Small Electrical, Mechanical, and Biomechanical Systems of Electromagnetic Radiation

Abstract

This thesis presents novel solutions to certain emerging problems related to electrically small radiating systems and antennas for effectively increasing the radiation efficiency and/or bandwidth of physically small antennas radiating at low frequencies. The thesis introduces the concept of fragmented antennas for the first time. It also provides a completely novel solution for implementation of mechanical antennas with frequency multiplication and phase modulation capabilities for the first time. These concepts are borrowed to develop mechano-electromagnetic radio concept for biological cells to explain how communication can occur in community of cells. The proposed mechanical antenna provides unique capabilities for communication at very-low frequency band (3-30 kHz) and lowers. In mechanical antennas, the radiation is mainly induced through accelerating (rotating) electric charges or permanent magnets by means of fast electric motors. This work presents a novel phase modulation and frequency multiplication scheme for radiation at frequencies up to seven time rotation frequency of their mechanical motor and at the same time provides phase modulation capability. This is done by incorporating two pairs of orthogonal bow-tie shape high-μ magnetic material plates through which super magnetic bar is rotated by a fast electric motor. By moving the angular position of the magnetic plates, it is shown that the phase and amplitude of the EM signal can be modulated. This thesis also reports on the feasibility of formation of an electrically large antenna at low frequencies using a number of miniaturized antennas through electromagnetic coupling for achieving high bandwidth. The proposed fragmented antenna system is intended for a linear flight formation of small UAVs carrying individual antennas. Inductively end-loaded folded dipole antennas are used as the individual antenna that can provide radiation at the desired frequency over a narrow bandwidth. The overall dimensions and the total mass of the individual elements are 12×10×10cm (0.096λ_0× 0.08λ_0× 0.08λ_0 at 240MHz) and 18g, respectively. Each miniaturized antenna can only provide 2.4 MHz (~1%) bandwidth and 25 Ω input impedance. It is shown that a cluster of three of such elements operating in the vicinity of each other, the center element can provide 18.4 MHz bandwidth (an improvement of 770%) through inductive coupling while the other two elements are loaded with optimal reactive elements. The fundamentals of operation of embedded radios within cellular structures and biofilms is based on mechanical antennas. Certain bacterial cells within their biofilms are equipped with elastic helical fibers called amyloid fibrils which pose permanent electric dipole. We propose that the cells transmit electromagnetic (EM) signal to their surrounding environment through mechanical vibration of these fibrils. Different vibrational modes associated with fibrils including cantilever beam mode, longitudinal spring vibrational mode, and transverse spring modes are investigated indicating potential EM signaling within kHz-MHz, GHz, and sub-THz ranges, respectively. A novel and theoretical Multiphysics model based on coupled system of electrical and mechanical structures is also proposed to study the impact of this signaling on crowd of fibrils in a biofilm sample. Next, to demonstrate the advantage of EM-based communication, using communication channel theory, we have compared performance of EM signaling with its biochemical counterpart (quorum sensing) and shown that EM signaling provides much higher data rate, 5 to 7 orders of magnitude, and over much longer ranges. Thus, it could be potentially more efficient and a preferred method for communication among cells.