Topology optimization of chiral metamaterials with application to underwater sound insulation

Chiral metamaterials have been proven to possess many appealing mechanical phenomena,such as negative Poisson's ratio,high-impact resistance,and energy absorption.This work extends the applications of chiral metamaterials to underwater sound insulation.Various chiral metamaterials with low acoustic impedance and proper stiffness are inversely designed using the topology optimization scheme.Low acoustic impedance enables the metamaterials to have a high and broadband sound transmission loss(STL),while proper stiffness guarantees its robust acoustic performance under a hydrostatic pressure.As proof-of-concept demonstrations,two specimens are fabricated and tested in a water-filled impedance tube.Experimental results show that,on average,over 95%incident sound energy can be isolated by the specimens in a broad frequency range from 1 k Hz to 5 k Hz,while the sound insulation performance keeps stable under a certain hydrostatic pressure.This work may provide new insights for chiral metamaterials into the underwater applications with sound insulation.

Research on fast detection method of infrared small targets under resourceconstrained conditions

Infrared small target detection is a common task in infrared image processing.Under limited computa⁃tional resources.Traditional methods for infrared small target detection face a trade-off between the detection rate and the accuracy.A fast infrared small target detection method tailored for resource-constrained conditions is pro⁃posed for the YOLOv5s model.This method introduces an additional small target detection head and replaces the original Intersection over Union(IoU)metric with Normalized Wasserstein Distance(NWD),while considering both the detection accuracy and the detection speed of infrared small targets.Experimental results demonstrate that the proposed algorithm achieves a maximum effective detection speed of 95 FPS on a 15 W TPU,while reach⁃ing a maximum effective detection accuracy of 91.9 AP@0.5,effectively improving the efficiency of infrared small target detection under resource-constrained conditions.

Effects of Cl- Ions on the Corrosion Behaviour of Low Alloy Steel in Deaerated Bicarbonate Solutions

The effect of Cl- ions on corrosion evolution of NiCu low alloy steel during immersion tests （up to 70 days） in deaerated 0.05 mol/L bicarbonate solutions was investigated by in-situ electrochemical mea- surements combined with X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electron probe microanalysis （EPMA） characterisations. The results showed that due to the acceleration of substrate dis- solution in the presence of Cl, corrosion of NiCu low alloy steel underwent only two stages, i.e., a quick oxidation process followed by a final metastable passive state, without the initial slow anodic dissolu- tion as observed in the Cl--free bicarbonate solution. The main components of the formed rust layer in the Cl--free bicarbonate solution were α-FeOOH and Fe3O4, while apart from α-FeOOH, Fe6（OH）12CO3 was found evident instead of Fe3O4 in the Cl-containing solution. Metastable pits were only found in the Cl-containing solution where Cl- accumulated after the immersion test, confirming the attack of Cl on the substrate after penetrating the formed corrosion product layer.

Corrosion Evolution of Low Alloy Steel in Deaerated Bicarbonate Solutions

Corrosion evolution during immersion tests （up to 43 days） of NiCu steel in deaerated 0.1 mol/L bicarbonate solutions was investigated by electrochemical measurements, scanning electron microscopy （SEM） and X-ray diffraction （XRD）. Results show that NiCu steel transformed from the anodic dissolution in the early stage of immersion to a metastable passive state in the final stage as the open-circuit potential value shifted positively, which was aroused by the precipitation of corrosion products. This process was mainly promoted by the trace amount of oxygen. Simultaneously, dominant cathodic reaction transformed from the hydrogen evolution in early stage to reduction processes of corrosion products in later stages. Possible corrosion processes were discussed with the assistance of a corresponding Pourbaix diagram.

A thru-reflect-line calibration for measuring the characteristics of high power LDMOS transistors

The impedance and output power measurements of LDMOS transistors are always a problem due to their low impedance and lead widths.An improved thru-reflect-line(TRL) calibration algorithm for measuring the characteristics of L-band high power LDMOS transistors is presented.According to the TRL algorithm,the individual two-port S parameters of each fixture half can be obtained.By de-embedding these S parameters of the test fixture,an accurate calibration can be made.The improved TRL calibration algorithm is successfully utilized to measure the characteristics of an L-band LDMOS transistor with a 90 mm gate width.The impedance of the transistor is obtained,and output power at 1 dB compression point can reach as much as 109.4 W at 1.2 GHz, achieving 1.2 W/mm power density.From the results,it is seen that the presented TRL calibration algorithm works well.