When a plane ultrasonic wave (a sound wave at higher frequency than humans can hear) travels through a fluid which has particles or droplets suspended in it, the particles/droplets scatter the wave by sending some of it in other directions. A very similar effect produces a rainbow when sunlight is scattered by water droplets in the air. With ultrasonic waves, which are compressional waves, scattering by the particles can also convert some of the wave into other wave types, namely thermal and shear waves. These processes take energy away from the ultrasonic wave which causes a reduction in its amplitude. By measuring the attenuation (loss in amplitude) and the wave speed for an ultrasonic wave travelling through the suspensions, we can find out the concentration of particles, how big they are, or something about their properties e.g. their density. Since these sorts of materials (suspensions of particles) have many uses e.g. foods, healthcare products, agrochemicals, drug delivery systems, a way of measuring their properties is a crucial element of a production process and of great importance in a number of industries. In order to understand the measurements we make, we need to use a model, a set of equations and calculations which tell us how the properties of the particles and fluid affect the loss of amplitude and speed of the wave. The model we use has two parts: a multiple scattering theory, and a model for the scattering from a single particle. For some time, the model we used has been limited because it made some approximations about the two other wave types (the thermal and shear waves) which are produced at the particles; it assumed that those waves die away in a very short distance, and do not have any effect on the particles nearby. Although they do die away in a very short distance, they can affect the neighbouring particles when the suspension is very concentrated (i.e. there are a lot of particles in a small space). The thermal and shear waves themselves can be scattered by particles nearby and may be partly converted back into a compressional wave (an ultrasonic wave). This means we did not lose as much of the energy from the compressional wave as we thought. The process of wave conversion and re-conversion is referred to as multi-mode scattering and for many years, its effect has been ignored because we did not have a suitable model to calculate it. Last year, a group of researchers at Le Havre (France), published a new version of the multiple scattering theory, which does include this multi-mode scattering, over 40 years after the original multiple scattering model was published. This is a useful development, but at the moment the model exists as a set of rather abstract mathematical equations which include many terms which we do not yet know how to calculate. What we propose to do is to transform this model into a form which enables online ultrasonic monitoring in a pipe. We will work out which parts of those equations make the most difference to the measured ultrasonic speed and attenuation (energy loss) in typical suspensions. We will develop some new models for scattering by a single particle so that we can work out how much energy is converted between wave modes. These models will take the form of sets of equations which will be solved by computer (numerical models), and also some forms which can be written directly in mathematical notation (analytical models). To demonstrate that the models developed in the project are valid, experimental measurements will be made of the attenuation and wave speed in suspensions at relatively high concentrations 10-30% by volume, and for a range of particle sizes. The outcomes of the project will be a model in a form which can be used in online ultrasonic instrumentation. This will enable ultrasonics to be used with confidence as a process monitoring technique in a wide range of industrial contexts.

This network grant is focused on acoustics and pursues two main aims: (i) transfer new experimental techniques, models and scientific insights; (ii) promote mobility between universities, industry and other non-academic beneficiaries. In this respect, the UK has a critical mass and international reputation in acoustics which needs to be maintained and enhanced. Acoustics-related research in the UK is internationally leading and underpins key technological areas such as healthcare, manufacturing, defense, energy, digital communications and transport. However, the knowledge transfer and adoption of recent developments in physical acoustics, signal processing and numerical methods by industry and other end users (e.g. consultants and government bodies) needs improving. There are several reasons for this. Firstly, there is no existing single point of access network/central hub in the UK which brings the key academic and industry players together. Acoustics-related research in the UK's universities is fragmented, often applied to specific topics and length scales and suffers from inadvertent duplication. As a result, it is difficult for industry to engage with, or understand what is happening in, academia, how acoustics research relates more widely to industry needs and who in academia is the right person or which organisation to engage with in order to solve a particular industry need. Secondly, academia is clearly failing to demonstrate to the end users the value of their acoustics-related research in applications, thus failing to overcome the sector inertia for their research to have a stronger non-academic impact. Thirdly, there is no network/central hub for the coordination of the acoustics-related research through which a university can engage beyond their very specific, parochial partners, disseminate their work more widely and efficiently to the sector and generate a future road map of research which bears support from a majority of end users. We will establish a network for the wider coordination of acoustics-related research to enable better communication with industry and multiple avenues of research and innovation. It will support the EPSRC/UKRI Delivery Plan to promote the success of the UK's industry and academia through top quality research. This Acoustics Network aligns with the EPSRC expectation for a research network, which is "... expected to lead to new collaborative multidisciplinary research proposals and some may develop into virtual centres of excellence, providing critical mass of analytical expertise." The current RCUK/UKRI funding of acoustics-related research amounts to £94M which includes £62M support from the EPSRC. This funding covers research in general acoustics, audio engineering, ultrasonics and noise. Unlike other research disciplines, acoustics related research is not currently directly supported by an EPSRC Centre for Doctoral Training (CDT). However, there are several CDTs which can directly benefit from acoustics related research. Therefore, there is a clear need for better coordination for the activities in acoustics to reduce fragmentation and overlap, and to use existing and future funding streams more efficiently. This is important to ensure that the quality of the critical mass of the acoustics-related research in the UK continues to stay internationally leading in the foreseeable future. Given the importance of acoustics and the value of the research funding in this area, the Acoustics Network will serve to promote this research discipline and to communicate the ongoing work beyond the acoustics research community and to the general public. In this respect, the network will be able to establish a website, software depository, hold workshops and conferences, produce newsletters, use publications by Learned Societies and Trade Associations and social media to communicate their work much more widely that is currently done.