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.

The hygroscopic and electrical resistance characteristics of lithium chloride are investigated. Then an evaluation is made of the lithium chloride characteristics that would be suitable in development of a dew point hygrometer with measurement accuracy of + 0. 3 c. The development of a 12 volt battery-powered hygrometer is presented with circuit details and performance characteristics. Lithium chloride phase transition hygrometers tend to oscillate under certain conditions. A damping control is presented as part of the circuit details and recordings of the response characteristics and effectiveness of damping are presented showing effective control of the oscillations with a wide range of humidity transients.

<p>Each year, over 13,000 people in the United States die from a primary malignant brain tumor. Currently, primary BTs are treated most commonly by surgery, radiotherapy, and systemic chemotherapy, though each of these methods carries a risk of complications or acute side effects.</p><p>Ultrasound hyperthermia has been investigated as way to open the blood-brain barrier for improved chemotherapeutic drug delivery, but previous methods have involved either invasively removing skull bone via surgery or non-invasively dealing with the high ultrasound attenuation, reflection, and phase aberration resulting from the skull and its variable thickness. Dual-mode ultrasound transducers for image-guided therapy have also been investigated for several applications; in some instances, phased arrays are ideal, allowing control over the ultrasound energy deposition pattern and inherent spatial registration between imaging, treatment, and monitoring.</p><p>Additionally, thermosensitive liposomes can be configured to encapsulate drugs and actively target regions of tumor angiogenesis. When used in combination with localized hyperthermia, thermosensitive liposomes can provide targeted control of drug release that may enhance chemotherapeutic efficacy in many clinical settings. Meanwhile, catheter devices and endovascular techniques are used by interventional neuroradiologists to treat various intracranial diseases, including intracranial aneurysm and dural venous sinus thrombosis. These procedures can be extended to the treatment of intracranial tumors (advancement of a 5 Fr catheter as far as the frontal portion of the superior sagittal sinus has been demonstrated).</p><p>The objective of the work presented in this dissertation was the realization of a dual-mode catheter transducer for a minimally-invasive, vascular approach to deliver localized, image-guided ultrasound hyperthermia to an intracranial tumor target. Toward this end, a series of prototype ultrasound transducers were designed, simulated, built, and tested for imaging and therapeutic potential.</p><p>Two 14-Fr phased-array prototypes were built with PZT-5H ceramic and tested for real-time 3D intracranial imaging and focused-beam hyperthermia capability. These were able to visualize the lateral ventricles and Circle of Willis in a canine model, and generate a temperature rise over 4&deg;C at a 2-cm focal distance in excised tissue.</p><p>Single-channel intravascular ultrasound (IVUS) coronary imaging catheters as small as 3.5 Fr were then considered as a construction template; several possible transducer apertures were simulated before fabricating prototypes with PZT-4. The transducers exhibited a dual-frequency response, due to the presence of thickness-mode and width-mode resonances. A thermal model was developed to estimate the +4&deg;C thermal penetration depth for a given transducer aperture, predicting an effective therapeutic range of up to 12 mm with a 5 × 0.5 mm aperture.</p><p>A 3.5-Fr commercial mechanical IVUS catheter was retrofitted with a PZT-4 transducer and tested for 9-MHz imaging performance in several animal studies, successfully visualizing anatomical structures in the brain and navigating a minimally-invasive vascular pathway toward the brain. An identical PZT-4 transducer was used to build a 3.3-MHz therapy prototype, which produced a temperature rise of +13.5&deg;C at a depth of 1.5 mm in live xenograft brain tumor tissue in the mouse model.</p><p>These studies indicate that a minimally-invasive catheter transducer can be made capable of visualizing brain structures and generating localized hyperthermia to trigger drug release from thermosensitive liposomes in brain tumor tissue.</p> / Dissertation

