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Technological advances require novel solutions for contactless energy transfer. Many engineering applications require unique approaches to power electrical components without using physical wires. In the past decade, awareness of the need to wirelessly power electrical components spawned many forays into the field of wireless power transfer (WPT). WPT techniques include capacitive energy transfer, electromagnetic inductive power transfer, electromagnetic radiative power transfer, electrostatic induction, and acoustic energy transfer. Acoustic energy transfer (AET) has many advantages over other methods. These advantages include lower operating frequency, shorter wavelengths enabling the use of smaller sized receiver and transmitter, extended transmitter-to-receiver distance therefore more manageable design constraints, achieving lower attenuation, higher penetration depth, and no electromagnetic losses. Most AET systems operate in the ultrasonic frequency range and are more commonly referred to as ultrasonic acoustic energy transfer (UAET) systems. Through-wall UAET systems are constructed of a transmitter bonded to a transmission elastic layer, which in turn is bonded to a receiver. The transmitter and receiver layers are constructed of a piezoelectric material. Piezoelectric materials behave according to the piezoelectric effect, which is when a material generates an electric charge in response to mechanical strain. The transmitter utilizes the reverse of the piezoelectric effect. A sinusoidal input voltage is applied to the transmitter, inducing vibrations in the transmitter. The vibration-induced acoustic waves emanating from the transmitter travel through the initial bonding layer, the transmission layer, and the final bonding layer to the receiver. In turn, the acoustic waves cause the receiver to deform and undergo strain. This induces a flow of charge in the receiver, which is an electric current. The receiver feeds current to a resistive load. In this manner, energy is acoustically transferred between two transducers without wires. The performance of UAET systems can be evaluated based on power transfer efficiency, voltage magnification, and input admittance. UAET systems require extensive modeling before experimental assembly can be attempted. The analytical models of UAET are either based on the mechanics of the constitutive relations of piezoelectricity and solid mechanics or using equivalent circuit methods. The equivalent circuit method approximates the physics of the UAET system with electrical assumptions. The mechanics-based method is the most comprehensive description of the physics of all the intermediate layers in a UAET system. The mechanics-based method has been based on the assumption that the UAET system is operated in the thickness mode of vibration, i.e., piston-like vibration mode where the transmitter and receiver disks vibrate only in the thickness direction. This poses an issue for disks with aspect ratios between 0.1 and 20 because the piezoelectric transducers vibrate in both the radial and thickness modes. In addition to this assumption, most of the works on UAET models only have accounted for the piezoelectric and transmission layers. The effects of the bonding layers were not considered. Bonding the piezoelectric layers to the transmission layer introduces epoxy material with mechanical properties that are not accounted for. The epoxy layers are extra barriers to the transmission that introduce attenuation and alter the vibrational and acoustical behaviors of the UAET system. Investigations into UAET commonly focus on metal through-wall applications. Alternate transmission layer materials are not investigated and the impact of varying mechanical properties on the performance of a through-wall UAET system has not been comprehensively studied. Even with the metal transmission layers, the impact of the metal thickness has not been extensively investigated thoroughly. This work addresses the issues of the thickness-mode assumption in UAET modeling, the effects of epoxy layers, the impacts of the metal layer geometry, and the performance of UAET systems with alternate transmission layer materials. Particularly, (1) we showed that the thickness-mode assumption, that has been used in the UAET modeling leads to inaccurate results. (2) We modified the available acoustic electro- elastic theoretical modeling to include the effects of radial modes as well as the epoxy bonding layers. (3) We showed that the geometry of the elastic/metal layer requires optimization for peak system efficiency. (4) The results show that using alternate transmission layer materials impacts the performance of UAET systems. The results of this work were investigated using an improved 5-layer analytical model and finite element modeling in COMSOL Multiphysics. Master of Science Wireless power transfer (WPT) is an innovative solution to the problem of powering sophisticated technological applications. Such instances include the powering of implanted medical devices, recharging inaccessible sensor networks, and wireless powering of components in sealed containers. Acoustic energy transfer (AET) is a feasible WPT method that addresses these needs. AET is based on the propagation of acoustic waves to a piezoelectric receiver which converts the vibrations caused by incident acoustic waves into electrical energy. Most AET systems operate in the ultrasonic frequency range, and so AET can also be referred to as ultrasonic acoustic energy transfer (UAET). Through-wall UAET systems are constructed from a transmitter that is bonded to a transmission elastic layer. The transmission layer is bonded to a receiver. The transmitter and receiver are made of a piezoelectric material. This thesis addresses the modeling process of through-wall UAET systems. In previous works, the fundamental assumption has been that such systems vibrate purely in the thickness mode. Additionally, other investigations did not comprehensively analyze the effects of the bonding layers, ascertain the performance of non-metal transmission layers, or provide practical insight on the effect of the resistive loading on such systems. This work addresses all these issues with a mathematical framework and finite element modeling results.

