Piezoelectric Materials – The Most Common Unknown Power Source

With new practical applications being developed every day, the piezoelectric industry is expected to reach roughly $41 billion within the coming three years, with a compound annual growth rate of nearly 6%. This boom will allow for the further development and implementation of high-tech amorphous and film-based piezoelectric polymers in the modern world.

What are Piezoelectric Materials?

Piezoelectric materials allow for us to harness kinetic energy, by transforming force into an electric charge.  First defined by the Curie brothers in 1880, Piezoelectricity has become a fundamental principle exploited in modern technology.

Piezoelectricity refers to a substances ability to produce an electrical charge when mechanical stress is applied. This electrical charge is produced by forced asymmetry.  In piezoelectric materials, positive and negative charges are separated from each other, while remaining aligned in a symmetrical pattern.  When mechanical stress is applied to the substance, this symmetry is lost, resulting in the production of an electric charge.

PVDF beta phase.

Another unique property of the materials is the random nature and presence of Weiss domains (magnetically oriented without external magnetic influence).

It was later discovered that these same materials demonstrated a direct inverse property to the electric effect.  It was found that if an electric charge was applied to the material, repeatable mechanical deformation would occur within the material.  This discovery gave great utility to such materials, as it essentially doubled their prospective use-cases.

Manufacturers and Innovators

Before we dive in to examples of real-world use-cases, the following are a trio of leading companies that leverage piezoelectric materials throughout a variety of products integral in modern electronics.

Notably, analysts for Barron's currently list each of the following stocks as either ‘over' or ‘buy'.

Stoneridge (SRI)

Listed on the NYSE, Stoneridge (SRI) has seen its shares increase in value over the past year by more than 30% at time of writing.  While revenue at Stoneridge took a hit during the height of COVID, 2021 saw a nearly 20% rebound to $770M

Stoneridge employs over 5,000 people, and operates out of the State of Michigan.

Methode Electronics (MEI)

Listed on the NYSE, Methode Electronics Inc. has seen its shares increase in value over the past year by nearly 15% at time of writing.  Over the past 4 years, Methode Electronics has managed to continue growing its revenue between 2.36% and 10.13% each year.  For 2022, revenue topped $1.16B.

Methode Electronics employs over 7,000 people, and operates out of the State of Illinois.

Kimball Electronics Inc. (KE)

Listed on Nasdaq, Kimball Electronics Inc. has seen its shares increase in value over the past year by more than 32% at time of writing.  Where the companies listed above struggled from 2019-2020, Kimball Electronics managed to continually boast increasing revenues.  Totaling $1.35B for 2022, this marks a 4.47% increase over 2021.

Kimball Electronics employs over 7,000 people, and operates out of the State of Indiana.

Modern Advancements

Traditionally, naturally occurring piezoelectric substances were used to demonstrate the effect.  Most commonly, the material of choice was quartz.  When the limits of naturally occurring substances were reached, man-made ceramics became the popular choice.  Designed in 1952, and still one of the most popular piezoelectric ceramic today is PZT (lead zirconate titanate).  However, with drawbacks such as limited deformation, fragility, and a high mass density, PZT is not ideal for every application.

In 1964 PVDF (poly vinylidene fluoride) was developed.  PVDF has a semi-crystalline structure and creates charges several times greater than quartz.  Although this man made polymer addressed many of the drawbacks of PZT, it had various of its own – piezoelectric breakdowns at high temperatures, and degradation.  With recent technological advancement and increasing demands, PZT and PVDF may have reached their limits.

In the early 2000’s institutes such as GAIKER-IK4 began to develop what are known as amorphous piezoelectric polymers.  By utilizing an amorphous structure, much higher temperatures can be endured by the substance.  Since the piezoelectric effects are not relying on the crystalline structure which breaks down at higher temperatures, the amorphous structures make for a much more rugged polymer.

These amorphous polymers are being developed because they offer higher levels of deformation, large weight reduction, and greater ruggedness.  By achieving this, the field of applications for the materials now allows for the incorporation of aerospace and electronic devices.  With the new amorphous piezoelectric polymers and films being developed, failure during use will occur at temperatures of roughly 150°C and greater.  Degradation of the substance will occur at roughly 400°C.  While this may limit their use in extreme conditions, the vast majority of applications fall within an appropriate range.

Like many new substances, these polymers are being developed by using PVDF and PVT as the fundamentals.  Attempting to keep positive attributes from each material while eliminating as many disadvantages as possible.  Although such products are newer polymers, they are modeled after the current working models.

By utilizing an amorphous structure, extensive testing must be done on optimum vitreous transition temperatures.  This value is directly linked to the strength of piezoelectric properties the material will possess.  The amorphous structure demonstrates and relies on short range order to produce a piezoelectric effect instead, of long range order as seen in crystalline structures.  In addition to this, many are opting to incorporate polyimides into the structure of the materials due to their mechanical, dielectric, and thermal properties, with the polyimides ensuring poling of molecules regardless on their positioning.

Use-Cases

Past and current applications of piezoelectric materials include many inconspicuous items such as lighters, quartz clocks and even engine management systems.  The most common use for them currently would be in sensors and actuators.  While suitable piezoelectric materials have been applied for these use cases, future applications demand a more versatile material.  Thankfully developing piezoelectric polymers are just that – versatile.  With constant advancements in our understanding of material science, and their ability to display direct inverse effects, the number of applications in which they can be used continues to increase.  Some intriguing present and potential future applications include,

Mobile and Wearable Electronics

Talk powered cell phones and wearable devices.  By utilizing the pressure created within the microphone due to sound waves, piezoelectric polymers can hopefully one day create enough power needed to use the phone.  While it is unlikely that this concept will remove the need for a battery altogether any time soon, it does create the possibility of extending battery life in low-drain wearable smart devices.

