Frequency-modulated Wave Research Articles

Electromagnetism - Properties of Erythrocytes

At the onset of blood flow, red blood cells (RBCs) align along the central plane of the vessels. In capillaries, RBCs transform from a biconcave disk into a parachute shape. As blood transitions from the arterial to the venous end, the hemoglobin in erythrocytes alters its magnetic susceptibility. Within approximately 0.6-0.8 seconds, oxygen is displaced from RBCs through diffusion. This study explores the fundamentals and interconnections of these processes.
 
 Blood samples from 35 different healthy individuals were analyzed. The research examined magnetic field induction in ferromagnetic toroids, formed by the alternative electric field with a square wave signal, and studied the AC in the secondary coil - a tube filled with blood. This study discusses the impact of RBC geometry and hemoglobin allosteric transitions on electric signal generation and its relevance to cellular metabolic activity in the body.
 
 The findings suggest that the AC field, originating from the heart's rotational dipole, can generate a magnetic field in RBCs, facilitating the allosteric transformations of hemoglobin. Hemoglobin's thermoelastic expansion and magnetostriction cause biconcave membrane oscillations at ultrasound frequencies. The resulting electroacoustic wave rotates charges at the cell's z-potential area, aids RBC migration into the flow plane, and enhances trans capillary diffusion of substances.
 
 An electroacoustic standing wave emerges between the oscillating RBCs, coinciding with the wavenumber of externally penetrating infrared light. The synergic influence on hemoglobin in capillaries causes the RBC membrane to create a temporally frequency-modulated wave, carrying resonance molecular frequencies. This wave regulates biochemical processes within and outside body cells.

Frequency combs in optically injected terahertz ring quantum cascade lasers

Quantum cascade lasers (QCLs) have emerged as promising candidates for generating chip-scale frequency combs in mid-infrared and terahertz wavelengths. In this work, we demonstrate frequency comb formation in ring terahertz QCLs using the injection of light from a distributed feedback (DFB) laser. The DFB design frequency is chosen to match the modes of the ring cavity (near 3.3 THz), and light from the DFB is injected into the ring QCL via a bus waveguide. By controlling the power and frequency of the optical injection, we show that combs can be selectively formed and controlled in the ring cavity. Numerical modeling suggests that this comb is primarily frequency-modulated in character, with the injection serving to trigger comb formation. We also show that the ring can be used as a filter to control the output of the DFB QCL, potentially being of interest in terahertz photonic integrated circuits. Our work demonstrates that waveguide couplers are a compelling approach for injecting and extracting radiation from ring terahertz combs and offer exciting possibilities for the generation of new comb states in terahertz, such as frequency-modulated waves, solitons, and more.

Advancing Stepped-Waveform Radar Jamming Techniques for Robust False-Target Generation against LFM-CFAR Systems.

This study investigates the utilization of a stepped wave frequency modulation jamming technique in radar systems. The objective is to enhance the effectiveness and robustness of false target jamming in the presence of linear frequency modulation (LFM) radars employing constant false alarm rate (CFAR) detection. The proposed method combines stepped frequency modulation with full pulse delay/sum repeat jamming to enhance resilience against uncertainties in target parameters. Theoretical analysis and simulation experiments are conducted to establish relationships between key jammer parameters, such as frequency slope and power compensation, and performance metrics, like false target distribution and CFAR masking. The results demonstrate that the proposed technique effectively maintains a dense distribution of false targets surrounding the protected target, even in the presence of uncertainties in position and signal-to-noise ratio. In comparison to existing methods, the utilization of stepped-waveform modulation enables improved control over target distribution and CFAR masking. Adaptive power allocation compensates for parameter errors, thereby enhancing robustness. Simulation results reveal that the proposed approach significantly reduces the probability of detecting the true target by over 95% under uncertain conditions, while previous methods experienced degradation. The integration of stepped waveforms optimizes false target jamming, thereby advancing electronic warfare capabilities in countering advanced radar threats. This study establishes design principles for resilient jamming architectures and supports enhanced survivability against radars employing pulse compression and CFAR detection. Moreover, the concepts proposed in this study have the potential for extension to emerging radar waveforms.

Advances in Silicon-Based Integrated Lidar.

