Using RF to scan an object

Hi,

In relation to my Master's thesis, I'm looking to build a device that may detect the material of an object residing in a plastic bag by beaming it with radiowaves at several frequencies and measuring how much is received at the other end. Since different materials have different absorptivity, transmissivity, and reflectivity, measuring how much is received at different frequencies at the other side may paint a picture of what materials are inside the bag.

My question is, how does one go about generating such a small range wave and reading it's (I guess) strength at the other side using arduino?

Someone has mentioned making a coil and feeding it with a certain frequency of AC current at several frequencies quickly after one other, and then do a fast fourier transform at the other side. I do not know the required hardware for this or how one programatically create these frequencies from arduino.

Can anyone help?

Thanks in advance.

Use one of the cheap DDS chips like an AD9850.

ebay search term: RF sweep generator. look at the ones that look like an Arduino project
ebay search term: SDR; Software defined Rado

figure out how to generate and receive in lockstep. Read the RSSI Received Signal Strength Indicator of the SDR as you step through the frequencies