This letter proposed advantageous in-uniform gradient cross-section (GCS) channels which weaken the dependence of the coiled-up anechoic metasurface on the total channel length. The privilege of GCS channels was revealed by studying Fabry-Pérot absorbers with designed channel widths. A theoretical framework was set up to explain the inherent sound absorbing mechanism, from which the overall performance as well as dominant working frequencies of linear and exponential GCS channels can be predicted. With proper GCS channel design, the proposed structures were experimentally and theoretically proven to achieve lower absorption frequencies in comparison with conventional uniform cross-section absorbers with the same exterior geometry. Through a parametric study on the near-perfect absorption frequency range of GCS absorbers, the strong tunability brought by GCS was confirmed, suggesting the possibility of on-demand frequency-oriented absorber design. Serving as an approach for acoustic impedance transferring, promising features of GCS can be extensively applied in existing coiled-up anechoic metasurfaces.

According to actual needs, generalized signcryption scheme can flexibly work as an encryption scheme, a signature scheme or a signcryption scheme. In this paper, firstly, we give a security model for identity based generalized signcryption which is more complete than existing model. Secondly, we propose an identity based generalized signcryption scheme. Thirdly, we give the security proof of the new scheme in this complete model. Comparing with existing identity based generalized signcryption, the new scheme has less implementation complexity. Moreover, the new scheme has comparable computation complexity with the existing normal signcryption schemes.

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Security and efficiency are the two main challenges for designing a smart home system. In this paper, by incorporating Chinese remainder theorem (CRT) into the elliptic curve Diffie–Hellman (ECDH), a lightweight key agreement protocol for smart home systems is constructed. Firstly, one-way hash authentication is used to identify the sensor nodes instead of mutual authentication to reduce the authentication cost. Secondly, the CRT is introduced to enhance the security of the original ECDH key agreement. Security analysis showed that the proposed protocol can validate the data integrity and resist the replay attack, the man-in-middle attack, and other attacks. Performance analysis and experiments showed that the protocol achieves high security with low communication and computation costs, and can be implemented in smart home systems.