Motivated by previous relevant research on phononics including both active and passive phononics, the interest of faster turnability and more functions of the active phononics of further study led to this proposing research topic: magnetic field tunable active functional phononics. The first design of magnetic field tunable reciprocal--non-reciprocal transmission acoustic device was established, material was characterized, and numerical simulation has been performed. The simulation results show clear T-symmetric breaking non-reciprocity due to energy level splitting effect with Doppler effect – an acoustic Zeeman effect. Inspired by this preliminary work, further experiments were planned to demonstrate this effective Zeeman effect in phononics and effectively charged phonons in water based ferro-fluid. The objectives of this work as the next series of tasks were to illustrate acoustic Zeeman effect and acoustic Landau levels in various strength of magnetic field to investigate a design non-reciprocal sound device with magnetic field switching, which could be controlled on the amount of non-reciprocity with the strength of magnetic field. Once this new field first discovered by the proposed study tasks, more active tunable magnetic field phononics devices could be designed and exemplified in terms of both simulations and experiments. Faster and more controllable active phononic devices could be designed and made based on this study. The experimental maximum non-reciprocity was measured as 22 dB difference and the amount of the non-reciprocity can be further controlled by adjusting the strength of the external magnetic field. The remote pumping system in the device worked as expected and did not introduce any impact of the cavity properties.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Soft, serene insect songs add an intrinsic aesthetic value to the landscape. Yet these songs also have an important biological relevance. Acoustic signals across the landscape carry a multitude of localized information allowing organisms to communicate invisibly within their environment. Ensifera are cryptic participants of nocturnal soundscapes, contributing to ambient acoustics through their diverse range of proclamation songs. Although not without inherent risks and constraints, the single most important function of signalling is sexual advertising and pair formation. In order for acoustic communication to be effective, signals must maintain their encoded information so as to lead to positive phonotaxis in the receiver towards the emitter. In any given environment, communication is constrained by various local abiotic and biotic factors, resulting in Ensifera utilizing acoustic niches, shifting species songs spectrally, spatially and temporally for their optimal propagation in the environment. Besides the importance of Ensifera songs from an ethological point of view, the multitude of species-specific signals provide an acoustic tapestry representing species diversity across ecological gradients and over time. Acoustic inventorying and monitoring of the landscape can reflect the environmental status of ecological systems, from natural to disturbed by human influence. In contrast to traditional survey techniques, sound recording and interpretation is a non-invasive method that allows for the detection and classification of highly cryptic, yet insightful indicators of ecosystem change. Here, acoustic monitoring was used across diverse ecological gradients to improve understanding of species diversity patterns, and how they change in response to both natural gradients and in response to the human dominated landscape mosaic. This study was undertaken in three geographic locations from tropical rain forest of Brunei, Borneo, to the landscapemosaic of plantation forestry in KwaZulu-Natal, South Africa, and to the botanically rich, mountain fynbos region of the Cape Floristic Region, also in South Africa. Each region provided a diverse and particular landscape to test the value of acoustic surveys for determining local diversity patterns across natural gradients and to assess the value of the technique for assessing the impact human influence across landscapes. In tropical rainforests, an entire acoustic guild was investigated to determine how acoustic species partition their acoustic communication channels spectrally, temporally and spatially, to avoid acoustic interference. The overall assemblage showed considerable spectral partitioning. Diurnally active species showed low temporal niche overlap, whereas nocturnal species did not utilize temporal partitioning. Lack of nocturnal temporal partitioning suggests other mechanisms of acoustic avoidance are sufficient to avoid acoustic overlap, or that there are insufficient cues to partition nocturnal acoustic environments. Acoustic species also utilized spatial partitioning, with distinct acoustic assemblages at vertical heights and with elevation. Utilization of a range of different strategies allow many species to communicate with conspecifics with little or no interference from other species in a signal rich environment. Acoustic profiling was also undertaken in KwaZulu-Natal, South Africa, across a plantation forestry landscape mosaic with diverse ecological gradients containing both alien and indigenous vegetation, as well