Richard J. Dewhurst

• BSc, PhD, DSc, FInstP, FINDT, CEng, CPhys
• Professor Emeritus at The University of Manchester

Since 1991, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of this journal believe that such a prize is an opportunity to thank authors for submitting their work, and serves as an integral part of the on-going quality review of the journal. The current breadth of topical areas that are covered by MST has made...

This paper describes a novel technique using an elctromagnetic acoustic transducer (EMAT) for biomedical photoacoustic measurements. The physical principle underlying and EMAT sensor is based on the detection of electromagnetic signals, which are responses from the interaction of ultrasonic waves and magnetic fields within the electrically conducti...

A look at the history of this journal reveals some significant trends in the evolution of measurement science and shows how key papers published in the journal have influenced these developments.

Since 1991, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of this journal believes that such a prize is an opportunity to thank authors for submitting their work, and serves as an integral part of the on-going quality review of the journal. The current breadth of topical areas that are covered by MST has mad...

In this issue, we are delighted to publish the second in a series of articles under the banner of Perspectives. The series commenced in late 2008, when Udo Kaatze [1] published an article about the powerful technique of dielectric spectrometry for liquid measurements. In addition to examining the very wide frequency range from 10-6 Hz to 10-13 Hz,...

In this issue, we are delighted to publish the second in a series of articles under the banner of Perspectives. The series commenced in late 2008, when Udo Kaatze [1] published an article about the powerful technique of dielectric spectrometry for liquid measurements. In addition to examining the very wide frequency range from 10⁻⁶ Hz to 10⁻¹³ Hz,...

To date, most Photoacoustic (PA) imaging results have been from soft biotissues. In this study, a PA imaging system with a near-infrared pulsed laser source has been applied to obtain 2-D and 3-D images from both soft tissue and post-mortem dental samples. Imaging results showed that the PA technique has the potential to image human oral disease, s...

Dental caries is a disease wherein bacterial processes damage hard tooth structure. Traditional dental radiography has its limitations for detecting early stage caries. In this study, a photoacoustic (PA) imaging system with the near‐infrared light source has been applied to postmortem dental samples to obtain 2‐D and 3‐D images. Imaging results...

From 1991 to 2004, Measurement Science and Technology had awarded a Best Paper prize. The Editorial Board of this journal believed that such a prize was an opportunity to thank authors for submitting their work, and that it served as an integral part of the on-going quality review of the journal. The current breadth of topical areas that are covere...

Since 1991, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of this journal believes that such a prize is an opportunity to thank authors for submitting their work, and serves as an integral part of the on-going quality review of the journal. The current breadth of topical areas that are covered by MST has mad...

Sensors are very important for measurement science and technology. They serve as a vital component in new measurement techniques and instrumentation systems. Key qualities of a good sensor system are high resolution, high reliability, low cost, appropriate output for a given input (good sensitivity), rapid response time, small random error in resul...

This paper describes two applications of laser/ electromagnetic acoustic transducer (EMAT) systems. The first application uses laser-generated ultrasound for the characterisation of rear surface artificial defects (vertical slots) in metal samples. An EMAT sensitive to in-plane motion was used to detect these ultrasonic waves. B-scan images were us...

One of the contributing factors to graphite degradation is oxidation. In order to detect this type of degradation, samples with different levels of oxidation have been studied. Longitudinal velocity measurements were carried out on these samples, using laser ultrasound techniques. These techniques have the advantage that they are non-contact, and t...

In this paper, we report on sequential decreases in the amplitude of photoacoustic (PA) signals from nanosecond laser pulse irradiation of various samples. These samples include biological tissues, such as dental-enamel and chicken/turkey breast as well as some non-biological samples. Laser energy densities in the range of 80mJ/cm2 to 300mJ/cm2 wer...

A new magnetic arrangement is described for use with an in-plane electromagnetic acoustic transducer (EMAT) for detecting laser-generated ultrasound. The magnetic flux density was modelled and validated. Modelling was accomplished in 3D using finite element software to predict new magnet spatial distributions. A configuration was found which increa...

Rayleigh waves have been used to measure anisotropy in metal alloys using a transient Rayleigh pulse and an eight-element electromagnetic acoustic transducer array. The array spacing determined sensor separation, so that velocity measurements were made independent of the source-to-detector distance. Elimination of this distance, which would normall...

