For metal crack nondestructive detection, most conventional crack sensors are unable to realize the crack direction detection. In this work, a direction-sensitive microwave sensor is proposed for metal crack detection. The proposed sensor consists of a rectangular patch resonator and two perpendicular coupled feeding ports, which improves the current distribution on patch surface and the sensitivity for crack direction detection. The performances of the proposed sensor are verified by simulation and measurement experiments. The results show that the width sensitivities of two feeding ports are 100 MHz/mm and 63.3 MHz/mm, respectively, and the sensitivity of the sensor for crack direction detection are 6.10 MHz/5 degrees and 1.93 MHz/5 degrees, respectively. Due to the advantages of a simple structure, low profile, large coverage area and high sensitivity, the proposed sensor has a great application potential in nondestructive detection fields.

The time-domain coding metasurface (TDCM) offers a rapid and efficient approach for manipulating frequency spectra of electromagnetic waves. To date, not only finite-order harmonics can be generated and coded discretely, frequency modulation of continuous waves has also been investigated. However, limited phase-tuning speed still constrains the modulation bandwidth and practical applications. Here, we report a TDCM capable of nanosecond-level phase tuning as fast as 20 ns within a full 360° tuning cycle. Unlike conventional varactor-based approaches, the proposed TDCM adopts a reconfigurable PIN-diode array, reducing transition time between adjacent states to only several nanoseconds. Furthermore, this approach can be extended to Ku- and even millimeter-wave bands, overcoming the frequency constraint of varactors. To validate its effectiveness, we built a C-band frequency-modulated continuous-wave radar prototype with the metasurface as the signal generator. A high-quality 10-MHz-bandwidth FMCW signal was generated, enabling accurate measurement of a flying drone’s range and speed.

Passive radar jamming is a class of attractive approaches that can interfere with radar signals and essentially destroy the detection capability of the radar. In previous passive jamming schemes based on metasurfaces, almost all demonstrated jamming is amplitude invariant and limited to only change phase related properties of the radar echo, which restricts more jamming functions. Here, we report a recognition deception based on an amplitude–phase-independent metasurface. This metasurface can simultaneously achieve similar amplitude attenuation levels for different phase-shifting states as well as small phase fluctuation across different amplitude attenuation levels within a full 360^∘ phase-shifting cycle. Besides that, this metasurface also behaves small inherent internal loss. With such a metasurface, not only a simple false target jamming can be realized, but also the recognition deception based on the imitation of micro-motion features including both micro-Doppler signatures and flicker mechanisms for aerial targets can come true. The independent manipulation functionalities of the metasurface are validated in measurements. Moreover, with numerically derived, time-variant coding sequences, the effectiveness of the recognition deception as different kinds of aerocrafts as well as the same kind of aerocrafts with different numbers of rotors is experimentally demonstrated by mimicking their reflected signals.

Aiming at the requirement of polarimetric radiometer for Ortho-Mode Transducer (OMT), a Ka-band OMT with high isolation is proposed in this paper. The design details of Ka-band OMT is firstly described and simulation experiments are performed. The simulation results show that the −10dB impedance bandwidth is larger than 7.5GHz, and the isolation level is better than 60dB, which is realized by coupling aperture parameters optimization. The designed OMT can be easily fabricated with 3D printing technology.