Application Cases

Experiment Name: Experimental Study of Ultrasonic Guided Wave Transducers

Experiment Purpose: Active structural health monitoring (SHM) employs actuators to apply excitation signals to structures and sensors to receive response signals, enabling real-time online monitoring of in-service engineering structures. This method effectively facilitates the assessment of structural remaining life and fault diagnosis. The piezoelectric ultrasonic guided wave detection method is widely applied and highly promising. Due to the direct and converse piezoelectric effects of piezoelectric materials, piezoelectric elements can serve as both actuators and sensors. However, piezoelectric vibrators used as actuators, such as PZT, typically exhibit multiple vibration modes, generating complex guided waves that complicate subsequent signal processing. Piezoelectric sensors for SHM are permanently deployed on structures, and the ideal material is a low-profile sensor that conforms to the structure. In this experiment, lightweight and flexible P(VDF-TrFE) material is used as the sensor to test its ability to receive ultrasonic guided waves. An interdigital ultrasonic guided wave transducer is designed to excite specific wavelength guided waves, and the guided wave signals are thoroughly analyzed.

Testing Equipment: ATA-2161 high-voltage amplifier, function generator, piezoelectric elements, oscilloscope, test structure, etc.

Experiment Process:

Figure 1: Ultrasonic Guided Wave Transducers for Structural Health Monitoring and Test Flowchart

The experiment utilizes highly visual software to modulate pulses at a certain frequency and imports the sine pulse signal into the function generator as the signal source. When outputting the signal, the function generator is set to pulse mode with a burst period adjusted to 10ms to avoid continuously exciting ultrasonic guided waves, which would cause signal overlap and interfere with subsequent analysis. The function generator is connected to the ATA-2161 high-voltage amplifier, which branches into two signal sources. One BNC connector is directly linked to the oscilloscope as a reference signal, while the amplified voltage signal is connected to the piezoelectric element via a rubber head to apply a high-voltage pulse signal. In the experiment, the peak-to-peak voltage of the pulse wave is set to 4V, and the amplification factor of the high-voltage amplifier is 25 times. UV-curable adhesive is used to connect the wires to the piezoelectric elements, taking care to avoid loose contacts that could cause short circuits. The oscilloscope's sampling frequency is set to 10k to ensure the authenticity of the received signal, and the level is adjusted to obtain a stable received signal. Additionally, during the equipment connection process, to maximize device power, the output impedance of the current source should match the input impedance of the load. The test platform and process are shown in Figure 1.

Figure 2: Simulated impedance spectrum of a PZT disc. The inset shows a schematic diagram of the radial contraction and expansion vibration mode of the PZT at 300kHz.

Firstly, a PZT ceramic disc is used as the driving element, and P(VDF-TrFE) is used as the sensor for the experiment. The optimal working frequency of the piezoelectric ceramic is near its resonant frequency. Using software, the coupled physics field of the electrostatic field and solid mechanics is selected for frequency-domain analysis, yielding an impedance spectrum in the 0-1MHz frequency range. Three sets of resonant peaks appear within the frequency domain. The two peaks in Figure 2 correspond to the resonant and anti-resonant frequencies of the PZT, while the other two sets of resonant peaks are at higher frequencies and are smaller, so the focus is on the resonant peak below 500kHz. The size of the resonant frequency is closely related to the dimensions of the piezoelectric vibrator itself. In the experiment, a circular disc with a diameter of 8mm and a thickness of 0.4mm is selected. The simulation results can intuitively observe the strain of the piezoelectric vibrator at the resonant frequency, as shown in the inset of Figure 2, where its vibration mode is radial bimodal vibration, with contraction and expansion along the radial direction.

Experimental Results:

Figure 3: Displacement fields (a) X, (b) Y, (c) Z directions, and (d) total displacement of ultrasonic guided waves generated by a PZT disc excited by a 300kHz sine pulse wave

A three-dimensional simulation model of PZT and 304 stainless steel plate is established using software to obtain the propagation of ultrasonic guided waves in a solid medium generated by PZT as a driver under the excitation of a 300kHz sine pulse signal, as shown in Figure 3. When voltage is applied in the polarization direction, the piezoelectric response modes d31, d32, and d33 of the PZT have the same physical properties in directions 1 and 2, producing the same displacement, while the deformation in direction 3 is the out-of-plane displacement perpendicular to the large face of the flat plate. Therefore, the displacement generated in the Z direction is omnidirectional. The total displacement is isotropic, and the PZT disc can serve as an omnidirectional driver.

High-Voltage Amplifier Recommendation: ATA-2161

Figure: Specification Parameters of the ATA-2161 High-Voltage Amplifier

This material is organized and released by Aigtek. For more case studies and product details, please continue to follow us. Xi'an Aigtek has become a widely recognized supplier of instruments and equipment in the industry with a broad range of products and considerable scale. Free trials of demo units are supported.