Microwave Resonator Sensor Research Articles

Monitoring the residual capacity of activated carbon in an emission abatement system using a non-contact, high resolution microwave resonator sensor

The accumulation of non-desorbed species or heel buildup reduces the capacity and lifetime of adsorbents used in cyclic adsorption/desorption processes. This study investigates the changes in the physical, chemical, and dielectric properties of beaded activated carbon (BAC) and their relation to the adsorbent residual capacity (i.e., residual lifetime) during cyclic adsorption/desorption using a non-contact, high-resolution microwave resonator sensor. The resonant frequency of the sensor responds to changes in the dielectric properties of the medium surrounding the sensor. BAC samples with different degrees of capacity reduction as indicated by the apparent density, BET surface area, total pore and micropore volumes were tested. A linear correlation (R2 = 0.93) between the apparent density of the BAC samples and the resonant frequency shift of the sensor was observed, irrespective of heel composition indicating that the effect of adsorbent porosity on dielectric property variation is more important than heel composition. The sensor’s ability for fast and continuous measurement makes it an ideal candidate for real-time monitoring of adsorbent capacity status in cyclic adsorption/desorption processes.

Passive microwave resonant sensor for detection of deep tissue injuries

Deep tissue injuries (DTIs) are a perilous class of pressure ulcers in people with reduced mobility and sensation such as the elderly and people with spinal cord injury. DTIs initiate at deep bone-muscle interfaces and progress outwards, causing extensive tissue damage prior to their visual detection at the skin level. Here, we present a wearable sensor for detecting DTIs at their early stages of development. The sensor emits a 0.1 mW microwave to the depth of tissue and its impedance is monitored at different times. The impedance variations are analyzed and a single assessment parameter is generated for monitoring the presence of DTI and its stage of progression. This sensor can detect lesion phantoms as small as 0.5 mL through a layer of tissue which is thicker than 140 mm. The proposed sensor has the potential to be used as a low-cost prognostic device for DTIs, tumors or blood clots.

Distinguishing between Deep Trapping Transients of Electrons and Holes in TiO2 Nanotube Arrays Using Planar Microwave Resonator Sensor.

A large signal direct current (DC) bias and a small signal microwave bias were simultaneously applied to TiO2 nanotube membranes mounted on a planar microwave resonator. The DC bias modulated the electron concentration in the TiO2 nanotubes and was varied between 0 and 120 V in this study. Transients immediately following the application and removal of DC bias were measured by monitoring the S-parameters of the resonator as a function of time. The DC bias stimulated Poole-Frenkel-type trap-mediated electrical injection of excess carriers into TiO2 nanotubes, which resulted in a near-constant resonant frequency but a pronounced decrease in the microwave amplitude due to free electron absorption. When ultraviolet illumination and DC bias were both present and then stepwise removed, the resonant frequency shifted due to trapping-mediated change in the dielectric constant of the nanotube membranes. Characteristic lifetimes of 60-80, 300-800, and ∼3000 s were present regardless of whether light or bias was applied and were also observed in the presence of a hole scavenger, which we attributed to oxygen adsorption and deep electron traps, whereas another characteristic lifetime >8000 s was only present when illumination was applied, and is attributed to the presence of hole traps.

Characterising Dynamic Instability in High Water-Cut Oil-Water Flows Using High-Resolution Microwave Sensor Signals

Abstract In the present study, multi-scale entropy algorithm was used to characterise the complex flow phenomena of turbulent droplets in high water-cut oil-water two-phase flow. First, we compared multi-scale weighted permutation entropy (MWPE), multi-scale approximate entropy (MAE), multi-scale sample entropy (MSE) and multi-scale complexity measure (MCM) for typical nonlinear systems. The results show that MWPE presents satisfied variability with scale and anti-noise ability. Accordingly, we conducted an experiment of vertical upward oil-water two-phase flow with high water-cut and collected the signals of a high-resolution microwave resonant sensor, based on which two indexes, the entropy rate and mean value of MWPE, were extracted. Besides, the effects of total flow rate and water-cut on these two indexes were analysed. Our researches show that MWPE is an effective method to uncover the dynamic instability of oil-water two-phase flow with high water-cut.