Energy efficient appliances and devices are becoming increasingly necessary as emissions from electricity production continue to increase the severity of global warming. Many of such appliances have not been substantially redesigned since their creation in the early 1900s. One device in particular which has arguably changed the least and consumes the most energy during use is the electric clothes dryer. The common form of this technology in the United States relies on the generation of thermal energy by passing electrical current through a metal. The resulting heat causes liquid within the clothing to evaporate where humid air is ejected from the control volume. While the conversion of energy from electrical to thermal through a heating element is efficient, the drying characteristics of fabrics in a warm humid environment are not, and much of the heat inside of the dryer does not perform work efficiently. In 2016, researchers at Oak Ridge National Laboratory in Knoxville, Tennessee, proposed an alternative mechanic for the drying of clothes which circumvents the need for thermal energy. This method is called direct-contact ultrasonic clothes drying, utilizing atomization through direct mechanical coupling between mesh piezoelectric transducers and wet fabric. During the atomization process, vertical oscillations of a contained liquid, called Faraday excitations, result in the formation of standing waves on the liquid surface. At increasing amplitudes and frequencies of oscillation, wave peaks become extended and form "necks" connecting small secondary droplets to the bulk liquid. When the oscillation reaches an acceleration threshold, the droplet momentum is sufficient to break the surface tension of the neck and enable the droplets to travel away from the liquid. For smaller drops where surface tension is high, a larger magnitude of acceleration is needed to reach the critical neck lengths necessary for droplet ejection. The various pore sizes within the many fabrics comprising our clothing results in many sizes of droplets retained by the fabric, affecting the rate of atomization due to the differences in surface tension. In this study, we will investigate the physical processes related to the direct contact ultrasonic drying process. Beginning with the electrical actuation of the transducer used in the world's first prototype dryer, we will develop an electromechanical model for predicting the resulting deformation. Various considerations for the material properties and geometry of the transducer will be made for optimizing the output acceleration of the device. Next, the drying rates of fabrics in contact with the transducer will be modeled for identification of parameters which will facilitate timely and energy efficient drying. This task will identify the first ever mechanically coupled drying equation for fabrics in contact with ultrasonic vibrations. The ejection rate of the water atomized by the transducer and passed through microchannels to facilitate drying will then be physically investigated to determine characteristics which may improve mass transport. Finally, future considerations and recommendations for the development of ultrasonic drying will be made as a result of the insight gained by this investigation. Doctor of Philosophy Energy efficient appliances and devices are becoming increasingly necessary as emissions from electricity production continue to increase the severity of global warming. Many of such appliances have not been substantially redesigned since their creation in the early 1900s. One device in particular which has arguably changed the least and consumes the most energy during use is the electric clothes dryer. The common form of this technology in the United States relies on the generation of thermal energy by passing electrical current through a metal. The resulting heat causes liquid within the clothing to evaporate where the humid air is ejected from the control volume. While the conversion of energy from electrical to thermal through a heating element is efficient, the drying characteristics of fabrics in a warm humid environment are not, and much of the heat inside of the volume does not perform drying as efficiently as possible. In 2016, researchers at Oak Ridge National Laboratory in Knoxville, Tennessee, proposed an alternative mechanism for the drying of clothes which circumvents the need for thermal energy. This method is called direct-contact ultrasonic clothes drying, and utilizes a vibrating disk made of piezoelectric and metal materials to physically turn the water retained in clothing into a mist, which can be vented away leaving behind dry fabric. This method results in the water leaving the fabric at room temperature, rather than being heated, which bypasses the need for a substantial amount of energy to convert from the liquid to gas phase. The first ever prototype dryer shows the potential of being twice as efficient as conventional dryers. This investigation is based around improving the device atomizing the water within the clothing, as well as understanding physical processes behind the ultrasonic drying process. These tasks will be conducted through experimental measurements and mathematical models to predict the behavior of the atomizing device, as well as computer software for both the parameters experimentally measured, and items which cannot be measured such as the flow in very small channels. The conclusions of this study will be recommendations for the future development of direct contact ultrasonic drying technology.

