Application Cases

Experiment Name: Underwater Acoustic Device Directional Emission Performance Experiment

Research Direction: Acoustic Metamaterials, Pentamode Metamaterials, Directional Emission

Experiment Objective:
To verify the directional emission performance of an irregular Luneburg lens device filled with pentamode materials in an underwater acoustic environment.

Test Equipment:
Signal generator, ATA-214 power amplifier, acoustic source transducer, hydrophone, data signal acquisition system, etc.

Experimental Procedure:
Based on the reciprocity of acoustic emission and reception, this experiment focuses on testing the directional reception performance. The arrangement of the acoustic device and measurement equipment is shown in Figure 1. The underwater acoustic device under test is placed at a water depth of 350 mm. A transducer is positioned at the same depth to the left of the device, and its emission signal is controlled via connections to a signal generator and the ATA-214 power amplifier. A hydrophone, suspended at the same depth behind the device, is controlled by a stepper motor to move horizontally across the width of the water tank. The hydrophone is connected to a data signal acquisition system, converting the received acoustic signals into electrical signals. The data is then collected and analyzed using data analysis software on a computer.

Figure 1: Schematic Diagram of Underwater Experimental Setup

Figure 2: Actual Underwater Experimental Setup

Experimental Setup:
This directional emission experiment for the device was conducted in a water tank at the Structural Laboratory of the School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology, where environmental noise is relatively low. The experiment required approximate plane-wave conditions and steady-state scattering conditions. The pulsed sinusoidal wave used in this experiment had a frequency of 40 kHz and a wavelength of 37.5 mm, which is about 5% of the water tank depth, largely satisfying the plane-wave condition. For steady-state scattering conditions, pulsed sinusoidal waves were used to emit signals toward the model, and the filtered waveforms from the collected echoes were analyzed. The underwater acoustic device model has a maximum length of 100 mm, a maximum width of 114 mm, a bottom width of 62 mm, and a height of 10 mm, with two 1-mm-thick thin plates placed above and below. The material used for the device is photosensitive resin, with a density of 1140 kg/m³, Young's modulus of 2.2 GPa, and Poisson's ratio of 0.4. For the geometric parameters of the metamaterial, the maximum cell length is $a=2\text{mm}$, the cavity width is $d=0.201\text{mm}$, and the angular width between adjacent cavities is $\alpha =60^{\circ }$.

Figure 3: Schematic Diagram of the Underwater Acoustic Device

Experimental Results:
For the acoustic wave reception experiment of the irregular Luneburg lens device in an underwater environment, the measured data were processed to obtain frequency-domain signals in the range of 20 kHz to 40 kHz. The sound pressure amplification curves for directional reception were plotted at four frequencies—23 kHz, 27 kHz, 31 kHz, and 34 kHz—and compared with corresponding finite element simulation results, as shown in Figures 4 to 7. Analysis of the curves reveals that the experimental and simulation results exhibit similar trends, with peaks observed at the central measurement points (the middle of the device’s bottom edge). Some differences in numerical values between experimental and simulation results were noted at certain measurement points. Regarding the half-energy width of the peaks, the experimental values are slightly larger than the simulation values. The experimental values are notably larger near 23 kHz, while the experimental and simulation values correspond well near 34 kHz. Overall, the actual device achieved plane-wave focusing within the frequency range of 23 kHz to 34 kHz. Based on the reciprocity of acoustic emission and reception, the directional emission characteristics of the device were indirectly validated through this experiment, demonstrating the effectiveness of the designed underwater directional emission device.

Figure: Specifications of the ATA-214 High-Voltage Amplifier