Jun Wu

Residual gas noise limits the measurement accuracy of space-borne inertial sensors and is critical for space-borne gravitational wave detection. Unlike conventional sensors, space-borne inertial sensors exhibit complex boundaries, anisotropy, and multiple outgassing sources, leading to non-uniform gas distributions. However, this phenomenon and its effect on residual gas noise have not been discussed in previous studies. This study focuses on the analysis of non-uniform gas distribution and its effect on residual gas noise in space-borne inertial sensors. Non-uniform gas distribution was simulated and characterized with a quasi-Gaussian distribution. A model for residual gas noise in constrained spaces with non-uniform gas distribution was developed and analyzed. Results show that the gas distribution within the inertial sensor's constrained space differs from that in free space. Non-uniform gas distribution leads to extra noise, which reaches up to 2.02 × 10−16 (N/Hz1/2). This additive value accounts for about 20% of TianQin's total noise budget. The extra noise originates from prolonged gas molecule escape time and gradient-induced external friction. This study evaluated the non-uniform gas distribution, and its findings are significant for the space-borne gravitational wave detectors.

Material strain is one of the factors affecting contact electrification. Previous works have investigated the influence of polymer strain on contact electrification from the perspective of material transfer by means of experimental methods. However, the detailed electron transfer mechanism, which is the most fundamental form of contact electrification mechanism, is still unclear. In this work, the effect and its mechanism of polydimethylsiloxane (PDMS) tensile strain on contact electrification with polytetrafluoroethylene (PTFE) are investigated via first-principles calculations. The results show that the number of electrons transferred from the PDMS to the PTFE increases with the stretched ratio. In addition, the possibility of breakage on the PDMS main chain caused by tensile strain is considered. The result shows that the total number of transferred electrons from the broken fragments is much less than that of the original PDMS molecule. Moreover, the fragment of PDMS molecules with the oxygen dangling bond can even obtain electrons from the PTFE molecule. This work can provide a theoretical basis for understanding the influence mechanism of polymer strain on contact electrification from the perspective of electron transfer.

This work presents a new low-voltage, magnetic-less ion pump that utilizes the pyroelectric principle. Both the electron emission and high-voltage to realize an ion pump are supplied by pyroelectric material, whose activation only requires 5 V drive voltage. Structure optimization of the pyroelectric ion pump is carried out in order to reduce outgassing during an operating period to achieve a better pumping performance. The outgassing characteristics of the optimized ion pump are investigated by simulation and experiment, and its pumping performance is experimentally tested and the pumping speed is calculated using experimental data. The results show that the outgassing of a Ti tube structure ion pump is approximately two-orders-of-magnitude lower compared to that of a Ti plate structure ion pump. The pyroelectric ion pump can further reduce the system limiting pressure from 2.8 × 10−6 Pa achieved by a turbomolecular pump unit to 1.81 × 10−6 Pa, with the estimated pumping rate of 1.6 l/s that exceeds most reported magnetic-less ion pumps. The pyroelectric ion pump demonstrates great potential in low-drive voltage, magnetic-less high-vacuum pumping for the high precision sensors using atomic interferometers technology.

The electrostatic force induced by charge transfer during contact electrification is one of the main components of adhesion force at the solid interface. Some studies found that the magnitude of charge transfer and the consequently electrostatic force can be tuned by the external electric field. However, the detailed mechanism is still lacking in understanding. In this study, the effect of external electric field on copper/silica contact electrification and adhesion is studied via first-principles and molecular mechanics calculations and the mechanism is revealed by electrostatic potential and adhesion energy analysis. It is proved that the external electric field can affect the contact potential difference, which is the driving force of contact electrification, thus influencing the magnitude of charge transfer and electrostatic force. When the electric field direction is the same as the electron transfer direction, the contact electrification can be suppressed, leading to the decrease in the ratio of electrostatic force to van der Waals force. In particularly, the contact electrification and electrostatic force can be completely eliminated when applying a specific electric field intensity. This can provide an inspiration for quantitatively studying the source of adhesion force at solid interface.

A fluorinated polyimide film is synthesized toward the transparent triboelectric nanogenerator applied on touch screen surface to convert the mechanical energy into electrical energy.