Compact Microwave Research Articles

Nonreciprocal transmission of surface acoustic waves induced by magneotoelastic coupling with an anti-magnetostrictive bilayer

In this study, we report giant nonreciprocal transmission of shear-horizontal surface acoustic waves (SH-SAWs) in a ferromagnetic bilayer structure with negative–positive magnetostriction configuration. Although the directions of magnetization in the neighboring layers are parallel, SH-SAWs can excite optical-mode spin waves (SWs) via magnetoelastic coupling at relatively low frequencies, which is much stronger than acoustic-mode SWs at high frequencies. The measured magnitude nonreciprocity or isolation of SH-SAWs exceeds 40 dB (or 80 dB/mm) at 2.333 GHz. In addition, maximum nonreciprocal phase accumulation reaches 188° (376°/mm). Our theoretical model and calculations provide an insight into the observed phenomena and demonstrate a pathway for further improving nonreciprocal acoustic devices toward highly compact microwave isolators and circulators.

A Versatile, Machine-Learning-Enhanced RF Spectral Sensor for Developing a Trunk Hydration Monitoring System in Smart Agriculture

This paper comprehensively explores the development of a standalone and compact microwave sensing system tailored for automated radio frequency (RF) scattered parameter acquisitions. Coupled with an emitting RF device (antenna, resonator, open waveguide), the system could be used for non-invasive monitoring of external matter or latent environmental variables. Central to this design is the integration of a NanoVNA and a Raspberry Pi Zero W platform, allowing easy recording of S-parameters (scattering parameters) in the range of the 50 kHz–4.4 GHz frequency band. Noteworthy features include dual recording modes, manual for on-demand acquisitions and automatic for scheduled data collection, powered seamlessly by a single battery source. Thanks to the flexibility of the system’s architecture, which embeds a Linux operating system, we can easily embed machine learning (ML) algorithms and predictive models for information detection. As a case study, the potential application of the integrated sensor system with an RF patch antenna is explored in the context of greenwood hydration detection within the field of smart agriculture. This innovative system enables non-invasive monitoring of wood hydration levels by analyzing scattering parameters (S-parameters). These S-parameters are then processed using ML techniques to automate the monitoring process, enabling real-time and predictive analysis of moisture levels.

Rapid Surrogate-Aided Multicriterial Optimization of Compact Microwave Passives Employing Machine Learning and ANNs

Rapid Surrogate-Aided Multicriterial Optimization of Compact Microwave Passives Employing Machine Learning and ANNs

Compact polarization-insensitive microwave metamaterial absorber with hepta-band characteristics

This paper presents an ultra-thin and compact metamaterial absorber (MMA) capable of achieving near-perfect absorption peaks across the C, X, Ku, and K frequency bands. The MMA structure features a modified metallic plus-shaped resonator surrounded by symmetric L-shaped resonators within a compact size of 13 × 13 mm2. The absorber exhibits seven absorption peaks at different resonant frequencies including 4.23, 6.48, 10.62, 12.92, 14.03, 17.39, and 18.11 GHz. With a thickness of 0.0225λ and a compact size of 0.1833λ at the lowest frequency, the absorber offers remarkable thinness and compactness. Different characteristics of the absorber, such as normalized impedance, surface current distribution, and electric field distribution, are also examined. The polarization-insensitive behavior of the MMA is assessed through absorption and reflection responses under different polarization and incident angles. The Equivalent Circuit Model (ECM) of the metamaterial absorber is also designed to accurately represent the MMA unit cell across all resonant frequencies. Experimental validation of the proposed MMA confirms its performance consistency with simulation results. The proposed MMA design holds potential for applications in defense, detection, and sensing. The sensing ability of the MMA is analyzed using simulations at different refractive index values.

