Microwave resonant sensor for measurement of ionic concentration in aqueous solutions

Nitrate efflux from agricultural lands in the Midwestern United States mixes with surface streams and creates hypoxic conditions in the Gulf of Mexico, which lead to destruction of aquatic ecosystems. Besides, excess nitrate in drinking water poses a serious threat to human health, including blue baby syndrome, birth defects, and cancer. The current nitrate management techniques are inefficient and expensive, and a major reason for this is the lack of low-cost, effective ionic concentration monitoring systems. The dependence of nitrate concentration on local hydrology means that laboratory techniques yield incomplete data, whereas the available real-time monitoring techniques have drawbacks like exorbitant cost, ion selectivity issues, and others. This research aims to bridge the gap between reliable concentration monitoring and economic feasibility by developing a low-cost, effective, real time ion monitoring system which is field deployable and sensitive to changes in ionic concentration at agriculturally-relevant levels. In this work, a resonant sensor is designed using an open-ended coaxial transmission line which can be evanescently perturbed by a liquid sample and shows a shift in its resonant frequency on change of ionic concentration of the sample. The dimensions of the coaxial resonator are optimized to ensure high sensitivity to changes in the ionic concentration of the sample at relevant concentrations, low manufacturing costs, and small physical dimensions to enable field deployment. The resonant sensor design is followed by the design and optimization of a suitable coupling structure which can take two-port transmission measurements to measure the characteristics of the resonator. Finite Element Analysis (FEA) simulations are carried out using ANSYS HFSS, using as input data the complex permittivity of aqueous solution samples with varying concentrations of nitrate, sulfate, and chloride ions. Deionized water is taken as a reference sample, and a clear correlation between shift in resonant frequency and ionic concentration is observed for each of the three resonant modes studied, with the sensor being highly sensitive to concentration changes at agriculturally relevant concentrations. Appropriate fitting functions are implemented to represent the correlations between resonant frequency and ion concentration, and discussion on the feasibility of the designed sensor for field deployment is presented

Fourier Analysis of Signal Waveforms in An Ideal Concurrent Dual-Band Class-D Power Amplifier

Recently, a concurrent dual-band class-D power amplifier has been demonstrated to overcome the limitations of reduced efficiency in concurrent dual-band linear power amplifiers. However, the configuration could not be symbolically analyzed like its single-band counterpart due to the complicated nature of dual-band signals. This paper aims to provide a theoretical basis for idealized concurrent dual-band class-D operation. It applies an alternate representation of the sum of two sinusoids which helps the formulation of a technique to analytically extract the complex Fourier series coefficients of the current and voltage waveforms of the power amplifier. Expressions for output power and efficiency are derived, showing a theoretical drain efficiency of 100%. The theoretically obtained results are validated using observations from literature as well as independent Harmonic Balance simulation

Coaxial microwave resonant sensor design for monitoring ionic concentration in aqueous solutions

Nitrate efflux from agricultural lands mixes with surface streams and adversely affects both human health as well as aquatic life. Currently, there is a lack of low-cost, effective, real-time systems for monitoring ion concentration. In this work, a microwave resonant sensor is designed using an open-ended coaxial transmission line, which can be evanescently perturbed by a liquid sample, and a suitable coupling structure which allows transmission measurements. The sensor is developed to have high sensitivity at agriculturally relevant concentrations, low manufacturing costs, and small dimensions to be potentially field deployable. Finite Element Analysis simulations are carried out using ANSYS HFSS, employing complex permittivity data of aqueous solution samples with varying concentrations of nitrate, sulfate, and chloride ions. Appropriate functions are determined that model the correlations between resonant frequency and ion concentration, and discussion on the feasibility of the sensor for field deployment is presented

Towards Wireless Characterization of Solvated Ions with Uncoated Resonant Sensors

Uncoated resonant sensors are presented here for wireless monitoring of solvated ions, with progress made toward monitoring nitrates in agricultural runoff. The sensor, an open-circuit Archimedean coil, is wirelessly interrogated by a portable vector network analyzer (VNA) that monitors the scattering parameter response to varying ionic concentrations. The sensor response is defined in terms of the resonant frequency and the peak-to-peak amplitude of the transmission scattering parameter profile (|S21|). Potassium chloride (KCl) solutions with concentrations in the range of 100 nM – 4.58 M were tested on nine resonators having different length and pitch sizes to study the effect of sensor geometry on its response to ion concentration. The resonant sensors demonstrated an ion-specific response, caused by the variations in the relative permittivity of the solution, which was also a function of the resonator geometry. A lumped circuit model, which fit the experimental data well, confirms signal transduction via change in solution permittivity. Also, a ternary ionic mixture (composed of potassium nitrate (KNO3), ammonium nitrate (NH4NO3), and ammonium phosphate (NH4H2PO4)) response surface was constructed by testing 21 mixture variations on three different sensor geometries and the phase and magnitude of scattering parameters were monitored. It was determined that the orthogonal responses presented by resonant sensor arrays can be used for quantifying levels of target ions in ternary mixtures. Applications of these arrays include measuring the concentration of key ions in bioreactors, human sweat, and agricultural waters. Preliminary results are shown for calibration standards and real waterway samples in Iowa, USA

