5 ms·

I remember this article from the same site a while back - https://hforsten.com/heartbeat-detection-with-radar.html https://hforsten.com/heartbeat-detection-with

by jcims 3y ago

I remember this article from the same site a while back - https://hforsten.com/heartbeat-detection-with-radar.html https://hforsten.com/heartbeat-detection-with-radar.html I bought some cheap 10ghz and 24ghz dopper radar units off of amazon and started tinkering with them. You can absolutely pick up heartbeats and breathing just visually in the spectrogram. Here's a few samples from that era: 10ghz pointed at ceiling fan: https://www.youtube.com/watch?v=tIiFvByf1CQ https://www.youtube.com/watch?v=tIiFvByf1CQ 10ghz pointed straight up underneath a quarter that I flipped and allowed to land on the surface https://www.youtube.com/watch?v=8riretP8ylE https://www.youtube.com/watch?v=8riretP8ylE 10ghz pointed at a quarter spin on the surface https://www.youtube.com/watch?v=5lnYvJoxRak https://www.youtube.com/watch?v=5lnYvJoxRak The comb filtering of the signal from the spinning surface is really cool. 10ghz module on amazon - https://www.amazon.com/HiLetgo-Microwave-Detector-Wireless-10-525GHz/dp/B01N6AIF1L https://www.amazon.com/HiLetgo-Microwave-Detector-Wireless-1...

spxneo 3y ago
interesting does/can it work behind structures? is it safe to point this at yourself?
- lobocinza 3y ago
  I have a "human presense sensor" which is a 5GHz radar. It works behind structures, detection is weird sometimes but much better than a passive infrared sensor for this use case.
- KeplerBoy 3y ago
  yes, it's safe. It's not that different from regular WiFi or cellular signals. It's non ionizing (aka it doesn't have enough energy to instantly destroy cells unlike uv radiation) but it can heat up tissue, which is linked to cancer and worse (think microwave ovens).
  - a_random_canuck 3y ago
    There’s no risk of cancer from heating up tissue.
    - dimitrios1 3y ago
      But there is a risk of dying from heating up tissue.
    - SheldonSteves 3y ago
      There is but it's sun burn type risks, not nuclear reactor type. A few unlucky people have been literally cooked to death by military radar. It's as awful as it sounds.
      - ftrobro 3y ago
        Isn't sun burn damage and nuclear reactor damgage the same type but at different magnitudes? If your skin becomes red and hot a few hours after being exposed to the sun it's because your immune system is killing off cells that had their DNA damaged. The damage is not caused by heat but by radiation. https://www.thenakedscientists.com/articles/questions/why-do-you-go-red-when-sunburnt https://www.thenakedscientists.com/articles/questions/why-do...
      - deleted 3y ago
        [deleted]
      - Dylan16807 3y ago
        > It's as awful as it sounds. Well to me it sounds like you'd get heat stroke and pass out before anything reaches particularly painful temperatures, because it's heating you pretty evenly and not via contact, but maybe that's not the right way to think about it? At higher frequencies I would guess it gets closer to normal burning?
        azalemeth 3y ago
        This isn't really correct I'm afraid. The cause of SAR is predominantly dielectric losses and the loss tangent is a strong function of tissue type -- CSF, fat and bone are really quite different in terms of epsilon r and sigma, and one has to solve Maxwell with a human voxel model to work out SAR effectively which computationally is a pain. Once tissue heating has occurred what happens next is well described by the bioheat equation, which is basically the thermal diffusion equation with a massive percussion term. The blood supply is very different to different tissue types and the depth at which peak heating occurs is a very strong function of wavelength. For frequencies, the combination of these effects means that your eyes are most at risk -- water like and terrible blood supply. This gives rise to the first piece of advice I was given when a graduate student playing with electron paramagnetic resonance -- never look down a waveguide and treat them like a loaded gun!

by jcims 3y ago

spxneo 3y ago

interesting does/can it work behind structures? is it safe to point this at yourself?

lobocinza 3y ago
I have a "human presense sensor" which is a 5GHz radar. It works behind structures, detection is weird sometimes but much better than a passive infrared sensor for this use case.
KeplerBoy 3y ago
yes, it's safe. It's not that different from regular WiFi or cellular signals. It's non ionizing (aka it doesn't have enough energy to instantly destroy cells unlike uv radiation) but it can heat up tissue, which is linked to cancer and worse (think microwave ovens).
- a_random_canuck 3y ago
  There’s no risk of cancer from heating up tissue.
  - dimitrios1 3y ago
    But there is a risk of dying from heating up tissue.
  - SheldonSteves 3y ago
    There is but it's sun burn type risks, not nuclear reactor type. A few unlucky people have been literally cooked to death by military radar. It's as awful as it sounds.
    - ftrobro 3y ago
      Isn't sun burn damage and nuclear reactor damgage the same type but at different magnitudes? If your skin becomes red and hot a few hours after being exposed to the sun it's because your immune system is killing off cells that had their DNA damaged. The damage is not caused by heat but by radiation. https://www.thenakedscientists.com/articles/questions/why-do-you-go-red-when-sunburnt https://www.thenakedscientists.com/articles/questions/why-do...
    - deleted 3y ago
      [deleted]
    - Dylan16807 3y ago
      > It's as awful as it sounds. Well to me it sounds like you'd get heat stroke and pass out before anything reaches particularly painful temperatures, because it's heating you pretty evenly and not via contact, but maybe that's not the right way to think about it? At higher frequencies I would guess it gets closer to normal burning?
      - azalemeth 3y ago
        This isn't really correct I'm afraid. The cause of SAR is predominantly dielectric losses and the loss tangent is a strong function of tissue type -- CSF, fat and bone are really quite different in terms of epsilon r and sigma, and one has to solve Maxwell with a human voxel model to work out SAR effectively which computationally is a pain. Once tissue heating has occurred what happens next is well described by the bioheat equation, which is basically the thermal diffusion equation with a massive percussion term. The blood supply is very different to different tissue types and the depth at which peak heating occurs is a very strong function of wavelength. For frequencies, the combination of these effects means that your eyes are most at risk -- water like and terrible blood supply. This gives rise to the first piece of advice I was given when a graduate student playing with electron paramagnetic resonance -- never look down a waveguide and treat them like a loaded gun!