What is a Piezoelectric Actuator : Working & Its Applications

The piezoelectric actuator is an essential part of many smart & electromechanical systems along with signal processing units and types of sensors. In many smart systems, actuators work like responding units. At present, there is a lot of progress in non resonance piezoelectric actuators like step motors, multilayer ceramic actuators, resonance ultrasonic motors & inertial motors. These actuators generate a small displacement through a high force capacity once voltage is applied. These are used in many applications like handling & generation of high pressures or forces within dynamic and static situations and ultra-precise positioning, etc. This article discusses an overview of a piezoelectric actuator and its working with applications.

What is a Piezoelectric Actuator?

A piezoelectric actuator is a transducer, used to change an electrical signal into an accurately controlled physical displacement or stroke by using piezoelectric effect based on electromechanical coupling rather than electromagnetic induction. If the stroke is avoided, then useable energy will develop. The exact movement control afforded by these actuators is mainly used to change machining tools, mirrors, lenses, or other apparatus finely.

A piezo actuator is used to control hydraulic valves which work like a special-purpose motor, small-volume pump & in other applications which uses force or movement. The piezoelectric actuator diagram is shown below.

As compared to electromagnetic actuators, piezoelectric actuators have some features like flexible design, compact size & provide sub-micrometer or nanometer positioning.

Piezoelectric Actuator Working Principle & Operation

The working principle of a piezoelectric actuator is, once the voltage is applied to piezoelectric actuators then they generate a small displacement through a high force capacity, so these are used in many applications like ultra-precise positioning, in high forces handling & generation in stationary or dynamic conditions.

The configuration of the piezoelectric actuator can change greatly based on application. These devices are Ultrasonic actuators which are designed specifically to generate strokes of numerous micrometers at ultrasonic frequencies above 20 kHz. They are particularly used for positioning, controlling vibration & quick switching applications.

The important specifications of piezoelectric actuators mainly include force, displacement, & operating voltage. The factors that need to consider while using these actuators are capacitance, stiffness & resonant frequency.

The term stiffness is used to describe the energy required to attain a certain deformation of an arrangement. For piezoelectric actuators, stiffness is the energy required to extend the device through a certain quantity, usually stated in terms of Newtons for each micrometer. The capacitance is a task of the excitation voltage frequency and resonance is the frequency where the piezoelectric actuators react with the highest o/p amplitude.

Types of Piezo Actuators

Piezo actuators are available in different types like stack, stripe, longitudinal, shear, tube, and contracting.

Piezo Stack Actuators

A Piezo stack actuator is used to provide a low stroke through a high blocking energy. Based on your design necessities, this type of actuator is either discrete or co-fired. If it is certainly discrete, then its complex structures are designed by using discs or individually stacking finished piezoelectric ceramic rings & metal electrode foil through an adhesive. The typical operating voltage ranges from 500V to 1,000V.

If the actuators are co-fired stack actuators then these are also known as monolithic stacks which do not use adhesives. But, they use high-temperature sintering of the ceramic pile & complete electrode. The operating voltage of these can be 200 volts. In any case, co-fired or discrete, it is feasible to insulate them protectively from mechanical stresses & environmental impacts. Attaining this normally involves coating materials, bare stacks, or covering them within stainless steel.

Stripe Actuators

The Stripe Actuator is known as a bending actuator, used to generate a large mechanical deflection reasonably in response to an electrical signal. In sequence, this deflection gives a big stroke through the least blocking force as compared to the stack actuator.

This type of actuator uses two thin piezoelectric ceramic layers that are connected. They are usually in the coinciding polarization direction through an electrically parallel connection. Once we apply an electrical input, one ceramic layer bonds whereas the other one enlarges so that the actuator will bend.

