The Manipulation of Sound with Acoustic Metamaterials

The original work presented in this thesis pertains to the design and characterisation of resonant-cavity-based acoustic metamaterials, with a focus on airborne sound. There are five separate experimental chapters, each with a unique approach to the design of periodic structures that can support and manipulate air-bound acoustic surface waves via diffractive coupling between resonant-cavities. The first two chapters concern measurement of the acoustic transmission though various kinds of periodic slit-arrays, whilst the latter three chapters utilise a near-field imaging technique to directly record and characterise the dispersion of trapped acoustic surface waves. The first experimental chapter investigates the effect that thermodynamic boundary layers have on the Fabry-Perot-like cavity resonances that are so often utilised in acoustic metamaterial design. At audio frequencies, these boundary layers have a decay length that is typically more than two orders of magnitude smaller than the width of the resonating slit-cavities, hence it may naively be assumed that their effect can be ignored. However, by studying in detail the effect that reducing slit-cavity width has on the frequency of the measured cavity-resonance, for both a single slit cavity and a slit-cavity array, it is found that these boundary layer effects become significant on a far larger scale than their characteristic thickness. This is manifested in the form of a reduction in the resonant frequency as the slit-width is narrowed. Significant attenuation of the resonance and a 5% reduction in the effective speed of sound through the cavity is measured when the boundary layers form only 5% of the total width of each slit. Hence, it is both shown that the prevalent loss free treatment of acoustic slit-cavities is unrealistic, and that one may control the effective speed of sound through the slit-cavities with a simple change in slit-width. The second chapter explores the effect of ‘compound’ grating structure on trapped acoustic surface waves, a compound grating having a basis comprised of more than one resonating element. The angle dependent acoustic transmission spectra of four types of aluminium slit-array are recorded, and for the compound gratings, it is found that sharp dips appear in the spectra that result from the excitation of a ‘phase-resonance’. This occurs as new degrees-of-freedom available to the acoustic near-field allow the fields of adjacent cavities within a unit-cell to be both out-of-phase and strongly enhanced. By mapping the transmission spectra as a function of in-plane wavevector, the dispersions of the modes supported by each sample are determined. Hence, the origin of the phase-resonant features may be described as acoustic surface waves that have been band-folded back into the radiative regime via diffraction from higher in-plane wavevectors than possible on a simple grating. One of the samples is then optimised via numerical methods that account for thermodynamic boundary layer attenuation, resulting in the excitation of a sharp, deep transmission minimum in a broad maximum that may be useful in the design of an acoustic filter. The third chapter introduces the near-field imaging technique that can be utilised to directly characterise acoustic surface waves, via spatial fast Fourier transform algorithms of high-resolution pressure field maps. The acoustic response of a square-lattice open-ended hole array is thus characterised. It is found that over a narrow frequency band, the lattice symmetry causes the acoustic surface power flow to be channelled into specific, predictable directions, forming ‘beams’ with a well defined width. In chapter four, the existence of the ‘acoustic line mode’ is demonstrated, a type of acoustic surface wave that may be supported by a simple line of open-ended hole cavities. The near-field imagine technique is again used to extract the mode dispersion. This acoustic line mode may be readily manipulated, demonstrated by arrangement of the line of holes into the shape of a ring. The existence of this type of mode offers a great deal of potential for the control of acoustic energy. Chapter five explores the effect of ‘glide-symmetry’ on a pair of acoustic line modes arranged side-by-side. A control sample not possessing glide- symmetry is first characterised, where measurement of the acoustic near- fields show that this sample supports two separate modes at different frequencies, with their phase either symmetric or anti-symmetric about the mirror plane between the lines of holes. One of these lines is then shifted along its periodicity by half of a grating pitch, thus creating glide-symmetry. The resulting sample is found to support a single hybrid mode, capable of reaching a much larger in-plane wavevector than possible on a simple grating with no gaps in its band-structure, and displaying a region of negative dispersion. The third sample demonstrates how one may increase the coupling strength between the two lines of holes via manipulation of the cavity shape, thus enhancing the glide-symmetry effect. The thesis concludes with preliminary investigations into other possible ways of manipulating acoustic surface waves, such as with the use of ‘screw-symmetry’.DST

Occupational Therapy and Rehabilitation Engineering-a case study

This is a case study of the occupational therapy rehabilitation process of a teenage girl who presented in 1997 with a rare neurological condition diagnosed as rapid onset Dystonia Parkinsonism. She was helped to obtain some of the occupational performances of her choice by assistive technology devices tailored to her needs by the rehabilitation engineering department, and in this paper we wish to point out how collaboration between our departments can be of benefit to patients, and how essential microelectronic technology is in the occupational therapy environment

Introduction to 'groundwater for Wellness'

The ground b elow our feet acts as a vast store of water, nearly 30% of all freshwater resources on earth are found underground . This ‘groundwater ’ exists in the pores between grains of rock or soil, within fractures in the rock , or even in large cave systems . Groundwater originates as rainfall or snowmelt that soaks into the ground continuing downwards , under the influence of gravity , until it reaches a zone in which all the available spaces are saturated with water – the top of this zone is called the water table. The level of the water tab le varies across different terrains, climates and rock types, and over time. Rocks that store and transmit important quantities of ground water and provide critical resources are called aquifers