Silicon-based Lidar is an ideal way to reduce the volume of the Lidar and realize monolithic integration. It removes the moving parts in the conventional device and realizes solid-state beam steering. The advantages of low cost, small size, and high beam steering speed have attracted the attention of many researchers. In order to facilitate researchers to quickly understand the research progress and direction, this paper mainly describes the research progress of silicon-based integrated Lidar, including silicon-based optical phased array Lidar, silicon-based optical switch array Lidar, and continuous frequency-modulated wave Lidar. In addition, we also introduced the scanning modes and working principles of other kinds of Lidar, such as the Micro-Electro-Mechanical System, mechanical Lidar, etc., and analyzed the characteristics of the Lidars above. Finally, we summarized this paper and put forward the future expectations of silicon-based integrated Lidar.

Pulse-Width Modulation Technique With Harmonic Injection in the Modulating Wave and Discontinuous Frequency Modulation for the Carrier Wave for Multilevel Inverters: An Application to the Reduction of Acoustic Noise in Induction Motors

An implementation of a harmonic injection pulse width modulation frequency-modulated triangular carrier (HIPWM-FMTC) control strategy applied to a multilevel power inverter feeding an asynchronous motor is presented. The aim was to justify the reduction in acoustic noise emitted by the machine compared with other strategies in the technical literature. In addition, we checked how the THD at the inverter output was reduced compared to the other control techniques used as a reference. The proposed strategy is based on frequency modulation of the triangular carrier. The main advantage of the proposed method is that only one control parameter is required for modifying the electrical spectrum. Therefore, the mechanical natural frequencies and spatial harmonics of the machine can be avoided, and acoustic noise can be reduced. The effectiveness of the technique was demonstrated after laboratory validation by comparing the acoustic results for a 1 kW motor. The results obtained from the laboratory tests are presented and compared with those of other acoustic measurements using different PWM strategies.

Photonic-aid dual-formats LFM signals generator for joint radar-communication system

(Objective) A photonic-aid approach to generate dual-formats linearly frequency modulation (LFM) signals for a joint radar-communication (JRC) system is proposed and verified by simulation. (Methods)In this scheme, a polarization division integrated modulator is employed to perform double sideband modulation to a driving RF signal with both sub-MZMs biased at the maximum transmission point. A driving LFM signal is applied to a followed Mach-Zehnder modulator (MZM) to achieve frequency multiplication. Then, the generated optical signal is fed to a polarization modulator (PolM) to perform data modulation. By changing the passband of the optical filter (OF) and polarization rotation of the polarization controller (PC), frequency quadrupled chirp polarity modulated or binary phase shift keying (BPSK) LFM signals of each format can be obtained. (Results) A simulation is carried out, and dual-formats LFM waveforms with chirp ranges of 16–24 GHz, 20–26 GHz, and 32–36 GHz are generated. Applications on both radar and communication are demonstrated, and the range resolution of the generated signal is improved by 3 times. By using chirp polarity modulation, triangular wave frequency modulation (FM) signal is produced to achieve moving target detection. The efficiency of anti-jamming communication is also verified. For BPSK-LFM waveforms, optical de-chirping operation and coherent demodulation are successfully performed. The trade-off between radar and communication performance is also studied. A BPSK-LFM signal with its communication rate improved by over 28 times while SSR of optical de-chirping only descended by 6.52 dB is obtained via intra-pulse coding, a minor phase difference of BPSK modulation and DSSS technology.

Strip SAR image simulation of a composite vehicle-ground model.

In this paper, the strip synthetic aperture radar (SAR) image of a composite vehicle-ground model is simulated by combining the electromagnetic scattering algorithm and radar imaging algorithm. A linear frequency modulated wave is incident on the composite model, which is partitioned into a mass of triangular patches. In the "stop-and-go" radar mode, for each patch, the amplitude of scattered echo in the frequency domain is solved by a hybrid method of physical optics (PO)-shooting and bouncing ray (SBR)-physical theory of diffraction (PTD). For the composite model, the total scattered echo in terms of range frequency and azimuth time is obtained by the vector superposition of echo on patches. Then the SAR image of the composite model is generated by the range-Doppler algorithm. In numerical simulations, both the electromagnetic scattering of a target by the SBR-PTD method and composite scattering by the PO-SBR-PTD method are validated and evaluated by comparing with the multilevel fast multipole method (MLFMM) in FEKO software. Moreover, the SAR image of the composite vehicle-ground model is also compared with the real image in Moving and Stationary Target Acquisition and Recognition database, which verifies the feasibility of the proposed method. SAR images of the composite model for different incident angles are also presented and analyzed.

