question: How do piezoelectric crystals work in guitars?
comment: Piezoelectric crystals commonly have a perovskite structure. It is a crystal structure that looks like a cubic cage with usually a small atom at the center. As the atom in the middle is positively charge and the cage is mostly negatively charge, any deviation from the cubic symmetry would cause a dipole moment (think of it like static electricity, positive charges attract negative charges). So, if you disturb the crystal by means of stretching, compressing, hitting, vibrating, etc, you'll get a voltage. That voltage does work. In the case of piezoelectric pick up, the voltage follows the vibration of the string which creates a sound signal.
passages: Piezoelectric, or piezo, pickups represent another class of pickup. These employ piezoelectricity to generate the musical signal and are popular in hybrid electro-acoustic guitars. A crystal is located under each string, usually in the saddle. When the string vibrates, the shape of the crystal is distorted, and the stresses associated with this change produce tiny voltages across the crystal that can be amplified and manipulated. Piezo pickups usually require a powered pre-amplifier to lift their output to match that of electromagnetic pickups. Power is typically delivered by an on-board battery.
   In 2000, it was shown that an actuator can be made of paper. The wood fibers, called cellulose fibers, are aligned so that there is a dipolar orientation. This allows the material to become piezoelectric. To enhance the effect, the material can be poled for further alignment. D33 responses for cellular polypropylene are around 200 pC/N. Some applications of cellular polypropylene are musical key pads, microphones, and ultrasound-based echolocation systems.
  
  Section::::Materials.:Aromatic short peptide self-assemblies.
   Section::::Mechanism.
   More recently, there is growing concern regarding the toxicity in lead-containing devices driven by the result of restriction of hazardous substances directive regulations. To address this concern, there has been a resurgence in the compositional development of lead-free piezoelectric materials.
   BULLET::::- Bismuth ferrite (BiFeO) is also a promising candidate for the replacement of lead-based ceramics.
  
  BULLET::::- Sodium niobate NaNbO
  
  BULLET::::- Barium titanate (BaTiO)—Barium titanate was the first piezoelectric ceramic discovered.
  
  BULLET::::- Bismuth titanate BiTiO
  
  BULLET::::- Sodium bismuth titanate NaBi(TiO)
  
  So far, neither the environmental effect nor the stability of supplying these substances has been measured.
  
  Section::::Materials.:III–V and II–VI semiconductors.
   BULLET::::- Barium titanate (BaTiO)—Barium titanate was the first piezoelectric ceramic discovered.
  
  BULLET::::- Lead zirconate titanate (Pb[] with 0 ≤ "x" ≤ 1)—more commonly known as PZT, lead zirconate titanate is the most common piezoelectric ceramic in use today.
  
  BULLET::::- Potassium niobate (KNbO)
  
  BULLET::::- Sodium tungstate (NaWO)
  
  BULLET::::- BaNaNbO
  
  BULLET::::- PbKNbO
   BULLET::::- DNA
  
  BULLET::::- Viral proteins, including those from bacteriophage. One study has found that thin films of M13 bacteriophage can be used to construct a piezoelectric generator sufficient to operate a liquid crystal display.
  
  Section::::Materials.:Synthetic crystals.
  
  BULLET::::- Langasite (LaGaSiO), a quartz-analogous crystal
  
  BULLET::::- Gallium orthophosphate (GaPO), a quartz-analogous crystal
  
  BULLET::::- Lithium niobate (LiNbO)
  
  BULLET::::- Lithium tantalate (LiTaO)
  
  Section::::Materials.:Synthetic ceramics.
  
  Ceramics with randomly oriented grains must be ferroelectric to exhibit piezoelectricity. The macroscopic piezoelectricity is possible in textured polycrystalline non-ferroelectric piezoelectric materials, such as AlN and ZnO. 
  
  The family of ceramics with perovskite, tungsten-bronze and related structures exhibits piezoelectricity:
   Section::::Application.
  
