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- All Subjects: Electrical Engineering
- Genre: Masters Thesis
Description
ABSTRACT This work seeks to develop a practical solution for short range ultrasonic communications and produce an integrated array of acoustic transmitters on a flexible substrate. This is done using flexible thin film transistor (TFT) and micro electromechanical systems (MEMS). The goal is to develop a flexible system capable of communicating in the ultrasonic frequency range at a distance of 10 - 100 meters. This requires a great deal of innovation on the part of the FDC team developing the TFT driving circuitry and the MEMS team adapting the technology for fabrication on a flexible substrate. The technologies required for this research are independently developed. The TFT development is driven primarily by research into flexible displays. The MEMS development is driving by research in biosensors and micro actuators. This project involves the integration of TFT flexible circuit capabilities with MEMS micro actuators in the novel area of flexible acoustic transmitter arrays. This thesis focuses on the design, testing and analysis of the circuit components required for this project.
ContributorsDaugherty, Robin (Author) / Allee, David R. (Thesis advisor) / Chae, Junseok (Thesis advisor) / Aberle, James T (Committee member) / Vasileska, Dragica (Committee member) / Arizona State University (Publisher)
Created2012
Description
The reconfigurable intelligent surface (RIS) shown in this work is a programmable metasurface integrated with a dedicated microcontroller that redirects an impinging signal to the desired direction. Its characteristic allows the RIS to act as a mirror for microwave signals. Unlike a perfect electric conductor (PEC), the RIS has much more flexibility in redirecting signals. This work involves the measurement of a passive, fixed beam, 25x32 element mmWave RIS that operates at 28.5 GHz. Bistatic and monostatic measurement setups are both used to find the radar cross section (RCS) of the RIS. The process of creating the measurement setups and the final measurement results is discussed. The measurement setup is further characterized using the High-Frequency Structure Simulator (HFSS) software and the final measurement results are compared to analytical solutions computed using MATLAB. The first prototype of the RIS has a loss of 8.4 dB when compared to a PEC and is physically curved. There is also a side lobe at the boresight of the RIS board that is only 8 dB less than the main beam in best-case scenario. This curvature causes issues with the monostatic measurement because it changes the phase that arrives at the RIS. The second prototype of the RIS has only 5.84 dB of loss compared to PEC. This measurement setup behaves mostly as expected when comparing the measurement results to the analytical solutions and given the limitations of the setup. A collimating lens was used as a part of the setup which reflects part of the incoming signal. The edge of the lens also causes diffraction. These factors contribute to multipath interference arriving at the receive antenna and increases measurement error. The lens also creates unequal amplitude illumination across the surface of the RIS which changes the RCS pattern. Using the lens allows a more space-efficient setup while still obtaining relatively constant phase illuminating across the RIS board.
ContributorsTjahjadi, Brian (Author) / Trichopoulos, Georgios C (Thesis advisor) / Aberle, James T (Committee member) / Imani, Seyedmohammadreza F (Committee member) / Arizona State University (Publisher)
Created2022
Description
The micromotions (e.g. vibration, rotation, etc.,) of a target induce time-varying frequency modulations on the reflected signal, called the micro-Doppler modulations. Micro-Doppler modulations are target specific and may contain information needed to detect and characterize the target. Thus, unlike conventional Doppler radars, Fourier transform cannot be used for the analysis of these time dependent frequency modulations. While Doppler radars can detect the presence of a target and deduce if it is approaching or receding from the radar location, they cannot identify the target. Meaning, for a Doppler radar, a small commercial aircraft and a fighter plane when gliding at the same velocity exhibit similar radar signature. However, using a micro-Doppler radar, the time dependent frequency variations caused by the vibrational and rotational micromotions of the two aircrafts can be captured and analyzed to discern between them. Similarly, micro-Doppler signature can be used to distinguish a multicopter from a bird, a quadcopter from a hexacopter or a octacopter, a bus from a car or a truck and even one person from another. In all these scenarios, joint time-frequency transforms must be employed for the analysis of micro-Doppler variations, in order to extract the targets’ features.