Development of Microwave Components Using Additive Manufacturing: A Review

In modern telecommunication, there is a growing demand for lightweight, low-cost, and compact microwave components with high transmission functionalities, especially for applications requiring multiple high-performance antennas to provide multi-beam capabilities. Additive manufacturing (AM), also known as three-dimensional (3D) printing, has emerged as a promising solution to meet these demands due to its simplicity, fast prototyping capabilities, and enhanced fabrication accuracy. AM technology has found widespread adoption across various industries, including space-borne, satellite, handheld wireless systems, biomedical, mechanical, electrical, optical, and environmental applications. In particular, AM-based microwave components offer significant advantages, including reduced weight compared to traditional aluminum prototypes, with savings of up to two-thirds of the weight. This paper presents a comprehensive review of the AM process, materials used, and microwave components developed using AM technology. The review encompasses various aspects, including fabrication techniques, performance characteristics, and applications of AM-based microwave components, providing insights into the advancements, and potential future directions of this innovative approach.

Compact silicon-based Ka-band tunable-phase photonic microwave frequency downconverter.

In this paper, a compact silicon-based photonic microwave frequency downconverter with broadband operation capability and continuous phase shift tunability is proposed and experimentally demonstrated. The photonic converter mainly comprises two micro-ring modulators (MRMs) connected in parallel and a cascaded resonator-based optical bandpass filter (OBPF) whose size is merely 200 × 700 µm2. In the proposed device, a radio frequency (RF) signal and a local oscillator (LO) signal drive the two MRMs for realizing the electro-optic conversion. The OBPF is utilized for selecting the first-order sidebands of both RF and LO signals. By manipulating the phase difference between the RF and LO optical sidebands through thermal-optic effect, the phase of the obtained intermediate frequency (IF) signal from a photodiode can be tuned continuously. Experimental results demonstrate a 137° phase shift while the RF signals of 20 and 40 GHz are downconverted to an IF signal of 0.4 GHz, which indicates the photonic microwave downconverter can be used in the Ka-band phased-array receiver.

Microwave metamaterial microstrip line with enhanced refractive index and its application to compact a Wilkinson power divider

A new microwave metamaterial microstrip line (meta-MSL) is studied by integrating planar mushroom metamaterial structures into a conventional MSL. The meta-MSL is featured with an enhanced effective refractive index than the conventional, extracted from numerical demonstrations using the S-parameter method. The extraordinarily increased refractive index is found to be associated with weak dispersion and low dissipation loss, making the meta-MSL particularly beneficial to compact a microwave Wilkinson power divider (WPD). One metamaterial WPD (meta-WPD) is built using new meta-MSLs. Full-wave numerical calculations reveal that the new meta-WPD has low insertion losses, low reflections, and high isolations between the output ports, working as a good substitute for the conventional WPD. However, the new meta-WPD is exceptional in its small size, which is particularly useful in mobile and wireless applications where compact microwave components are in critical demand.

Quantitative determination of cadmium content in peanut oil using microwave detection method combined with multivariate analysis

This research introduced an innovative application of microwave detection technology to quickly and precisely quantify cadmium concentration in peanut oil. Using the principle of free space measurement, a compact microwave detection device was fabricated, and obtain a transmission index with a frequency range of 2.5 GHz to 11.5 GHz and a step size of 10 MHz. Firstly, the preprocessed transmission index is selected by using three feature extraction algorithms: competitive adaptive reweighting sampling (CARS) algorithm, boot­strapping soft shrinkage (BOSS) algorithm, and iteratively variable subset optimization (IVSO) algorithm, and quantified them with the least square support vector regression (LSSVR) model. Then, two intelligent optimization algorithms, sine cosine algorithm (SCA) and firefly algorithm (FA) were used to optimize the parameters of the LSSVR model. Compared with the original LSSVR model, the coefficient of determination (RP2) is improved after three feature extraction algorithms and two parameter optimization algorithms, and the root average square error (RMSEP) is also decreased. Among these algorithms, feature extraction algorithm CARS and parameter optimization algorithm FA have the best prediction results. When the two are coupled, the CARS-FA-LSSVR model shows the best generalization performance, with RP2 of 0.9944 and RMSEP of 1.3075 mg∙kg-1. Through this research, it can be seen that high-precision detection of heavy metal cadmium content in peanut oil can be achieved by using microwave detection method combined with the stoichiometric model and can be extended to the detection of heavy metal content in other foods, providing a new way of idea for food safety detection.

