Ultrasonic Wave Generation and Emission

Scanning Acoustic Microscopy (SAM) uses piezoelectric crystals or other types of transducers to generate high-frequency ultrasonic pulses. These ultrasonic waves have a specific frequency range, typically from several megahertz to hundreds of megahertz, depending on the required detection resolution and penetration depth.

Propagation and Interaction of Ultrasonic Waves

When ultrasonic waves enter a sample, they travel through different material layers and interact with interfaces between materials by reflecting, refracting, or transmitting.

If there are internal defects in the material (such as voids, cracks, delaminations), the ultrasonic waves will produce abnormal reflection signals at these defect sites because the acoustic impedance of the defect areas differs from that of the surrounding material.

Signal Acquisition and Processing

The reflected ultrasonic waves are captured by the same or another receiver and converted into electrical signals. This process involves transforming mechanical vibrations into measurable electronic signals.

The strength of the received signal and the time delay provide information about the internal structure of the sample, such as interface locations, thickness, and any existing defect characteristics.

Image Reconstruction

By moving the sample stage or the transducer, scanning can be performed across the entire surface of the sample, collecting data from multiple points.

All collected data are used to construct two-dimensional or three-dimensional ultrasonic images that reveal various layers and structural features within the sample.

These images can display the distribution of internal defects, such as the position, size, and shape of voids; the direction and length of cracks; and the quality of bonding between different material layers.