A Piezoelectric Transducer is a device that converts mechanical energy, like pressure, into an electrical signal and can also perform the reverse, turning an electrical signal into mechanical motion.
The latest mechanism is used for exemple in Ultrasonic Testing.
The name comes from the Greek word “piezo”, which means “to press” or “squeeze”. This effect was first demonstrated by brothers Jacques and Pierre Curie back in 1880.
This dual functionality allows them to work as sensors, detecting physical forces, and as actuators that create precise movements.
The precision of this technology is an important aspect of its usage.
In medical diagnostics, for instance, ultrasound transducers must comply with strict guidelines.
But how can a solid material create a voltage just from being pressed?
That’s what we will try to explain in this article!
The working principles behind piezoelectricity and the materials that make it possible. We will also cover the different transducer types, their most common applications, important industry standards, and selection factors for your engineering projects.
Table of Contents
How Piezoelectric Transducers Work ?
At the heart of these devices is a phenomenon called the piezoelectric effect.
Certain materials (often crystals or special ceramics) generate an electrical charge when you apply mechanical stress to them.
The process also works in reverse, which is known as the reverse piezoelectric effect.
If you apply an electrical voltage across the same material, it will physically deform, changing its shape slightly.
That’s not really something you can observe with your eyes.
This dual capability allows a piezoelectric transducer to act as both a sensor and an actuator.
When used as a sensor, a mechanical force like pressure or vibration compresses the piezoelectric material. This action displaces the balanced positive and negative charges within its crystalline structure, creating an electrical dipole.
The result is a measurable voltage that is directly proportional to the applied force.
In certain operational modes, this charge generation is consistent regardless of the element’s size.
Operational Modes
Engineers can cut and arrange piezoelectric materials in three main modes. Each one dictate how they respond to force a different way.
The transverse mode works by applying force along one axis and generating a charge on an axis perpendicular to the force.
In this mode, the amount of charge produced depends on the element’s geometry, following the relationship :
In simpler terms :
When you press the material in one direction (y), it creates an electric response in another direction (x), and how strong that response is depends on the material’s properties and its shape.
This allows engineers to customize the sensor’s sensitivity by changing its physical dimensions.
In the longitudinal mode, the charge is generated along the same axis as the applied force.
The charge output :
In simpler words :
When you press or stretch the material along its length, it creates an electric charge in that same direction and stacking more layers makes the effect stronger.
It’s strictly proportional to the applied force and is not dependent on the element’s size or shape.
The shear mode, which is the last one, produces a charge at a right angle to an applied shearing force.
Similar to the longitudinal mode, the resulting charge :
Which mean, when you twist or shear the material, it produces an electric charge and
stacking more layers increases the output.
Once again, it’s directly proportional to the force applied.
Electrical Properties and Equivalent Circuits
To analyze performance, a Piezoelectric Transducer can be modeled as a voltage source with an output that changes with frequency.
In simple terms, here is what it looks like:
Basic Model
The simplest representation treats the sensor like a battery (voltage source) connected to a capacitor. The capacitor mimics how electrical charge builds up on the sensor’s surface when you press on it.
Alternative View:
You can also think of it as a current source (charge pump) working alongside that same capacitor.
Both versions say the same thing: the more force you apply, the more electrical charge the sensor produces.
Frequency Limitations:
The sensor’s internal resistance and any external device connected to it act like a filter.
This filter prevents the sensor from detecting very low-frequency vibrations or slow movements. There’s a minimum frequency below which it won’t respond effectively.
Advanced Models:
For precise engineering, we use more complex models that treat the sensor like a mechanical system translated into electrical terms.
It’s done using components like coils (inductors) and capacitors to mimic how the physical structure behaves.
This helps predict exactly how the sensor will perform under different conditions.
Piezoelectric Materials for Transducers
Choosing the right material for a piezoelectric transducer is an important call to make.
The material defines the device’s sensitivity, durability, and temperature limits.
We can group these materials into three main families: piezoelectric ceramics, single-crystal materials, and modern thin-film materials.
Ceramic Materials
The most common ceramic you will encounter is lead zirconate titanate, known as PZT.