Due to ample bandwidth, THz radiation provides richer radar signals than the microwave systems. Thus, a Terahertz (THz) micro-Doppler radar is developed in this work for the detection and characterization of the micro-Doppler signatures of quadcopters. The radar is implemented as a continuous-wave (CW) radar in monostatic configuration and operates at a low-THz frequency of 270 GHz. A linear time-frequency transform, the short-time Fourier transform (STFT) is used for the analysis the micro-Doppler signature. The designed radar has been built and measurements are carried out using a quadcopter to detect the micro-Doppler modulations caused by the rotation of its propellers. The spectrograms are obtained for a quadcopter hovering in front of the radar and analysis methods are developed for characterizing the frequency variations caused by the rotational and vibrational micromotions of the quadcopter. The proposed method can be effective for distinguishing the quadcopters from other flying targets like birds which lack the rotational micromotions.
Due to ample bandwidth, THz radiation provides richer radar signals than the microwave systems. Thus, a Terahertz (THz) micro-Doppler radar is developed in this work for the detection and characterization of the micro-Doppler signatures of quadcopters. The radar is implemented as a continuous-wave (CW) radar in monostatic configuration and operates at a low-THz frequency of 270 GHz. A linear time-frequency transform, the short-time Fourier transform (STFT) is used for the analysis the micro-Doppler signature. The designed radar has been built and measurements are carried out using a quadcopter to detect the micro-Doppler modulations caused by the rotation of its propellers. The spectrograms are obtained for a quadcopter hovering in front of the radar and analysis methods are developed for characterizing the frequency variations caused by the rotational and vibrational micromotions of the quadcopter. The proposed method can be effective for distinguishing the quadcopters from other flying targets like birds which lack the rotational micromotions.
ContributorsKashyap, Bharath Gundappa (Author) / Trichopoulos, Georgios C (Thesis advisor) / Balanis, Constantine A (Committee member) / Aberle, James T (Committee member) / Arizona State University (Publisher)
Created2018
Description
This thesis is a study of Bandwidth limitation of basestation power amplifier and its Doherty application. Fundamentally, bandwidth of a power amplifier (PA) is limited by both its input and output prematch networks and its Doherty architecture, specifically the impedance inverter between the main and auxiliary amplifier. In this study, only the output prematch network and the Doherty architecture follows are being investigated. A new proposed impedance inverter in the Doherty architecture exhibits an extended bandwidth compared to traditional quarterwave line.
Base on the loadline analysis, output impedance of the power amplifier can be represented by a loadline resistor and an output shunt capacitor. Base on this simple model, the maximum allowed bandwidth of the output impedance of the power amplifier can be estimated using the Bode-Fano method. However, since power amplifier is in fact nonlinear, harmonic balance simulation is used to loadpull the device across a broad range of frequencies. Base on the simulated large signal impedance at maximum power, the prematch circuitry can be designed. On a system level, the prematch power amplifier is used in Doherty amplifier. Two different prematch circuitries, T- section and shunt L methods are investigated along with their comparison in the Doherty architecture at both back off power and peak power condition. The last section of the thesis will be incorporating the proposed impedance inverter structure between the main and auxiliary amplifiers.
The simulated results showed the shunt L prematch topology has the least impedance dispersion across frequency. Along with the new impedance inverter structure, the 65% efficiency bandwidth improves by 50% compared to the original impedance inverter structure at back off power level.
Base on the loadline analysis, output impedance of the power amplifier can be represented by a loadline resistor and an output shunt capacitor. Base on this simple model, the maximum allowed bandwidth of the output impedance of the power amplifier can be estimated using the Bode-Fano method. However, since power amplifier is in fact nonlinear, harmonic balance simulation is used to loadpull the device across a broad range of frequencies. Base on the simulated large signal impedance at maximum power, the prematch circuitry can be designed. On a system level, the prematch power amplifier is used in Doherty amplifier. Two different prematch circuitries, T- section and shunt L methods are investigated along with their comparison in the Doherty architecture at both back off power and peak power condition. The last section of the thesis will be incorporating the proposed impedance inverter structure between the main and auxiliary amplifiers.
The simulated results showed the shunt L prematch topology has the least impedance dispersion across frequency. Along with the new impedance inverter structure, the 65% efficiency bandwidth improves by 50% compared to the original impedance inverter structure at back off power level.
ContributorsYang, Nick (Author) / Pan, George (Committee member) / Aberle, James T (Committee member) / Yu, Hongyu (Committee member) / Arizona State University (Publisher)
Created2014