Phase Method for Visualization of Hidden Dielectric Objects in the Millimeter Waveband

Abstract

A method of detecting dielectric objects hidden behind an opaque barrier located on a reflective background, based on the distortion of interference fringes, is proposed in this article. Experiments conducted in the millimeter wavelength range demonstrated the effectiveness of the method under consideration, which does not require a holographic image reconstruction. Such a system can be classified as contour imaging.

Measurements of Small Frequency Differences by Dual Mode 4 MHz Quartz Sensors

“…In such a way, extremely low changes of reactance due to a change in some external (nonelectrical) physical quantity can be detected (for capacitance changes in a region of zF and inductance changes in a region of pH), which is applicable for strain sensing, nanopositioning, measurements of an eccentric motion, dielectric properties of liquids and density of liquids, bacterial adhesion, middle-ear hearing devices, visualization of hidden dielectric objects, etc. [ 4 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Because the quartz crystal-based sensors transform a reactance into a frequency, they are applicable in biosensing, medicine and specific measurements in chemistry [ 24 , 25 , 26 , 27 , 28 ].…”

“…However, when we measure the frequency difference (the crystals in the oscillator act as sensors), the measurement error depends on the chosen method [ 30 ]. If changes of the equivalent circuit of the quartz crystals are in the aF or zF region (in the case of the capacitive effect) or in the pH region (in the case of an inductive effect), changes in the resonant frequency, which are typical in measurements of a mechanical displacement, nanopositioning, eccentric motion, strain sensing, dielectric properties of liquids and density of liquids, low pressure, etc., are very low [ 4 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ]. It is of crucial importance that these small changes of the resonant frequency are measured as accurately as possible, before they are transformed into the measured quantity.…”

Multiple Quartz Crystals Connected in Parallel for High-Resolution Sensing of Capacitance Changes

“…Because the change in frequency is measurable already for extremely low changes in the reactance (for capacitance changes in the region of aF and zF), the method is useful for several applications, such as mechanical displacement, nanopositioning, eccentric motion, strain sensing, dielectric properties of liquids, density of liquids, small volumes, low pressure, etc. [10][11][12][13][14][15][16][17][18]. In addition, when the reactance-tofrequency conversion is used, quartz crystals are applicable as biosensors, in medicine and at specific chemical measurements [14,[19][20][21][22][23][24].…”