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An absorptive coding metasurface (ACM) is proposed to achieve radar cross section (RCS) reduction in this paper. In the design progress of the ACM, two different lossy coding elements are proposed at first, which can both be regarded as a composite composed of a two-layer resistive frequency selective surface (RFSS) and a polarization conversion metasurface (PCM). The two-layer RFSS has a certain wave-absorbing property due to ohmic loss. In addition, the PCM can achieve ultra-wideband linear polarization conversion, and the polarization-converted reflected waves in the two coding elements under the same incidence will differ by nearly 180° in phase because the sub-unit-cell structures in them are perpendicular to each other. Thus, based on the two lossy coding elements, the ACM is proposed, which can achieve ultra-wideband RCS reduction due to absorption and phase cancelation. Numerical simulations demonstrate that the RCS of the ACM under normal incidence can be reduced more than 10 dB in the ultra-wide frequency band from 6.9 to 41.2 GHz with a relative bandwidth of 142.6%. Moreover, it has the advantages of polarization-insensitivity and wide incident angle. Finally, one effective experimental verification is carried out, and a reasonable agreement is observed between the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Most of the research on identifying and classifying signal models is limited to single signals such as AM, QAM or PSK, and there is a lack of research on the parameters of the identified signals. To make up for this deficiency, an OA (Optimality Confidence and Amplitude Ratio factor) algorithm model is proposed to identify and classify 13 kinds of modulation signals, including 2 kinds of analogue modulation signals (AM and FM), 11 kinds of signal digital modulation (M-SK and M-QAM). Based on the characteristics of the constellation diagram, Confidence and Amplitude Ratio factors are constructed to identify and classify signals with different parameters such as 'Format", "Centre Frequency" and "Sample Rate' and different modulation types. In addition, because of the mis-judgement and confusion problems in identifying classification signals, a three-layer optimisation algorithm is proposed to optimise the OA algorithm model. Numerical simulation results show that the comprehensive identification efficiency of the proposed optimisation algorithm is increased by 18.84%. [ABSTRACT FROM AUTHOR]

In this work, an ultra-wideband reflective polarization conversion metasurface (PCM) is proposed at first. Because the PCM is an anisotropic structure that is symmetric with respect to both x- and y-axes, and the reflection phase difference under x- and y-polarized incidences is close to 180° in an ultra-wide frequency range, the PCM can achieve both linear polarization conversion and circular-polarization (CP) maintaining reflection in the ultra-wide frequency band from 8.3 to 41.3 GHz except for near the frequency point of 38.8 GHz. Moreover, when its unit cell structure is rotated by 90°, its cross-polarized reflection coefficient under LP incidence, together with the co-polarized reflection coefficient under CP incidence, will be changed by almost 180° in phase. Thus, based on the PCM, an ultra-wideband coding diffusion metasurface (CDM) is further proposed for radar cross section (RCS) reduction. The simulation and experiment results indicate that the CDM can achieve effective RCS reduction in the ultra-wide frequency band of 8.2–41.7 GHz under normal incidence with arbitrary polarization; in addition, an ultra-wideband RCS reduction can still be realized under oblique incidence with an incident angle less than 45°, which shows that the CDM is of good application value in radar stealth technology. [ABSTRACT FROM AUTHOR]

In this study, a coding diffusion metasurface (CDMS) based on a circular-polarization (CP)-maintaining metasurface is proposed for radar cross-section (RCS) reduction. The CP-maintaining metasurface can achieve ultra-wideband CP-maintaining reflection, and its main reflection phase under CP incidence can be adjusted at will by the Pancharatnam-Berry phase generated by the rotation of its unit cell, so it can be used to design CDMS. Thus, based on the CP-maintaining metasurface, the 2-bit CDMS is proposed. The simulated and measured results demonstrate that the CDMS can achieve highly effective and ultra-wideband RCS reduction under arbitrarily polarized incidences, compared with a pure metallic plate of the same size, its RCS can be reduced by more than 10 dB under normal incidence in the ultra-wide frequency band of 7.1-33.6 GHz with a relative bandwidth of 130.2%; moreover, when the incident angle is increased to 40°, an ultra-wideband RCS reduction can still be achieved. [ABSTRACT FROM AUTHOR]

In the communication, a monopolarized and a dual-polarized polarization-rotating frequency-selective surfaces (PR-FSSs) are designed successively. The two PR-FSSs are both a three-layer aperture-coupled-patch periodic structure. When they are interpreted as an array of antenna-filter-antenna (AFA) modules, because polarization directions of the upper and lower antennas in each AFA module are orthogonal to each other, they can both realize polarization rotation and frequency selection at the same time. The monopolarized PR-FSS is designed first, its relative bandwidth reaches up to 13.58% although there is a maximum insertion loss of 0.8 dB in the band. The final-designed dual-polarized PR-FSS can be regarded as the combination of two orthogonal monopolarized one, so it can work under both $x$ - and $y$ -polarized incidences, its relative bandwidth is still up to 9.81%; moreover, the maximum insertion loss in the passband is very low. The performances of the two PR-FSSs are both verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

