Resonant Inductive Coupling Research Articles

A fully analytic treatment of resonant inductive coupling in the far field

For the application of resonant inductive coupling for wireless power transfer, fabrication of flat spiral coils using ribbon wire allows for analytic expressions of the capacitance and inductance of the coils and therefore the resonant frequency. The expressions can also be used in an approximate way for the analysis of coils constructed from cylindrical wire. Ribbon wire constructed from both standard metals as well as high temperature superconducting material is commercially available, so using these derived expressions as a basis, a fully analytic treatment is presented that allows for design trades to be made for hybrid designs incorporating either technology. The model is then extended to analyze the performance of the technology as applied to inductively coupled communications, which has been demonstrated as having an advantage in circumstances where radiated signals would suffer unacceptable levels of attenuation.

A Wireless Sensor Readout System—Circuit Concept, Simulation, and Accuracy

In this paper, we present an electronic readout system for wireless passive sensors based on inductively coupled LC resonant circuits. The proposed system consists of a reader coil inductively coupled to the sensor circuit, an analog frontend circuit, and a digital signal processing unit. The analog frontend circuit generates a dc voltage representing the sensor resonance curve. The frequency of the reader coil driving signal is continuously readjusted by the digital signal processing unit. Based on analytical calculation and system simulation, we derive a model for the achievable accuracy of the overall sensor and readout system. The accuracy is limited by noise and systematic errors due to the measurement principle. We show how to design the digital signal processing system for optimal insensitivity to voltage noise. The noise sensitivity of the measurement system is inversely proportional to the square of the quality factor of the LC sensor. This means that minimizing the losses of the sensor is of crucial importance to obtain a wireless measurement system with a high range and a good insensitivity to noise. Subsequently, we outline an approach to calculate the sensor resonance frequency, quality factor, and inductive coupling factor from the available voltage signals in the signal processing unit using linear fitting functions. The accuracy of our approach is exemplified by a system simulation for typical sensor parameters. For the system studied, we show that the relative linearization error of the sensor resonance frequency measurement is below 0.02%. Taking the general models presented for both the noise sensitivity and linearization error into account, it is possible to estimate the maximum distance and accuracy for any wireless sensor system based on an inductively coupled LC resonator.

A novel resonant inductive magnetic coupling wireless charger with TiO2 compound interlayer

A nonradiative energy transformer exploiting TiO2 nano-powder and (C4H6O2)x latex as a combined interlayer is proposed. The transformer works on ‘strong coupling’ between two coils (i.e., resonators), which are physically separated from each other by distances that are longer than the characteristic sizes of each resonator, to realize efficient wireless energy transfer. Nonradiative energy transfer between the two resonators is facilitated through the coupling of their resonant-field evanescent tails. Finite element analysis and experiments have been carried out to facilitate quantitative comparison. The efficiency of the proposed system is 70.6% at 5 cm and 26.3% at 15 cm at an operating frequency of 1.74 MHz. When compared with typical magnetic inductive coupling energy transmission devices with low dielectric constants, the efficiency of the proposed system is much higher.

NMR signal detection using inductive coupling: Applications to rotating microcoils

Sensitivity in solid-state nuclear magnetic resonance can be improved by the use of rotating microcoils (1). The connection to the rest of the electronics is performed through resonant inductive coupling. This mode of detection of nuclear induction has major advantages as it provides a wireless way to obtain extremely high radio-frequency amplitudes per unit current under sample rotation and thus improved sensitivity for size-limited samples. We review the circuit electronics and discuss experimental optimization of the probe and coil parameters. We also present alternative geometries for coupling between rotating coils and we explicitly calculate the signal enhancement. Two practical cases are presented, namely a standard magic angle sample spinning probe and a double sample rotation probe. We conclude with a theoretical discussion about the limits of detection attainable with coil miniaturization. © 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part A 38A: 33–51, 2011.

Efficient weakly-radiative wireless energy transfer: An EIT-like approach

Inspired by a quantum interference phenomenon known in the atomic physics community as electromagnetically induced transparency (EIT), we propose an efficient weakly radiative wireless energy transfer scheme between two identical classical resonant objects, strongly coupled to an intermediate classical resonant object of substantially different properties, but with the same resonance frequency. The transfer mechanism essentially makes use of the adiabatic evolution of an instantaneous (so called “dark”) eigenstate of the coupled 3-object system. Our analysis is based on temporal coupled mode theory (CMT), and is general enough to be valid for various possible sorts of coupling, including the resonant inductive coupling on which witricity-type wireless energy transfer is based. We show that in certain parameter regimes of interest, this scheme can be more efficient, and/or less radiative than other, more conventional approaches. A concrete example of wireless energy transfer between capacitively-loaded metallic loops is illustrated at the beginning, as a motivation for the more general case. We also explore the performance of the currently proposed EIT-like scheme, in terms of improving efficiency and reducing radiation, as the relevant parameters of the system are varied.

Diagnostics of reactive RF plasmas

Experimental characterization of the plasma state as well as the neutral gas phase in a low pressure discharge is presented. A radiofrequency supply produces plasma driving an electrical discharge in a gas mixture through a resonant inductive coupling. The plasma state has been characterized by means of electrostatic probes, optical emission spectroscopy. Mass spectroscopy of the neutral and of the charged species has been performed too, sampling the gas phase inside the discharge. Results on Ar/SF 6 plasmas are presented to study the effect of argon doping on the production of reactive atomic fluorine in the discharge. More efficient application of Ar/SF 6 plasmas to surface fluorination of polymers could be expected in view of these results.

Resonant inductive coupling of RF EPR resonators in the presence of electrically conducting samples

A new method of matching for radio frequency EPR resonators is proposed. It uses resonant inductive coupling and is particularly suitable for studies with lossy conducting samples. The equivalent circuit of the resonant inductive coupling method is presented and a theoretical analysis of the equations that produce the critical coupling coefficient is discussed. A prototype resonant inductive coupling suitable for loop gap resonators operating at about 200 MHz has been developed and tested. Experimental results obtained with saline solutions show the advantages of resonant inductive coupling in terms of the coupling coefficient, RF magnetic field amplitude and field homogeneity. This matching method has been especially designed for CW EPR applications, in which the adoption of critical coupling is important for optimization of sensitivity. Moreover, resonant inductive coupling should also produce benefits for pulsed EPR studies.