Analysis of Various Pickup Coil Designs in Nonmodule-Type GaN Power Semiconductors.

Gallium nitride (GaN) devices are advantageous over conventional Silicon (Si) devices in terms of their small size, low on-resistance, and high dv/dt characteristics; these ensure a high integrated density circuit configuration, high efficiency, and fast switching speed. Therefore, in the diagnosis and protection of a system containing a GaN power semiconductor, the transient state for accurate switch current measurement must be analyzed. The pick-up coil, as a current sensor for switch current measurement in a system comprising a surface-mount-device-type nonmodular GaN power semiconductor, has the advantages of a higher degree-of-freedom configuration for its printed circuit board, a relatively small size, and lower cost than other current sensors. However, owing to the fast switching characteristics of the GaN device, a bandwidth of hundreds MHz must be secured along with a coil configuration that must overcome the limitations of relatively low sensitivity of the conventional current sensor. This paper analyzes the pick-up coil sensor models that can achieve optimal bandwidth and sensitivity for switch current measurement in GaN based device. So four configurable pick-up coil models are considered and compared according to coil-parameter using mathematical methods, magnetic, and frequency-response analysis. Finally, an optimal coil model is proposed and validated using a double-pulse test.

A Novel Antenna for Partial Discharge Measurements in GIS Based on Magnetic Field Detection.

This paper presents a new concept for partial discharge measurements in gas insulated systems (GIS). The proposed technique uses a novel GIS magnetic antenna that measures the magnetic field produced by partial discharges (PD) propagating in GIS. The foundations of the measurement technique and the magnetic antenna design are presented together with laboratory measurements. The magnetic antenna performance and the sensitivity of the acquisition system are studied. The bandwidth of the measurement system is in the high frequency and very high frequency (HF⁻VHF) range. Laboratory experiments demonstrate the suitability of the novel magnetic antenna-based measuring system for PD in GIS for corona, surface discharges, and free moving particles in SF6.

Detection of RF unsafe devices using a parallel transmission MR system.

PURPOSE: The permanent presence of devices (pacemakers) inside a patient, or the need to use other devices (catheters), for diagnosis and treatment, usually represents a contraindication for a magnetic resonance examination. To help overcome this problem, a novel and noninvasive magnetic resonance system-based concept is proposed to detect potentially unsafe radio frequency (RF) conditions of such devices to ensure patient safety. METHODS: This concept makes use of parallel transmit technology by monitoring currents in individual RF transmit coil elements during RF transmission using suitable current sensors. For interventional devices, current changes can be directly measured, whereas for implanted devices, the use of reference signals is proposed, which cannot be measured in the patient. RESULTS: Coupling of unsafe devices to transmit coils led to detectable current changes in the elements because of energy absorption into the device. The concept was successfully tested on interventional and implantable devices and turned out to be so sensitive that even very weak RF coupling to these devices was detectable. CONCLUSION: In this study, basic feasibility to detect RF unsafe conditions was successfully demonstrated. In the future, RF patient safety may be improved in the presence of implanted devices, as well as during interventions using this concept.