Mohammad Abdolrazzaghi

Microbead-assisted high resolution microwave planar ring resonator for organic-vapor sensing

A microbead-assisted planar microwave resonator for organic vapor sensing applications is presented. The core of this sensor is a planar microstrip split-ring resonator, integrated with an active feedback loop to enhance the initial quality factor from 200 to ∼1 M at an operational resonance frequency of 1.42 GHz. Two different types of microbeads, beaded activated carbon (BAC) and polymer based (V503) beads, are investigated in non-contact mode for use as gas adsorbents in the gas sensing device. 2-Butoxyethanol (BE) is used in various concentrations as the target gas, and the transmitted power (S21) of the two port resonator is measured. The two main microwave parameters of resonance frequency and quality factor are extracted from S21 since these parameters are less susceptible to environmental and instrumental noise than the amplitude. Measured results demonstrate a minimum resonance frequency shift of 10 kHz for a 35 ppm concentration of BE exposure to carbon beads and 160 kHz for the polymer based ad...

Robust Ultra-High Resolution Microwave Planar Sensor Using Fuzzy Neural Network Approach

In this paper, we develop a robust and fault-tolerant approach to microwave-based sensitive measurements using fuzzy neural network (FNN). Microwave chemic-identification, recently, is employing active planar ring resonators to enhance the resolutions significantly. However, in practice, when the technology of resolution improves, the results become more prone to minor variations in the measurement setup and user error. In order to eliminate these unwanted and uncontrollable deviations from the final allocations, we propose a novel and robust approach that uses more than one parameter out of measurements and incorporates FNN as a machine learning architecture at the post processing stage of sensing to obtain fault-tolerant classification. We have compared different membership functions used in the FNN and shown improvement in assigning accuracy from 49% (single parameter-dependent) up to 81.5% (three parameters-dependent) on an average of four materials, such as isopropanol-2 (IPA), ethanol, acetone, and water.

Enhanced Q double resonant active sensor for humidity and moisture effect elimination

In this paper, high-resolution ultra-high Q double resonant sensor is developed to eliminate humidity and moisture effect in microwave chemical sensing in uncontrolled environment. Double uncoupled split-ring resonators with close resonant frequencies are assisted with active circuitry to increase their quality factor from 51 and 54 up to 150k and 210k at 1.365 GHz and 1.6 GHz, respectively. The purpose of the second resonator is set to calibrate the erroneous effect of ambient humidity and sand moisture in measurement. Based on the proposed technique, root of mean-square-error of processed results of measuring water in humid air was significantly reduced from 169k down to 27k. Material detection with wet-sand surrounding was verified successfully and the materials impacts are completely distinguished from that of the wet sand.

Wireless Communication in Feedback-Assisted Active Sensors

A novel wireless high-resolution resonant-based microwave sensor is presented for chemical sensing applications. A combination of antenna with a planar microstrip resonator increases the flexibility, durability, and reliability while extending the application of the sensor to areas with limited access and harsh environments. The main core of this sensor is a passive planar resonator, which operates at 1.41 GHz and is reinforced by a regenerative active feedback circuitry. The regenerative active feedback loop compensates the power loss of the sensor and, as a result, provides an extremely high-quality factors. Four bow-tie slot antennas of the moderate gain of 5 dB, linearly polarized over the frequency span of 1.35-2 GHz is used to communicate in short range. The sensor model is implemented using the finite-element method and a complete set of simulation is presented. The simulation results are confirmed by the measurements for resonant profile variation in material sensing. The initial quality factor of the fabricated sensor, considering the antennas and resonator loss is Q ≈22000, which broadens the range of sensing platforms into classification of low concentrated (0.003125-0.1 g/mL) salt water as well as material detection of common chemicals such as IPA, acetone, ethanol, methanol, and water.

Strongly Enhanced Sensitivity in Planar Microwave Sensors Based on Metamaterial Coupling

Limited sensitivity and sensing range are arguably the greatest challenges in microwave sensor design. Recent attempts to improve these properties have relied on metamaterial (MTM)-inspired open-loop resonators coupled to transmission lines (TLs). Although the strongly resonant properties of the resonator sensitively reflect small changes in the environment through a shift in its resonance frequency, the resulting sensitivities remain ultimately limited by the level of coupling between the resonator and the TL. This paper introduces a novel solution to this problem that employs negative-refractive-index TL MTMs to substantially improve this coupling so as to fully exploit its resonant properties. A MTM-infused planar microwave sensor is designed for operation at 2.5 GHz, and is shown to exhibit a significant improvement in sensitivity and linearity. A rigorous signal-flow analysis of the sensor is proposed and shown to provide a fully analytical description of all salient features of both the conventional and MTM-infused sensors. Full-wave simulations confirm the analytical predictions, and all data demonstrate excellent agreement with measurements of a fabricated prototype. The proposed device is shown to be especially useful in the characterization of commonly available high-permittivity liquids as well as in sensitively distinguishing concentrations of ethanol/methanol in water.

