טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentMorag Yahav
SubjectPerformance Bounds of Induction-Based Systems
Incorporating High-Frequency Effects
DepartmentDepartment of Electrical Engineering
Supervisor Assistant Professor Yoash Levron
Full Thesis textFull thesis text - English Version


Abstract

Induction power transfer and magnetic communication systems deliver power through coupled low-frequency magnetic fields, rather than by radiation. Induction power transfer is utilized in energy harvesting, wireless charging of electric vehicle, biomedical applications, and many more. Magnetic communication systems are used in two primary operation modes: the first is Near-Field Communication, where short-range communication is deliberately required as in wireless card payment, smartphone communication, and wireless body area networks. The second type is Through-the-Earth Communication, where data is transmitted from the surface of the earth to underground or underwater locations. In these applications, coil transducers are typically favorable compared to radio-frequency antennas regarding size .

Such systems are usually analyzed assuming magneto-quasistatic conditions, which neglect high-frequency phenomena such as skin and proximity effects, radiation losses, and the self-resonance of the coil. These assumptions are justified by the relatively low frequency used, in which the near-field components are dominant. However, the resulting models are non-physical in the sense that performance grows monotonically with an increase of frequency and coil size. This leads to overestimation of possible performance, and to non-optimal designs. Currently, the limits magneto-quasistatic models are not fully understood .

To bridge this gap, this research investigates the influence of high-frequency effects on the performance of magnetic induction-based systems used for sensing, power transfer, and communication. We first seek to better understand these effects and their importance in different types of systems, and then apply the results to develop performance bounds for each system, in order to optimize their designs .

It is found that the signal-to-noise ratio, power efficiency, and channel capacity in typical systems are impaired by skin and proximity effects at medium frequencies. Another major finding is that the typical dominant effect in high frequencies is radiation losses. In addition, the maximal operating frequency is limited by the self-resonance of the coil, and by the coil size. For each type of system, we show the existence of an optimal operating frequency zone, in which the performance is maximized .

A significant finding of this work concerns magnetic communication systems that operate in the presence of general media. The optimal operating frequency is shown to be located in the radiative near-field, instead of in the reactive near-field, implying that the magneto-quasistatic analysis may not be sufficiently accurate. Indeed, a magneto-quasistatic and full-wave comparison analysis show that the former significantly underestimates the potential channel capacity compared to those obtained by a full-wave analysis .

It is also shown that the self-resonance is dictated by the properties of the medium that exists in close vicinity to the coil. Therefore, encapsulation of the coil can significantly reduce the influence of the surrounding medium and correspondingly extend the high-frequency restrictions. The primary effects presented in this work are validated by electromagnetic simulations .