Zhe Wu

This research proposes a novel method for detecting transparent oil–water two-phase flow in microfluidic chips using a near-field scanning microwave microscope (NSMM). This approach enables nonintrusive characterization of the intrinsic localized properties of fluids; crucially, it dispenses with additives and visible tracer particles, imposes no constraints on sample color, and preserves the fluids’ native state throughout the measurement process. NSMM achieves successful detection of transparent dimethicone-water two-phase flow in microfluidic chips, with results validating its reliable discrimination between the dimethicone and water phases. A comparison of these results with those obtained via optical detection confirms a high level of consistency. This work presents a groundbreaking solution for industrial applications, including oil extraction and chemical synthesis, addressing the critical demands of component analysis and flow regime detection.

This work investigates the parasitic surface conduction (PSC) effect suppression in silicon‐integrated single‐crystalline LiNbO3 (LN) thin-film by two-times He+ implanted high-resistivity Si (HR‐Si) substrate. First, the effect of He+ implantation energy on vacancy defects depth distribution in HR-Si is studied. The trap layer thickness induced by one-time He+ implantation is less than 500 nm, which is insufficient for PSC effect suppression. Therefore, two-times He+ implantations are adopted. The trap layer thickness induced by two-times He+ implantations is 670nm, which is sufficient for PSC effect suppression. In the experiment, the resistivity and carrier concentration of the He+ implanted samples annealed at different temperatures are studied. Results indicate that the sample annealed at 600 °C can suppress the PSC effect, and subsequent lower‐temperature annealing has little effect. Two single‐crystalline LN thin-film wafers based on HR-Si substrates with and without He+ implantation are fabricated. Finally, loss characteristics of the two wafers are measured. Compared with the wafer without ion implantation, the wafer with two-times He+ implanted HR-Si substrate exhibits a higher Q-value. This work indicates that the single‐crystalline LN thin-film on two-times He+ implanted HR‐Si substrate can suppress the PSC effect. This may pave a new way to realize higher-performance surface-acoustic-wave devices.

With the continuous scaling and increasing operating frequencies of microwave integrated circuits, accurate characterization of on-chip microwave signal propagation and field distributions has become increasingly important for ensuring circuit reliability and performance stability. To address this challenge, we have developed a beat-frequency-enhanced near-field scanning microwave microscopy, which enables in situ, non-destructive characterization of the microwave field distributions on microstrip line surfaces under operating conditions. When the probe–sample distance and the surrounding dielectric environment are kept constant, the oscillation amplitude of the transmission coefficient S21, ΔS21can serve as a relative indicator of the surface microwave field strength of the microstrip line. The experimental results demonstrate that ΔS21 exhibits a positive correlation with the input signal power applied to the sample. Furthermore, as the input signal frequency of the sample approaches the resonant frequency of the probe–sample coupling, the detection sensitivity of ΔS21 to the input signal power is significantly enhanced, with a minimum detectable power as low as −40 dBm. Surface scanning results reveal clear visualization of microwave field strength distributions for both standard and defective microstrip lines, in good agreement with simulation data. The proposed technique offers a promising pathway for real-time diagnostics of high-frequency integrated circuits, combining high sensitivity, non-destructive evaluation, and compatibility with practical operating environments.

A slow-wave structure (SWS) with a staggered double-grid structure is a critical component in high-frequency traveling wave tubes (TWTs), but its performance is often affected by deep-groove fabrication-induced defects. By employing a dual-port quarter-wavelength coaxial resonator, the near-field scanning microwave microscope (NSMM) system achieves strong evanescent coupling and enables electromagnetic parameter imaging of the deep-groove structure. Guided by near-field perturbation theory, the introduction of local protrusion defects causes measurable shifts in the resonant frequency, providing a direct electromagnetic signature of structural imperfections. A comparison between optical imaging and near-field scanning images confirms that the defect locations correspond one-to-one. The NSMM successfully identified a protrusion defect with a height of approximately 50 μm within a deep-groove structure of 100 μm depth. It confirms the feasibility of the NSMM for non-destructive characterization of deep-groove defects induced by etching in the field of microelectromechanical systems, offering a promising tool for structural integrity assessment in microelectromechanical systems (MEMS) and vacuum electronic device fabrication.

