You've no doubt noticed that radios works better in some places than others. This has to do with the way radio waves work and the degree to which the waves are absorbed by surrounding objects. Glass is a substance that absorbs very little of radio waves, enabling a radio to work best when it’s near a window versus the center of your house.
Radio waves are a type of electromagnetic radiation. Electromagnetic radiation is made up of particles called photons, which carry an electrical charge as they travel through the air. This type of radiation is harmless due to its low power and simple form, which is necessary to carry a radio signal. The speed of change between positive and negative voltage is what gives the radio wave its frequency. A receiver is then set to that frequency to receive the radio signal.
Radio waves are affected by two different types of substances called conductors and dielectrics. Conductors include many types of metals: copper, aluminum, silver and gold, but also salt water and metal-reinforced concrete to some extent. When the radio wave hits a conductor, the signal is either bounced back from the surface or partially absorbed while the rest is reflected away. This is why radios often work poorly in metal or concrete buildings.
Glass and other non-metallic substances fall under a class called dielectrics. The dielectric differs from the conductor in that radio waves will pass through these substances to some extent. Transmission isn't perfect: Some of the electromagnetic radiation is absorbed by the dielectric generating a small amount of heat. Besides glass, fresh water, paper and plastic are other examples of dielectric substances.
Scientists have formulated a scale to measure the amount of effect of a dielectric or conductor on a radio wave. This is called the attenuation coefficient. Dielectrics will have a lower measurement, while conductors will have a higher one -- obviously because more of the radio waves will be blocked. Glass is one of those substances with a low attenuation coefficient.
The effects on radio waves from glass are minimal. Since there's some degree of absorption, signal strength will be slightly less than having the same radio outside in the open air. There's also another factor to consider, and that’s the materials around the glass. A radio inside a home will work better than the same radio inside a car. This is because the home is made up of more dielectric substances than the car, which has a lot of metal, a conductive substance. This is why the antenna for a car radio is placed outside the car.
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