What Is an AE Sensor?
An AE Sensor is a type of vibration sensor that detects a specific vibration (AE wave).
AE stands for Acoustic Emission, a phenomenon in which acoustic waves are emitted as elastic waves when a part of an object is deformed or damaged, or when a shock is applied.
AE Sensors are used to detect this phenomenon, which is caused by minute degradation that occurs long before the object is completely damaged.
AE Sensors are used for predictive maintenance of industrial facilities and quality control of products.
Applications of AE Sensor
AE Sensors are used in a variety of applications, including product quality control and safety control. There are two types of AE sensors: a narrow-band type that reacts strongly in a specific narrow frequency band and a wide-band type that reacts in a wide frequency band, which can be used for different purposes.
1. Narrow-Band Type AE Sensor
Narrow-band AE Sensors are used in applications such as predictive maintenance of motor deterioration and detection of defects in metal welding such as pipes. Narrow-band AE Sensors do not react to vibrations from normally operating motors or welding, but can detect AE waves that are generated only when an abnormality occurs.
2. Wide-Band AE Sensor
The wide-band AE Sensor is used to detect foreign objects inside products and to detect signs of landslides in the ground. By using the broadband AE Sensor, it is possible to detect minute fragments of solder falling from a unit board inside a product or minute vibrations that may be a precursor to a landslide in the ground.
Principle of AE Sensor
AE Sensor detects AE waves by using a special piezoelectric element. Materials commonly used as piezoelectric elements are lithium niobate, lead niobate, and lead zirconate titanate (PZT). These elements are characterized by the fact that an electric charge is generated when pressure is applied. Therefore, by bringing these piezoelectric elements into contact with a vibrating object, they can receive a voltage from the piezoelectric element and function as a sensor.
In addition, these piezoelectric elements output a strong voltage when subjected to pressure from vibrations in the ultra-high frequency range (10 kHz to several MHz), such as AE waves, making it possible to detect only vibrations in a specific frequency band.
Other Information on AE Sensor
1. Difference Between AE Sensor and Vibration Sensor
Both sensors use piezoelectric elements to convert mechanical vibration into electricity. However, they differ in the frequency range for which they are suitable. Vibration acceleration sensors are suitable for detection in a relatively low frequency range, such as 5 to 20 kHz.
AE Sensors, on the other hand, detect higher frequency vibrations than vibration sensors. By detecting higher frequencies, early defects can be detected at an early stage.
In some cases, AE sensors have been applied to low-speed rotating bearings, which are difficult to diagnose with vibration sensors. This is because AE Sensor captures acoustic emissions, which are energy waves generated by micro-level breakdown.
Acoustic emissions are like ripples on the surface of water. When metal-to-metal contact occurs, acoustic emissions propagate through the metal of the equipment surface and are detected by the AE Sensor. Since acoustic emissions are generated even from small scratches and friction, it is possible to detect problems at an early stage.
2. Installation of AE Sensor
When installing AE Sensor, the mounting position is important. If the AE sensor can be mounted directly on the object to be detected, it has the best detection sensitivity and is not a problem.
On the other hand, if it is not possible to mount the AE sensor directly on the target, it is important to mount it as close as possible to the target. An acoustic path must be formed between the target and the AE Sensor, and when installing the AE Sensor, silicone grease or similar material should be applied to the surface of the target to make it adhere to the AE Sensor, so that the acoustic emissions generated by the AE Sensor can be detected.
Acoustic emissions have a high frequency and are difficult to propagate in air. Therefore, when mounting the AE Sensor, it is important to adhere it closely to the object to be detected. Furthermore, it is also important to install the sensor after thorough verification using a prototype.