Jian Chen

Quantum tunneling has driven considerable advances in theoretical physics, the proliferation of quantum devices, and the development of information technologies. However, the dependence of electron tunneling behavior on the dielectric medium within the tunneling region remains controversial. To this end, a theoretical model for tuning quantum tunneling barrier height through dielectric dependence was established, which comprises the effects of interface dipole, image potential, and external stimuli. Notably, the model revealed a negative exponential relationship between barrier height and dielectric constant. This finding was further experimentally evidenced by using an Au atomic quantum tunneling probe featuring a sub-3 nm gap across different dielectric media. Furthermore, the dynamic control of barrier height was achieved through ultrasound-induced dielectric modulation within the tunneling region. These findings open new avenues for the development of broadband acoustic quantum devices and enable atomic-scale imaging within opaque and biological materials.

The layered configuration and strong anisotropy of carbon fiber-reinforced polymer (CFRP) laminates pose critical challenges on accurate imaging of internal defects. Three-dimensional (3D) imaging is desirable for comprehensive evaluation, but it is traditionally formed by stitching a series of two-dimensional (2D) images, which is complicated and time-consuming. Here, an anisotropic volumetric total focusing method (AV-TFM) for CFRP laminates by using a 2D phased array was proposed. Firstly, the elastic constants were derived from the full matrix data. Then, the simplified QP-wave group velocity formula was derived to directly correlate the velocity and its angle. Therefore, the group velocities at any angle can be simply calculated. Finally, the anisotropic effect was corrected for 3D imaging by total focusing method efficiently and precisely. Simulations and experiments were conducted on different CFRP laminates with internal defects to verify the effectiveness of AV-TFM. Results prove that AV-TFM enables accurate volumetric imaging of anisotropic CFRP laminates, providing a simple and comprehensive avenue for non-destructive evaluation of large CFRP components during manufacturing and in service.

The ability to manipulate acoustic fields in a real-time and high-resolution manner can open up many opportunities for engineering and medical applications. Realising this would demand an acoustic metamaterial that can modulate acoustic waves in a programmable manner. We achieve this goal using a crosslinked semi-crystalline polymer for which any arbitrary modulus pattern can be repeatedly encoded/erased in roughly 13 minutes. Critically and surprisingly, the material allows acoustic wave transmission with low attenuation, despite its multiphase nature. With the modulus pattern and acoustic transparency, reconfigurable phase holograms can be created. Combined with an electrically switchable and compact partitioned piezo-electric transducer, the device allows generating acoustic fields with a high modulation resolution of 10000 pixels/cm² at an ultra-fast switching rate of 50000 fps for specified dynamic holography, far exceeding existing approaches. By programming the semi-crystalline polymer with different phase holograms, together with the selective excitation of partitioned piezo-electric transducer for incident wavefront modulation, it allows an unprecedented opportunity to create acoustic movies and remote thermal writing, with strong implications for many other future technological possibilities.

Ultrasonic detection of delamination in stringer-stiffened panels made of carbon fiber-reinforced plastics (CFRPs) presents a critical challenge due to their complex geometry, complicated properties and large size. In this work, a delamination detection method using the wavefield curvature of the A₀-mode Lamb wave is proposed. Firstly, the underlying mechanism is numerically investigated to examine the interactions between the A₀-mode Lamb wave and delamination at different sites of the stringer. Then, the wavefield curvature sensitive to local anomalies is revealed owing to the higher-order derivative nature. Thereafter, the proposed method is utilized to detect delamination in the fabricated CFRP specimens and the results are compared with X-ray computed tomography, confirming the feasibility and effectiveness of the proposed method. This viable method, capable of detecting delamination in larger CFRP stringers, will find great potential in the efficient non-destructive testing of CFRP structures in different applications.

Traditional methods for acoustic field visualization require considerable effort for capturing large amounts of acoustic data to achieve a high resolution field map, highly limiting their widespread use. In this study, we propose an approach for acoustic field visualization based on physics-informed neural networks (PINNs) by using a small amount of data, subsequently realizing accurate acoustic source localization. First, we present a PINN model integrated with an acoustic Helmholtz equation and adaptive sampling, the performance of which is testified via numerical simulations. The “no mesh” character of PINN enables achieving high resolution acoustic field visualization without requiring the capture of numerous data in advance. Furthermore, we experimentally validate the performance of the proposed method, which demonstrates that the acoustic sources can be precisely localized with sparse field data acquisition within a small area. This work would find potential applications in various acoustics, such as acoustic communication, biomedical imaging, and virtual reality.

Flexible micro/nano motors responsive to light sources are highly desirable. Conventional photothermal (PT) techniques have provided significant light-actuation methods; however, the dynamic responses of these devices in high frequency domain are severely restricted by the frequency response limitation. To overcome this limitation, the thermal-, electric-, and acoustic-near field interactions in the PT process and its accompanied photoacoustic (PA) process are investigated, and a plasmon enhanced PA actuation method is proposed. The significant improvement in PA oscillation by strong localized surface plasmon resonance provides a powerful means to realize a broadband response laser motor without the frequency response limitation. This PA laser motor could generate PA oscillation of over 5 µm by pulse laser with repetition frequencies of 1 Hz to 20 kHz and has a maximum value of 18.8 µm at the mechanical resonant frequency. It demonstrates the effectiveness of this PA laser motor in offsetting the shortcomings of the PT actuation method. The device requires no electrical or chemical energy, and it has potential benefits, such as bionic research into insect flapping, vocal-cord vibration, and muscular movement in fields including micro/nano physics, biochemistry, and clinical medicine.

A single acoustic metamaterial with multifunctional use is highly needed for various applications. Herein, a bifunctional acoustic metamaterial for beam switching between the focusing beam and bottle beam is demonstrated, which consists of a groove structure for binary phases and a partitioned piezoelectric transducer (p-PZT) for incident wavefront modulation. The p-PZT is divided into inner and outer regions for selective excitation, and the focusing beam and bottle beam can be switched in real-time by applying different exciting signals on the p-PZT. Theoretical calculation, numerical simulation, and experimental measurement are conducted to verify the effectiveness of the proposed bifunctional acoustic metamaterial for beam switching. Furthermore, the focal plane of both the focusing beam and bottle beam can be linearly tuned by the operating frequency. This work may find potential applications in medical ultrasonic therapy, sound printing, and biological particle manipulation.