What is the Advantage and Disadvantage of Crystal Piezoelectric Materials
What is a Piezoelectric Material? Working, Advantages and Limitations
Piezoelectric materials have been around since the late 80’s and paved way for many game-changing inventions. Serving in the form of SONAR in world war these materials have now caught eyes of the inventors for their mystic characteristics. Wireless Sensor Networks, Internet of Things rules the technical era of the 21st century. To keep these novelties up and running, power requirement has become the greatest challenge. Hunt for a sustainable, reliable, renewable energy source caused researchers to stumble upon trailblazing power harvesters- the piezoelectric materials. Let’s set on a voyage to explore these new age power harvesters.
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What is Piezoelectric Material?
To know what a piezoelectric material is one has to know what does the term piezoelectric stand for?. In PIEZOELECTRICITY the term” piezo” stands for pressure or stress. Thus piezoelectricity is defined as “Electricity generated by application of mechanical stress or tension” and the materials that exhibit this property comes under the category of piezoelectric materials. The credit for the discovery of these materials goes to Sir Jacques Curie (–) and Pierre Curie (–). While experimenting with certain crystalline minerals like quartz, cane sugar, etc… they found that application of force or tension on these materials generated voltages of opposite polarities with magnitudes propositional to the applied load. This phenomenon was named as Direct Piezoeffect.
In the following year, Lippman discovered the Converse effect stating that one of these voltage-generating crystals, when exposed to an electric field, lengthened or shortened according to the polarity of the applied field. Piezoelectric materials came into recognition with their role in WW1 when Quartz was used as resonators in SONAR. During the period of WW2, synthetic piezoelectric material was discovered, which later led to the intense development of piezoelectric devices. Before using a piezoelectric material one must know what characteristics make these materials piezoelectric.
Properties of Piezoelectric Material and How does it Work?
The secret of piezoelectric materials lies in their unique atomic structure. Piezoelectric materials are ionically bonded and contain positive and negative ions in the form of pairs called unit cells. These materials are available in nature as an anisotropic dielectric with non-Centrosymmetric crystal lattice i.e. they don’t have any free electrical charges and the ions lack a center of symmetry.
Direct Piezoelectric Effect
When mechanical stress or friction is applied on these materials the geometry of the atomic structure of the crystal changes due to net movement of positive and negative ions with respect to each other, resulting in electric dipole or Polarization. Thus the crystal changes from a dielectric to a charged material. The amount of voltage generated is directly proportional to the amount of stress or tension applied to the crystal.
Converse Piezoelectric Effect
When electricity is applied to these crystals electric dipoles appear, forming the dipole movement which causes deformation of the crystal, thus giving rise to converse piezoelectric effect as shown in the figure.
Synthetic Piezoelectric Materials
Manmade piezoelectric materials like piezoelectric ceramics exhibit spontaneous polarization (ferroelectric property) i.e. dipole exists in their structure even when no electric field is applied. Here the amount of piezoelectric effect produced strongly depends on their atomic structure. The dipoles present in the structure forms domains-regions where the neighboring dipoles have the same alignment. Initially, these domains are randomly oriented thus causing no net polarization.
By applying a strong DC electric field to these ceramics when they pass through their Curie point the domains get aligned in the direction of applied electric field. This process is called poling. After cooling to room temperature and removing the applied electric field, all domains maintain their orientation. After completion of this process, the ceramic exhibits the piezoelectric effect. Natural existing piezoelectric materials like quartz do not display ferroelectric behavior.