<p>Piezoelectric micromachined ultrasound transducer (pMUT) two-dimensional (2D) arrays have been proposed as an alternative to conventional bulk-PZT thickness-mode transducers for high frequency, forward-looking, catheter-based ultrasound imaging of the cardiovascular system. The appeal of pMUTs is based on several key advantages over conventional transducer technologies, including high operational frequencies, small element size, and low cost due to their microelectromechanical system (MEMS) silicon-based fabrication. While previous studies have demonstrated acoustic performance characteristics suitable for ultrasound image formation, pulse-echo B-mode imaging of tissue and tissue-like phantoms using 2D pMUT arrays small enough for forward-looking catheter-based applications have been demonstrated only at Duke University by Dausch et al.</p><p>Having demonstrated the suitability of 2D pMUT arrays for tissue imaging, an important step is to demonstrate effective design control. The frequency of operation is a fundamental component of transducer design. Previous modeling efforts for pMUT vibration have used classical/Kirchoff thin plate theory (CPT) or Mindlin thick plate theory, however pMUTs with geometric dimensions similar to those explored here, have not been modeled with experimental comparison to physical devices.</p><p>It is hypothesized that the frequency of vibration of pMUTs can be predictively modeled based on experimental data from various pMUT configurations. Experimental frequency results were acquired and used to develop an empirical model based on a modified Mindlin thick plate theory. This dissertation presents the development of the frequency design theory culminating in a set of predictive design equations for the frequency of vibration of 2D pMUT arrays aimed at improving their use in high-frequency, forward-looking, catheter-based ultrasound imaging applications.</p> / Dissertation

The piezoelectric transducer for vibration-energy harvesting is constructed of a piezoelectric layer, bottom electrode and a top electrode. In order to obtain an appropriate transducer for the low-frequency operating; environmentally-friendly and long-term, the flexible substrate, the piezoelectric layer, and the additional mass-loading (tip mass) have been investigated thoroughly. This study investigates the feasibility of a high-performance ZnO and AlN based piezoelectric transducer for vibration-energy harvesting applications. Firstly, the piezoelectric transducer is constructed of a Cu/ZnO/ITO/PET structure. Both scanning electron microscopy and X-ray diffraction indicate that, among the favorable characteristic of the ZnO piezoelectric film include a rigid surface structure and a high c-axis preferred orientation. Hence, an open circuit voltage of 1.87 V for the ZnO piezoelectric transducer at a vibration frequency of 100 Hz is obtained by an oscilloscope. After rectifying and filtering, the output power of the generator exhibits an available benefit of 0.07 £gW/cm2 with the load resistance of 5 M£[. Secondly, this investigation introduces novel means of integrating high-performance piezoelectric transducers using single-sided ZnO and AlN films with a flexible stainless steel substrate (SUS304). Hence, the SUS304 substrate exhibits the long-term stability under vibration. The single-sided ZnO and AlN transducers are deposited on the SUS304 substrate at a temperature of 300 oC by an RF magnetron sputtering system. Scanning electron microscopy and X-ray diffraction of piezoelectric films reveal a rigid surface structure and a high c-axis-preferred orientation. A mass loading at the front-end of the cantilever is critical to increase the amplitude of vibration and the power generated by the piezoelectric transducer. The open circuit voltage of the single-sided ZnO power generator is 10.5 V. After rectification and filtering through a capacitor with a capacitance of 33 nF, the output power of the single-sided ZnO generators exhibited a specific power output of 1.0 £gW/cm2 with a load resistance of 5 M£[. Finally, this investigation fabricates double-sided piezoelectric transducers for harvesting vibration-power. The double-sided piezoelectric transducer is constructed by depositing piezoelectric thin films on both the front and the back sides of SUS304 substrate. The titanium (Ti) and platinum (Pt) layers were deposited using a dual-gun DC sputtering system between the piezoelectric thin film and the back side of the SUS304 substrate. Scanning electron microscopy and X-ray diffraction of piezoelectric films reveal a rigid surface structure and highly c-axis-preferring orientation. The maximum open circuit voltage of the double-sided ZnO power transducer is approximately 18 V. After rectification and filtering through a 33 nF capacitor, a specific power output of 1.3 £gW/cm2 is obtained from the double-sided ZnO transducer with a load resistance of 6 M£[. The variation of the power output of ¡Ó0.001% is obtained after 24-hour continuous test. The maximum open circuit voltage of the double-sided AlN power transducer is approximately 20 V. After rectification and filtering through a 33 nF capacitor, a specific power output of 1.462 £gW/cm2 is obtained from the double-sided AlN transducer with a load resistance of 7 M£[.