We describe the phenomenon of a sudden decrease in the amplitude of photoacoustic signals arising from nanosecond laser pulse irradiation of biological samples, measured in vitro. Several dental enamel and chicken/turkey breast samples are examined. Moderate optical energy densities (i.e., about 300 mJ/cm2) are used, typical of those exploited in p...

Since 1991, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of this journal believes that such a prize is an opportunity to thank authors for submitting their work, and serves as an integral part of the on-going quality review of the journal. The current breadth of topical areas that are covered by MST has mad...

The paper presents a novel design of an electromagnetic acoustic transducer (EMAT) for non-contact ultrasonic measurements. An EMAT sensor has been miniaturized with an overall receiver size to 1.0 cm diameter. It has been combined with a specially designed low noise preamplifier. Calibration procedures with a Michelson interferometer revealed that...

This paper presents an enhanced in-plane electromagnetic acoustic transducer (EMAT) for detecting laser-generated ultrasound. Instead of using post-processing of numerical data to enhance signal-to-noise, the paper describes a new EMAT design to increase the magnetic flux density applied to the sample. The EMAT's magnetic flux density was modelled...

Enhancement of signal amplitudes from Rayleigh wave interaction at solid surface features has been investigated when signals were detected by an in-plane electromagnetic acoustic transducer (EMAT). A laser-ultrasound system was used to inspect surface-breaking slots, serving as artificial defects. Nd:YAG laser pulses were delivered onto a metal sur...

For the interpretation of photoacoustic waveforms, a diffraction correction method is presented based on an exact Lommel diffraction formulation. It is already known that tissue optical absorption coefficients may be determined by using a time resolved analysis. Normally, corresponding experiments measure signals close (a few mm) to a photoacoustic...

A measurement technique using ultrasonic interferometry is described for non-contact, quantitative measurement of acoustic vibrations. A pair of low-cost ultrasonic transducers was used in a transmit–receive mode to direct a 40 kHz carrier wave to the surface of a solid target vibrating acoustically, such as a speaker cone. Demodulation of return s...

We present a description of a system for dynamic alignment of a novel Fourier transform Michelson interferometer which is operating in the near infrared (NIR) band. The technique relies on detection of the phase difference between four photodetectors mounted around the main detector. The system is controlled by a computer in real time. It uses a po...

This paper describes the application of a frequency domain synthetic aperture focusing technique to photoacoustic imaging. The photoacoustic probe consisted of a laser delivery fiber-optic (diameter of 600 μm, plastic coated silica) combined with a polymer (PVDF) transducer for ultrasonic detection. This system had a broadband frequency response in...

The current demand for versatile medical diagnostics has created a significant increase in the development of NIR spectroscopic techniques due to the relative transparency of body fluids and soft tissue in this spectral region. Specifically the non-invasive determination of blood substrates is a desirable measurement as a guide to the pathological...

This paper describes the application of a frequency domain synthetic aperture focusing technique to photoacoustic imaging. The photoacoustic probe consisted of a laser delivery fiber-optic (diameter of 600 mum, plastic coated silica) combined with a polymer (PVDF) transducer for ultrasonic detection. This system had a broadband frequency response i...

This paper describes the application of a diffraction correction method based on an exact Lommel diffraction formulation applied to an optoacoustic signal. It is already known that the optoacoustic signal contains valuable information about tissue optical properties. Using time-resolved analysis, the tissue optical absorption coefficient can be eas...

Synthetic aperture focusing techniques (SAFT) have been applied to B-scan images of artificial defects produced by a scanning photoacoustic probe operating under water. The probe consisted of a fibre-optic laser beam delivery system combined with a polymer (PVDF) transducer mounted at the tip of the probe for ultrasonic reception. This system had a...

This paper describes a software development environment suitable for advanced signal processing and feedback control algorithms for interferometry. The significance of software fast prototyping tools is illustrated where theoretically challenging algorithms are to be implemented. Specifically, a case is discussed where advanced control is deemed ne...

The enhancement of signals from Rayleigh wave interaction at solid surface features is described, for the case when signals arise from laser-ultrasound/electromagnetic-acoustic transducer (EMAT) detection system. Transient surface acoustic waves were detected by an in-plane EMAT receiver. B-scan images from surface slot or surface edge interactions...

Quantitative time-of-flight analysis of laser-generated shear waves and longitudinal-shear mode-converted waves has demonstrated an effective method for non-contact monitoring of the thickness of metal plates. Q-switched Nd:YAG laser pulses with energies of approximately 18 mJ, delivered to the material surface via an optical fibre and focused to a...

