Since the time people found out that the most dependable sources of energy generations will come to a point of extinction and we would run short for it after some decades or so and the earth would become a place without Electricity. And imagine if that would happen all those systems and technologies we rely on so much would stop running. Most importantly INTERNET will stop forever! And that would be a great blow. So, even before they realized the importance of Internet, even before it actually came to existent or even before Internet became a technology which is the center for all technological developments, they started working for alternative sources of energy generations.
Many of the alternative sources have already become a full-fledged Generation Plant and while some are still in the Laboratories to experiment their potential and their application in practical. Among these alternative sources of energy one which has not entered a full-fledged generation industry is Piezoelectricity or Electricity form Piezoelectric Crystals.
What is Piezoelectric Crystals?
The piezoelectric effect was discovered in 1880 by two French physicists, brothers Pierre and Paul-Jacques Curie, in crystals of Quartz, tourmaline, and Rochelle salt (potassium sodium tartrate). They took the name from the Greek word “Piezein”, which means “To Press”.
Crystals which acquire a charge when compressed, twisted or distorted are said to be piezoelectric. This provides a convenient transducer effect between electrical and mechanical oscillations.
Quartz demonstrates this property and is extremely stable. When an external force is applied on to a quartz crystal, there will be a change in the voltage generated across the surface. This change is measured by its corresponding value of sound or vibration.
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.
In technical terms:
“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).”
How Piezoelectric Effect is generated?
For generating Piezoelectric Effect, a natural quartz crystal has to be cut in the shape of a thin plate of rectangular or oval shape of uniform thickness. Each crystal has three sets of axes – Optical axes, three electrical axes OX1, OX2, and OX3 with 120 degree with each other, and three mechanical axes OY1, OY2 and OY3 also at 120 degree with each other. The mechanical axes will be at right angles to the electrical axes. Some of the parameters that decide the nature of the crystal for the application are:
- Angle at which the wafer is cut from natural quartz crystal
- Plate thickness
- Dimension of the plate
- Means of mounting
If an electric stress is applied in the directions of an electric axis (X-axis), a mechanical strain is produced in the direction of the Y-axis, which is perpendicular to the relevant X-axis. Similarly, if a mechanical strain is given along the Y-axis, electrical charges will be produced on the faces of the crystal, perpendicular to the X-axis which is at right angles to the Y-axis.
Inverse Piezoelectric Effect
The piezoelectric effect can be reversed, which is referred to as the inverse piezoelectric effect. This is created by applying electrical voltage to make a piezoelectric crystal shrink or expand. Using the inverse piezoelectric effect can help develop devices that generate and produce acoustic sound waves. Examples of piezoelectric acoustic devices are speakers (commonly found in handheld devices) or buzzers.
Advantages of Piezoelectricity
- High Frequency Response – They offer very high frequency response that means the parameter changing at very high speeds can be sensed easily.
- High Transient Response – The piezoelectric transducers can detect the events of microseconds and also give the linear output.
- High Output – They offer high output that be measured in the electronic circuit.
- Small Size – These are very compact and small in size having tough rugged construction.
- Barium titanate and quartz can be made in any desired shape and form. It also has a large dielectric constant. The crystal axis is selectable by orienting the direction of orientation.
Disadvantages of Piezoelectricity
- Output is low – The output obtained from the piezoelectric transducers is low, so external electronic circuit has to be connected.
- Since the device operates with the small electric charge, they need high impedance cable for electrical interface.
- The relative humidity rises above 85% or falls below 35%, its output will be affected. If so, it has to be coated with wax or polymer material.
- Forming into shape – It is very difficult to give the desired shape to the crystals with sufficient strength.
- It is not suitable for measurement in static condition. The output may vary according to the temperature variation of the crystal.
Examples of Piezoelectric Transducers
- Rochelle Salt
- Polarized barium Titanate
- Ammonium Di-hydrogen
- Lithium Sulphate
- Etylene Diamine Tartrate
- The collagen in bone is also a piezoelectric
- Ordinary Sugar
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. Piezoelectric Transducers are perfect device to be used for their conversion. These transducers have been put to many applications in our day to day life as listed below:
- In ultrasound equipment, a piezoelectric transducer converts electrical energy into extremely rapid mechanical vibrations – so fast, in fact, that it makes sounds, but ones too high-pitched for our ears to hear. These ultrasound vibrations can be used for scanning, cleaning, and all kinds of other things.
- Due to its excellent frequency response, it is normally used as an accelerometer, where the output is in the order of (1-30) mV per gravity of acceleration.
- The piezoelectric transducers are more useful for the dynamic measurements, i.e. the parameters that are changing at the fast rate. This is because the potential developed under the static conditions is not held by the instrument. Thus piezoelectric crystals are primarily used measurement of quantities like surface roughness, and also in accelerometers and vibration pickups.
- The automotive companies used piezoelectric transducers to detect detonations in the engine blocks.
To use this technology for power generation in full-fledged way the experiments are still going on. Well in the next blog we would discuss about some possible uses that we can have of the piezoelectric crystals to generate energy at our homes.