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The 15^th Anglo-French Physical Acoustics Conference (AFPAC) was held at Selsdon Park Hotel, near London, United Kingdom, on 13-15 January 2016. The venue was an excellent location to exchange ideas, regardless whether this took place in the conference room, over lunch, at the drinks reception, or in the bar after the conference dinner. A total of 65 papers were presented at the conference. There were over 80 delegates from institutions covering five countries.

On the first day of AFPAC, the Institute of Physics joined forces with the National Physical Laboratory (UK) to host a special session on cavitation. The Cavitation User Forum, a bi-annual event specifically dedicated to applications of high power ultrasound, brought together experts from academia and from the cleaning, processing and medical industries. This session was kicked off with an invited talk by Dr David Fernandez Rivas (University of Twente, The Netherlands), on the reproducibility of sonochemistry and ultrasonic cleaning.

The Cavitation User Forum was followed by a special session on biomedical ultrasound, co-sponsored by the Medical Physics Group of the Institute of Physics, which featured a keynote talk by Prof Robin Cleveland (University of Oxford) on ultrasonic surgery. The session included talks on acoustic microscopy of live cells, histotripsy, phase-insensitive ultrasound computed tomography for the diagnosis of breast cancer, high-intensity focused ultrasound and the biomedical applications of solitary wave impulses generated by granular chains

The second day featured an invited presentation by Prof Tim Leighton (University of Southampton, UK) on the acoustic bubble, which discussed ocean, cetacean and extra-terrestrial acoustics, and cold water cleaning. Prof Christ Glorieux (KU Leuven, Belgium) discussed the applications of photothermal and photoacoustic methods using different spatiotemporal excitation patterns. A broad range of physical acoustics topics was reviewed that day. Work was presented on phononic crystals, high resolution imaging of in-depth rough interfaces, shear wave reconversion in nano-fluids and the prediction of radiation by finite-sized sources in semi-infinite isotropic plates. The field of non-destructive evaluation was well represented, with a presence from institutions such as Imperial College London, University of Nottingham and Université de Montpellier.

During the Conference Dinner, the 2015 Bob Chivers prize was awarded to Dr Bo Lan for his paper entitled "Experimental and computational studies of ultrasound wave propagation in hexagonal close-packed polycrystals for texture detection".

On the final day of the conference, Prof Olivier Dazel (Université du Maine, Le Mans, France) gave an invited talk discussing the past present and future of the modelling of sound absorbing materials.

The UK organising committee was particularly happy to welcome the many French contributors that travelled to Selsdon Park and would like to thank Alain Lhémery and the Société Française d'Acoustique (SFA) for publicising the event in France. We are happy to announce that many of the presented papers will be published in the conference proceedings in Journal of Physics: Conference Series. We would also like to draw the reader's attention to the upcoming 16^th AFPAC conference that is scheduled to take place on 23-25 of January 2017 at the Laboratoire de Mécanique et d'Acoustique, Marseille, France.

Pierre Gélat (UCL, United Kingdom), Theodosia Stratoudaki (University of Nottingham, United Kingdom), Rachel Edwards (University of Warwick, United Kingdom), Robert Malkin (University of Bristol), Nader Saffari (UCL, United Kingdom) and Alain Lhémery (CEA, France)

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

This paper summarizes the content of a plenary lecture on the author's personal research into the interactions between bubbles and sound fields, covering particular topics involving the climatically important gas exchange between atmosphere and ocean, the implications of bubbly ocean water to marine mammals that use sound, and the opportunities afforded by incorporating acoustical sensors onto probes launched to investigate other worlds in our solar system. It closes with recent data on the opportunities of bubble acoustics to investigate methods of cold water cleaning.

Medical ultrasound scanners are typically calibrated to a speed of sound corresponding to the soft tissue average of 1540 m s⁻¹. In regions of different sound speed, for example, organs and tumours, the B-mode image becomes geometrically distorted from the true tissue cross-section, due to refraction and the misrepresentation of length. A ray model is developed to predict this distortion for a generalized two-dimensional object with atypical speed of sound, and verified against ultrasound images of a test object. We quantify the areal image distortion as a function of the key dependencies, including the speed of sound mismatch, the scanning format, the object size and its elongation. Our findings show that the distortion of area can be significant, even for relatively small speed of sound mismatches. For example, a 5% speed mismatch typically leads to a 10 – 20% distortion in area. These findings have implications for the accuracy of ultrasound-based evaluation of area and volume.

