Search Results (76)

Radiofrequency ablation (RFA) is a foundational interventional technology in pain management. Despite the diversity of available systems, conventional thermal, internally cooled, bipolar, and pulsed radiofrequency (PRF) all share one biophysical mechanism: high-frequency alternating current (AC) drives tissue ions to oscillate, generating frictional heat within the tissue surrounding the electrode. This localized heating produces predictable patterns of coagulative necrosis shaped by tissue electrical conductivity, electrode geometry, power delivery, and perfusion-related heat dissipation. Classical and contemporary bioheat models, including the Pennes bioheat equation, describe how these variables determine lesion size and morphology. Advances in device engineering have reshaped lesion characteristics through internally cooled probes, bipolar strip-lesioning systems, and pulsed platforms that modulate neural activity while preserving structural integrity. These innovations broaden therapeutic options by enabling targeting of anatomically variable structures, such as the sacral lateral branches, and intraosseous targets, including the basivertebral nerve (BVN). Emerging technologies—high-voltage PRF, hybrid pulsed–thermal systems, and electroporation-based pulsed-field ablation—reflect a growing emphasis on tissue selectivity, energy efficiency, and safety. This narrative review traces the historical development of radiofrequency neurotomy, examines the biophysical principles governing lesion formation (including the Pennes bioheat equation and the roles of current density, impedance, and perfusion), and details the engineering distinctions among modalities. Clinical applications across spinal, joint, and peripheral nerve targets are presented to illustrate how these physical and engineering differences translate into procedural decision-making, and emerging modalities such as high-intensity focused ultrasound (HIFU) and pulsed-field ablation are discussed in the context of the biophysical principles they extend or depart from. Full article

The increasing replacement of synchronous generators (SGs) by grid-following (GFL) and grid-forming (GFM) inverters is reshaping the dynamic bus characteristics of modern power systems. This transition makes a fixed ideal-voltage-source representation of the upstream main grid increasingly inadequate, especially when the interaction between inverter controls and network dynamics becomes significant. This paper investigates how the upstream grid bus admittance evolves with changes in source composition and observation location. An existing whole-system closed-loop impedance modeling framework is adopted. First, the parameter-dependent port characteristics of individual GFL and GFM inverters are analyzed to identify the frequency ranges dominated by external grid strength, synchronization mechanisms, and inner control loop dynamics. All frequencies reported herein are expressed in the synchronous $dq$ frame. Five representative scenarios are then constructed on the IEEE 16-machine 68-bus system to describe the transition from SG-dominated operation to GFL-rich and SG/GFL/GFM hybrid operation. The results show that increasing GFL penetration together with SG decommissioning does not cause a uniform change in bus admittance, but redistributes the low-frequency resonance characteristics among different locations. At 40% GFL penetration, disconnecting the corresponding SGs changes the dominant peak at electrically remote buses from 56.2 dB at 1.32 Hz to 66.0 dB at 2.44 Hz. When the GFL share is kept at 40% and 15% GFM capacity is introduced, the dominant low-frequency peaks decrease by 8.9 dB and 14.0 dB for buses close to generation sources and electrically remote buses, respectively, while the corresponding average low-frequency magnitude variations decrease by 20.6 dB and 14.7 dB. However, the dependence of bus admittance on network location remains evident. These results indicate that future transmission and distribution interface equivalents should account for source composition, observation location, and frequency dependence rather than relying solely on a fixed grid equivalent. Full article

Breast cancer remains a significant cause of cancer-related mortality in Africa, where late-stage diagnosis, limited access to specialised care, and underrepresentation in biomedical research continue to impede improvements in patient outcomes. At the same time, rapid advances in tumour biology, molecular diagnostics, and precision oncology are fundamentally reshaping our understanding of breast cancer globally. This review examines recent developments in breast cancer clinical research, highlighting how these developments are shaping the future of diagnostics and targeted therapeutics. We further discuss emerging technologies, including multi-omics, liquid biopsy, and artificial intelligence, and consider their potential to advance precision oncology. Importantly, we evaluate these advances within the African context, where limited molecular data, restricted access to diagnostic infrastructure, and resource constraints continue to challenge clinical implementation. Improving outcomes across the continent will require more than the adoption of emerging technologies; it will depend on generating African-relevant biological evidence, expanding representation in genomic research, and integrating molecular, clinical, and environmental data to develop equitable, context-specific precision medicine strategies. Such an approach offers the potential to transform breast cancer management while reducing longstanding disparities in cancer care across Africa. Full article