as boarding large natural protected areas. Areas covered in alien timber or non-endemic grass were devoid of acoustic signals. Managed areas that were mowed and heavily grazed were not effective in maintaining the natural complement of nocturnal acoustic species. Within natural vegetation patches inside plantations, acoustic species richness increased with plant heterogeneity and patch size. Patches of indigenous vegetation within the plantation matrix effectively reduced the contrast of transformed landscapes with surrounding natural areas, with indigenous forest patches containing a highly characteristic acoustic species assemblage. Within the botanically rich, mountain fynbos region of the Cape Floristic Region, acoustic profiling was conducted across gradients of elevation, season and vegetation. Across these gradients, katydid acoustic signals were identified and characterized for the first time. This resulted in the discovery of two new katydid species and a novel sound producing structure in a carabid beetle, a species previously unknown to produce sound. Acoustic diversity across seasonal and elevational gradients increased with increasing temperatures. Climatic variability along the elevational gradient produced variation in seasonal phenology. Katydids also utilized high frequency acoustic signals, which is probably an adaptation to overcome background noise from wind, so prevalent in this area. Furthermore, despite producing conspicuous signals for mate attraction and pair formation, katydids were found not to be part of bat-eared fox diet, an insectivorous, nocturnal predator that uses its characteristic large ears to detect sounds made by invertebrate prey. This study shows the value of using acoustic emissions from katydids to identify acoustic diversity patterns across ecological gradients and in response to human impacts on the landscape. / AFRIKAANSE OPSOMMING: Sagte, rustige insekliedjies voeg ‘n intrinsieke estetiese waarde aan die landskap. Tog is hierdie liedjies ook van belangrike biologiese waarde. Akoestiese seine oor die landskap dra ‘n magdom plaaslike inligting wat organismes in staat stel om onsigbaar te kommunikeer binne hul omgewing. Langhoringsprinkane is kriptiese deelnemers van die nagtelike klankomgewing en dra by tot die omringende akoestiek deur hul verskeidenheid van proklamasieliedjies. Alhoewel dit nie sonder inherente risiko’s en beperkings is nie, is die belangrikste funksie van seine seksuele advertering en paarvorming. Vir akoestiese kommunikasie om effektief te wees, moet seine hul geënkodeerde inligting handhaaf, sodat dit sal lei tot positiewe fonotaksis in die ontvanger teenoor die emittor. In enige gegewe omgewing, word kommunikasie beperk deur verskeie plaaslike abiotiese en biotiese faktore. Dit lei tot die gebruik van akoestiese nisse deur langhoringsprinkane, wat hulle liedjies spektraal, ruimtelik en temporeel aanpas vir optimale verspreiding in die omgewing. Benewens die belang van die langhoringsprinkaan liedjies uit ʼn etologiese oogpunt, bied die menigte spesie-spesifieke seine ʼn akoestiese tapisserie wat spesiesdiversiteit verteenwoordig oor ekologiese gradiënte en oor tyd. Akoestiese opname en monitering van die landskap kan die omgewingstoestand van ekologiese stelsels weerspieël, van natuurlike tot menslik versteurde stelsels. In teenstelling met tradisionele opnametegnieke, is klankopname en interpretasie ʼn nie-indringende metode wat dit moontlik maak om hoogs kriptiese, nog insiggewende indikators van ekosisteemverandering op te spoor en te klassifiseer. In hierdie studie is akoestiese monitering gebruik oor diverse ekologiese gradiënte om ons begrip te verbeter van spesies diversiteitspatrone, en hoe dit verander in reaksie op beide natuurlike gradiënte en in reaksie op die menslik gedomineerde landskapmosaïek. Hierdie studie is onderneem in drie geografiese liggings: tropiese reënwoud in Brunei, Borneo, die landskapmosaïek van plantasiebosbou in KwaZulu-Natal, Suid-Afrika, en die plantryke, bergfynbos-streek van die Kaap Floristiese Streek, ook in Suid-Afrika. Elke streek het 'n diverse en besondere landskap verskaf om die waarde van akoestiese opnames te toets vir die bepaling van plaaslike diversiteitspatrone in natuurlike gradiënte, asook om die waarde van die tegniek te bepaal vir die beoordeling van die impak van menslike invloed oor landskappe. In tropiese reënwoude, is 'n hele akoestiese gilde ondersoek om te bepaal hoe akoestiese spesies hul akoestiese kommunikasiekanale spektraal, ruimtelik en temporeel verdeel om akoestiese inmenging te vermy. Die algehele groep het aansienlike spektrale verdeling getoon. Dagaktiewe spesies het lae temporele nisoorvleueling getoon, terwyl nagtelike spesie nie temporele verdeling benut het nie. Gebrek aan nagtelike temporele verdeling dui daarop dat ander meganismes van akoestiese vermyding voldoende is om akoestiese oorvleueling te vermy, of dat daar onvoldoende seine is om nagtelike akoestiese omgewings te verdeel. Akoestiese spesies het ook ruimtelike verdeling benut, met verskillende akoestiese spesiesversamelings op vertikale hoogtes en met hoogte bo seevlak. Die gebruik van 'n verskeidenheid van strategieë maak dit moontlik vir spesies om te kommunikeer met min of geen inmenging van ander spesies in 'n seinryke omgewing. Akoestiese