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Title:Acoustically driven piezoelectric radiating elements
Author(s):Breen, Michael
Director of Research:Gong, Songbin
Doctoral Committee Chair(s):Gong, Songbin
Doctoral Committee Member(s):Bernhard, Jennifer; Lee, Minjoo Lawrence; Zhou, Jin
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Piezoelectric Transducer, Acoustic Antenna, MEMS, VLF, LF
Abstract:This work reports the development of novel acoustically driven, lead zirconate titanate (PZT) piezoelectric radiators for very low frequency (VLF: 3-30 kHz) and low frequency (LF: 30-300 kHz) communication. The low propagation loss of electromagnetic radiation below 1 MHz exhibits great potential for low-power, long-range communication systems. However, the fundamental reduction in efficiency as antenna size decreases below a wavelength (30 m at 1 MHz) has made portable communication systems in the VLF and LF ranges impractical. A paradigm shift from electrical antennas to acoustically driven antennas operating at resonant wavelengths up to 105 times smaller than electrical antennas offers great potential for portable, low-power communication systems in the very low frequency and low frequency range. In this dissertation, a theoretical analysis is presented for the primary methods of implementing acoustically driven radiating elements, investigating both the radiation and matching efficiencies comprising the total antenna efficiency. Radiation from the linear movement of unipolar charge driven both piezoelectrically and capacitively, the piezoelectrically actuated rotation of fixed dipole charges, and from alternating dipoles inside strain driven piezoelectrics are all presented and analyzed in terms of their design parameters and fundamental challenges. Unipolar and fixed dipolar charge-based approaches are unable to sustain sufficient charge density to achieve efficient radiation due to electrical breakdown and charge decay respectively. The dynamic polarization flipping inside strain driven piezoelectric alternating dipole antennas (PADAs) circumvents the decay and breakdown complications of static charge approaches and is well suited to surpassing the efficiency of equivalent electrical antennas by multiple orders of magnitude. Here, a VLF PZT PADA is demonstrated which leverages a high piezoelectric coupling (d31 = 108 pC/N) and moderate quality factor (Q = 1340) to achieve an efficiency that surpasses that of similarly sized dipole antennas by more than 6000 times, significantly improving the portable VLF antenna state-of-the-art. The moderate Q allows the PADA to be directly modulated with bit rates up to 60 bit/s without the need for additional circuitry. However, despite the increased efficiency, the radiated power of the PADAs demonstrated to date remains limited for long-distance communication applications and significant improvements radiated power are required to approach commercial viability. The maximum radiated power of PADAs utilizing high Q, moderate permittivity materials, such as LiNbO3, have been limited by electrical field breakdown near the resonator due to large induced surface charge density. High coupling, high permittivity materials, such as PZT, offer increased field confinement and thus greater effective piezoelectric currents without breakdown. However, the diminished Q results in increased heat dissipation and a corresponding loss in radiation efficiency due to thermal nonlinearity. To overcome the power handling limitation of individual PADA elements, a PZT rod PADA is presented exhibiting enhanced efficiency and power handling compared to the initial PZT disk prototype. A thickness extensional mode using a higher coupling d33 mode is utilized to increase the PADA FoM and radiation efficiency. An eight-element proof of concept array is fabricated to demonstrate the potential of parallelism to bolster power handling and radiated power. The eight-element array exhibits a 17-fold increase in radiation efficiency and 5-fold increase in radiated field strength, demonstrating the potential of larger PADA arrays for extending communication ranges.
Issue Date:2020-05-01
Type:Thesis
URI:http://hdl.handle.net/2142/108111
Rights Information:Copyright 2020 Michael Breen
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05


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