abstract: This thesis presents approaches to develop micro seismometers and accelerometers based on molecular electronic transducers (MET) technology using MicroElectroMechanical Systems (MEMS) techniques. MET is a technology applied in seismic instrumentation that proves highly beneficial to planetary seismology. It consists of an electrochemical cell that senses the movement of liquid electrolyte between electrodes by converting it to the output current. MET seismometers have advantages of high sensitivity, low noise floor, small size, absence of fragile mechanical moving parts and independence on the direction of sensitivity axis. By using MEMS techniques, a micro MET seismometer is developed with inter-electrode spacing close to 1μm, which improves the sensitivity of fabricated device to above 3000 V/(m/s^2) under operating bias of 600 mV and input acceleration of 400 μG (G=9.81m/s^2) at 0.32 Hz. The lowered hydrodynamic resistance by increasing the number of channels improves the self-noise to -127 dB equivalent to 44 nG/√Hz at 1 Hz. An alternative approach to build the sensing element of MEMS MET seismometer using SOI process is also presented in this thesis. The significantly increased number of channels is expected to improve the noise performance. Inspired by the advantages of combining MET and MEMS technologies on the development of seismometer, a low frequency accelerometer utilizing MET technology with post-CMOS-compatible fabrication processes is developed. In the fabricated accelerometer, the complicated fabrication of mass-spring system in solid-state MEMS accelerometer is replaced with a much simpler post-CMOS-compatible process containing only deposition of a four-electrode MET structure on a planar substrate, and a liquid inertia mass of an electrolyte droplet encapsulated by oil film. The fabrication process does not involve focused ion beam milling which is used in the micro MET seismometer fabrication, thus the cost is lowered. Furthermore, the planar structure and the novel idea of using an oil film as the sealing diaphragm eliminate the complicated three-dimensional packaging of the seismometer. The fabricated device achieves 10.8 V/G sensitivity at 20 Hz with nearly flat response over the frequency range from 1 Hz to 50 Hz, and a low noise floor of 75 μG/√Hz at 20 Hz. / Dissertation/Thesis / Ph.D. Electrical Engineering 2014

Os modelos existentes de propagação de ondas de ultra-som em meios líquidos e sólidos consideram a geração e recepção das ondas produzidas por transdutores simulados segundo o modelo do pistão plano ou com excitações cuja amplitude varia radialmente no pistão. Esses modelos são simplificados e não explicam completamente o comportamento real de transdutores de ultra-som interagindo com líquidos e sólidos. As verificações experimentais de propagação da onda de ultra-som em meios líquidos mostram que a onda de borda é diferente da onda plana. Observa-se também a existência de outras ondas não previstas nos modelos anteriores. Essas ondas são conhecidas como ondas head. A utilização do método dos elementos finitos (MEF) para a modelagem de propagação de ondas de ultra-som, incluindo o transdutor piezelétrico, permite a obtenção de resultados realísticos, conseguindo assim descrever com maior precisão o comportamento do transdutor e das ondas de ultra-som se propagando em diferentes meios e interagindo com defeitos que se comportam como refletores. Apesar disso, os resultados desses modelos dependem das características precisas dos materiais que compõem o transdutor. O transdutor de ultra-som é composto por uma cerâmica piezelétrica, por camadas de casamento e de retaguarda que geralmente são compósitos de epóxi com alumina e epóxi com tungstênio respectivamente, e pelo encapsulamento. Neste trabalho é analisada a resposta transiente de um transdutor circular de 2 MHz, com diâmetro de 12,7 mm, banda larga. O modelo do transdutor foi implementado com o método de elementos finitos. A análise transiente pelo MEF é implementada com o software ANSYS. Na primeira parte do trabalho o transdutor é analisado no modo de transmissão em água. Os resultados do modelo com MEF foram comparados com os resultados do modelo do pistão plano e com verificações experimentais obtidas em tanque de imersão com um hidrofone tipo agulha. Na segunda parte é realizada a análise do transdutor operando em modo pulso-eco radiando em peças de teste com e sem defeito, utilizando acoplamento direto e acoplamento por buffer de água. Os resultados do MEF apresentam boa concordância com os resultados obtidos experimentalmente. / Simple models for ultrasonic wave propagation in liquid and solid media consider the wave generation and reception by transducers that behave as plane pistons. These models are simplified and they do not explain completely the behavior of an ultrasonic transducer when interacting with other media. Experimental verifications of ultrasonic wave propagation in liquid show that the pressure amplitude of the edge wave is different from the plane wave. Also it is observed the existence of other types of waves not foreseen in these previous models. These waves are known as head waves. More realistic models for ultrasonic wave propagation are obtained using the finite element method (FEM). These models include the piezoelectric transducer, thus, describing with higher precision the behavior of the transducer and the ultrasonic waves propagating in different mediums and interacting with defects. The precision of the models depends on the accurate determination of the mechanical and electrical properties of the involved materials. The ultrasonic transducer is composed by a piezoelectric ceramic, a matching layer and a backing layer that are generally made by epoxy/alumina and epoxy/tungsten composites respectively. In this work it is analyzed the transient response of a circular transducer of 12.7 mm diameter and 2 MHz center frequency. The transducer model was implemented with the finite element method. The FEM transient analysis was executed in the ANSYS software. In the first part of the work the transducer is analyzed in transmission mode in water and the MEF results are compared with the plane piston model and with experimental verifications using a hydrophone. In the second part it is carried at the transducer analysis operating in pulse-echo mode radiating into test pieces with and without defects, using direct and water buffer coupling. The MEF results show good agreement with the results obtained experimentally in the laboratory.