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 sensor's 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.

Towards microwave imaging of cells.

Integrated detection techniques that can characterize the morphological properties of cells are needed for the widespread use of lab-on-a-chip technology. Herein, we establish a theoretical and experimental framework to use resonant microwave sensors in their higher order modes so that the morphological properties of analytes inside a microfluidic channel can be obtained electronically. We built a phase-locked loop system that can track the first two modes of a microstrip line resonator to detect the size and location of microdroplets and cells passing through embedded microfluidic channels. The attained resolution, expressed in terms of Allan deviation at the response time, is as small as 2 × 10-8 for both modes. Additionally, simulations were performed to show that sensing with higher order modes can yield the geometrical volume, effective permittivity, two-dimensional extent, and the orientation of analytes. The framework presented here makes it possible to develop a novel type of microscope that operates at the microwave band, i.e., a radar for cells.

Contactless Asphaltene Detection Using an Active Planar Microwave Resonator Sensor

In this paper, a noncontact real time method for asphaltene concentration measurement and precipitation detection is presented. An active high sensitivity microwave resonator sensor is utilized to monitor asphaltene particles and its complex permittivity at 1.2 GHz. The sensor utilizes a microstrip microwave resonator with an active feedback loop to compensate for the environmental loss and to enhance the quality factor of the sensor by several orders of magnitude (>10K). The sensor is utilized to directly measure the concentration of the liquid through monitoring its complex permittivity. It is also illustrated that time-based measurements can be used to increase the accuracy by providing two independent data sets, i.e., concentration and time constant. Next, heptane is mixed with different concentrations of asphaltene and monitored in real time. The results demonstrate the capability of noncontact measurement of the precipitation process at different asphaltene concentrations. The findings exhibit a sub...

High-Efficiency Microwave Planar Resonator Sensor Based on Bridge Split Ring Topology

This letter presents a high efficiency and accurate measurement of microwave resonator sensor using microstrip planar structural technology. The structure is designed based on the bridge split ring topology. The sensor has the ability to characterize liquid solvents using the extraction of polynomial fitting technique. The bridge equivalent circuit configuration allows the electromagnetic wave to focus on the sensing medium in order to gain high electric flux density, thus react as pushing effect for high Q factor. The bridge structure amplifies the electric field distribution. As demonstrated by the results, the unloaded Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> -factor improves more than 400 over the narrow bandwidth at operating frequency of 2.3 GHz, and provides less than 10-dB insertion loss. By comparison, this design has an identical performance goal and provides excellent sensing capability which can be implemented in pharmaceutical, biomedical, and beverage industries application.

The Software Design of SiBCN Temperature Sensor Wireless Sweep Signal Receiving and Dispatching System Based on FPGA

SiBCN (silicon boron carbon nitrogen) wireless passive microwave resonant cavity temperature sensor is a new type of sensor under the development trend of radio frequency microwave technology. Based on the working principle of the sensor, the software design of SiBCN temperature sensor wireless sweep transceiver system based on FPGA is carried out on the basis of the existing wireless sweep signal transceiver system hardware. Let the signal source send the 11.0GHz ~ 11.6GHz range sweep signal to the sensor. The feedback signal of the sensor is filtered and the resonant frequency is obtained. The detection of temperature is based on the correspondence between the resonant frequency and the temperature.Through the analysis of the measured results, the system software design meets the requirements, and the temperature and frequency change rate is about 421.2KHz / °C.

Dielectric analysis of liquid solvents using microwave resonator sensor for high efficiency measurement

ABSTRACTA microwave ring resonator sensor has been practically applied as a micro‐volume sensor dedicated to solvent characterization with perspectives for chemical substances. The tested microliter range liquid solution is placed on capillary glass which is a compatible medium for planar sensor integration. The electrical response between electric field and solvent is converted into a predictable relationship between dielectric properties and the relative permittivity of the solution. A compact split ring resonator has been fabricated and tested with several common solvents on trace amount of volume. The result achieved recorded a very high Q factor of 525 making it practically suitable for beverages industry application. Good agreement has been achieved between the theoretical, simulation, and parameters measurement where the measurement errors of the complex permittivity is less than 0.5%, validating the concept of the accurate characterization theory using planar sensor. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:367–371, 2017

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.

