In recent years, microwaves have moved from the kitchen and telecommunications to a surprising variety of industrial applications: recognizing materials, locating objects, measuring temperature and humidity. Let's look at the physics that makes it possible — and why they are complementary to X-rays.
Microwaves are electromagnetic radiation with frequencies roughly between 300 MHz and 300 GHz, corresponding to wavelengths from about a meter to a millimeter. Unlike X-rays, they are non-ionizing: their photons have too little energy to tear electrons away. They don't interact by "breaking" atoms, but by setting charges and dipoles in motion — and that's exactly what makes them extraordinary sensors.
The real leap was technological rather than physical. The spread of 5G, of solid-state radar (low-cost) and of millimeter-wave electronics has made available cheap, compact and reliable components once reserved for military radar and laboratories. Today a microwave sensor fits in a few square centimeters. This has opened up industrial applications unthinkable until recently, exploiting a unique quality: microwaves penetrate non-conductive materials (plastic, glass, ceramic, food, wood) and are extremely sensitive to their electrical properties.
When a microwave meets a material, what matters is its dielectric permittivity, a complex quantity: the real part (ε′) describes how much energy the material stores by polarizing, the imaginary part (ε″) describes how much energy it absorbs (and dissipates as heat). Two key phenomena:
On top of this comes theDoppler effect: if the object moves, the reflected wave changes frequency, making it possible to measure speed and motion. And with techniques like FMCW radar (frequency-modulated), distance is obtained with great precision.
Different materials have different permittivities: by measuring how the wave is slowed, absorbed and reflected, you can distinguish and classify materials, even inside packaging or mixed streams — useful in sorting and quality control.
With radar andmicrowave imaging (also with antenna arrays), objects are located and their position and outline reconstructed, even through optically opaque materials.
Microwave radiometry measures the natural thermal emission of a body at these frequencies, from which temperature is inferred without contact; and since dielectric properties depend on temperature, active measurements are sensitive to it too. Humidity, finally, is measured very well precisely because water dominates the dielectric response: small variations in water content produce clear signals.
Unlike X-ray detectors — which count photons — microwave sensors are radio-frequency devices:
The challenge isn't "seeing" the signal, but interpreting it: extracting useful information from reflections, phases and frequencies requires electromagnetic modeling and dedicated algorithms.
We're often asked which technology is "better". The answer is that they look at different things:
| Property | Microwaves | X-rays |
|---|---|---|
| Ionizing | No — safe, no heavy shielding | Yes — radiation protection needed |
| Plastic, glass, ceramic | penetrate | penetrate |
| Metals | reflected | penetrate (attenuated) |
| Sensitivity to water/humidity | very high | low |
| What they're sensitive to | dielectric properties | density and atomic number (Z) |
| Spatial resolution | coarser | very high |
That's why we consider them complementary: the choice — or the combination — depends on the problem. Mastering both, with the same physics culture, is what lets us propose the right solution and not the one we "happen to have in the catalog".
Let's assess together whether microwaves, X-rays or a combination are the right path for your case.
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