The characteristics of laser-triggered spark gaps, initiated by a switched-out pulse of about 7 ps from a model-locked Nd: glass laser system, are investigated. The formation time delay of breakdown across the gap can be of the order of 1 ns and is found to increase as the gap voltage is reduced. Comparison with spark gaps triggered by Q-spoiled na...

In this work, a non-steady-state photo-emf receiver has been used to detect the lower frequency fundamental a0 Lamb waves in mild steel. Experimentally, the Lamb waves are laser-generated in the thermoelastic regime using a Q-switched, 20 ns, pulsed Nd:YAG laser and a line source. Typical Lamb waves had centre frequencies of 250 kHz but with freque...

For non-contact non-destructive evaluation (NDE), a laser/EMAT system is an alternative to a more expensive all optical laser-ultrasound system. Several design options of the electromagnetic acoustic transducer (EMAT) are available, permitting inspection of electrically conducting materials. In this paper, we describe a system capable of monitoring...

We have described an ophthalmic laser-ultrasound probe and have shown that, in its early prototype form, it is capable of generating dimensional information for both the anterior and posterior chambers of the eye. Laser pulse energies of about 2 mJ in 8 ns were required to produce laser-ultrasound signals, and these were delivered from a fibre opti...

This paper is in the form of a progress report. Our experience in attempting to build miniature intravascular probes has been mixed. The forward looking version of the probe has performed well, although to date no in vivo experiments have been undertaken. The sideways looking device proves extremely difficult to construct and we may have to rely on...

A laser/EMAT system is described for non-contact monitoring of metal thickness. In a B-scan imaging configuration, quantitative time-of-flight analysis of laser-generated shear waves and longitudinal-shear mode-converted waves can be used as an effective method for thickness monitoring. Q-switched Nd:YAG laser pulses with energies of ~18 mJ were de...

For the last seven years, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of the journal believes that awarding such a prize is an opportunity to say `thank you' to authors for submitting their best material, and serves as a focus for their on-going quality review. The working party, composed of Professors R J...

Breakdown in the rare gases caused by picosecond laser pulses from a Nd:glass laser is investigated. Threshold intensity for breakdown is measured as a function of pressure and measured values compared with those expected from theory. It is shown that an implicit assumption has been made in past theoretical treatments which may not apply on picosec...

The removal of unwanted dissolved gas from a liquid is an important unit operation in many processes; gas chromatography has a degassing stage for example; photoresist substrates are degassed before being applied to silicon chips. The degassing technologies used in these cases include membrane, vacuum and ultrasound. Another important application i...

An experimental investigation has been made of laser-induced breakdown thresholds in the rare gases, using single picosecond pulses from a ruby laser with time durations of 18+or-4 ps. Breakdown threshold intensity measurements, carried out at pressures below approximately 7000 Torr, were always pressure-dependent. The results show important differ...

Breakdown threshold intensity measurements have been made in oxygen and nitrogen using single picosecond pulses from one of three laser systems operating at 1.06, 0.69 and 0.53 mu m. The results are compared with those made previously to confirm that in high radiation fields ( gamma <or=1), a breakdown threshold regime exists which is only weakly d...

Emission spectra in the range 10-250 AA from plasmas produced by picosecond laser pulses from a variety of solid targets are presented. These spectra provide some useful information about the state of ionization of the plasma and other plasma parameters such as temperature. Some of the results obtained are compared with the predictions of detailed...

A Q-switched flashlamp-pumped Nd:YAG laser has been operated in a burst mode at repetition rates up to 1 kHz, and output energies up to 35 mJ obtained. Use of thyristor controlled resonant-charging techniques, electrolytic energy-storage capacitors and an efficient laser-pumping cavity allowed operation in bursts of up to 75 pulses. A drop in outpu...

Using laser-generated Rayleigh waves in the thermoelastic regime as an ultrasonic source, a range of ultrasonic detector systems have been evaluated experimentally for their sensitivity. Systems examined were those based on electromagnetic acoustic transducers (EMATs), a non-steady state photo-emf detector, a confocal Fabry-Pérot interferometer (CF...

Laser-generated ultrasound has found a number of niche applications in non-destructive testing and evaluation and there is now a growing trend to examine potential applications for materials characterization in medicine. Conventional ultrasound techniques for measuring various important dimensions within the eye are in extensive use. However, one p...

