Piezo Fan: The Silent Revolution in Cooling Technology

1.Introduction
2.Core Principles
3.Piezo Fans vs Traditional Rotary Fans
4.Application Areas
5.Conclusion

Introduction
A silent revolution in the management of heat the electronics industry has a constant and growing challenge. And as we make electronic devices more powerful and small, these devices are generating more heat in ever smaller areas. Over the past 10 years, the heat flow density in modern processors and power electronics has increased exponentially and has effected the thermal management with conventional cooling options to their limits.
Conventional rotary fans have been a typical problem-solving approach for thermal management for a very long time. While they have served the industry well, their inherent limitations are increasingly becoming obvious. Rotating mechanisms require physical space, ball bearings introduce friction and wear, mechanical motion necessarily creates noise. In many modern applications, the above drawbacks are unacceptable, so engineers have been looking for alternative cooling technologies.
Piezo fans are such an alternative solution. As solid state cooling equipment without any rotating parts, piezo electric fans have the potential to be a quiter, more reliable and potentially more compact way of creating airflow. This blog explains how piezo fans work, why they are important and where they are already making a meaningful difference.

Core Principles
It is necessary to understand piezo fan technology to obtain a good knowledge about its basic operatic principles: the inverse piezo electric effect, resonance based design and airflow generation by the fluid dynamic process.
The Inverse of the Piezoelectric Effect
Piezoelectric fans are constructed around piezo electric material, such as lead zirconate titanate (PZT) ceramics. These materials have a special physical behavior that they experience mechanical deformation upon applying an electrical voltage. When the voltage is removed they revert to their original shape. BeStar Sensortech Co., Ltd., as one of China's leading suppliers of multilayer piezoelectric ceramics and advanced electronic components, is committed to continuous innovation in piezoelectric technology and possesses strong capabilities in production and supply.
The piezoelectric actuator is made to expand and contract rhythmically by the application of an alternating current (AC) voltage. This periodic deformation is the basis of the operation of piezo fans. The actuator is adhered to a thin flexible blade or membrane. As the piezoelectric material moves back and forth it causes the attached blade to vibrate, generating the mechanical movement required to move air.
Resonance-Based Design
Resonance has a very important role in piezo fan performance. Any flexible structure will have one or more natural frequencies at which it will vibrate most efficiency. In piezo fans, the blade of the fan is designed by engineers to run to its basic or basic resonance frequency, also called the first-order natural frequency.
Operating at resonance makes the displacement of the blade much more pronounced. Relatively small deformation of the piezoelectric actuator can results in large amplitude motion of the blade. This makes any movement of the blade several millimeters or even centimeters, possible by a small amount of electrical energy. Without resonance, the motion of the blades would be restricted and the generation of flow through the air put a lot less effective.
Typical piezo fans have a frequency range of between 50Hz and 300Hz. The exact frequency is calculated based on blade geometry, material properties in addition to blower target airflow.
Fluid Dynamics and Synthetic Jet Creating
The oscillating blade produces air flow by means of a mechanism called synthetic jet formation. As the blade moves forward, it pushes air outward; and as it moves backward, it makes air in on itself. At first sight, such opposite motions may seem to cancel each other out.
However, there is an important asymmetry brought about by fluid dynamics. Vortices are created at the edges of the blades as it oscillates its way through each cycle, taking momentum away from the fan. In time, this produces a net flow of composite direction, and this in spite of the purely oscillatory motion of the blade. This phenomenon is referred to as a zero net mass flux jet or synthetic jet.
In this way, piezo fans are capable of efficiently pumping air in the form of pulsating jets. These are jets capable of being focused very precisely onto sources of heat then to achieve localized cooling. In some situations the inherently unsteady flow of air can even improve heat transfer over that of a steady flow of air generated by rotary fans.

Piezo Fans vs Traditional Rotary Fans
1.Size and Form
Some of the most remarkable features and benefits of piezo fans is that they have a very thin profile. Without motors, bearings or impeller housings, they can be made as flat devices that are only a few millimeters thick. In comparison, rotary fans have a minimum thickness to house a mechanical part.
2.Acoustic Performance
Low noise is one of the characteristic features of piezo cooling fans. Rotary fans have many sources of noise such as turbulence, motor and bearing friction. Piezo fans completely do away with motors and bearings. Their oscillating blades provide much lower levels of noise, often at frequencies that are less noticeable to the human ear.
3.Reliability and Service Life
With no rotating part and there are no sliding parts, there are fewer wear mechanisms found in piezo fans. Traditional fan bearings wear with the problems associated with friction and lubricant breakdown. Piezo fans by contrast are able to operate longer, which makes them very useful in applications where repairs are difficult or undesirable.
4.Power Efficiency
Piezo electric fans are energy efficient typically. By operating at resonance, they are capable of converting an electrical energy into mechanical motion with a little loss. This efficiency is particularly useful for battery-powered devices, since getting them with lower power consumption has a direct impact on devices' work times.
5.Airflow Capability
The main drawback of the current piezo fan technology is the volume of airflow. A single piezo fan normally generates less air than a similar sized rotary fan of the same size. For applications that require a high air throughput more than one piezo fan may be required or even traditional fans may be favoured. However, in the application of targeted cooling of localized hot spots, piezo fans will be very good at this purpose.

Application Areas
Piezo fans are becoming more prevalent in an extensive variety of constructions where their particular features come with distinct advantages.
Consumer Electronics
Ultrathin laptops, tablets and foldable smartphones are the earmark of the minimal thickness of piezo fans. They are usually used to cool individual localized components such as voltage regulators or memory chips. In VR and AR headsets, the operation must be silent in order to maintain immersion to the user, so piezo fans are quite attractive.
Emerging Use Cases
Medical devices such as portable ventilators and diagnostic use some quiet operation and reliability of piezo electric fans. In the field of telecommunications, small 5G modules produce significant heat in small enclosures where the use of piezo fans provides a good cooling effect with minimal acoustic noise.

Conclusion
Piezo fans are a real innovation in the process of thermal management. By eliminating rotating parts and making use of the inverse piezoelectric effect, they provide a combination of ultra-thin form factor, quiet operation, high reliability and energy efficiency that is unique to them.
Although current designs are limited in the range of their airflow, their advantages make them ideal for many modern applications. As the size of electronic devices keeps shrinking and the performance standards set by consumers for equipment to operate silently become more challenging, piezo cooling fans will play an increasingly larger role.
As the technology of materials, MEMS combination and intelligent control continues to improve, the development of piezoelectric fans is also gradually improving. And the quiet revolution in cooling technology is already upon us, and piezo fans show us that the future of thermal management might not be about turning faster, but vibrating smarter.

BeStar Sensortech Co., Ltd. leverages its extensive experience in multilayer piezoelectric ceramic materials to develop strong core competencies in material research and development, technological innovation and large-scale production. As a manufacturer of multilayer piezoelectric ceramics, we welcome you to contact our engineering team for expert advice and quotations if you have any needs.