Abstract
Implantable acoustic transmitters have been used in the last 20 years to track fish movement for fish survival and migration behavior studies. However, the relatively large weights and sizes of commercial transmitters limit the populations of studied fish. The surgical implantation procedures may also affect fish adversely and incur a significant amount of labor. Therefore, a smaller, lighter, and injectable transmitter was needed, and similar or better acoustic performance and service life over those provided by existing commercial transmitters was desired. To develop such a small transmitter, a number of technical challenges, including design optimization of the piezoelectric transducer, needed to be overcome. Our efforts to optimize the transducer focused on improving the average source level in the 180° range in which the signal was not blocked by the transmitter body. We found that a novel off-center tube transducer improved the average source level by 1.5 dB. An acoustic reflector attached to the back of the transducer also improved the source level by 1.3 dB. We found that too small a gap between the transducer and the component placed behind it resulted in distortion of the beam pattern. Lastly, a tuning inductor in series with the transducer was used to help optimize the source level. The findings and techniques developed in this work contributed to the successful development and implementation of a new injectable transmitter.
Highlights
In the past 20 years, salmon recovery and potential detrimental impact of hydroelectric dams on fish survival have been receiving great national attention because of their environmental and economic importance [1,2,3]
The relatively large sizes of acoustic transmitters limit the populations of fish that can be tagged and studied because of the tag burden imposed on the fish
An example is the small transmitter developed for the Juvenile Salmon Acoustic Telemetry System (JSATS), which is a fish monitoring system developed by the US Army Corps of Engineers (USACE), Portland District; Pacific Northwest National Laboratory (PNNL); and National Oceanic and Atmospheric Administration, Fisheries
Summary
In the past 20 years, salmon recovery and potential detrimental impact of hydroelectric dams on fish survival have been receiving great national attention because of their environmental and economic importance [1,2,3]. The main challenge of developing such an injectable transmitter was how to achieve the same or better acoustic performance and the service life provided by existing transmitters in a much smaller and lighter package, as the reduction in the package size requires a more compact device, a smaller battery, and smaller electrical components that are often less efficient than their larger counterparts. By improving the designs of all the three primary components of the transmitter, an injectable transmitter (shown in figure 1) was successfully developed by PNNL for JSATS in 2013 [7] This new transmitter is able to produce an average source level of 155 dB (reference: 1 μPa at 1 m) and has a service life of 130 days at a 3 s ping rate. The optimization techniques of the transducer discussed are focused primarily on methods for redirecting the input electrical energy to the transducer toward the directions in which tagged fish are more likely to be detected by the receiving hydrophones
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