TIME DOMAIN MEASUREMENT OF HIGH FREQUENCY COMPLEX PERMITTIVITY AND PERMEABILITY OF TRANSMISSION LINE ENCLOSED MATERIAL SAMPLE

• US 3,693,080 A
• Filed: 12/21/1970
• Issued: 09/19/1972
• Est. Priority Date: 12/21/1970
• Status: Expired due to Term

• Current Assignee: Alexander M. Nicolson, Gerald F. Ross
• Original Assignee: Alexander M. Nicolson, Gerald F. Ross
• Inventors: Ross, Gerald F., Nicolson, Alexander M.
• Primary Examiner(s): Corcoran, Robert J.
• Application Number:
  US05/099,948
• Time in Patent Office: 638 Days
• Field of Search: 324/57,58,58.5
• US Class Current: 324/638
• CPC Class Codes: G01N 22/00 Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more G01N3/00 - G01N17/00, G01N24/00 take precedence
• CPC Class Codes: G01R 27/2664 Transmission line, wave guide (closed or open-ended) or strip - or microstrip line arrangements

Abstract

The forward and back scattered energy of a sample exposed to an incident impulse of electromagnetic energy in a transmission line is sampled by a drift compensated sampling system and the incident wave and reflected and transmitted responses are employed in performing discrete Fourier transformations in a computation process yielding complex permittivity and complex permeability of the material of the sample.

Claims

1. Apparatus for measuring the high frequency permittivity and permeability characteristics of a transmission line-enclosed sample of material comprising:

impulse wave generator means for exciting said transmission line for generating in the presence of said sample corresponding forward and backward scattered waves, reflector means for reflecting said forward scattered wave through said sample of material, wave sampling means coupled to said transmission line between said impulse wave generator means and said sample of material, wave sample-and-hold means for controlling said wave sampling means and for holding representations of said impulse wave, said forward scattered wave, and said backward scattered wave, general purpose computing means responsive to said wave sampleand-hold means adapted to be programmed to compute said high frequency characteristics in response to said held wave representations, and display means responsive to said computing means for displaying said high frequency characteristics when computed.

2. Apparatus as described in claim 1 wherein the transmission propagation times between said impulse wave generator means and said wave sampling means, between said wave sampling means and the mid-point of said sample of material, and between the mid-point of said sample of material and said reflecting means are substantially in the ratio of 4 to 2 to 1.

3. Apparatus as described in claim 1 wherein said transmission line, in the vicinity of said sample of material comprises coaxial transmission line means having:

an outer conductor portion having a removable sector, and a removable inner conductor portion, said inner and outer conductor portions cooperatively supporting said sample of material when in place in said transmission line, and said sample of material being in the form of an apertured disk having substantially parallel sides.

4. Apparatus as described in claim 1 wherein said general purpose computing means is adapted to be programmed for:

digitizing said held wave representations of said impulse wave, of said forward scattered wave, and of said backward scattered wave, performing discrete Fourier transforms on said representations, computing from said Fourier transforms the respective reflection and transmission scattering coefficients of said material, and computing from said scattering coefficients said permittivity and permeability characteristics of said material.

5. Apparatus for measuring the high frequency permittivity and permeability characteristics of a transmission line enclosed sample of material comprising:

impulse wave generator means for exciting said transmission line, branching power dividing means having an interior junction with said transmission line responsive to said impulse wave generator means for combining said impulse wave with a delayed version of said impulse wave for forming a modified wave having first and second amplitude values, said first value characterizing a substantially zero slope portion of said modified wave, said second value characterizing a portion of said wave having a slope substantially greater than zero, said modified wave interacting with said sample of material for generating forward scattered waves, means for reflecting said forward scattered wave through said sample of material, wave sampling means coupled to said transmission line between said power divider means and said sample of material, wave sample-and-hold means for sampling and holding representations of said impulse wave, of said forward scattered wave, and of said backward scattered wave and utilizing said first and second reference amplitude values for compensating said wave sample-and-hold means for substantially eliminating the effects therein of drift, general purpose computer means for subjecting said sampled and held representations of saiD impulse, of said forward scattered wave, and of said backward scattered wave to respective discrete Fourier transformations and for calculating measures of said characteristics from said Fourier transformations.

6. Apparatus as described in claim 5 wherein said branching power dividing means includes a branching transmission line connected at said interior junction and shorted at its end opposite to said junction.

7. Apparatus as described in claim 6 wherein the respective transmission propagation times between said interior junction and said short of said shorted branch of said power divider, between said interior junction of said power divider and said wave sampling means, between said wave sampling means and the mid-point of said sample of material, and between the mid-point of said sample of material and said reflecting means are substantially in the ratio of 3 to 4 to 2 to 1.