Nikolay Tal

Design of magnetic transmitters with efficient reactive power utilization for inductive communication and wireless power transfer

An important figure of merit in magnetic communication systems is the reactive power delivered to the transmitting coil. This work proposes a systematic design approach for magnetic transmitters that emphasizes the limitation of available reactive power. The proposed design is formulated as an optimization problem, in which reactive power of the magnetic transmitter is minimized, under the constraint of a desired field at the far receiver. While the resulting optimization problem is multi-dimensional and non-linear, this work shows that an optimal solution exists for a flat disc in which currents are distributed symmetrically in respect to the disc center.

Increasing the Sensitivity of Search Coil Magnetometer by Capacitive Compensation

This letter proposes a compensation method that aims to increase the sensitivity of search coil magnetometers. The method is based on internal capacitive compensation of the magnetic devices, which enables to increase the device resonance frequency, without reducing the number of turns. The method is verified theoretically and tested experimentally.

Thermodynamic Signal-to-Noise and Channel Capacity Limits of Magnetic Induction Sensors and Communication Systems

Magnetic communication systems are typically used when the medium contains matter, or when short-range communication is of interest. Previous works have disregarded impediments to transmission performance due to skin and proximity effects and radiation resistance, although such effects may be significant. This paper addresses these effects and proposes improved upper bounds on the signal-to-noise ratio (SNR) and channel capacity. It is shown that the performance of magnetic communication systems is limited by skin and proximity effects at medium frequencies and by radiation resistance at high frequencies. A conclusion is that the sensitivity of magnetic induction sensors cannot be made arbitrarily high, since the noise associated with radiation resistance increases substantially in large coils. Another conclusion is that the potential SNR of any magnetic structure peaks at a particular frequency.

Design optimization of transmitting antennas for weakly coupled magnetic induction communication systems

This work focuses on the design of transmitting coils in weakly coupled magnetic induction communication systems. We propose several optimization methods that reduce the active, reactive and apparent power consumption of the coil. These problems are formulated as minimization problems, in which the power consumed by the transmitting coil is minimized, under the constraint of providing a required magnetic field at the receiver location. We develop efficient numeric and analytic methods to solve the resulting problems, which are of high dimension, and in certain cases non-convex. For the objective of minimal reactive power an analytic solution for the optimal current distribution in flat disc transmitting coils is provided. This problem is extended to general three-dimensional coils, for which we develop an expression for the optimal current distribution. Considering the objective of minimal apparent power, a method is developed to reduce the computational complexity of the problem by transforming it to an equivalent problem of lower dimension, allowing a quick and accurate numeric solution. These results are verified experimentally by testing a number of coil geometries. The results obtained allow reduced power consumption and increased performances in magnetic induction communication systems. Specifically, for wideband systems, an optimal design of the transmitter coil reduces the peak instantaneous power provided by the transmitter circuitry, and thus reduces its size, complexity and cost.

DESIGN OF EFFICIENT AIR CORE INDUCTORS USING A PARTIAL ELEMENT EQUIVALENT CIRCUIT METHOD

This paper proposes an optimization method to improve the efficiency of air core inductors, which are frequently employed in near field communication, wireless power transfer, and power conversion systems. We propose a modification to the PEEC based method, which aims at further reducing the computational complexity associated with complex 3D topologies. The main idea is to optimize 3D structures based on a 2D analysis. The device low frequency behavior is estimated based on the full 3D topology, while corrections resulting from high frequency effects are estimated based on a 2D approximation. As a result, since 2D formulations are used to estimate the high frequency effects, it is possible to obtain small mesh sizes, and hence to decrease the computational load, enabling a fast iterative design process. In addition, the proposed method requires no special commercial software, and can be easily implemented in Matlab. Results are compared to a standard commercial FEM tool, CST EM studio, and the results match well.

MAGNETIC INDUCTION ANTENNA ARRAYS FOR MIMO AND MULTIPLE-FREQUENCY COMMUNICATION SYSTEMS

In magnetic induction communication systems, channel capacity is often a major bottleneck that limits the system performance. This paper proposes a method to increase the channel capacity in such systems by means of an antenna array. A central challenge in the design of magnetic antenna arrays is to achieve low intra-array coupling along with high gain. These two properties are essential for increasing the channel capacity in comparison to single antenna communication systems of comparable volume.The method proposed in this paper utilizes circular loop antennas to reduce the intra-array coupling using magnetic flux cancellation.The mathematic approach employed in this paper considers each coil as a system of coupled inductors, where each inductor is a single turn loop, and the total coil self and mutual inductances are computed by summing the appropriate single turn loop inductances. Volume efficient coil topologies are identified, and an optimization method is proposed to minimize the intra-array coupling, subject to a required inductance. The proposed method allows to design volume efficient, up to 3 × 3, array, or pyramidal shaped 4 × 4 arrays. The results are verified experimentally using the multiple-frequency communication mode.

Power transfer limits and optimal operation frequency in induction power transfer systems incorporating high-frequency effects

Wireless power transfer systems based on magnetic induction are usually modeled using the magneto-quasi-static approximation, and by neglecting skin effects and radiation losses. These assumptions imply that the extracted power can grow unlimitedly by increasing frequency or coil size. To bridge these gaps, this work proposes general expressions for the actual received power. In this work, we analyze an induction power transfer system, comprised of serially-compensated transmitter and receiver coils. The output power and efficiency as a function of the input power are derived. A primary result is that the receivers output power and the system efficiency are inherently limited by radiation losses at high frequencies and impaired by skin and proximity effects at medium frequencies. Our proposed approach provides a design tool for estimating the maximal power that can be delivered through a given system, and the corresponding optimal operation frequency.

The effects of radiation resistance on the signal to noise limits of magnetic sensors and communication systems

This paper considers the influence of radiation resistance on the signal to noise (SNR) ratio in magnetic induction sensors and communication systems. It is shown that a magnetic sensor or receiver has a specific optimal frequency in which its SNR is maximal. It is also found that although magnetic induction systems are designed to operate under a magneto-quasi-static approximation, the radiation resistance may be a dominant noise factor even at low frequencies.

Study of a thin applicator for Microwave Ablation of liver malignant tumor

Microwave Ablation (MWA) is a minimally invasive method for treatment of malignant tumors. This paper studies a thin interstitial applicator that produces a nearly spherical ablation zone in malignant liver tumor and investigates how the frequency of operation can affect the quality of MWA procedure. The paper then proposes a similar thin applicator but much shorter for MWA.