Technical note
Terahertz vs Ultrasound Thickness Measurement
Terahertz and ultrasound both read thickness from reflected signals: ultrasound needs contact and reaches into metals, terahertz is non-contact and resolves individual layers in coatings, polymers, and composites.
Thickness measurement methods
Several technologies measure material thickness, but two of the most commonly used are ultrasound and terahertz.
Both read the time between reflections from internal interfaces to recover layer geometry. The differences come from what they use to probe the material and how that interacts with different material types.
Key differences
Ultrasound and terahertz both analyze reflections, but they suit different measurement contexts.
Ultrasound
Ultrasound sends acoustic waves into a material. Each internal boundary produces a reflection, and the time between reflections converts into thickness once the speed of sound in the material is known.
- Requires contact with the surface, usually via a coupling medium.
- Widely used for metals, where acoustic transmission is strong.
- Best suited to thicker structures where reflections are well separated in time.
Terahertz
Terahertz uses electromagnetic signals rather than acoustic waves. In Chameleon, photoconductive antennas paired with a broadband continuous-wave light source and an optical delay line generate and detect the signal.
- Non-contact: the probe never touches the sample.
- Suited to multilayer polymers, coatings, and composites.
- Resolves individual internal layers, not just the stack total.
Choosing the right method
The choice between ultrasound and terahertz comes down to the material and the question.
For metal thickness measurement, ultrasound remains the workhorse. For multilayer coatings, polymers, and composites, terahertz is the better fit because it sees through the surface and resolves the layers underneath without contact.
The two are complementary rather than competitive: pick the probe that matches the material you are looking into.
