Piezoelectricity (from the Greek piezo, πιέζω, "squeeze or squeeze") is a phenomenon that occurs in certain crystals that, when subjected to mechanical stress, acquire an electrical polarization in their mass, appearing a potential difference and electric charges on their surface. Quartz crystals behave in a similar way to LC tanks, and are also known as "Crystal Resonator"), with the advantage of being able to generate stable and insensitive oscillation frequencies.
This phenomenon also occurs in reverse: they deform under the action of internal forces when subjected to an electric field. The piezoelectric effect is normally reversible: when the crystals are no longer subjected to an external voltage or electric field, they recover their shape.
Piezoelectric materials are natural or synthetic crystals that lack a center of symmetry. A compression or shear causes dissociation "Dissociation (chemical)") of the centers of gravity of electrical charges, both positive and negative. As a consequence, elementary dipoles appear in the mass and, by influence, charges of opposite sign arise on the facing surfaces.
Pyroelectricity
In 1824, Sir David Brewster demonstrated piezoelectric effects using La Rochelle salt,[1] deciding to name the effect pyroelectricity.[2].
Piezoelectric material groups
There are two groups of materials:
History of piezoelectric materials
The property of piezoelectricity was first observed by Pierre and Jacques Curie in 1881 studying the compression of quartz. By subjecting it to the mechanical action of compression, the charges of the matter are separated. This causes a polarization of the charge, which causes sparks to fly.
For the property of piezoelectricity to occur in matter, it must crystallize in systems that lack a center of symmetry (that have dissymmetry) and, therefore, a polar axis. Of the 32 crystalline classes, the mentioned center does not exist in 21. In 20 of these classes the piezoelectric property occurs, to a greater or lesser extent. Gases, liquids and solids with symmetry do not have piezoelectricity.
Piezoelectric power generation
Introduction
Piezoelectricity (from the Greek piezo, πιέζω, "squeeze or squeeze") is a phenomenon that occurs in certain crystals that, when subjected to mechanical stress, acquire an electrical polarization in their mass, appearing a potential difference and electric charges on their surface. Quartz crystals behave in a similar way to LC tanks, and are also known as "Crystal Resonator"), with the advantage of being able to generate stable and insensitive oscillation frequencies.
This phenomenon also occurs in reverse: they deform under the action of internal forces when subjected to an electric field. The piezoelectric effect is normally reversible: when the crystals are no longer subjected to an external voltage or electric field, they recover their shape.
Piezoelectric materials are natural or synthetic crystals that lack a center of symmetry. A compression or shear causes dissociation "Dissociation (chemical)") of the centers of gravity of electrical charges, both positive and negative. As a consequence, elementary dipoles appear in the mass and, by influence, charges of opposite sign arise on the facing surfaces.
Pyroelectricity
In 1824, Sir David Brewster demonstrated piezoelectric effects using La Rochelle salt,[1] deciding to name the effect pyroelectricity.[2].
Piezoelectric material groups
There are two groups of materials:
History of piezoelectric materials
The property of piezoelectricity was first observed by Pierre and Jacques Curie in 1881 studying the compression of quartz. By subjecting it to the mechanical action of compression, the charges of the matter are separated. This causes a polarization of the charge, which causes sparks to fly.
If pressure is exerted on the ends of the polar axis, polarization occurs: electron flow is directed towards one end and generates a negative charge, while a positive charge is induced at the opposite end.
When narrow glass sheets with a large surface area are used, the high voltage obtained – necessary for the spark to jump – is greater. The narrow sheets are cut so that the polar axis crosses said faces perpendicularly.
The current generated is proportional to the area of the plate and the rate of change of the pressure applied orthogonally "Orthogonality (mathematics)") to the surface of the plate.
Another important application of piezoelectricity results from the inverse property being fulfilled:
The first practical application of piezoelectricity, which arises from the quality of transforming a mechanical signal (pressure) into an electrical signal (electric current), is that of sonar.
At the end of the First World War it was discovered that the sound waves produced by submarines could be detected by a piece of quartz submerged in water, in which the currents generated were measured and made it possible to detect the direction coming from the sound.
The sonar consists of a probe (piezoelectric) which is a transducer; That is to say: it works according to the following sequence of events:
Crystal classes of substances containing piezoelectricity
Within the 32 crystallographic groups there are 21 that do not have a center of symmetry. Of these, about 20 directly exhibit piezoelectricity (number 21 is cubic class 432). Ten of them are polar; That is to say: they present instantaneous polarization, because their unit cell contains an electric dipole, and the material exhibits pyroelectricity. Of these – when the direction of the dipole can be reversed by applying an electric field – some are also ferroelectric. The crystallographic classes are:
Piezoelectricity equations
The constitutive equations of piezoelectric materials combine stresses, strains and electrical behavior:
D is the electric flux density, is the permittivity and E is the electric field:.
S is the strain and T is the stress.
