Floppy Capacitors

The variety of borderline magical materials now commonplace in even commoditized technology is frankly stupefying. The most exotic behavior, comprehensible only through the wizardry of physics and chemistry and the outré runes of advanced mathematics, is now taken completely for granted. Let's pay a moment of homage to some weird results of Materials Science, and the awe-inspiring applications to which engineers have put them.

Piezoelectric materials create electricity when you squeeze them. They're like physical functions that transform pressure into voltage. We use them in doorbells and microphones, and lots of other stuff. There’s also a reverse piezoelectric effect whereby some objects, when exposed to an electric field, change their shape or size. Reverse piezoelectrics are used in ultrasound: A rapidly oscillating sheet of reverse piezoelectric ceramic acts as a “speaker” to generate ultrasound waves. It is weird that we can make materials dance for us by subjecting them to fields of invisible energy.

Thermoelectric materials turn temperature differentials into electricity (the Seebeck effect) or vice versa (the Peltier effect). If you're in a warm room in cold weather, and you stick one end of a thermoelectric pole out the window, you get free electricity (except insofar as you're paying to heat that room in the first place). In practice, we use thermoelectrics to build heat pumps for refrigeration; but research is underway toward reclaiming energy from otherwise wasted heat.

Semiconductors either prevent or allow the flow of electricity, depending on their environment. Most materials are either electrical insulators (like the rubber sheath of your laptop’s power cable) or conductors (like the metal wire inside that sheath). Semiconductors are like insulators, except that when we put them in certain electric fields, they become conductors. Computer microprocessors use semiconductors in billions of tiny switches, whereby the state of each switch (either insulating or conducting) controls other switches, and so on, almost the way billions of neurons in the human brain interact to produce higher order phenomena like thought.

Effects so simple they might be mistaken for mere novelties can be combined to create awe-inspiring technology. Consider the mind-blowing example of floppy capacitors. (Floppy isn't a technical term, but an accurate one.) Most modern electronics are made deliberately rigid, so that their size, shape, and behavior are consistent even if you shake them. (If you're old enough to remember portable CD players, you’ll appreciate the fact that modern music players don't skip as you jog.) But it is possible to make floppy electronics that are easily deformed by acceleration. In particular, the electrical properties of simple devices called capacitors change as they're deformed. You know the visceral feeling you get when an elevator starts moving or comes to a stop? Floppy capacitors “feel” it too.

The change in floppy capacitors’ behavior as they get jerked around has been leveraged to create accelerometers. When your smartwatch tells you it's time to get off your duff and stand up for a minute, your watch is using a built-in accelerometer to tell when you last stood up or sat down.

Accelerometers are key components of automobile airbags. Microcontrollers monitor the output of accelerometers, checking for sudden deceleration, and constantly sending a single bit of information (either true or false) to the airbag deployment system: Are we crashing right now? The United States Department of Transportation estimates that over a recent 30-year period, airbags saved the lives of over 50,000 people. All thanks to the magnificent insight that floppy electronics could be more than a novelty. (Inventor Allen Breed earned his degree in Mechanical Engineering after patenting the modern airbag.)

There’s no telling what we'll discover next—what bizarre properties of matter and energy, or what novel uses we'll put them to. Whatever they may be, engineers will be the people who turn the possible into the practical, and the interesting into the invaluable.