To realize the free falling test mass (TM) in gravitational wave detection in space, an alternative current (AC) electrostatic control strategy is proposed and developed. It is significant to test and verify the AC control actuation scheme on the ground. In this paper, a two-stage torsion pendulum is used to test the performance of the AC control actuator of inertial sensor for Tianqin project. First, the pendulum facility combined with a TM, a capacitive position sensor and an AC control actuator is constructed. Experimental results show that the sensitivities of the pendulum achieve 4.2 × 10 −11 N Hz −1/2 at 6 mHz and 1.6 × 10 −13 Nm Hz −1/2 at 15 mHz, respectively, and the pendulum provides a chance to realize the performance test of two degree-of-freedom sensitivities of the actuator, experimental verification of AC control strategy and so on, which is first reported to test performance of the AC control actuator of a space inertial sensor on the ground.

Space gravitational wave detection requires suppression of magnetic disturbances on the test mass (TM), yet faces dual challenges: precise control of the spacecraft magnetic field is constrained by design limits, and celestial activity can cause short-term field enhancements, both risking exceedance of the TM's disturbance budget. Accurate acquisition of the magnetic field and its gradient at the TM is thus critical for in-orbit assessment and compensation. Since magnetometers cannot be placed directly on the TM, an indirect scheme is adopted, deploying sensors around the TM and applying a field-recovery method. Existing recovery approaches, however, are susceptible to interference from the ambient space magnetic field, leading to biased estimates. To address this, we optimize the method to effectively suppress the influence of the space magnetic field, achieving unbiased estimation of both the field and its gradient. Simulations demonstrate that the optimized method not only delivers unbiased estimates but also reduces the recovery error to as low as 1 & times;10-8 T (Hz 1/2)-1 for the magnetic field and 2 & times;10-8 T m -1 (Hz 1/2)-1 for its gradient. After correction with the reconstructed field and gradient, the residual magnetic disturbance is lowered to 1 & times;10-16 m s -2 (Hz 1/2)-1, meeting the requirements for space gravitational wave detection missions.

The inertial sensor (IS) is one of the most critical units in space-based gravitational wave detection projects. Due to the machining process and assembly errors of the IS head (ISH) in the IS, the electrostatic force in the non-sensitive direction of the test mass (TM) will produce a cross-coupling effect in the sensitive direction, which couples the non-sensitive axis actuation acceleration into an acceleration noise along the sensitive axis. The path that non-sensitive axis force and torque influence the residual acceleration of the sensitive axis, via the capacitance gradient, is constructed. A capacitance measurement device equipped with an ISH and a three-terminal mode to ensure the excellent measurement performance was constructed to measure the nominal capacitance and the derivative of the sensing/actuation capacitance along the six degrees of freedom. The simulation values are consistent with the experimental values within the error range. The electrostatic cross-coupling from non-sensitive directions into the sensitive direction, on the order of 10-3-10-4, is evaluated via the experimental capacitance gradients. The residual disturbance acceleration noise of the sensitive axis on the TM contributed by the non-sensitive axis actuation acceleration noise is approximately 8.0 & times; 10-17 m s-2 Hz-1/2 around 1 mHz.

Controlling the residual potential of test masses via the photocurrent-equilibrium mechanism is a promising method for space-based gravitational-wave detectors. This paper systematically investigates the photocurrent-equilibrium mechanism under the cooperative interaction between photon distribution and electric field. An analytical model for the residual potential is developed, and all photoelectric combinations that achieve zero residual potential are identified. Furthermore, a photoelectric decoupling method is proposed and experimentally validated using a torsion pendulum system. The results demonstrate a linear relationship (R-2 > 0.99) between the residual potential at equilibrium and instantaneous injection voltage for both illumination cases (test mass illumination and electrode housing illumination), enabling control within +/- 7 mV and meeting the requirements of space-based gravitational-wave detectors. This study elucidates the cooperative mechanism of photoelectricity and provides critical experimental validation for in-orbit applications.