These equations can be combined into a single equation where the relationship between load and deformation is considered:.
d represents the piezoelectric constants of the material, and the superscript E indicates that the magnitude is measured under constant or zero electric field, and the superscript T indicates that it is a transposed form of matrix "Matrix (mathematics)").
This can be rewritten in matrix form like this:.
Uses
One of the most widespread uses of this type of crystal is in electric lighters. Inside they have a piezoelectric crystal which the ignition mechanism suddenly hits. This sharp blow causes a high concentration of electrical charge, capable of creating an electric arc or spark, which ignites the lighter.
Another important application of a piezoelectric crystal is its use as a vibration sensor. Each of the pressure variations produced by the vibration causes a current pulse proportional to the force exerted.
A mechanical vibration has easily been converted into an electrical signal ready to be amplified. Simply connect an electrical cable to each of the "Face (geometry)" faces of the crystal and send this signal to an amplifier. For example, in piezoelectric pickups#Pizoelectric_pickups "Pickup (electric instrument)") of guitar.
A very important additional application of piezoelectricity, but in this case the other way around, occurs in the fuel injectors of internal combustion engines. By applying a potential difference to a piezoelectric material, the injector is opened, which allows the fuel, at very high pressure, to enter the cylinder. The use of piezoelectric injectors makes it possible to control, with enormous precision, the injection times and the amount of fuel introduced into the engine. This results in improvements in consumption, features and performance of different engines.
For the property of piezoelectricity to occur in matter, it must crystallize in systems that lack a center of symmetry (that have dissymmetry) and, therefore, a polar axis. Of the 32 crystalline classes, the mentioned center does not exist in 21. In 20 of these classes the piezoelectric property occurs, to a greater or lesser extent. Gases, liquids and solids with symmetry do not have piezoelectricity.
If pressure is exerted on the ends of the polar axis, polarization occurs: electron flow is directed towards one end and generates a negative charge, while a positive charge is induced at the opposite end.
When narrow glass sheets with a large surface area are used, the high voltage obtained – necessary for the spark to jump – is greater. The narrow sheets are cut so that the polar axis crosses said faces perpendicularly.
The current generated is proportional to the area of the plate and the rate of change of the pressure applied orthogonally "Orthogonality (mathematics)") to the surface of the plate.
Another important application of piezoelectricity results from the inverse property being fulfilled:
The first practical application of piezoelectricity, which arises from the quality of transforming a mechanical signal (pressure) into an electrical signal (electric current), is that of sonar.
At the end of the First World War it was discovered that the sound waves produced by submarines could be detected by a piece of quartz submerged in water, in which the currents generated were measured and made it possible to detect the direction coming from the sound.
The sonar consists of a probe (piezoelectric) which is a transducer; That is to say: it works according to the following sequence of events:
Crystal classes of substances containing piezoelectricity
Within the 32 crystallographic groups there are 21 that do not have a center of symmetry. Of these, about 20 directly exhibit piezoelectricity (number 21 is cubic class 432). Ten of them are polar; That is to say: they present instantaneous polarization, because their unit cell contains an electric dipole, and the material exhibits pyroelectricity. Of these – when the direction of the dipole can be reversed by applying an electric field – some are also ferroelectric. The crystallographic classes are:
Piezoelectricity equations
The constitutive equations of piezoelectric materials combine stresses, strains and electrical behavior:
D is the electric flux density, is the permittivity and E is the electric field:.
S is the strain and T is the stress.
These equations can be combined into a single equation where the relationship between load and deformation is considered:.
d represents the piezoelectric constants of the material, and the superscript E indicates that the magnitude is measured under constant or zero electric field, and the superscript T indicates that it is a transposed form of matrix "Matrix (mathematics)").
This can be rewritten in matrix form like this:.
Uses
One of the most widespread uses of this type of crystal is in electric lighters. Inside they have a piezoelectric crystal which the ignition mechanism suddenly hits. This sharp blow causes a high concentration of electrical charge, capable of creating an electric arc or spark, which ignites the lighter.
Another important application of a piezoelectric crystal is its use as a vibration sensor. Each of the pressure variations produced by the vibration causes a current pulse proportional to the force exerted.
A mechanical vibration has easily been converted into an electrical signal ready to be amplified. Simply connect an electrical cable to each of the "Face (geometry)" faces of the crystal and send this signal to an amplifier. For example, in piezoelectric pickups#Pizoelectric_pickups "Pickup (electric instrument)") of guitar.
A very important additional application of piezoelectricity, but in this case the other way around, occurs in the fuel injectors of internal combustion engines. By applying a potential difference to a piezoelectric material, the injector is opened, which allows the fuel, at very high pressure, to enter the cylinder. The use of piezoelectric injectors makes it possible to control, with enormous precision, the injection times and the amount of fuel introduced into the engine. This results in improvements in consumption, features and performance of different engines.