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This Letter focuses on extracting the heartbeat information using ultra‐wideband impulse radar, and a new method that can extract not only the heart rate but also the timing of the heartbeat with high accuracy is proposed herein. As the first step towards achieving this goal, radar pulses are projected towards a human body, and the reflected pulses are accumulated along the time axis at specific time intervals. The accumulated pulses pass through a digital filter to reveal the heartbeat information and are converted to a greyscale image. A pattern that reflects the heartbeats is used as a template to find similar patterns in the entire image. After all the significant patterns are found, the timing information corresponding to the locations where the patterns appear is calculated, and this indicates the time when the heartbeats actually occur. From the experimental results, the authors confirmed that the proposed method could estimate the heart rate with high accuracy and extract the timing information of the heartbeats. [ABSTRACT FROM AUTHOR]

A formula for the optimal relation between the width of a planar conductor (w0), the total width of parallel straight planar conductors (W), and the number of the parallel conductors (N) for the minimum ohmic resistance is presented. The formula is verified for the frequency range between 2 and 27.12 MHz according to N by using the finite element method. By experimentation, it is also shown that the proposed formula can be applied to design low‐loss circular planar coils. [ABSTRACT FROM AUTHOR]

An effective calculation method for AC resistance and the inductance of planar rectangular spiral coils is proposed. For the calculation, a volume filament model and its equivalent circuit are provided. By using the method, AC resistance and inductance are calculated accurately in megahertz frequency range by including both skin and proximity effects. The method is verified with experiments and used to optimise rectangular spiral coils for the maximum quality factor (Q‐factor) at 6.78 MHz. A small planar rectangular coil is shown to have the maximum Q‐factor when the width of the innermost coil loop is about a half of that of the outermost coil loop. [ABSTRACT FROM AUTHOR]

A planar coil of multiple loops connected in series and in parallel is proposed for wireless power transfer (WPT). The current direction in each loop is mixed in forward and in reverse. The proposed coil gives uniform mutual inductance and enables simple impedance matching for free‐positioning WPT. [ABSTRACT FROM AUTHOR]