Sensors detect changes in the environment and convert them into electrical energy. A piezoelectric sensor senses mechanical changes in the outside world and translates them into an electrical signal, which is monitored to measure those changes. Piezoelectric 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.
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 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.
Advantages and Disadvantages
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.
Piezo sensors have very high response time to rapidly changing parameters, high transient response to detect those changes, and thus, high output to be measured. Their ability to self-generate voltage and harvest energy from mechanical impacts also eliminates the need for an external power source. Some key characteristics of these PZT sensors include high voltage output, elastic compliance, wide frequency measuring range, overload stability, and impact and environmental resistance. Their ability to detect minute disturbances in virtually any environment makes piezoelectric sensors ideal in many applications. The main restriction on piezoelectric sensors is their inability to operate in static environments. With minimal environmental change around a sensor it begins to lose its charge (this occurs at low frequency changes and high temperatures as well), causing decreased signals and corrupt data.
Applications for piezo ceramic sensors involving sound are extremely common, such as sensing vibrations in microphones and amplifiers.
Piezoelectric sensors are most applicable in fast processes, such as explosions. This is due to their material’s quick responsiveness and resistance to deformity. In the example of explosions, piezoelectric sensors can quickly measure the changes in pressure, making them an invaluable tool for scientists.
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.
One use of piezoelectric sensors is found in accelerometers. 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.
Another common design utilizes a tube with a piezoelectric sensor at both ends. The tube is filled with a heavy liquid, then positioned parallel to the expected movement. These two sensors are polarized in opposite directions to respond to movement in both directions. These types of designs are commonly used in a wide range of applications, including laboratory environments and automobile functions.
Piezoelectric sensors play a prominent role in the healthcare industry. Ultrasound equipment utilizes piezoelectric sensors by sending sound waves to monitor pregnancies and even perform non-invasive surgical procedures, such as breaking up kidney stones. Piezo sensors can also be used to measure pulse, manufacture PPE and medical equipment, and define accurate and specific droplet size for microdosing and nebulizers. Industrial applications for piezo sensors include aerospace, automotive, nuclear, and even underwater research where they must withstand temperature and pressure. Engine knock sensors, pressure sensors, and sonar equipment all rely extensively on the accuracy of piezoelectric sensors.
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