# Open Coaxial Resonator Type Microwave Dielectrometer

PATENT No.3691812

Open Coaxial Resonator Type Microwave Dielectrometer makes accurate measurement possible using an evanescent mode of an open coaxial resonator, which acts as a measurement probe.

When a sample material is placed on the probe, the evanescent electrical field leaks from the probe tip into the sample material. This electrical field changes with the dielectric properties of the material, which in turn changes the resonant frequency and the Q-factor of the whole cavity. The dielectric properties are then calculated from the changed resonance. The highly accurate measurement algorithm to compute the complex permittivity, uses the electromagnetic-field distribution and resonant characteristics of the evanescent mode computed by the 3D EM-field simulator, "CST MICROWAVE STUDIO".

Electric field distribution near the measuring point

Coaxial resonator

The technical article regarding the measurement principle of this system was presented in the IEEE Microwave Theory and Techniques.

R. Inoue, et al., "Data Analysis of the Extraction of Dielectric Properties From Insulating Substrates Utilizing the Evanescent Perturbation Method
", IEEE Trans. Microwave Theory Tech., vol. 54,no. 2, pp. 522-532, Feb. 2006.

### Specifications

(Provisional Figures)

Frequency range |
0.8 - 18GHz |

Frequency point |
5 discrete frequency points |

Measurement range |
ε: 1-15 tanδ: 0.001-0.1 |

Max. measurement error |
ε: ±1% tanδ: ±5% |

Sample Shape |
Arbitrary shape with at least one flat surface.
10mm × 10mm × 0.5mm or the larger. |

## FAQ

#### General

Q1. What is the open coaxial resonator type microwave dielectrometer ?

#### A1.

The open coaxial resonator type microwave dielectrometer is the system which measures dielectric properties at microwave frequencies. This system has 2 types, which use either a synthesized sweep oscillator (an alternative to a network analyzer) or a network analyzer.

Q3.
What is the difference between this system and the conventional system?

#### A3.

The strongest point of the microwave dielectrometer is its ease of use. This system enables fast and non-destructive measurement of dielectric materials, because the probe can handle materials of any shapes as long as there is one flat surface. In addition, the microwave dielectrometer has highly accurate measurement software. By simply placing the material on the surface of the probe, and following an easy step-by-step operation of the software wizard, the measurement is achieved for complex dielectric properties very accurately and very simply.
(*Please see the movies titled "1.AET Microwave Dielectrometer" and "4.Actual Measurement" on the top page.)

Q4.
What is the difference between this system and the conventional system?

#### A4.

The tool to measure is a unique measurement probe called a "coaxial resonator"(PATENT No.3691812). The measurement can be chosen at a five-point simultaneous measurement mode or single-frequency measurement mode.

Type1: 0.8/2.45/4.2/5.8/7.6GHz Type2: 1/3/5/7/9GHz

Type3: 2/6/10/14/18GHz

Choose the specific frequency from the "frequency setting" list.

The result of 5-points simultaneous measurement

The probe can handle materials of any shapes as long as there is one flat surface. The non-destructive measurement is
achieved by simply placing the material on the surface of the probe. It is suitable to measure for various solid-state samples such as plastics, ceramics, various resin, liquid crystal polymer, connector, glass, and others.

(*Please see the movie titled "

3.Open Coaxial Probe" on the top page.)

Q5.
What is the measurement principle using this probe?

#### A5.

If a sample material is placed on the probe, the evanescent electrical field leaks from the probe tip into the sample material. This electrical field changes with the dielectric properties of the material, which in turn changes the resonant frequency and the Q factor of the whole cavity. The dielectric properties (εr, tanδ) are then calculated from the changed resonance.

(*Please see the movie titled "3.Open Coaxial Probe" on the top page.)

Q6.
How good is the accuracy and what is important for accurate measurements?

#### A6.

The random error of the epsilon is estimated to be less than 1%, and the error of the tangent delta is less than 5%. The absolute accuracy will be confirmed by the reference materials. Two different materials are used as references. By calculating the relative difference between the measurement results of the references and a sample material, external error sources (eg.room temperature) are eliminated. Most important for accurate measurements is a firm contact between the sample material and the surface of the coaxial probe. Only a tiny gap might significantly change measurement results. Microwave Dielectrometer has a vacuum absorption attachment equipped on the probe tip. The sample contacts with the probe firmly and the stable and accurate measurement is possible.
(*Please see the movie titled "1.AET Microwave Dielectrometer" on the top page.)

#### Materials to be tested

Q1. What are the requirements for the sample material?

#### A1.

The materials to be tested are required to have at least one flat and smooth surface (larger than 10mm × 10mm). The sample shape is arbitrary and the sample dimension should be larger than 10mm × 10mm × 0.5mm. To measure thin film materials, the film have to be stacked to get a total thickness greater than 0.5mm.

Q3.
What is the reason of the limitation of the properties?

#### A3.

The evanescent field does not penetrate deep enough into high epsilon materials, which makes an accurate measurement of the dielectric constant difficult. For small loss tangent, the total loss of the probe is relatively higher than the conventional cavity resonator because of the leakage of the evanescent field. This is the main reason for the difficulty of measuring very small dielectric losses. We recommend the resonant cavity type microwave dielectrometer for the measurement of the sample with high epsilon and very small dielectric losses.

#### System Option

Q1. What are the reference materials?

#### A1.

Microwave Dielectormeter uses the two different reference materials with well known dielectric properties. By calibrating the measurement parameters with these materials, this system achieves a quantitative accuracy. We use the two single crystals of SiO2 and MgO as the reference materials.

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