission channel are demonstrated for a given simplified set of design parameters.

Proceedings, Oct 1, 2007

When fluid flow approaches zero, the measurement uncertainty of ultrasonic flow meters (USMs) inc... more When fluid flow approaches zero, the measurement uncertainty of ultrasonic flow meters (USMs) increases, unless specific precautions are made. At zero flow, the measured transit times of upstream and downstream propagation are not necessarily equal, resulting in a zero flow timing offset, which becomes highly important in the low-velocity flow range, and provides false flow detection and degraded accuracy of the USM in this range. Possible precautions may be (a) "zero flow adjustment" or (b) exploitation of reciprocal operation of the USM. In the present paper, reciprocal operation of USMs is discussed on basis of general electro-acoustical principles. The paper extends earlier literature by (a) taking into account the finite electrical impedances of the electronics and transducers, (b) deriving design criteria for reciprocal operation of USMs, and (c) demonstrating reciprocal operation and validity of the theoretical results, also for transducers not being equal in performance. Laboratory measurements are made over a range of pressures, temperatures and signal excitation levels, for a USM custody transfer meter for natural gas. Consequences for USMs are significant, such as (a) simplified "zero flow adjustment" procedures, (b) cost reduction, and (c) improved accuracy, linearity and robustness at low flow velocities in relation to changes in temperature and pressure, ageing drift, etc. The results show the significance and potentials of utilizing reciprocity in USM technology, as well as improvements already achieved by realizing reciprocal operation in high precision flow meters for custody transfer metering of natural gas and petroleum liquids.

Acoustic beam diffraction phenomena for normal beam incidence to a viscoelastic plate, such as re... more Acoustic beam diffraction phenomena for normal beam incidence to a viscoelastic plate, such as resonance frequency downshift, beam narrowing, and axial signal enhancement near certain leaky Lamb modes, have been demonstrated in recent years, as compared to plane-wave analyses. A close correlation between these phenomena and apparantly different guided-wave dispersion phenomena, including negative group velocity, has been shown by [Aanes et al., Proc. IEEE Int. Ultras. Symp., Taipei, Taiwan, 2015]. It was proposed that the beam diffraction phenomena depend on the size of the mode's NGV region being excited. In the present work, such possible connection between the mentioned beam diffraction phenomena in the frequency region of the S1 leaky Lamb mode, and the gradual excitation of this mode's NGV region, is investigated. A detailed study shows a close correlation between these beam diffraction phenomena and the portion of the S1 leaky mode's NGV region being excited.

In a comparison of theoretical models and experimental results, the traditional MMOT and Mason mo... more In a comparison of theoretical models and experimental results, the traditional MMOT and Mason models for isolated R and TE modes in thin circular piezoceramic disks, have been found to yield a reasonable agreement with FEM and experimental results in their expected ranges of validity, i.e. for D/T≫ηn, and D/T≫1, respectively. (Here, ηn is root No. N of the R mode resonance frequency equation.) However, deviations have been observed between the results using Brissaud's model for coupled R and TE modes, and both the experimental results and the other theoretical model results, even for large D/T ratios. Reasons for such deviations are suggested and discussed

arXiv (Cornell University), Apr 30, 2019

A system model is used, describing the voltage-to-voltage transfer function for an ultrasonic tra... more A system model is used, describing the voltage-to-voltage transfer function for an ultrasonic transmit-receive transducer pair based on simulations using a finite element model for piezoelectric transducers (FEMP). The piezoelectric ceramic elements used in this work are cylindrical Pz27 disks vibrating radially in air at room temperature and 1 atm, over a frequency range up to 300 kHz. Comparisons are made between measurements and simulations. Effects of uncertainties in alignment are examined, together with comparisons with prior work.

