Radar Level Dielectric Constant Calculator
Check how well a radar or guided wave radar (GWR) signal reflects from a surface or interface, and convert the apparent thickness of an upper liquid layer into its real thickness.
- Γ = (√ε₁ − √ε₂) ÷ (√ε₁ + √ε₂) = −0.7269
- Reflected power = Γ² = 52.85 %
- Real thickness = apparent ÷ √ε₁ = 1,000 ÷ 1.4142 = 707.1 mm
Radar Reflection Formulas
Reflected power = Γ²
v = c ÷ √εr ; real thickness = apparent thickness ÷ √εupper
ε₁ and ε₂ are the dielectric constants of the upper and lower media (vapour ≈ 1), Γ the amplitude reflection coefficient at normal incidence and c the speed of light. In an upper liquid layer the radar wave slows by √ε, so the transmitter must know εupper to place the interface correctly.
Worked example
Oil (εr 2) over water (εr 80): Γ = 0.73 and about 53 % of the power reflects, a strong interface. An apparent oil layer of 1000 mm is really 707 mm thick.
Frequently Asked Questions
Why does dielectric constant matter for radar?
The reflected signal depends on the dielectric contrast at the surface. Low εr products return weak echoes.
How does GWR measure an interface?
Part of the pulse reflects at the top surface and the rest travels through the upper liquid to reflect at the interface. Knowing εr of the upper layer corrects for the slower speed.
What εr do common liquids have?
Water about 80, alcohols about 18 to 33, oils and hydrocarbons about 1.8 to 3. Check vendor tables for your product and temperature.
Learn more on the blog
Guided wave radar vs non contact radar
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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