RF signal Attenuation inside a closed concrete chamber

[yousafzai82]

Hi.

I am planning to use GSM/GPRS based telemetric gauge inside a closed concrete chamber. As RF signal is not considerably attenuated in media like concrete as compared to free space loss at 10 meter distance.

I guess i wouldn't face any low signal problem inside the closed concrete chamber. Correct me if i am missing something....

 

[FvM]

Steel reinforcement may be a more serious problem, but the mesh usually has sufficient openings to pass 3G waves.

 

[jiripolivka]

Steel reinforcement may be a more serious problem, but the mesh usually has sufficient openings to pass 3G waves.

Attenuation through concrete wall depends on the thickness, if steel is there, etc. For GPS, expect 16-30 dB for a 15-cm thick wall.. If the concrete is moist, or if salty water is in it expect even more.

Communicating inside a concrete chamber may be easy but for high data rates, multipath may be a problem.

Google recent research papers on using GPS in concrete buildings. It should not work, sometime it does but as concrete has a permittivity around 6, delay is affected which is essential for GPS positioning.

 

[biff44]

a big component of concrete is iron oxide, which makes for an excellent RF absorber. So going thru concrete means it will be attenuated a log per length.

If you are talking about TX and RX antennas inside of the same concrete room, you will be fine. If you are talking about a TX antenna in another room, and an RX antenna in the concrete room, expect additional 10 to 30 dB path loss, even if the ceiling of the room is not concrete.

 

[yousafzai82]

Let me explain it more elaborately.

Expected dimensions of the chamber are as follows:
The area of the chamber is 60cm*100cm and it has 50cm hight. Side walls will be made of bricks 9cm thickness. The top side is made of concrete of 10cm thickness.

Please check the attached two files for reference. If we consider attenuation compared to 10m free space attenuation the GSM signals should work inside the chamber. I am using RF at GSM/GPRS frequencies.

 

[FvM]

Are you talking about attenuation compared to open field signal of local GSM network or transmission between two antennas? In the latter case, how are they placed?

The brick attenuation numbers in th etable gives an order of magnitude. I expect, that they are rather caused by reflection losses than bulk absorption. In so far the actual attenuation will strongly depend on geometries.

 

[yousafzai82]

I am using GSM/GPRS Module SIM900D inside the chamber. You can consider it as mobile phone. It has a SIM card and it is sending the reading on fixed IP and is also sending SMSs to the different users. I can also use a small glass window on one side of the chamber if it may help a bit. You can suggest some hard materials used as a window for RF signals.

 

[FvM]

I assume, that you'll have sufficient field strength inside the chamber.

 

[yousafzai82]

I am going for this design. I will post after i get results what ever.

 

[vfone]

The best way is to evaluate yourself the OTA (Over the Air) performances of the setup, doing relative measurements.
Small concrete chambers gives inconsistent radiated results due to: attenuation (through material), scattering (incident on a rough surface), reflections (surface dimension comparable to wavelength), refractions (waves moving through different mediums), diffraction (occurs at the edges of the chamber), etc.