Using Titanium as antenna in implantable tracking system

Question

I have some question regarding using titanium as antenna. I have to think about an implantable tracking system for animals. One of the requirements is that it should be as small as possible. Other requirements is that it should has good range and transmission power, while being super low power.

For this I am thinking of using CC430F5137 uC that has embedded radio (433MHz) and wake on radio capabilities. The design should also have accelerometer and temperature sensor as well. This components added together, will exceed the maximum length and diameter of the capsule I have in mind which is around 2(w) by 8(l) cm dimensions.

So basically it will be a battery and PCB inside some sort of bio safe capsule. This forces using an external antenna, basically a piece of wire that exits the capsule. Since the only metal I know that does not react with body is titanium, what would be your thoughts about this?

The length would be something around 8cm (considering 1/8 of wavelength)

Also it comes the problem of soldering the titanium on PCB which I believe it is not possible, unless I think of a socket that antenna goes in and fixes in place.

please let me know what you think.

Answer 1

Wow, 2x8cm is absolutely huge for this application. If you have a look at this quesiton: What are the smallest microcontrollers? you'll see there are very nice microcontrollers smaller than 2x2mm. There are also many accelerometers which are 2x2mm, and a few down to 1.7x1.0mm (Memsic MXC6226XC). Chip antennas work with high efficiency while being much, much smaller than 1/8 of wavelength.

Your biggest problems will be:

• regulatory approvals (IACUC anyone? as mentioned by Scott above)

• biocompatibility (embedding in medical-grade silicone may work)

• battery capacity (or energy harvesting?) and

• absorption of RF by the body (salt water is a short circuit in RF), consequently very limited range (a few meters)

This will be a tough project no matter what.

Answer 2

The wire should be insulated, and the insulation needs to be biocompatible. The conductor need not be biocompatible.

Frankly, the environmental demands on such systems can be impressive and surprising to someone that hasn't used them. Keeping in mind that device failure would mean unnecessarily inconveniencing an animal, I'd recommend going to the pros, like http://www.telonics.com/wildlife.php or http://www.blueskytelemetry.co.uk/wildlife_tracking.asp

Whoever is running the investigation will have an easier time getting the study through a review committee if you take that approach.