Exploring Critical Perspectives of Toxic and Bad Leadership Through Film

© 2015, © The Author(s) 2015. The Problem This article considers concepts of toxic and bad leadership from a critical, post-structuralist perspective and illustrates how this can be conveyed to management students through the use of film analysis. In response to the paucity of critical approaches within toxic and bad leadership studies, we suggest that film is a useful way of developing in-depth discussion in student and management groups to uncover underlying subtleties and complexity in leadership theory and practice. The Solution We connect to film clips from Batman: The Dark Knight, and explain how this film is used with students and managers to illustrate the ambiguous nature of “good” and “bad” leadership and explore the fluid, shifting, and relational nature of these two concepts. We conclude that students and managers can recognize this more readily through viewing, discussing, and analyzing film clips such as the ones discussed herein. The Stakeholders University lecturers and students, executive educators and managers, general human resource development (HRD) professional

Alcohol-related brain damage: A mixed-method evaluation of an online awareness-raising programme for frontline care and support practitioners

INTRODUCTION: Alcohol-related brain damage (ARBD) is an umbrella term referring to the neurocognitive impairments caused by excessive and prolonged alcohol use and the associated nutritional deficiencies. This study evaluated the outcomes of an online research-informed training program for ARBD which aimed to improve client outcomes by promoting support staff's awareness and confidence in working with clients who may have (or who are at risk of developing) the condition. METHODS: Staff working within a large non-governmental non-profit housing organisation (n = 883) enrolled in the training program. Questionnaires were used pre- and post-training to collect self-reported awareness of ARBD and confidence in supporting individuals with the condition. Semi-structured interviews were conducted with 27 staff members approximately 10 weeks post-completion of the program. Interviews were audio-recorded, transcribed verbatim and analysed by employing qualitative content analysis. RESULTS: Findings from the questionnaires indicated a significant increase in all measures after completing the training program. Three main themes were developed based on the interview data: changes to awareness and understanding; professional practice; and training-specific characteristics. Participants reported changes in their ability to identify potential service users with ARBD and confidence in doing so. DISCUSSION AND CONCLUSION: Our findings demonstrate that online training programs can be effective in improving support staff's ability to identify ARBD, potentially leading an increase in signposting service users to relevant services. The research-informed nature of the training demonstrates that translating research findings directly to frontline workers can have a substantial impact and may improve outcomes for this client group

The AHK-Wales Report Card 2018: Policy Measures - is it possible to ‘score’ qualitative data?

Comprehensive and meaningful policy analysis in the field of physical activity is difficult, not least because of the variable influence of other policy domains. However, in 2011 a Policy Assessment Tool (PAT) was developed by members of the WHO European Network for the Promotion of Health-Enhancing Physical Activity (HEPA Europe) and tested in several different countries. In 2014, Wales joined a global initiative, active healthy kids (AHK) Global Alliance, that supported the development of country level ‘Report Cards’ scoring a range of indicators that influence physical activity amongst children and young people, one of which was labelled ‘Government Strategies and Investments’. For the first two Report Cards this indicator and its associated ‘score’ was informed subjectively by expert consensus. In 2018, it was decided to utilize the Policy Audit Tool Version 2 (PAT v2) developed by HEPA Europe to aid analysis and to develop and test a scoring rubric aligned to the tool. The subsequent process indicated that the tool could be applied and translated into a ‘grade’ that could be used in conjunction with the other indicators of the AHK Report Card to generate overall Report Card grades. The use of both the HEPA PAT v2 and the scoring rubric offers an opportunity to provide greater consistency and potential for developing both comparative and trend data when assessing policy impact on physical activity in children and young people. These tools should be utilized by the AHK Global Alliance in future Report Cards

Editorial: Macrocognition: The Science and Engineering of Sociotechnical Work Systems

The increasing complexity of work systems and changes in the nature of workplace technology over the past century have resulted in an exponential shift in the nature of work activities, from physical labor to cognitive work. Modern work systems have many characteristics that make them cognitively complex: They can be highly interactive; comprised of multiple agents and artifacts; information may be limited and distributed across space and time; task goals are frequently ill-defined, conflicting, dynamic and emergent; planning may only be possible at general levels of abstraction or require adaptive solutions; some degree of proficiency or expertise is required; the stakes are often high; and uncertainty, time-constraints and stress are seldom absent. To complicate matters further, cognition in complex work settings is typically constrained by broader professional, organizational, and institutional practice and policy. These features of cognitive work present significant challenges to scientific methodology and theory, and subsequent design of reliable interventions. Historically, philosophers and scientists have attempted to understand the mental activities experienced during cognitive work at multiple levels of analysis using divergent methods. Some have examined cognition at an associative, contextual, functional or holistic level, relying on naturalistic methods to understand the higher mental processes as they work in harmony during goal-directed behavior. Others have embraced experimental methods and favored internal over external validity, often reducing cognition to a psychology of fundamental acts, such as short-term memory access with millisecond shifts in attention. More recently, Macrocognition has evolved as a complementary paradigm. Macrocognitive researchers have studied the cognitive functions and processes associated with skilled, adaptive, collaborative, and resilient cognitive work in the context of the aforementioned complexities of psychotechnical and sociotechnical work systems. Typically, this research has been carried out using cognitive task analytic techniques that draw on both naturalistic and (quasi-)experimental methods. The primary goals of research in Macrocognition are to better understand cognitive adaptations to complexity, to increase our theoretical understanding of the organism-environment relations by studying the mapping between cognitive work and real-world demands, and to promote use-inspired research capable of improving system performance