No description available.

This work deals with comparison of individual types of electroacoustic transducers, their properties and practical use. Furthermore, design and manufacture of a magnetoplanar transducer, its integration into headphones and the production of headphone amplifier. The first chapter summarizes all types of electroacoustic transducers, their properties, advantages, disadvantages, and their use in practice. The second chapter deals with the classes of amplifiers. The third chapter deals with the choice of design of a magnetoplanar transducer, headphones, and selected type of headphone amplifier. The last chapter describes the production process of individual parts of the headphones, transducer and amplifier, including the final measurement.

Many industrial processes such as printing and cleaning, as well as products like adhesives, coatings, and biological testing devices, rely on the wetting of liquids on a surfaces. Wetting is commonly controlled through material selection, coatings, and/or surface texture, but these means are sensitive to environmental conditions. Wetting is influenced by variables like surface tension, density, the surface chemistry, local energy barriers like surface roughness, and how the droplet is placed on the surface. Wetting of droplets can also be influenced externally in many ways such as introducing surfactants, applying electrical fields, or by dynamically excitation. Low-frequency, high amplitude vibration can initiate wetting changes prompted by droplet contact line oscillations that exceed the range of stable contact angles inherent of a droplet on a solid surface. The study of ultrasonic vibration wetting and spreading effects is sparse [1, 2], and is usually only qualitatively analyzed. Therefore, the specific goal of this thesis is somewhat unique, but also has potential as a means to controllably reverse surface adhesion. High frequency vibration effects and the governing mechanisms are relatively uncharacterized due to difficulties posed by the spatial and temporal scales. To investigate, droplets of 10, 20, and 30 µL are imaged as they vibrate on a hydrophobic surface forced via a piezoelectric transducer over different high frequencies (>10 kHz). Wetting transitions occur abruptly over a range of parameters, but coincide with transducer resonance modes. The magnitude of contact angle change is dependent on droplet volume and surface acceleration, and remains after cessation of vibration, however new droplets wet with the original contact angle. A more detailed investigation of this phenomenon was necessary to obtain a better understanding. This required repeatable testing conditions, which relies heavily on surface integrity. However, some “hydrophobic” coatings are sensitive to extended water exposure. To determine which hydrophobic coatings may be appropriate for investigating dynamic wetting phenomena, samples of glass slides coated with a series of fluoropolymer coatings were tested by measuring water contact angle before, during, and after extended submersion in deionized water and compared to the same coatings subjected to ultrasonic vibration while covered in deionized water. Both methods caused changes in advancing and receding contact angle, but degradation rates of vibrated coatings, when apparent, were significantly increased. Prolonged soaking caused significant decreases in the contact angle of most coatings, but experienced significant recovery of hydrophobicity when later heat-treated at 160 C. Dissimilar trends apparent in receding contact angles suggests a unique degradation cause in each case. Roughening and smoothing of coatings was noted for coatings that were submerged and heat-treated respectively, but this did not correlate well with the changing water contact angle. Degradation did not correspond to surface acceleration levels, but may be related to how well coatings adhere to the substrate, indicative of a dissolved coating. Most coatings suffered from contact angle degradation between 20-70% when exposed to water over a long period of time, however the hydrophobic fluoropolymer coating FluoroSyl was found to remain unchanged. For this reason it was found to be the most robust coating for providing long term wetting repeatability of vibrated droplets. Droplets (10 to 70 µL) were imaged on hydrophobic surfaces as they were vibrated with ultrasonic piezoelectric transducers. Droplets were vibrated at a constant frequency with ramped amplitude. Spreading of droplets occurs abruptly when a threshold surface acceleration is exceeded of approximately 20,000 m/s2. Droplet contact area (diameter) can be controlled by varying acceleration levels above the threshold. The threshold acceleration was relatively independent of droplet volume, while initial contact angle impacts the extent of spreading. Wetting changes remain after cessation of vibration as long as the vibrated droplet remained within the equilibrium contact angle range for the surface (> the receding contact angle), however new droplets wet with the original contact angle except for some cases where vibration of liquid can affect the integrity of the coating. Reversible wettability of textured surfaces is a desired effect that has various industry applications where droplet manipulation is used, like biomedical devices, coating technologies, and agriculture [3-5].

