This paper presents a simple, compact, and low-power method for generating extremely low-frequency radio signals below ~500 Hz. This paper is motivated by the prohibitively large size and low efficiency of conventional antennas operating in this frequency range. The successful generation of time-varying magnetic fields produced by the physical rotation of a 3 cm ³ permanent magnet is demonstrated. Ground plane and receiver orientation effects are analyzed both theoretically and experimentally. Observations as a function of distance from the source indicate that the fields are dominated by the static component, rather than by the radiation component, of the generated field. Based on these observations, the electromagnetic radiation emitted by a spinning magnet source is predicted to be weak. Nevertheless, static magnetic signaling using this technique is proven to be both possible and practical at frequencies below ~500 Hz and at distances in excess of 100 m.

An electrodynamic wireless power transmission (EWPT) approach that utilizes mechanically responsive receivers to safely deliver power in cluttered environments is presented. Mainstream WPT techniques are predominately based on near-field inductive coupling of two coils (MHz) or directed, far-field RF transmission (GHz) between a transmitter and a receiver. These approaches face significant technical hurdles (safety concerns, detuning, parasitic heating) in real-world scenarios where electrically conductive media exists in between the transmitter and receivers. The EWPT approach presented here relies on electrodynamic coupling between a magnetic near-field produced by a transmitter and a permanent magnet in the receiver. This approach enables wireless power delivery using low-frequency (<1 kHz) fields, which facilitates transmission through and around common electrically conductive media such as metal objects, people, etc. Here, we present an electromechanical model of a rotating magnet receiver in order to analyze the transient and steady-state dynamics of the receiver magnet. We then experimentally demonstrate wireless power transmission with an efficiency of 7% to a 3 cm ³ receiver achieving 1.3 W (0.42 W cm ⁻³ power density) at 1 cm and 9 mW at 9 cm. These experimental results are well matched by simulations. Lastly, we demonstrate simultaneous charging of two wearable electronic devices in a cluttered environment.

We report the fabrication and testing of a multilayer flexible screen-printed coil that can be used to generate low-frequency (<1 kHz) magnetic fields for applications such as electrodynamic wireless power transmission (EWPT). Compared to traditional coil-forming methods, screen printing enables rapid fabrication of thin, light weight, conformable, and flexible structures. The flexibility is demonstrated by repeated bending of a stack of up to three layers for a curvature (inverse bending radius) of 53.2 . We also demonstrate wireless power transmission of 1 mW of power at a distance of 4 cm between the flexible receiver and transmitter. The effect of the flexibility is observed through a 32% power increase when the receiver is bent concavely and a 20% output power decrease when the stack is bent convexly. It is also seen that the insertion of a 0.2 mm-thick soft-magnetic material sheet increased the magnetic field by 41% from its original value. Mechanical cycling was also performed for the stack. After 10 000 bending cycles, a 16.4% increase in the coil resistance was measured for a 0.33 Hz frequency and 78% increase for a 1 Hz cycling frequency, respectively. Screen printed 3D flexible transmitter coils can enable the incorporation of EWPT for wireless charging in applications such as healthcare and consumer-based electronics.