Decoding the Sensor of Radar Level Transmitter – Myth
If you work with radar level transmitters, you’ve seen this on countless spec sheets: Sensor Material: Stainless Steel. This is one of the most persistent technical myths in our field.
Here’s the hard truth: A radar sensor can never be made of stainless steel.
1. The Physics Problem
The reason is fundamental physics: Radar signals cannot pass through metal.
A metal sensor would block the radar signal completely (as metal has a very high di-electric and is radio-opaque). For a radar to function, its sensing face must be “radio-transparent” to let the signal out and the echo back in.
2. The True Sensor Materials
The actual material at the “sensor front”—the critical window between the electronics and your process—is always a non-metallic polymer or ceramic.
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PTFE (Teflon)
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PEEK
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Ceramic
These materials allow electromagnetic waves to pass through freely, enabling reliable measurement.
3. The Role of Stainless Steel
So, where does the “stainless steel” come from?
It’s the process connection—the flange, thread, or housing that surrounds the true sensor and attaches the device to your tank.
This ‘stainless steel’ terminology is a legacy term carried over from older 26 GHz and 6 GHz radars. These units used large metal horn antennas to act as a waveguide, focusing the long-wavelength signal. Even then, a non-metallic plug (sensor) was at the base.
With modern 80 GHz and 140 GHz radar and the special chirp antenna, the high frequency creates a naturally narrow, focused beam. This eliminates the need for a bulky metal horn, allowing for the compact PTFE and ceramic-front sensors we use today and conveniently call the PTFE Lens Antenna.
The Takeaway
When a datasheet says “Stainless Steel Sensor,” it’s describing the process connection, not the active sensing element.
The real sensor is the non-metallic front that lets the signal travel freely.