Feature sponsored by Test & measurement
the heart of its new underwater acoustics laboratory. The new lab is a big step forward in research on sound waves travelling through water as it effectively provides a miniaturised version of the ocean. Experiments are possible on sound wave’s behaviour in different water layers and their reflections from the ocean’s most diverse ground materials such as rocks, sand or mud. The miniaturisation means that the highest precision is needed from the measurement equipment as the experimental results are scaled up afterwards to indicate what would happen in the real world. The new laboratory water tank is
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rectangular and measures 3.6m long by 1.2m wide with a maximum water depth of 0.91m. The research involves using a hydrophone for the signals or chirps which are generated by an Arbitrary Waveform Generator (AWG), the Spectrum model M2p.6546-x4. This PC-card generates signals with 24 V output swings that are then amplified before being broadcasted by a hydrophone. After travelling through the tank, the signals are detected by another hydrophone and processed by a Spectrum M2p.5932-x4 digitizer card. The transmitter and receiver are each held by a robotic arm that positions and orientates them within the water so that source and receiver can be positioned as required.
The tank enables experiments to be done
on how the seafloor affects sound waves bouncing off it. A pure rock bottom will have a different effect compared to sand or mud or layers of different materials. “It is even more complicated,” explains Dr. Traci Neilsen, the professor in charge of the project, “because water is not homogeneous. Changes in temperature and salinity change the sound speed and cause the waves to bend, similar to how a mirage happens. We plan to examine the impact of water temperature changes on machine learning for localising sound sources. These tank studies are more repeatable, efficient, and cost effective than ocean experiments and will allow us to develop techniques that can then be tested on ocean data.” Adam Kingsley, the PhD student responsible
for the acquisition software, says: “We chose Spectrum products because they have proved to be able to deliver the extremely high level of precision and synchronisation that we require. Because this tank is effectively a miniaturisation of a huge body of water, timing precision is vital for the results to be meaningful when scaled up.” The pair of Spectrum PCIe-cards are housed in an external PCIe chassis in the main control console, accurately synchronised together using a Star-Hub module by Spectrum.
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he Acoustics Research Group at the Department of Physics and Astronomy, Brigham Young University, Utah, USA has chosen Spectrum Instrumentation’s leading-edge digitizers and signal generators to form
Measuring underwater
acoustics Sound waves studied in a simulated ocean with high-precision PCIe
measurement cards Spectrum’s digitizers and AWGs are being used in a new underwater acoustics laboratory...
Figure 1: The water tank with the two robotic arms to position the transmitter and receiver October 2022 Instrumentation Monthly
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