#2651 Microwave tissue digestion and flame atomic absorption spectroscopy for measuring tissue sodium content in CKD patients

Abstract Background and Aims Skin and muscle sodium accumulation has been demonstrated in CKD patients and may contribute to progression of the disease. Various methods are available for measuring tissue sodium content. However, the accuracy and reproducibility of these methods remain unknown. Dry ashing is the most used digestion method, but is expensive, time consuming and has a risk of incomplete digestion. This study compared microwave digestion, dry ashing, and two electrolyte quantification methods for quantifying tissue sodium and potassium. Method We compared microwave digestion (Ethos LEAN Compact Microwave Digestion System, Milestone SRL) and dry ashing (Nabertherm S27) as sample preparation methods, and flame atomic absorption spectroscopy (FAAS, Model 425 Flame Photometer, Sherwood Scientific) and inductively coupled plasma optical emission spectrometry (ICP-OES, Varian 720-ES, Varian Inc.) as electrolyte quantification methods. Skin and muscle samples were obtained from rats and mice, and human skin samples were used. Tissues biopsies were cut in three pieces and digested separately. The methods were compared using interclass correlation coefficient (ICC) and Bland-Altman analysis. The third piece of tissue was microwave-digested by another operator to test inter-operator reproducibility by calculating the ICC and absolute overall mean difference. Results With microwave digestion and FAAS median (IQR) human skin concentration was 114.8 (99.2-157.0, n = 12) mmol/L, confirming tissue sodium storage. When including all tissues, FAAS and ICP-OES showed high agreement for sodium (ICC 0.98, bias –0.00008 mmol/g, n = 141 and potassium (ICC 0.98, bias –0.005 mmol/g, n = 141). Microwave digestion and ashing showed agreement for sodium (ICC 0.93, bias –0.002 mmol/g, n = 61) and potassium (ICC 0.93, bias –0.02 mmol/g, n = 61). The inter-operator agreement was good for sodium (ICC 0.95, absolute mean difference (SD) 0.044 mmol/g (0.073), n = 70) and potassium (ICC 0.96, absolute mean difference (SD) 0.031 mmol/g (0.032), n = 70). Conclusion Microwave digestion with FAAS is a reliable and consistent method for sodium and potassium trace analysis in animal and human tissues compared to ashing and ICP-OES, respectively. This method showed more quantification of cations than the most frequently reported method, representing an easier, and less time-consuming way to quantify tissue sodium in CKD research.

Compact maze-shaped meta resonator for high-sensitive S-band low permittivity characterization

This paper proposed a compact, high-sensitive S-band microwave sensor for low permittivity characterization. The proposed microwave sensor is inspired by a metamaterials-based maze-shaped split-ring resonator (MS-SRR) configuration, and its overall dimensions are 25 mm × 20 mm × 0.79 mm. The unloaded state of the proposed sensor achieved two robust band-stop notches in its transmission response at 2.77 GHz and 3.08 GHz, respectively. These distinctive features enable the real-time measurement of permittivity in low-permittivity materials. The MS-SRR configuration accomplished strong electric-field intensity, which increased the interaction between the field and testing material, resulting in a highly sensitive measurement. A sensitivity of 11.91% is observed for the first resonance peak and 12.01% for the second peak within the permittivity range from 1 to 2.0. Moreover, the proposed sensor is also competent in measuring the permittivity range between 3 and 10 with a sensitivity of 9.47%–4.93% for the first peak and 9.57%–4.83% for the second peak. The resonance frequency shifting by the influence of material under test (MUT) is presented as a function of permittivity using a regression model. The simulated, measured and formulated results agree well. Finally, the proposed compact and high-sensitive microwave sensor holds promise for low permittivity characterization applications.

