What Are Piezoelectric Sensors?
Piezoelectric products known as piezo sensors detect changes in the environment and convert them into electrical energy. A piezoelectric sensor senses mechanical changes in the environment and produces a useable electrical signal output, which can be used to measure the mechanical changes or generate displacement with the electrical output. Piezo sensors take on two forms to accomplish this: active and passive. Active PZT sensors use a transmitter-receiver system releasing intermittent ultrasonic pulses to gauge the environment. Passive PZT sensors, as the name implies, wait for a signal, like a microphone, and convert that into output. These piezo sensors operate below their resonant frequency for maximized range. Piezoelectric sensors are mostly used in measuring vibrations, acceleration, strain, force, and movement. They are utilized for infinite applications across a broad range of industries due to their ability to both operate in confined spaces and high temperatures, and yield high frequency response, transient response, and output.
Detailed Mechanics
Detailed Mechanics of Piezoelectric Sensors
Active sensors, also known as transducers, utilize a transmitter-receiver system. The transmitter operates at its resonant frequency to optimize efficiency, periodically sending out ultrasonic signals. The receiver, upon obtaining a signal, generates an electric impulse. The delay is analyzed to determine distance or depth. Examples of this can be seen in level sensors or ultrasonic sensors. This system is referred to as a transducer when it both transmits and receives signals. Passive piezo sensors are much simpler. These specifically shaped piezo ceramics generate electricity after receiving a signal and are inactive when no signal is present. Passive piezo sensors often operate below their resonance frequency to optimize their sensing range. Common applications include touch switches and accelerometers.
There are many types of piezoelectric sensors for various applications. All piezo sensors can be custom made into different shapes depending on their use, including piezo tubes, piezo strips, piezo discs, and piezo plates. Here are a few of the most common piezoelectric sensors based on application:
Piezoelectric pressure sensors are used to measure dynamic changes in pressure, typically liquid or gaseous pressure changes. Pressure piezo sensors are commonly used in measuring explosions, blasts, turbulence, and engine combustion. Pressure sensors are able to detect these changes in pressure very rapidly, generating an electrical signal that can be used to produce the appropriate mechanical response needed to adapt to pressure changes.
Force piezoelectric sensors measure dynamic force along a single axis. Dynamic force can include compression, tensile, shear, and torque force. When a dynamic force is applied, the piezoelectric crystals deform under this force and produce an electrical signal. This electrical output can then be used to measure the force applied.
A piezoelectric accelerometer converts changes in mechanical acceleration, vibration, or shock into a measurable electrical output. When the accelerometer piezo sensor is subjected to an accelerative force, it produces an electrical signal proportional to the amount of force applied. A slab of piezoelectric material is held perpendicular to the expected movement, and a block of material is loaded onto the slab. When the object accelerates, the block presses onto the piezoelectric slab creating a charge, which is then passed on to an amplifier or computer. One type of accelerometer, vibration piezoelectric sensors, are commonly used in data acquisition systems in aerospace, automotive, and manufacturing applications to analyze vibration data in real time.
Ultrasonic piezoelectric sensors are often used to measure distance, liquid levels, and flow. They can also be used in cleaning equipment and medical equipment. Ultrasonic piezo sensors are often placed outside the medium being measured to receive relevant information. Often, two ultrasonic piezoelectric elements are utilized with one acting as the transmitter and one acting as the receiver (sensor). This is known as a piezoelectric transducer. The piezo transmitter emits ultrasonic pulses that are reflected back to the piezoelectric sensor and converted into a readable measurement. This works via the piezoelectric effect by converting electrical energy to ultrasonic energy, and vice versa. These sensors perform best when operated at the resonant frequency, which is determined by the material and dimensions of the piezo component. The closer the piezo component is to its resonant frequency, the higher the signal and amplitude of vibration.
Advantages and Disadvantages
Advantages and Disadvantages of Piezoelectric Sensors
Piezoelectric sensors are a trusted piezoelectric product in many settings and applications. Piezoelectric sensors have the natural advantage of high elasticity, which is comparable to some metals. This allows for a highly linear relationship between input and output over a wide range, while maintaining high reaction speeds. Most non-piezo sensors cannot replicate this level of reaction. Piezoelectric sensors are very versatile and can withstand various environmental extremes, such as high temperatures (up to their Curie point), magnetic fields, and radiation, which would otherwise compromise sensory data. They are very rugged in construction, making them the ideal sensor for tough environments where non-piezo sensors would intermittently fail.
