The right T-shirt may increase medical implant’s battery life

Enlarge / Once you're done testing, you can set the transmitter to "roast." (credit: Brandon Zeman)

Although pacemakers led the way, I think it's reasonable to expect that our human bodies are going to end up containing many more active devices. These might mean long-term implants that provide aid to problematic organs, or they could be temporary devices that provide evidence to diagnose a condition or deliver medicine to a specific location. Many of these devices would need to be able to communicate with the outside world, which has proven to be more difficult than expected. The solution, however, may be as simple as changing your shirt.

I was surprised to learn that internal medical devices consume relatively high levels of power as they communicate with the outside world. It's not that things like low-energy Bluetooth don't work, but they use far more power when transmitting from inside the body than they do outside of the body. The problem turns out to be something called "total internal reflection."

Totally into reflection

You may remember learning about Snell's law and total internal reflection at school, but if not, don't worry-I'm a trained explainer. When light travels across an interface between two materials, its direction of travel will change. Going from something like air to glass will result in a light ray traveling closer to perpendicular to the interface. But going from glass to air results in a light ray ending up with an angle closer to parallel. If the angle of the ray in air is already close to parallel to the interface, the light ray in the glass cannot bend far enough; instead, it's reflected. Since the light wave is inside the glass, we refer to this as total internal reflection.

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