Microwave resonant sensor for measurement of ionic concentration in aqueous solutions

Nitrate efflux from agricultural lands in the Midwestern United States mixes with surface streams and creates hypoxic conditions in the Gulf of Mexico, which lead to destruction of aquatic ecosystems. Besides, excess nitrate in drinking water poses a serious threat to human health, including blue baby syndrome, birth defects, and cancer. The current nitrate management techniques are inefficient and expensive, and a major reason for this is the lack of low-cost, effective ionic concentration monitoring systems. The dependence of nitrate concentration on local hydrology means that laboratory techniques yield incomplete data, whereas the available real-time monitoring techniques have drawbacks like exorbitant cost, ion selectivity issues, and others. This research aims to bridge the gap between reliable concentration monitoring and economic feasibility by developing a low-cost, effective, real time ion monitoring system which is field deployable and sensitive to changes in ionic concentration at agriculturally-relevant levels. In this work, a resonant sensor is designed using an open-ended coaxial transmission line which can be evanescently perturbed by a liquid sample and shows a shift in its resonant frequency on change of ionic concentration of the sample. The dimensions of the coaxial resonator are optimized to ensure high sensitivity to changes in the ionic concentration of the sample at relevant concentrations, low manufacturing costs, and small physical dimensions to enable field deployment. The resonant sensor design is followed by the design and optimization of a suitable coupling structure which can take two-port transmission measurements to measure the characteristics of the resonator. Finite Element Analysis (FEA) simulations are carried out using ANSYS HFSS, using as input data the complex permittivity of aqueous solution samples with varying concentrations of nitrate, sulfate, and chloride ions. Deionized water is taken as a reference sample, and a clear correlation between shift in resonant frequency and ionic concentration is observed for each of the three resonant modes studied, with the sensor being highly sensitive to concentration changes at agriculturally relevant concentrations. Appropriate fitting functions are implemented to represent the correlations between resonant frequency and ion concentration, and discussion on the feasibility of the designed sensor for field deployment is presented.</p

Radiofrequency circuit design for next-generation wireless sensing and communication

Industry 4.0 is transforming how we live and work by creating a smarter and more interconnected world. Advancements in wireless connectivity, in terms of speed, capacity, reliability, security, and cost-effectiveness, are critical to support Industry 4.0 applications. This dissertation contributes to the research on radiofrequency (RF) circuits to meet modern wireless connectivity demands for low-cost, real-time, contact-free sensing and power-efficient, high-bandwidth communication. The first part of this dissertation concerns spiral inductor-capacitor (LC) resonant sensors, which have emerged as a low-cost, rapidly scalable, and wireless solution for several real-time sensing applications in agriculture, biomanufacturing, and healthcare. Although the sensors themselves are highly cost-effective, traditional techniques to wirelessly interrogate them require expensive laboratory equipment, which are often not portable and need technical expertise to operate. Alternatively, custom readout techniques from literature suffer from high cost, high cost, narrow operating frequency range, and low range of usable distances for wireless interrogation. Hence, a new simple, low-cost, and portable readout design platform for LC resonant sensors is developed in this work. The operation of the proposed readout is theoretically analyzed to identify design constraints and tradeoffs, following which the implementation of the readout system hardware on a printed circuit board is presented. The fabricated system operates between 1 and 100 MHz, consumes 1.26 W, and experiments demonstrated reliable and repeatable operation with interrogation distances up to 5 cm. The second part of this dissertation focuses on RF power amplifiers which form the most power and area-consuming stage of RF transmitter systems. A push-pull concurrent dual-band class-D power amplifier was previously demonstrated in literature with the potential to meet modern carrier aggregation requirements. Although experiments showed promising results, the configuration did not render itself to symbolic analysis. This work uses an alternate representation of a sum of sinusoids to analytically derive the complex Fourier series coefficients of all voltages and currents of the power amplifier, which lead to expressions for output power and efficiency, finally demonstrating a theoretical drain efficiency of 100%. Harmonic Balance simulation was used to validate the theory. Furthermore, the push-pull architecture requires an output balun, and implementing a discrete power amplifier at GHz frequencies necessitates using a distributed balun instead of a three-wire transformer. Previous work showed that this substitution caused an efficiency degradation of the power amplifier and hypothesized that imperfect termination of a traditionally designed balun’s common mode signals was the culprit. This dissertation uses a mixed-mode S-parameter analysis to derive the common mode termination requirements of distributed baluns for concurrent dual-band operation. Subsequently, a generalized design modification procedure is developed for dual-band distributed baluns to enable concurrent use operation. The modification prevents common mode power loss without disturbing the balun’s other performance metrics. A concurrent dual-band tapped stepped impedance balun was designed and tested to validate the developed approach