Acoustic-structural interaction is the key to understand a wide range of engineering problems such as membrane-based dynamic pressure sensors, hearing devices for sound source localization, and acoustic absorbers for noise reduction. Despite tremendous developments in the last decades, there is still a fundamental size limitation in these areas. In the case of dynamic pressure sensors, sensitivity usually suffers for miniature sensors; the available acoustic directional cues proportionally decrease with size, which adversely affects the localization performance; thick panels are required to achieve superior sound attenuation, particularly for low-frequency sound. It is the motivation of this dissertation research to address the abovementioned size limitation that involves acoustic-structural interaction. The overall goal of this dissertation work is to achieve an enhanced understanding of the acoustic-structural interaction between diaphragms and air cavity and to apply this understanding to develop high-performance miniature acoustic sensors and noise reduction metamaterials. First, a finite element method (FEM) model and large-scale device are developed to understand how the interaction between the diaphragm and its backing air cavity affects the equivalent mass, stiffness, and damping of air-backed diaphragms. The numerical and experimental study shows that the complex interaction cannot be captured by the commonly used lump model. Then, air-backed graphene diaphragms are used to develop fiber optic sensors with sub-millimeters footprint and high sensitivity. Two different configurations are designed to enhance the sensor sensitivity limited by the backing air cavity. One is to increase the mechanical sensitivity by using a larger backing volume, the other is to increase the optical sensitivity by using silver-graphene composite diaphragm. Next, acoustic metamaterials with air-coupled diaphragms as unit cells are developed to achieve perfect acoustic absorption with thickness much smaller than the sound wavelength, which cannot be realized using natural materials. Finally, an expanded configuration of two diaphragms coupled by an air-filled tunnel is experimentally developed to mimic the hearing system of small vertebrates. The goal is to amplify the small directional cues available to the small animals so that a high angular resolution can be achieved. This dissertation provides a quantitative and mechanistic explanation for the interaction between the diaphragms and the sealed air cavity. It offers several frameworks for the development of miniature pressures, directional sensors, and thin sound absorbers. / Mechanical Engineering

Medical ultrasound technology accounts for over half of all imaging tests performed worldwide. In comparison to other methods, ultrasonic imaging is more portable and lower cost, and is becoming more accessible to remote regions where traditionally no medical imaging can be done. However, conventional ultrasonic imaging systems still rely on expensive PZT-based ultrasound probes that limit broader applications. In addition, the resolution of PZT based transducers is low due to the limitation in hand-fabrication methods of the piezoelectric ceramics. Capacitive Micromachined Ultrasonic Transducers (CMUTs) appears as an alternative to the piezoelectric (PZT) ceramic based transducer for ultrasound medical imaging. CMUTs show better ultrasound transducer design for batch fabrication, higher axial resolution of images, lower fabrication costs of the elements, ease of fabricating large arrays of cells using MEMS fabrication, and the extremely important potential to monolithically integrate the 2D transducer arrays directly with IC circuits for real-time 3D imaging. Currently most efforts on CMUTs are silicon based. Problems with current silicon-based CMUT designs include low pressure transmission and high-temperature fabrication processes. The pressure output from the silicon based CMUTs cells during transmission are too low when compared to commercially available PZT transducers, resulting in relatively blurry ultrasound images. The fabrication of the silicon-based cells, although easier than PZT transducers, still suffers from inevitable high temperature process and require specialized and expensive equipment. Manufacturing at an elevated temperature hinders the capability of fabricating front end analog processing IC circuits, thus it is difficult to achieve true 3D/4D imaging. Therefore novel low temperature fabrication with a low cost nature is needed. A polymer (Parylene) based CMUTs transducer has been investigated recently at UCF and aims to overcome limitations posted from the silicon based counterparts. This thesis describes the numerical simulation work and proposed fabrication steps of the Parylene based CMUT. The issue of transducer cost and pressure transmission is addressed by proposing the use of low cost and low temperature Chemical Vapor Deposition (CVD) fabrication of Parylene-C as the structural membrane plus graphene for the membrane electrodes. This study focuses mainly on comparing traditional silicon-based CMUT designs against the Parylene-C/Graphene CMUT based transducer, by using MEMS modules in COMSOL. For a fair comparison, single CMUT cells are modeled and held at a constant diameter and the similar operational frequency at the structural center. The numerical CMUT model is characterized for: collapse voltage, membrane deflection profile, center frequency, peak output pressure transmission over the membrane surface, and the sensitivity to the change in electrode surface charge. This study took the unique approaches in defining sensitivity of the CMUT by calculating the membrane response and the change in the electrode surface charge due to an incoming pressure wave. Optimal design has been achieved based on the simulation results. In comparison to silicon based CMUTs, the Parylene/Graphene based CMUT transducer produces 55% more in volume displacement and more than 35% in pressure output. The thesis has also laid out the detailed fabrication processes of the Parylene/Graphene based CMUT transducers. Parylene/Graphene based ultrasonic transducers can find wide applications in both medical imaging and Non destructive evaluation (NDE).