A high-efficiency acquisition method of LED multispectral images using Gray code based square wave frequency division modulation

LED illumination-based multispectral imaging (LEDMSI) is a fast, convenient, and effective multispectral image acquisition technique. The square wave frequency division modulation (SFDM) and the integral sampling of the camera can build an efficient match pattern. With regards to image quality decline problems due to the ringing effect caused by the drive module while square wave high-low level conversion in the SFDM-LEDMS system. This paper proposes a multispectral image acquisition method combining Gray code and square wave frequency modulation. The micro control unit was used to generate a series of frequency division square waves in Gray code mode followed by LEDs of different wavelengths modulated by SFDM-square waves as a light source. Subsequently, the camera was used to simultaneously collect a sequence of multi-spectral images followed by single-wavelength images using differential accumulation demodulation. Finally, the no-reference image quality assessment (NR-IQA) was used to evaluate the quality of each single-wavelength image obtained by Binary code and Gray code. We deployed five wavelengths as examples to verify the effectiveness of the proposed method. The accumulated results indicated an improvement of the image quality in terms of information and gradient using Gray code. In conclusion, the present study can provide an effective image acquisition alternative for household medical equipment.

A Novel Strategy for Signal Denoising Using Two-Layer SVD and Its Application to Rub-Impact Fault Diagnosis of Aeroengine

The rub-impact fault, which occurs in the aeroengine, can cause frequency modulation (FM) in its vibration signal. Oscillated instantaneous frequency (IF) is a phenomenon of such a modulation mode, which carries critical fault information from the aeroengine. In this paper, by using Variational Mode Decomposition (VMD), the vibration signal can be decomposed into several signal components. Two-layer Singular Value Decomposition (SVD) is utilized to reduce the signal noise of each signal component and instantaneous frequency of each signal component. The intra–wave FM feature of the signal are presented through the Hilbert transform (HT) analysis. The proposed method is validated with numerical simulation and then demonstrated on aeroengine data with the rub-impact fault. The proposed method is suitable for the analysis of modulated signals and is a valid tool for detecting the rub-impact faults in aeroengines.

Expansion and compression of the momentum distribution of atoms in the field of the counter-propagating frequency-modulated waves

Expansion and compression of the momentum distribution of atoms in the field of the counter-propagating frequency-modulated waves

Suppression of Noise Amplitude Modulation Interference in Triangle Frequency Modulation Detector Based on FrFT

The target detection problem for a triangle wave frequency modulation (TWFM) detection system in the presence of the noise amplitude modulation (NAM) interference is considered in this paper. The range measuring principle based on Chirp Z Transform (CZT) and velocity measuring principle based on Moving Target Detection (MTD) are respectively introduced. Exploiting the observation that the NAM interference often affects the TWFM detector's detection performance, we present an anti-interference method based on Fractional Fourier Transform (FrFT) to suppress the NAM jamming. Simulations show that the method proposed in this paper can excise the NAM interference effectively. Moreover, all proposed methods are realized by FPGA for the first time, and then the outside field experiments verify the feasibility of these techniques.

Research on effective jamming style of projectile-carried communication for FH communication radio under common modulation systems

This work addresses the effective jamming style of projectile-carried communication for frequency hopping radio with different modulation by applying simulation verification via OPNET platform to construct the projectile-carried communication jamming system model. A general projectile-carried communication jamming style based on the signal combination of sweep saw-tooth wave and noise frequency modulation is proposed and analyzed. The network model of projectile-carried communication jamming system is constructed, and then the model building process of frequency hopping radio from the two aspects of transmitter model and receiver model is deeply elaborated. We demonstrate that the general projectile-carried communication jamming style has good jamming effect on the frequency hopping radio receivers with five modulation modes of 2FSK, 2PSK, 2DPSK, MSK and GMSK by comparing the simulation results, including receiving throughput, end-to-end delay, time delay of wireless channel access, delivery rate of synchronized header message, signal-to-noise ratio, bit error rate, packet loss rate, remaining power of jammer. Among them, the bit error rate of radio receiver with five modulation modes is more than 20%.

