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Circuit Could Swap Ultracapacitors for Batteries

MIT engineers are developing a circuit that gets enough out of ultracapacitors to make them usable in medical implants

3 min read

21 June 2010—This week, at the VLSI Circuits Symposium, in Honolulu, a team of engineers from MIT reported that they have invented an energy-storage chip that overcomes one of the last remaining technical hurdles that have kept ultracapacitors from replacing batteries as the energy-storage device of choice for the tiniest electronics.

Ultracapacitors offer several advantages over batteries: High energy density, rapid recharge, and a virtually unlimited number of charge-discharge cycles are but a few. One of the drawbacks of ultracapacitors is that their voltage decreases along with their state of charge; the voltage in a battery remains relatively stable. By the time an ultracapacitor reaches a 25 percent state of charge, its voltage has dropped by half. (The voltage of a lead-acid battery at this state of charge would decrease only by roughly 5 percent.) Because chips usually operate in a fairly narrow voltage range, such a steep drop would cause failures, such as read-write memory errors.

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The Transistor at 75

The past, present, and future of the modern world’s most important invention

1 min read
A photo of a birthday cake with 75 written on it.
Lisa Sheehan

Seventy-five years is a long time. It’s so long that most of us don’t remember a time before the transistor, and long enough for many engineers to have devoted entire careers to its use and development. In honor of this most important of technological achievements, this issue’s package of articles explores the transistor’s historical journey and potential future.

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