The stable operation of doubly fed induction generator (DFIG) systems under weak-grid and off-nominal-frequency conditions is important for reliable wind-power integration. However, the phase-locked loop (PLL) dynamics can degrade DFIG impedance and damping, while conventional single-PLL reshaping may suffer from compensation drift under grid-frequency deviations and often relies on a high-pass filter. Therefore, this paper proposes an integrated Double-PLL-Based impedance-reshaping strategy for DFIG systems. Firstly, a complete DFIG admittance model incorporating the rotor-side converter, grid-side converter, DC link, and PLL dynamics is established to identify the critical coupling channel responsible for the adverse impedance characteristics. Secondly, a supplementary rotor-current compensation path is constructed to directly reshape the adverse impedance characteristics and improve system damping. Thirdly, the relative phase angle between the main and auxiliary PLLs is used to generate a frequency-adaptive compensation signal, thereby avoiding continuous compensation drift under persistent frequency deviations and reducing reliance on a dedicated high-pass filter. In this complete strategy, the compensation path directly performs impedance reshaping, while the Double-PLL-Based implementation provides frequency adaptation. Finally, generalized Nyquist analysis and MATLAB/Simulink simulations demonstrate improved impedance matching and oscillation suppression under the considered weak-grid and continuous-frequency-deviation conditions, while hardware-in-the-loop (HIL) experiments corroborate the robustness under PLL-parameter variations. Full article

Portable handheld bioprinters represent a transformative advancement in personalized skin regeneration, bypassing the logistical constraints of stationary lab-based systems by enabling real-time, in situ fabrication of bioengineered constructs directly within the wound bed. This review aims to evaluate the current state of their development and clinical translation. One of the foci is placed on the stringent physicochemical requirements for bioinks, where we examined the critical balance between bioadhesion—facilitated by functional groups—and mechanical cohesion necessary for maintaining structural integrity during deposition, while RGD motifs are considered primarily as promoters of integrin-mediated cell adhesion. Preclinical studies have demonstrated promising effects of bioprinted constructs on wound healing and tissue organization; however, human evidence for handheld and direct in situ skin bioprinting remains limited, and clinical efficacy has yet to be established in controlled studies. Nevertheless, widespread adoption is hindered by inferior printing fidelity relative to stationary counterparts, a lack of standardized GMP-compliant bioink production, and regulatory ambiguity that impedes clear classification as either medical devices or biologics. Practical barriers, including intraoperative sterility assurance and operator training, also remain unresolved. Looking ahead, we discuss how the convergence of, in particular, artificial intelligence for real-time wound morphometry, closed-loop process control, and smart, self-healing biomaterials promises to surmount these obstacles. We conclude that these synergistic innovations may propel handheld bioprinters from experimental prototypes toward clinical tools with the potential to reshape reconstructive surgery and emergency wound care, although their clinical value will require validation in appropriately designed human studies. Full article

This paper proposes a current-feedback active damping strategy to address the high-frequency oscillations in permanent-magnet synchronous generator (PMSG)-based grid-connected systems. The core idea is an active damping controller with coordinated multi-index tuning that jointly considers the impedance–intersection margin, dominant-resonance suppression depth, sideband component increment, and total harmonic distortion. First, positive- and negative-sequence GSC output impedance models are established by incorporating the inner current loop, phase-locked loop, sampling delay, and filter dynamics, and their accuracy is verified through frequency sweep tests. Based on these models, the high-frequency stability mechanism is analyzed using an impedance-based criterion, and parameter sweep studies identify the key control and delay parameters affecting the high-frequency impedance characteristics. Subsequently, a current-feedback active damping controller is designed to reshape the GSC output impedance while minimizing its influence on non-target frequency components. Finally, case studies demonstrate that the proposed strategy eliminates adverse high-frequency impedance intersections and suppresses the target oscillation. Comparison with a virtual-admittance method further confirms a more favorable balance between stability enhancement and power-quality preservation under the investigated operating condition. Full article

Parallel converter operation enables flexible capacity expansion of energy-storage power conversion systems. However, parallel converter interactions, filter-inductor saturation, and grid-strength variations increase the risk of resonance instability. The measured current-inductance characteristic is incorporated into an operating-point-dependent closed-loop Norton model. The grid current of an individual converter is decomposed into self-reference, parallel converter coupling, and grid-voltage-disturbance responses. It reveals that converter-side inductance attenuation shifts the internal and parallel resonances to higher frequencies and increases resonance-instability risk, whereas converter number and grid impedance primarily reshape the parallel resonance. A coordinated active-damping method is then developed: PCC voltage feedforward weakens common-network interaction, and capacitor-voltage feedback increases local LCL-filter damping. Simulation and experimental results validate the feasibility and effectiveness of the proposed control method. Experiments with two parallel converters validated the proposed control method. Stable transient current responses were achieved during a simultaneous current-reference step from 50 to 120 A, while the grid-current THD and power-sharing deviation remained below 3% and 5%, respectively. Full article