  Currently, industrial and manufacturing is the largest application market for piezoelectric devices, followed by the automotive industry. Strong demand also comes from medical instruments as well as information and telecommunications. The global demand for piezoelectric devices was valued at approximately US$14.8 billion in 2010. The largest material group for piezoelectric devices is piezoceramics, and piezopolymer is experiencing the fastest growth due to its low weight and small size.
  
  Piezoelectric crystals are now used in numerous ways:
  
  Section::::Application.:High voltage and power sources.
  
  Direct piezoelectricity of some substances, like quartz, can generate potential differences of thousands of volts.
   The semiconductors where the strongest piezoelectricity is observed are those commonly found in the wurtzite structure, i.e. GaN, InN, AlN and ZnO. ZnO is the most used material in the recent field of piezotronics.
  
  Since 2006, there have also been a number of reports of strong non linear piezoelectric effects in polar semiconductors.
  
  Such effects are generally recognized to be at least important if not of the same order of magnitude as the first order approximation.
  
  Section::::Materials.:Polymers.
   Electric lamellophone
  
  Electric lamellophones are lamellophones (struck metal tongue instruments) that have been electrified with an electro-magnetic pickup (like on electric guitars) or contact piezo pickup.
  
  Section::::Piezo pickup lamellophones.
  
  There is a distinct difference between the piezo and the electro-magnetic pickup. Most electric lammellophones feature piezo pickups. The piezo sound contains more treble and has more problems with feedback when amplified (distorted) heavily.
   BULLET::::- Piezoelectric actuator. A single crystal or a number of crystals are expanded by applying a voltage for moving and controlling a mechanism or system.
  
  Section::::Application.:Frequency standard.
  
  The piezoelectrical properties of quartz are useful as a standard of frequency.
   Though the original aim of the resonator was increased volume, some modern instruments incorporate electric pickups and related technology. Many modern makers produce instruments with one of a variety of pickup types—and some players retrofit pickups to non-electric instruments. Most commonly, resonator guitars use piezoelectric pickups (contact type transducers) placed under the bridge or elsewhere on the instrument, or use specialized microphones placed inside the instrument or directly in front of the cone to preserve the resonator's distinctive tone.
   Tire company Goodyear has plans to develop an electricity generating tire which has piezoelectric material lined inside it. As the tire moves, it deforms and thus electricity is generated.
  
  Section::::Application.:Potential applications.:Photovoltaics.
   BULLET::::- Piezoelectric (or "piezo") pickups (also called "piezo" pickups) use a transducer to convert vibrations in the instrument's body or bridge into an electrical signal. They are typically mounted under the bridge saddle or near the bridge and produce a different tone from magnetic pickups, often similar to that of an acoustic bass. Piezo pickups are often used in acoustic bass guitars to allow for amplification without a microphone.
   The neck and fretboard (2.1) extend from the body. At the neck joint (2.4), the neck is either glued or bolted to the body. The body (3) is typically made of wood with a hard, polymerized finish. Strings vibrating in the magnetic field of the pickups (3.1, 3.2) produce an electric current in the pickup winding that passes through the tone and volume controls (3.8) to the output jack. Some guitars have piezo pickups, in addition to or instead of magnetic pickups.
   The last type of guitar is commonly called an "acoustic-electric" or "electro-acoustic" guitar, as it can be played either "unplugged" as an acoustic, or plugged in as an electric. The most common type is a piezoelectric pickup, which is composed of a thin sandwich of quartz crystal. When compressed, the crystal produces a small electric current, so when placed under the bridge saddle, the vibrations of the strings through the saddle, and of the body of the instrument, are converted to a weak electrical signal. This signal is often sent to a pre-amplifier, which increases the signal strength and normally incorporates an equalizer. The output of the preamplifier then goes to a separate amplifier system similar to that for an electric guitar.
   The use of piezoelectricity in sonar, and the success of that project, created intense development interest in piezoelectric devices. Over the next few decades, new piezoelectric materials and new applications for those materials were explored and developed.
   Piezoelectric transducers are often used as contact microphones to amplify sound from acoustic musical instruments, to sense drum hits, for triggering electronic samples, and to record sound in challenging environments, such as underwater under high pressure. Saddle-mounted pickups on acoustic guitars are generally piezoelectric devices that contact the strings passing over the saddle. This type of microphone is different from magnetic coil pickups commonly visible on typical electric guitars, which use magnetic induction, rather than mechanical coupling, to pick up vibration.
  