Piezoelectric Equation
Piezoelectric Effect can be described with the following Piezoelectric Coupling Equations
Direct piezoelectric effect: S = sE .T+ d. E
Converse piezoelectric effect: D = d.T+εT.E
Where,
D = electric displacement vector
T = the stress vector
sE = matrix of elastic coefficients at constant electric field strength,
S = strain vector
εT = dielectric matrix at constant mechanical strain
E = electric field vector
d = direct or converse piezoelectric effect
The electric field applied in different directions generates different amounts of stress in piezoelectric materials. So sign conventions are used along with coefficients to know the direction of applied field. To determine the direction, axes 1, 2, 3 are used analogously to X, Y, Z. Poling is always applied in the direction of 3. The coefficient with double subscripts relates electrical and mechanical characteristics with the first subscript describing the direction of the electric field in accordance with the voltage applied or charge produced. The second subscript gives the direction of mechanical stress.
Electromechanical coupling coefficient occurs in two forms. The first is the actuation term d, and the second is the sensor term g. The piezoelectric coefficients along with their notations can be explained with d33
Where,
d specifies applied stress is in 3rd direction.
3 specifies electrodes are perpendicular to the 3rd axis.
3 specifies piezoelectric constant.
How Piezoelectric Material Works?
As explained above piezoelectric materials can work in two modes:
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- The direct piezoelectric effect
- Converse piezoelectric effect
Let take an example for each to understand the application of these modes.
Heal-Strike Generator using Direct Piezoelectric Effect:
DARPA has developed this device to equip soldiers with a portable power generator. The piezoelectric material implanted in the shoes experiences mechanical stress when the soldier walks. Due to direct piezoelectric property, the material produces electric charge due to this mechanical stress. This charge is stored in the capacitor or batteries which thereby can be used to charge their electronic devices on the go.
Quartz Crystal Oscillator in Watches using Converse Piezoelectric Effect
Watches contain a quartz crystal. When electricity from the battery is applied to this crystal through a circuit converse piezoelectric effect occurs. Due to this effect upon application of electric charge the crystal starts to oscillate with a frequency of times per second. The microchip present in the circuit counts these oscillations and generates a regular pulse per second that spins the second hands of the watch.
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Additional resources:Siemens SIPLACE ASM 517 NOZZLE 03012042 - SMT Reflow Oven
Uses of Piezoelectric Materials
How to Select a Disc Spring - Use, Load, Etc. | MW Components
Due to its unique characteristics, piezoelectric materials have acquired an important role in various technological inventions.
Use of Direct Piezo Effect
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- In Japan’s train stations the concept of “crowd farm” was tested where the footsteps of the pedestrians’ on the piezoelectric tiles embedded on the road can generate electricity.
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- In a nightclub in London builds first eco-friendly floor made up of piezoelectric material that can generate electricity to power up light bulbs when people dance on it.
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- Piezoelectric effect finds useful application as mechanical frequency filters, surface acoustic wave devices, bulk acoustic wave devices, etc…
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- Sound and ultrasound microphones and speakers, ultrasonic imaging, hydrophones.
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- Piezoelectric pickups for guitars, biosensors to power up pacemaker.
- Piezoelectric elements are also used in the detection and generation of sonar waves, single-axis and dual-axis tilt sensing.
Uses of Converse Piezoelectric Effect
- Actuators and motors
- Micro-precision placement and micro-precision adjustments in lenses for microscopes.
- Needle driver in printers, miniaturized motors, bimorph actuators.
- Multilayered actuators for fine positioning in optics
- Injection systems in automotive fuel valves etc…
By Coupling Electrical and Mechanical Fields:
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- For investigation of the atomistic structure of materials.
- To monitor structural integrity and detect faults at early stages in civil, industrial and aerospace structures.
Advantages and Limitations of Piezoelectric Materials
The advantages and limitations of piezoelectric materials include the following.
Advantages
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- Piezoelectric materials can operate at any temperature conditions.
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- They have low carbon footprint making them the best alternative for fossil fuel.
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- Characteristics of these materials make them the best energy harvesters.
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- Unused energy lost in the form of vibrations can be tapped to generate green energy.
- These materials can be reused.
Limitations
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- While working with vibrations these devices are prone to pick up unwanted vibrations also.
