Clamp-on ultrasonic flowmeters suffer from crosstalk—i.e., measurement errors due to the interference of signals generated in solid regions and solid–fluid interfaces with the required signal from the fluid. Although several approaches have been proposed to alleviate crosstalk, they only work in specific ranges of flow rates and pipe diameters, and some also introduce additional issues. We propose a novel clamp-on system design where the transmitting and receiving wedges are embedded with directional noise filtering mechanisms based on phononic crystals (PnCs) possessing directional band gaps (DBGs). PnCs are artificial materials consisting of periodic structures arrayed in a matrix medium exhibiting band gaps – i.e., frequency ranges where waves are attenuated – due to Bragg scattering. DBGs enable PnCs to propagate waves in specific directions while suppressing them in other directions. By guiding the input signal through the transmitting wedge to the wall, we minimize the generation of noise signals due to secondary reflections within the wedge. Similarly, by using the directionality of the DBG PnC in the receiver, we limit the effects of noise signals (that arrive in different directions) in the receiver. We numerically verify the DBG PnC embedded wedges’ performance by comparing wave propagation aspects of the PnC embedded clamp-on system with a standard clamp-on device. To that end, we develop accurate wave propagation models based on the Discontinuous Galerkin finite element method. By incorporating DBG PnCs into the wedges, we obtain about 20dB increase in the signal-to-noise ratio compared to the clamp-on system with standard wedges.

中文翻译：

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定向带隙声子结构，用于衰减外夹式超声波流量计中的串扰


外夹式超声波流量计存在串扰，即由于固体区域和固液界面中产生的信号与流体所需信号的干扰而导致的测量误差。尽管已经提出了几种方法来减轻串扰，但它们仅适用于特定的流速和管道直径范围，并且有些还引入了其他问题。我们提出了一种新颖的夹持系统设计，其中发射和接收楔块嵌入了基于具有定向带隙 （DBG） 的声子晶体 （PnC） 的定向噪声滤波机制。PnC 是由排列在基质介质中的周期性结构组成的人造材料，由于布拉格散射而表现出带隙——即波衰减的频率范围。DBG 使 PnC 能够在特定方向上传播波，同时在其他方向上抑制波。通过将输入信号通过发射楔块引导到墙壁上，我们可以最大限度地减少由于楔块内的二次反射而产生的噪声信号。同样，通过在接收器中使用 DBG PnC 的方向性，我们可以限制接收器中噪声信号（到达不同方向）的影响。我们通过比较 PnC 嵌入式夹持式系统的波传播方面与标准夹式器件，对 DBG PnC 嵌入式楔块的性能进行了数值验证。为此，我们基于间断伽辽金有限元方法开发了精确的波传播模型。通过将 DBG PnC 集成到楔块中，与带有标准楔块的夹持式系统相比，我们的信噪比增加了约 20dB。