Its high sensitivity has made it a great choice.
It generates a signal roughly 100 times stronger than natural crystals, making it excellent for detecting subtle forces.
PZT manufacturing offers great advantages:
- Low production cost
- Ability to create multiple geometric shapes
- Design flexibility
PZT are made through a process called “sintering”.
Basically, it’s heating powdered material at high temperatures to fuse the particles together into a solid mass without fully melting them.
PZT doesn’t have piezoelectric properties naturally.
The ability must be created artificially through a process called “poling”.
This is how we do it:
Raw PZT is heated and exposed to a strong electric field. This forces the material’s internal crystal structures to align in one direction.
This alignment is what produces the piezoelectric effect.
They generally operate up to 250°C (<~300°C), but pushing past their Curie temperature will permanently remove their piezoelectric properties.
It’s high sensitivity make it an excellent choice for Non Destructive Testing equipments.
Single-Crystal Materials
Single-crystal materials offer long-term stability.
Natural crystals like quartz, gallium phosphate, and tourmaline are less sensitive than PZT but are incredibly consistent.
Here a quick overview of how to choose between those:
- Quartz is the most reliable. It barely loses any electrical charge over time, which is why it powers the clocks in watches for exemple. You can trust it to keep accurate time for years.
- Gallium phosphate is the best a heat resistance. While most materials give up around 300°C, this one keeps working perfectly even above 500°C.
- Tourmaline generates an electrical signal when temperature changes. (Scientists call this “pyroelectricity” but basically it’s kind of a built in thermometer.)
Single crystals give you stability and precision, but you pay for it with lower sensitivity and higher cost compared to PZT.
Thin Film and Composite Materials
When you need to work with very high frequencies or in tiny spaces, thin film materials are the best option available.
Produced with advanced methods like sputtering or chemical vapor deposition, these materials are built for :
- Ultra-high frequencies (above 100 MHz): used in medical ultrasound, radar, and 5G technology
- Miniaturized devices: smartphone sensors, wearable health monitors, MEMS devices
Options available in this category:
Piezo-polymers and composites: flexible materials that bend and still produce electrical signals. Used in wearable devices, flexible sensors, and medical patches.
Rochelle salt: historically produced one of the stronger piezoelectric signals among natural materials, but modern ceramics now exceed its performance. But it’s complex: it hates moisture and breaks down above 46°C. So it’s mostly confined to labs and specialized applications.
Smart composite materials: you take PZT particles and mix them throughout aluminum, kind of like chocolate chips in cookie dough.
When the material gets stressed (bent, cracked, or vibrated), the PZT particles inside detect it and send an electrical signal.
This is why the “smart” in the name stands for, because it’s like having thousands of tiny alarm bells embedded throughout the structure.
But those materials have tradeoffs.
They are technically advanced but often expensive and less durable than traditional ceramics or crystals.
Types and Shapes of Piezoelectric Transducers
One of the most interesting characteristics of piezoelectric materials is their manufacturing versatility.
Unlike many other electronic components, they can be produced in a wide variety of shapes and sizes.
This adaptability is the main reason you find them in so many different products and industries.
The geometry of a piezoelectric transducer is directly tied to its job.
A specific shape is chosen to optimize how it responds to mechanical stress or how it generates physical movement.
Its form is a very important parameter for performance in any given application.
Common Transducer Geometries
Circular shapes like discs and rings are very common.
You can find disc transducers in automotive sensors and ultrasonic cleaning systems, while ring transducers are often used in medical devices for tasks like dental cleaning.
Plates and blocks are simple, solid shapes ideal for measuring vibration or pressure. They are frequently used as core components inside accelerometers or high power ultrasonic generators.
Tube or cylinder transducers are used for applications that need precision, such as controlling fluid flow, scanning microscopy, and microdosing medication.
Strip transducers are thin, active layers bonded to a passive base. Their ability to bend makes them useful for pump controls and touch activated switches.
Bimorph and unimorph transducers are layered components designed for motion:
- Bimorph has two active layers that create a bending action,
- Unimorph uses one active layer for single-direction deformation.
Both are useful for creating precise movement in actuators and sensors.
