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Carbonate reservoirs are usually diffcult to map and identify in seismic sections due to their complex structure, lithology and diagenetic frabrics. The Midland Basin, located in the Permian Basin of West Texas, is an excellent example of these complex carbonate structures. In order to obtain a better characterization and imaging of the carbonate buildups, an acoustic impedance inversion is proposed here. The resolution of the acoustic impedance is the same as the input seismic data, which is greatly improved with the addition of the low frequency content extracted from well data. From the broadband volume, high resolution maps of acoustic impedance distributions were obtained, and therefore the locations of carbonate buildups were easily determined. A correlation between acoustic impedance and porosity extracted from well data shows that areas with high acoustic impedance were correlated with low porosity values, whereas high porosities were located in areas of low acoustic impedance. Theoretical analyses were performed using the time-average equation and the Gassmann equation. These theoretical models helped to understand how porosity distributions affect acoustic impedance. Both equations predicted a decrease in acoustic impedance as porosity increases. Inversion results showed that average porosity values are 5% [plus or minus] 5%, typical for densely cemented rocks. Previous studies done in the study area indicate that grains are moderately to well-sorted. This suggests that time-average approximation will overestimate porosity values and the Gassmann approach better predicts the measured data. A comparison between measured data and the Gassmann equation suggests that rocks with low porosities (less than 5%) tend to have high acoustic impedance values. On the other hand, rocks with higher porosities (5% to 10%) have lower acoustic impedance values. The inversion performed on well data also shows that the fluid bulk modulus for currently producing wells is lower than in non-productive wells, (wells with low production rates for brine and hydrocarbons), which is consistent with pore fluids containing a larger concentration of oil. The acoustic impedance inversion was demonstrated to be a robust technique for mapping complex structures and estimating porosities as well. However, it is not capable of differentiating different types of carbonate buildups and their origin.

ABSTRACT In this study, the properties of the high impedance surface structure are studied. We proceed to design the low profile and miniature high impedance surface structure. In order to conform to the IC chips of RFID and reduce the influence of metal objects, we add a layer of electromagnetic band-gap (EBG) structure on the back of the antenna. The EBG behaves as a high impedance surface, similar to a perfect magnetic conductor. This property of the EBG structure is able to isolate the antenna and backside environment and reduce the metallic effect. In order to achieve the requirements of small size and low cost on RFID tag antenna, we design the miniature, low profile and low cost high impedance surface structure. In this study, we use the slots and chip capacitance to miniaturize the dimension. Both approaches can reduce the influence of metallic objects. Although using slots can reduce the metallic effect, it does not have the advantage of low profile. Using chip capacitor can miniaturize the dimension and reduce metallic effect effectively. It also has advantages of low profile, low cost and low sensitivity to the frequency of the tag antenna. Finally, the high impedance surface structures are fabricated and measured when they combine with the tag antenna attached to the metallic object. The measured results agree with simulated ones well.

This thesis proposes methodology to design a balun with imaginary impedance. Under given specification, including center frequency, size, output impedance, our methodology can be used to evaluate its feasibility of implementation using high-DK LTCC(Low Temperature Cofired Ceramic) process. We then extend the design to incorporate a filter, which can simplify the circuit to reduce the required components. An example of our design operating at 2.4 GHz is implemented. Its size is 1600¡Ñ800¡Ñ650 um3, showing significant miniature. The simulation and measurement results are shown to verify the effectiveness of our design.

<p>A theoretical approach to calculating impedance of metallicmagnetic/conductor layered structures is developed. Thefrequency range considered extends to the ferromagneticresonance region of soft magnetic films (of the order of 1GHz). The analysis includes the effects of screening of thehigh frequency fields by eddy currents as well as the dynamicsand relaxation of the magnetization of the ferromagneticsub-system. Analytical expressions for the impedance as afunction of frequency and material parameters and geometry ofmagnetic sandwich stripes are obtained. Two maincross-sectional layouts are considered: amagnetic/conductor/magnetic sandwich stripe with and withoutflux closure at the edges along the stripe length - with andwithout the magnetic film enclosing the conductor strip. Theimportance of good magnetic flux closure for achieving largespecific inductance gains and high efficiency at GHzfrequencies is emphasized.</p><p>The theoretical results obtained were used to design andanalyze magneticfilm inductors produced using iron nitridealloy films. Patterned sandwiches, consisting of two Fe-N filmsenclosing a conductor film made of Cu, were fabricated onoxidized Si substrates using lift-off lithography. Theinductors exhibited a 2-fold specific inductance enhancement at1 GHz. The magnetic contribution to the total flux in thenarrow devices was less then predicted theoretically, which wasattributed to hardening of the magnetic material at the edgesof the strip leading to incomplete flux closure. Material anddesign issues important for further improving the performanceof the devices are discussed.</p>

Thesis (M. Phil.)--University of Hong Kong, 1973. / Mimeographed.