Conventional integer-order parameter designs of grid-forming inverters provide limited degrees of freedom for impedance adjustment, motivating the exploration of additional approaches for flexible impedance reshaping across different frequency ranges. This paper establishes a full fractional-order grid-forming inverter (FFO-GFMI) by incorporating fractional-order inductor-capacitor (LC) filters, corresponding decoupling control, and fractional-order multi-loop controllers into a conventional grid-forming inverter. Based on the harmonic linearization method, positive- and negative-sequence impedance models of the FFO-GFMI are developed to characterize its broadband impedance characteristics. The developed models are validated through impedance scanning, and the effects of fractional-order parameters on broadband impedance characteristics are systematically investigated. The results reveal that fractional-order LC filters mainly regulate medium- and high-frequency resonance characteristics, while fractional-order control loops provide effective low- and medium-frequency impedance reshaping. Furthermore, load-step simulations demonstrate that the selected fractional-order configuration improves dynamic performance, reducing the active power settling time from 0.3121 s to 0.1974 s and the active power overshoot from 19.75% to 4.51%. Full article

DC-link voltage synchronization control (DVSC), or matching control, offers a simple grid-forming (GFM) solution for two-stage photovoltaic (PV) systems by linking the DC-link voltage to converter frequency. However, its low-frequency damping is sensitive to grid strength and power-transfer level. This paper investigates the damping and synchronization characteristics of DVSC-based grid-forming PV systems under varying operating conditions. A reduced-order small-signal model is developed to decompose the contributions of the DVSC loop, electrical network, and terminal-voltage regulation. The analysis reveals that the basic DVSC loop provides no inherent damping, while the interaction between voltage regulation, grid impedance, and transferred power may introduce negative damping or reduce the synchronizing margin. The operating-condition-dependent limitations of lead-phase correction and q-axis voltage feedforward are then identified. To supplement these methods, DC-link-voltage-feedback d- and q-axis voltage stabilizers are designed and integrated with DVSC reshaping in a composite stabilization scheme. Eigenvalue analysis and OPAL-RT real-time simulations demonstrate the complementary damping characteristics of the four stabilizing paths. Full article

Although the weak-grid stability of grid-following inverters has been widely studied, traditional SCR-based assessment mainly describes grid strength and does not directly quantify the minimum SCR required for stable operation under a specified active-power command. This paper uses a critical-SCR-oriented operating-boundary evaluation to compare the control-dependent dynamic stability requirement with the physical steady-state feasibility limit. It proposes a channel-specific impedance-reshaping extension that retains the PLL-related q-q and d-q compensation paths and adds a voltage-loop-related q-d compensation path. The added path reduces the control-induced dynamic critical SCR, thereby allowing stable operation at lower SCR than with the original control structure. Firstly, the steady-state critical SCR is derived from the steady-state power-transfer relation under a specified active-power command to define the physical feasibility lower bound, and the dynamic critical SCR is identified using a scanning procedure based on the generalized Nyquist criterion. The resulting control-induced SCR gap quantifies the additional grid-strength requirement introduced by the control dynamics. Secondly, a simplified d-q admittance representation is used to relate established PLL-related and voltage-loop-related coupling effects to the corresponding compensation paths. Thirdly, the proposed channel-specific impedance-reshaping design is used to mitigate these effects while retaining the selected voltage-loop bandwidth, and an anti-drift correction is further introduced to improve implementation robustness. Frequency-domain analysis and time-domain simulations validate the dynamic critical-SCR evaluation, while hardware-in-the-loop experiments demonstrate the real-time operation of the proposed controller. The results show that it moves the dynamic critical-SCR boundary close to the steady-state physical boundary and improves the weak-grid stability margin. The hardware-in-the-loop results further confirm bounded operation under SCR and frequency steps. Full article

Parallel-inverter microgrids are prone to PCC voltage distortion during islanded operation with nonlinear and unbalanced loads. Virtual-impedance methods can reshape inverter output impedance, but they also add control complexity and may introduce extra voltage drops. This paper proposes a droop-based PI-QPR control strategy to improve PCC voltage quality in islanded parallel-inverter microgrids. The droop scheme generates the fundamental voltage and frequency references, and the PI-QPR voltage outer loop regulates the fundamental, negative-sequence, and dominant low-order harmonic voltage components in the dq synchronous reference frame. The PI regulator is used for the fundamental component, while QPR branches at 2ω₀ and 6ω₀ compensate the negative-sequence component and the dominant fifth- and seventh-order harmonics. No additional virtual-impedance loop is introduced. Two-inverter hardware-in-the-loop (HIL) tests were conducted under nonlinear and unbalanced load conditions. Compared with the traditional voltage controller, the proposed controller reduces the measured three-phase PCC-voltage THD from 5.79–6.02% to 2.41–2.79%, confirming improved PCC voltage quality in the tested islanded condition. Full article

