In-situ Measurement of Electromagnetic properties of Material

The (EM) characterization of materials is of interest to a variety of research areas including the detection of buried objects. Conventional measurement techniques were focused on measuring only the complex permittivity of the material under test while their magnetic properties (permeability) were assumed to be unity. Recent interests on characterizing permeable materials, such as volcanic soil, make measurement of both the permittivity (ε*) and the permeability (μ*) of material equally important for accurate and reliable interpretation of data and cost effective detection and classification of buried targets.

In order to measure the electromagnetic properties of the materials at microwave frequencies, the reflection/transmission methods are required to estimate both complex permittivity and permeability over broadband frequency ranges. Beside the conventional off-line (laboratory) measurement method, in-situ method of material characterization complex is essential to extract accurate material characteristics without disturbing material’s environmental properties. Our group has recently developed a novel in-situ and broadband probe (40 MHz – 1 GHz) for material characterization including both the complex permittivity and permeability measurements [27]. The probe design uses two sections of multi-conductor TEM transmission lines and unique post processing algorithm for the determination of both ε* and μ* from S-parameters measurements. The in-situ probe development (see Fig. 1) involves the design of junctions and transitions to achieve good impedance matching throughout the system. Using numerical simulation, the number and diameter of the outer conductors were optimized to minimize radiation losses and undesired higher mode. Prototype probe was manufactured and experimentally tested to evaluate its performance. Broadband In-situ probes which can cover up to 10 GHz or lower to 100 KHz are being designed and their prototype will be manufactured and tested.

Fig. 1. (a) Two sections of coaxial probe are joined across the undisturbed soil section of interest, (b) Photograph of the developed prototype of the in-situ probe.

Deliverables & milestones

  1. Simulation of the multi-conductor TEM transmission line and optimize the configuration.
  2. Development of the post-processing and calibration algorithm and their verification using simulation.
  3. Prototypes of multi-conductors TEM waveguide and transient structure to verify the simulation results.
  4. Separate prototype will be constructed to cover different frequency bandwidth.

 

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