The microwave nondestructive testing (MNDT) technique is an attractive candidate for defect detection in the dielectric structures as microwave signals can penetrate inside and interact with the insides of the dielectric material. In this research, a novel MNDT technique is presented for defect detection combining the time domain reflectometry (TDR) technique, the wavelet decomposition analysis (WDA) technique, and an artificial neural network (ANN), which has good generality and can be applied to various dielectric materials with different thicknesses. This method is based on scanning the dielectric material with an open-ended rectangular waveguide (OERW) operating from 18 to 26.5 GHz with 201 frequency points and analyzing its reflections using the proposed algorithm. The method was validated by simulation and experiments successfully. In the simulations, two typical kinds of dielectric materials were used to verify the generality and accuracy of this proposed method. The accuracies of these two dielectric materials were 96% and 90%, respectively. A 2-D image of detection can be constructed by performing repetition of the process with a certain step on the xy plane of a material, which is illustrated by simulations. Meanwhile, the sensitivity analysis was performed by studying the similarity quantified using the Pearson’s coefficient correlation. Eventually, some FR4 samples were machined to demonstrate the feasibility of this method. The acceptable accuracy is 86% of the experimental result.

Near-field imaging based on an electromagnetic sensor has been widely used for nondestructive detection. An approach to detect the near-surface defects in pipeline coatings and dielectric pipelines is proposed. Based on the characteristics of resonant frequency shifts, a novel method using artificial neural network (ANN) is established to quantitatively evaluate circular-section shape defects in pipes, such as air bubbles in pipeline coating layers or qualitative characterize non-circular section-shape defects. The proposed method has three important modules: a new resonator for data acquisition, a signal-processing algorithm for data preprocessing, and an ANN for quantitative imaging. In the designed sensor, we extend the tip of the sensing ring and introduce an appending in the ring gap for high sensitivity. Simulations show that the sensor can detect a defect with a radius as small as 0.7 mm. The raw resonant frequency shifts obtained by the sensor scanning at an angle interval around the specimen first are preprocessed by curve fitting, sampling, and adaptive data interpolation or truncation. Then, using an ANN, the relationships among resonant frequency shifts, external radius of the specimen, and defect size are modeled for imaging of circular-section shape defects. Preliminary simulations and measurements illustrate the efficacy of the method. Consequently, a contactless, high-resolution, near-field imaging measurement based on sensor scanning for inspecting pipe structures is obtained.

The Microwave Nondestructive Testing (MNDT) method has been increasingly used for inspecting wood characteristics. In this work, a MNDT method is established for effective and accurate detection and analysis of wood subsurface structural defects. A microwave near-field probe loaded with a split-ring resonator is proposed to bring in strong electric field, which is directly attached to the trailing end of the coupled microstrip line. High-resolution, light weight, low-cost, and compactness are some of the advantages of the sensor. The designed sensor is used for detecting subsurface structural defects under the thin paint layer of wood. Here, S21 values are used to analyze the characteristics of wood. Different width and depth defects of wood samples with different moisture content levels were measured. The experimental results show that the maximum relative error between the actual widths and measured widths is less than 10%. The spatial resolution is approximately 0.42λ₀ at a resonant frequency of 9 GHz. The results demonstrate that the designed probe can accurately trace defects in wood with different moisture content levels without striping the upper coating of the paint.

In this letter, a broadband rectifying metasurface (RMS) antenna for simultaneous wireless information and power transfer (SWIPT) is proposed. By integrating an RMS with a slot-coupled antenna, the proposed design enables the concurrent collection of energy and information in different frequency bands, simplifying the SWIPT receiving system. First, an RMS is developed to harvest broadband electromagnetic (EM) energy across 4.4–6.4 GHz. The top patch of the RMS unit is designed as an asymmetric orthogonal dipole, which expands the impedance bandwidth by optimizing the length ratio of its long and short arms. Rectifier diodes and inductors are directly integrated into the RMS unit to realize rectification and form direct current (DC) transmission path. Then, a 5 × 5 patch on the top of the RMS is regarded as a radiating patch, and a rectangular slot is etched in the center of the ground plane of the RMS, to form a slot-coupled antenna for information collection in the 2.4–2.5 GHz. Measurement results indicate the energy harvesting efficiency exceeding 60% in the 4.4–6.4 GHz, along with the gain of over 4 dBi in the 2.4–2.5 GHz, confirming its effectiveness in both energy and information collection.

A novel concept of wideband polarization-insensitive reconfigurable reflectarray antenna (RRA) is proposed by using an identically spin-locked metasurface. Different from the geometric phase (φ_L = −φ_R), identically spin-locked phase that is the same for left- and right-handed circular polarization (LCP & RCP) states (φ_L = φ_R), which can be realized by decoupling the dual-helicity. Since any polarization wave is a superposition of LCP and RCP waves, the same phase can be imparted to any polarization wave under the condition of identically spin-locked phase. The 1-bit reflected phase for any incident wave can be controlled dynamically by altering the orientation state of each element with 0° or 90° through micromotors. For demonstration and possible applications, a prototype composed of 30 × 30 elements is fabricated and measured, which is applied to beam scanning. Numerical and experimental results illustrate that our RRA can work in dual linear polarization (LP) and dual CP states, reaching a wide-angle beam scanning up to ±40°. The maximum measured gains in x-LP and RCP channel are 26.4 dB at 15 GHz and 25.9 dB at 15.2 GHz, respectively, and a 3 dB gain bandwidth more than 27%. These findings hold significant promise for the advancement of versatile beam scanning, which provides promising applications in wireless communication and radar systems.

Lightning rods, while essential for protecting weather radars from direct lightning strikes, act as persistent non-meteorological scatterers that can interfere with signal transmission and reception and thereby degrade detection accuracy and product quality. Existing studies have mainly focused on X-band and C-band systems, and robust, measurement-based quantitative assessments for S-band dual-polarization radars remain scarce. In this study, a controllable tilting lightning rod, a high-precision Far-field Antenna Measurement System (FAMS), and an S-band dual-polarization weather radar (SAD radar) are jointly employed to systematically quantify lightning-rod impacts on antenna electromagnetic parameters under different rod elevation angles and azimuth configurations. Typical precipitation events were analyzed to evaluate the influence of the lightning rods on dual-polarization parameters. The results show that the lightning rod substantially elevates sidelobe levels, with a maximum enhancement of 4.55 dB, while producing only limited changes in the antenna main-beam azimuth and beamwidth. Differential reflectivity ($Z_{DR}$) is the most sensitive polarimetric parameter, exhibiting a persistent positive bias of about 0.24–0.25 dB in snowfall and mixed-phase precipitation, while no persistent azimuthal anomaly is evident during freezing rain; the co-polar correlation coefficient (${\rho }_{hv}$) is only marginally affected. Collectively, these results provide quantitative, far-field evidence of lightning-rod interference in S-band dual-polarization radars and provide practical guidance for more reasonable lightning-rod placement and configuration, as well as useful references for $Z_{DR}$-oriented polarimetric quality-control and correction strategies.