Last Updated on May 6, 2023 by You Ling
Piezoelectric materials have revolutionized the fields of sensors, actuators, and transducers due to their unique ability to convert electrical energy to mechanical energy and vice versa. With a wide range of applications in industries such as medical, aerospace, automotive, and consumer electronics, it is essential to understand the key differences and characteristics of these devices. This article provides an overview of piezoelectric transducers and actuators, as well as their characteristics, and highlights the primary differences between the two devices.
1、What is a piezoelectric transducer?
A piezoelectric transducer refers to a converter made using the direct and inverse piezoelectric effects of piezoelectric materials. As the name implies, a converter is a device that can convert energy. Piezoelectric transducers use the piezoelectric effect of certain single-crystal materials and the electrostrictive effect of certain polycrystalline materials to convert electrical energy and acoustic energy. Due to their high electroacoustic efficiency, large power capacity, and adaptable structure and shape for different applications, they are widely used in the field of power ultrasound.
2、What is a piezoelectric actuator?
A piezoelectric actuator is a converter that converts electrical energy into mechanical displacement or stress based on the piezoelectric effect, and vice versa. They are widely used as high-precision positioning mechanisms because they can control small mechanical displacements at high speeds, producing large forces, stable displacements, and convenient operation.
3、Advantages of piezoelectric transducers
Sensitivity:
Refers to the efficiency of the transducer’s conversion capability. High sensitivity indicates a high conversion efficiency.
Resonant frequency:
Refers to the frequency at which the transducer resonates.
Directivity:
Refers to the intensity of the transmitted or received signals in all direction angles of the transducer’s radiating surface.
Temperature resistance:
Refers to the high and low temperature limits within which the transducer can function properly.
Pressure resistance:
Refers to the high and low pressure limits within which the transducer can function properly.
Electrical parameters:
Refers to the impedance, capacitance, and inductance of the transducer itself.
Amplitude:
Refers to the vibration amplitude of the transducer at a fixed drive voltage.
Voltage limit:
The maximum voltage value of the transducer. Long-term voltages exceeding this value can cause the depolarization of the piezoelectric ceramic.
Sealing:
Refers to the transducer’s sealing in liquids.
Corrosion resistance:
Refers to the transducer’s resistance to corrosive environments.
4、Advantages of piezoelectric actuators
Displacement:
In a stacked actuator, each piezoelectric element has alternating polarity and an electric field is applied parallel to the polarization direction. When a voltage is applied, strain or displacement is induced in the polarization direction. The movement of the piezoelectric element equals the amount of voltage applied multiplied by the piezoelectric coefficient (the piezoelectric coefficient d33 is related to the efficiency of converting electrical energy into mechanical energy). Since they are connected mechanically in series, the total movement of the stacked piezoelectric actuator is the movement of a single element multiplied by the number of elements in the stack. The total displacement of a stacked actuator is typically between 0.1% and 0.15% of the actuator length.
Voltage and electric field:
Stacked piezoelectric actuators are generally classified as low voltage (below 200 V) or high voltage (up to 1000 V), referring to the maximum input voltage of the maximum stroke. The magnitude of the applicable voltage depends on the material and thickness of each element. Therefore, the electric field increases as the layer thickness decreases. Similarly, for a given electric field, the driving voltage must decrease as the layer thickness decreases.
Force and stiffness:
Actuator stiffness has a significant impact on force generation, which is determined by the elastic modulus of the piezoelectric ceramic material, the cross-sectional area of the actuator, and its length. Despite their small size, stacked piezoelectric actuators have a force density of around 30 N/mm allowing them to generate tens of thousands of Newtons of useful force. It is important to note that in steady-state operation (no motion, constant force), there is no current flow and no power supply is needed. Stacked actuators can also maintain their position when the power is off, without generating heat.
Tensile strength and preloading force:
Stacked piezoelectric actuators often withstand both compressive and tensile forces, particularly during high dynamic motion. The tensile strength of stacked actuators largely depends on the method of pressing the individual element layers together and is usually an order of magnitude lower than the compressive strength. Preloading the actuator with a force greater than the applied tensile load ensures that the actuator always remains in compression and can operate in high dynamic, bidirectional applications. Successful integration of stacked piezoelectric actuators requires any applied force to be purely axial and compressive. Manufacturers usually provide various mounting options to help prevent bending, shearing, or torsional forces.
5、Differences between piezoelectric transducers and piezoelectric actuators
Piezoelectric transducers can be described as a combination of piezoelectric sensors and piezoelectric actuators.
When discussing piezoelectric devices, the terms transducer and actuator are often used interchangeably. However, when motion or force is the main goal, people usually refer to piezoelectric actuators, while transducers are more commonly used when the goal is sensing or high-frequency applications (such as ultrasonics, flow, or distance measurement). Actuators usually do not operate in resonance, while transducers usually do. Both essentially respond to external pressure by generating electrical charges, and vice versa, they change their shape when an electric field is applied.
Piezoelectric transducers use the piezoelectric effect of certain single-crystal materials and the electrostrictive effect of certain polycrystalline materials to convert electrical energy and acoustic energy. They can convert electrical energy and mechanical energy interchangeably.
Piezoelectric ultrasonic transducers come in various shapes, such as disks, plates, or tubes, and have different performance levels. They can be adapted to application requirements by using different piezoelectric ceramic materials, electrodes, and assembly techniques. They are present wherever ultrasonics are needed, such as flow metering, structural monitoring, and many medical applications.
Piezoelectric sensors convert physical, acceleration, pressure, or other inputs into electrical signals, serving as inputs for data processing systems. They only convert mechanical energy into electrical energy.
Piezoelectric actuators come in stacked and multilayer versions with different force ratings, displacements of up to hundreds of microns, and piezoelectric bending actuators reaching millimeter levels. Their basic characteristics, such as millisecond response times and high dynamics, along with virtually unlimited resolution, make them indispensable in applications ranging from industrial production or distribution to ultra-precision positioning.
6、Conclusion:
In summary, piezoelectric transducers and actuators are versatile devices that leverage the unique properties of piezoelectric materials for various applications. While both types of devices can convert electrical energy into mechanical energy and vice versa, they differ in their primary objectives and operational characteristics. Piezoelectric transducers focus on sensing and high-frequency applications, while piezoelectric actuators are designed to produce precise motion or force. Understanding the differences and characteristics of these devices is crucial for selecting the appropriate one for a specific application, enabling the efficient utilization of piezoelectric technology across numerous industries.
