This work presents a planar microwave resonator sensor equipped with vertically self-aligned TiO2 nanotubes to enable real-time and contactless liquid characterization. The microwave sensor operates based on detecting a resonator response as it changes under exposure to UV light. This was used for liquid characterization by quantifying the transmission of ultraviolet (UV) light through a liquid sample and its subsequent absorbance by the TiO2 nanotube membrane. A microwave split ring resonator (SRR) was designed and simulated to operate with a resonant frequency of 8.73 GHz, resonant amplitude of -12 dB, and a quality factor of 103. The SRR was fabricated alongside an anatase-TiO2 nanotube membrane with a nanotube length of 20 μm, a wall thickness of 10 nm, and a tube diameter of 120 nm. The membrane was placed within the ring gap of the resonator to absorb any transmitted UV light which in turn would alter its dielectric properties. In this way, the designed sensor measured the ultraviolet transmission of a solution of S1813 photoresist in ethylene glycol (EG) and related the solvent concentration to a change in the transmission profile, without requiring contact or near-field proximity between the resonator sensor and the solution. Measuring different concentrations of S1813 photoresist in ethylene glycol, ranging from 0 to 100 v/v%, resulted in accurately calculated sensitivities of 0.18 MHz/%, 0.029 dB/%, and 0.45/% in resonant frequency, resonant amplitude, and quality factor, respectively. The achieved integration of TiO2 nanotube membranes for liquid characterization by analyzing microwave property variation may offer unique avenues for real-time liquid and UV detection and enable more comprehensive liquid and chemical analysis in comparison to conventional microwave sensor devices.

TiO2 nanotube-integrated microwave planar resonator sensor for ultraviolet transmission-based liquid characterization

This study proposes a single-port dual-band independent microwave sensor for detecting solid materials. The sensor structure consists of a pair U-shaped resonators connected by a power divider and a microstrip feed line with an impedance of 50 Ohms with two different sensing hotspots. The <inline-formula> <tex-math notation="LaTeX">$1^{\text {st}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$2^{\text {nd}}$ </tex-math></inline-formula> resonators operate at a frequency of 1.200 GHz and 2.100 GHz, respectively. The type of material under test (MUT) is a standard material with a size of 10 mm <inline-formula> <tex-math notation="LaTeX">$\times10$ </tex-math></inline-formula> mm (RO5880, RO4003C, and FR4). The proposed sensor had a very high accuracy compared with both of using permitivitty from datasheet and calibrated frequency from simulation for the <inline-formula> <tex-math notation="LaTeX">$1^{\text {st}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$2^{\text {nd}}$ </tex-math></inline-formula> resonator, respectively. Moreover, the pair of the U-shaped resonators had independent performances and they did not affect each other when the MUT was loaded. Furthermore, it can also operate with single-port measurement, which is a more efficient resource. Finally, the proposed microwave sensor can be a promising solution for detecting different permittivity of solid materials independently with high accuracy for applications such as the food industry, material quality control, and biomedical.

Dual-Band Independent Permittivity Sensor Using Single-Port With a Pair of U-Shaped Structures for Solid Material Detection

Buildup of saltwater ice can cause serious issues in many industries if not identified. This work presents a comparison between electrically and magnetically coupled planar microwave resonators for saltwater ice detection applications. Due to the highly coupled nature of both sensors, the frequency splitting phenomenon occurs resulting in each sensor having two resonant frequencies. The proposed electrically coupled resonator has operational frequencies of 4.726 GHz and 4.942 GHz whereas the magnetically coupled resonator has operational frequencies of 4.647 GHz and 4.960 GHz. The quality factor of the low and high frequency for the electrically coupled resonator were 260 ± 2 and 175 ± 2 respectively and were 195 ± 2 and 260 ± 2 respectively for the magnetically coupled resonator. The sensitivity of each sensor was investigated through simulation. Experiments were conducted using reverse osmosis (RO) water and saltwater with 5% and 10% salt concentrations. These experiments demonstrated the magnetically coupled sensor to be sensitive to the formation of both RO ice and saltwater ice, whereas the electrically coupled sensor could only detect the presence of RO ice due to the increased conductivity of saltwater. This magnetically coupled sensor is a proof of concept for saltwater ice sensing and is well suited for the application due to its high sensitivity, low-cost, and real-time sensing capabilities. 