Spaceborne gravitational wave detection missions impose stringent thermal stability requirements at the microkelvin level on inertial sensors in the millihertz band. Although finite element modeling can predict low frequency thermal transfer behavior, its accuracy is limited by uncertainties in material properties, thermal contacts, assembly details, and boundary conditions. In this study, a frequency domain identification method is proposed and experimentally verified based on a thermal equivalent model of the TianQin space inertial sensor. First, under a small signal linear time invariant approximation, normalized transfer function magnitudes are obtained by referencing the temperature responses at the measurement locations to the source side temperature perturbation. Second, a thermal equivalent model is developed based on the dominant heat transfer path and the frequency dependent variation of transfer function magnitudes. Finally, the proposed method is assessed through comparison between finite element model (FEM) predictions and experimental results in the 0.2 mHz to 6 mHz band. The measured transfer function magnitudes agree with the frequency dependent attenuation trend predicted by the FEM. The fitted dominant time scales are also consistent between the experiment and the FEM at representative electrode housing (EH) and supporting frame (SF) locations. This method provides measured transfer function magnitude data for FEM correlation and thermal stability assessment during the development stage of core payloads for space gravitational wave detection missions.

Abstract Space-based gravitational wave detection imposes extremely stringent requirements on the acceleration noise of test mass (TM), with magnetic effect being one of the significant noise sources. Prior assessments of magnetic effects have only considered the translational acceleration of the center of mass. This work systematically evaluates the disturbing forces and torques produced by magnetic effects on all six degrees of freedom, with particular emphasis on the magnetic torque noise and the resulting force noise coupled into the sensitive axis. Based on the derivation of magnetic potential energy, a finite element calculation method for estimating magnetic torque noise is established, which incorporates the spatial distributions of both the residual magnetic moment and the magnetic susceptibility. The resulting residual acceleration noise along the optical sensitive axis is then calculated, taking into account the crosstalk effects of the center-of-mass to centroid offset, electrostatic coupling, and TM-laser interferometer coupling. This noise lies on the order of 10 -17 ms -2 Hz -1/2 @0.1 mHz. The results indicate that the main contribution to magnetic torque noise comes from the coupling between the residual magnetic moment and the spacecraft's magnetic field, while the contribution from magnetic inhomogeneity accounts for 16%.

We propose a novel ultra-broadband mid-infrared metamaterial absorber by employing the finite-difference time-domain (FDTD). The absorber achieves an average absorption rate of 98.18% because the bandwidth covers the range from 9.72 to 19.97 & micro;m, which is 10.25 & micro;m wide, with absorption reaching as high as 99.94% and 99.40% at the two resonant peaks, respectively. To understand the origin of such high efficiency in more detail, we observe that these effects are caused by a combination of localized surface plasmon resonance (LSPR), magnetic polaritons (MPs), and cascaded Fabry-P & eacute;rot cavity resonances. The synergistic interplay of these mechanisms produces the ultra-broadband absorption response. Furthermore, the absorption spectra of the absorber remain nearly unchanged under both transverse electric (TE) mode and transverse magnetic (TM) mode polarizations, indicating good-polarization insensitive performance; moreover, the absorber has good angle stability, maintaining its performance over an incident angle range of up to 60 degrees.

Cesium lead bromide (CsPbBr3) is a fully inorganic halide perovskite material known for its excellent optoelectronic properties, offering significant advantages for applications in aerospace and nuclear fields. To evaluate its radiation hardness under neutron exposure, the transport process of 1-14 MeV neutrons in CsPbBr3 was simulated using the Geant4 Monte Carlo toolkit. This study focuses on the primary damage characteristics, systematically analyzing the primary knock-on atom (PKA) spectrum and non-ionizing energy loss (NIEL). The simulation results indicate that most PKAs are distributed in the low-energy range. As the incident neutron energy increases, PKA types become more diverse, introducing transmutation products such as 77-81Se, 133Xe, 76As, and 205Hg. Furthermore, a distinct anomaly is observed at lower neutron energies (∼3 MeV), where the displacement of Pb atoms exhibits a localized peak directly attributed to its prominent (n, n) elastic scattering resonance, although the overall macroscopic damage remains heavily dominated by the Br sublattice. Crucially, the calculated NIEL, number of displaced atoms (Nd), and displacements per atom (dpa) exhibit a non-monotonic dependence on incident neutron energy, initially increasing and then decreasing beyond ∼10 MeV. This trend is primarily driven by the transition from elastic to inelastic scattering dominance, coupled with increased ionizing energy partitioning at higher PKA energies. This paper provides fundamental data on the primary damage state of CsPbBr3, establishing an essential source term basis for subsequent multiscale simulations of defect evolution.

