Path Loss Models and Material Attenuation

Compare free-space, log-distance, and ITU indoor path loss with material attenuation and fade margin

animation
path-loss
link-budget
propagation
materials
wireless
intermediate
A guided path-loss workbench for seeing how distance, frequency, environment, walls, and receiver sensitivity change wireless link reliability.
Animation Path loss Material attenuation

Path Loss Models and Material Attenuation

Step through how distance, frequency, environment, and walls reduce received signal power. The goal is to decide whether a wireless IoT link still has enough fade margin to be reliable.

Log-distanceModel
84.0 dBTotal loss
-70.0 dBmReceived power
20.0 dBFade margin

Goal

Predict whether the receiver hears the transmitter after distance loss and obstacle loss are added.

Try first

Start with Office Wi-Fi, then add concrete or metal. Watch the margin drop even if distance stays the same.

Watch

The signal line, curve point, formula, material budget, received power, and diagnosis update together.

Why it matters

A link can fail because of walls, frequency, or low margin, not only because the nodes are far apart.

Deployment scenario

Office Wi-Fi with a few light walls. It shows why 2.4 GHz may work across rooms but loses margin quickly through dense materials.

Propagation model

Playback

Link controls

35 m
2400 MHz
14 dBm, 0 dBi antenna assumption
-90 dBm

Environment and materials

n = 3.0, ITU N = 30
0 floors
3 x 4 dB
1 x 3 dB
0 x 12 dB
0 x 20 dB

Analysis stages

Start with the separation between transmitter and receiver. Doubling distance adds about 6 dB only in the free-space part of the model.
Use the chosen model before adding materials.Expected calculation
Distance and frequency set the baseline loss.Observed evidence
Margin is still positive.Working diagnosis

Signal path

The line shows the selected wireless path. Obstacles add fixed attenuation on top of the distance model. The receiver changes color when fade margin becomes weak or negative.

healthy margin weak margin link below sensitivity D/G/C/M = drywall/glass/concrete/metal

Calculation details

The log-distance model starts from free-space loss at 1 m, then applies the environment exponent.

Link diagnosis

Fade margin is received power minus receiver sensitivity. Positive margin means the receiver can hear the signal, but reliable links need extra margin.

Received power curve

The orange point is the current distance. The dashed red line is receiver sensitivity; a reliable design normally keeps the point above that line with margin.

Beginner ramp

dBm is signal power on a logarithmic scale. A change of 3 dB is about half or double power, and a change of 10 dB is a factor of ten.

What to notice

Distance loss, material loss, and receiver sensitivity are separate. A short link can still fail if a metal door or concrete wall sits in the path.

Design rule

A positive margin only means the link is mathematically above sensitivity. Practical IoT links often need 10 dB or more for fading, battery voltage, antenna placement, and interference.

Formula guide
  • FSPL = 32.44 + 20log10(f_MHz) + 20log10(d_km).
  • Log-distance = FSPL at 1 m + 10nlog10(d_m/1 m).
  • ITU indoor teaching form = 20log10(f_MHz) + Nlog10(d_m) + floor loss - 28.
Material guide
  • Drywall is modeled here as 4 dB per wall.
  • Glass is modeled here as 3 dB per pane or partition.
  • Concrete is modeled here as 12 dB per wall.
  • Metal is modeled here as 20 dB because it can be close to opaque at many IoT frequencies.
Frequency tradeoff
  • Higher frequency usually has more free-space loss for the same distance.
  • Lower frequency often penetrates better and travels farther.
  • Higher frequency may offer more bandwidth or smaller antennas, so the best choice depends on the application.
Practice 1

Choose Office Wi-Fi and switch between FSPL and Log-distance. Which model is more realistic indoors?

Practice 2

Choose Basement Sensor. Remove concrete walls one by one. How much margin does each wall recover?

Practice 3

Choose Sub-GHz Building and then increase frequency toward 2400 MHz. What happens to received power?