A Microwave Ring Resonator Sensor for Early Detection of Breaches in Pipeline Coatings

A planar microwave resonator sensor is designed, customized, and fabricated to detect coating breaches in industrial steel pipelines. The sensor, which utilizes a ring-shaped resonator to maximize the sensitivity at its core, is tuned to 2.5 GHz with a quality factor of 280. In the setup, the sensor is grounded to a piece of steel pipeline with an Epoxy-100 coating, which provides the substrate beneath the microstrip structure. It is demonstrated that any change in the gap height between the substrate layer and the pipeline, from 0 to 3.5 mm, produces a significant resonant frequency variation and bandwidth change in the sensors response. The sensor structure demonstrates sensitivity and selectivity to air and water penetration to the breach. The sensor structure described in this work is a compact, low-cost solution and has potential for further miniaturization in mobile applications which may serve as a method for pipeline breach detection.

Sensitivity enhancement of split ring resonator based liquid sensors

Here, a planar microwave liquid sensor, including an embedded channel in the substrate is reported. The device has been designed to resonate at 5 GHz with a quality factor of 110. A comparison between the proposed structure and the conventional ones with fluidic channel on the surface of the resonator is made to demonstrate the sensitivity enhancement of the proposed design. Our comparison results regarding to sensitivity demonstrates a possibility of up to 400 % improvement for low permittivity materials while the channel is embedded inside the substrate. A very simple implementation process is also proposed.

Highly sensitive miniaturized bio-sensor using 2-layer double split ring resonators

THz biosensors are used to detect the presence of materials in Biomedical Science, especially thin DNA strands, therefore needs considerably high sensitivity. In this paper, we introduce a new structure made up of Metamaterials, which is used for identification of very thin analytes according to their dielectric constants. Procedures for lowering the resonant frequency and increasing the sensitivity of the sensor, simultaneously, are presented. High sensitivity of (Δf_r/f_r = 2.73% for Δε_r = 1), in average, is reported and 10 nm thick DNA (ε_r = 3.2) was detected due to miniaturization techniques.

Fast-forward solver for inhomogeneous media using machine learning methods: artificial neural network, support vector machine and fuzzy logic

Encountering with a nonlinear second-order differential equation including ϵr and μr spatial distributions, while computing the fields inside inhomogeneous media, persuaded us to find their known distributions that give exact solutions. Similarities between random distributions of electric properties and known functions lead us to estimate them using three mathematical tools of artificial neural networks (ANNs), support vector machines (SVMs) and Fuzzy Logic (FL). Assigning known functions after fitting with minimum error to arbitrary inputs using results of machine learning networks leads to achieve an approximate solution for the field inside materials considering boundary conditions. A comparative study between the methods according to the complexity of the structures as well as the accuracy and the calculation time for testing of unforeseen inputs, including classification, prediction and regression is presented. We examined the extracted pairs of ϵr and μr with ANN, SVM networks and FL and got satisfactory outputs with detailed results. The application of the presented method in zero reflection subjects is exemplified.

A Novel Technique for Determining the Adsorption Capacity and Breakthrough Time of Adsorbents Using a Noncontact High-Resolution Microwave Resonator Sensor

A newly developed noncontact high-resolution real-time microwave sensor was used to determine the breakthrough time and adsorption capacity of adsorbents/adsorbates with different dielectric properties. The sensor is a microwave microstrip planar resonator with an enhanced quality factor using a regenerative feedback loop operating at 1.4 GHz and an adjustable quality factor of 200-200000. Beaded activated carbon (BAC, microwave-absorbing) and a polymeric adsorbent (V503, microwave transparent) were completely loaded with 1,2,4-trimethylbenzene (nonpolar) or 2-butoxyethanol (polar). During adsorption, variations in the dielectric properties of the adsorbents were monitored using two microwave parameters; quality factor and resonant frequency. Those parameters were related to adsorption breakthrough time and capacity. Adsorption tests were completed at select relative pressures (0.03, 0.1, 0.2, 0.4, and 0.6) of adsorbates in the influent stream. For all experiments, the difference between the breakthrough time (t5%) and the settling time of the quality factor variation (time that the quality factor was 0.95 of its final value) was <5%. Additionally, a linear relationship between the final value of the resonant frequency shift and adsorption capacity was observed. The proposed noncontact sensor can be used to determine the breakthrough time and adsorption capacity.