Broadband tunable acoustic metasurface based on piezoelectric composite structure with two resonant modes

In this letter, we propose a deep-wavelength tunable acoustic metasurface composed of a fixed piezoelectric composite structure with a broad operating frequency range. The metasurface unit has two tunable resonant frequencies determined by specific external inductors and can continuously modulate the phase of transmitted wave. The influence of the inductors on the resonant frequencies are studied by simulation and experiment. Moreover, the functions of acoustic beam steering and focusing by the designed metasurface at three arbitrarily chosen frequencies are verified in simulation. This work may have good potential in design of acoustic metasurfaces with broadband operating frequencies.

Performance analysis of vortex acoustic wave based on uniform circular array

As a carrier for information and energy, acoustic waves have been applied in underwater communication widely, however, the narrow band and low transmission speed are the main problems. Whether in the field of optics or electromagnetic waves, the orbital angular momentum (OAM) represents the natural properties of the spiral phase structure. By introducing the OAM into the acoustics field, the transmission capacity and spectrum efficiency of the underwater acoustic communication system can be expanded. Based on the analysis and detection of the vortex acoustic wave generated by the circular array of transducers, we studied the array generation method of the spiral acoustic beam, and gave the characteristics of the vortex acoustic beam when propagating under the water. In the direction of the main axis, the uniform circular array was used to generate different topological acoustic vortex. To determine the relationship between the OAM topology mode and the transducer array, the spiral acoustic waves in different topology modes were generated, and the number of array elements, array radius, transmission frequency, etc. were investigated to give the effects on OAM acoustic vortex.

Investigation on the Inspection Technology of GH3535 Alloy Butt Weld With Linear Array Probe

The critical problem to accurately characterizing defects in GH3535 alloy weld is the deflection of the acoustic beam and scattering due to the coarse columnar grains. Signal-to-noise ratio is an important index to indicate whether the grain scattering is severein the ultrasonic inspection. In this paper, the phased array ultrasonic testing of GH3535 alloy butt weld was studied using sector scan mode with linear array probe. The soundfield characteristics of the linear array probe with different focusing parameters were analyzed, and the signal-to-noise ratio in the detection was calculated. The results show that: the acoustic beam of the linear array probe can cover the weld,based on the removal of weld reinforcement. The signal-to-noise ratio of transverse hole with φ3mm located at the weld-fusion lineis more than 15dB, when the front end ofthe probe is located directly above the transverse hole of weld-fusion line.

Thermally Tunable Acoustic Beam Splitter Based on Poly(vinyl alcohol) Poly(N-isopropylacrylamide) Hydrogel

In this study, we demonstrated a thermally tunable acoustic beam splitter using a poly(vinyl alcohol) poly(N-isopropylacrylamide) hydrogel (PVA-pNIPAM). The nature of PVA-pNIPAM hydrogel offers exceptional temperature-dependent physical properties due to its phase transition around its lower critical solution temperature. The acoustic impedance of the hydrogel can be tuned below, above, or matched to that of water by changing the environmental temperature. An acoustic wave propagating in water can be split into transmitted and reflected components by the PVA-pNIPAM hydrogel slab on varying its angle of incidence. The intensity ratio between the reflected and the transmitted componence can be adjusted by tuning the temperature of the medium. The acoustic beam can be entirely reflected at a temperature corresponding to the matched impedance between hydrogel and water. The beam-splitting behavior was observed for acoustic waves from both a monochromatic wave and broadband pulse source. In addition, the phase of beam split pulses can be reversed by selecting the hydrogel’s operating temperature.

Moving object detection and tracking based on Doppler ultrasound

Fetal health monitoring during pregnancy has become a necessary procedure. Fetal heart rate (FHR) monitoring can determine fetal development or presence of heart disease and evaluate fetal well-being. The FHR measurement uses typically an acoustic probe-based Doppler ultrasound. Doppler ultrasound method transmits a continuous wave signal to the abdomen of a pregnant woman to receive a reflected signal from the fetal heart. Periodic displacement of the heart tissue produces the Doppler effect and the phase change of the reflected wave is proportional to the velocity of the fetal heart. The reflected signal is modulated into a phase signal and the received signal is demodulated to detect the heart rate. The current clinician system consists of a single probe and requires the probe to be manipulated to the optimal position to measure FHR. The system is highly dependent on trained diagnostic experts. The movement of the pregnant woman and the fetus leads to the misaligned acoustic beam which degrades the reliability of the measurement. This work presents a detection and tracking system using a Doppler signal to compensate for the target's movement. The system is implemented by integrating multi-channel probes interfaced to a Doppler signal converter with a 2-degree of freedom (DOF) motor device. This work describes the characteristics of two key components: Doppler signals of multi-channel probes according to the direction of the acoustic beam and the algorithm with a 2-DOF tracking system.

Experimental demonstration of negative refraction with 3D locally resonant acoustic metafluids

Negative refraction of acoustic waves is demonstrated through underwater experiments conducted at ultrasonic frequencies on a 3D locally resonant acoustic metafluid made of soft porous silicone-rubber micro-beads suspended in a yield-stress fluid. By measuring the refracted angle of the acoustic beam transmitted through this metafluid shaped as a prism, we determine the acoustic index to water according to Snell’s law. These experimental data are then compared with an excellent agreement to calculations performed in the framework of Multiple Scattering Theory showing that the emergence of negative refraction depends on the volume fraction $$\Phi$$ Φ of the resonant micro-beads. For diluted metafluid ($$\Phi =3\%$$ Φ = 3 % ), only positive refraction occurs whereas negative refraction is demonstrated over a broad frequency band with concentrated metafluid ($$\Phi =17\%$$ Φ = 17 % ).