MICROWAVE TISSUE DIGESTION AND FLAME ATOMIC ABSORPTION SPECTROSCOPY FOR MEASURING TISSUE SODIUM CONTENT IN HYPERTENSIVE AND CARDIOVASCULAR RISK PATIENTS

Objective: Skin sodium accumulation has been demonstrated in hypertensive patients and may contribute to the pathophysiology of hypertension. Various methods are available for measuring tissue sodium content. However, the accuracy and reproducibility of these methods remain unknown. Dry ashing is the most used digestion method, but is expensive, time consuming and has a risk of incomplete digestion. This study compared microwave digestion, dry ashing, and two electrolyte quantification methods for quantifying tissue sodium and potassium. Design and method: We compared microwave digestion (Ethos LEAN Compact Microwave Digestion System, Milestone SRL) and dry ashing (Nabertherm S27) as sample preparation methods, and flame atomic absorption spectroscopy (FAAS, Model 425 Flame Photometer, Sherwood Scientific) and inductively coupled plasma optical emission spectrometry (ICP-OES, Varian 720-ES, Varian Inc.) as electrolyte quantification methods. Skin and muscle samples were obtained from rats and mice, and human skin samples were used. Tissues biopsies were cut in three pieces and digested separately. The methods were compared using interclass correlation coefficient (ICC) and Bland-Altman analysis. The third piece of tissue was microwave-digested by another operator to test inter-operator reproducibility by calculating the ICC and absolute overall mean difference. Results: With microwave digestion and FAAS median (IQR) human skin concentration was 114.8 (99.2-157.0, n=12) mmol/L, confirming tissue sodium storage. When including all tissues, FAAS and ICP-OES showed high agreement for sodium (ICC 0.98, bias -0.00008 mmol/g, n=141 and potassium (ICC 0.98, bias -0.005 mmol/g, n=141). Microwave digestion and ashing showed agreement for sodium (ICC 0.93, bias -0.002 mmol/g, n=61) and potassium (ICC 0.93, bias -0.02 mmol/g, n=61). The inter-operator agreement was good for sodium (ICC 0.95, absolute mean difference (SD) 0.044 mmol/g (0.073), n=70) and potassium (ICC 0.96, absolute mean difference (SD) 0.031 mmol/g (0.032), n=70). Conclusions: Microwave digestion with FAAS is a reliable and consistent method for sodium and potassium trace analysis in animal and human tissues compared to ashing and ICP-OES, respectively. This method showed more quantification of cations than the most frequently reported method, representing an easier, and less time-consuming way to quantify tissue sodium in hypertension and cardiovascular research.

Coplanar Waveguide (CPW) Loaded with Symmetric Circular and Polygonal Split-Ring Resonator (SRR) Shapes

This paper investigates the performance of coplanar waveguide (CPW) structures loaded with symmetric circular and polygonal split-ring resonators (SRRs) for microwave and RF applications, leveraging their unique electromagnetic properties. These properties make them suitable for metamaterials, sensors, filters, resonators, antennas, and communication systems. The objectives of this study are to analyze the impact of different SRR shapes on the transmission characteristics of CPWs and to explore their potential for realizing compact and efficient microwave components. The CPW-SRR structures are fabricated on a dielectric substrate, and their transmission properties and spectrogram are experimentally characterized in the frequency range of 4 GHz to 10 GHz with the rotation angles of the SRR gap. The simulation results demonstrate that the resonant frequencies and magnitude of the transmission coefficient of the CPW-SRR structures are influenced by the geometry of the SRR shapes and the rotation angles of the SRR gap, with certain shapes exhibiting enhanced performance characteristics compared to others. Moreover, the symmetric circular and polygonal SRRs offer design flexibility and enable the realization of miniaturized microwave components with improved performance metrics. Overall, this study provides valuable insights into the design and optimization of CPW-based microwave circuits utilizing symmetric SRR shapes, paving the way for advancements in the miniaturization and integration of RF systems.

