On the Application of Microwave Calibration-Independent Measurements for Noninvasive Thickness Evaluation of Medium- Or Low-Loss Solid Materials

Abstract

Abstract-Microwave methods require some sort of calibration before physical (thickness, flaw, etc.) and electrical (permittivity, permeability, etc.) measurements of materials. It is always attractive to devise a method which not only eliminates this necessity but also saves time before measurements. Microwave calibration-independent measurements can be utilized for this goal. However, in the literature, these measurements are only applied for electrical measurements of materials. In this research paper, we investigate the performance of microwave calibration-independent measurements for thickness evaluation of dielectric materials to increase the potential of available microwave techniques for thickness evaluation of dielectric materials. We derive an explicit expression for thickness estimation of dielectric materials from calibration-independent measurements for the adopted calibration-independent technique. We also propose a criterion for increasing the performance of measurements. We conducted thickness measurements of six dielectric specimens with different lengths to validate the derived expressions and the proposed criterion for thickness measurements.

A New Method for Evaluation of Thickness and Monitoring Its Variation of Medium- And Low-Loss Materials

“…First, the accuracy of physical measurements increases for thicker samples. Second, the ability of any measurement instrument to resolve or detect measurements at sequentially and linearly separated frequencies for thicker samples is greater than for thinner samples [33]. In addition, we observed that the accuracy of thickness evaluation for Plexiglas slabs is better than that of PTFE slabs.…”

“…The microwave methods generally applied to materials testing and evaluation are free-space [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], waveguide transmission line [25][26][27][28][29][30][31][32][33], and open-ended waveguide coaxial methods [34][35][36][37][38][39][40][41][42][43]. While open-ended waveguide or coaxial (or parallel plate) methods are very sensitive to materials' (and composite structures') properties (thickness, disbonding, delamination, and etc.…”

“…Waveguide transmission-line methods are one of the most accurate non-resonant methods [25][26][27][28][29][30][31][32][33]. Besides, measurements by these methods are highly repetitive.…”

Rubber Tire Dust-Rice Husk Pyramidal Microwave Absorber

“…The dielectric constant is equivalent to relative permittivity (ε r ), or the absolute permittivity (ε) is relative to the permittivity of free space (ε 0 ) [56][57][58][59][60][61][62][63][64][65]. The dielectric constant of a material also affects the velocity of microwave signals when it moves through the material.…”

On the microwave photonics based pulsed-time-of-flight techniques in the measurement of the thickness of dielectric sheets

“…Microwave measurements are preferred in various applications such as defining material properties [1], microwave radars [2], measurement of the frequency response of RF and millimeter wave circuits and components, and characterizing radio channels [3]. This is due to the good penetration properties of microwaves.…”