Proposed research object aims to develop and implement the novel imaging technique to delineate tissue boundaries based on electrical impedance of tissues.

 There are two concentrations in this project. One is to explore the possibility to construct negative acoustic impedance by electronic techniques, and the other is to see whether such method can be utilized to build effective sound absorber using electromagnetic actuator (here we adopt the moving-coil loudspeaker as sample) with a shunt circuit. Our study begins with analytical analysis, and the result shows that it is impossible to gain independent control of basic acoustic impedance components (mass, stiffness and damping) by simple circuits. Two alternative designs are put forward as a compromise. One is the series circuit with NIC to simulate the negative acoustic impedance, and another is the series-parallel circuit with NIC. Theoretical prediction shows that we can indeed obtain broadband negative mass and local negative stiffness by these two types of circuits, and that we can achieve broadband noise control with simple electronic shunt circuits despite fact that completely independent control over each parameter is not possible. We argue that these conclusions represent significant technological and economic advantage worthy of further development. All analytical results are validated by experiments with satisfactory agreement. The sample loudspeaker with shunt circuit is tested with acoustic impedance tube. The rig consists of a DC powered op-amp circuit and a loudspeaker. An efficient Matlab code controls the excitation sound generation and data acquisition with AD/DA cards. Two typical and most interesting results are summarized here. In the first, a series type circuit with NIC is used to construct negative equivalent mass and local (banded in frequency domain) negative stiffness. We experimentally demonstrated that it is rather easy to reduce original mass of the loudspeaker to half of its original value and it could be reduced to almost zero. This is evidenced by a very flat sound absorption coefficient curve from 100 Hz to 1000 Hz. The second circuit is a series-parallel circuit. It’s an improved design from the first type. This type of circuit can, to a certain extent, decouple the stiffness and mass controls. The results show that we can reduce mass globally (in the frequency domain) and stiffness at low frequencies. The original mass of the sample loudspeaker is almost eliminated and the stiffness at low frequencies is reduced too. In terms of the spectrum of sound absorption coefficient, it manifests itself through a broadband absorption with prominent improvement in the low frequency region. Finally, potential applications for our designs are discussed. A tunable low frequency resonance absorber is designed. Prediction results point out that, by choosing the right parameters of the circuit, we can achieve 100% absorption at any given low frequency. Thin absorber is another potential application. With the same dimension, the performance of a thin absorber is much better than that of the standard sound absorption construction. A 90% noise absorption from 300Hz-600Hz and 50% absorption from 250Hz-1000Hz is achieved by our new design. The dimension can be further reduced in theory. Finally, a broad-band absorber with 50% or more absorption over 80Hz-1000Hz is demonstrated. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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One key element of underwater transducer design is the acoustic baffle. Acoustic baffles isolate a structure, such as a submarine hull, from noise and vibration produced by the active elements of the transducer and vice versa. Baffle materials must meet many conflicting requirements such as the need to be lightweight while providing high acoustic isolation. Currently Syntactic Acoustic Damping Material (SADM) is widely used as the primary acoustic baffle material. However, SADM baffles have many undesirable characteristics such as high density, poor machinability, high lead content and depth dependent acoustical behavior. The study of baffle materials is an under-represented area of sonar design. Most sonar transducer research focuses on the electrically active materials and their response to a variety of conditions. Relatively fewer studies have been devoted to understanding the effects of the supporting and baffle materials. This work considers the effects of the entire hydrophone system on the response while developing a method for aiding in proper system material selection. This was accomplished by first developing a model for a transducer's response in a variety of conditions. The response was validated with numerical finite-element models and experiments. Next, a generic model was developed that allows any number of layers with any material to be analyzed. This generic model is applied in concert with a material optimization method to aid in the selection of materials that will improve the transducer's response. The tools are finally applied to a simple real world problem to illustrate its strengths and weaknesses. / text