This paper presents an investigation of the transmitted power in a wireless power transfer system that employs a metamaterial. Metamaterials are a good means to transfer power wirelessly, as they are composed of multiple inductively-coupled resonators. The system can be designed and matched simply through magneto-inductive wave theory, particularly when the receiver inductor is located at the end of the metamaterial line. However, the power distribution changes significantly in terms of transmitted power, efficiency and frequency if the receiver inductor slides along the line. In this paper, the power distribution and transfer efficiency are analysed, studying the effects of a termination impedance in the last cell of the metamaterial and improving the system performance for the resonant frequency and for any position of the receiver inductor. Furthermore, a numerical characterisation is presented in order to support experimental tests and to predict the performance of a metamaterial composed of spiral inductor cells with very good accuracy.

Harmonic resonances are part of the power quality (PQ) problems of electrified railways and have serious consequences for the continuity of service and integrity of components in terms of overvoltage stress. The interaction between traction power stations (TPSs) and trains that causes line resonances is briefly reviewed, showing the dependence on infrastructure conditions. The objective is monitoring of resonance conditions at the onboard pantograph interface, which is new with respect to the approaches proposed in the literature and is equally applicable to TPS terminals. Voltage and current spectra, and derived impedance and power spectra, are analyzed, proposing a compact and efficient method based on short-time Fourier transform that is suitable for real-time implementation, possibly with the hardware available onboard for energy metering and harmonic interference monitoring. The methods are tested by sweeping long recordings taken at some European railways, covering cases of longer and shorter supply sections, with a range of resonance frequencies of about one decade. They give insight into the spectral behavior of resonances, their dependency on position and change over time, and the criteria needed to recognize genuine infrastructure resonances from rolling stock emissions.

Receiver position sensing is investigated in a dynamic wireless power transfer (DWPT) system for electric vehicle (EV) charging. Exploiting the peculiar behaviour of the resonator arrays input impedance, it is possible to identify the position of the receiver coil by exciting the first array resonator with a signal at a proper frequency and measuring the resulting current. An analytical expression of the input impedance of the resonator array coupled with the EV receiver coil placed in a generic position is provided; its sensitivity to different circuit parameters is also analysed. The outline of a simple and effective algorithm for the localization of the EV is proposed and applied to a test case.

The measurement of conducted emissions of Switched Mode Power Supplies (SMPSs) is discussed for the 2-1000 kHz frequency range, analyzing variability caused by setup elements and test conditions. The tested SMPSs have 12 VDC output and about 20 W nominal power. They are fed by a controlled AC power supply, instead of mains, through a Line Impedance Stabilization Network and various loading levels are applied. Identified causes of variability (supply voltage and frequency variations, thermal stabilization influencing internal mechanisms of emissions) indicate a relevant impact on the spread of measured conducted emissions, ranging from a fraction of dB to about 10 dB (sample standard deviation). Such phenomena represent a cause first of all of systematic error, but also of increased uncertainty. No EMC standards are known to take them into account, nor the scientific literature reports extensive quantification, as in the present case. The shift of the line spectrum of emission consequential to a mains frequency change revealed to be exploitable also for better identification of internal sources of emission.