Reflection
Radio wave reflection occurs when radio waves hit the surface of a substance and are reflected by the substance to a medium they originated from.
Depending on the material you choose, you’ll need to set proper reflection percentage values for it. The characteristics of surfaces determine the reflection percentage. For example glass, metal or ceramic surfaces have a higher reflection coefficient due to a lesser roughness and amount of pores, which allows the signal to be reflected almost without being absorbed.
Metal surfaces can reflect up to 100% of waves, creating significant obstacles for a traveling WiFi signal, whereas rough materials like gypsum, concrete or wood, absorb a major portion of the signal energy, reflecting only a fraction of it. The absorption of signal by rougher surfaces is explained by the fact that they diffuse it, making it lose its intensity.
Please refer to the instructions below on how to select an appropriate reflection value according to the building material in your surveyed space. If you can’t find a specific material in NetSpot’s list, select the one that has the closest characteristics:
| Type of material | Reflection, % |
|---|---|
| Bookshelf | 5 |
| Bamboo | 10 |
| Wood | 10 |
| Drywall (or Gypsum Board) | 15 |
| Office shelf | 15 |
| Vinyl Siding | 15 |
| Brick | 20 |
| Concrete Blocks | 20 |
| Plaster and Lath (Wood) | 20 |
| Retail shelf | 20 |
| Earth (or Mud) | 25 |
| Fiber Cement Panels | 25 |
| Granite | 25 |
| Concrete | 30 |
| Glass | 30 |
| Stone | 30 |
| Stucco | 30 |
| Thermoblock | 30 |
| Tiles | 30 |
| Plywood, rough | 30 |
| Plaster and Lath (Metal) | 40 |
| Warehouse shelf | 40 |
| Iron | 60 |
| Aluminium | 70 |
| Copper, highly polished | 70 |
Absorption
Absorption is an important factor determining how efficient a certain material is in absorbing radio waves upon encounter.
Here are the steps to follow to set a proper absorption value for your building material:
- Calculate the signal absorption through a wall in dBm (r1)
- Position an AP at least 16 ft (5 meters) away from the wall with no obstacles between the AP and the wall;
- Make sure the antenna is directed towards the wall;
- Take measurements of WiFi signal level (RSSI) next to the wall on a straight line (perpendicularly) from the AP, then go around the wall to take a similar measurement, but behind that wall. Take several measurements slightly away from each other to find an average;
- Calculate the absolute difference.
- Calculate the signal absorption in a space free of obstacles in dBm (r2)
- In case you have enough space free of obstacles (e.g. walls), then calculate the absolute difference for your radio signal at the same distances, as in item 1;
- When you don’t have a possibility to perform the above-mentioned, then take any value from 0 to 4 dBm (the thicker the wall and the larger the difference between measurements between the sides of the wall, the higher the value is to be taken).
- Subtract the absorption over free space from the absorption through the wall:
r = r1 – r2.
- Use the following formula to calculate the absorption:
absorption = r / (width * 8),
where the width is that of the wall in meters.