Wideband vibrational electromagnetic energy harvesters with nonlinear polyimide springs based on rigid-flex printed circuit boards technology

Abstract

A wideband vibrational electromagnetic energy harvester employing nonlinear spring effects is proposed and demonstrated. The harvesters were designed and fabricated by commercial rigidflex printed circuit boards technology. Rigid FR-4 boards were used for mechanical support and coil winding, whereas flexible polyimide films were patterned for mechanical springs and mass platforms. Two sets of coils were patterned and fabricated in the harvester with an internal coil resistance of about 16 Ω each. Two rare-earth magnets were attached to the central platform as shuttle mass. The total dimension of the harvester was 20×20×4 mm 3 . In vibration tests, nonlinearity could be observed even at 0.1 g rms vibration level due to the spring hardening effect. The frequency for peak induced voltage increased from 187 Hz at low vibration to 382 Hz at 5 g rms vibration. The effective half-power bandwidth increased from 8 Hz at 0.1 g rms to 32 Hz at 1 g rms and 52 Hz at 5 g rms due to the hysteresis in frequency response. For a matched load and 1 g rms vibration at 250 Hz, the maximum output power was 160 nW, corresponding to a power density of 100 nW cm −3 .

Rigid-Flex PCB Technology with Embedded Fluidic Cavities and Its Application in Electromagnetic Energy Harvesters

“…When subjected to an external vibration, the vibrational force causes the shuttle mass in the harvester to move with respect to the rigid device frame. In EM harvesters [ 3 , 4 , 5 , 10 , 11 , 17 , 18 , 19 ], the shuttle mass is a permanent magnet and such displacement causes magnetic flux variation in the surrounding transduction coils. Thus, the vibrational energy is converted to electric energy by the induced electromotive force (EMF) in the coils.…”

“…In [ 29 ], the Rigid-Flex PCB technology was used to fabricate an EM/piezoelectric harvester where the PI layer was used to support the piezoelectric bimorph. In [ 10 ], a wide-band EM energy harvester with a more complex rigid-flex structure was demonstrated based on a commercial Rigid-Flex PCB process. This harvester had its transduction coil windings and support mechanical frame designed and fabricated in rigid FR-4 boards, whereas the mass platform and elastic suspension beams were constructed in the flexible PI film.…”

“…However, only standard PCB materials, such as copper, fiberglass cloth, and epoxy binder, which were non-magnetic, were used in [ 10 ]. Therefore, the magnetic flux from the permanent magnet in the harvester could not be confined and guided efficiently through the transduction coils.…”

“…Vibrational energy harvesters have also been implemented in PCB [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. In particular, an electromagnetic (EM) energy harvester was demonstrated in Rigid-Flex PCB structures [ 10 ]. In further development of this device, embedded cavities were milled in the rigid PCB and filled with ferrofluid (FF) to improve the EM coupling and, thus, enhance output [ 11 ].…”

Research of piezoelectric energy harvesting systems based on cantilevers with irregular cross-sections

“…Liu and et al (2013) also proposed circular suspension structure as multi-frequency harvester. Multi-frequency energy harvesters have several different designs which have wide spectrum of applications (Mallick and et al 2017;Chiu and et al 2016;Han and et al 2014a ). However, the main similarity of these harvesters is several resonant frequencies at narrow frequency range.…”