Magnetically coupled planar microwave resonators for real-time saltwater ice detection

Buildup of saltwater ice can cause serious issues in many industries if not identified. This work presents a comparison between electrically and magnetically coupled planar microwave resonators for saltwater ice detection applications. Due to the highly coupled nature of both sensors, the frequency splitting phenomenon occurs resulting in each sensor having two resonant frequencies. The proposed electrically coupled resonator has operational frequencies of 4.726 GHz and 4.942 GHz whereas the magnetically coupled resonator has operational frequencies of 4.647 GHz and 4.960 GHz. The quality factor of the low and high frequency for the electrically coupled resonator were 260±2 and 175±2 respectively and were 195±2 and 260±2 respectively for the magnetically coupled resonator. The sensitivity of each sensor was investigated through simulation. Experiments were conducted using reverse osmosis (RO) water and saltwater with 5% and 10% salt concentrations. These experiments demonstrated the magnetically coupled sensor to be sensitive to the formation of both RO ice and saltwater ice, whereas the electrically coupled sensor could only detect the presence of RO ice due to the increased conductivity of saltwater. This magnetically coupled sensor is a proof of concept for saltwater ice sensing and is well suited for the application due to its high sensitivity, low-cost, and real-time sensing capabilities.

Magnetically coupled Planar Microwave Resonators for Real-Time Saltwater Ice Detection

In this paper, a photo-excited switchable terahertz metamaterial (MM) polarization converter/absorber has been presented. The switchable structure comprises an orthogonal double split-ring resonator (ODSRR) and a metallic ground, separated by a dielectric spacer. The gaps of ODSRR are filled with semiconductor photoconductive silicon (Si), whose conductivity can be dynamically tuned by the incident pump beam with different power. From the simulated results, it can be observed that the proposed structure implements a wide polarization-conversion band in 2.01–2.56 THz with the conversion ratio of more than 90% and no pump beam power incident illuminating the structure, whereas two absorption peaks operate at 1.98 THz and 3.24 THz with the absorption rates of 70.5% and 94.2%, respectively, in the case of the maximum pump power. Equivalent circuit models are constructed for absorption states to provide physical insight into their operation. Meanwhile, the surface current distributions are also illustrated to explain the working principle. The simulated results show that this design has the advantage of the switchable performance afforded by semiconductor photoconductive Si, creating a path towards THz imaging, active switcher, etc.

Photo-Excited Switchable Terahertz Metamaterial Polarization Converter/Absorber

In this paper, a sensor using modified Split Ring Resonators (SRRs) is designed, simulated, fabricated, and used for advanced investigation and precise measurements of the real part and imaginary part solid dielectrics’ permittivity. Adding vertical strips tightly coupled to the outer ring of the SRR leads to the appearance of two resonant frequencies at 1.24 GHz and 2.08 GHz. This modified geometry also assures an improved sensitivity. Using the full wave electromagnetic solver, both the unloaded and loaded sensors are investigated. The numerical simulations are used to develop a mathematical model based on a curve fitting tool for both resonant frequencies, allowing to obtain analytical relations for real and imaginary parts of permittivity as a function of the sample’s thickness and quality factor. The sensor is designed and fabricated on 1.6 mm thick FR-4 substrate. The measurements of different samples, such as transparent glass, acrylic glass, plexiglass, and Teflon, confirm that the modified SRR sensor is easy to implement and gives accurate results for all cases, with measurement errors smaller than 4.5%. In addition, the measurements highlight the importance of the second resonant frequency in the cases in which numerical limitations do not allow the usage of the first resonant frequency (1 mm thick sample).