Microwave ring resonator-based non-contact interface sensor for oil sands applications

This paper presents the design, fabrication, and characterization of a non-contact microwave resonator sensor for liquid–liquid interface detection. The core of this sensor is a microwave planar ring resonator tuned at 5.25GHz with a Q factor of 180. The geometry and materials of the designed sensor were optimized for higher sensitivity by finite element modeling and simulations. Here we demonstrate the detection of different liquid–liquid interfaces such as water–olive oil, water–olive oil–ethanol, and rag layer samples using microwave resonator method. In the proposed sensor, the resonance frequency demonstrated a maximum variation of 5.7% for water to rag layer interface. To increase the accuracy of the sensor in the interface detection, quality factor is also measured and demonstrated a maximum variation of 85% depending on the materials. The proposed sensor provides a non-contact real time, cost-effective, robust method for interface detection, which has potential applications in the oil sands industry.

Design considerations for high-Q bandpass microwave oscillator sensors based upon resonant amplification

A series of microwave resonant oscillator sensors were designed and characterized using bandpass planar and volumetric electrical resonators having loaded quality factor (Q) values in the range of 2 to 20. The use of these resonators in positive feedback circuits yielded sensor Q-factors of up to 2 × 107, demonstrating Q-factor amplifications on the order of 106. It is shown that the Q-factor amplification can be increased in a positive feedback system through the selection of feedback loop group delay, allowing use of resonators with lower static, loaded Q-factor values. A low-frequency electromagnetic interference sensing application is demonstrated for two resonant oscillator configurations, showing considerable frequency sensitivity to 45 kHz emitters.

In-Situ Monitoring of the Bulk Density and the Moisture Content of Rapidly Flowing Particulates Using a Microwave Resonance Sensor

The resonant frequency and conductance of an open-reflection microwave resonance sensor overlaid with rapidly stirring microcrystalline cellulose (moisture content range 0%-6.4% and effective bulk density range 0.225-0.375 g cm-3) were recorded noninvasively in the frequency range of 700-740 MHz. With these data, empirical calibration models were developed that allowed simultaneous, accurate predictions of moisture content, and effective bulk density in-situ. Standard errors of calibration were found to be 0.32% for moisture content determination and 0.014 g cm-3 for effective bulk density determination. This paper shows that microwave resonance sensors can be used to monitor the material properties of very rapidly flowing materials that other techniques cannot.

Simulation of a non-invasive glucometer based on a microwave resonator sensor

In this paper a simulation of a microwave resonator sensor for constructing a non-invasive blood glucose meter is presented. A relationship between changes of the dielectric permittivity of the blood and the frequency response of S parameters of the sensor is observed. This can lead to a measuring procedure in which the glucose level present has a correlation with the value of the frequency resonance of the sensor. The test bank consists of a planar spiral microwave resonator over which the individual under test places his/her finger. This modifies the initial frequency resonance of the resonator because of the change produced in the measuring procedure over the dielectric permittivity of the resonator. Simulations show a correlation between dielectric permittivity blood changes, and changes in the value of the frequency resonance, in the frequency response of S parameters of the resonator.

A Microwave Resonant Sensor for Concentration Measurements of Liquid Solutions

This paper presents the design, fabrication, and characterization of a microwave resonator as a tool for concentration measurements of liquid compounds. The sensing device is a rectangular waveguide cavity tuned at 1.91 GHz, which exploits the fundamental TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> mode in a transmission-type configuration. The coupling structure is optimized by means of a finite element code so as to achieve a high <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -factor. According to the type of substance inside the mixture, its concentration is conveniently related to changes of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> scattering parameter (transmission coefficient) in terms of: 1) resonance frequency; 2) 3-dB bandwidth; and 3) amplitude at the resonance frequency. Experimental tests on liquid solutions in controlled conditions are presented to evaluate the performance of the device.

