The Gravity Recovery and Climate Experiment (GRACE) gravity mission has become a leading platform for monitoring temporal changes in the Earth’s global gravity field. However, the usability of GRACE data is severely limited by 11 months of missing data between the GRACE and GRACE Follow-on (GRACE-FO) missions. To date, several approaches have been proposed to fill this data gap in the form of spherical harmonic coefficients (an expression of the Earth’s gravity field, SHCs). However, systematic analysis to reveal the characteristics and consistency of the datasets produced by these latest gap-filling techniques is yet to be carried out. Here, three SHC gap-filling products are systematically analyzed and compared: (1) Combining high–low satellite-to-satellite tracking with satellite laser ranging (SLR) observations (QuantumFrontiers, QF), (2) SLR-based recovery incorporating the GRACE empirical orthogonal function decomposition model proposed by the Institute of Geodesy and Geoinformation at the University of Bonn (hereafter, denoted as IGG), and (3) applying the singular spectrum analysis approach (SSA). The results show that (1) the SHCs of the QF, IGG, and SSA data are consistent up to degree 12; (2) the IGG and SSA data give similar results over the 11 gap months, but the IGG shows a faster increase in the mean ocean water mass and the SSA appears to better capture the interannual variation in the terrestrial water storage; and (3) the noise level increases significantly in the high-degree terms (l > 16) of the QF data, so these data are only applicable for large-scale mass migration research. These results provide a reference for users to select a gap-filling product. Finally, we propose a new scheme based on the triple collocation method to derive a weight matrix to fuse these three datasets into a more robust solution.

Rubber bearings are critical components of base-isolated structures; therefore, it is essential to monitor their deformation states. Current rubber bearing deformation monitoring requires three displacement sensors to track triaxial displacements. This method introduces errors in suppressing off-target displacement interferences, which reduces measurement accuracy. In addition, the simultaneous requirements for a wide measurement range and high sensor sensitivity are mutually restrictive in design. To address the problem, an L-shaped lever structure cantilever-beam 3-dimensional displacement sensor was proposed. A rotational mechanism equipped with an angular sensor is designed at the bottom of the sensor housing, allowing for the acquisition of three-dimensional displacement information through vector decomposition calculations based on displacement and angle data monitored by a single sensor. This approach mitigates the adverse effects of monitoring accuracy by using multiple sensors. Utilizing its amplification principle, an L-shaped lever amplifies the monitored displacement. It transfers it to the cantilever beam, thereby increasing the surface bending strain of the beam and enhancing sensitivity. The experimental results show that the proposed sensors exhibit a high sensitivity of 50.28 mV/mm in the 0-120mm range while achieving a high accuracy of 0.49%F.S. And the 3-dimensional spatial displacement measurement error was less than 2 mm. The dynamic displacement measurement error was less than 0.4 mm. The 3-dimensional displacement sensor studied in this study meets the requirements for sensitivity and accuracy of rubber bearings.

In this study, we investigated the realization of maximum tuning range of a random fibre laser by adjusting the pump wavelength and power as well as changing the lengths of single-mode and erbium-doped fibres (SMF and EDF) to achieve hybrid erbium-Raman gain. With this hybrid gain, the widest tuning range was 90 nm (1524–1614 nm), optimal pump wavelength was 1489 nm, optimal SMF length was 10 km, and optimal EDF length was 15 m. The lasing power flatness is greatly improved with this optimization. Numerical results indicate that the optical conversion efficiency is as high as 71.1%, with a pump power of 2.7 W and an optical signal-to-noise ratio over 55 dB. Hence, this work effectively optimizes and inspires the exploration of and new schemes for broad wavelength tuneable and high-efficiency random fibre lasers.

Orbital angular momentum beams have been extensively researched due to their ability to enhance the channel capacity of microwave systems. Metasurface near-field calculations of different sizes have been completed. Near-field calculations with Gaussian noise for metasurfaces of different sizes were also completed. The presence of noise suggests that the vortex electric field generated by the small metasurface of the vortex wave may experience disturbance and be overwhelmed by strong noise. On the other hand, the large vortex wave metasurface exhibits superior anti-noise capability. Its anti-interference characteristic was verified by conducting full-wave simulations on metasurfaces of l = −3 and l = −5. Based on the OAM spectral analysis, the mode purity of the generated vortex waves was calculated in detail. Simulation results indicated that a large-scale metasurface exhibits stronger anti-interference capability, which may inspire the design and research of vortex wave metasurfaces in the future.

In this letter, an ultrawideband stacked structure metasurface is designed to minimize the backward RCS across a frequency range of 5–40 GHz. The stack structure design demonstrated a maximum RCS reduction at 19 GHz, achieving an impressive reduction of 18.11 dBsm compared to a PEC of the same dimensions. The proposed metasurface exhibits the capability to scatter incident plane waves in various directions under both normal and oblique incidence conditions. Additionally, the calculated quantized encoding phase can facilitate further RCS reductions of 3–6 dBsm within the frequency range of 8–25 GHz. Consequently, this work effectively designs and promotes research on low RCS metasurfaces across different frequencies.