Ultrasonic gas flow meters for volumetric flow rate fiscal metering of natural gas (USMs) may pos... more Ultrasonic gas flow meters for volumetric flow rate fiscal metering of natural gas (USMs) may possibly also be used for mass and energy flow rate measurement, partially based on velocity of sound (VOS) measurement. To establish the accuracy of the VOS measurements given by the USM, and for traceability purposes, an independent and high-accuracy VOS measurement cell may be used as reference. To include relevant effects of dispersion, the cell should preferably work in the operational frequency range of USMs, e.g. 100-200 kHz, with natural gas under high pressure. Three different transient methods are investigated, aiming to realize a VOS measurement cell, and they are seen to have several common experimental uncertainty sources. In the present work, a two-distance method is discussed in more detail as an example, and some results from measurements in an insulated chamber with air at 1 atm and ca. 25 ◦ C are presented. The relative expanded measurement uncertainty was estimated according to ISO guidelines to 282 ppm (95 % conf. level). One major source of measurement uncertainty was experienced to be small convection currents in the chamber. Without these, the expanded uncertainty would have been about 162 ppm. Such convection effects are expected to be strongly reduced in a properly designed measurement cell. The VOS measurement results were compared with predictions from a VOS model for standard air, including dispersion (J. Acoust. Soc. Amer. 93 (5), pp. 2510-2516, 1993), resulting in a mean deviation of -18 ppm with a two standard deviation spread in the data of 190 ppm over the temperature range.

arXiv (Cornell University), Apr 8, 2016

The interaction of ultrasonic waves with fluid-embedded viscoelastic plates, pipes, and shells, h... more The interaction of ultrasonic waves with fluid-embedded viscoelastic plates, pipes, and shells, have been subject to extensive theoretical and experimental studies over several decades. In normal-incidence through-transmission measurements of a water-embedded solid plate using ultrasonic piezoelectric transducer sound fields, significant deviations from plane wave theory have recently been observed. To quantitatively describe such measured phenomena, finite element modeling (FEM), also combined with an angular spectrum method (ASM), have been used for three-dimensional (3D) simulation of the voltage-to-sound-pressure signal propagation through the electro-acoustic measurement system consisting of the piezoelectric transducer, the waterembedded steel plate, and the fluid regions at both sides of the plate. The observed phenomena of frequency downshift of the plate resonance, increased sound pressure level through the plate, and beam narrowing / widening, are ascribed to the finite angular spectrum of the beam, that excites a region of negative and zero group velocity for the leaky Lamb mode in question.

Journal of the Acoustical Society of America, May 1, 2017

Accurate knowledge of the sound field generated by an ultrasonic transducer is important in certa... more Accurate knowledge of the sound field generated by an ultrasonic transducer is important in certain applications, such as custody transfer oil and gas flow measurement. Near- and farfield diffraction effects may influence on the measurement result, demanding a need for control of magnitude and phase influences. In many situations, the simplified model of a planar and uniformly vibrating baffled piston is used to approximate the transducer’s sound field. The Rayleigh distance of the piston model is often used as a measure of the near- and farfield transition range. Real transducers typically exhibit a non-uniform vibration distribution at the front, with significant side and rear vibration. It is of interest to investigate the accuracy of the traditional piston and Rayleigh distance approaches for real transducer sound fields. A circular and baffled Pz27 piezoelectric ceramic disk with diameter 12.7 mm and thickness 2.0 mm is studied, operating in air. Finite-element modeling, supported by analytical and numerical modeling, is used to investigate the near- and farfield sound pressure field over the 0-500 kHz range, including radiation at the two lowest radial modes of the piezoelectric disk. Significant nearfield effects are observed well beyond the Rayleigh distance, both on and off the acoustic axis.

IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, Oct 1, 2017

Plane-wave theory for fluid-embedded isotropic plates is often used in ultrasonic guided-wave app... more Plane-wave theory for fluid-embedded isotropic plates is often used in ultrasonic guided-wave applications, and to estimate wall thickness, corrosion, or sound velocities in plates and pipes. In such structures, measured ultrasonic transmission through the solid material is affected by acoustic beam diffraction effects, and the results may deviate from plane-wave descriptions, which are insufficient to describe the complex effects that occur. When exciting a fluid-embedded steel plate with a pulsed ultrasonic beam at normal incidence, resonance frequency downshift, axial sound pressure level (SPL) increase, and beam narrowing have been observed, for measured resonance peaks in the frequency regions of certain leaky Lamb mode branches of the plate. In the ranges of other leaky Lamb mode branches, the effects observed are different. Measurements, finite element and angular spectrum modeling are used to indicate a close connection between these beam diffraction phenomena and the backward wave characteristics of certain leaky Lamb mode pairs, in the frequency and Poisson's ratio regions around coincidence of two Lamb mode cutoff frequencies of similar symmetry. In particular, such observations made for the steel plate's fundamental thickness-extensional (TE) mode appear to be caused by acoustic beam excitation of the backward wave regions of the − and leaky Lamb modes. Index Terms-Finite transducer aperture effects, guided waves, negative group velocity, zero group velocity, complex dispersion spectrum, backward wave, fluid-embedded plate.

2015 IEEE International Ultrasonics Symposium (IUS), 2015

The plane wave theory of fluid-embedded viscoelastic plates is often used in waveguide applicatio... more The plane wave theory of fluid-embedded viscoelastic plates is often used in waveguide applications, and to estimate wall thickness and sound velocities in plates and pipe walls. In normal-incidence through-transmission measurements, downward frequency shift, signal amplification, and distorted beam patterns, as compared to plane-wave theory, have been observed for resonant peaks in frequency bands near certain Lamb modes. These phenomena are here studied using three models, accounting for 3D description of the transducer's sound field. Finite element modelling, angular spectrum modelling, and a combination of these, are used to simulate the signal propagation through a system consisting of a piezoelectric transducer and a water-embedded steel plate. This includes description of the transducer (its electro-acoustical coupling, vibration, and radiation in water), excitation of viscoelastic leaky Lamb modes in the plate, and the subsequent transmitted sound field in water. The models, capable of accurately describing the measured sound field phenomena, are used to investigate the observed deviations between measurements and plane-wave theory, by varying Poisson's ratio for the plate over the range 0.01 - 0.49.

1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027)

Piezoceramic disks with a front layer of varying thickness have been investigated using the FE me... more Piezoceramic disks with a front layer of varying thickness have been investigated using the FE method. Emphasis is laid on the frequency bands around the fundamental thickness extensional mode (TE1) and the first radial mode (R1) of the disks. The influence of varying the density and the compressional and shear velocity of the front layer material has been investigated using electrical input conductance, average displacement and mode shapes. For the frequency band around the TE1 mode, agreement with 1D transmission line model simulations has been found, and further interpretation has been possible. For the frequency band around the R1 mode, similar effects to the ones for the frequency band around the TE1 mode are seen for a front layer material with low characteristic impedance. For higher-impedance front layer materials, the situation changes significantly

Acta Acustica united with Acustica

Several authors have presented resonance frequency spectra of piezoceramic disks calculated using... more Several authors have presented resonance frequency spectra of piezoceramic disks calculated using the Finite Element (FE) method, but the accuracy in these frequency spectra has often not been very high, with relative errors of up to several percent in the calculated resonance frequencies. In the present work, frequency spectra with a maximum relative error of 150 ppm in all calculated resonance frequencies are presented for some of the materials which have been subjected to similar analyses in earlier works; PZT-5A, PZT-5H, PbTiO3, BaTiO3 and Pb(ZrTi)O3. The bound for the relative error is found using an a priori error estimator for the calculation of resonance frequencies of piezoceramic disks using the FE method. The error estimator is found based on convergence tests for disks of different piezoceramic materials with varying diameter over thickness ratios. Some work on a corresponding error estimator for electrical and mechanical response functions is also presented.