Experimental Research on Granule Moisture Measurement by Microwave Resonance Technology in a Fluidized Bed Dryer

Drying is one of the most important methods for industrial processing while the granule moisture is a critical quality attribute (CQA) which has a significant influence on the finished product quality. In-line measurement of granule moisture during fluidized bed drying is getting more imperative to meet more stringent product quality specifications. Nowadays, several methods have been applied to measuring the granule moisture in-line. Comparing to other methods, microwave resonance (MR) technology provides more representative results due to its independency of both the particle density and the bed density. In the current study, one MR sensor was mounted onto an industrial fluidized bed dryer to monitor the real-time moisture of granules. The drying experiments were performed at different drying air temperatures and flow rates. The comparison between the results of in-line and off-line granule moisture measurements, namely MR technology and loss on drying caused by infrared light (LOD/IR), was presented. Furthermore, the influences of inlet air temperature and flow rate on the performance of the MR sensor were investigated. As a conclusion, the MR method, which is independent of the drying air temperature and flow rate, provided more accurate results when the granule moisture was below 25% (wet basis). Therefore, it is a promising method to be applied in real-time measurement of the granule moisture and predict the end-point in fluidized bed drying processes as well.

Utilizing microwaves for the determination of moisture content independent of density

Abstract Bulk density and moisture content are both very important powder-processing parameters that affect, among other things, the material's flowability and compressibility, as well as the final product's quality. Many traditional microwave methods to determine these parameters rely on the calculation of the real (e′) and imaginary (e″) components of the sample's relative complex permittivity. These parameters can also be calculated directly from raw sensor measurements. Using the conductance and frequency at resonance of an open-reflection microwave resonance sensor allowed the determination of a sample's moisture content (MC) with a high degree of accuracy. The method was applied to static samples of microcrystalline cellulose (MC range 0.568–6.163% and density range 0.280–0.499 g/cm3) and α-lactose monohydrate (MC range 5.59–8.69% and density range 0.346–0.691 g/cm3). The results indicated that the described method predicts moisture content accurately and independent of density fluctuations. As a result, the described method has been shown to be a viable alternative to other established microwave moisture content calibrations.

Microwave sensor based on a single stereo-complementary asymmetric split resonator

Stereo-complementary asymmetric split resonator (Stereo-CASR) perforated on a copper sheet is proposed for designing microwave resonator sensor. The effect of the degree of asymmetry on the frequency response is thoroughly studied. Compared with traditional planar ASR, stereo-CASR exhibits a nearly 100% transmission at resonate state and possesses a much higher Q factor. The performance of the stereo-CASR assisted microwaves sensor is validated by full wave simulation. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22:545–551, 2012. © 2012 Wiley Periodicals, Inc.

Complex Dielectric Properties of Microcrystalline Cellulose, Anhydrous Lactose, and α-Lactose Monohydrate Powders Using a Microwave-Based Open-Reflection Resonator Sensor

The real (ε') and imaginary (ε″) components of the complex permittivity of anhydrous lactose and microcrystalline cellulose (MCC) under different bulk densities, moisture contents (MCs), and times of hydration (for anhydrous lactose) were measured nondestructively using a microwave resonator sensor operating in the range of 700-800 MHz. Measurements of sensor resonant frequency and conductance allow, through calibration, determination of the complex dielectric properties ε' (relative permittivity) and ε″ (relative dielectric loss) of the test material. Characteristic graphs of ε″ versus ε' - 1 curve for each powder were generated as a function of bulk density and MC. Such data can be used to develop empirical models for the simultaneous in situ measurement of the bulk density and MC of the powders. Unlike MCC, anhydrous lactose is converted to its hydrate form in the presence of moisture, which causes a reduction in the amount of physisorbed and "free" water and a subsequent change in the dielectric properties. For powders such as anhydrous lactose that can form a crystal hydrate in the presence of moisture, a combination of techniques such as vibrational spectroscopy together with microwave resonator measurements are appropriate to characterize, in situ, the physical and chemical properties of the powder.