I have a UWB radar that Im playing with. The problem is that my algorithms at the moment can clearly, reliably and validly pick up 1-2mm movements of a pendulum i've set up. However, when I use it on my chest to find my heart, things doesnt work. The radar should be set up so that the waves penetrate skin and bone, but I am not entirely sure. The antennae are specced specifically to be able to pick up a heartbeat (or penetrate human tissues).

In terms of math, I first do despiking and a bandpass filter around 0.1 - 5 hz, followed by a principle component analysis to reduce the number of samples/sensors. Then I either do a FFT plus some stuff to find the most pronounced frequencies of the top 5 principle components, or I search for the best fit sinuswave (as the heartbeat can be described as such afaik) to the top 5 principle components.

While these methods give similar results when used on a pendulum, they break down when trying to find the heartbeat. The radar can nicely penetrate wood, and plastic and other stuff. Any ideas?

Bonus question: We had some ultrasound gel at the lab, and i tried to see if removing the "air" component would help, but then all signal dropped. Is ultrasound gel absorbing the radar pulses?

Thanks alot!

  • $\begingroup$ What frequencies are you working at? And whats the bandwidth of the UWB signal? $\endgroup$ – learner Jul 7 '14 at 18:48
  • $\begingroup$ The specs of the antennae Im working with has a bandwith of 1-10 ghz, and a -10db cut off freq. I am not sure if the antennae is actually having these specs. Skin absorbtion is at around 10 ghz, and I expect that most frequencies above 6 ghz would not penetrate so well to the depth of the heart, but that still leaves room. Does this answer your question? $\endgroup$ – Sevenius Jul 8 '14 at 8:41
  • $\begingroup$ Whats the transmit power? and 2ndly plz make sure u r putting the antenna in correct orientation cuz I discovered once I was doing opposite to what I was suppose to do. $\endgroup$ – learner Jul 8 '14 at 15:44
  • $\begingroup$ Im unsure about the transmit power exactly, but it is very low power near field device. Novelda, if that says something to you. And yes, it is pointing in the right direction :) I think it might have to do with the antennae specced for 2-3 cm peak range. $\endgroup$ – Sevenius Jul 9 '14 at 9:37
  • $\begingroup$ What I found is that you need to keep it at a distance from the chest, and it will sense your heartbeat by detecting the movement of chest. I don't think you can get these frequencies to penetrate that deep into the human body. $\endgroup$ – learner Jul 9 '14 at 10:45

I am also working on UWB bio radar to detect the heart beats. But the problem is that breath signal is also mixed up with heart signal. I am trying to remove the breath signal (0.25 to 0.7 Hz) and to get the heart frequency signal (1 to 4 Hz). Currently I am also using an ultrasound sensor to detect heart signal.

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  • $\begingroup$ I finally managed to detect the heart with the UWB radar. Two points I found: 1, using a pass band filter for breath gives me an artificial 1(ish)hz heartbeat, even when I don't measure the heart, so be careful with the filters. And 2, I used some gel to dampen the waves on the backside of the antennaes. Might be points to pursue for you. I also cut out the first 100ms and last 100 ms of all measurements, which helped loads on reducing noise in the signal. $\endgroup$ – Sevenius Oct 3 '14 at 14:11

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