Co-investigator Anantha Chandrakasan
Powering machine health monitoring sensors with the motions from the machinery allows install-and-forget implementation of the machine health monitoring net- work. Electromagnetic MEMS based-transducer provides an efficient interface between industrial machines and the rest of the vibration-based energy harvesting system. Implementing the mechanical harvester’s spring system on silicon, allows the mechanical system and the circuit to be manufactured through the same process, cutting down on both assembly time and complexity.
The transducer design uses a modified version of the classic 4 bar linkage spring design. The long beams are tapered such that the end connecting to the guide rod is wider than the connecting region to the shuttle, which houses the magnet. This alleviates the stress experienced at the joints of the beam, which is the typical weak point of the structure. With the tapered beam, the current design achieves a full stroke of 1.6mm and is more robust with regard to handling during the assembly process.Thedesignalsooffersgood modal separation, with the modal frequency of the first undesirable mode several hundred Hz above the desired, horizontal translational mode.
The coils are manually wound using 42 AWG enamel coated copper wires with two coils placed at 150mm above and below the magnet’s plane of motion. The coils and the spring system are each fixed in a plastic package. When attached to the source of vibration, the harvester’s magnet vibrates in between the coils, inducing an EMF in the coils in accordance with Lenz’s Law. The coils are connected in series, and the induced voltages add to produce an output voltage, which is interfaced with custom designed circuitry for energy harvesting. The assembled mechanical harvester can deliver 1mW of output power at resonance with a matched load.