Eakhwan Song

An Effective and Efficient Approach for Radiated Emission Prediction Based on Amplitude-Only Near-Field Measurements

A new approach is proposed for modeling electromagnetic emissions of a printed circuit board (PCB) based on amplitude-only near-field measurement data. Magnetic dipoles placed over the top layer of the PCB are introduced as the equivalent of actual radiated sources. A restarted optimization procedure based on a differential evolution algorithm is developed to determine the parameters of the dipoles (number, position, and moment components) via minimizing the difference between the measured magnetic near field and that radiated by the dipoles. These equivalent dipoles can be used to predict the radiated emissions of the PCB once being determined. The proposed approach does not need the phase of the measured near fields, and its computational complexity is very low. Numerical results are presented to demonstrate the validity and efficiency of the proposed approach.

Reduction of electromagnetic field (EMF) of wireless power transfer system using quadruple coil for laptop applications

In this paper, we proposed an effective coil design for electromagnetic field (EMF) noise reduction from the wireless power transfer system by using quadruple coils in transmitter and receiver for laptop computer application. By using quadruple coils for transmitter and receiver, EMF noise was significantly reduced with negligible change in induced voltage. 3D simulations and the field distributions are shown and the pros and cons are of the quadruple coil designs are discussed.

A Component-Level Radio-Frequency Interference Evaluation Method for Mobile Devices

In this letter, a radio-frequency interference (RFI) evaluation method for highly integrated mobile devices, such as smartphones and tablets, is proposed. A near-field specification for noise-emitting components in mobile devices is developed based on near-field emission measurements and RF sensitivity measurements of mobile devices with the bit-error-rate (BER) test. To devise the specification, a derivative relation between the near-field strength of noise sources and the system-level RF sensitivity is newly suggested using the theoretical relationship between the signal to interference and noise ratio and the probability of error in communication systems, and verified with empirical measurements. Using the proposed algorithm, an RFI evaluation specification for commercial camera modules widely used in modern smartphones was established at several RF communication bands.

A Magnetic-Field Resonant Probe With Enhanced Sensitivity for RF Interference Applications

High-sensitive field probes are highly desirable for radio-frequency (RF) interference studies, where ultralow noise levels are of interest. By incorporating an LC resonant circuit in a differential-loop probe, together with a Marchand balun, a magnetic-field probe with enhanced sensitivity is developed. Its equivalent circuit model and design methodology are established. The design is validated by measurements. The measured relative sensitivity in terms of |S21| of the proposed probe increases by approximately 8.63 dB at the resonant frequency of 1.575 GHz compared to that of a conventional design. The advantage of the proposed probe is validated through its application in the measurement of a microstrip trace and a real-world cell phone design.

Far-field prediction from amplitude-only near-field measurements using equivalent electric currents

A general and flexible approach is presented for predicting far-field radiated emissions from a device using phaseless magnetic near-field scan data, which is based on the replacement of the actual radiating sources by an equivalent set of electric currents over a planar surface near the device. These equivalent currents used to predict the far-field radiated emissions are determined from near-field scan data by solving two independent nonlinear inverse problems with a global optimization algorithm. Numerical examples are presented to demonstrate the validity and capability of the presented approach.

A differential evolution based equivalent source approach for predicting electromagnetic emissions using near-field scanning

The radiated emission from a device under test is predicted by using an equivalent dipole approach which is based on amplitude-only near-field scanning. The method needs minimizing an objective function to determine the parameters of the equivalent dipoles. The objective function usually exhibits many local minima, and this limits the application of local optimization algorithms. A restarted differential evolution algorithm is hence proposed to overcome the limitation. Experimental data are used to verify the presented approach.

Optimization procedure of complex permeability for a wireless power transfer system

Wireless power transfer (WPT) is fundamentally based on Faradays law of induction and uses relatively strong magnetic field to transfer the required power from the source to the load without any electrical contact. To reduce the leakage magnetic field and enhance the magnetic coupling between the coils, soft magnetic material such as ferrite is frequently used. However, it is hard to determine the optimum magnetic properties to meet the various design requirements such as the cost, the efficiency and the regulations for the time-varying electromagnetic field (EMF) exposure. In this paper, we present the procedure to find the optimum complex permeability satisfying the following design requirements: the transfer efficiency of 90% and the minimum levels of EMF around the coils. The results show that solely maximizing the real part of complex permeability or minimizing the magnetic loss tangent is unsuitable to meet the given design requirements for the WPT system.

An electromagnetic interference (EMI) evaluation method for components in mobile devices

In this paper, a component-level electromagnetic interference (EMI) evaluation method for multi-functional mobile devices is proposed. The proposed method is based on the extraction of a statistical transfer function between the component-level and the system-level radiated emissions. Based on the transfer function, near-field specifications for the component-level EMI evaluation are developed with the transfer function and the system-level EMI regulation of CISPR. The proposed evaluation method is experimentally verified with 86 real mobile phones with a good correlation between the component-level and the system-level evaluation results.