Nowadays, there is a growing demand for high frequency-bandwidth mm-wave (30-300 GHz) electronic wireless transceiver systems to support applications such as high data-rate wireless communication and high resolution imaging. Such mm-wave systems are becoming more feasible due to the extreme transistor downscaling in silicon-based integrated circuits, which enabled densely-integrated high-speed elec- tronics operating up to more than 100 GHz with low fabrication cost. To further enhance system integrability, it is required to implement all wireless system compo- nents on the chip. Presently, the last major barrier to true System-on-Chip (SoC) realization is the antenna implementation on the silicon chip. Although at mm-wave frequencies the antenna size becomes small enough to fit on chip, the antenna performance is greatly deteriorated due the high conductivity and high relative permittivity of the silicon substrate. The negative e↵ects of the silicon substrate could be avoided by using a metallic reflecting surface on top of silicon, which e↵ectively isolates the antenna from the silicon. However, this approach has the shortcoming of having to implement the antenna on the usually very thin silicon oxide layer of a typical CMOS fabrication process (10’s of μm). This forces the antenna to be in a very close proximity (less than one hundredth of a wavelength) to the reflecting surface. In this regime, the use of conventional metallic reflecting surface for silicon shielding has severe e↵ects on the antenna performance as it tends to reduce the antenna radiation resistance resulting in most of the energy being absorbed rather than radiated. In this work, the use of specially patterned reflecting surfaces for improving on- chip antenna performance is investigated. By using a periodic metallic surface on top of a grounded substrate, the structure can mimic the behavior of a perfect mag- netic conductor, hence called Artificial Magnetic Conductor (AMC) surface. Unlike conventional ground plane reflecting surfaces, AMC surfaces generally enhance the radiation and impedance characteristics of close-by antennas. Based on this property, a ring-based AMC reflecting surface has been designed in the oxide layer for on-chip antennas operating at 94 GHz. Furthermore, a folded dipole antenna with its associ- ated planar feeding structures has been optimized and integrated with the developed ring-based AMC surface. The proposed design is then fabricated at KAUST clean- room facilities. Prototype characterization showed very promising results with good correlation to simulations, with the antenna exhibiting an impedance bandwidth of 10% (90-100 GHz) and peak gain of -1.4 dBi, which is the highest gain reported for on-chip antennas at this frequency band without the use of any external o↵-chip components or post-fabrication steps.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / SuperfÃcie de ouro modificada com as espÃcies 1,4-ditiano (1,4-dt) e 4- mercaptopiridina (pyS), foram estudadas neste trabalho. Para a realizaÃÃo desse estudo foram utilizadas as seguintes tÃcnicas eletroquÃmicas: polarizaÃÃo linear com eletrodo de disco rotatÃrio, voltametria cÃclica, voltametria de pulso diferencial, impedÃncia eletro-hidrodinÃmica e espectroscopia de impedÃncia eletroquÃmica. Outras tÃcnicas tambÃm deram suporte, tais como, microscopia de forÃa atÃmica (MFA), microscopia de superfÃcie por tunelamento (MST), espectroscopia RAMAN e microbalanÃa de quartzo (MBQ). Para as superfÃcies modificadas com a molÃcula 1,4-dt, foi observado a diminuiÃÃo do processo redox [Fe(CN)6]3-/4- com o aumento do tempo de imersÃo do eletrodo de ouro na soluÃÃo modificadora. Estes resultados sugerem que taxa de recobrimento da superfÃcie de ouro, com esta espÃcie, aumenta com o tempo de modificaÃÃo. Os resultados de impedÃncia eletro-hidrodinÃmica juntamente com as micrografias MFA e MST revelam que esta superfÃcie està parcialmente bloqueada apresentando defeitos sobre o filme formado. Os resultados de espectroscopia RAMAN sugerem que esses defeitos podem ser resultantes da adsorÃÃo das conformaÃÃes diferenciadas na forma de âcadeiraâ e âbarcoâ da molÃcula 1,4 dt. Por outro lado, os resultados eletroquÃmicos com as superfÃcies modificadas com a espÃcie pyS indicam um aumento do processo de transferÃncia de carga com o aumento do tempo de imersÃo do eletrodo de ouro na soluÃÃo modificadora. Este resultado sugere a perda do poder de cobertura para a superfÃcie de ouro modificada com esta espÃcie. Os resultados de MFA reforÃam os resultados anteriores para esta espÃcie demonstrando que esta superfÃcie apresenta maiores quantidade de defeitos para tempos mais longos de modificaÃÃo. As curvas de variaÃÃo de freqÃÃncia (ΔF) versus tempo de modificaÃÃo indicam um aumento de massa na superfÃcie de ouro modificada com a espÃcie 1,4-dt, enquanto que para a espÃcie pyS observa-se um processo de desorÃÃo, confirmando qualitativamente os resultados obtidos anteriores para estas duas molÃculas. / Modified gold surface with organosulfur species, 1,4-dithiane (1,4-dt) and 4- mercaptopyridine (pyS), was studied in this work. The study was carried out using the following electrochemical techniques: linear polarization with rotate disk electrode, cyclic voltammetry, differential pulse voltammetry, electrohydrodynamic impedance and electrochemical impedance spectroscopy. Other techniques also gave support, such as, atomic force microscopy (AFM), Scanning tunneling microscopy (STM), RAMAN spectroscopy and quartz crystal microbalance (QCM). For the modified gold surface with the 1,4-dt, it was observed the decrease of the redox-active [Fe(CN)6]3- species with the increase of the immersion time of the gold electrode in the modifier solution. These results suggest that the fractional coverage increases with the modification time. The electrohydrodynamic impedance results together with the MFA and MST results suggest that this surface is partially blocked presenting defects on the formed film. The RAMAN spectra suggest that those defects can be resulting of the adsorption of the different configuration of the modifier molecules (1,4-dt) on the surface ("trans" and "gauche"). The electrochemical results about the modified gold surfaces with the molecule pyS indicate an increase of the electron transfer process with the increase of the immersion time, which suggests the loss of the covering power on the modified gold surface with this species. The AFM results agree the previous results demonstrating that this surface presents larger amount of defects for longer modification times. The frequency curves variation (ΔF) versus the immersion time indicate a mass increase on the modified gold surface with the species 1,4-dt and a process desorption for the species pyS confirming the results obtained previously.

No description available.

Empirical models based on flow resistivity are commonly used to determine the bulk properties of porous sound absorbing materials. The bulk properties include the complex wavenumber and complex characteristic impedance which can be used directly in simulation models. Moreover, the bulk properties can also be utilized to determine the normal incidence sound absorption and specific acoustic impedance for sound absorbing materials of any thickness and for design of layered materials. The sound absorption coefficient of sound absorbing materials is measured in an impedance tube using wave decomposition and the measured data is used to determine the flow resistivity of the materials by least squares curve fitting to empirical equations. Results for several commonly used foams and fibers are tabulated to form a rudimentary materials database. The same approach is then used to determine the flow resistivity of compressed sound absorbing materials. The flow resistivities of the compressed materials are determined as a function of the compression ratio. Results are then used in conjunction with transfer matrix theory to predict the sound absorptive performance of layered compressed absorbers with good agreement to measurement.