Magnetic Flux Guidance Using H Structures for Miniature Transducers

Limited magnetic flux has been a significant restriction in the applicability of scaled-down inductive energy, sensing and actuating devices. Magnetic flux concentration could potentially address this challenge by offering higher flux density B and thereby higher transduction power density, sensitivity and force in the small scale. In this paper, a study of flux concentration from a flux path perspective is presented. Numerical simulations show that high permeability cylindrical cores can achieve a flux concentration ratio in the scale of their aspect ratio, as they gather flux from their reachable vicinity. Flux guiding structures such as H-shapes can concentrate the flux incident to their surface and guide it through a small cross-section, achieving a higher concentration ratio. In an experimental study, a flux concentration factor of 6 is reported using a single 5 mm diameter, 20 mm high cylinder, and an additional increase factor of 4.3 from the addition of 70 mm × 12 mm × 2 mm flanges. A total B amplification ratio of 26 is demonstrated. As an application demonstrator, this approach is employed in an inductive energy harvester yielding 11.4 mW average power output (0.3 mW/g) from a 0.12 mT RMS, 800 Hz field.