The sensitivity of an ultrasonic probe refers to its capability to convert electrical signals and acoustic signals in an ultrasonic testing system, as well as its performance in detecting micro defects. The specific definition is as follows:

Core Definition

Probe sensitivity characterizes the efficiency of converting electrical pulses into ultrasonic waves (transmitting end) and converting reflected acoustic waves into electrical signals (receiving end), which directly determines the system’s ability to identify the smallest defects. The higher the sensitivity, the smaller the detectable defect size.

Correlation of Key Performance Indicators

Signal-to-Noise Ratio and Minimum Signal Detection: The maximum operational sensitivity is represented by the minimum peak voltage of identifiable echo signals when the signal-to-noise ratio is greater than 6 dB, reflecting the probe’s capability to receive weak signals.

Metrological Characteristics: From the perspective of sensors, sensitivity is the ratio of the change in output response to the change in input excitation, serving as a core response characteristic of the probe.

Influencing Factors

Probe sensitivity is restricted by internal structural design, including physical parameters such as the material properties of piezoelectric wafers, attenuation control of damping blocks, and optimization of matching layers. These factors jointly determine the energy conversion efficiency and signal resolution.

Relationship with System Sensitivity

Probe sensitivity is the foundation of the sensitivity of an ultrasonic testing system (combined performance of instrument and probe). However, system sensitivity is also affected by parameter adjustments such as instrument gain and suppression settings. In practical operation, reference reflectors (e.g., artificial defect test blocks) shall be used to calibrate the contribution of the probe in the system.

Note: Probe sensitivity must be distinguished from testing sensitivity (defect detection capability under actual working conditions). The latter is a system-level parameter adjusted via instrument settings, while probe sensitivity is its inherent physical property.

Improving the sensitivity of ultrasonic probes requires multi-dimensional optimization in material selection, structural design, signal processing, operational calibration and other aspects. The specific strategies are as follows:

1. Optimization of Core Materials and Structure

Piezoelectric Wafer Upgrade

Adopt piezoelectric materials with a high electromechanical coupling coefficient (such as PZT-5H or single-crystal materials) to improve electro-acoustic conversion efficiency.

Enhance the piezoelectric performance of wafers through a precise polarization process, which directly affects transmitting and receiving sensitivity.

Internal Structural Design of Probe

Damping Block Optimization: Control the attenuation coefficient of damping materials to balance signal resolution and energy loss.

Matching Layer Improvement: Adopt a multi-layer matching structure with gradient acoustic impedance to reduce acoustic wave reflection loss at the interface between the probe and the medium.

Advanced Probe Technology: Technologies such as AFM moment energy probes improve acoustic performance through special structural design.

2. Signal Processing and Hardware Enhancement

Drive Circuit Upgrade

Raise the transmitting voltage to 50–150 Vp-p for open probes, or 200–800 Vp-p for long-distance testing to enhance the intensity of acoustic pulses.

Replace ordinary drive chips with switching tubes to support high-current transient output.

Receiver Signal Processing

Optimize the signal-to-noise ratio (SNR) of the amplifier circuit; for instance, adopt 24-bit high-precision ADC chips to improve the ability to capture weak signals.

Embed dynamic filtering algorithms to suppress environmental noise interference.

3. Probe Adaptation and Parameter Adjustment

Frequency Adaptation Adjustment

Reducing the frequency (25–32 kHz) can minimize air attenuation, suitable for long-distance detection but at the cost of resolution.

Increasing the frequency (e.g., adopting high-frequency probes) can enhance the sensitivity and resolution of shallow imaging.

Scanning Parameter Optimization

Adjust gain and pulse repetition frequency to ensure the signal-to-noise ratio exceeds 6 dB.

Apply TGC (Time Gain Compensation) to correct signal attenuation caused by depth variation.

4. Operational Calibration and External Condition Control

Coupling and Contact Force Optimization

Ensure sufficient coupling between the probe and the testing surface to eliminate air gaps (by using special coupling agents).

Adopt a constant force control system (e.g., hybrid active-passive force controlled end effector) to maintain stable contact pressure and avoid signal fluctuation.

Environmental Factor Management

Control ambient temperature to prevent sound velocity drift from affecting the calibration accuracy of the time base line.

Reduce the roughness of the tested surface to lower acoustic wave scattering loss.

Regular Calibration and Quality Control

Calibrate probe sensitivity and time base line using standard test blocks (e.g., reference test blocks with artificial defects).

Conduct periodic inspections of frequency response, linearity and other indicators to ensure probe performance complies with the standard YY/T 1089.

5. Integration of Advanced Technologies

High-resolution probes directly enhance the ability to capture image details, applicable to micro defect detection.

Note: In practical applications, it is necessary to balance resolution, penetration depth and system compatibility. For example, increasing the drive voltage shall match the upper voltage withstand limit of the probe, and lowering the frequency will compromise resolution.

Above photo of transducer is 20-150MHz.