Gastrointestinal (GI) disease development and progression is often characterised by cellular and tissue architectural changes within the mucosa and sub-mucosa layers. Current clinical capsule endoscopy and other approaches are heavily reliant on optical techniques which cannot detect disease progression below the surface layer of the tissue. To enhance the ability of clinicians to detect cellular changes earlier and more confidently, both quantitative and qualitative microultrasound (μUS) techniques are investigated in healthy ex vivo porcine GI tissue. This work is based on the use of single-element, focussed μUS transducers made with micromoulded piezocomposite operating at around 48 MHz.

To explore the possibility that μUS can detect Crohn's disease and other inflammatory bowel diseases, ex vivo porcine small bowel tissue samples were cannulised and perfused with phosphate-buffered saline followed by various dilutions of polystyrene microspheres. Comparison with fluorescent imaging showed that the microspheres had infiltrated the microvasculature of the samples and that μUS was able to successfully detect this as a mimic of inflammation. Samples without microspheres were analysed using quantitative ultrasound to assess mechanical properties. Attenuation coefficients of 1.78 ± 0.66 dB/mm and 1.92 ± 0.77 dB/mm were obtained from reference samples which were surgically separated from the muscle layer. Six intact samples were segmented using a software algorithm and the acoustic impedance, Z, for varying tissue thicknesses, and backscattering coefficient, BSC, were calculated using the reference attenuation values and tabulated.

An Electro-Magnetic Acoustic Transducer (EMAT) is a non-contact source used in Ultrasonic Testing (UT) which generates three types of dynamic excitations into a ferromagnetic part: Lorentz force, magnetisation force, and magnetostrictive effect. This latter excitation is a strain resulting from a magnetoelastic interaction between the external magnetic field and the mechanical part. Here, a tensor model is developed to transform this effect into an equivalent body force. It assumes weak magnetoelastic coupling and a dynamic magnetic field much smaller than the static one. This approach rigorously formulates the longitudinal Joule's magnetostriction, and makes it possible to deal with arbitrary material geometries and EMAT configurations. Transduction processes induced by an EMAT in ferromagnetic media are then modelled as equivalent body forces. But many models developed for efficiently predicting ultrasonic field radiation in solids assume source terms given as surface distributions of stress. To use these models, a mathematical method able to accurately transform these body forces into equivalent surface stresses has been developed. By combining these formalisms, the magnetostrictive strain is transformed into equivalent surface stresses, and the ultrasonic field radiated by magnetostrictive effects induced by an EMAT can be both accurately and efficiently predicted. Numerical examples are given for illustration.

Elastic guided wave (GW) propagation is involved in various non-destructive testing (NDT) techniques of plate-like structures. The present paper aims at describing an efficient model to predict the GW field radiated by various sources attached at a distance of the straight boundary of an isotropic plate, a configuration often encountered in typical examinations. Since the interpretation of GW propagation and scattering in plates is made easier by the use of modal description, the model is derived in the classical theoretical framework of modal solutions. Direct radiation by a uniform source of finite size in an isotropic plate can be efficiently modelled by deriving Fraunhofer-like approximation. A rigorous treatment is proposed based upon i) the stationary phase method to describe the field after reflection at a plate edge, ii) on the computation of modal reflection coefficients for an arbitrary incidence relative to the edge and iii) on the Fraunhofer approximation to account for the finite size of the source. The stationary phase method allows us to easily express the amplitude of reflected modes, that is to say, the way waves spread, including reflections involving mode conversions. The computation of modal reflection coefficients for plane GW at oblique incidence was recently treated in the literature and our work for this very problem simply consisted in adapting it to the SAFE calculation we use to compute modal solutions.

The overall computation of the direct and reflected contributions is numerically very efficient. Once the total field is computed at a given frequency, the time-dependent field is obtained by simple Fourier synthesis.

This article is a discussion about the origin of friction noise produced when rubbing solids having rough surfaces. We show that noise emerges from numerous impacts into the contact between antagonist asperities of surfaces. Prediction of sound sources reduces to a statistical problem of contact mechanics. On the other hand, contact is also responsible of dissipation of vibration. This leads to the paradoxical result that the noise may not be proportional to the number of sources.