For the last six years, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of the journal believes that awarding such a prize is an opportunity to say `thank you' to authors for submitting their best material, and serves as a focus for their on-going quality review. The working party, composed of R J Dewhurst, P...

There is a clinical need for an instrument capable of measuring properties of the eye beyond those presently available. In this paper, a new laser ultrasound technique is discussed for assessing the characteristics of eyes—using a novel form of probe. Laser-ultrasound transients were generated within bovine eyes using a frequency doubled Nd: YAG Q-...

During the last decade, significant advances in the field of remote detection of ultrasound have taken place. Optical systems with increasing sensitivity for monitoring ultrasound on samples with optically rough surfaces have been developed, so that some designs are now moving from the research laboratory into industrial environments. In this revie...

A new intravascular device is being developed for use in laser angioplasty procedures. Guidance is achieved using thermoelastically derived ultrasound generated by a Q-switched Nd:YAG laser operating at a wavelength of 532 nm and delivered by an optical fibre. The design is compatible with that required for delivery of a therapeutic (ablative) beam...

A versatile phase-stepping speckle shearing interferometer is described that employed a calibrated liquid crystal as its phase modulator, operating at 514nm. By implementation of an algorithm upon phase-stepped shearographic images it was possible to create a phase map, that provided quantitative data regarding the derivative of any out-of-plane su...

An experiment is described in which the absorption spectrum of the Rydberg series of sodium (principal quantum number, n>or=4) is studied in a strong non-resonant laser field. The field is generated from a PTM laser oscillator/amplifier system operating at 1.06 mu m, producing 250 MW in a 10 ns pulse. After splitting, most of the beam is focused in...

To detect ultrasound remotely, an optical detection scheme is described which uses a confocal Fabry-Perot interferometer and conjugate detection. A conjugate signal is derived from the interferometer by making simultaneous use of signals derived from optical back reflection, and optical transmission, through the interferometer. Theoretical analysis...

Inaccurate field formulas for light transmitted through Fabry - Pérot interferometers have been identified in the open literature. A phase lag between the first emerging ray with respect to the incident ray is generally omitted. Such an error is not important when only one type of emerging ray is investigated. However, when more than one type of ra...

A mathematical and physical description of a confocal Fabry-Perot interferometer used for the measurement of ultrasound is presented. It analyses the interferometer performance in terms of ultrasonic transfer functions derived for rays of types 1-4. Instrument performance is modelled for two different schemes of operation, namely transmission and r...

A non-contact scanning system is described which is capable of producing two-dimensional ultrasonic images of defects in opaque materials. Lasers are used both for generation and detection of ultrasound. Short-duration high-power ( approximately 2 MW) laser pulses are used to generate ultrasound on the surface of a sample. Such ultrasound in the fo...

Knife-edge and differential optical beam deflection (OBD) techniques are capable of non-contact broadband measurement of laser-generated ultrasound. We describe a fibre-optic sensor based on both knife-edge and differential schemes, which has an angular deflection sensitivity of ~ 1 μrad. This sensitivity was sufficient to detect a Rayleigh wave pr...

Angioplasty has become a common procedure for the treatment of arteriosclerosis, and a popular form of angioplasty is balloon angioplasty. The procedure involves the insertion of a balloon into the artery at the location of the blockage. The balloon is then inflated so that the blockage is compressed. This method has disadvantages in that the occlu...

For monitoring temporal modulation of a laser-generated asymmetric (a₀) Lamb wave, a non-contact fibre optic sensor has been used. Simultaneously, an electromagnetic acoustic transducer (EMAT) sensed in-plane acoustic transients of the symmetric (s₀) Lamb wave. Measurements in 75 μm thick aluminium film show that a₀...

Ultra sound is now routinely used in the non-destructive testing of materials, but most techniques involve immersing the object to be tested in a water bath. This can be time-consuming and impractical, particularly when testing large numbers of objects on a production line. An ideal testing method would be able to detect the ultrasonic signals remo...

Techniques based on laser-induced surface acoustic waves have been developed with the potential for characterizing thin films. They enable variations of elastic parameters, density and film thickness to be detected. Previous work has demonstrated that from the measurement of the frequency dependence of the surface wave velocity, film parameters may...

A set of laser ultrasound directivity patterns have been presented for samples irradiated within a water medium. The forward-going pattern for aluminium was used to validate the experimental technique and showed reasonable agreement with theory. The backwards-going patterns measured in gelatine showed significant sideways going energy at angles of...