Characterisation of frequency modulated wave of NIR photons transport in human lower forearm phantom

Free-space broadband frequency modulated near infrared (NIR) photon technique is used to model and characterise the optical behaviour in a lower forearm human phantom. NIR system measures the broadband insertion loss (IL) and the insertion phase (IP). Different penetration depth and path-related modulated photon movement is analysed. The study is divided into two stages. The first stage dedicated to performing broadband IL and IP measurements in a back-scattering method. The second stage dedicates to modelling the photon behaviour in stage 1 using a finite element simulator called as COMSOL. Results in both stages are analysed and compared using a signal processing method to identify the frequency modulated photon stamp associated with different layers and verifies the accuracy of the 3D FE modelling. Error shown to be less than 6% and results gives a clear understanding of how the modulated waves of photons behave when traveling in the human forearms phantom.

Characterisation of frequency modulated wave of NIR photons transport in human lower forearm phantom

Characterisation of frequency modulated wave of NIR photons transport in human lower forearm phantom

Suppression of Wind Ripples and Microwave Backscattering Due to Turbulence Generated by Breaking Surface Waves

The role of wave breaking in microwave backscattering from the sea surface is a problem of great importance for the development of theories and methods on ocean remote sensing, in particular for oil spill remote sensing. Recently it has been shown that microwave radar return is determined by both Bragg and non-Bragg (non-polarized) scattering mechanisms and some evidence has been given that the latter is associated with wave breaking, in particular, with strong breaking such as spilling or plunging. However, our understanding of mechanisms of the action of strong wave breaking on small-scale wind waves (ripples) and thus on the radar return is still insufficient. In this paper an effect of suppression of radar backscattering after strong wave breaking has been revealed experimentally and has been attributed to the wind ripple suppression due to turbulence generated by strong wave breaking. The experiments were carried out in a wind wave tank where a frequency modulated wave train of intense meter-decimeter-scale surface waves was generated by a mechanical wave maker. The wave train was compressed according to the gravity wave dispersion relation (“dispersive focusing”) into a short-wave packet at a given distance from the wave maker. Strong wave breaking with wave crest overturning (spilling) occurred for one or two highest waves in the packet. Short decimeter-centimeter-scale wind waves were generated at gentle winds, simultaneously with the long breaking waves. A Ka-band scatterometer was used to study microwave backscattering from the surface waves in the tank. The scatterometer looking at the area of wave breaking was mounted over the tank at a height of about 1 m above the mean water level, the incidence angle of the microwave radiation was about 50 degrees. It has been obtained that the radar return in the presence of short wind waves is characterized by the radar Doppler spectrum with a peak roughly centered in the vicinity of Bragg wave frequencies. The radar return was strongly enhanced in a wide frequency range of the radar Doppler spectrum when a packet of long breaking waves arrived at the area irradiated by the radar. After the passage of breaking waves, the radar return strongly dropped and then slowly recovered to the initial level. Measurements of velocities in the upper water layer have confirmed that the attenuation of radar backscattering after wave breaking is due to suppression of short wind waves by turbulence generated in the breaking zone. A physical analysis of the effect has been presented.

Harmonic frequency combs in quantum cascade lasers: Time-domain and frequency-domain theory

Harmonic frequency combs, in which the lasing modes are separated by a period of tens of free spectral ranges from each other, have been recently discovered in quantum cascade lasers (QCLs). There is an ongoing debate how the harmonic combs can be formed and stable under continuous pumping. Here we reproduce the harmonic state of lasing in QCLs by space-time-domain numerical simulations and show that the corresponding optical wave has a frequency-modulated nature, with the fundamental beat note in the electron population being suppressed. To understand the physics behind the formation and stability of the harmonic state, we develop a frequency-domain linearized analytic theory which analyzes the stability of single-mode lasing with respect to the harmonic state formation and the instabilities of the resulting harmonic state. Our analysis shows how the instability of a single lasing mode can result in the growth of harmonic side modes. The coupling between the two side modes leads to enhancement of the gain for frequency-modulated waves as compared to the gain for amplitude-modulated waves. The dependence of the sideband gain spectrum on group-velocity dispersion is also studied. While the instability of a single lasing mode with respect to the growth of side bands separated by many free spectral ranges does not prove that the harmonic state can be self-starting, we analyze the instability of three strong harmonic modes and demonstrate that the harmonic state can be stable and self-supported.