Hand-held electron spin resonance scanner for subcutaneous oximetry using OxyChip.

Electron spin resonance (ESR) is used to measure oxygen partial pressure (pO2) in biological media with many clinical applications. Traditional clinical ESR involves large magnets that encompass the subject of measurement. However, certain applications might benefit from a scanner operating within local static magnetic fields. Our group recently developed such a compact scanner for transcutaneous (surface) pO2 measurements of skin tissue. Here we extend this capability to subsurface (subcutaneous) pO2 measurements and verify it using an artificial tissue emulating (ATE) phantom. We introduce a new scanner, tailored for subcutaneous measurements up to 2 mm beneath the skin's surface. This scanner captures pulsed ESR signals from embedded approximate 1-mm oxygen-sensing solid paramagnetic implant, OxyChip. The scanner features a static magnetic field source, producing a uniform region outside its surface, and a compact microwave resonator, for exciting and receiving ESR signals. ESR readings derived from an OxyChip, positioned approximately 1.5 mm from the scanner's surface, embedded in ATE phantom, exhibited a linear relation of 1/T2 versus pO2 for pO2 levels at 0, 7.6, 30, and 160 mmHg, with relative reading accuracy of about 10%. The compact ESR scanner can report pO2 data in ATE phantom from an external position relative to the scanner. Implementing this scanner in preclinical and clinical applications for subcutaneous pO2 measurements is a feasible next phase for this development. This innovative design also has the potential to operate in conjunction with artificial skin graft for wound healing, combining therapeutic and pO2 diagnostic features.

Compact 3D monolithic microwave integrated circuit bandpass filter based on meander resonator for 5G millimeter-wave

Bandpass filters for millimeter-wave band applications are typically designed using resonators. However, the design of a multilayer coplanar waveguide (CPW) monolithic microwave integrated circuit (MMIC) bandpass filter for 5G millimeter-wave band, n257 with operating frequencies from 26.5 to 29.5 GHz is still not available. Therefore, in this work, a compact bandpass filter for 5G millimeter-wave application was designed with multilayer CPW MMIC bandpass filter based on a meander resonator. The meander resonator of the bandpass filter was designed using low-loss multilayer CPW lines. In designing the bandpass filter, the resonator length and perturbation was utilized to optimize the resonance and bandwidth, and meander resonator was used to miniaturize the bandpass filter. As result, a compact bandpass filter with size of 0.75×0.75 mm<sup>2</sup> for 5G millimeter-wave band n257 was achieved. It has bandwidth of 3 GHz, an insertion loss of -2.87 dB and a return loss of -11.1 dB at frequency 28 GHz.

Microwave quantum diode

The fragile nature of quantum circuits is a major bottleneck to scalable quantum applications. Operating at cryogenic temperatures, quantum circuits are highly vulnerable to amplifier backaction and external noise. Non-reciprocal microwave devices such as circulators and isolators are used for this purpose. These devices have a considerable footprint in cryostats, limiting the scalability of quantum circuits. As a proof-of-concept, here we report a compact microwave diode architecture, which exploits the non-linearity of a superconducting flux qubit. At the qubit degeneracy point we experimentally demonstrate a significant difference between the power levels transmitted in opposite directions. The observations align with the proposed theoretical model. At − 99 dBm input power, and near the qubit-resonator avoided crossing region, we report the transmission rectification ratio exceeding 90% for a 50 MHz wide frequency range from 6.81 GHz to 6.86 GHz, and over 60% for the 250 MHz range from 6.67 GHz to 6.91 GHz. The presented architecture is compact, and easily scalable towards multiple readout channels, potentially opening up diverse opportunities in quantum information, microwave read-out and optomechanics.