Icing on aircraft wings is one of the leading causes of aircraft crashes. It is mainly caused due to accumulation of ice or snow on the wing surface due to impact with supercooled droplets when passing through clouds at high altitudes, causing loss of lift obtained by the wings. It was found that droplet impact characteristics are dependent on droplet size, surface roughness, surface material hydrophobicity, and droplet impact velocity. As a continuation of the study of droplet impact contact characteristics by varying surface roughness and impact velocity, this study focuses on droplets impacting the vibrating surface at frequencies between 2-7 kHz. Atomization (water drop splitting into smaller droplets and ejecting from the surface) has been observed at different rates for all frequencies. The first set of data is collected by keeping roughness constant and increasing the amplitude of the vibration to observe the critical amplitude at which atomization is initiated. The surface roughness is varied for the second set of experiments. The data is quantified using image processing of the high-speed videos to obtain the rate of ejection for each case. / Master of Science / Icing on aircraft wings is among the leading causes of crashes, which involves small freezing water drops sticking to the wing surface thus reducing the lift. This study is an investigation to experimentally observe how small water droplets interact with surfaces vibrating at high frequencies when impacted. Surface roughness, materials, droplet velocities, and frequency of vibration have been varied and the droplet was captured using high-speed photography to study their effect on the aforementioned interaction. Glass, PET-G. and aluminum having specific roughness were fabricated using laser and chemical etching. Atomization (water drop splitting into smaller droplets and ejecting from the surface) has been observed at different rates for all frequencies. A relation between the amplitude of the vibration and the rate of atomization was found. The effect of varying frequencies and surface roughness has also been documented.

No description available.

In an increasingly data-driven society, sensors and actuators are the bridge between the physical world and the world of "data." Electroacoustic transducers convert acoustic energy into electrical energy (or vice versa), so it can be interpreted as data. Piezoelectric materials are often used for transducer manufacturing, and recent advancements in additive manufacturing have enabled this material to take on complex geometric forms with micro-scale features. This work advances the additive manufacturing of piezoelectric materials by developing a model for predictive success of complex 3D printed geometries in Mask Image Projection-Stereolithography (MIP-SL) by accounting for mechanical wear on Polydimethylsiloxane (PDMS). This work proposes a framework for the rapid manufacture of 3D printed transducers, adaptable to a multitude of transducer element forms. Using the print model and transducer framework, latticed hydrophone elements are designed and tested, showing evidence of selectively tunable sensitivity, resonance, and directivity pattern. These technology advancements are extended to enable a workflow for users to input polar coordinates and receive an acoustic element of a continuously tuned directivity pattern. Investigation into customer problem spaces via tech-push methods are adapted from the NSF's Lean Launchpad to reveal insight to the problems faced in hydrophone applications and other neighboring problem spaces. / Master of Science / In an increasingly data-driven world, sensors are the bridge between the physical world and the world of "data." The better the sensor; the better the data. Electroacoustic transducers are sensors that convert acoustic sound energy into electrical energy or vice versa. These are observed in the world around us as microphones, speakers, ultrasound devices, and more. In the early 1900's, piezoelectric materials became one of the dominant methods for transducer creation, and recent advancements in additive manufacturing have enabled this material to take on highly complex geometric forms with micro-scale feature sizes. Further advancements to additive manufacturing of piezoelectric materials are contributed through development of a model for predicting the success of complex 3D printed geometries in an Mask Image Projection-Stereolithography (MIP-SL) by accounting for mechanical wear on the Polydimethylsiloxane (PDMS) print window. This work proposes a framework for the rapid manufacture of 3D printed transducers, adaptable to a multitude of element forms. Using the developed print model and transducer framework, latticed hydrophone elements are designed and tested, showing evidence of selectively tunable sensitivity, resonance and beampattern. The advancements in technology are extended to enable a workflow for users to input polar coordinates and receive an acoustic element of continuously tuned beampattern. Investigation into customer problem spaces via tech-push methods are adapted from NSF's Lean Launchpad and reveals great insight to the problems faced in hydrophone applications and other neighboring industry spaces.