profielsamestelling is ook onderneem in KwaZulu-Natal, Suid-Afrika, oor 'n plantasiebosbou landskapmosaïek met diverse ekologiese gradiënte wat beide uitheemse en inheemse plantegroei, sowel as groot, natuurlike, beskermde gebiede ingesluit het. Gebiede wat bestaan het uit uitheemse timmerhoutbome of nie-endemiese gras, was heeltemal sonder akoestiese seine. Bestuursgebiede wat gesny en swaar bewei was, het nie doeltreffend die natuurlike komplement van nagtelike akoestiese spesies gehandhaaf nie. In natuurlike plantegroei fragmente binne plantasies, het akoestiese spesiesrykheid toegeneem met plantverskeidenheid en fragmentgrootte. Fragmente van inheemse plantegroei binne die plantasiematriks het effektief die kontras van getransformeerde landskappe met omliggende natuurlike gebiede verminder, en inheemse woudefragmente het hoogs kenmerkende akoestiese spesiesversamelings gehad. Binne die plantryke bergfynbosstreek van die Kaap Floristiese Streek, was akoestiese profielsamestelling gedoen oor gradiënte van hoogte bo seevlak, seisoen en plantegroei. Oor hierdie gradiënte, is langhoringsprinkaan akoestiese seine geïdentifiseer en gekenmerk vir die eerste keer. Dit het gelei tot die ontdekking van twee nuwe langhoringsprinkaan spesies en 'n nuwe klankvervaardiging struktuur in 'n Carabid kewer, 'n spesie wat nie voorheen bekend was om klank te produseer nie. Akoestiese diversiteit oor gradiënte van seisoen en hoogte bo seevlak het toegeneem met toenemende temperature. Variasie in klimaatstoestande oor die gradiënt van hoogte bo seevlak het variasie in seisoenale fenologie veroorsaak. Langhoringsprinkane het ook hoë frekwensie akoestiese seine benut, wat waarskynlik 'n aanpassing is om agtergrondgeraas van die wind, wat so algemeen is in hierdie gebied, te bowe te kom. Verder, ten spyte van die vervaardiging van opvallende seine vir maataantrekking en paarvorming, het langhoringsprinkane nie deel gevorm van die bakoorjakkals se dieet nie. Hierdie is 'n insekvretende, nagtelike roofdier wat gebruik maak van sy kenmerkende groot ore om klanke op te spoor wat gemaak word deur invertebraatprooi. Hierdie studie toon die waarde van die gebruik van akoestiese seine van langhoringsprinkane om akoestiese diversiteitspatrone te identifiseer oor ekologiese gradiënte en in reaksie op menslike impakte op die landskap.

Particle separation is of great interest to many biological and biomedical applications. Flow-based methods have been used to sort particles and cells. However, the main challenge with flow based particle separation systems is the need for a sheath flow for successful operation. Existence of the sheath liquid dilutes the analyte, necessitates precise flow control between sample and sheath flow, requires a complicated design to create sheath flow and separation efficiency depends on the sheath liquid composition. In addition, current gold standard active separation techniques are only capable of separation based on particle size; hence, separation cannot be achieved for same-size particles with different densities. In this dissertation, a sheathless acoustic-based microfluidic platform using surface acoustic wave for not only size-dependent but also density-dependent particle separation has been investigated. In this platform, two different functions were incorporated within a single microfluidic channel with varying the number of pressure node and position. The first function was to align particles on the center of the microfluidic channel without adding any external sheath flow. The second function was to separate particles according to their size or density. Two different size-pairs of polystyrene particles with different diameters (3 µm and 10 µm for general size-resolution, 3 µm and 5 µm for higher size-resolution) were successfully separated. Also, the separation of two 10 µm diameter, different-density particle streams (polystyrene: 1.05 g/cm3, melamine: 1.71 g/cm3) was successfully demonstrated. The effects of the input power, the flow rate, and particle concentration on the separation efficiency were investigated. A range of high separation efficiencies with 94.8-100 % for size-based separation and 87.2 - 98.9 % for density-based separation were accomplished. In this dissertation, an acoustic-based microfluidic platform using dual acoustic streaming for active mixing has also been investigated. The rapid and high efficiency mixing of a fluorescent dye solution and deionized water in a microfluidic channel was demonstrated with single acoustic excitation by one interdigital transducer (IDT) as well as dual excitation by two IDTs. The mixing efficiencies were investigated as a function of applied voltage and flow rates. The results indicate that with the same operation parameters, the mixing efficiency with dual-IDT design increased to 96.7 % from 69.8 % achievable with the traditional single-IDT design. The effect of aperture length of the IDT on mixing efficiency was also investigated. Additionally, the effects of the polydimethylsiloxane (PDMS) channel wall thickness on the insertion loss and the particle migration to the pressure node due to acoustic radiation forces induced by SAW have been investigated. The results indicate that as the PDMS channel wall thickness decreased, the SAW insertion loss is reduced as well as the velocity of the particle migration