# Dielectric constant of human body

Discussion in 'General Electronics Chat' started by seppelin, Jan 15, 2009.

1. ### seppelin Thread Starter New Member

Jan 15, 2009
1
0
I came out to this topic searching for some information on the dielectrical constant of salt water since that approaches the human body. To make a device detecting the approximity of human body mass.. instead of the air.. Presumeably it should be working nice, though I believe the dielectrical constant changes over the frequency domain. So I should be looking for the right electromagnetic frequency to have the biggest dielectrical constant having the biggest response, since air(relative dielectric 1) should have a rather flat dielectrical constant over the frequency domain.

2. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,181
410
Dielectric constant and resistivity are NOT the same things. One is imaginary, one is real. Surprisingly, sea water and fresh water have ABOUT the same dielectric constant...but very different resistivities, of course.

The Navy did extensive testing on this, for ELF radio experiments. I'll try to dredge up the studies for your. It was actually pretty interesting,

Eric

Nov 4, 2008
2,181
410

Nov 4, 2008
2,181
410

Apr 20, 2004
15,815
293
6. ### Dave Retired Moderator

Nov 17, 2003
6,960
164
Yes it does change over the frequency domain; however note that the permittivity of the human body is complex with a relative dielectric constant and a dielectric loss factor, which in a more practical sense manifests itself as the conductivity, and will be discernible for water particularly with high salinity. Note: both these parameters are independent functions of frequency (and temperature too).

Dave

7. ### Dave Retired Moderator

Nov 17, 2003
6,960
164
KL7AJ has referred to it as resistivity, where as I have referred to it as conductivity - they account for the same physical aspect where:

$\sigma = \frac{1}{\rho}$

Dave

8. ### 111 222 New Member

Nov 25, 2017
2
0
Thanks for the info. I was aware of the Navy studies, but your descriptive info is helpful.