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The effect of the fish body on the source level and beam pattern of an acoustic fish tag signal was investigated through laboratory experiments and an analytical method. In laboratory experiments, the source level and beam pattern were measured in both a tag-only group and a tag-in-fish group. In the analytical method, both forward and backward scattering were calculated by assuming the acoustic tag was a point source and the swimbladder was an air-filled prolate spheroid. The mean source level of five tested tags decreased by ∼4 dB after implantation in fish bodies, which is important for designing fish migration studies using acoustic telemetry.

Acoustic emissions from current energy converters remain an environmental concern for regulators because of their potential effects on marine life and uncertainties about their effects stemming from a lack of sufficient observational data. Several recent opportunities to characterize tidal turbine sound emissions have begun to fill knowledge gaps and provide a context for future device deployments. In July 2021, a commercial-off-the-shelf hydrophone was deployed in a free-drifting configuration to measure underwater acoustic emissions and characterize a 25 kW-rated tidal turbine at the University of New Hampshire's Living Bridge Project in Portsmouth, New Hampshire. Sampling methods and analysis were performed in alignment with the recently published IEC 62600-40 Technical Specification for acoustic characterization of marine energy converters. Results from this study indicate acoustic emissions from the turbine were below ambient sound levels and therefore did not have a significant impact on the underwater noise levels of the project site. As a component of Pacific Northwest National Laboratory's Triton Field Trials (TFiT) described in this Special Issue, this effort provides a valuable use case for the IEC 62600-40 Technical Specification framework and further recommendations for cost-effective technologies and methods for measuring underwater noise at future current energy converter project sites. [ABSTRACT FROM AUTHOR]

The development of flexible and stretchable sensors has been receiving increasing attention in recent years. In particular, stretchable, skin-like, wearable sensors are desirable for a variety of potential applications such as personalized health monitoring, human-machine interfaces, and environmental sensing. In this paper, we review recent advancements in the development of mechanically flexible and stretchable sensors and systems that can be used to quantitatively assess environmental parameters including light, temperature, humidity, gas, and pH. We discuss innovations in the device structure, material selection, and fabrication methods which explain the stretchability characteristics of these environmental sensors and provide a detailed and comparative study of their sensing mechanisms, sensor characteristics, mechanical performance, and limitations. Finally, we provide a summary of current challenges and an outlook on opportunities for possible future research directions for this emerging field. [ABSTRACT FROM AUTHOR]