Fourier Analysis of Signal Waveforms in An Ideal Concurrent Dual-Band Class-D Power Amplifier

Recently, a concurrent dual-band class-D power amplifier has been demonstrated to overcome the limitations of reduced efficiency in concurrent dual-band linear power amplifiers. However, the configuration could not be symbolically analyzed like its single-band counterpart due to the complicated nature of dual-band signals. This paper aims to provide a theoretical basis for idealized concurrent dual-band class-D operation. It applies an alternate representation of the sum of two sinusoids which helps the formulation of a technique to analytically extract the complex Fourier series coefficients of the current and voltage waveforms of the power amplifier. Expressions for output power and efficiency are derived, showing a theoretical drain efficiency of 100%. The theoretically obtained results are validated using observations from literature as well as independent Harmonic Balance simulation

Fourier Analysis of Signal Waveforms in An Ideal Concurrent Dual-Band Class-D Power Amplifier

Recently, a concurrent dual-band class-D power amplifier has been demonstrated to overcome the limitations of reduced efficiency in concurrent dual-band linear power amplifiers. However, the configuration could not be symbolically analyzed like its single-band counterpart due to the complicated nature of dual-band signals. This paper aims to provide a theoretical basis for idealized concurrent dual-band class-D operation. It applies an alternate representation of the sum of two sinusoids which helps the formulation of a technique to analytically extract the complex Fourier series coefficients of the current and voltage waveforms of the power amplifier. Expressions for output power and efficiency are derived, showing a theoretical drain efficiency of 100%. The theoretically obtained results are validated using observations from literature as well as independent Harmonic Balance simulation.This is a manuscript of an article published as Roy, Subhanwit, and Nathan M. Neihart. "Fourier Analysis of Signal Waveforms in An Ideal Concurrent Dual-Band Class-D Power Amplifier." IEEE Transactions on Circuits and Systems II: Express Briefs (2020). DOI: 10.1109/TCSII.2020.2980732. Posted with permission.</p

Coaxial microwave resonant sensor design for monitoring ionic concentration in aqueous solutions

Nitrate efflux from agricultural lands mixes with surface streams and adversely affects both human health as well as aquatic life. Currently, there is a lack of low-cost, effective, real-time systems for monitoring ion concentration. In this work, a microwave resonant sensor is designed using an open-ended coaxial transmission line, which can be evanescently perturbed by a liquid sample, and a suitable coupling structure which allows transmission measurements. The sensor is developed to have high sensitivity at agriculturally relevant concentrations, low manufacturing costs, and small dimensions to be potentially field deployable. Finite Element Analysis simulations are carried out using ANSYS HFSS, employing complex permittivity data of aqueous solution samples with varying concentrations of nitrate, sulfate, and chloride ions. Appropriate functions are determined that model the correlations between resonant frequency and ion concentration, and discussion on the feasibility of the sensor for field deployment is presented.This is a manuscript of a proceeding published as Roy, Subhanwit, Nathan M. Neihart, and Nicola Bowler. "Coaxial microwave resonant sensor design for monitoring ionic concentration in aqueous solutions." In 2018 IEEE International Instrumentation and Measurement Technology Conference (I2MTC). IEEE, 2018. doi: 10.1109/I2MTC.2018.8409878. Posted with permission.</p

Low-Cost Portable Readout System Design for Inductively Coupled Resonant Sensors

Spiral coil-based LC resonant sensors have seen many applications in agriculture, healthcare, biomanufacturing, and consumer electronics. Traditional techniques to interrogate such sensors using vector network analyzers are expensive and often not portable, whereas custom readouts suffer from either high cost, low range of usable interrogation distances, or low frequency range. This paper proposes a new simple, low-cost, and portable readout design based on the technique of coherent demodulation. A complete theoretical analysis examining how the interrogation distance is related to other circuit parameters is presented. Finally, a complete readout system was implemented using printed circuit board technology and commercially available off-the-shelf components. The system operates between 1-100 MHz and the fabricated system consumes 1.26 W. Measurements show that the system operates reliably and repeatably with interrogation distances up to 5 cm.This is a manuscript of an article published as Roy, Subhanwit, Yee Jher Chan, Nigel F. Reuel, and Nathan M. Neihart. "Low-Cost Portable Readout System Design for Inductively Coupled Resonant Sensors." IEEE Transactions on Instrumentation and Measurement (2022). DOI: 10.1109/TIM.2022.3173277. Copyright 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Posted with permission