To build a tag

We had 5 days to prep 4 tags—should be doable, right? Add a couple extra pairs of hands to help and it should be a walk in the park…right?

Maybe I should start with the fact that I had no experience refurbishing and prepping tags before the Tag Workshop hosted by Dr. Markus Horning at ASLC.

The idea of hosting this Tag Workshop grew out of the need to refurbish some heat flux biologgers (read more about these tags in my previous blog) for my upcoming fieldwork in the spring, and retrofit additional sensors, and on a shoestring budget at that.

The perfect place to learn how to work with bio-logging equipment!

Science on a shoestring budget = innovation and creativity

These tags were originally manufactured by Wildlife Computers (Redmond, WA) for an NSF-funded project investigating thermoregulation in Weddell seals, more than 10 years ago. Since these tags have been attached to many other animals during their lifetime (Weddell seals, elephant seals, Steller sea lions), they were now due for some rejuvenation. This also gave us the opportunity to consider different sensor configurations than what is typically provided.

The shoestring budget meant that we do the work of replacing batteries ourselves, and that rather than using fancy but expensive waterproof interchangeable connectors we ‘hardwired’ the sensors to the electronics. The shoestring budget is also why I am using old, ‘surplus’ tags rather than buying new tags that can cost several thousand dollars each, depending on their configuration.

But, giving these tags new juice isn’t as easy as popping off a lid and switching out some double-A batteries. The tags also needed some fresh new sensors, and following all this work they should ideally be pressure-tested and recalibrated to make sure nothing was damaged or altered in functionality. So, I flew up to Alaska to learn how to properly take apart old tags, rebattery them, connect new sensors, and waterproof the entire tag so that they’re as good as new!

Luckily, an awesome group of students and scientists joined the workshop to learn these skills with me, and help prep my tags because it definitely was not as easy or quick as I thought it would be. Shout out to Renae, Philina, Skyla, Greg, and Jess for helping out! Check out what they had to say about the tag workshop below.

Into the lab!

During this week-long workshop, we got a glimpse of what it takes to put together a functional tag. I must confess I now have a much greater appreciation for the design considerations and intricacies involved in building tags—and the many, many steps involved.

From pouring silicone molds…

An old tag is used as a positive to create a mold using a 2-part silicone mixture. In case you’re wondering, the video is NOT slowed down—that’s real time. The silicone is just that viscous and slow to pour

…to chiseling away at old tags to salvage the reusable parts. 

After chiseling down to expose the circuit board, which functions as the ‘brain’ of the tag, we were able to remove the wires and clean out the vias (the 8 holes visible on the right circuit board) so that new wires could be attached to connect the new sensors.

When things don’t go according to plan…

Battery replacement turned out to be the trickiest task. As part of our safety training on the first day, we got plenty of forewarning about how dangerous and explosive lithium primary batteries can be. Then, we actually got a taste of what could go wrong (and how best to react) when the battery cells are incidentally punctured while trying to spot weld tabs onto them. Our saving grace—a tub full of sodium bicarbonate (a.k.a. baking soda).

The sodium bicarbonate serves to soak up the leaking electrolytes of a punctured battery cell. If the two electrolytes that are normally separated by a membrane within the battery combine too quickly in large amounts, a runaway reaction (a.k.a. explosion) will occur.

When things go right, this is what the tag in progress looked like:  

At this stage, new wires have been soldered into the vias of the circuit board and the battery has tabs that connect it to the appropriate wires that will allow it to power the tag. Finally, the half put-together tag is placed into one of the pre-made silicone molds and filled with a 2-part epoxy to waterproof the tag.

As a side note, these tags are of an older design and are comparably large, and thus somewhat less challenging for re-battery and re-configuration work than some of the latest and greatest designs, which due to their much smaller size are impossible to work on without highly specialized equipment, if at all. That said, after the epoxy has cured overnight under heat and pressure, the cast tag was removed from the silicone mold. It’s finally starting to look like a whole tag again!

But without the sensors, it’s not a very useful device for getting any data.

The main sensors for this physiological biologger are small round disks that measure heat flux (made by Concept Engineering, Old Saybrook, CT). (What’s heat flux?)

While previous steps may have been easier with other people helping, this next step actually required three hands to complete because three things needed to come into contact at the same time—the flimsy colored cables of the sensor, the solder, and the tip of the hot soldering iron.

Working under the scope to solder the sensors onto the tag while borrowing a steady third hand from Renae. (We quickly learned too much caffeine did not make doing this any easier!)

After a bit of teamwork soldering the colored cables of the sensors onto the correct copper wires sticking out of the tag, we now had a functional tag!

This tag has 3 sensors connected to it: 2 heat flux sensors and one other blue cable that will eventually have a thermistor connected to its other end. Other sensors within the tag also record diving behavior data (e.g. depth, acceleration).

While it is a functional tag at this stage, it would not last very long on the back of a diving seal. These tags and especially all cable connections must be waterproof and pressure resistant to survive the depths of these animals’ dives. After testing the sensor outputs via a computer interface to confirm everything is working, the tag goes back into a new mold one more time to cast the rest of the wires in epoxy.

Last but not least, another layer of waterproofing with flexible marine sealant will help prevent water from seeping into the tag through the wires.

Creativity goes a long way when you need to jury-rig contraptions to hold things in place while they cure. A stand with some popsicle sticks and clips served to hold the cables straight up while the marine silicone sealant (the white paste covering the top of the tag and black nylon sheath of the cables) cured overnight

I think I speak for everyone when I say I learned a ton this week and have gained an appreciation for the progress that has been made in biotelemetry and biologging technologies. We’ve come a long way from the first mechanical TDR (see pictures here) that was built in the 1960s by Dr. Gerry Kooyman to the modern high-tech marvels made by Wildlife Computers, but there’s always still an opportunity for trying new ideas and the application of novel sensors not standardly provided by manufacturers.

We’d all like to especially thank Markus for taking the time to teach us these skills and being patient with us when it took 5 minutes to successfully connect one sensor, while he could do it in 10 seconds.

Here are some lasting impressions from the workshop:

How excellent it is to be able to re-purpose tags for more than just a one-time use! Considering the initial expense of the tags, it is nice to know that if they are recovered, they can be re-purposed for another deployment on the same study, or used in a new study (as is the case for your [Arina’s] research)!”  -Skyla, Graduate Student at UAA

I was blown away at the delicacy of the process. It was like trying to capture a moth without getting wing dust on you.”  -Renae, ASLC Research Associate

“The workshop was really rewarding for me because it gave me an appreciation for the capabilities and limitations of biologging technologies, which is invaluable when designing studies, particularly on free-ranging marine mammals.” -Greg, Graduate Student at UAA

Written by: Arina Favilla, Graduate Student at University of California Santa Cruz.

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