The resistivity imaging system is specifically designed for the precise measurement of resistivity distributions within drilled columnar core samples. Its coaxial symmetric configuration enables the non-destructive characterization of electrical properties, with broad applications in oil and gas exploration, reservoir evaluation, and geological research. By integrating a ring return electrode and full-circumference electrode arrays, the system can acquire core-scale resistivity data in conductive media environments. The self-developed imaging software employs advanced processing algorithms—including depth correction, amplitude normalization, and image enhancement—to transform raw resistivity measurements into high-resolution surface imaging maps. Experimental results demonstrate that the system can resolve features such as cracks with a minimum width of 0.5 mm and pores with a minimum inner diameter of 0.4 mm in granite core, providing a novel technical approach for the fine-scale characterization of core materials.

Near-field microwave microscopy (NSMM) is a promising technique for the non-destructive, high-resolution imaging of electrical and dielectric properties at the microscale. However, its performance is highly sensitive to the probe-to-sample distance, often requiring extremely close proximity, which limits its practical application in device manufacturing, especially in scenarios involving coatings and packaging. In this study, we propose a distance inversion method based on a dual-port symmetrical microwave probe to improve imaging performance at larger, safer scanning distances. This method utilizes the correlation between probe height and resonant frequency to compensate for distance-induced signal distortions. The experimental results demonstrate that even at a probe–sample distance of 80 µm, clear and distinguishable NSMM images of printed circuit boards (PCBs) can be obtained. The imaging resolution reached 13 µm. The defect structure with dimensions of 130 × 130 µm² on the PCB was successfully identified. The signal-to-noise ratio was significantly enhanced after applying the correction method. This approach not only improves the robustness and flexibility of NSMM in industrial scenarios but also extends its applicability to packaged or coated electronic devices, offering a valuable tool for advanced non-destructive testing.

Traditional anti-counterfeiting techniques and methods are inadequate to meet the modern, sophisticated anti-counterfeiting requirement in banknotes. We applied our homemade near-field scanning microwave microscopy (NSMM) for penetrating imaging of concealed anti-counterfeiting features in banknotes. This NSMM imaged and characterized several vital concealed anti-counterfeiting features in the banknotes, including the dynamic color-shifting security threads, color-changing denomination numbers, magnetically embedded security threads, and white watermarks. At the same time, with the obstruction of red ink, near-field microwaves still penetrated the medium layer to characterize the detailed information of the security threads successfully. Additionally, the cavity perturbation method was used to obtain the effective permittivity of 3.65 and 3.62 for the windowing security thread and middle-embedded security thread. The thickness of the watermark was calculated to be about 3.3 μm with the calibrated fit method.

In this work, a scanning inverse spin Hall effect measurement system based on a shorted coaxial resonator has been built, which provides a high throughput method to characterize spin transport properties. The system is capable of performing spin pumping measurements on patterned samples within an area of 100 × 100 mm². Its capability was demonstrated with Py/Ta bilayer stripes deposited on the same substrate with different thicknesses of Ta. The results show that the spin diffusion length is about 4.2 nm with a conductivity of about 7.5 × 10⁵ Ω⁻¹ m⁻¹, which leads to the conclusion that the intrinsic mechanism of spin relaxation of Ta is the Elliott–Yafet interactions. The spin Hall angle of Ta is estimated to be about −0.014 at room temperature. The setup developed in this work provides a convenient, efficient, and nondestructive way to obtain the spin and electron transportation characteristics of the spintronic materials, which will fertilize this community by developing new materials and figuring out their mechanism.

In this article, a method of illustrating the electromagnetic properties of liquid specimens is proposed by our homemade near-field scanning microwave microscopy (NSMM). By introducing the fundamental theorem of NSMM and conducting a simulation on the configuration of the whole system, parameters including quality factor and resonant frequency in electrolyte liquid specimen vary with types of the solution as well as their concentration. By conducting the line scanning testing method, the relation of concentration of a specified solution concerning its corresponding electromagnetic properties is clarified. Eventually, yeast cells are tested at living or dead status with point scanning and line scanning separately. The NSMM experiment results exhibit a substantial capacity for biologic samples in a liquid environment.

The limitation of mechanical manufacturing will result in a small tilt angle of the sample stage in the horizontal direction, which decreases the spatial resolution of imaging in near-field scanning microwave microscopy (NSMM). In this paper, we focus on the tilt correction and improve the spatial resolution of the NSMM image. The results of electromagnetic simulation and line scan measurement demonstrate the critical parameters affecting the sensitivity of NSMM, such as the length of the probe extending out of the cavity, the tip–sample distance, and the tip apex size. The tilt images can rotate successfully to the horizontal plane with the tilt correction methods, and the local average and re-interpolation are applied to denoise the images. Experimental NSMM images of copper thin film grid, coin texture, lithography mask, and leaf vein are obtained. The images before and after correction verify the improvement of the spatial resolution with all the above methods.