# Dielectric constant of human body

#### seppelin

Joined Jan 15, 2009
1
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.

#### KL7AJ

Joined Nov 4, 2008
2,229
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

#### Dave

Joined Nov 17, 2003
6,970
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
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

#### Dave

Joined Nov 17, 2003
6,970
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.
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

#### 111 222

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