Wireless Power for Autonomous Sensor Systems
Main challenges for tomorrow's WPT technologies
Description of the magnetodynamic WPT technology.
Magnetodynamic WPT is based on a transmitter system generating a time-varying magnetic field and a receiver comprising a magnet physically moving within a receiver coil. The time-varying magnetic field from the transmitter creates a force or a torque on the magnet that moves or rotates, respectively. Its motion changes the magnetic flux in the receiver coil and generates power into a load by electromagnetic induction. The maximum frequency of operation is limited by how fast the magnet can physically move in the system, which is typically less than 1 kHz.
The transmitter is either a coil supplied by an ac current, or a rotating permanent magnet driven by a motor. In our approach, the receiver magnet is sensitive to magnetic torques and tends to rotate to align its magnetization with the time-varying magnetic field from the transmitter. The magnet can either rotates continuously around its axis, or, if coupled with a mechanical torsion spring for example (restoring torque), oscillates around an equilibrium position. The change of magnetic flux in the receiver coil induces an electromotive force at its terminals. The ac power can be then rectified and regulated to supply an electronic system or charge a battery.
Intrinsically, the low frequency of operation should generate a lower power than for high-frequency technologies. However, this phenomenon is compensated by a larger change in magnetic flux in the receiver coil (i.e. larger coupling).
Additionally, a higher magnetic flux change can be obtained when the magnet rotates around its axis instead of translating. Moreover, a receiver sensitive to magnetic torque is more beneficial compared to being sensitive to magnetic force, since the torque depending on the field amplitude decays less rapidly with the distance than the force depending on the field gradient.
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