This paper proposes a phase-compensated enhanced second-order generalized integrator phase-locked loop (ESOGI-PLL) to suppress the frequency coupling effect (FCE) and its associated power quality degradation in grid-following inverters (GFLIs). An output impedance model incorporating FCE dynamics is formulated via signal perturbation analysis to quantify grid-current harmonic amplification and weak-grid instability boundaries. To suppress the FCE, the proposed ESOGI-PLL structurally embeds a phase-lead compensator, directly neutralizing the inherent phase lag of conventional filters. Simulation results demonstrate that the proposed ESOGI-PLL effectively mitigates PLL-induced frequency coupling, thereby improving the output-current quality and stability of GFLIs under weak-grid conditions. Compared with the synchronous reference frame phase-locked loop (SRF-PLL), the total harmonic distortion (THD) of the grid-current decreases from 24.33% to 2.47% under harmonic disturbances, while the transient settling time is significantly reduced, confirming the effectiveness of the proposed approach in enhancing both dynamic performance and output-current quality. Full article

Hybrid systems integrating grid-following (GFL) and grid-forming (GFM) inverters are increasingly deployed in renewable-energy-dominated power systems. However, impedance coupling between the two inverter types may induce low-frequency oscillations and high-frequency resonances, particularly under weak-grid conditions and varying power injections. This paper clarifies the stability mechanism of a hybrid GFL/GFM inverter system and develops a frequency-segmented active damping strategy. Small-signal impedance models are first derived for the GFL inverter, the GFM inverter, and the overall hybrid system, incorporating the control loops, digital delay, LC filters, interconnection branch impedances, and external grid impedance. Impedance decomposition, Bode plots, and Nyquist criteria are then employed to quantify the influence of power operating points and grid strength on system stability. The results indicate that increasing the GFL inverter output power weakens the stability margins in both low- and high-frequency ranges, whereas variations in the GFM inverter output power provide only limited impedance reshaping in the targeted oscillation bands. On this basis, a low-frequency damping loop is designed on the GFM inverter side, while a high-frequency damping loop based on capacitor-current feedback is implemented on the GFL inverter side. Simulation results confirm that the proposed strategy suppresses low-frequency oscillations and high-frequency harmonic components, maintains stable operation in the hybrid system under high GFL power injection, and reduces the THD of the PCC current from 14.52% to 0.62%. Full article

This paper presents a metasurface filtering antenna based on unequal rectangular patch elements. The design is implemented with only two dielectric layers: the upper PCB carries the metasurface radiator, and the lower PCB supports a Y-shaped microstrip feeding network. A radiation null near 3.3 GHz is obtained by dividing the four corner units of the metasurface into 2 × 2 subarrays, which reshapes the current paths around the central aperture and causes destructive spatial radiation. For the upper stopband, a second null appears at 3.84 GHz because the fields coupled from the opposite-phase currents on the Y-shaped feed branches cancel in the far field. Measurements indicate that the antenna provides a 10 dB impedance bandwidth of 3.43–3.60 GHz, or 9.85% in fractional bandwidth. Within the passband, the measured average realized gain reaches 7.51 dBi. The lower and upper stopbands exhibit radiation suppression levels of 15.61 dB and 14.08 dB, respectively. The boresight cross-polarized field is also more than 20 dB below the co-polarized field, confirming satisfactory radiation quality. These results make the proposed antenna suitable for compact 5G front-end integration. The proposed design provides a balanced combination of low profile, compact aperture, measured gain, and two band-edge radiation nulls. Full article

The main purpose of this study is to overcome the difficulty of maintaining high-quality zero-voltage switching (ZVS) in resonant converters over wide operating ranges. Conservative designs ensuring light-load ZVS inevitably generate excessive reactive current, causing severe circulating losses and body diode conduction under heavy loads. To resolve this intrinsic trade-off, this paper proposes an active closed-loop optimal ZVS control strategy utilizing a DC-biased variable resonant inductor. The core mechanism actively shifts the tank impedance to dynamically reshape the primary current. By integrating the primary current during each dead time, the real-time integrated charge is actively regulated to track an optimal reference limit defined by the switch parasitic capacitance and dc-bus voltage. Consequently, the variable inductor continuously regulates the tank current toward the optimal ZVS boundary, ensuring the parasitic capacitance is completely discharged just before the turn-on instant. Validations via simulation and a 192 W hardware prototype confirm the method’s efficacy. The strategy completely eliminates light-load hard switching and significantly suppresses heavy-load body diode conduction without compromising output voltage regulation. Compared to conventional active schemes, this approach achieves full-range optimal ZVS without requiring additional high-frequency switching devices, establishing a highly efficient shift from passive parameter design to active boundary tracking. Full article