Smart materials are intelligent materials that change their structural, chemical, mechanical, or thermal properties in response to an external stimulus such as heat, light, and magnetic and electric fields. With the increase in usage of smart materials in many sensitive applications, the need for a remote, wireless, efficient, and biologically safe stimulus has become crucial. This dissertation addresses this requirement by using high intensity focused ultrasound (HIFU) as the external trigger. HIFU has a unique capability of maintaining both spatial and temporal control and propagating over long distances with reduced losses, to achieve the desired response of the smart material. Two categories of smart materials are investigated in this research; shape memory polymers (SMPs) and piezoelectric materials. SMPs have the ability to store a temporary shape and returning to their permanent or original shape when subjected to an external trigger. On the other hand, piezoelectric materials have the ability to convert mechanical energy to electrical energy and vice versa. Due to these extraordinary properties, these materials are being used in several industries including biomedical, robotic, noise-control, and aerospace. This work introduces two novel concepts: First, HIFU actuation of SMP-based drug delivery capsules as an alternative way of achieving controlled drug delivery. This concept exploits the pre-determined shape changing capabilities of SMPs under localized HIFU exposure to achieve the desired drug delivery rate. Second, solving the existing challenge of low efficiency by focusing the acoustic energy on piezoelectric receivers to transfer power wirelessly. The fundamental physics underlying these two concepts is explored by developing comprehensive mathematical models that provide an in-depth analysis of individual parameters affecting the HIFU-smart material systems, for the first time in literature. Many physical factors such as acoustic, material and dynamical nonlinearities, acoustic standing waves, and mechanical behavior of materials are explored to increase the developed models' accuracy. These mathematical frameworks are designed with the aim of serving as a basic groundwork for building more complex smart material-based systems under HIFU exposure. Doctor of Philosophy Smart materials are a type of intelligent materials that have the ability to respond to external stimuli such as heat, light, and magnetic fields. When these materials respond, they can change their structural, thermodynamical, mechanical or chemical nature. Due to this extraordinary property, smart materials are being used in many applications including biomedical, robotic, space, microelectronics, and automobile industry. However, due to increased sensitivity and need for safety in many applications, a biologically safe, wireless, and efficient trigger is required to actuate these materials. In this dissertation, sound is used as an external trigger to actuate two types of smart materials: shape memory polymers (SMPs) and piezoelectric materials. SMPs have an ability to store a temporary (arbitrarily deformed) shape and return to their permanent shape when exposed to a trigger. In this dissertation, focused sound induced thermal energy acts as a trigger for these polymers. A novel concept of focused ultrasound actuation of SMP-based drug delivery capsules is proposed as a means to solve some of the challenges being faced in the field of controlled drug delivery. Piezoelectric materials have an ability to generate electric power when an external mechanical force is applied and vice versa. In this study, sound pressure waves supply the external force required to produce electric current in piezoelectric disks, as a method for achieving power transfer wirelessly. This study aims to solve the current problem of low efficiency in acoustic power transfer systems by focusing sound waves. This dissertation addresses the fundamental physics of high intensity focused ultrasound actuation of smart materials by developing comprehensive mathematical models and systematic experimental investigations, that have not been performed till now. The developed models enable an in-depth analysis of individual parameters including nonlinear material behavior, acoustic nonlinearity and resonance phenomena that affect the functioning of these smart systems. These mathematical frameworks also serve as groundwork for developing more complex systems.