Modulation Index Research Articles

Wolf Tones and Humidity in Violins

This paper attempts to, perhaps for the first time in this type of studies, quantitatively evaluate the severeness (as defined in this paper) of the undesired wolf tones on a violin as the surrounding humidity changes. The severity of the wolf tones was evaluated by a skilled violinist under various humidity conditions. It was found that a total duration and frequency of occurrence of wolf tones during a set period time are largest around 50% humidity, a humidity at which violins are recommended to be maintained for optimizing the projection across the entire register of the instrument, whereas other characteristics of the wolf tones, such as modulation index and the period, did not exhibit significant changes over the humidity change. When the humidity deviates from 50%, the total durations and the occurrence frequency of the wolf tones both diminishes. On the other hand, the amplitude (i.e. volume) of the wolf tones are larger on the lower humidity and the higher humidity ends, and was smallest around 50% humidity. These findings may shed new light on the traditional theories and analysis of wolf tones as well as on evaluations of various wolf tones elimination methodologies. It was also found that although the evaluation method involved some subjectivity, this way of evaluating the wolf tones had consistency and a good degree of reliability, paving a new way to quantify the wolf tones.

Mitigation of common mode voltage in ultra sparse matrix converters using auxiliary shoot‐through switches for wind energy systems

SummaryThis paper targets to minimize the peak common mode voltage (CMV) in ultra sparse matrix converters (USMC) by applying new zero vectors for the space vector modulation technique (SVM). Conventional zero vectors in the SVM raise the peak CMV by 42.23%. An increased magnitude of CMV is associated with the occurrence of leakage current, hence resulting in insulation degradation. So, the reduction of peak CMV is necessary for USMC. The proposed method offers suitable switching arrangements using auxiliary shoot through (AST) switches to minimize the peak‐to‐peak CMV. This proposed method holds the advantages of the conventional method, like a wide range of modulation index and zero current switching at the rectifier side, and also reduces the CMV problem. This paper also provides a comparative analysis of the existing reported methods and the proposed method. The effectiveness of the proposed method is validated through both simulation and experimental results.

Quantitative Assessment of Fungal Biomarkers in Clinical Samples via an Interface-Modulated Optical Fiber Biosensor.

Invasive fungal infections pose a significant public health threat. The lack of precise and timely diagnosis is a primary factor contributing to the significant increase in patient mortality rates. Here, an interface-modulated biosensor utilizing an optical fiber for quantitative analysis of fungal biomarkers at the early stage of point-of-care testing (POCT), is reported. By integrating surface refractive index (RI) modulation and plasmon enhancement, the sensor to achieve high sensitivity in a directional response to the target analytes, is successfully optimized. As a result, a compact fiber-optic sensor with rapid response time, cost-effectiveness, exceptional sensitivity, stability, and specificity, is developed. This sensor can successfully identify the biomarkers of specific pathogens from blood or other tissue specimens in animal models. It quantifies clinical blood samples with precision and effectively discriminates between negative and positive cases, thereby providing timely alerts to potential patients. It significantly reduces the detection time of fungal infection to only 30 min. Additionally, this approach exhibits remarkable stability and achieves a limit of detection (LOD) three orders of magnitude lower than existing methods. It overcomes the limitations of existing detection methods, including a high rate of misdiagnosis, prolonged detection time, elevated costs, and the requirement for stringent laboratory conditions.

Long-Period Grating with Asymmetrical Modulation for Curvature Sensing

We propose and demonstrate a curvature sensor based on long-period fiber grating (LPFG) with asymmetric index modulation. The LPFG is fabricated in single-mode fiber with femtosecond laser micromachining. The grating structure is not introduced in the central fiber core, but is located off-axis with a distance of a few micrometers. Experimental results indicate that the offset distance has direct influence on the grating spectra. By utilizing such an asymmetric structure, two-dimensional vector curvature sensing can be realized. For an LPFG with an offset distance of 6 μm, the curvature sensitivity is around 29 nm/m−1 in the 0° and 180° direction and about 20 nm/m−1 in the 90° and 270° direction. The difference in curvature sensitivity in different bending directions makes the sensor capable of distinguishing the curvature orientation. The temperature response of the sensor is also experimentally investigated, and results indicate that the sensor has a very low temperature cross-sensitivity of 0.003 m−1/°C. The characteristics of high curvature sensitivity, two-dimensional bending direction identification, and compact structure make the device an ideal candidate to be applied in the field of power grid health monitoring and intelligent robotics.