Modified Split Ring Resonators Sensor for Accurate Complex Permittivity Measurements of Solid Dielectrics

The ionosphere is the region in the space that is restricted in distance above the Earth and it contains free electrons and ions that disturb the electromagnetic waves when the waves pass through it. Several models were used to investigate the ionosphere conditions. These models use mainly two parameters to evaluate the perturbations in the ionosphere. These parameters are the electron density and TEC (Total Electron Content) which they control the ability of reflections frequencies in the ionosphere. The propagation characteristics were investigated. This paper uses four models to estimate the ionosphere perturbations. The goal of this paper was to choose the most efficient model that gives the best image that evaluates the ability of reflections shortwaves in the ionosphere. All these computations did not take the Sunspot number in considerations.

Investigation of the Different Models Performance for Evaluating the Disturbance in the Ionosphere

A microstrip highly sensitive differential sensor for complex permittivity characterization of urine samples was designed, fabricated and tested. The sensing area contains two pairs of open-stub resonators, and the working frequency of the unloaded sensor is 1.25 GHz. The sensor is easily implemented on an affordable substrate FR-4 Epoxy with a thickness of 1.6 mm. A Teflon beaker is mounted on the sensor without affecting the measurements. Numerically, liquid mixtures of water and urine at different percentages were introduced to the proposed sensor to evaluate the frequency variation. The percentage of water content in the mixture varied from 0% (100% urine) to 100% (0% urine) with a step of 3.226%, thus giving 32 data groups of the simulated results. Experimentally, the mixtures of: 0% urine (100% water), 20% urine (80% water), 33% urine (66% water), 50% urine (50% water), 66% urine (33% water), and 100% urine (0% water) were considered for validation. The complex permittivity of the considered samples was evaluated using a nonlinear least square curve fitting in MATLAB in order to realize a sensing sensitivity of about 3%.

Differential Microstrip Sensor for Complex Permittivity Characterization of Organic Fluid Mixtures

In this paper a new approach for first order Chebyshev parallel coupled Bandpass filter resonant at 1 GHz is presented to obtain better results (wideband rejection, high selectivity and low bandpass insertion loss) compared to conventional design. The proposed filter (a tri-formation consisting of CSRR, SRR and stubs of stepped impedance are loaded microstrip resonator) can be configured, by laying split ring resonator (SRR) and complementary split ring resonator (CSRR) with 50 Ω microstrip lines, in addition to effect of loading two stubs of stepped impedance around center of midline microstrip with impedance line 55.36 Ω of parallel coupled. The proposed filter produces high selectivity from passband to stopband transition equals to 307.5 dB/GHz and an excellent wide stopband performance extend from 1.22 GHz to 5 GHz (harmonics repression till for 5 ƒ0); all are bellow -20 dB excepting one transmission zero of -19 dB, that can be eliminate the harmonic superior frequencies without using any external Bandstop filter. Also, enhancement low bandpass insertion loss level, where it reaches 0.25 dB at fundamental centered frequency (ƒ0 = 0.96 GHz) with 21% bandwidth. The proposed filter is designed and simulated with computer aided of Ansoft HFSS software package which ordinarily used in microwave application.

First order parallel coupled BPF with wideband rejection based on SRR and CSRR

the ionosphere can be described as a complex natural world. The whole edifice of contemporary science stands on the shoulders satellite communication interconnected theories. The ionosphere has crude arguments. The ionosphere is a giant layer that extends from 80 to 1000 km above Earth. The ionosphere contains free electrons and ions. These particles contribute to disturb the propagation of the electromagnetic waves that pass through the ionosphere. These particles could refract or disperse the electromagnetic waves that pass through the ionosphere. This paper will study the impact of the reflection and the absorption in the ionosphere for the propagation of the electromagnetic waves and what is the relation among them. The comprehension of absorption of the ionosphere is coming from VOACAP model. VOACAP model is an indirect track to extract the estimation values of the absorption in the ionosphere.

Amer Abbood Al-Behadili

Papers

Modified Split Ring Resonators Sensor for Accurate Complex Permittivity Measurements of Solid Dielectrics

Investigation of the Different Models Performance for Evaluating the Disturbance in the Ionosphere

Differential Microstrip Sensor for Complex Permittivity Characterization of Organic Fluid Mixtures

First order parallel coupled BPF with wideband rejection based on SRR and CSRR

Evaluation of the Strenght of Reflection and Dispersion of High Frequency in the Ionosphere by VOACAP model