Harmonic instability in a quantum cascade laser with Fabry–Perot cavity

A new state of instability called harmonic instability, which is characterized by the appearance of side modes separated by multiple of free spectral range from each other, was discovered in quantum cascade lasers (QCLs) a few years ago. However, a detailed analysis using a model beyond the two-level density-matrix (DM) equations as well as incorporating phenomena such as the detuning of the primary-mode frequency from the line-center frequency and the frequency dependence of the background refractive index, resulting in group velocity dispersion (GVD), has not been performed yet. In this paper, we present a comprehensive analysis of harmonic instability in a QCL with a Fabry–Perot (FP) cavity. Starting from three-level DM equations, which include the resonant tunneling phenomenon and scattering rates between all three states, and then by using Maxwell's equation, we derive a closed-form expression for the gain of the side modes, from which quantities pertinent to instability can be determined. We also take the aforementioned phenomena into account in our theory. By using our theory, we show the way of determining primary-mode detuning from the line center. Furthermore, we study the effects of GVD on instability in detail, showing that the output from an FP QCL demonstrates the characteristic of a frequency-modulated wave up to a certain value of dispersion. Above this value, because of the significant deviation of the side-mode amplitude ratio from unity, the output shows neither frequency-modulated-like nor amplitude-modulated-like behavior.

Частотно-модулированные УНЧ волны в околоземном космическом пространстве

Частотно-модулированные УНЧ волны в околоземном космическом пространстве

Transient amplification characteristics of frequency modulated wave in semiconductor plasmas

We perform an analytical investigation of modulational interaction of an electromagnetic pump wave in a transversely magnetized weakly polar semiconductor plasma medium. Based on the hydrodynamic model, a critical examination of frequency modulational amplification is made in a moderately doped III–V semiconductor crystal (n-GaAs) duly shined by pulsed 10.6 µm CO2 laser. The effect of electron-LO phonon interaction and coupled magnetoplasma excitations on the nonlinear interaction of a laser beam adds new dimension to the analysis. Steady state and transient gain coefficients, threshold pump intensity and optimum-pulse duration for the onset of modulational instability are estimated. The paper concentrates on the study of gain characteristics mainly in transient region. Effect of doping and applied magnetic field on the threshold pump intensity and growth rate has been significantly analysed. Graphical analysis interprets strong dependence of transient amplification characteristics on these parameters. So a judicious choice of physical parameters may develop growth at much lower pump intensity improving the cost effectiveness of the system. These results may help to be important for understanding and improving the performance of modulator.

Pulse width modulation technique with harmonic injection in the modulating wave and discontinuous frequency modulation for the carrier wave to reduce vibrations in asynchronous machines

A new carrier-based pulse-width modulation (PWM) technique to control power inverters is presented in this study. To generate the output waveform, this technique compares a harmonic-injection modulating wave and a frequency-modulated triangular carrier wave. The instantaneous frequency for the carrier wave is adjusted according to a periodic function synchronised with the fundamental term of the modulating wave. The main motivation for using this technique compared to a classic PWM sinusoidal technique revolves around the reduction of total harmonic distortion, the reduction of the distortion factor and the shift of temporal harmonics to higher frequencies for any modulation frequency order. Experimental results show that it is possible to optimise the time harmonics generated to minimise vibrations produced by an induction motor when it is fed with a DC/AC converter controlled by the proposed control strategy. This is made possible by using a control parameter that modifies the instantaneous frequency of the carrier wave without modifying the number of pulses per period of the modulating wave, i.e. the mean value of the carrier wave frequency. The proposed technique is applied to an open loop-controlled inverter that operates an induction motor, helping to reduce the vibration levels produced.