Longitudinal Actuators

Longitudinal actuators are also known as piezo stacks which are formed by coating several piezo elements on top of each other so that each element’s expansion effect will generate a useful force & movement. These types of actuators use the piezoelectric effect for generating linear displacements which range from 0.1 – 0.15% of the length of the actuator. The force density of these actuators is high typically 30 N/mm^2 range and also high resonant frequencies so that these actuators are used in dynamic applications.

Shear Actuators

These types of actuators are related to longitudinal type actuators because they have multiple piezo elements layers but they vary in how the voltage is applied & the type of motion formed. In shear piezo actuators, the different elements are horizontally polarized & the electrical field can be applied orthogonally.

The resulting displacement takes place within the horizontal plane so that a shear-type motion can be created. These actuators’ height is restricted through bending & shear stresses, although they are frequently merged within multi-axis systems by longitudinal actuators.

Tube Actuators

Tube actuators include radial polarization & also use the transverse piezoelectric effect to make displacement. These types of actuators experience radial, axial, or lateral motion based on the voltage applied which is relative to the electrodes. These actuators are not appropriate for generating forces; however, they supply micron-level travel for pumping, nanoliter dosing & scanning microscopes applications.

Contracting Actuators

Flat actuators including two piezo elements can generate contracting motion once both elements operate mutually. These types of actuators utilize the transverse piezoelectric effect to generate motion in one direction only. Contracting piezo actuators have little displacement up to 20 microns however can produce 100’s of Newton’s force.

Once this type of actuator is mounted to a substrate or a base, then a bending actuator can be created. In a bending type actuator, the voltage applied can cause one piezo element to increase whereas the other contracts.

Advantages

The advantages of the piezoelectric actuator include the following.

• Simple design
• Least moving parts,
• High-reliability characteristics
• These are simply optimized for particular applications like a non-magnetic, cryogenic, ultra-high vacuum & high stiffness.
• High force for each unit areaResolution is unlimited
• Vacuum &Clean Room Compatible
• Generation of High Force
• No Wear & Tear
• Energy consumption is low
• No Magnetic Fields
• Quick Response
• Operates at Cryogenic Temperatures

Where are Piezoelectric Actuators used?

The applications of piezoelectric actuators include the following.

• A piezoelectric actuator is used to adjust different types of equipment like lenses, machining tools, mirrors, etc.
• These are used in various precision motion control-based applications.
• These actuators are also used to control hydraulic valves which work like a special-purpose motor or a small-volume pump
• These are used in applications where force or movement is required.
• These are used in different industries like aviation, automotive, consumer electronics, medical, aerospace due to many benefits.
• Piezo actuators are used in braille & precision knitting machines.
• Piezo actuators are used in mobile phones and video cameras equipped with microphones due to silent drive characteristics.
• These actuators don’t need lubrication to function, so used in vacuum & cryogenic environments.

What are piezoelectric actuator materials?

The most commonly used piezo actuator materials are modified lead zirconate titanate ceramics.

What is a piezo stack actuator?

When various piezo elements are arranged on top of each other then it is known as a piezo stack actuator. These actuators operate in different environments like cryogenic conditions, vacuum, & the presence of magnetic fields. These are used in the aerospace, consumer electronics, and semiconductor industries & automotive.

What are the two parameters which are considered in piezo actuators?

Two parameters are considered usually in piezo actuators are blocking force (Fb) & free deflection (Xf). Blocking force is the highest force that can be produced once the maximum voltage is applied & the actuator is not permitted to move. Similarly, free deflection is the movement attained once the maximum voltage is applied & no force is generated.

What does a piezoelectric actuator do?

The piezoelectric actuator changes an electrical signal into an exactly controlled physical displacement This is used to control hydraulic valves, operate like a special-purpose motor or a small-volume pump, and is used in applications where force or movement is required.

Thus, this is all about an overview of the piezoelectric actuator and it’s working. The main function of this actuator is the inverse piezoelectric effect because once we apply voltage, then the actuator will expand or contract but, once we block the piezo actuator from moving, then it will produce a force. Here is a question for you, what are the disadvantages of a piezoelectric actuator?