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- Resistance and Durability apply limits to devices when used to tap energy from pavements and roads.
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- The mismatch between stiffness of piezoelectric material and pavement material.
- Less known details of these devices and the amount of research done till date is not sufficient to exploit full usage of these devices.
What is a Piezo Transducer? | Advantages & Functions | APC
Jump To: What are Piezo Transducers | Advantages and Limitations | Frequencies and Amplitudes | Different Modes | Parts and Functions | Types of Transducers | Measuring Efficiency | Applications and Uses
What is a Transducer?
A transducer is any device used to convert energy from one form to another – typically when converting input energy into output energy. For transduction to occur, a change from one form of energy must also take place, such as a conversion from mechanical to electrical energy or vice versa. There are many types of transducers and the uses of transducers are widespread, impacting us in many ways. A common example is a microphone, which converts the input energy – or the sound waves produced by a voice or instrument – to output energy, or the electrical impulses in the form of amplified sound.
How Does a Transducer Work?
Transducers work through a conversion of energy and sound. Types of electroacoustic transducers include hydrophones, which convert changes in water pressure to an electrical output, and pickups on musical instruments such as guitars, which convert the vibration of the instrument’s strings into an electrical impulse.
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What are Piezoelectric Transducers?
Piezoelectric transducers are a type of electroacoustic transducer that convert the electrical charges produced by some forms of solid materials into energy. The word “piezoelectric” literally means electricity caused by pressure. An early application of piezo transducer technology occurred during World War I with the use of sonar, which used echoes to detect the presence of enemy ships. Small piezo transducers were also mostly present in landline phones. They sat inside the ringer and helped to generate a noticeable noise to alert people to incoming calls. In addtion, piezoelectricity finds a home inside quartz watches as well, which is what keeps them so precise.
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- Self-generating: Due to their materials’ ability to produce voltage while under the influence of some energy, piezo transducer circuits do not require an external power source.
- Accessible: Piezoelectric transducer circuits, due to their small dimensions and large measuring range, are easy to handle, install and use.
- High-frequency response: A much higher-than-normal frequency response means the parameters of these transducers shift quickly.
- Flexibility: Due to how most of the materials used in construction can be shaped into different shapes and sizes, you can apply these transducers in various fields.
- Small electric charge: While they might be self-generating, you’ll require a high impedance cable to establish a connection with an electrical interface.
- Affected by various environments and conditions: Piezo transducers cannot measure output in the static condition, and temperature and humidity variations can affect output.
- Naturally low output: While some materials produce output rates that are relatively higher than their counterparts, output is still low in most respects. You’ll need to attach it to an external circuit.
Frequencies and Amplitudes for Piezo Transducers
Oscillation of piezo elements starts when AC voltages are applied. Their incredibly fast response — in the range of microseconds and lower — allow them to be of use in a wide range of applications, even including the generation of ultrasound, with frequencies all the way up to 20 MHz.
Because of their extreme sensitivity to the piezoelectric effect, it’s possible to create piezo transducers for applications ranging from sensors to ultrasound power generation. Doing so includes higher energy densities and frequencies ranging from 20 to 800 kHz.
In this range of frequencies and amplitudes, piezo transducers that produce ultrasound energy are of excellent use in various medical and industrial processes. In the healthcare sector, these applications range from the removal of dental plaque to the ultrasound crushing of kidney stones. In industrial settings, piezoelectric transducers are ideal for use in various bonding, cleaning and welding processes.
Different Modes of Piezo Transducers
Certain physical quantities — such as force and stress — are difficult to measure directly. In these instances, piezoelectric transducer output voltages are in direct proportion to any stresses and/or forces that are applied to the piezo material. Through the different modes of transducer measures, a scale can be set up to efficiently and accurately measure an applied force or stress.
However, it should be noted that since the voltage output of materials undergoing the piezoelectric effect is relatively low with high impedance, piezo transducers often require some sort of amplifier or auxiliary circuitry to work effectively.