Advantages and Limitations
Like anything in engineering, those devices comes with both benefits and tradeoffs. When you need to use one in your projects it’s important to take them into consideration.
Advantages
They are self generating, creating their own electrical signal when pressure is applied without needing an external power source.
They also have a high modulus of elasticity up to 1011 N/m², a stiffness level similar to many metals. This makes the device mechanically tough, with almost no bending under load.
These devices also provide excellent performance.
They possess a very high natural frequency and show consistent linearity over a broad amplitude range.
This gives them a fast frequency response, letting them react in microseconds and generate ultrasound up to 20 MHz. They are, in some cases, also unaffected by electromagnetic fields and radiation, which makes them very reliable in harsh conditions.
Flexibility at manufacturing step is also big plus.
The materials used can be shaped into many different forms and sizes to fit specific application needs. They also work well even at low voltages, which adds to their versatility.
Comparing them to other sensor types shows their performance advantage.
The table below, using information from Gautschi (2002), shows how they measure up against other common designs on sensitivity and measurement range.
| Principle | Strain sensitivity [V/με] | Threshold [με] | Span to threshold ratio |
|---|---|---|---|
| Piezoelectric | 5.0 | 0.00001 | 100,000,000 |
| Piezoresistive | 0.0001 | 0.0001 | 2,500,000 |
| Inductive | 0.001 | 0.0005 | 2,000,000 |
| Capacitive | 0.005 | 0.0001 | 750,000 |
| Resistive | 0.000005 | 0.01 | 50,000 |
As you can see, piezoelectric sensors combine very high sensitivity with low detection threshold.
This leads to a great ability to measure a wide spectrum of forces, from the smallest to the very large.
Limitations
Despite their advantages, piezoelectric transducers are not ideal for everything.
One important constraint is their inability to measure truly static, or unchanging, forces.
When a steady force is applied, the transducer generates a fixed amount of electrical charge. This charge gradually leaks away because of imperfect insulation and internal resistance, causing the signal to decay.
The electrical output from these devices is quite small.
This tiny charge requires special cables and external amplifiers to make the signal usable.
Adding amplifiers can sometimes introduce their own electrical errors or noise into the measurement.
This is a tradeoff you must consider for precision applications.
These transducers can also be sensitive to their surroundings.
Variations in temperature and humidity can affect their output, making them less reliable in uncontrolled environments.
Elevated temperatures are particularly problematic, causing a drop in internal resistance and sensitivity.
For example, quartz sensors need active cooling systems when operating at temperatures above 300°C.
Even in energy harvesting, a constant source of ambient energy can cause a slow loss of electrons, leading to a decreasing power output over time.
Applications and Real World Usage
So far, we’ve learned that piezoelectric transducers are clever devices that convert mechanical stress into electrical signals, and vice versa.
But, what is it used for in the real world?
Their ability to act as both sensors and actuators, combined with their many shapes, makes them a very powerful component to use in engineering.
This versatility is why you find them in almost every high tech industry.
Since manufacturers began using them in the 1950s for quality assurance and process control, their use has expanded into the industrial, aerospace, automotive, medical, and consumer electronics sectors.
They are a go to tool for research and development teams pushing the boundaries of technology.
An accelerometer uses a tiny seismic mass to measure motion, while a pressure sensor uses a thin membrane to detect force.
You will find them monitoring combustion inside an engine, helping a car with automatic braking, or powering ultrasonic cleaners that scrub parts with high frequency vibrations.
The medical field relies heavily on this technology for patient safety and diagnostics. Beyond imaging, piezoelectric transducers are used in surgical tools and to break up kidney stones.
You interact with piezoelectric transducers every day, often without realizing it.
They are in microphones that capture your voice, the buzzers in security alarms, automatic sliding doors, and the touch pads on mobile phones.
This wide range of uses shows just how deeply this technology is integrated into modern life.
Energy Harvesting
Those components offer a method to generate power by converting ambient mechanical vibrations into usable electrical energy.
This capability is useful for applications where cabled power or batteries are too expensive or physically unviable to implement.
Instead of needing a dedicated power line, the device can source its own energy from the surrounding environment.
