Theoretical and Numerical Analysis of a Novel Electrically Small and Directive Antenna

Theoretical and Numerical Analysis of a Novel Electrically Small and Directive Antenna
Author: Jeffrey Elloian
Publisher:
Total Pages: 272
Release: 2014
Genre:
ISBN:

Abstract: Small antennas have attracted significant attention due to their prolific use in consumer electronics. Such antennas are highly desirable in the healthcare industry for imaging and implants. However, most small antennas are not highly directive and are detuned when in the presence of a dielectric. The human body can be compared to a series of lossy dielectric media. A novel antenna design, the orthogonal coil, is proposed to counter both of these shortcomings. As loop antennas radiate primarily in the magnetic field, their far field pattern is less influenced by nearby lossy dielectrics. By exciting two orthogonal coil antennas in quadrature, their beams in the H-plane constructively add in one direction and cancel in the other. The result is a small, yet directive antenna, when placed near a dielectric interface. In addition to present a review of the current literature relating to small antennas and dipoles near lossy interfaces, the far field of the orthogonal coil antenna is derived. The directivity is then plotted for various conditions to observe the effect of changing dielectric constants, separation from the interface, etc. Numeric simulations were performed using both Finite Difference Time Domain (FDTD) in MATLAB and Finite Element Method (FEM) in Ansys HFSS using a anatomically accurate high-fidelity head mesh that was generated from the Visible Human Project® data. The following problem has been addressed: find the best radio-frequency path through the brain for a given receiver position -- on the top of the sinus cavity. Two parameters: transmitter position and radiating frequency should be optimized simultaneously such that (i) the propagation path through the brain is the longest; and (ii) the received power is maximized. To solve this problem, we have performed a systematic and comprehensive study of the electromagnetic fields excited in the head by the aforementioned orthogonal dipoles. Similar analyses were performed using pulses to detect Alzheimer's disease, and on the femur to detect osteoporosis.

Electrically Small Loop Antenna Loaded by a Homogeneous and Isotropic Ferrite Cylinder -

Electrically Small Loop Antenna Loaded by a Homogeneous and Isotropic Ferrite Cylinder -
Author: D. V. Giri
Publisher:
Total Pages: 52
Release: 1973
Genre:
ISBN:

A theoretical treatment was developed for the problem of an electrically small loop antenna loaded by an infinitely long, homogeneous, isotropoc but lossy ferrite rod. The loop which carries a constant current was idealized to be a delta-function generator. An effective magnetic current (volts) is expressed explicitly in the form of an inverse Fourier integral. The contribution to the total current from the simple pole which can be associated with the surface wave is called the transmission current while the contribution from the branch cut giving rise to the radiated field is, correspondingly, the radiation current. Also, the asymptotic behavior of the current very near the delta-function source was investigated. Two values of electrical radii of the rod are considered and for one of the cases the magnetic current is plotted for a range of values of the permeability of the ferrite rod.

Research on electrically small antennas

Research on electrically small antennas
Author: Hans H. Meinke
Publisher:
Total Pages: 36
Release: 1962
Genre: Antennas (Electronics)
ISBN:

Research has shown that an improvement of the impedance behaviour of an antenna whose length is very small as compared to the wave length in free space, can be obtained by achieving a greater bandwidth of the antenna. A bandwidth enlargement of the antenna can be obtained by the effect of an additional radiation for the same input voltage. No additional radiation occurs for radiators whose height is smaller than 1/20 the wavelength in air and whose surrounding dielectric also does n t extend eyond its height. Additional radiation is obtained by using dielectric with antennas whose height is 1/20 to 1/10 of the wavelength in air. The additional radiation observed was very small. The use of dielectric caused an increase in the inductance and capacitance per unit length of the antenna which is considered as an inhomogeneous line. (Author).

Electrically Small Antenna Studies

Electrically Small Antenna Studies
Author: E. H. Newman
Publisher:
Total Pages: 43
Release: 1979
Genre:
ISBN:

This report summarizes the work on U.S. Army Research Office Grant No. DAAG29-76-C-0067 from 15 October 1975 to 14 October 1978. Three areas related to small antennas were investigated: wires in the presence of dielectrical ferrites, closely spaced thin wires, and small antenna location synthesis. Each of these areas resulted in a journal publication, which are included in the Appendixes. (Author).