Technical Support

The focusing principle of a scanning acoustic microscope differs from that of a traditional optical microscope. It mainly ensures clear acoustic signals in the focused area by adjusting the Z-axis distance between the ultrasonic probe and the sample as well as scanning parameters. The specific operation steps are as follows:

1. Basic Focusing Procedure

Initial Setting and Sample Fixation

Place the sample steadily on the sample stage with a flat surface to avoid inclination that may affect the acoustic wave propagation path.

Fill the gap between the probe and the sample with a coupling medium (such as water or special gel) to reduce acoustic wave scattering loss.

Select an ultrasonic probe with an appropriate frequency — high-frequency probes deliver higher resolution, while low-frequency ones offer stronger penetration.

Coarse Adjustment of Working Distance (Z-axis)

Adjust the probe height via control software or manual knob to move the probe close to the sample to a preset safe distance (usually several millimeters).

Observe the real-time waveform in A-scan mode under low-magnification scanning to preliminarily confirm signal intensity.

Fine Focus Adjustment and Signal Optimization

Switch to C-scan mode, select the target focusing depth layer, and finely tune the Z-axis position until the reflected signal of this layer reaches the maximum strength.

Adjust Gain and Threshold to enhance the contrast between defects and the background, preventing signal saturation or excessively weak signals.

If the image is blurry, perform astigmatism calibration (similar to electron microscope operation) to eliminate acoustic beam distortion.

Multi-mode Verification of Focusing Effect

Verify via B-scan longitudinal section: check whether the depth distribution of defects is clear; re-fine the Z-axis if delamination appears blurred.

Auxiliary judgment through T-scan (transmission mode): stable transmission signals indicate proper focusing.

2. Advanced Skills and Precautions

Application of Auto-Focus Function

Some instruments are equipped with an auto-focus system (similar to scanning electron microscopes), which quickly locks the focal plane by identifying the maximum signal intensity point through algorithms.

Troubleshooting Common Issues

Blurred image: Check whether the coupling medium is evenly applied, whether the probe frequency matches the sample material, or recalibrate the probe center position.

Unstable signal: Eliminate factors such as loose samples, environmental vibration and electromagnetic interference.

Safe Operation

Prevent the probe from colliding with the sample by setting Z-axis safety limit; shield electromagnetic interference during high-sensitivity testing.

The core of SAM focusing lies in the precise control of the acoustic focal plane, which requires coordinated optimization of hardware adjustment (probe distance) and software parameters (gain, scanning mode). Modern instruments are usually integrated with semi-automatic workflows, while manual calibration remains an essential procedure.