Using an RF signal to determine the material of an object


I am posting this after doing research on the forum, hoping this topic has not been posted before. I am attempting to do a project in where I transmit an RF signal, through an object, and receive the signal on the other side. By doing so, I should be able to determine whether the signal was attenuated and by how much, in order to determine the material of the object.

However, I am trying to figure out whether or not I am able to read the signal. What I mean by that, is it possible to see at what frequency the signal is being transmitted, and then at what frequency the signal is being received at or attenuated to?

I am also wondering if it is even possible to do so. I have seen the "transmitting data" video where they show "Hello World" being transmitted in the terminal...trying to do something similar but show the frequency attenuated in the terminal instead.

Unless I have been researching it in the wrong sense, I have not been able to understand or figure out how to exactly do this. Hopefully, someone can give me some insight on how this would work.

Thank you so much, I really appreciate it!

I just found a project that was done and this is what I am going for, just in my case using the Arduino board and the transmitter and receiver module with antennas hooked up to a laptop.

Not sure I understand the bit about so called frequency shift, why would an RF signal passing through an object change in frequency ?

As for attenuation, then there are a number of RF modules out there that will report the received signal strangth, RSSI, so you can do a before and after comparison, i.e. signal strength with no object versus signal strength with object in path. Doubt there would be enough precision in the RSSI reading to be very useful though.

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A (maybe, but I do not think so) useful device would be rather complicated, to transmit a series of different frequencies (and also different power strength) at a fixed distance from the reciever (with the material in between).
The reciever end should plot the signal strength (Y axis) vs frequency (X axis) to show a "fingerprint" of the current material. Then you would have to save different fingerprint samples for future reference.
Plotting data is easy to do, just choose "Tools" -> "Serial Plotter" in IDE. But all the rest is very difficult...

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A Raman spectroscope finds out the composition by reflected X-rays, and works.

I doubt measuring the absorption of RF signals will give you much information,
conductive objects will probably just block RF.

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From working with others, I was told that RF signals are attenuated differently by different materials, so placing the object between the two antennas will create a difference in the signal strength. So, based on the signal strength at the receiver, I would want to calibrate and program the board to print in the terminal what material the object is made out...hopefully, that is a little more clear on what I meant.

I think maybe that is where my wording was wrong...RSSI could potentially work, I will research more on that. Thank you for your reply!

I will try this out, thank you for your reply!

The materials that I would be testing out are metal, non-metal hard objects, a liquid or gas. So, it could possibly work for the non-conductive materials,

I will research more on the spectroscope, thank you for your rpely!

Before you get to far in this project, take time to figure out HOW you are going to ensure the RF energy is actually going through the test material and not going around the test material.
How you ensure the signal is only going through a liquid or a gas and not also testing the material that is enclosing the gas or liquid?
Do you realize the signal is going through gas when it goes through the AIR?

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Have you a link to this?

What range of frequencies are you considering?

For example you can work out the moisture content of a sample of grain by looking at the absorption of a specific micro wave frequency. But this doesn’t tell you that it is grain.

The simple attention characters is not going to tell you what substance you have. For example all metals will be the same. This is not the sort of thing you can do with home made equipment. An instrument to do this in any great detail is going to cost probably more than your house. They are called network analysers and even these have a limited maximum frequency.

There has been research in this area for over 70 years:

Just not widely represented in the mainstream.


I recall that radar works by reflection from a material, not a signal passing through a material like the OP is proposing.

Just antenna orientation, however.

This seems to be an application that uses that principle

with x-rays

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google - magnetic permeability

I am attempting to do a project in where I transmit an RF signal, through an object, and receive the signal on the other side. By doing so, I should be able to determine whether the signal was attenuated and by how much, in order to determine the material of the object.

IMO, attenuation will be difficult to utilize (solely) as various materials (minerals) will cause RF beam divergence which is both a function of density and sample thickness. Identically thin sheets of materials can be profiled somewhat with attenuation, but as the list of identifiable materials grow, software using only attenuation will become difficult, perhaps impossible.

Think of the RF transmitting antenna (omnidirectional) being a light bulb. The receiver can be considered a photocell. Clear glass and colored glass can be differentiated. But various colors could give the similar attenuation for a fixed lamp. The lamp would need to be varied in color (sweep through light frequencies) to provide another measured dimension to assist the software algorithm to hopefully differentiate materials (spectrum.)

RF is just a lower frequency than light, so similar issues apply. Dealing with random thicknesses (different absorption == different attenuation) becomes increasingly more complex as the internal reference data is expanded. Then we also have that omnidirectional antenna issue where most energy is directed away from the sample.

Thank you for your insight Paul, I will make sure to understand which one it is.

Thank you for your reply!

Yes, here is the link - Using Inexpensive 433 MHz RF Modules with Arduino - YouTube

I was not sure yet what range, I was still trying to figure out if I would be able to send and receive the signal. But, from what I have seen the 433MHz range is what most are using for their projects. And yes I have researched the network analyzers as well, they are very expensive!

Thank you for your reply!

Thank you for the link, I will take a look at it. Thank you for your reply!

This is exactly what my project is based upon!! I probably should have included that in my post, my apologies.

But essentially, I am trying to do the same with two antennas and place the object in between and see what the material is of the object.

Will do, thank you for your reply!