It should be noted that piezoelectric materials have been used in microphones for nearly 100 years at this point.  Rather than the end goal being to charge a device though, these applications allow for the conversion of soundwaves in to electricity for the purpose of recording and playback in a cost-effective manner.

Dampening Systems

Another application is the use of piezoelectric materials in dampening systems.  Companies such as HEAD have incorporated this idea into its tennis rackets and skis in an effort to absorb/dampen vibrations.  When an impact occurs on the racket or ski, the reciprocal effect is harnessed by sending the electric signal created to an inverse material providing an opposing force.  This results in an effective dampening system.

This same concept is being applied to noise and vibration reduction in cars, homes, and in hazardous workplace environments.  One example of such an environment would be Bitcoin mining farms.  Not only are vibrations harmful to electronic equipment over the long run, there have been various instances of surrounding communities in which these operations take place complaining about the resulting noise and vibrations resulting from the use of ASIC devices.  In many similar scenarios, piezo-based actuators are used as a solution to dampen each of these effects.  With sound waves being created in cars, homes, and machinery by materials reverberating, this noise can also be eliminated, or at least reduced, with traditional methods such as an adhesive dampening material.  These materials work passively though, and are very heavy and expensive.  They typically work by lowering a materials resonant frequency.  Exploiting the properties of piezoelectric polymers solves this problem by taking the more active and dynamic approach described above.

Cleaning Solutions

To demonstrate just how versatile the use cases for piezoelectric materials are, consider work being done by companies like Solar PiezoClean.  In this instance, the company is coating solar panels with a piezoelectric film.  The purpose is to offer a low maintenance means of keeping solar panels clean – a key to ensuring optimal efficiency.

This process involves applying an electric charge to the film, which then vibrates at a specific frequency and pitch that allows for dust and dirt to simply fall off with help from gravity.  What this all means is savings in water and manpower, while increasing longevity and efficiency of coated panels.  A simple, but ingenious solution to a problem that is only growing as solar installations become more commonplace.

More common implementations of piezoelectric materials in such a manner include ultrasonic cleaning devices like jewelry cleaners.

Aerospace

Earlier we mentioned the use of piezoelectric materials within the aerospace sector.  Here, planes can make use of such materials to monitor structural integrity and stressors through the measurement of electric charges produced – a use case that can allow not only for increased safety, but greater efficiencies by allowing for engineers to simultaneously cut weight and strengthen structures where needed.

Move beyond our atmosphere, and piezoelectric actuators are used in many satellites.  The ability to operate with extreme precision allows for such actuators to make micro-thrusters capable of proper satellite positioning.

HealthCare Diagnostic Tools

As our ability to create smaller and smaller devices improves, we are now using piezoelectric materials in various diagnostic tools within healthcare.  An example of this is Intravascular Ultrasound (IVUS).  IVUS is a process which allows for tiny probes to generate imaging from within blood vessels.  This is done through the use of ultrasound transducers built with piezoelectric single crystals.

Piezoelectric materials are also used in certain dentistry equipment.  Similar to the cleaning solution being utilized by SolarClean described above, this equipment relies on ultrasonic waves, produced by applying an electrical current to the piezoelectric materials, to clean/remove plaque from teeth.

Sonar

Sonar (Sound Navigation and Ranging) systems can be used to provide imaging, or for communication.  Examples of imaging include topographic mapping of ocean floors, or every-day fishfinders.  Meanwhile communication can be achieved through the creation of sound waves.  Each of these processes are made possible through the use of piezoelectric transducers.

Despite being developed over 100 years ago, Sonar continues to play an important role today.  The most recent widespread example of this would be its implementation in self-driving cars, which typically use a combination of Sonar, LIDAR, and radar to track and interpret surroundings.

Energy Harvesting

Finally, a very intriguing application would be large scale energy production.  Piezoelectric polymers are being developed to place in high traffic areas, including various factories, sport fields, train stations, and more around the world.  A 1cm³ piece of quartz is capable of producing up to 4,500V of electricity when 175lbs of force is applied.  With each footstep to hit the ground in such stations creating this electricity, there is the potential to harness huge amounts as it is created daily – greatly increasing efficiency and electricity costs for the building.

Beyond foot traffic, many have envisioned a future in which roadways are embedded with such materials, creating electricity to power street lights and signs as cars exert physical force on them.

When combined, future technologies like wireless car charging being developed by Electreon, and powered surfaces by companies like Pavegen, will hopefully one day allow for reduced battery sizes in vehicles, and a much more efficient and clean way to keep electric vehicles charged.

Final Word

Overall, the potential of piezoelectric materials is just beginning to be realized.  Photovoltaic effects that make Solar energy possible were discovered in the mid-1800’s, and are only now becoming practical for widespread use.  Piezoelectric materials are no different, and as research and development in to these materials continues, increases in efficiency and durability follow suit.  Modern scientific advancements are only now allowing us to realize, or at least understand, the full potential of this source for energy, with the use-cases listed here (electricity generation, sound dampening, sonar, sensors, acutators, etc) being only a select few out of countless possibilities.