2007 IEEE Ultrasonics Symposium Proceedings, 2007

When fluid flow approaches zero, the measurement uncertainty of ultrasonic flow meters (USMs) inc... more When fluid flow approaches zero, the measurement uncertainty of ultrasonic flow meters (USMs) increases, unless specific precautions are made. At zero flow, the measured transit times of upstream and downstream propagation are not necessarily equal, resulting in a zero flow timing offset, which becomes highly important in the low-velocity flow range, and provides false flow detection and degraded accuracy of the USM in this range. Possible precautions may be (a) "zero flow adjustment" or (b) exploitation of reciprocal operation of the USM. In the present paper, reciprocal operation of USMs is discussed on basis of general electro-acoustical principles. The paper extends earlier literature by (a) taking into account the finite electrical impedances of the electronics and transducers, (b) deriving design criteria for reciprocal operation of USMs, and (c) demonstrating reciprocal operation and validity of the theoretical results, also for transducers not being equal in performance. Laboratory measurements are made over a range of pressures, temperatures and signal excitation levels, for a USM custody transfer meter for natural gas. Consequences for USMs are significant, such as (a) simplified "zero flow adjustment" procedures, (b) cost reduction, and (c) improved accuracy, linearity and robustness at low flow velocities in relation to changes in temperature and pressure, ageing drift, etc. The results show the significance and potentials of utilizing reciprocity in USM technology, as well as improvements already achieved by realizing reciprocal operation in high precision flow meters for custody transfer metering of natural gas and petroleum liquids.

IEEE Ultrasonics Symposium, 2005.

Ultrasonic gas flow meters for volumetric flow rate fiscal metering of natural gas (USMs) may pos... more Ultrasonic gas flow meters for volumetric flow rate fiscal metering of natural gas (USMs) may possibly also be used for mass and energy flow rate measurement, partially based on velocity of sound (VOS) measurement. To establish the accuracy of the VOS measurements given by the USM, and for traceability purposes, an independent and high-accuracy VOS measurement cell may be used as reference. To include relevant effects of dispersion, the cell should preferably work in the operational frequency range of USMs, e.g. 100-200 kHz, with natural gas under high pressure. Three different transient methods are investigated, aiming to realize a VOS measurement cell, and they are seen to have several common experimental uncertainty sources. In the present work, a two-distance method is discussed in more detail as an example, and some results from measurements in an insulated chamber with air at 1 atm and ca. 25 ◦ C are presented. The relative expanded measurement uncertainty was estimated according to ISO guidelines to 282 ppm (95 % conf. level). One major source of measurement uncertainty was experienced to be small convection currents in the chamber. Without these, the expanded uncertainty would have been about 162 ppm. Such convection effects are expected to be strongly reduced in a properly designed measurement cell. The VOS measurement results were compared with predictions from a VOS model for standard air, including dispersion (J. Acoust. Soc. Amer. 93 (5), pp. 2510-2516, 1993), resulting in a mean deviation of -18 ppm with a two standard deviation spread in the data of 190 ppm over the temperature range.

A modified free-and far-field three-transducer reciprocity calibration method has been utilized t... more A modified free-and far-field three-transducer reciprocity calibration method has been utilized to determine the receiving voltage sensitivity, M V , of a piezoelectric disc. The measurement results are compared to finite element modelling (FEM). A system model has been employed to give a theoretical description of the measurement system at hand, allowing corrections to be made accounting for laboratory instrumentation, diffraction and attenuation in air. A technique to isolate different noise contributors has been utilised to obtain two different signal-tonoise ratio (SNR) analyses. It is shown that the SNR given coherent noise drops significantly, compared to that of random noise, for a certain frequency range when the piezoelectric discs are moved closer together. All work is performed on piezoelectric discs radiating in air at room temperature at approximately 1 atm, with the first radial mode, R1, at about 100 kHz. The frequency range of interest is 100-300 kHz, though only a subset of this, 50-140 kHz, is investigated in the current work.

arXiv (Cornell University), Apr 30, 2019

Experimental acoustic laboratory measurement methods for hydrate-bearing poroelastic solid media ... more Experimental acoustic laboratory measurement methods for hydrate-bearing poroelastic solid media are biefly reviewed. A measurement example using the Fourier spectrum method is given, for compressional and shear wave velocities in hydrate-bearing Bentheim sandstone.