2/2012

"Hello, can you hear me?"

cell phone

Modern construction materials can interfere with cell
phone signals. Enclosing a house in a metal envelope
turns it into a makeshift Faraday cage, preventing
radio waves from entering or escaping the space within.

What can you do, if you live in a new home and have constant problems with poor cell phone reception and dropped calls?

Growing energy consumption and the escalating effects of climate change are spurring the adoption of more energy-efficient building solutions. Energy-efficiency is especially important in the northern countries, such as Northern Europe, Northern America and Russia, where houses need to be properly insulated, as heating accounts for a lion's share of the total energy usage of households. The trend is spreading to the rest of Europe and warmer climates, driven by stricter regulations that also apply to cooling systems.

However, tightly sealed homes have brought on a new problem: cell phone signals may be unable to penetrate the walls.

High-density construction materials block signals

To improve the energy performance of buildings, the construction industry has introduced new insulation products incorporating multiple layers of metal sheets. Metal alloys are also found in selective glazing, window frames and doors.

The downside is that the metal shell obstructs the progress of radio waves.

"The inconvenience of poor cell phone reception is one thing, but if emergency calls won't go through it can even be fatal," says Ari Asp from the Department of Communications Engineering at TUT.

"Measurements conducted at TUT indicated severe problems originating from the attenuation of radio signals, as they increase up to 35 dB for individual construction materials for cellular frequencies around 2 GHz," adds Jarno Niemelä from the same department. 

Hence, there is a clear need to find a solution to the problem.

What's there to be done?

Several solutions have been proposed but none are without problems.

One alternative, though expensive and slow, would be to build more base stations to increase coverage. Another option is to install a repeater that picks up a weak signal through a donor antenna and amplifies it while sending it throughout your home. The latter method is used by operators but banned to the general public, as repeaters interfere with the cellular network.

The third alternative is to drill so-called "RF holes" into the building structure. However, they compromise the integrity of the building envelope and thereby reduce energy-efficiency and increase noise levels. In a worst-case scenario, they may even cause moisture problems.

"In material based solutions, the most cost-effective alternative is to integrate antennas or other type of passive systems into the windows, window frames or walls already at the construction stage," says Ari Asp.

Future work

As there are several solutions for delivering and improving radio signal levels indoors, subsequent research will, among others, focus on the assessment of different solutions and their applicability as a whole. In addition, researchers will investigate passive antenna arrangements to find alternative ways to maximize signal strength.

 

Text: Tuuli Laukkanen
Photo: Rodeo.fi

 

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