In space gravitational wave detection missions, the gravity and its gradients produced by the spacecraft on the two Test Masses (TMs) are commonly referred to as the Self-Gravity(SG). It is an important source of TM disturbances in gravitational wave detection and other drag-free space missions and will affect the TM acceleration noise in many ways. The SG can be reduced by adding Balance Masses (BMs). But for typical space gravitational wave detectors, in which the sensitive axes of the two TMs are at an angle of 60 degrees, the couplings of different SG components of two TMs make the gravity compensation process complicated in practice, which is normally an iterative process. This paper analyses the correspondence between the SG components of the two TMs and the spherical harmonics of different orders, and proposes a compensation method based on spherical multipole expansion. This method allows independent design of the BMs for most of the main SG components, without couplings and iterations. To verify this method, a self-gravity compensation simulation is carried out by using a demonstrating spacecraft structural model for TianQin gravitational wave detection mission. Three sets of BMs are designed on the outer surface of the inertial sensor vacuum chamber, to compensate for the two linear accelerations and one linear gradient that exceed the requirements. The results show that the SG components after compensation are two orders of magnitude lower than the initial level, and all the components meet the preliminary requirements of TianQin mission. This study could provide reference for the engineering design and development of the spacecraft and inertial sensor payload for space gravitational wave detection missions.

In space-based gravitational wave detection, charge management is used to reduce unwanted electrostatic noise by controlling the absolute charge of the test mass (TM). However, the charge management process will cause periodic interruptions in the scientific measurements. In order to minimize the frequency and influence of the interruptions, this paper proposes a method to optimize the electrostatic noise by adding a common voltage to all the actuation electrodes, to precisely adjust the potential difference between the TM and the electrodes. Theoretical analyses and simulation evaluations indicate that the permissible limit of accumulated charge on the TM can be extended from 107 e to 108 e, while maintaining the same electrostatic noise requirement level of 4x10-16 m/s2/Hz1/2. This approach shows that it allows a tenfold extension of the charge management period, significantly reducing interruptions in gravitational wave detection.

TianQin is a future space-based gravitational wave (GW) observatory targeting the frequency window of 10−4–1 Hz. A large variety of GW sources are expected in this frequency band, including the merger of massive black hole binaries, the inspiral of extreme/intermediate mass ratio systems, stellar-mass black hole binaries, Galactic compact binaries, and so on. TianQin will consist of three Earth orbiting satellites on nearly identical orbits with orbital radii of about 105 km. The satellites will form a normal triangle constellation whose plane is nearly perpendicular to the ecliptic plane. The TianQin project has been progressing smoothly following the ‘0123’ technology roadmap. In step ‘0’, the TianQin laser ranging station has been constructed and it has successfully ranged to all the five retro-reflectors on the Moon. In step ‘1’, the drag-free control technology has been tested and demonstrated using the TianQin-1 satellite. In step ‘2’, the inter-satellite laser interferometry technology will be tested using the pair of TianQin-2 satellites. The TianQin-2 mission has been officially approved and the satellites will be launched around 2026. In step ‘3’, i.e. the TianQin-3 mission, three identical satellites will be launched around 2035 to form the space-based GW detector, TianQin, and to start GW detection in space.

Measuring and reducing the stray potentials of space inertial sensors is of great significance for gravitational wave detection. Because of the actual configuration of inertial sensors, the optical displacement reading can, however, only be applied to the stray potential measurement of the sensitive axis. This article proposes to use capacitance sensing instead of optical reading for stray potential measurement in six degrees of freedom. According to theoretical models and design parameters, the in-orbit measurement resolution of the proposed method can reach 1 mu V, which meets the requirements for gravitational wave detection. Additionally, a torsion pendulum device is established on the ground to conduct stray potential measurement experiments. Experimental results show that the measurement resolution is 0.47 mV based on capacitive sensing at the modulation frequency of 0.001 Hz, which is consistent with theoretical expectations on the ground. This work validates the feasibility of the capacitive sensing-based measurement method, providing a new solution for stray potential measurement during gravitational wave detection.

