Multilayer Piezoelectric Actuators vs. Electromagnetic Actuators: A Technical Comparison and Application Analysis

1.Introduction
2.How Each Technology Works
3.Side by Side Technical Comparison
4.Use Cases and Decision Making
5.Bestarsensor: Multilayer Piezoelectric Actuators 
6.Conclusion

Introduction
Actuators are needed to do more than ever in today's industrial automation. Smaller, faster, more precise motion control systems are used in semiconductor manufacturing, medical robots and other optical systems than were used even ten years ago.
There are certain demands that engineers place on actuators today. First, they need small physical size. They need fast response times. For some applications, they need to work in places where magnetic fields can't be used. Such demand takes many applications beyond the capability of conventional electromagnetic actuators.
The two preferred technologies are the electromagnetic actuators and the multilayer piezoelectric actuators. They're mature, stable and readily available technologies. However, the physics behind these technologies are completely different, and have similar yet critically different characteristics in the areas that are of most importance for precision motion control applications.
Bestarsensor designs Multilayer Piezoelectric Ceramics for precision actuation. This blog aims to give an objective technical comparison of the technologies to assist engineers in their choice of technology.

How Each Technology Works
1. Electromagnetic Actuators
Electromagnetic actuators produce mechanical energy from electrical energy via magnetism. A current carrying coil will produce a magnetic field. The field then works on a permanent magnet or ferromagnetic member to make a force. By varying the current, you can control the force and position.
The Lorentz force, which is the basis for motors, solenoids, voice coil actuators and linear motors. The technology is mature, easy to control with any driver electronics and can provide large strokes, even over long distances.
Mechanically, such technology often consists of a coil, a magnet it moves relative to and some kind of bearing or guide system. There will be a gap between the moving and fixed parts. Some degree of friction, wear and magnetic hysteresis must be expected.
2. Multilayer Piezoelectric Actuators
Piezoelectric actuators are based on a very different concept. Some types of ceramics deform when a voltage is applied. It's known as the inverse piezoelectric effect. If you apply a positive voltage, for instance, it will grow slightly. Apply a negative voltage and it contracts.
The displacement per single layer of ceramic is very small, on the order of nanometers per volt. But make the device multilayered. A stack of many thin ceramic layers in series electrically and parallel mechanically, results in the addition of all the deflection values. This results in a solid stack of ceramic that produces useful displacement for acceptable drive potentials.
The device has no coils, no magnets and no moving parts. The ceramic stack is a solid state device. It expands and contracts in solid form, there is no interface friction, gap or wear.

Side by Side Technical Comparison
The table below summarises the key performance differences between the two technologies across the parameters that matter most in precision applications.

Use Cases and Decision Making
1. Inkjet Print Heads: High Frequency Precision Valves
Inkjet print heads need to eject droplets at very high repetition rates (up to tens of thousands of droplets per second). Droplets must be ejected consistently on a highly controlled basis. Electromagnetic valves are not guaranteed to operate at these rates. The inductance of the coil limits the speed-current can be applied and removed, thus limiting the speed of actuation.
Piezoelectric actuators have no such limitation. They can operate to tens of kilohertz in real world settings, and further in specialised products. That's why industrial inkjet heads, ultrafast dispensing controls and other fluid control applications that need precise metered volumes at high speed now use piezoelectric technology.
2. Sub Nanometre Adjustment in Optical and Lithography
Lithography systems in semiconductor manufacturing systems require sub nanometre positioning of optical elements. Optical alignment systems need to adjust mirrors to better than a wavelength of light. This cannot be achieved with an electromagnetic actuator system without a fine stage.
Piezoelectric actuators are the solution. They have a linear relationship between applied voltage and displacement, no backlash and no stiction. They have position resolution determined only by the capabilities of the drive electronics. Closed loop systems that enable sub nanometre resolution are available in a miniature package with precision amplifiers.
For this reason, piezo stages are at the heart of semiconductor inspection tools, adaptive optics, fibre optic alignment and confocal microscopes.
3. Micro Pump for Medical & Biopharma
Miniaturisation in medical technology continues to increase. Smaller, lightweight and efficient actuator mechanisms are needed for implantable drug delivery, point of care diagnostic devices, and tool tips for surgery. 
Electromagnetic actuators don't scale well. The force they generate decreases rapidly as size decreases.
Piezoelectric actuators scale well. The stack, with multiple layers, has high force in the cubic centimetre range. 
Piezoelectric pumps with membrane actuation can accurately move and dispense fluid at low power consumption, and can be used for medical devices that are battery operated and need to be low power.
Another application is surgical robotics. The tips of minimally invasive tools require small size, high force and fine position control. Piezoelectric components deliver these capabilities in a small form factor impossible with electromagnetically operated components.

Bestarsensor: Multilayer Piezoelectric Actuators 
Bestarsensor designs and produces multilayer ceramic piezoelectric actuators using leading edge co firing technologies. There are several features of their components.
1. High Output Force Density
The multilayer co fired process employed by Bestarsensor allows for many thin ceramic layers to be assembled into a small package. The many layers in this stack produce cumulative displacement and force. This allows for a high blocking force and usable displacement output while occupying a small volume.
2. Long Term Cycle Stability
Bestarsensor uses rigorous material sourcing and manufacturing procedures to ensure the composition of the ceramic for the entire stack. This allows it to maintain reports displacement output across hundreds of millions of cycles. 
3. Precise Manufacturing and Lower Drive Voltages
The thinner the individual layers in a stack, the more layers that are involved. This leads to a lower electric field across each layer. Lower electric field across each layer means that a lower applied voltage is needed to achieve the same displacement. Reducing the drive voltage makes design of drive electronics easier and reduces insulation stress on the ceramic layers, which enhances reliability. Bestarsensor's ability to control the thickness of layers during sintering impacts the electrical performance, as well as the life of the actuator.

Conclusion
Electromagnetic actuators and piezoelectric actuators do not compete for the same market. Their capabilities are very different and the key to using them is to be clear about the application.
If the application requires long stroke, low voltage easy to implement drive electronics, and the cost is critical, then electromagnetic actuators are still the actuators of choice. They are ideal for general automation, linear motion, millimetre level positioning accuracy and more.
If the application demands sub micrometer scale positioning accuracy, operation at high frequency, low heat dissipation and static power consumption, or operation in high magnetic fields, the piezoelectric multilayer actuator is superior to electromagnetic devices.
The trends in precision manufacturing drive the operating conditions that favour using piezoelectric actuation. Micro technology, shorter cycle times, tighter tolerances and energy efficiency is common to all industries. Bestarsensor's multilayer piezoelectric components are ready to address engineers facing these challenges, delivering the technical specifications and manufacturing precision demanded by precision applications.