Engineers from MIT report that they may have found a
feasible way for ultracapacitors to be used in place of batteries. They have
invented an energy-storing chip that could help ultracapacitors conquer one of
the last technical obstacles, so that they can replace batteries in tiny
electronics.
Background
Ultracapacitors have a high-energy density, quick recharge,
and a seemingly endless number of charge-recharge cycles. But because voltage
decreases as their state-of-charge drops, they haven't been able to replace
batteries which produce a relatively secure voltage. At 25% charge, the voltage
of ultracapacitors is half of its full charge capacity, compared to the 5% drop
in voltage at ΒΌ charge in lead-acid batteries.
The Chip
This 1.3mm x 1.4mm chip proposes to get the most charge out
of ultracapacitors, while maintaining a constant voltage using four parallel,
connected 2.5-volt 250-mF ultracapacitors. When the charge drops to below 25%
charge, the energy chip redirects the connections so that two ultracapacitors
are in series. The sum of these two series ultracapacitors makes 2.5V.
Once the two pairs drop down to supplying less than 1.25V,
there is more rerouting until all of the ultracapacitors are in series, which
causes the voltage to rise back to 2.5V. This configuration will cause 98% of
the original charge to be utilized.
Future Improvements
The next stage of the project focuses on making tiny, energy
chip-powered, implantable medical devices. These devices will focus on
supervising patients with neurological conditions that cause tremors.
William Sanchez, the lead graduate student of the project,
suggests that there are a few improvements yet to be made. The efficiency of
the device's DC-DC converter needs to be improved. A version of the energy chip
is expected to be at 65% to 85% efficient for this summer, whereas the goal for
commercial applications is 90%.
Resources:
IEEE
Spectrum – Circuit Could Swap Ultracapacitors for Batteries
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