Temperature fluctuation is a major disturbance for the space-based gravitational wave detectors, especially for the strain sensitivity of the TianQin inertial sensor. Comprehensive low-frequency thermal stability of the inertial sensor are essential inputs to the thermal design and the thermal diagnostics. However, the relative contributions of the different heat transfer effects within the vacuum chamber, as well as the effect of rarefied gas, remain undefined. In this work, the various heat transfer processes are decoupled and analyzed, particularly the rarefied gas heat transfer based on the frequency domain thermal framework. The results indicate that the thermal radiation accounts for only 4.55 % of the total heat transfer within the inertial sensor, and the rarefied gas heat transfer contributes even less. In order to meet the error budget, the temperature fluctuations along the x-axis direction of the vacuum chamber in the inertial sensor should be limited to 1 mK/Hz1/2. Moreover, the thermocouples on the vacuum chamber should be arranged in pairs.

Methanol adsorption and decomposition on Pt- and Ni-decorated TiO2(110) surfaces were examined using density functional theory (DFT) calculations. Furthermore, the impact of oxygen vacancies was studied. Results indicated that the Pt10/TiO2(110) and Ni10/TiO2(110) surfaces possessed distinct active centers and exhibited varying catalytic activities for the adsorption and decomposition of CH3OH. Additionally, at the interfacial site, the energy barrier for CH3OH decomposition on the Pt10/TiO2(110) surface was lower than that on the Ni10/TiO2(110) surface, indicating that the catalytic activity of Pt10/TiO2(110) was higher than that of Ni10/TiO2(110). An analysis revealed that the unique adsorption structure of CH3O* and charge transfer at the interfacial site, along with the fluxionality of metal clusters, played decisive roles in the decomposition of CH3OH. This work not only contributes to the development of efficient CH3OH photocatalysts but is also crucial for understanding the basic mechanism of supported catalysts for CH3OH decomposition.

Charge management is a critical technology for space-based gravitational-wave detection, where the controllability of ultraviolet (UV) light plays a key role in determining performance. Although the solutions with light source and optical fiber have been widely adopted, they may experience performance degradation in space due to irradiation effects and parameter drift that would introduce uncertainty. This article presents a novel discharge solution that embeds micro-light-emitting diodes (LEDs) into the inertial sensors, avoiding the usage of optical fibers to simplify the optical pathway and enhance the system's reliability. The experiments based on the torsion pendulum validate that the proposed solution can control the potential of test mass within 10 mV, which demonstrates the feasibility of charge management in gravitational-wave detection.

Electroreduction of nitrate (NO3-) has emerged as a promising strategy for producing ammonia (NH3) at room temperature in recent years. However, the formation of the less electron-consuming H2 byproduct seriously limits the conversion efficiency of NO3- to NH3. In this study, we identify that N-doped Co3O4 can effectively convert NO3- to NH3 with a high performance (NH3 yield rate: 7.18 +/- 0.59 mg h-1 cm-2, faradaic efficiency: 96.7 +/- 0.88%), which is significantly higher than that of pure Co3O4 (NH3 yield rate: 4.95 +/- 0.54 mg h-1 cm-2) and most reported Co-based catalysts (Table S1, ESI). Density functional theory (DFT) calculations coupled with X-ray absorption near-edge structure (XANES) experiments reveal that N-doping in Co3O4 releases more positive charge on the Co atom site due to charge compensation. This oxidized Co atom site enhances the adsorption of NO3- while weakening the adsorption of H+ through Coulombic interactions, thus improving NO3RR activity. Overall, our study provides an efficient electrocatalyst to avoid the formation of the H2 byproduct to facilitate the conversion of NO3- to NH3, and opens new avenues towards achieving green ammonia production by controlling Coulombic interactions.