Transducer Parts & Functions
While many materials can show the piezoelectric effect, the best ones must also possess at least a few of the most desirable qualities. Such characteristics include consistent stability, high output, malleability and resistance to extreme temperatures and humidity. That said, no known material exhibits all of those qualities simultaneously.
Originally, crystals made from quartz took hold as the primary material for piezoelectric crystal transducers. Quartz offers superior stability and slow measuring at varying parameters due to low leakage rates, which means it can provide excellent accuracy — hence why watches most often use them. While they’re still in widespread use, quartz also yields a rather low output, meaning it can’t keep up adequately with demands of more sophisticated technology.
In the early s, quartz crystals began to give way to piezoelectric ceramic as the primary transducer material. The advantages offered by a ceramic transducer when compared to other materials include ceramic’s ability to be manufactured in a wide variety of shapes and sizes, its capability of operating efficiently at low voltage, and its ability to function at temperatures up to 300 degrees Celsius.
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Types of Transducers
Due to the ability to produce a ceramic transducer in numerous sizes and shapes, ceramic transducers can be easily adapted to a wide variety of industrial applications. Consequently, they allow for complete customization to meet a customer’s specific needs. Today, the most commonly used ceramic transducer manufacturing materials are lead zirconate titanate compositions, a trend that traces its origins to the s. As ceramic transducer technology has continued to evolve, the use of piezo-polymers and composites has likewise gained acceptance.
Another material that works incredibly well in transducers is Rochelle salt, which is a synthetic crystal. Of every medium that shows signs of the piezoelectric effect, Rochelle salt produces the highest output of any other material discovered thus far. However, it does have its drawbacks, which can hold back its success in certain environments. These synthetic crystals cannot come into contact with any moisture, nor can they be used at a temperature above 115 degrees Fahrenheit.
If you are willing to trade off sensitivity for peak output, synthetic crystals can produce a distinct edge in performance over natural crystals.
The Piezoelectric Ultrasonic Transducer
A piezoelectric ultrasonic transducer generates ultrasonic activity, meaning it measures the pressure of sound waves above the frequencies that can be heard by the human ear. It functions by rapidly expanding and contracting when appropriate electrical frequency and voltage is applied. Typically used in cleaning systems, the expansion and contraction causes the ultrasonic cleaner transducer’s diaphragm, which serves as the pressure-sensing element of the unit, to vibrate introducing ultrasonic activity into the cleaning tank in the process. The piezoelectric ultrasound transducer also offers the advantages of high electroacoustic efficiency while minimizing heat generation.
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Applications and Uses for Electric Transducers
Piezoelectric transducers can be used for numerous applications that use electric power for industrial, environmental and personal use. Air transducers, for instance, are frequently used in automobile, proximity and level sensors – think of the automatic sliding doors you encounter at grocery stores, airports and hotels. They are commonly used in residential products like motion and object detectors, pest deterrents and home security alarms. They are commonly used in residential products like motion and object detectors, pest deterrents and home security alarms.
Manufacturers implement them into common electronic devices too such as toys, games and remote control units. You’ll also find them in inkjet printers, electric toothbrushes and buzzers.
What factors affect the performance of piezoelectric devices?
The performance of piezoelectric devices is influenced by material properties, such as stability and output, with ceramics often preferred over quartz for their higher efficiency and temperature resistance. Environmental conditions, including temperature and humidity, can also affect output, and devices often require high-impedance connections due to their low electric charge.
APC International, Ltd. — Putting Your Piezoelectric Equipment Needs First
At APC International, Ltd., we know from experience how to listen to our customers’ needs so that our role as a trusted supplier of piezoelectric ceramics and devices becomes that of a trusted partner. That’s why, whether you’re in the first stages of designing a prototype or you need a critical component mass produced, our expert staff and state-of-the-art production facility are ready to supply you with the piezo products and services you should expect from an industry leader.
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