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An active mechanical Willis meta-layer with asymmetric polarizabilities.

ABSTRACT: Willis materials exhibit macroscopic cross-coupling between particle velocity and stress as well as momentum and strain. However, Willis coupling coefficients designed so far are intrinsically coupled, which inhibits their full implementation in structural dynamic applications. This work presents a means to eliminate these limitations by introducing an active scatterer in a mechanical meta-layer that exploits piezoelectric sensor-actuator pairs controlled by digital circuits. We experimentally demonstrate abilities of the Willis meta-layer, in beams and plates, for independently engineering transmission and reflection coefficients of flexural waves in both amplitude and phase and nonreciprocal wave propagations. The meta-layer is described by a flexural wave polarizability tensor, which captures independent higher-order symmetric-to-symmetric and symmetric-to-antisymmetric couplings. The active meta-layer is adaptive in real time for reconfigurable broadband operation thanks to its programmability. This work sheds a new light on unsurpassed control of elastic waves, ranging from vibration protections to ultrasonic sensing and evaluation of engineering structures.

SUBMITTER: Chen Y

PROVIDER: S-EPMC7378557 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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An active mechanical Willis meta-layer with asymmetric polarizabilities.

Chen Yangyang Y Li Xiaopeng X Hu Gengkai G Haberman Michael R MR Huang Guoliang G

Nature communications 20200723 1

Willis materials exhibit macroscopic cross-coupling between particle velocity and stress as well as momentum and strain. However, Willis coupling coefficients designed so far are intrinsically coupled, which inhibits their full implementation in structural dynamic applications. This work presents a means to eliminate these limitations by introducing an active scatterer in a mechanical meta-layer that exploits piezoelectric sensor-actuator pairs controlled by digital circuits. We experimentally d ...[more]

PMID: 32704039

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Project description:BackgroundCircle of Willis is the main structure that provides constant and regular blood flow to the brain, protects the brain from ischemia. Stroke has remained the second leading cause of death globally in the last fifteen years. It is the fifth leading cause of death in the United States. It is also the leading cause of serious adult disability. Interlinked problems related to ischemic stroke are become increasing nowadays. Strong evidence is needed about the pooled measure of association between the circle of Willis (COW) and ischemic stroke. Therefore, this systematic review and meta-analysis were intended to provide compressive and up to date evidence on the association between the variations of COW and ischemic stroke using the available studies.MethodsPubMed, Google Scholar, Science Direct, and Cochrane Library databases were systematically searched. All essential data were extracted using a standardized data extraction template. The heterogeneity across studies was assessed by using the Cochrane Q test statistic, I2 test statistic, and P-values. A fixed-effect model was used to estimate the pooled effect of the measure association between COW and ischemic stroke.ResultsIn this meta-analysis, 2,718 participants were involved. The pooled measure of association between COW and ischemic stroke was 1.38 (95% CI 0.87, 2.19). Therefore, this indicated that the presence of any variation in COW was 1.38 times more likely to develop ischemic stroke as compared to the patent COW. The presence of hypoplasia/incompleteness in a posterior communicating artery (PcomA) [Pooled OR: 1.34 (95% CI 0.80, 2.25)] and anterior communicating artery (AcomA) [Pooled OR: 1.32 (95% CI 0.81, 2.19)] were a contributing factor for the development of ischemic stroke. Hypertension was the most common comorbid condition, followed by diabetes mellitus, smoking, coronary artery disease, and hyperlipidemia.ConclusionsThere was a non-significant positive association between COW variation and ischemic stroke in this meta-analysis.

Dataset Information

An active mechanical Willis meta-layer with asymmetric polarizabilities.

Publications

An active mechanical Willis meta-layer with asymmetric polarizabilities.

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