The high-precision electrostatic accelerometer is the key payload for satellite gravity measurement, so ground testing and verification of its performance is critical. Our group has previously developed a series of test benches that can be used to provide a ground test environment of 10(-9 )m/s2/Hz( 1/2 )level. In this article, a novel performance evaluation device for high-precision accelerometers based on an active vibration isolation system (AVIS) is proposed. An electrostatic accelerometer with a theoretical noise level of 10(-10 )m/s2/Hz( 1/2 ) is used as the motion sensor, and the active feedback control is carried out in combination with the four-wire pendulum. The system noise model is further analyzed in detail. The experimental results show that the vibration transmissibility of this system using acceleration sensing is better than that using velocity sensing, which verifies the effectiveness of the proposed method. The total residual noise level on the test bench measured by the seismometer is verified to be about 1x10(-9 )m/s2/Hz( 1/2 ) from 0.5 to 0.8 Hz, while the performance of the electrostatic accelerometer itself is evaluated to be 7x10(-10) m/s2/Hz( 1/2 ) from 0.3 to 0.6 Hz.

Precision torsion pendulums can be used to test space-borne inertial sensors with measurement ranges significantly smaller than Earth's surface gravitational acceleration. In this system, the gravity on the test mass is counterbalanced by the tension of the suspension fiber, enabling the sensor to enter its operational state. Through optimized design configurations, the system can effectively suppress the effects of ultra-low-frequency (around several mHz) seismic noise. This study addresses the mid-to-high frequency ground vibration effects, which conventional torsion pendulum schemes fail to suppress, proposing a novel torsion pendulum testing scheme integrated with an active vibration isolation system. This article introduces the design and theoretical analysis of an inertial sensor testing system with this scheme and shows the experimental validation of the improved seismic effect suppression. The experiments demonstrate that isolating mid-to-high frequency ground vibrations improves the noise floor testing of the inertial sensor, with the measured noise reaching the level of about 2 × 10-10 m/s2/Hz1/2, which reveals the intrinsic noise of the inertial sensor.

High-precision and high-efficiency gravity calculation is a critical challenge in astrophysics, geophysics, and aerospace engineering. In space gravitational wave detection, the self-gravity effect of a spacecraft on its test mass is a significant perturbing force, typically evaluated through numerical methods. Traditional approaches involve steps including the grid-based discretization and the sixfold integration, which are computationally complex and inefficient, particularly for high complexity structures. This paper proposes a novel finite element method for simulating gravitational effects by solving the partial differential equations of the gravitational field. Using the Physics Builder module in COMSOL Multiphysics, a gravitational field interface is developed to directly solve the partial differential equations of gravitational field, enabling efficient and accurate gravity calculations. This method not only simplifies the computational process and enhances efficiency but also is suitable for objects of arbitrary shapes. The method is validated by simulating the gravity of basic geometric shapes and comparing the results with those obtained using the multipole expansion method, demonstrating an error margin below 0.014%. The simulation is also compared with the traditional method of discretized integration, and the proposed method performs a significantly higher efficiency. Additionally, the paper analyzes the self-gravity of a test mass with indents and corners for the TianQin space gravitational wave detection spacecraft, revealing a 0.18% deviation compared to a standard cubic test mass. This approach offers a robust and versatile tool for gravity calculations in complex scenarios.

The rapid and sensitive detection of hazardous substances is essential for safeguarding human health. This work presented the synthesis of laccase immobilized on N-doped carbon nanonets (N-doped carbon nanonets-lac) biosensor and its application for the photothermal detection of hydroquinone. The N-doped carbon nanonetslac biosensor demonstrated rapid response and precise detection of hydroquinone in 5 s, along with excellent sensitivity, good tolerance to metal ions and organic compounds, outstanding selectivity, and storage stability. Thanks to the photothermal effect of N-doped carbon nanonets, the N-doped carbon nanonets-lac biosensor was demonstrated as a photothermal biosensor for hydroquinone detection. The N-doped carbon nanonets-lac biosensor exhibits a highly sensitive current response under illumination, with a detection limit as low as 0.14 mu M (S/N = 3) and an extensive response range of 1-1000 mu M. Furthermore, the N-doped carbon nanonetslac biosensor showed reliable performance in photothermal analysis of tap and Yangtze River water samples, highlighting its technical effectiveness in detecting contamination of toxic compounds in real water samples.