due to acoustic forces increased significantly. As an example, reducing the side wall thickness of the PDMS channel from 8 mm to 2 mm in the design results in 31.2 % decrease in the insertion loss at the resonant frequency of 13.3 MHz and 186 % increase the particle migration velocity at the resonant frequency of 13.3 MHz with input power of 27 dBm. Lastly, a novel acoustic-based method of manipulating the particles using phase-shift has been proposed and demonstrated. The location of the pressure node was adjusted simply by modulating the relative phase difference (phase-shift) between two IDTs. As a result, polystyrene particles of 5 µm diameter trapped in the pressure node were manipulated laterally across the microfluidic channel. The lateral displacements of the particles from -72.5 µm to 73.1 µm along the x-direction were accomplished by varying the phase-shift with a range of -180° to 180°. The relationship between the particle displacement and the phase-shift of SAW was obtained experimentally and shown to agree with theoretical prediction of the particle position.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / This paper describes the design and successful development of an acoustic modem for potential use in underwater ecological sensor networks. The presentation includes theoretical study, design and development of both software and hardware, laboratory experiments, full-scale field tests, and the documentation and analysis of field-test results.

This work is centered on low-frequency and high-frequency multiphysics problems of piezoelectric structures submerged in a quiescent fluid domain for the applications of vibration energy harvesting, biomimetic actuation, and contactless acoustic energy transfer. In the first part of this research, Macro-Fiber Composite (MFC)-based piezoelectric structures are employed for underwater mechanical base excitation and electrical biomimetic actuation in bending mode at low frequencies (the fundamental underwater bending resonance being in the infrasonic frequency range). The MFC technology (fiber-based piezoelectric composites with interdigitated electrodes) exploits the effective 33-mode of piezoelectricity, and strikes a balance between structural deformation and force levels for actuation to use in underwater locomotion, in addition to offering high power density for energy harvesting to enable battery-less aquatic sensors. Following in-air electroelastic composite model development, the fundamental research problem is to establish semi-analytical models that can predict the underwater dynamics of thin MFC cantilevers for different length-to-width aspect ratios. In-air analytical electroelastic dynamics of MFCs is therefore coupled with added mass and nonlinear hydrodynamic damping effects of fluid to describe the underwater electrohydroelastic dynamics in harvesting and actuation. To this end, passive plates of different aspect ratios are tested to extract and explore the repeatability of the inertia and drag coefficients in Morison’s equation. The focus is placed on the first two bending modes in this semi-empirical approach. In particular, electrode segmentation is studied for performance enhancement in the second bending mode. Additionally, nonlinear dependence of the output power density to aspect ratio is characterized theoretically and experimentally in the underwater base excitation problem. In the second part of this work, Ultrasonic Acoustic Energy Transfer via piezoelectric transduction is investigated theoretically and experimentally. Contactless energy transfer using acoustic excitation offers larger distances of power transmission as compared to well-studied inductive method. Various transmitter configurations (e.g. spherical, cylindrical, and focused) are explored for energy transfer to a piezoelectric receiver bar (operating in the longitudinal/thickness mode) that is shunted to a generalized resistive-reactive circuit. Fixed-free and free-free mechanical boundary conditions of the receiver are explored in detail. The resulting multiphysics analytical model framework is compared with finite-element simulations and experiments conducted in fluid (water and oil). Optimal piezoelectric receiver material and electrical loading conditions are sought for performance and bandwidth enhancement.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Underwater acoustic (UWA) telemetry requires wideband waveforms for anti-multipath which are simultaneously easy to equalize and demodulate. The Walsh/m-sequence waveforms proposed here are robust to multipath and with appropriate time-guard bands do not require equalization. For example, in the UCSB prototype acoustic modem, a data rate of 133 bps is achieved using 8-ary Walsh signaling with an 11.2 msec. symbol duration. Demodulation is performed using noncoherent detection, and hence accurate phase tracking, which is difficult to achieve in the UWA channel, is not required. However, telemetry from unmanned underwater vehicles (UUVs) is more problematic due to large Doppler shifts resulting from platform motion. A new receiver algorithm based on Matching Pursuits is proposed which combines channel and Doppler shift estimation. Symbol-error rate (SER) simulation results are presented for the UWA modem under realistic Doppler/multipath conditions.