Angioplasty has become a common procedure for reducing the effects of constrictions in human arteries caused by the build up of fatty deposits, thrombosis and calcification (arteriosclerosis). An intraluminal laser ultrasound probe has been designed and constructed. The probe allows the use of a small pulsed laser to generate ultrasound on the tiss...

This paper reports on the activities of three research groups at UMIST pursuing work in the area of microsensors. Such work is by definition multi-disciplinary and places enormous demands on those engaged in it. This being so, it is reasonable to begin by asking the question "is it necessary to use microminiature techniques?". In presenting the exa...

Coating technology is used in a variety of applications, for example to improve the wear properties or to improve the bonding properties of a surface. The properties of such surfaces depend on the mechanical properties of the coating, namely its Young’s modulus and its thickness. To be able to predict the performance of such coatings it is necessar...

Following the development of a small laser-ultrasound probe, theoretical and experimental parameters have been identified for the modelling of polymer transducers used as ultrasonic receivers. A laser-ultrasound signal is used as a standard input signal to the transducer. Using a o one-dimensional model as an approximation, a system identification...

C-scan images are presented of artificial defects in carbon fiber composite materials derived from a laser ultrasound imaging system. Detection of ultrasound has been achieved from natural material surfaces, by an actively stabilized Fabry-Perot interferometer in conjunction with an argon-ion laser source. Recent measurements have been made in what...

Characteristics of laser-ultrasound signals are presented from photoacoustic interaction with a layered, optically absorbing medium surrounded by a transparent fluid. A thermoelastic model is presented describing the interaction, with signal predictions in the fluid arising from polymer transducer detection. By taking the optical absorption coeffic...

A model is presented describing the thermoelastic photoacoustic interaction in a layered medium within a transparent fluid, where a polymer transducer is used for the detection of ultrasonic pulses. By taking the optical absorption coefficient and finite layer thickness into account, the amplitude and shape of photoacoustic transients are calculate...

Some mathematical CAD packages are inadequate in computing the composite functions involving the product of an exponential function and an error function complement. These functions arise in physical applications, such as problems in diffusion. Their importance warrants a composite treatment. If their component factors are computed individually, di...

To detect ultrasound remotely, an optical detection scheme is described which uses a confocal Fabry-Pérot interferometer and conjugate detection. A conjugate signal is derived from the interferometer by making simultaneous use of optical back-reflection, and optical transmission, through the interferometer. Theoretical and experimental results have...

For non-contact testing applications laser-ultrasound systems offer advantages of truly remote and point detection. In our experiments, a flexible fibre-optic sensor was used for the detection of thermoelastically-generated Lamb waves. The optical detection system consisted of a single mode fibre which delivered a 14mW probe spot on the sample surf...

Laser-generated ultrasonic Lamb waves have been measured in metallic thin films with a novel fibre-optic beam deflection technique. Instrumentation consisted of a flexible fibre-optic sensor used for the detection of thermoelastically-generated Rayleigh and Lamb waves. It used a single mode fibre which delivered a 14 mW probe beam onto the sample s...

We have previously reported our observations that, at laser wavelengths of 1,064 and 532 nm, following repeated exposure to short pulses at power density levels well below those reported to cause permanent damage to biological tissue, the photoacoustic signal detected using an ultrasound probe diminishes significantly. Examination by electron micro...

A differential fibre-optic device has been developed for noncontact detection of laser-generated ultrasound. Using a 5 mW He-Ne laser as the source, laser beam delivery on to the sample of the surface utilised a singlemode fibre and lens combination. When photoacoustic ultrasonic transients propagated across the surface, the incident spot was pertu...

Interest in medical diagnostic ultrasound has progressively increased over the last two decades. The advent of sophisticated technology has enhanced the reliability and the user-friendliness of ultrasound systems, together with significant improvement in the quality of data available to clinicians. Much of the development work has been based on ext...

An overview is presented of recent developments in the use of laser-generated ultrasound. Until the late 1980s, implementation of laser-ultrasound instruments in industry was impeded by a lack of detection sensitivity. Various optical detection schemes were investigated, including the Michelson interferometer, interferometers incorporating phase co...

A new type of probe is presented, which combines an ultrasound receiver constructed from piezoelectric polymer materials with a coaxial optical fibre for laser-induced ultrasound. The initial application of this probe, which may be further miniaturized, is in intra-arterial imaging and therapy. Overall diameters of the prototype probes presently ra...

