Why do I have a big microwave absorption in tissue, when the tissue conductivity is high? I thougt the opposite would be correct. Can somebody explain the reason?
If you are referring to the microwave Ovens then this might be the possible reason,
Microwave Oven are basically meant to cook food i.e. water rich food. So anything which has a high content of water effectively absorbs microwave radiation and get hot.
EDIT1: for details on how microwave works..here
Now, since tissue contains water the above statements might hold.
NOTE : The Diagram was useless..I realised it much later... :( deleted for everyone's sake..
You can read the wikipedia (the link already mentioned), it describes the process called Dielectric heating.
The matter of conductivity of the organic tissue is tricky. For instance, the water is a dielectric, it consists of polarized H2O molecules, all the electrons are tightly bound. However when there are minerals dissolved in the water it's a conductor - due to the ions.
So the the "non-pure" water is being heated by oscillating EM field, although it's a conductor practically.