Compact wideband FSS-absorber-based low-RCS reflectarray antenna

This paper presents a method to realize compact broadband low-RCS ReflectArray(RA)antenna based on a Frequency Selective Surface(FSS)absorber and a reflective metasurface.Such an FSS absorber consists of a resistance-loaded lossy layer and an FSS layer,which is utilized to reach an absorption-transmission response.The bottom reflective metasurface works as a phase array,reshaping the quasi-sphere wave from the feeding antenna into the quasi-plane wave.As a demonstration,the low-RCS RA antenna is simulated,fabricated,and measured.The simulated and measured results show that the developed low-RCS RA antenna has an aperture efficiency of 42.7%and a gain of 25.4 dBi in the X band.In the meantime,it simultaneously reaches the 10 dB RCS reduction for the orthogonal polarizations at the S and C bands,corresponding to a fractal bandwidth of 120%.Specifically,the adopted patch-feeding antenna makes the RA antenna more compact than the horn-feed conventional ones.Furthermore,the proposed RA antenna uses a few layers of substrates,making it lower in cost and easier for fabrication.The proposed design may have potential application in integrated stealth communication systems.

Effects of Vessel and Water Temperatures on Direct Injection in Internal Combustion Rankine Cycle Engines

This study focused on the effects of vessel and water temperatures on direct injection in internal combustion Rankine cycle engines through experimental and numerical methods.First,a study was carried out with schlieren photography using a high-speed camera for simultaneous liquid–gas diagnoses.Water was directly injected into a constant-volume vessel that provided stable boundaries.We wrote a MATLAB program to calculate spray tip penetration and cone angle from the images.For the further extension of boundary conditions,a numerical model was established and calibrated in AVL-FIRE for the thorough analysis of injection characteristics.Both experimental and numerical results indicated that injection and vessel temperatures have different effects on spray tip penetration.An increase in injected water temperature leads to shorter spray tip penetration,while the spray tip penetration increases with increasing vessel temperature.However,increased injection and vessel temperatures can both decrease the spray cone angle.Moreover,the simulation results also suggested that heat conduction is a main factor in boosting evaporation under top dead center conditions.When the internal energy of water parcels surges,these parcels evaporate immediately.These results are helpful and crucial for internal combustion engines equipped with direct water injection technology.