Laser angioplasty is an alternative to the established balloon angioplasty techniques for the treatment of stenotic lesions and short occlusions in arterial disease. Because it does not require the lesion to be traversed, laser angioplasty, in some cases, offers treatment of longer occlusions; but in this situation the risk of complications is high...

A laser confocal Fabry-Perot interferometer (CFPI) is described for the sensing of ultrasound in opaque solids having optically rough surfaces. Stabilization was required to eliminate the optical frequency drift arising from various sources in both the CFPI and the argon-ion laser. Measurements showed that conventional proportional control was inad...

Ultrasonic Lamb waves have been measured with a quantitative optical beam deflection (OBD) technique. Calibration of the technique is derived for two cases of laser probe beam cross-section, one with a uniform beam and the other with a Gaussian beam intensity distribution. Expressions for angular beam deflection angle are derived for both cases in...

A new probe is described, in which an ultrasound receiver constructed from a piezoelectric polymer is combined with a forward-looking coaxial optical fibre for laser-induced ultrasound. The size of the transducer system is such that it offers in medicine both a diagnostic and therapeutic tool, and has potential for combining the role of intra-arter...

Ultrasonic transients with high frequency components have been used to interrogate the bond region of lap-bonded joints. With through-transmission measurements, based on a non-contact laser technique, wave arrival times have been identified in addition to internal reflections within the joint region. This knowledge has led to analysis of wave ampli...

A non-contacting laser ultrasound system has been developed to visualize laminar defects in carbon fiber composite materials. Laser-generated ultrasound (LGU) was produced from a Nd:YAG Q-switched laser. Ultrasound was detected with the use of an actively stabilized Fabry-Perot interferometer using a 400 mW argon-ion laser source. It detected ultra...

Surface‐breaking tight fatigue cracks in mild steel have been examined with laser‐generated ultrasonic pulses. Before the arrival of transmitted Rayleigh waves arriving at the detector, evidence is presented of a fast skimming longitudinal pulse which is also transmitted through the crack. Additionally, another ultrasonic feature is consistent with...

Laser ultrasound for NDE applications is reported in several places within this Review. Interest in the subject remains high, even though the cost of associated instrumentation remains high. Benefits associated with optical probing of a sample include potentially high spatial resolution, truly non-contacting transduction permitting non-contact C-sc...

Through-transmission ultrasonic NDT measurements have been performed with a noncontact laser combination system. High power (about 2 MW) laser pulses were used for the generation of longitudinal pulses in metallic samples. On reaching the far surface, ultrasound was detected with a 50 cm confocal Fabry-Perot interferometer. The interferometer analy...

This paper discusses the application of computer control to the inspection of small industrial components by laser scattering. A PC microcomputer-based system has been developed to analyse the light scattered by components being fed separately or in single file past a laser beam. This analysis allows the computer to monitor and select component ori...

A confocal Fabry-Perot interferometer for the detection of laser-ultrasound has been employed for C-scan image applications on industrial samples without special surface preparation. Automatic stabilisation of the interferometer has made this possible. A cascade control system has been developed to overcome the complex de-stabilising mechanism inhe...

The cross calibration of two optical detection techniques is described for the monitoring of laser‐generated Lamb waves. Measurements of Lamb waves using an optical beam deflection technique are compared with those using a Michelson interferometer technique. Analysis shows that phase changes in acoustic waveforms relate to the physical characterist...

The thickness of thin polyester film has been measured using ultrasonic Lamb waves which were generated and detected using noncontacting laser techniques. The uncertainty analysis of such a measurement technique has been examined. Systematic errors in both time of flight and distance between laser generation and detection points were estimated and...

Laser-based systems for non-contact generation and detection of ultrasound are being investigated at the CEGB's Marchwood Engineering Laboratories for application to remote non-destructive inspection problems. These include the in-situ inspection of the graphite bricks that make up the cores of Advanced Gas-Cooled Reactors (AGR's). The propagation...

An overview is presented of optical techniques used to detect ultrasound propagating in solids. Typically, the sensor system may be based on a beam deflection technique, a Michelson interferometer or a Fabry-Perot interferometer. In some cases, the systems offer a flat wideband frequency response up to frequencies in excess of 100 MHz. The techniqu...

By measuring the velocity of Lamb waves using photoacoustic generation, the molecular orientation in biaxially-stretched polymer film has been investigated.