RICHLAND -- A tiny but powerful battery developed at Pacific Northwest National Laboratory should allow researchers to learn more about Northwest salmon.
The batteries are small enough to allow tags to be injected into fish, including smaller and possibly younger fish than are being tagged now with devices that send out an acoustic signal.
"The smaller the tag, the better for fish," said fisheries biologist M. Brad Eppard with the Portland District of the Army Corps of Engineers. "And the better for fish, the more accurate and reliable our survival estimates."
Scientists use the tags to understand salmon migration and life cycle, with the Army Corps interested in determining the optimal way to operate its dams.
If smaller fish can be tagged, scientists can collect data on a sample of endangered fish that better represents the entire population to produce more accurate study results, Eppard said. Scientists also may be able to track fish earlier in the life cycle, including in the small streams crucial to their beginnings, according to PNNL.
Injecting, rather than surgically implanting the tags, is less stressful for the fish, officials say. It's also less expensive than the time-consuming process of implanting each tag and then stitching up the wound, which accounts for much of a study's cost. This should allow more fish to be studied for the same cost.
Scientists have been tracing the movement of salmon in the Columbia River with tags developed at the Department of Energy national lab in Richland that send out an acoustic signal that can be detected as far as about 300 yards away.
But the tags require batteries, and the smallest commercially available with enough power to be useful are silver oxide button microbatteries. They can be used only in salmon large enough to carry the weight of up to two button batteries and the tags must be surgically implanted in the salmon. The diameter of the batteries make the tags too large to inject into the fish.
"This was a major challenge which really consumed us these last three years," said Daniel Deng, a PNNL engineer, who was approached by the Army Corps of engineers to develop a better battery. "Either the batteries are too big, or they don't last long enough to be useful. That's why we had to design our own."
The battery that Jie Xiao, a PNNL materials science expert, and her team developed is just slightly longer than a grain of rice, but packs more than twice the power per ounce of button microbatteries.
Smaller batteries have been invented, with some tinier than the width of a human hair, but they don't hold enough energy to power acoustic fish tags.
Xiao and her team improved on the "jellyroll" technique commonly used to make household cylindrical batteries to design the new microbatteries, which use a different chemistry.
They laid down battery materials in layers one on top of each other that could be rolled up like a jellyroll, rather than creating a sandwich of materials as is done in button batteries. That solved one of the chief problems of making such a small battery -- when electrons are packed into a small space they get in the way of each other and don't flow easily or quickly along the routes required in a battery.
"We tried to pack as much active material as possible in without increasing resistance," Xiao said.
The batteries have enough power to send out an acoustic signal at a frequency fish cannot detect every five seconds for a month. They also send clearer signals in the cold water where salmon live than the current microbatteries.
PNNL scientists Samuel Cartmell and Terence Lozano made more than 1,000 of the new microbatteries by hand in a painstaking process. They cut and formed tiny snippets of materials, put them through a flattening device that resembles a pasta maker and then bound them together before hand-rolling them into tiny capsules.
They were used for a field trial in the Snake River last summer, with good results, according to PNNL.
The study showed that the new tags performed as well as the acoustic tags that used the button microbatteries.
The tags were injected into fish as small as a little under 4 inches, the same size as the smallest of those that have been studied acoustic tags with the button microbatteries.
Next, tags will be implanted in different size fish to determine what is the smallest size fish that can handle the new tags.
Salmon, and possibly lamprey, survival studies are planned in 2015 on the Columbia, Snake and Willamette rivers.
PNNL is interested in investigating additional uses for the new batteries, including applications in medical devices, Xiao said.
Battelle, which operates PNNL, has applied for a patent on the technology.
Details of the battery have been published online in Scientific Reports, a member of the Nature collection of journals. In addition to Xiao, Deng, Cartmell and Lozano, other authors of the paper include Honghao Chen, Qiang Wang, Huidong Li, Xilin Chen, Yong Yuan, Mark Gross and Thomas Carlson.
-- Annette Cary: 582-1533; firstname.lastname@example.org; Twitter: @HanfordNews