These systems are very strong at powering low energy devices, that just require milliwatts of power for equipment like wireless sensors or mechanical watches.
Their best use is when power needs are periodic and the frequency of the vibration is close to the harvester’s resonance frequency.
This principle applies to large industrial settings.
Transducers installed in train tracks can harvest energy from a train’s acceleration and pressure to generate power for monitoring equipments.
Another forward looking application is for the Internet of Things.
Sensors can receive ultrasonic signals and convert the resulting vibrations into an electrical charge, becoming self powering systems that function without battery replacements.
Selecting the Right Piezoelectric Transducer
Choosing the right transducer starts with a good overview of your project.
You need to identify what you are measuring, such as pressure, acceleration, or force. Think about the required frequency and amplitude ranges, along with the specific environmental conditions like temperature and humidity.
Your next choice is the material.
You might select ceramics for high sensitivity or single crystals for long term stability, balancing this with temperature tolerance and cost.
The geometry, be it a disc, ring, plate, or strip, affects mounting possibilities, space constraints, and directional sensitivity.
Pay attention to the electrical output and interface.
The small electric charge often means you will need an amplifier and special cables. You should also check that the material’s Curie point and degradation characteristics fit your maximum temperature.
Any characteristic you pick is a choice that depends on the usage and environnement you will put the transducer in.
Conclusion
A piezoelectric transducer is a versatile device that performs a two-way energy conversion.
It turns mechanical stress into an electrical signal, or takes an electrical signal and generates physical movement.
This dual function allows it to operate as a sensor detecting pressure and as an actuator creating motion. This make it a great component to use across industrial, medical, automotive, aerospace, and commercial fields.
The technology presents clear advantages.
These devices are self generating, so they do not need an external power source.
They offer a high frequency response, are mechanically rugged, and can be made in almost any shape.
The tradeoffs include an inability to measure static forces, a small electrical output that requires amplification, and sensitivity to environmental conditions like temperature.
Material choice dictates behavior:
- Ceramics offer high sensitivity,
- Single crystals provide stability,
- Thin films are suited for high frequency applications.
Making informed decisions on material, geometry, and design allows engineers to use piezoelectric technology for precise and reliable energy conversion.
Frequently Asked Questions
What is a piezoelectric transducer in simple terms?
It is a special device that converts mechanical energy like pressure or vibrations into an electrical voltage. It can also work in reverse, converting an electrical voltage into mechanical motion.
How does a piezoelectric transducer create electricity?
When you apply mechanical stress to certain crystals inside the transducer, their internal structure gets distorted. This distortion separates positive and negative charges, creating a measurable voltage across the material.
Can a piezoelectric transducer also create movement?
Yes. When an electric field is applied to the piezoelectric material, its crystal lattice deforms, causing the material to change its shape. This is known as the reverse piezoelectric effect.
Do piezoelectric transducers need batteries or an external power source?
When used as sensors, they are self generating. They produce their own electrical signal from applied mechanical force, so they do not need an external power supply to operate.
What is the main limitation of a piezoelectric sensor?
Its principal weakness is its inability to measure true static forces. The electrical charge produced from a constant force gradually leaks away, making these sensors ideal only for dynamic or changing measurements.
Why are PZT ceramics often preferred over natural crystals like quartz?
PZT ceramics generally have a much higher sensitivity, meaning they generate a larger electrical signal for a given force. They are also less costly to manufacture and can be cast into many different shapes.
What is the significance of a material’s Curie temperature?
The Curie temperature is the maximum temperature at which a piezoelectric material can function. If heated above this point, the material permanently loses its piezoelectric properties and will no longer work.
How is an accelerometer’s design different from a pressure sensor’s?
The key difference is how force is transmitted to the piezoelectric element. A pressure sensor uses a diaphragm to collect and focus pressure. An accelerometer attaches a small weight, called a seismic mass, that exerts force on the element during motion.
Why do piezoelectric sensors require high-impedance cables and amplifiers?
These sensors produce a small amount of charge and have a very high output impedance. Using high impedance electronics prevents the small electrical signal from leaking away, allowing for an accurate voltage measurement.
