Microstrip Ring Resonator for Soil Moisture Measurements

Accurate determination of spatial soil moisture distribution and monitoring its temporal variation have a significant impact on the outcomes of hydrologic, ecologic, and climatic models. Development of a successful remote sensing instrument for soil moisture relies on the accurate knowledge of the soil dielectric constant (epsilon(sub soil)) to its moisture content. Two existing methods for measurement of dielectric constant of soil at low and high frequencies are, respectively, the time domain reflectometry and the reflection coefficient measurement using an open-ended coaxial probe. The major shortcoming of these methods is the lack of accurate determination of the imaginary part of epsilon(sub soil). In this paper a microstrip ring resonator is proposed for the accurate measurement of soil dielectric constant. In this technique the microstrip ring resonator is placed in contact with soil medium and the real and imaginary parts of epsilon(sub soil) are determined from the changes in the resonant frequency and the quality factor of the resonator respectively. The solution of the electromagnetic problem is obtained using a hybrid approach based on the method of moments solution of the quasi-static formulation in conjunction with experimental data obtained from reference dielectric samples. Also a simple inversion algorithm for epsilon(sub soil) = epsilon'(sub r) + j(epsilon"(sub r)) based on regression analysis is obtained. It is shown that the wide dynamic range of the measured quantities provides excellent accuracy in the dielectric constant measurement. A prototype microstrip ring resonator at L-band is designed and measurements of soil with different moisture contents are presented and compared with other approaches

Planar Microwave Sensors for Accurate Measurement of Material Characterization: A Review

Microwave sensor is used in various industrial applications and requires highly accurate measurements for material properties. Conventionally, cavity waveguide perturbation, free-space transmission, open-ended coaxial probe, and planar transmission line technique have been used for characterizing materials. However, these planar transmission lines are often large and expensive to build, further restricting their use in many important applications. Thus, this technique is cost effective, easy to manufacture and due to its compact size, it has the potential to produce sensitivity and a high Q-factor for various materials. This paper reviews the common characteristics of planar transmission line and discusses numerous studies about several designs of the microstrip resonator to improve the sensor performance in terms of the sensitivity and accuracy. This technique enables its use for several industrial applications such as agriculture and quality control. It is believed that previous studies would lead to a promising solution of characterizing materials with high sensitivity, particularly in determining a high Q-factor resonator sensor

Soil moisture sensors based on metamaterials

In this paper novel miniature metamaterial-based soil moisture sensors are presented. The sensors are based on resonant-type metamaterials and employ split-ring resonators (SRR), spiral resonators and fractal SRRs to achieve small dimensions, high sensitivity, and compatibility with standard planar fabrication technologies. All these features make the proposedsensors suitable for deployment in agriculture for precise mapping of soil humidity

Microwave nondestructive evaluation of aircraft radomes

As the aviation industry continues to experience increased demand on maintenance turn-around time with decreased budgets, the airlines in particular seek advances in cost and efficiency for inspection technology. Such improvements not only increase aviation safety, but also lead to significant cost savings and avoidances. One particular inspection need is that of aircraft radomes, often found as the nosecone such as that seen in Figure 1.1, housing the plane\u27s weather radar. This structure, fabricated out of low-loss/permittivity composite materials (such as fiberglass), must appear as electrically transparent as possible to the radar. Like a window to the human eye, any variations (in the form of changes in the radome\u27s electrical permittivity) or excess material will make sensing the outside world through the structure difficult. Defects such as water ingression, excess paint, and impact damage hinder the radar\u27s ability to sense accurately. No field-ready technique exists to evaluate the electrical properties or electrical consistency of the radome

Microwave reflectometer for soil moisture and permittivity measurement

Microwave sensors are commonly used for aquametry measurements due to strong tendency of water molecule in absorbing microwave signals. Nowadays, meter-based microwave system is in demand as more applications need concept of being portable and simple. This thesis presents a microwave reflectometer, which operates between 2.2 GHz and 4.4 GHz. It can measure soil moisture content, m.c. up to 26 % with mean deviation between predicted and actual m.c. determined at ± 2.0 %. Five common soil samples found in southern region of Peninsular Malaysia, Johor were characterized based on macroscopic and microscopic experiments. Throughout the research, four microstrip ring resonantor sensors operating between 2.2 GHz and 4.4 GHz were designed with different angles of microstrip bends. (Conventional Sensor = 0.98 rad., Sensor A = 1.34 rad., Sensor B = 1.57 rad., and Sensor C = 1.64 rad.). Sensor B was chosen as the soil sensor. A critical study on the use of microstrip ring resonator sensors for the determination of both permittivity, er and m.c. from the measured scattering parameters (S-parameters) in conjunction with E5071C vector network analyzer (VNA) was presented. The relationship between the measured er and m.c. obtained from the oven drying method was established. From the results, it was observed that two dielectric relaxation conditions (bound and free water) exist in soil-water mixture. A semi-empirical equivalent lumped element model was created based on simulation data obtained from Microwave Office (AWR) software. The predicted er results from the model agree with the measured data using commercial HP85070D dielectric probe. The model successfully estimated er for the five common soil types with error of 2.5 %. By using inverse algorithm from the model, m.c. was predicted and was in good agreement with the standard oven drying method with its average error within ± 1.5 % for all soil samples. In general, microwave reflectometer with the proposed MRR sensor, provide nondestructive measurement for rapid determination of soil m.c. and er

Embeddable Soil Moisture Content Sensor based on Open–end Microwave Coaxial Cable Resonator

In This Paper, We Propose and Demonstrate a Novel Corrosion-Resistant, Embeddable Open-End Coaxial Cable Soil Moisture Sensor. This Microwave Resonator is Constructed using Two Reflectors Along the Coaxial Line. the First Reflector is a Metal Post at the Signal Input End, Short-Circuiting the Inner Conductor to the Outer Conductor. the Second Reflector Comprises a Welded Metal Plate Parallel to the Open-End of the Coaxial Line, Maintaining a Fixed Gap. a Moisture-Sensitive Polyvinyl Alcohol (PVA) Film is Inserted into This Gap. the Resonance Frequency of the Open-End Coaxial Cable Resonator is Highly Dependent on the Fringe Capacitance, Which Varies with Soil Moisture Levels. as Such, Tracking Resonance Frequency Changes Allows for Correlation with Soil Moisture Fluctuations. We Provide a Detailed Discussion of the Embeddable Open-End Microwave Coaxial Cable Resonator (EOE-MCCR) Mathematical Model and a Proof of Concept for Soil Moisture Measurement. the Demonstration Experiments Investigate Soil Moisture Content Ranging from 4% to 24%. the Prototype Device Exhibits a Soil Moisture Measurement Sensitivity of 0.76MHz% for Soil Moisture between 4% and 10%, and 1.44MHz% for Soil Moisture between 10% and 24%. the Soil Moisture Sensor Presented Here is Robust, Easy to Manufacture, Chemically Resistant, Low-Cost, and Suitable for Long-Term Applications and Potential Industrial Uses. This Innovative Sensor is Ideal for Sensing Applications in Harsh Environments, Advancing the Field of Chemical Trace Sensing

Metamaterial-Based Sensor Design Using Split Ring Resonator and Hilbert Fractal for Biomedical Application

In this research, a simple and efficient approach is presented to design a metamaterial-based sensitive sensor for biomedical applications. The metamaterial based sensor is designed to differentiate between different types of cancer cell lines based on their electrical properties. The sensor is designed by incorporating a single circular split ring resonator (SRR) and a Hilbert fractal curve. The SRR is used considering its capacitive and inductive resonance properties, thereby making the SRR a favorable candidate for sensing applications. Moreover, the Hilbert fractal curve was used as a defected ground structure to increase sensor sensitivity and selectivity. The Hilbert fractal ground will increase the capacitance and inductance of the sensor, thus increasing the sensor sensitivity. Different Hilbert curve orders were investigated. The fourth-order Hilbert curve was used in the final design because it showed the optimal performance among the orders. To verify the sensor functionality and selectivity, the proposed sensor was tested through three breast cancer cell lines. Measurement results were compared to simulated results obtained using high-frequency structure simulator (HFSS). In addition, support vector machine, which is an artificial neural network (ANN), was developed to classify the type of each cancerous cell based on resonance frequency

Determination of solid material permittivity using T-ring resonator for food industry

In this paper, we present a simple design of a T-ring resonator sensor for characterizing solid detection.  The sensor is based on a planar microwave ring resonator and operating at 4.2 GHz frequency with a high-quality factor and sensitivity. An optimization of the T-ring geometry and materials were made to achieve high sensitivity for microwave material characterizations. This technique can determine the properties of solid materials from range of 2 GHz to 12 GHz frequencies. Techniques of current microwave resonator are usually measuring the properties of material at frequencies with a wide range; however, their accuracy is limited. Contrary to techniques that have a narrowband which is normally measuring the properties of materials to a high-accuracy with limitation to only a single frequency. This sensor has a capability of measuring the properties of materials at frequencies of wide range to a high-accuracy. A good agreement is achieved between the simulated results of the tested materials and the values of the manufacturer’s Data sheets. An empirical equation has been developed accordingly for the simulated results of the tested materials. Various standard materials have been tested for validation and verification of the sensor sensitivity. The proposed concept enables the detection and characterization of materials and it has miniaturized the size with low cost, reusable, reliable, and ease of design fabrication with using a small size of tested sample. It is inspiring a broader of interest in developing microwave planar sensors and improving their applications in food industry, quality control and biomedical materials

A Comprehensive Review of Portable Microwave Sensors for Grains and Mineral Materials Moisture Content Monitoring

In this paper, a comprehensive review of portable microwave sensors for monitoring moisture content (MC) is presented. MC monitoring is crucial in different industries, particularly food and farming. Microwave-based approaches for measuring the MC of the grains and mineral materials are studied. These approaches are categorized into three groups: S-parameters, dielectric constant, and impedance measurements. While these methods are interrelated, they have differences. The investigated methods use different microwave antenna sensors for MC monitoring, such as coaxial probes, horn antennas, loop antennas, microstrip patch antennas, and frequency selective surface (FSS) antenna. State-of-the-art microwave sensors were investigated thoroughly to clarify the current challenges and possible solutions of MC monitoring. A comparison between the investigated sensors was made to determine their advantages and disadvantages. According to the comparison, sensors operating above 10 GHz suffer from cross-interference. Moreover, microstrip patches can monitor a wide MC range as extensive as 60%. At the same time, the FSS sensor has the highest sensitivity with an error as low as 0.023% at X-band. Microstrip patch and FSS antennas can be printed directly on a flexible, low-loss, and lightweight material to monitor the grain MC. The flexibility, compactness, portability, ease of environment-friendly fabrication, and high sensitivity are among the criteria determining the most suitable microwave sensors for industrial and consumer MC monitoring applications

Equivalent circuit characterization of a novel microstrip ring resonator bandpass filter

Abstract: Approximate equivalent circuit (EC) characterization of a novel microstrip-ring resonator (MRR) bandpass filter (BPF) for wireless application at the ISM frequency band of applications is presented. The proposed MRR is a combination of two bent half wavelength (λ/2) microstrip line sections together with a pair of end-coupled microstrip feed lines (E-CMFL) of λ/8 length each. The E-CMFL forms a pestle-like shape and runs across the center of the entire diameter. The pair is separated by a distance of 0.036λg at the center. The equivalent circuits of the MRRs, the E-CMFL, and the effects of differing various spacing between them were investigated using a 2D ADS circuit solver and subsequently by 3D EM commercial solvers. The findings indicate that the proposed EC is influenced by capacitances due to a resonator gap (g), resonator-microstrip feed line gap (d), the inter-feed line gap (i), the radius of MRRs (r), and the resonator head (m). The EC model that was derived has been validated both by analytical formulae and numerical simulations