Leti said the improvements reported could lead to "significant commercialization of vibration-powered systems."
The two papers were: "Self-Tunable Phase-Shifted SECE Piezoelectric Energy Harvesting IC with a 30nW MPPT achieving 446% Energy-Bandwidth Improvement and 94% Efficiency,” and "Electromagnetic Mechanical Energy Harvester IC with no off-chip Component and One switching period MPPT achieving up to 95.9% end-to-end Efficiency and 460% Energy Extraction Gain."
The first paper presents a system in which vibration energy is converted into electrical energy by means of a piezoelectric material fixed on a beam. The second explores converting vibration energy into electrical energy by means of an oscillating magnet in a coil. The harvesters in both approaches required specific IC interfaces to enhance the stored, harvested energy.
Battery-less functioning is highly desirable in sensors implanted in the human body or in critical environments such as automobiles, trains and aircraft, where battery change can be difficult and battery-failure dangerous. While the first paper focuses on small-scale energy harvesting for applications where the system must be as small as possible, i.e. inside the body, the second paper focuses on larger scale devices, such as home automation and aeronautic applications.
In the case of the first paper one of the key elements of progress is the increase in vibration bandwidth and the ability to make it adaptable so it can self-tune the resonant frequency. The harvesting and tuning are self-powered, and their consumption of about one microwatt is at least two orders of magnitude lower than the harvested energy from vibrations that are available in the environment (100microW to 1mW).
The second paper describes fabrication of a harvester IC that achieves the highest published end-to-end efficiency of up to 95.9 percent.
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