Current Issue : July - September Volume : 2016 Issue Number : 3 Articles : 4 Articles
A novel membrane-type acoustic metamaterial with a high sound transmission loss\n(STL) at low frequencies (500Hz) was designed and the mechanisms were investigated\nby using negative mass density theory. This metamaterial�s structure is like a\nsandwich with a thin (thickness=0.25mm) lightweight flexible rubber material within\ntwo layers of honeycomb cell plates. Negative mass density was demonstrated at\nfrequencies below the first natural frequency, which results in the excellent lowfrequency\nsound insulation. The effects of different structural parameters of the membrane\non the sound-proofed performance at low frequencies were investigated by\nusing finite element method (FEM). The numerical results show that, the STL can be\nmodulated to higher value by changing the structural parameters, such as the membrane\nsurface density, the unite cell film shape, and the membrane tension. The acoustic\nmetamaterial proposed in this study could provide a potential application in the\nlow-frequency noise insulation. C 2016 Author(s). All article content, except where\notherwise noted, is licensed under a Creative Commons Attribution (CC BY) license\n(http://creativecommons.org/licenses/by/4.0/). [http://dx.doi.org/10.1063/1.4942513]...
We propose an acoustic OFDM system for underwater communication, specifically for vertical link communications such as\nbetween a robot in the sea bottom and a mother ship in the surface. The main contributions are (1) estimation of time varying\nDoppler shift using continual pilots in conjunction with monitoring the drift of Power Delay Profile and (2) symbol-by-symbol\nDoppler compensation in frequency domain by an ICI matrix representing nonuniform Doppler. In addition, we compare our\nproposal against a resampling method. Simulation and experimental results confirm that our system outperforms the resampling\nmethod when the velocity changes roughly over OFDM symbols. Overall, experimental results taken in Shizuoka, Japan, show our\nsystem using 16QAM, and 64QAM achieved a data throughput of 7.5Kbit/sec with a transmitter moving at maximum 2 m/s, in a\ncomplicated trajectory, over 30m vertically....
We tackle a fundamental security problem in underwater acoustic networks (UANs). The S-box in the existing block encryption\nalgorithm is more energy consuming and unsuitable for resources-constrained UANs. In this paper, instead of S-box, we present a\nlightweight, 8-round iteration block cipher algorithm forUANs communication based on chaotic theory and increase the key space\nby changing the number of iteration round.We further propose secure network architecture of UANs. By analysis, our algorithm can\nresist brute-force searches and adversarial attacks. Simulation results show that, compared with traditional AES-128 and PRESENT\nalgorithms, our cryptographic algorithm can make a good trade-off between security and overhead, has better energy efficiency,\nand applies to UANs...
To combat severe intersymbol interference incurred by multipath propagation of sound waves in the underwater acoustic\nenvironment, we introduce an iterative equalization and decoding scheme by iteratively exchanging soft information between a\nlow-density parity check (LDPC) decoder and a decision feedback equalizer.We apply extrinsic information transfer (EXIT) charts\nto analyze performance of LDPC codes over the acoustic multipath channel. Furthermore, using differential evolution technique,\nwe develop an EXIT-aided method to optimize LDPC codes for the underwater acoustic channel. Design examples are presented\nfor two different realizations of the underwater acoustic channel that are generated by an acoustic ray tracing model. Computer\nsimulations show that the optimized LDPC codes outperform its regular counterpart or Turbo codes under the same coding rate\nand block length, with gains of 1.0 and 0.8 dB, respectively, at the bit error rate of 10âË?â??5....
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