Comparative study of single-phase multilevel cascaded transformerless inverters with different modulation methods

This paper presents an in-depth exploration of a single-phase multilevel cascaded H5 (CH5) transformerless inverter employing both phase-shifted PWM (PS-PWM) and level-shifted PWM (LS-PWM) methodologies. A comparative analysis is conducted with the conventional multilevel inverter (MLI) topologies, specifically the cascaded H-bridge (CHB) and H5 inverter configurations. The investigation delves into the impact of modulation index variations, load fluctuations, and modulation methods on the inverter's operational performance.While switches in the CHB-MLI operate continuously at the carrier frequency state using PS-PWM and LS-PWM methods, the CH5-MLI exhibits a unique behavior with some switches toggling at high frequency, while others synchronize with the grid frequency. The CH5-MLI topology demonstrates efficiency improvements and a reduction in total harmonic distortion (THD). Notably, employing the LS-PWM method yields more significant efficiency enhancements and THD reduction compared to the PS-PWM method. To analyze power loss characteristics under diverse operating conditions, the PLECS simulation environment is leveraged for calculating conduction and switching losses.The application of phase-shifted and level-shifted carrier-based pulse width modulation strategies to high and low-frequency switching switches results in minimized output harmonics, elevated operator safety, and enhanced overall reliability and efficiency. This work contributes significantly to the field by offering a detailed exploration of the CH5-MLI topology's dynamic behavior, modulation strategies, and their collective impact on performance metrics such as efficiency, THD, and power losses.

Ultra-broadband multi-channel orbital angular momentum mode generator using a helical long-period grating pair

We demonstrate an ultra-broadband multi-channel orbital angular momentum (OAM) mode generator using a helical long-period grating (HLPG) pair in a few-mode fiber. The numbers of the channel of the OAM mode generator can be flexibly adjusted by designing the cascaded length of the HLPG pair. When the cascaded length is 50 cm, the maximum channel number of OAM mode generator reaches 46, and the mode convert efficiencies of the channels are more than 90 %, which is, to the best of our knowledge, the highest number of channels among OAM mode converters. By reducing grating length and enhancing the refractive index modulation depth, the 3 dB bandwidth of the HLPG is significantly increased, and thus the wavelength range of the HLPG pair can be expanded. The maximum wavelength ranges of the channels with coupling efficiency greater than 90 % are measured to be 379 nm experimentally. By adjusting the spiral direction of the helical refractive index modulation, we can achieve multi-channel ± 1 order OAM mode conversion for each channel. The multi-channel OAM mode generator holds substantial potential for applications in mode division multiplexing systems, wavelength filters, and fiber sensing.

New multilevel inverter based on reduced switch basic cell for high voltage levels

AbstractIn this study, to solve total harmonic distortion (THD) and voltage stress on switches, challenges have been made by presenting a new multi‐level inverter (MLI). The proposed topology can operate with both symmetric and asymmetric sources. The proposed topology in symmetric and asymmetric mode with 18 switches can produce 17 and 49 voltage levels, respectively, with THD values of 4.14% and 1.45%, which passes the IEEE harmonic standard. The main advantage of the proposed topology is reducing the number of circuit devices, which reduces the price, volume, and complexity of the circuit by reducing the number of circuit devices. The proposed topology reduces the THD, the number of power electronics components, and voltage stress by increasing the output levels. The proposed topology is compared with other topologies and the advantage of the proposed topology is shown in terms of the number of switches and drivers. In addition, the proposed topology is compared in terms of the cost function. The power losses based on the thermal model of the proposed topology have been analysed and simulated. Simulation and experimental results are presented for different scenarios such as load type, load changes, and modulation index changes to validate the proposed topology.

Acoustic hologram-induced virtual in vivo enhanced waveguide (AH-VIEW).

Optical imaging and phototherapy in deep tissues face notable challenges due to light scattering. We use encoded acoustic holograms to generate three-dimensional acoustic fields within the target medium, enabling instantaneous and robust modulation of the volumetric refractive index, thereby noninvasively controlling the trajectory of light. Through this approach, we achieved a remarkable 24.3% increase in tissue heating rate in vitro photothermal effect tests on porcine skin. In vivo photoacoustic imaging of mouse brain vasculature exhibits an improved signal-to-noise ratio through the intact scalp and skull. These findings demonstrate that our strategy can effectively suppress light scattering in complex biological tissues by inducing low-angle scattering, achieving an effective depth reaching the millimeter scale. The versatility of this strategy extends its potential applications to neuroscience, lithography, and additive manufacturing.

Luminal mirror.

