A convenient method for complex permittivity measurement of thin materials at microwave frequencies

Abstract

A practical problem in the reflection method for measuring permittivity of thin materials is the difficulty in ensuring the sample is placed exactly at the waveguide flange. A small position offset of the dielectric slab will give rise to significant errors in calculating the permittivity. To circumvent this problem, a measurement method using a waveguide partially filled with a thin material slab has been developed. The material sample can be easily prepared and inserted into the guide through a longitudinal slot on the broad wall of the waveguide. Multiple material slabs can be measured rapidly because one does not have to disconnect the waveguide system for sample placement. The method is verified with measurement of Teflon, glass and FR4 fibreglass. The measured permittivity show good agreement with published data. Subsequently, the permittivity of a vegetation leaf was measured. The method presented in this paper is particularly useful in measuring the permittivity of a thin and narrow slab of natural materials such as a paddy leaf.

Measurement of Dielectric Constant of Thin Leaves by Moisture Content at 4mm Band

“…Chunk [13,14] reported some practical problems which have to be taken into account while measuring reflection and transmission. One of those problems is the difficulty to ensure the sample is placed exactly at the waveguide flange, since a small position offset of the dielectric sample will give rise to some errors in calculating the dielectric constant.…”

Permittivity Measurement of Thin Dielectric Materials From Reflection-Only Measurements Using One-Port Vector Network Analyzers

“…Due to their relative simplicity, nonresonant waveguide (or coaxial) transmission/reflection methods are presently the most widely used broadband measurement techniques [1]. These methods have effectively been applied to determine the relative complex permittivity (ε) of thin materials [9,12,[16][17][18]. It is not generally possible to locate thin samples to completely fill a coaxial line or rectangular waveguide section.…”

“…This is because transmission measurements take longitudinal averaging of variations in sample properties [21]. To overcome the problems arising from reflection S-parameters, transmission-only measurements can be employed [9,18]. Although the method in [18] does not require complete filling of the cross section of a waveguide section, it requires adequate sample thickness in order to obtain accurate measurement result.…”

“…To overcome the problems arising from reflection S-parameters, transmission-only measurements can be employed [9,18]. Although the method in [18] does not require complete filling of the cross section of a waveguide section, it requires adequate sample thickness in order to obtain accurate measurement result. As a solution to this problem, a transmission-only waveguide method can be utilized [9].…”

Thickness-Independent Complex Permittivity Determination of Partially Filled Thin Dielectric Materials Into Rectangular Waveguides

“…Various microwave techniques have been proposed to determine these properties of material under test [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. These methods can be divided into two groups as a) resonant and b) nonresonant methods [1].…”