In this work, an ultra‐wideband gradient metasurface (GM) is designed by using Pancharatnam–Berry (PB) phase. In the design process, a circular polarisation (CP)‐maintaining metasurface (CMM) is proposed at first, which can realise ultra‐wideband CP‐maintaining reflection in the frequency band of 7.7–19.9 GHz, moreover, PB phase will be generated in its co‐polarised reflection coefficient under CP incidence by rotating the anisotropic resonators in its unit cells. Thus, based on the CMM, an ultra‐wideband GM is designed by using PB phase. Both the simulation and experiment show that the designed GM can realise ultra‐wideband anomalous reflection under arbitrary polarised incidence, the reflected wave under CP incidence will be deflected to an anomalous direction and even be converted to a surface wave; but under linearly polarised and elliptically polarised incidences, the reflected wave will be separated into two beams. In addition, to design more anomalous reflection metasurfaces, the generation principle of PB phase, together with the root cause of the CP‐maintaining reflection of the proposed CMM, has been analysed in detail in the designing process. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-wideband circular polarization (CP) maintaining reflector is proposed based on an anisotropic metasurface, which is an orthogonal anisotropic structure with a pair of symmetrical axes u and v perpendicular to each other. The simulated results show that the reflector can realized CP-maintaining reflection under both right-handed and left-handed CP (RHCP and LHCP) incidences in the frequency band between 8.79 and 27.09 GHz, the fractional bandwidth is up to 102%. In addition, the physical mechanism of the CP-maintaining reflection has been analyzed in detail, and one useful formula has been derived, which can be used to calculate the cross- and co-polarization reflection coefficients under CP incidence according to the phase differences between the two reflection coefficients under u and v-polarized incidences. Finally, one effective experimental validation was carried out. [ABSTRACT FROM AUTHOR]

We propose an RFID tag anti-collision method using adaptive frame length adjustment. Based on the number of tags identified in the first frame, the original tag population can be estimated by solving a non-linear estimating equation. Subsequent frame lengths can be adaptively adjusted according to the number of remaining tags. The simulation results demonstrate the error rate of the proposed method to be less than 5% – superior to that of existing methods. Compared with the widely used dynamic frame slot ALOHA algorithm – adopted by EPC_C1 G2 standard – tag identification throughput performance increased by 50%. [ABSTRACT FROM AUTHOR]

Radio frequency identification (RFID) has recently experienced unprecedented development. Among many other areas, it has been widely applied in blood station management, automatic supermarket checkout, and logistics. In the application of RFID for large-scale passive tags, tag collision is inevitable owing to the non-cooperation mechanism among tags. Therefore, a tag anti-collision method is a key factor affecting the identification efficiency. In this paper, we propose a tag anti-collision method based on Aloha technology for RFID. It estimates the number of remaining tags using the secant iteration method. To achieve optimal identification efficiency, it adaptively and dynamically adjusts the lengths of the subsequent frames according to the principle that the length of a frame should be the same as the number of tags to be identified. For pseudo-solutions of tag population estimation while using secant iteration, we present an elimination method by two probing frames. The simulation results show that the estimation precision of our method can reach above 97%. Thus, it can meet the requirement of the tag anti-collision estimation accuracy. Its global throughput is obviously superior to the Q algorithm adopted by the current international standard, and it is close to the ideal system. It consequently outperforms existing schemes. [ABSTRACT FROM AUTHOR]

Solid state drives (SSD) are usually built using a NAND flash memory array. An SSD controller manages datastreams stripped to multiple flash memory channels. The device could be regarded as a level-0 structure of redundant array of independent disk (RAID), the technical term for a disk array system. This typical SSD controller architecture is called an intrinsic RAID (iRAID). An iRAID-based SSD controller has to execute sophisticated wear-leveling algorithms and dynamically calculate the lifespan of each flash memory chip as well as run error correction coding. redundant array of independent module (RAIM) was proposed to simplify the SSD controller by applying a group of standardized memory modules instead of raw flash memory chips. One of the widely recognized memory modules is the embedded multi-media card (eMMC) module, which is a small component, typically with a ball grid array package, and is found in consumer applications. In the paper, we have described the methods needed to optimize wear-leveling in an array of eMMC modules and deduced a formula to evaluate and optimize the lifespan of an RAIM-based SSD. A silicon SSD controller was implemented to verify the analysis. The positive result revealed that the lifespan of the RAIM-based SSD could be improved in consumer-grade eMMC modules. [ABSTRACT FROM AUTHOR]