  Section::::Varieties.:Fiber optic.
   Many semi-acoustic and acoustic guitars, and some electric guitars and basses, have been fitted with piezoelectric pickups instead of, or in addition to, magnetic pickups. These have a very different sound, and also have the advantage of not picking up any other magnetic fields, such as mains hum and feedback from monitoring loops. In hybrid guitars, this system allows switching between magnetic pickup and piezo sounds, or simultaneously blending the output. Solid bodied guitars with only a piezo pickup are known as silent guitars, which are usually used for practicing by acoustic guitarists. Piezo pickups can also be built into electric guitar bridges for conversion of existing instruments.
   BULLET::::- H-H-S (Mayones Legend “22” Anders Nyström signature, some ESP Stephen Carpenter Models, and Alembic Jerry Garcia Models)
  
  BULLET::::- H-S-S-H (Music Man Steve Morse Signature)
  
  BULLET::::- S-H (some Telecasters, Music Man “Valentine” James Valentine signature)
  
  BULLET::::- S-H-H (some early seven-string ESP Horizons)
  
  BULLET::::- S-H-S (Fender Wayne Kramer Signature)
  
  Section::::Piezoelectric pickups.
  
  Section::::Piezoelectric pickups.:Sensors.
   Piezotronics
  
  Piezotronics effect is using the piezoelectric potential (piezopotential) created in materials with piezoelectricity as a “gate” voltage to tune/control the charge carrier transport properties for fabricating new devices. Neil A Downie showed how simple it was to build simple demonstrations on a macro-scale using a sandwich of piezoelectric material and carbon piezoresistive material to make an FET-like amplifying device and put it in a book of science projects for students in 2006. The fundamental principle of piezotronics was introduced by Prof. Zhong Lin Wang at Georgia Institute of Technology in 2007.
   Generally, piezoelectric pickups are inexpensive and more common. Piezo elements come in the shape of ceramic discs, cylinders or a plastic film. They detect physical vibrations directly, sometimes placed in or on the body, or in some cases actual string vibrations directly, but more commonly general bridge vibrations are sensed. Some piezo setups have a separate pickup (or two, or even four in the case of some Barbera Transducer Systems pickups) within the bridge under each string. A few systems use transducers oriented in various directions to differentiate between bowed and plucked string motion. Operating a switch then selects the preferred mode.
   BULLET::::- The best-known application is the electric cigarette lighter: pressing the button causes a spring-loaded hammer to hit a piezoelectric crystal, producing a sufficiently high-voltage electric current that flows across a small spark gap, thus heating and igniting the gas. The portable sparkers used to ignite gas stoves work the same way, and many types of gas burners now have built-in piezo-based ignition systems.
   Piezoelectric crystal classes: 1, 2, m, 222, mm2, 4, -4, 422, 4mm, -42m, 3, 32, 3m, 6, -6, 622, 6mm, -62m, 23, -43m
  
  Pyroelectric: 1, 2, m, mm2, 3, 3m, 4, 4mm, 6, 6mm
  
  Section::::Crystal classes.:Related effects.
   Some electric guitar models feature piezoelectric pickups, which function as transducers to provide a sound closer to that of an acoustic guitar with the flip of a switch or knob, rather than switching guitars. Those that combine piezoelectric pickups and magnetic pickups are sometimes known as hybrid guitars.
  