VIDEO MATERIAL DISCLAIMER

There are materials, that when deformed develop electrical properties on some of its surfaces.  This is called the piezoelectric effect.   This video is a vivid demonstration of the electrical spark that can be generated when a hammer strikes a piezoelectric material.  Electricity generated in this manner is called the 'primary piezoelectric effect'.

Here's another video demonstrating the same thing.  One subtle difference here is that the piezoelectric sensor is mounted on a metal dish that rings like a bell.  This video shows the main impact, but also the vibration that lasts after the impact.

The piezoelectric effect has another attribute.  Shown above, a piezoelectric material generated electrical properties when deformed, but in this video it shows a piezoelectric material deforming as an electrical signal is applied.  What this plastic polymer piezoelectric device wiggle.  This is often referred to as the 'secondary piezoelectric effect'.

This is a nice overview of the piezoelectric effect, and notes various natural crystal piezoelectric materials, manufactured piezoelectric ceramics and piezoelectric polymer film.

Several naturally formed crystals exhibit piezoelectric properties, including tourmaline, lithium, bone, topaz and quartz.  This video shows a very common application of piezoelectricity in quartz watches.  

One of the earliest forms of piezoelectric crystals studied was Rochelle Salt.  Want to see how you can make these crystals at home?  Watch this video.

Quartz crystals can be artificially grown.  This is nice video showing the process

Polymer film... this video shows the polarization of a sheet of PDVF to impart piezoelectric properties.

I just love this video.  It pretty much shows the capability of using piezoelectric ceramics for harvesting energy.  Pound savagely on six elements for 20 seconds, store the energy in a capacitor and light a small LED for about 1 second.

This one works out a little better.  It uses a flexural element, which imparts more strain into the piezoelectric material and in turn more electrical energy is generated.

Energy harvesting to power implanted pacemakers is a brilliant idea, being currently researched by several facilities.  Pacemakers are designed to run on very low power.  A properly configured piezoelectric device will harvest a very small amount of energy with every beat of the heart.