We build a two-pass Mandarin Automatic Speech Recognition (ASR) decoder on mobile device (PDA). The first-pass recognizing base syllable is implemented by discrete Hidden Markov Model (HMM) with time-synchronous, tree-lexicon Viterbi search. The second-pass dealing with language model, pronunciation lexicon and N-best syllable hypotheses from first-pass is implemented by Weighted Finite State Transducer (WFST). The best word sequence is obtained by shortest path algorithms over the composition result. This system limits the application in travel domain and it decouples the application of acoustic model and the application of language model into independent recognition passes. We report the real-time recognition performance performed on ASUS P565 with a 800MHz processor, 128MB RAM running Microsoft Window Mobile 6 operating system. The 26-hour TCC-300 speech data is used to train 151 acoustic model. The 3-minute speech data recorded by reading the travel-domain transcriptions is used as the testing set for evaluating the performances (syllable, character accuracies) and real-time factors on PC and on PDA. The trained bi-gram model with 3500-word from BTEC corpus is used in second-pass. In the first-pass, the best syllable accuracy is 38.8% given 30-best syllable hypotheses using continuous HMM and 26-dimension feature. Under the above syllable hypotheses and acoustic model, we obtain 27.6% character accuracy on PC after the second-pass.

With the gain in momentum of the structural health monitoring field in the last two decades, the popularity of ultrasonic nondestructive testing (NDT) has grown. However, ultrasonic NDT requires an expert to perform the testing and can be time consuming and costly when measured wave patterns in testing become extremely complex. A computer simulation of these tests can be utilized as a guide during actual evaluations or as a tool to train technicians. Presented in this dissertation is the development of models which simulate such acoustic phenomena as may arise in NDT. These models were developed using the distributed point source method (DPSM) for its proven capability to represent ultrasonic fields.Four sets of boundary conditions that arise from different types of commonly used acoustic transducers are modeled, enabling the visualization of the ultrasonic fields produced by the transducers. The transducer models exhibit good agreement with existing analytical solutions.In addition, the effect of a small cavity located at or near the focal point of an acoustic microscope is discussed. For this application the DPSM technique is modified so that inversion of a large global matrix is avoided, significantly improving the computational efficiency. The model shows that, as the pressure goes to zero, the velocity increases at the location of a cavity. Simulations demonstrate that the microscope is able to sense changes in position of the cavity by variations in the measured ratio of reflected to incident acoustic force.The field generated by an interferometric acoustic microscope is also presented. Qualitative agreement between the DPSM model and the experimental results of fields generated in a homogeneous fluid are obtained for a three-element lens. In the presence of a solid interface, the pressure on the edges of a converging beam near the fluid-solid interface is greater for a three-element lens than for single-element lens. A multi-element lens is also shown to exhibit oscillations in the pressure slightly above the interface.

No description available.

The scanning tunneling microscope (STM) based on quantum tunneling can attain atomic-scale spatial resolution and help elucidate a wealth of phenomena in the microscopic world. However a limitation in scanning tunneling microscopy is the low temporal resolution due to readout circuit frequency rolloff at a few kHz. This limitation can be overcome by using downmixing directly in the tunneling junction. With this technology we measure the high frequency vibrational modes (~ 1 MHz) of MEMS doubly-clamped beams and explore the implication of STM downmixing for nanomechanics.

abstract: "Sensor Decade" has been labeled on the first decade of the 21st century. Similar to the revolution of micro-computer in 1980s, sensor R&D; developed rapidly during the past 20 years. Hard workings were mainly made to minimize the size of devices with optimal the performance. Efforts to develop the small size devices are mainly concentrated around Micro-electro-mechanical-system (MEMS) technology. MEMS accelerometers are widely published and used in consumer electronics, such as smart phones, gaming consoles, anti-shake camera and vibration detectors. This study represents liquid-state low frequency micro-accelerometer based on molecular electronic transducer (MET), in which inertial mass is not the only but also the conversion of mechanical movement to electric current signal is the main utilization of the ionic liquid. With silicon-based planar micro-fabrication, the device uses a sub-micron liter electrolyte droplet sealed in oil as the sensing body and a MET electrode arrangement which is the anode-cathode-cathode-anode (ACCA) in parallel as the read-out sensing part. In order to sensing the movement of ionic liquid, an imposed electric potential was applied between the anode and the cathode. The electrode reaction, I_3^-+2e^___3I^-, occurs around the cathode which is reverse at the anodes. Obviously, the current magnitude varies with the concentration of ionic liquid, which will be effected by the movement of liquid droplet as the inertial mass. With such structure, the promising performance of the MET device design is to achieve 10.8 V/G (G=9.81 m/s^2) sensitivity at 20 Hz with the bandwidth from 1 Hz to 50 Hz, and a low noise floor of 100 ug/sqrt(Hz) at 20 Hz. / Dissertation/Thesis / M.S. Electrical Engineering 2013