Modulated scatterer technique (MST) is based on illuminating a small antenna, usually a dipole, loaded with a PIN diode, with an electromagnetic wave. The scattered (or reflected) wave from the probe may then be used to determine dielectric properties of the material in which the probe is located or embedded. The PIN diode is turned "on " and "off" which not only changes the impedance of the probe, but also modulates (with the same rate) the reflection from the probe. A major challenge associated with MST is detecting and distinguishing the desired probe response in the ever-present reflections from surrounding structures and materials. This challenge can be overcome by incorporating a swept-frequency method into the measurements. A swept-frequency technique allows the use of the Fourier Transform method which results in separate detection of the reflection from the probe (similar to pulsed methods). Having the ability to discriminate the probe response renders the MST technique useful for multilayer structure applications as well. The probe can be placed in a given layer of a material, and the properties of that layer can be monitored (regardless of the presence of other layers). Additionally, the probe can be placed at an interface and changes in that interface (such as disbonding) can be detected. The ratio of the reflection from a probe, between the "on" and "off" states, has been shown to be a unique technique for evaluating properties of materials. This paper presents the basis and some results of applying swept-frequency MST for inspecting layered materials.

Meeting Name

IEEE Instrumentation and Measurement Technology Conference, 2008. IMTC 2008


Electrical and Computer Engineering

Keywords and Phrases

Electromagnetic Wave Scattering; Composite Materials; Condition Monitoring; Fourier Transforms; Inspection; Life Testing; Multilayers; Nondestructive Testing; Probes; Reinforced Concrete; Structural Engineering; Swept-Frequency Reflectometry

Document Type

Article - Conference proceedings

Document Version

Final Version

File Type





© 2008 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.