Quasioptical system for material characterization in millimeter/submillimeter-wave domain
Event details
| Date | 01.06.2015 |
| Hour | 10:30 › 11:30 |
| Speaker | Dr. Alireza Kazemipour (Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany) |
| Location |
PPB 019
|
| Category | Conferences - Seminars |
Measurement of intrinsic material properties, such as the complex permittivity and permeability, is very important in many areas. The relative permittivity is important in microwave and millimeter-wave engineering (substrates and dielectric components), agriculture, material engineering, and others.
Different measurement techniques could be used for different frequency bands and applications. For very low-loss materials, the microwave cavity technique gives best results, however, it is limited to a single frequency and measurement in millimeter-wave bands is problematic.
Another technique is inserting the measured sample into a rectangular or cylindrical waveguide. The sample preparation is complicated at very high frequencies.
The broadband free-space measurement techniques circumvent the problem of the precise fit of the sample to the waveguide or cavity walls. A disadvantage is the need of a flat and homogeneous sample with relatively large dimensions to avoid diffraction effects. This method has long been possible for material properties measurement at microwave frequencies using a vector network analyzer (VNA). With the advance of measurement instrumentation, free-space systems for millimeter/submillimeter waves became possible as well. Systems for material characterization in the submillimeter bands were presented. These systems use complicated design with large parabolic mirrors or lenses, high-cost corrugated horns, and sophisticated micrometer positioners to perform the relevant free-space calibration. Due to the Gaussian beam approximation assumption, these systems are referred to as quasi-optical systems. Measurement of material properties at terahertz (THz) frequencies has long been performed in the time domain with use of ultrawideband pulses. In particular, most materials, especially organic ones, have their vibration and rotational modes in the THz band. The measurement accuracy of these systems in the sub-THz regime is rather low and with poor resolution and the quasi-optical VNA systems represent a low-cost and higher accuracy alternative.
We present an easy-made setup with classic pyramidal horn antennas together with a practical comprehensive calibration process and simple data extraction algorithm. The detailed data-extraction process, measurement uncertainty analysis, and actual electromagnetic field pattern on the material plane, are presented. The system uses compact-size mirrors to cover the wide frequency range from 50 to 500 GHz and a reliable simple calibration method without need for precise positioning.
Different measurement techniques could be used for different frequency bands and applications. For very low-loss materials, the microwave cavity technique gives best results, however, it is limited to a single frequency and measurement in millimeter-wave bands is problematic.
Another technique is inserting the measured sample into a rectangular or cylindrical waveguide. The sample preparation is complicated at very high frequencies.
The broadband free-space measurement techniques circumvent the problem of the precise fit of the sample to the waveguide or cavity walls. A disadvantage is the need of a flat and homogeneous sample with relatively large dimensions to avoid diffraction effects. This method has long been possible for material properties measurement at microwave frequencies using a vector network analyzer (VNA). With the advance of measurement instrumentation, free-space systems for millimeter/submillimeter waves became possible as well. Systems for material characterization in the submillimeter bands were presented. These systems use complicated design with large parabolic mirrors or lenses, high-cost corrugated horns, and sophisticated micrometer positioners to perform the relevant free-space calibration. Due to the Gaussian beam approximation assumption, these systems are referred to as quasi-optical systems. Measurement of material properties at terahertz (THz) frequencies has long been performed in the time domain with use of ultrawideband pulses. In particular, most materials, especially organic ones, have their vibration and rotational modes in the THz band. The measurement accuracy of these systems in the sub-THz regime is rather low and with poor resolution and the quasi-optical VNA systems represent a low-cost and higher accuracy alternative.
We present an easy-made setup with classic pyramidal horn antennas together with a practical comprehensive calibration process and simple data extraction algorithm. The detailed data-extraction process, measurement uncertainty analysis, and actual electromagnetic field pattern on the material plane, are presented. The system uses compact-size mirrors to cover the wide frequency range from 50 to 500 GHz and a reliable simple calibration method without need for precise positioning.
Practical information
- Informed public
- Free
Organizer
- Prof. P. Ricci
Contact
- Prof. P. Ricci