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The objective of any data acquisition system is to make accurate measurements of physical phenomena. Many of the phenomena to be characterized contain data that is in the audio-frequency range between 0 and 50,000 Hertz. Examples include structural vibration, wind-tunnel measurements, turbine engines and acoustics in air and water. These tests often require a large number of channels and may be very expensive. In some cases, there may be only one opportunity to acquire the data. This paper describes a testing/measurement philosophy and the use of advances in available hardware/software systems to implement the requirements. Primary emphasis is on robustness (assurance that critical data is properly recorded), measurement/characterization of unexpected results (generated by accidents or unexpected behavior), and test safety (for both the test article and the facility). Finally, a data acquisition system that encompasses the features discussed is described.

In the open ocean acoustic scattering by SONAR sources can be dominated by large fish schools. Multiple scattering effects are strong and the individual fish air-filled swimbladders scatter in the 1-10 kHz frequency range for most fish sizes. Furthermore, these schools are typically large in comparison to the acoustic wavelength and the individual fish typically swim in nearly periodic arrangements with a separation distance of approximately one body length. Hence, this work takes the perspective that fish schools can be studied simply and effectively by invoking the formalism of Bloch waves in periodic media. Analysis of the periodic school is aided through the Bloch theorem which reduces the study of the entire school to the study of a unit cell containing a single fish swimbladder. Application of the Bloch formalism to the school requires study of acoustic reflection from a semi-infinite half-space composed of an infinite tessellation of air-filled swimbladders in water. This media is denoted a fluid phononic crystal (PC). The reflection is considered, using a finite element discretization of the unit cell and an expansion of Bloch waves for the transmitted wave field. Next, scattering from a large finite school is studied through the context of the Helmholtz-Kirchhoff integral theorem where the semi-infinite PC pressure, determined by the Bloch wave expansion, is used as the surface pressure. Validation of results is accomplished via comparison with a finite element model (two dimensions) and a low frequency analytical multiple scattering model (three dimensions). Analysis of the dispersion relationship of the infinite PC yields useful information for a large school, namely, the frequency corresponding to target strength peaks, even as wave incidence angles and internal fish spacing are varied. The scattering effects attributed to the shape and weak internal disorder of the finite school were investigated with the surface integral method and a perturbation scheme. A general model using Bloch formalism, that encompasses the internal fish structure, fish biologic properties, and realistic school effects such as varying school geometry and disorder, was formulated. Transient analysis of the frequency dependent scattering, using the proposed approach developed in this thesis, may assist SONAR operators better classify large fish schools based on the observed characteristics of the scattered field.

A metasurface or 2D metamaterial composed of a membrane array can support an interesting acoustic wave field. These waves are evanescent in the direction normal to the array and can propagate in the immersion fluid immediately above the metasurface. These waves are a result of the resonant membranes coupling to the fluid medium and propagate with a group and phase speed lower than that of the bulk waves in the surrounding fluid. This work examines and utilizes these evanescent surface waves using Capacitively Micromachined Ultrasonic Transducers (CMUT) as a specific example. CMUT arrays can generate and detect membrane displacement capacitively, and are shown to support the surface waves capable of subwavelength focusing and imaging. A model is developed that can solve for the modes of the membrane array in addition to transiently modeling the behavior of the array. It is found that the dispersive nature of the waves is dependent on the behavior of the modes of the membrane array. Two-dimensional dispersion analysis of the metasurface shows evidence of four distinct frequency bands of surface wave propagation: isotropic, anisotropic, directional band gap, and complete band gap around the first resonant frequency of the membrane. Some of the frequencies in the partial band gap show concave equifrequency contours capable of negative refraction. The dispersion and modal properties are also examined as to how they are affected by basic array parameters. Potential applications of this wave field are examined in the context of subwavelength focusing and imaging. Several methods of acoustic focusing are used on an array consisting of dense grid of membranes and several membranes spatially removed from the structure. Subwavelength acoustic focusing to a resolution of λ/5 is shown in simulations and verified with experiments. An imaging test is also performed in which a subwavelength defect is localized. This fundamental work in characterizing the waves above the membrane metasurfaces is expected to have impact and implications for transducer design, resonant sensors, 2D acoustic lenses, and subwavelength focusing and imaging.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy