Microwave Resonator Sensor Research Articles

Design of an Accurate, Planar, Resonant Microwave Sensor for Testing a Wide Range of Liquid Samples

In this paper, an inductively coupled capacitively loaded ring resonator (IC-CLRR)-based microwave resonant sensor has been proposed for the accurate identification of any unknown liquid sample and its permittivity estimation. The key element of this work is the sensor’s wide range capability towards the non-invasive testing of liquids covering a wide dielectric range of liquid samples, i.e., εr = 2 to 80. The proposed microwave sensor is etched over the FR-4 substrate and is excited by the microstrip line through inductive coupling. The placement of an unknown liquid sample in close proximity to the sensor alters its natural resonant frequency due to a change in effective inductance and capacitance as per the dielectric property of the liquid sample. Further, a mathematical formulation using curve fitting has also been derived. The measurement results show a good accuracy in estimating the permittivity and, thus, the unknown liquid identification capability of the designed sensor with a very low error (nearly 5%). This sensor design is simple to fabricate, cost-friendly, and small in size.

A low-cost reflection mode operated microwave resonator sensor for angular displacement detection

A low-cost microwave resonator sensor for angular displacement detection is proposed. The sensor uses a strip-loaded dielectric resonator (SLDR) as the key element. The sensor operates in the reflection mode, i.e. by producing a variation in the reflection coefficient (S11) according to the angular position of the SLDR relative to a microstrip transmission line. The primary advantage of the proposed strategy is its fixed-frequency operation enabling the S11 measurement with a low-cost reflectometer, thereby avoiding the costly vector network analyzer (VNA). Design modelling and initial analysis of the sensor are performed with ANSYS HFSS software. To demonstrate proof of concept, a sensor prototype is fabricated and experimentally characterized with a custom-made reflectometer. Results are compared against VNA-based measurements to be in decent agreement. The proposed sensor exhibits 0.43 dB/0 sensitivity over the dynamic range of 00–900.

High Responsive Microwave Resonator Sensor for Material Characterization

High Responsive Microwave Resonator Sensor for Material Characterization

Multi-parameter simultaneous extraction with a novel microwave sensor based on coupled resonators

This work presents a microwave resonant multi-parameter sensor devoted to the simultaneous extraction of three characteristics of a homogeneous solid sample: its dielectric permittivity, its loss tangent and its thickness. The device is composed of three coupled resonators in two different substrate boards, having the sample between the boards, in a sandwich configuration. Presence of the sample impacts the electrical response of the device, not only influencing resonators, but also by affecting inter-resonator couplings. A method to analyse the response of the device, allowing for the extraction of the desired characteristics of the sample is proposed, as well as an experimental calibration procedure. The model is built upon 990 simulations, calibrated with three reference-samples measurements and then tested over 18 experimental measurements, with good results, thereby validating the multi-parameter sensing approach.

Accurate thickness evaluation of thermal barrier coatings using microwave resonator sensor

Thermal barrier coatings (TBC) are frequently employed in aircraft engines and turbine blades for protection against high temperatures. Constant exposure to in-service stresses, however, leads to a variety of anomalies in TBC that could prove to be potentially catastrophic for the assemblies they protect. This raises the need for inspection using non-destructive techniques (NDT) to ensure the reliability and structural integrity of the coated assemblies. Thickness evaluation of the topcoat of the TBC is paramount to determining structural integrity of the TBC. Microwaves are particularly suited for such applications since they readily penetrate low loss TBC. However, the performance of previous microwave-based TBC thickness evaluation techniques was limited in accuracy to 15 μm. In this paper, accurate thickness evaluation of thermal barrier coating (TBC) is performed using a microwave resonator sensor operating at a relatively low frequency (<1 GHz). TBC thicknesses as low as 100 μm are evaluated based on shift in resonant frequency of the probe. Overall, practically relevant thicknesses ranging from 100 μm to 600 μm are evaluated herein and multiple trials are performed to ascertain repeatability and assess uncertainty in measurements. For a 250 μm thick TBC sheet, a mean error of 0.9 μm was accomplished which translates to 0.36 % error with a standard deviation of 1.5 μm. Compared to other microwave sensors reported in the literature, a better estimation accuracy is demonstrated in this work, in particular for thicknesses less than <250 μm.

Study on pollutants detection in natural gas pipeline based on circular probe microwave resonance sensor (CPMRS)

Pollutants, such as black powder, are commonly found in natural gas pipelines and are considered undesirable. These pollutants not only degrade the quality of natural gas, but also contaminate compressor components and can even corrode and damage the pipeline, leading to serious safety hazards such as pipeline blockages. This paper proposes and investigates a novel circular probe microwave resonance sensor (CPMRS) to dynamically measure pollutants in natural gas pipelines at an early stage. The influence of the circular probe structure on the CPMRS performance and the optimal structural parameters of the CPMRS are studied using finite element simulation software. An experimental platform is then set up to evaluate the resonance of the CPMRS in different working conditions. The results show that the resonance frequency shift can reach up to 4.27 MHz for the mass flow rate of 12.54–78.69 mg/s. Additionally, the results demonstrate that the magnitude of the phase change of CPMRS is considerably greater than the magnitude of the amplitude change. The results also indicate that CPMRS is more sensitive to pollutants and more resistant to flow velocity perturbation than ordinary transmission probe microwave sensors.

Dual-band microwave sensor based on cross-finger MCSRR Research

This paper presents a low-cost, easy-to-fabricate microwave resonant sensor for characterising the dielectric properties of solids. The designed sensor is based on a Rogers RT/duriod 5880 substrate with a cross-finger treated Multiple Complementary Split-Ring Resonator (MCSRR) structure etched on it, and this resonance unit is used to place the Material Under Test (MUT). The sensor operates at 5.8 GHz and 8.3 GHz resonant frequencies and uses offset resonance to detect the dielectric properties of different solids. The relationships established by the simulation were experimentally verified by the fabricated sensor. The percentage error between the calculated dielectric constant and the reference dielectric constant is less than 9.58% for a certain thickness of the sample to be tested, which verifies the feasibility of the proposed loaded cross-finger MCSRR sensor. Therefore, this sensor is expected to be a cost-effective and convenient solution.

Microwave Resonant Sensor Based on MCSRR Research

This paper presents a low-cost and easy-to-fabricate microwave resonant sensor for characterising the dielectric properties of solids and powders. The designed sensor is based on a FR-4 dielectric substrate with a Multiple Complementary Split-Ring Resonator (MCSRR) etched on its bottom, and this resonant unit is used to place the sample to be tested (Material Under Test, MUT). The sensor was operated at a resonant frequency of 4.9GHz and used the offset resonance to detect the dielectric properties of different solids and powders. The relationships established by the simulation were experimentally verified by the fabricated sensor. The percentage error between the calculated dielectric constant and the reference dielectric constant is less than 8.7% for a certain thickness of the sample to be tested, which verifies the feasibility of the proposed loaded MCSRR sensor. Therefore, this sensor is expected to be a cost-effective and convenient solution for accurate characterisation of solid, powder dielectric properties.

Analysis of the Uncertainty in measurements of Polymer Pellets using Microwave Resonant Sensors

Analysis of the Uncertainty in measurements of Polymer Pellets using Microwave Resonant Sensors

Measurement of Solid Concentration in Gas–Solid Flows Using a Microwave Resonant Cavity Sensor

Measurement of Solid Concentration in Gas–Solid Flows Using a Microwave Resonant Cavity Sensor

A microwave resonance thin-film sensor for real-time wireless temperature monitoring in composites manufacturing

Composites are of growing importance to today's industries. Curing or consolidation under certain temperatures is a vital process to manufacture composite parts. Great attention has been paid to monitoring the temperature of composite parts being processed. Wireless monitoring methods are extensively explored for their unique advantages in realizing real-time monitoring of specific temperature distribution of the part. Here, a flexible microwave resonance sensor is first introduced to achieve real-time wireless temperature monitoring of composites. When applied to curing processes with different heating rates, it was found that the sensing relationship of the sensor was varied. Through in-depth analysis, the relationship between peak frequencies and temperature was established with consideration of different heating rates. In several curing processes with different heating rates, the mean error of the thin film sensor using a heating rate-related relationship was about 4.23 °C. which can be reduced by more than 43 % compared with the method using a static relationship.

Microfabricated interdigital capacitive sensor and resonant sensor based on PPy/MoO3 hybrids for sensitivity-enhanced ammonia detection at room temperature

This paper proposes a microwave transduction-based gas sensor based on polypyrrole/molybdenum oxide composite (PPy/MoO3) hybrid material. Optimization of sensing material, measurement platform and fabrication techniques are carried out to achieve excellent ammonia gas real-time detection. Capacitance parameters analysis for the gas sensing response of capacitive sensor is proceeded based on PPy, MoO3, and PPy/MoO3 hybrids at room temperature. The results show that the PPy/MoO3 hybrid material exhibits a sensitivity-enhanced response to ammonia. The PPy/MoO3 capacitive sensor has good linearity (R2 =0.987), fast response, and good repeatability within 5–100 ppm ammonia concentration. Frequency parameters analysis for the gas sensing response of microwave resonator sensor is proceeded based on PPy/MoO3 hybrids in the range of 10 ppm to 100 ppm ammonia concentration at room temperature. The proposed microwave sensor has good linearity (R2 =0.991), good repeatability with 8 MHz standard deviation, high stability with gas response variation less than 2%, and anti-humidity capacity. Among 100 ppm concentration of isopropanol, acetone, ethanol, methanol and ammonia, ammonia exhibits 97.5 MHz frequency shift, which proves high sensitivity and good step toward selectivity. Therefore, this work could be regarded as a promising candidate in ammonia sensing application based on microwave solution.

A Tuned Microwave Resonant Sensor for Skin Cancerous Tumor Diagnosis

A Tuned Microwave Resonant Sensor for Skin Cancerous Tumor Diagnosis

Permittivity measurement of fluidics with high‐sensitivity by chandelier form microwave sensor

AbstractIn this manuscript, a microwave resonance sensor (MRS) was presented composed of interdigital structure, meander structure, chandelier‐form, and T‐shaped structure. The combination of four structures results in a good electromagnetic field strength at the sensing location. It caused increased sensitivity. Due to the high use of methanol in industry, samples have been selected from this material. The samples used are methanol and water solution and place on location sensing. For measurement was used samples with 80% methanol with a permittivity of 59%–10% methanol with a permittivity of 77. Also, tissue samples including sheep, chicken and fish have been used to measure the proposed sensor. The resonance frequency of the samples changes in the range of 2.14‐1.46 GHz. The sensitivity of the presented MRS is 2.6% and the Q‐factor is 1252.

Recent advances in TiO2 nanotube layers – A mini review of the latest developments in nanotube preparation and applications in photocatalysis and microwave sensing

AbstractSelf‐organized anodic TiO2 nanotube (TNT) layers prepared by anodization of Ti substrates have attracted great interest within the last 20 years, due to their unique properties and low‐cost synthesis. This mini review article aims to shortly summarize the most recent developments in the TNT layer synthesis and applications. It presents the synthesis of high aspect ratio (HAR) TNT layers in a short time by accelerating the TNT layer growth rates in lactic acid containing electrolytes. Furthermore, the etching of TNT layers towards TNT bundles of homogeneous size and single tube powders is discussed, as well as the possibility to grow TNT layers on non‐planar Ti substrates, which cannot be directly connected to the potentiostat (e.g., Ti spheres or 3D Ti meshes). As a relatively new application, the employment of TNT layers in microwave resonator sensors is introduced. Last, but not least, approaches of upscaling the TNT layer size from the laboratory scale towards significantly larger scale are outlined and reviewed.

An Interdigital Microwave Sensor Based on Differential Structure for Dielectric Constant Characteristics Measurement.

In this work, a microwave resonator sensor with a unique configuration consisting of three resonators and two feedlines is proposed. This novel design aims to improve the performance and functionality of microwave resonator sensors for various applications. The frequency response of the sensor to materials with different dielectric constants is simulated. The results show that the most sensitive region of the sensor is located on the first interdigital structure, and placing the materials in other regions would enhance the linear correlation of its frequency response. The sensor also exhibits the ability to distinguish whether the same material has defects and the ability to qualitatively detect subtle changes in dielectric constant. Finally, the proposed sensor is fabricated and measured under the condition consistent with the simulation environment. The measured results are basically consistent with the simulation results, which confirms the potential of this sensor in detecting dielectric constants and resolving materials with defects, and the response of the sensor to the materials under test demonstrates its potential in measuring different thicknesses and loss tangents.

Microwave substrate integrated waveguide resonator sensor for non-invasive monitoring of blood glucose concentration: Low cost and painless tool for diabetics

In this study, a microwave resonant sensor with an operation frequency of 9 GHz and a quality factor of 240 has been designed, fabricated and tested by fingertips of the users to control blood glucose levels. The proposed method includes the implementation of a band-pass filter in the substrate integrated waveguide cavity, which has been carried out using a modified split ring resonator. In this research, 4 volunteers with glucose level changes ranging from 92 to 141 mg dL−1 have been tested invasive (by a glucometer) and non-invasive (by the designed sensor). For this range of glucose level changes, the frequency detection resolution is 7.67 MHz (mg dL−1)−1.

Planar Microwave Sensor with High Sensitivity for Material Characterization Based on Square Split Ring Resonator (SSRR) for Solid and Liquid

Microwave resonator sensors are the most extensively used sensors in the food industries, quality assurance, medical, and manufacturing. Planar resonant technique is chosen as the medium for characterizing dielectric properties of material due to its compact in size, low cost and easy to fabricate. But these techniques have a low Q-factor and little sensitivity. This work uses the perturbation approach to overcome this technique's flaw, which is that Q-factor and resonant frequency are affected by the resonator's dielectric properties. This suggested sensor operated at 2.5GHz between 1GHz and 4GHz for material characterisation of solid and liquid samples. These sensors were constructed on a substrate made of RT/Duroid Roger 5880, which has a copper layer that is 0.0175 mm thick and has a dielectric constant of 2.2. This square split ring resonator (SSRR) sensor thus generates narrower resonant, low insertion loss, and a high Q-factor value of 430 at 2.5GHz. The SSRR sensor's sensitivity is 98.59%, which is higher than that of past studies. The application of the suggested sensor as a tool for material characterisation, particularly for identifying material attributes, is supported by this findings.

Research on the measurement method of gas-water two-phase flow based on dual-sensor system

Realizing the online accurate measurement of gas-water two-phase flow is of great significance for the natural gas industry. In this paper, a dual-sensor with the microwave resonant cavity sensor embedded in the throat of Venturi is proposed and both of the water volume fraction (WVF) and the separated flowrates of the two phases is attained by the method. To further improve the performance and the measurement accuracy of the sensor, a swirler is fixed inside the contraction section of the precession Venturi, which can regularize all flow patterns into spiral annular flow and reduce the influence caused by the nonuniform distribution of air and water. The microwave sensor response characteristics with WVF and Venturi over-reading (OR) characteristics have been researched through dynamic experiments, and the iteration method of OR model obtained by the precession Venturi and WVF model obtained by the microwave sensor is used to solve the gas and water flowrates respectively. The results show that gas phase flowrate relative error band of ±5% at a confidence probability of 86.08%, and Root Mean Square Error (RMSE) is 3.349%; while water flowrate relative error band of ±10% at a confidence probability of 87.70%, and RMSE is 9.680%, which suggests that the multi-sensor fusion technology provides a powerful solution for the measurement of separated flowrates of gas-water two-phase flow.

Sensitivity–Enhanced detection of acetone gas using MXene-Immobilized planar microwave sensor

This work presents the noncontact immobilization of Ti3C2Tx MXene on a planar microwave resonator sensor via a polyimide film to enhance the gas detection sensitivity, enabling the characterization of the part per million-level of acetone gas. Sandwiching a polyimide (PI) film confined an intense electromagnetic field between the resonator’s interdigital capacitor structure and the MXene layer, maintaining a significant interaction between the acetone gas molecules and the resonator’s EM field via the MXene layer. Therefore, contactless immobilization of the MXene layer enhanced the acetone gas detection sensitivity by 110% compared to the resonator gas sensor with MXene deposited directly on the resonator surface. As a proof of concept, two sensor prototypes were implemented using resonators with layers of PI film and MXene and resonators with MXene only and were applied to detect a wide range of acetone gas concentrations. Immobilizing the layers of PI film and MXene on the microwave resonator achieved a linear correlation between the resonant frequency and acetone gas concentration with high sensitivity (17.85 kHz/ppm, a fast response time (60 s), and recovery time (85 s).