5G mm-Wave Technology: Innovative Design of Integrating mm-Wave Wideband Antenna With a Compact CP Microwave Antenna for Diverse Applications

5G mm-Wave Technology: Innovative Design of Integrating mm-Wave Wideband Antenna With a Compact CP Microwave Antenna for Diverse Applications

Compact Microwave Circuit Design With Short Wavelength on Via-Guided Microstrip Lines

Compact Microwave Circuit Design With Short Wavelength on Via-Guided Microstrip Lines

5G millimeter‐wave MIMO DRAs with reduced mutual coupling

AbstractA novel simple decoupling technique is proposed to suppress the mutual coupling of a millimeter‐wave multiple‐input‐multiple‐output dielectric resonator antenna (DRA). The design to be decoupled consists of two microstrip‐line fed rectangular DRAs placed side‐by‐side on an RT‐Duroid substrate and operates near 26 GHz. First, the DRAs are placed at an appropriate separation distance to avoid any close coupling. Second, to reduce coupling further, a set of square ring cell loaded slot is employed on the ground plane in between the DRAs. These two arrangements together, potentially reduce the mutual coupling between the DR elements and substantially improves the in‐band isolation from 14 to 23 dB (min)/34 dB (max) between them. The design is very simple, compact, and easy to fabricate. The model is prototyped and characterized to demonstrate its feasibility for operation. This can be a suitable technique for fifth‐generation compact handheld microwave devices.

A compact and fully integrated FMCW radar transceiver combined with a dielectric lens

Abstract Electronic measurement systems in the THz frequency range are often bulky and expensive devices. While some compact single-chip systems operating in the high millimeter-wave frequency range have recently been published, compact measurement systems in the low THz frequency range are still rare. The emergence of new silicon-germanium (SiGe) semiconductor technologies allow the integration of system components, like oscillators, frequency multipliers, frequency dividers, and antennas, operating in the low THz frequency range, into a compact monolithic microwave integrated circuits (MMIC), which contains most components to implement a low-cost and compact frequency-modulated continuous-wave-radar transceiver. This article presents a single transceiver solution containing all necessary components. It introduces a $0.48\,\mathrm{THz}$ radar transceiver MMIC with a tuning range of $43\,\mathrm{GHz}$ and an output power of up to $-9.4\,\mathrm{dBm}$ in the SG13G3 $130\,\mathrm{nm}$ SiGe technology by IHP. The MMIC is complemented by a dielectric lens antenna design consisting of polytetrafluoroethylene, providing up to $39.3\,\mathrm d\mathrm B\mathrm i$ of directivity and half-power beam widths of 0.95∘ in transmit and receive direction. The suppression of clutter from unwanted targets deviating from antenna boresight more than 6∘ is higher than $24.6\,\mathrm d \mathrm B$ in E- and H-Plane.

A Compact Microwave Quadrature Hybrid Coupler Using Capacitive Composite Lines and Meandered Stubs

In this paper, a new structure of the quadrature hybrid coupler (QHC) with compact size is proposed using capacitive composite lines and meandered open stubs. The proposed coupler works at 1.6 GHz with a 0.4 GHz bandwidth, which shows 25% fractional bandwidth (FBW). The proposed QHC occupies only 15 mm × 15 mm (0.12 λ × 0.12 λ), while the typical QHC size is 32 mm × 32 mm (0.25 λ × 25 λ) at the same working frequency. In the designed structure, two symmetric meandered stubs and two symmetric π-shaped composite networks including capacitors and microstrip lines are applied together. The designed QHC has a small size and occupies only 22% of the area of the conventional QHC, resulting in a 78% size reduction. The designed prototype has been analyzed, fabricated and tested, and the experimental results verify the simulated and analysis results. The results show a better than 27 dB return loss, more than 28 dB isolation between the output ports and less than 0.4 dB insertion loss at the working frequency of 1600 MHz. With the achieved desirable specifications, the fabricated QHC is a suitable choice for wireless microwave applications.