Tunable cavity for material measurement

An apparatus for measuring material properties of a material under test comprising:

• a first tapered coaxial transmission line having a conductive first inner wall and a conductive first outer wall, wherein the first tapered coaxial transmission line is tapered such that a ratio of a radius of the first inner wall and a radius of the first outer wall is constant along a length of the first tapered coaxial transmission line;
• a coaxial tunable cavity having a first end and a second end and having a conductive second inner wall and a conductive second outer wall;
• wherein the second inner wall has a first radius equal to a maximum radius of the first inner wall and the second inner wall is connected on the first end of the coaxial tunable cavity to the first inner wall, and the second outer wall has a second radius equal to a maximum radius of the first outer wall and the second outer wall is connected on the first end of the coaxial tunable cavity to the first outer wall;
• a voltage-tunable reactive grid at a first location in the coaxial tunable cavity between the first end and the second end of the coaxial tunable cavity;
• a semi-reflective reactive grid at a second location in the coaxial tunable cavity between the voltage tunable reactive grid and the second end of the coaxial tunable cavity;
• wherein the apparatus for measuring the material properties of the material under test is configured to measure a relative permittivity and a relative permeability of the material under test placed between the voltage-tunable reactive grid and the semi-reflective reactive grid by tuning the tunable cavity to a desired resonant frequency, transmitting a first electromagnetic wave through the tapered coaxial transmission line to the coaxial tunable cavity, and analyzing a second electromagnetic wave received from the second end of the coaxial tunable cavity.

A method for measuring material properties of a material under test comprising:

• providing:
• a tapered coaxial transmission line having a conductive first inner wall and a conductive first outer wall, wherein the tapered coaxial transmission line is tapered such that a ratio of a radius of the first inner wall and a radius of the first outer wall is constant along a length of the tapered coaxial transmission line;
• a coaxial tunable cavity having a first end and a second end and having a conductive second inner wall and a conductive second outer wall;
• wherein the second inner wall has a first radius equal to a maximum radius of the first inner wall and the second inner wall is connected on the first end of the coaxial tunable cavity to the first inner wall, and the second outer wall has a second radius equal to a maximum radius of the first outer wall and the second outer wall is connected on the first end of the coaxial tunable cavity to the first outer wall;
• a first conductive annular ring coupled to the second inner wall;
• a second conductive annular ring coupled to the second outer wall, wherein the second conductive annular ring is concentric with the first conductive annular ring;
• at least one capacitor coupled between the first conductive annular ring and the second conductive annular ring;
• and
• a voltage-tunable reactive grid at a location in the coaxial tunable cavity between the first end of the coaxial tunable cavity and the first conductive annular ring and the second conductive annular ring;
• and
• measuring a relative permittivity and a relative permeability of the material under test placed between the first conductive annular ring and the second conductive annular ring and the voltage-tunable reactive grid by tuning the coaxial tunable cavity to a desired resonant frequency, transmitting a first electromagnetic wave through the tapered coaxial transmission line to the coaxial tunable cavity, and analyzing a second electromagnetic wave received from the tapered coaxial transmission line.

A method for measuring material properties of a material under test comprising:

• providing:
• a first tapered coaxial transmission line having a conductive first inner wall and a conductive first outer wall, wherein the first tapered coaxial transmission line is tapered such that a ratio of a radius of the first inner wall and a radius of the first outer wall is constant along a length of the first tapered coaxial transmission line;
• a coaxial tunable cavity having a first end and a second end and having a conductive second inner wall and a conductive second outer wall;
• wherein the second inner wall has a first radius equal to a maximum radius of the first inner wall and the second inner wall is connected on the first end of the coaxial tunable cavity to the first inner wall, and the second outer wall has a second radius equal to a maximum radius of the first outer wall and the second outer wall is connected on the first end of the coaxial tunable cavity to the first outer wall;
• a voltage-tunable reactive grid at a first location in the coaxial tunable cavity between the first end and the second end of the coaxial tunable cavity;
• and
• a semi-reflective reactive grid at a second location in the coaxial tunable cavity between the voltage tunable reactive grid and the second end of the coaxial tunable cavity;
• and
• measuring a relative permittivity and a relative permeability of the material under test placed between the voltage-tunable reactive grid and the semi-reflective reactive grid by tuning the tunable cavity to a desired resonant frequency, transmitting a first electromagnetic wave through the tapered coaxial transmission line to the coaxial tunable cavity, and analyzing a second electromagnetic wave received from the second end of the coaxial tunable cavity.