When a refractive index modulation of dispersive medium moves at the speed of light in vacuum, an incident electromagnetic wave, depending on its frequency, either is totally transmitted with a phase shift, or forms a standing wave, or is totally reflected with the frequency upshift. The luminal mirror converts a short incident pulse into a wave packet with an infinitely growing in time local frequency near the interface and with an energy spectral density that asymptotically is the inverse square of frequency. If the modulation disappears, the high frequency radiation is released.

Analysis and assessment of electrical and thermal performance of five‐phase voltage source inverter under different modulation strategies: Comparative study under balanced and unbalanced load

SummaryThis paper compares four modulation strategies applied to five‐phase voltage source inverters (5PH‐VSI). The modulation strategies under investigation are sine wave pulse width modulation (S‐PWM), fifth‐harmonic injection PWM (FH‐PWM), space vector‐PWM using two large vectors (2V‐SVPWM), and space vector‐PWM using two medium and two large vectors (4V‐SVPWM). The study utilizes simulations to analyze the results based on four performance criteria: low‐order harmonics (LOH), maximum modulation index (MMI), common mode voltage (CMV), and total harmonic distortion (THD) under balanced and unbalanced load. To validate the simulation results for these criteria, an experimental test‐bench is employed, which includes a 5PH‐VSI feeding an R‐L load, and controlled by a low‐cost STM32F4‐DISCOVERY microcontroller board. Additionally, a mathematical approach is used to calculate the total thermal losses (TTL) then simulations are performed using Piecewise Linear Electrical Circuit Simulation (PLECS) software to assess the modulation schemes based on additional thermal performance criteria: conduction losses (CL), switching losses (SL), TTL, the efficiency, and the maximum permissible heat sink thermal resistance (MPHTR) at the steady‐state regime. The results indicate that the 4V‐SVPWM method demonstrates superior efficiency in terms of THD. Furthermore, it showcases the lowest TTL at high switching frequencies, allowing for the best efficiency and minimizing MPHRT, therefore providing the largest margin for the heat sink thermal resistance design. On the other hand, the 2V‐SVPWM offers the highest MMI, but this comes at the cost of high TTL and some LOHs appearing. In addition, it exhibits the highest CMV for unbalanced load. S‐PWM and FH‐PWM offer the advantage of simpler implementation.

Holographic nanodiamond–polymer composite grating with unprecedented slow-neutron refractive index modulation amplitude

We demonstrate exceptionally high slow-neutron diffraction efficiency (≈ 70% of transmitted intensity diffracted to the first order) from a holographic nanodiamond–polymer composite grating of only tens of micrometers thickness at the average neutron wavelength of 5.3 nm. By meticulous choice of materials for extreme refractive index modulation in a thin grating structure, we overcome typical wavelength and angular selectivity issues usually encountered when pursuing high diffraction efficiencies with a thick grating. This achievement paves the way for the implementation of flux-efficient diffractive elements, well-suited for polychromatic beams, and weakly collimated slow-neutron beams.

Solid rocket motor propellant health monitoring based on oxide-doped curved long-period fiber grating.

A kind of curved long-period fiber grating(CLPFG) engraved by CO2 laser based on oxide-doped fiber was designed to monitor the structural integrity of propellant. The mechanical damage characteristics of the propellant were analyzed. The sensor model is constructed and the refractive index modulation characteristics of the CLPFG are analyzed. The strain coupling characteristics and the strain transfer efficiency of the interface between the CLPFG and the propellant are clarified. Propellant modules with implanted CLPFG were fabricated. The novel grating sensor has been effectively coated and structurally packaged. Conducted experiments on strain and temperature of propellant modules. The large strain measurement of propellant from 0 με to 24000 με is realized. Solved the thorny problem of large strain measurement for propellants. In addition, the temperature discrimination measurement in the temperature range of 30 ℃ to 250 ℃ can be realized. Sensor exhibit extremely high stability characteristics and has good compatibility with propellants. The sensor implantation and extraction structure has been designed to improve the survival rate of the sensor inside the solid rocket motors (SRM). Sensors can accurately measure the mechanical and thermal state parameters of propellants, providing effective data support for the health management of SRM.

