Published on December 14th, 2018 | by ozgun

What is Piezoelectricity?

You’ve probably used piezoelectricity (pronounced “pee-ay-zo-electricity”) quite a few times today. If you’ve got a quartz watch, piezoelectricity is what helps it keep regular time. If you’ve been writing a letter or an essay on your computer with the help of voice recognition software, the microphone you spoke into probably used piezoelectricity to turn the sound energy in your voice into electrical signals your computer could interpret. If you’re a bit of an audiophile and like listening to music on vinyl, your gramophone would have been using piezoelectricity to “read” the sounds from your LP records. Piezoelectricity (literally, “pressing electricity”) is much simpler than it sounds: it just means using crystals to convert mechanical energy into electricity or vice-versa. Let’s take a closer look at how it works and why it’s so useful!

What is Piezoelectricity?

Squeeze certain crystals (such as quartz) and you can make electricity flow through them. The reverse is usually true as well: if you pass electricity through the same crystals, they “squeeze themselves” by vibrating back and forth. That’s pretty much piezoelectricity in a nutshell but, for the sake of science, let’s have a formal definition:

Piezoelectricity (also called the piezoelectric effect) is the appearance of an electrical potential (a voltage, in other words) across the sides of a crystal when you subject it to mechanical stress (by squeezing it).
In practice, the crystal becomes a kind of tiny battery with a positive charge on one face and a negative charge on the opposite face; current flows if we connect the two faces together to make a circuit. In the reverse piezoelectric effect, a crystal becomes mechanically stressed (deformed in shape) when a voltage is applied across its opposite faces.


What is piezoelectricity used for?

There are all kinds of situations where we need to convert mechanical energy (pressure or movement of some kind) into electrical signals or vice-versa. Often we can do that with a piezoelectric transducer. A transducer is simply a device that converts small amounts of energy from one kind into another (for example, converting light, sound, or mechanical pressure into electrical signals).

The most recent innovation that uses piezoelectricity is in the sports industry, like tennis. In order to provide more comfort and power while attempting a shot, players requested racquet manufacturers to reduce the shock vibrations through the player’s arm. Piezoelectric fibres were embedded around the racquet throat and a computer chip embedded in the handle such that, when the ball is hit the fibres bent and produce charge which is transmitted to the silicon chip through a circuit. These charges are amplified and sent back to the fibres out of phase in an attempt to reduce the vibration by cancelling out the initial vibration produced when the ball was hit.

Wearable technologies that include fitness and activity wristband, monitors that observe distance, respiration, heart rate and even sleep patterns use piezoelectric sensors. The mechanical stress and vibrations of your body organs are converted into electrical signals and are transmitted via Bluetooth, Wi-Fi or any other wireless signals into your smartphone apps. Wireless blood pressure cuffs that measure patient’s blood pressure through a phone app is also based on piezoelectric energy harvesting technique. Smart watches that can manage texts, calls, and emails, smart clothing devices that monitor body movement and other vital signs, smart eyeglasses that can record photos, videos and connect to the Internet, all these wearable devices will use piezoelectricity in the imminent future.

Piezoelectricity is also used, much more crudely, in spark lighters for gas stoves and barbecues. Press a lighter switch and you’ll hear a clicking sound and see sparks appear. What you’re doing, when you press the switch, is squeezing a piezoelectric crystal, generating a voltage, and making a spark fly across a small gap.

If you’ve got an inkjet printer sitting on your desk, it’s using precision “syringes” to squirt droplets of ink onto the paper. Some inkjets squirt their syringes using electronically controlled piezoelectric crystals, which squeeze their “plungers” in and out; Canon Bubble Jets fire their ink by heating it instead.


Solid Mechanics, Finite Element and Material Science

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