Applications
- Microphone and instrument pickups
- Ultrasound equipment
- Noninvasive surgical equipment
- Pressure, force, strain, and torque measurement
- Liquid level and flow measurement
- Various automotive sensors in vehicles
- Vibration sensors
- Accelerometers
Applications of Piezoelectric Sensors
Applications for piezo ceramic sensors involving sound are extremely common, especially in the music industry. Piezoelectric disc sensors are often used to sense vibrations in microphones and amplifiers. Small piezo plates mounted to guitars are used to pick up the vibration of the strings and convert them to electrical signals.
Piezoelectric disc sensors also play a prominent role in the healthcare industry. Ultrasound equipment utilizes piezo disc sensors to read sound waves to monitor pregnancies and even aid in non-invasive surgical procedures, such as sensing kidney stones. Piezo tube and piezo disc sensors are found in an increasing number of medical equipment, especially those used to measure pulse, blood, and define accurate and specific droplet size for micro-dosing and nebulizers.
In the grander industrial scale, piezo sensors are often used to sense fast processes, such as explosions. This is due to their material’s quick responsiveness and resistance to deformity. In the example of explosions, piezoelectric disc sensors can quickly measure the changes in pressure, making them an invaluable tool for scientists. Industrial applications for piezoelectric sensors include aerospace, automotive, military, nuclear, and hydraulics where they must withstand extreme temperature and pressure. Engine knock sensors, pressure sensors, and sonar equipment all rely extensively on the accuracy of piezo disc sensors. The piezoelectric disc sensors pick up the vibrations and produce a voltage output which can be read to make any necessary adjustments. Piezo disc sensors can also be placed at the bottom or sides of a medium as measurement sensors for liquid levels or flow rate.
Another common design, accelerometer, utilizes a mass attached to a piezo plate or piezo disc to measure acceleration as a function of displacement. When an accelerative force is applied to the mass, it presses against the piezo element, generating an electrical output. This type of design is commonly used in a wide range of applications, including automobile functions such as motor bearings and wheel balancing, process control systems, machine vibration testing, shock and impact testing, and pitch orientation for aerospace applications. Medical applications also utilize piezoelectric accelerometers in fall detection devices for the elderly or injured, having the capability to send a signal for help if a fall is detected.
While there are still limitations in piezoelectric sensors operating in close-to-static conditions, computers have increased the range in which they can operate. By correcting calculable errors such as impedance, piezoelectric sensors have even been used to detect chemical subtleties in the air, such as aromas.
Shapes
Disc Piezo Sensors
Piezoelectric sensors in a disc shape are circular piezo elements often found in automotive functions, sound production and amplification, liquid and fluid level measurement, and ultrasonic applications. Learn more about disc piezoelectric sensors here.
Strip Piezo Sensors
Piezoelectric sensors in a strip shape are thin pieces of active piezoelectric material connected to a passive layer. There can either be two active piezoelectric layers sandwiched around a passive metal substrate (bimorph), or one active piezoelectric layer attached to a passive metal substrate (unimorph). Piezo strip bending sensors are often found in vibration and impact detection. Learn more about strip piezoelectric sensors here.
Ring Piezo Sensors
Piezoelectric sensors in a ring shape are used to detect changes in vibration or pressure and generate a useable electrical output. Piezo ring sensors are often found in ultrasonic applications, such as in dental, welding, and cleaning equipment. Learn more about ring piezoelectric sensors here.
Tube Piezo Sensors
Piezoelectric sensors in a tube shape are also known as piezoelectric cylinders. Piezo tube sensors are often utilized as level sensors, flow sensors, and fiber optic sensors in automotive, machinery, sonar, and scientific applications. Learn more about tube piezoelectric sensors here.
Bimorph Piezo Sensors
Piezoelectric bimorphs consist of two active piezoelectric layers often bonded to a metal substrate. This substrate acts as a passive layer between the two active layers of piezoelectric elements, allowing the piezo bimorph to bend and deform during the sensing process. One layer contracts and the other layer expands, causing a bending motion which produces an electrical current proportional to the mechanical input. Learn more about piezoelectric bimorph sensors here.
Unimorph Piezo Sensors
Piezoelectric unimorphs consist of one active piezoelectric layer often bonded to a passive metal substrate. Unimorphs deform in a single direction when activated by a mechanical input and translate the mechanical energy into electrical energy.
Plate and Block Piezo Sensors
Piezoelectric sensors in a plate or block shape are commonly used for vibration and pressure sensors. Plate and block piezo sensors are often found in ultrasonic applications and accelerometers in various industries, such as aerospace, automotive, and medical. Learn more about plate and block piezoelectric sensors here.