Optimal Hybrid Pulse Width Modulation for Three-Phase Inverters in Electric Propulsion Ships

Global interest in environmentally friendly ships has surged as a result of greenhouse gas reduction policies and the demand for carbon neutrality. Despite growing demand for electric propulsion systems, there is a lack of research and development on crucial components. Efficiency and stability are primarily influenced by the performance of inverters, which are essential for driving propulsion motors. Existing inverter control techniques can be of two types: continuous-PWM (pulse width modulation) methods for harmonic performance enhancement and discontinuous-PWM methods for efficiency improvement by reducing losses. However, there are limitations in that each PWM method exhibits substantial variations in inverter performance based on its operating conditions. To address these challenges, this study proposes the hybrid pulse-width-modulation (HPWM) method for optimal inverter operation. By analyzing the inverter’s operating conditions, the proposed HPWM method adopts various pulse-width-modulation (PWM) strategies based on a modulation index to achieve harmonic improvement and loss reduction. Our focus is on comparing and analyzing diverse PWM techniques under varying modulation indices and frequency conditions to attain the optimal operating conditions. Experimental validation of the proposed method was conducted using a 2.2 kW dynamometer. In comparison with existing PWM methods, the proposed method demonstrated superior performance.

High sensitivity Sagnac interferometric temperature sensor using stress region refractiveindex modulation.

An all-fiber temperature sensor employing intentional refractive index modulation is experimentally demonstrated. The sensor consists of four sections of polarization maintaining fiber (FPMF) sandwiched between multi-mode fiber (MMF). The stress region of two sections of polarization maintaining fibers (PMFs) is aligned and then anti-clockwise rotates one PMF in 10deg angles while the other keeps still. Finally, the discharge proceeds. The remaining two PMFs are fusion spliced with the same method. Then the prepared FPMF-MMF structure is connected to the 3dB coupler to construct a Sagnac loop. The temperature sensitivity reaches 1.49nm/°C for a temperature range from 16°C to 55°C. The proposed temperature sensor with easy fabrication and good linearity in measuring temperature can be a promising candidate for various applications in environmental monitoring and industrial production.

High-Performance Wireless Power and Data Transmission System for Medical Implant Devices Using ASK Modulation

Wireless power and data transmission (WPDT) solutions for medical implants are highly desired. However, achieving a high-power transmission efficiency and data rate simultaneously over an inductive link remains a significant challenge. This paper presents an innovative WPDT circuit that incorporates additional MOSFETs with an inductor in a Class-E power amplifier (PA), achieving amplitude-shift keying (ASK) modulation to address this issue. Firstly, the efficiency of the inductive power transmission link and Class-E PA was analyzed, providing design insights. Then, leveraging the insights, the proposed circuit was designed in such a way that it could effectively switch between two load networks to maintain high transfer efficiency for ASK modulation. Based on the load networks, the relationship between introducing the inductor’s value and the data modulation index (MI) was derived to help achieve the desired high-power transmission efficiency. Additionally, the design and calculation of the proposed circuit are also presented. Finally, the proposed circuit was validated through simulations and experiments, demonstrating a power delivery to a load of 84.1 mW with a power transmission efficiency of 70.8% at a data rate and carrier frequency of 3 Mbps and 16 MHz, respectively. Furthermore, the bit error rate (BER) is less than 10−6 with an MI of 10%.

Extension of Operating Range in Hybrid Cascaded H-Bridge Inverters with Capacitor Voltage Balancing Capability

In this article, a generalized control scheme is proposed to extend the operating range of three-phase hybrid cascaded H-bridge (HCHB) inverters into various voltage levels without necessitating alterations to the core structure or the integration of additional H-bridge submodules. This study addresses a critical challenge related to capacitor voltage drift at various modulation indices and power factors, which is a serious impediment to various applications. To overcome this challenge, a novel balancing control scheme has been developed based on the injection of two independent offset voltages to simultaneously control the DC-link and flying capacitors. A distinctive aspect of the proposed technique involves adjusting the common reference voltage to attain the nearest level in the same cluster, thereby mitigating the insufficiency of redundant switching states. The effectiveness of the proposed technique to regulate the capacitor voltages at various operating conditions has been verified through simulation and experimental results.

Amplitude modulation leads to the disappearance of relaxation oscillations in the Duffing system

Relaxation oscillations are pervasive in diverse areas of natural sciences and engineering, and exploring the dynamical mechanisms of relaxation oscillations is one of the most significant issues. Typical relaxation oscillations can be observed in the Duffing system. Recently, amplitude modulation has emerged as a novel control mechanism for investigating the behavior of fast-slow dynamics in systemic tension oscillations. It has demonstrated the ability to prolong the quasi-static slow process of the system and increase the number of bifurcation points. However, the exploration of the mechanistic aspects of amplitude modulation is still in its early stages, with many unreported dynamical mechanisms. Among these, investigating the modes of relaxation oscillations induced by amplitude modulation is one of the most important issues. Therefore, this manuscript focuses on studying the effect of amplitude modulation on relaxation oscillations, using the classical forced Duffing system as a representative model. Significantly, we report an intriguing finding for the first time, revealing a new amplitude-modulated mechanism by which the disappearance of relaxation oscillations can be induced. By employing the fast-slow analysis, we have examined the underlying dynamical mechanisms, revealing a strong correlation with the modulation index of amplitude modulation. Notably, when the system operates under low amplitude modulation, an extension of the quasi-static process is observed, manifesting as a prolonged slow process. Conversely, under high amplitude modulation, relaxation oscillations suddenly disappear. Our results serve to enrich the potential mechanisms of amplitude modulation, and our analysis provides a reference for investigating the dynamical behavior induced by amplitude modulation in other dynamical systems.

Photon Generation Scheme of 32‐Fold Millimeter‐Wave Signal Based on Mach‐Zehnder Modulator

AbstractThis paper proposes a 32‐tupling frequency millimeter‐wave (MMW) filter‐free system based on four Mach‐Zehnder Modulators (MZM) connected in parallel and cascaded with a simple radio‐fiber (RoF) link structure. The four MZMs are all at the maximum transmission point (MATP), and the radio frequency (RF) driving voltage phase difference between MZMs is π /2. The center carrier is suppressed by using an optical attenuator (OATT) and an optical phase shifter (OPS). Two parallel MZMs can generate ±8th order and ±12th order optical sidebands, and the ±4th order optical sidebands can be suppressed by adjusting the modulation index m of the MZM, using cascaded two dual‐parallel MZMS(DPMZM) and the phase difference of the RF signal source is π/4 to generate ±16th order optical sidebands. The theoretical analysis and simulation experiments are performed for the scheme proposed in this paper. The results show that the simulated and theoretical values of the optical sideband suppression ratio (OSSR) for ±16th order optical sideband signals are 60.02 and 59.96 dB, respectively, and the simulated and theoretical values of the RF sideband suppression ratio (RFSSR) for the 32‐tupling MMW signal are 56.34 and 53.94 dB, respectively.

Realization of a Three-Switch Leg/Phase Inverter for Nine-Phase Variable Pole– Phase Induction Machine With Phase Grouping Concepts

In this paper, a 3-switch leg/phase inverter topology is realized for 9-phase variable pole-phase induction motor (9Ph-VPIM) drives. The 3-switch legs (3SL) in the proposed inverter are controlled with two non-intersecting phase shifted references to achieve a 3-level voltage excitation for each phase winding. These two non-intersecting references per leg limit the possible modulation index (MI) and may require a higher DC link voltage. The split winding concept and the phase grouping solutions are used to enhance the MI. In the split winding concept, phase winding of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2n</i> pole machine is divided into <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> number of distinct windings and excited with the same voltage for attaining a uniform air gap flux. These coils are called cognate voltage coils (CVC). With these CVCs, different possible groupings are proposed to enhance the MI of a proposed 3SL/phase inverter. The symmetrical and efficient phase grouping solutions are analyzed and tested with an improved modulation index. Moreover, the proposed 9Ph-VPIM drive is controlled with carrier-based 3-φ SVPWM to further enhance the DC link voltage utilization. The proposed inverter will feed the effective phase by a 3-level voltage with suppressed harmonics resulting in a superior torque ripple. The proposed 3SL/phase inverter fed 5-hp 9Ph-VPIM drive is validated with the experimental prototype.

A Novel Virtual Space Vector Modulation With Optimized Neutral-Point Voltage Control Capability for Ten-Switch Three-Phase Three-Level Inverter

Ten-switch three-phase three-level inverter (TP-TLI) is receiving more attentions owing to the reduced system cost compared to traditional TP-TLIs. However, it still faces serious neutral-point voltage (NPV) balance problem. This article proposes a novel virtual space vector modulation (NVSVM) with optimized neutral-point voltage control (NPVC) capability. A set of virtual vectors are selected to generate zero NP current. By analyzing the vector synthesis principle over the full modulation areas, a new control degree, which is utilized to optimize the NPVC capability and reduce line voltage THD, is introduced. Besides, a dead time compensation method based on volt-second balance is also given to reduce the switching loss. The NVSVM not only improves the NPVC capability without dc offset and obvious ac oscillations in NPV under full range of modulation index and power factor (PF) conditions, but also reduces line voltage THD and the switching loss. Theoretical analysis shows that the available NP current for the proposed NVSVM is about 2.75 times greater at most than that for traditional VSVM. Simulation and experimental results are given to validate the effectiveness of the NVSVM and control strategies.