Signal Frequency Research Articles

An Integrative Review of Brainwave Entrainment Benefits for Human Health.

Brainwave Entrainment (BWE) is a noninvasive method of neuromodulation based on the principle that auditory or visual stimulation at a specific frequency can lead the brain's electrocortical activity to oscillate at the frequency of the external signal or its multiples. This phenomenon could be used to alter physiological and psychological states. Therefore, we conducted an integrative review to answer the question: "What are the observed benefits of BWE on human health and well-being?" We searched for studies published in the last ten years in the Directory of Open Access Journals (DOAJ), EMBASE, Virtual Health Library (BVS), PubMed, SciELO, and Cochrane Library databases in April 2024. Searches were conducted in English, Portuguese, and Spanish. A total of 84 studies were included in our review. Studies showed improvements in various conditions, such as pain, sleep disturbances, mood disorders, cognition, and neurodegenerative disorders. In conclusion, our findings align with previous reviews and underscore the need for further research on BWE, particularly with larger sample sizes, robust control groups, and randomized clinical trial designs. Nevertheless, BWE demonstrates promising therapeutic potential and may support the management of various health conditions, enhancing individuals' quality of life.

Reanalysis on Performance of Microwave Phase Detector for Multisignals

Microwave phase detectors (MPDs) are key components of instantaneous frequency measurement (IFM) receivers and phase interferometer direction finding (PIF-DF) receivers. In conventional analyses, there is seldom a major quantitative discussion of MPD characterization when multiple signals arrive at the same time, which is often the case in complex and noisy electromagnetic environments. We have reanalyzed the characteristics of MPDs with respect to filter effects acting on more than two RF signals and differential amplifiers, which are not considered in conventional analyses. First, a step-by-step mathematical model of the signal flow is developed, which creates a cross term between the two signals and naturally introduces intermodulation effects. Second, the new response characteristics of the MPD are evaluated by simulation. Finally, the intermodulation effects of zero-forcing and extreme-forcing were found simultaneously in the crosspoint frequency and near-frequency regions of multiple signals, which led to significant deviations and errors in the output of the MPD. This effect may have significant implications for IFM and PIF-DF receivers.

Analysis and application of a 3D chaotic system with an extremely extensive range of amplitudes and offset boosting

Abstract The study of high-dimensional chaotic systems has been the subject of considerable research interest, whereas the complex characteristics of low-dimensional chaotic systems have been largely overlooked. A new dimensional (3D) chaotic system containing only two kinds of nonlinear terms is constructed based on the Lorenz system to enrich the theory of chaotic systems and improve the complex properties of low-dimensional chaotic systems. The system lacks a symmetric structure; however, under the influence of the symmetric parameter α, the system attains a symmetric state and can produce attractors with a symmetric structure. Under the parameter β, the system can realize the regulation of amplitude, frequency, and nonlinear offset boosting of three signals simultaneously. The parameter γ can realize the control of two signal amplitude and frequency at the same time. The system always remains chaotic when the parameters β and γ are varied in a great range. In addition, this 3D chaotic system has offset boosting behavior in arbitrary single and multiple directions, and the offset constant has a wide range of values. These features provide great convenience for secure communications and weak signal engineering applications. Further, analog circuit simulations and DSP (Digital Signal Processor) hardware circuits confirm the parametric modulation of the system and the offset boosting behavior in any direction. Moreover, taking advantage of the extensive offset range, a synchronization controller is designed for the drive and response systems. Finally, the modulation of offsets with a wide range of values realizes the encrypted transmission of binary digital information and lays the foundation for future engineering applications.

Measuring Precipitation via Microwave Bands with a High-Accuracy Setup

The urgent need for timely and accurate precipitation estimations in the face of ongoing climate change and the increasing frequency and/or intensity of extreme weather events underscores the necessity for innovative approaches. Recently, several studies have focused on estimating the precipitation rate through induced attenuation of radio frequency (RF) signals, which are abundant in modern communication systems. Most research has concentrated on frequencies exceeding 10 GHz, as attenuation at lower frequencies is minimal, posing measurement challenges. This study aims to confront this limitation by introducing a high-precision experimental setup capable of detecting this subtle attenuation at frequencies under 10 GHz. The setup includes a transmitter and receiver optimized for operation at 2.07, 4.63, and 6.22 GHz, where minimal worldwide research exists. A power resolution below 10−5 dB in preliminary measurements demonstrated its effectiveness in quantifying signal attenuation due to precipitation across the specified frequencies. Moreover, a strong power law relationship was observed between signal attenuation and precipitation rate for all three frequencies, while, as expected, the higher the frequency, the more pronounced the signal attenuation was.

A Wide Range Duty‐Cycle PWM Generator Using Oxide‐TFTs on a Flexible Substrate

ABSTRACTThis work presents an experimental characterization of a novel clocked regenerative comparator with oxide TFT (a‐IGZO) technology on a flexible substrate. The circuit functionality is demonstrated as a wide range duty‐cycle PWM signal generator with a triangular input signal. The regenerative latch in the comparator is implemented with diode‐load–based inverters. The proposed circuit has shown a linear variation in the duty‐cycle from 12% to 84%, when the reference voltage () is varied from 0.5 to 3.3 V, respectively, in the clocked comparator. Further, a reliable operation is observed up to an input signal frequency of 2 kHz at a supply voltage of 4 V, with a power dissipation of 20 W. This circuit would find potential applications in wearable bio‐medical and neuromorphic computational systems.

Near-Field Direct Writing Based on Piezoelectric Micromotion for the Programmable Manufacturing of Serpentine Structures

Serpentine microstructures offer excellent physical properties, making them highly promising in applications in stretchable electronics and tissue engineering. However, existing fabrication methods, such as electrospinning and lithography, face significant challenges in producing microscale serpentine structures that are cost-effective, efficient, and controllable. These methods often struggle with achieving precise control over fiber morphology and scalability. In this study, we developed a near-field direct writing (NFDW) technique incorporating piezoelectric micromotion to enable the precise fabrication of serpentine micro-/nanofibers by incorporating micromotion control with macroscopic movement. Modifying the fiber structure allowed for adjustments to the mechanical properties, including tunable extensibility and distinct characteristics. Through the control of the frequency and amplitude of the piezoelectric signal, the printing errors were reduced to below 9.48% in the cycle length direction and 6.33% in the peak height direction. A predictive model for the geometrical extensibility of serpentine structures was derived from Legendre’s incomplete elliptic integral of the second kind and incorporated an error correction factor, which significantly reduced the calculation errors in predicting geometric elongation, by 95.85%. The relationship between microstructure bending and biomimetic non-linear mechanical behavior was explored through tensile testing. By controlling the input electrical signals, highly ordered serpentine microstructures were successfully fabricated, demonstrating potential for use in biomimetic mechanical scaffolds.

Dynamically programable real-time controller for a 2D scanning fibre microscope

A programmable controller for a 2D Lissajous scanning fibre microscope is described. Source motion is based on a vibrating cantilever formed by dip-coating two cylindrical silica fibres. Orthogonal modes are excited by a piezoelectric actuator oriented at 45° to the principal axes. Back-scattered signals are detected using a mode-stripping photodiode to collect cladding modes in a dual numerical aperture confocal scheme. Optical feedback is generated by a shaped reflecting aperture with amplitude-coded reflectivity. Electrical pulses from the detector are separated into low- and high-mode feedback signals using window detectors. The low mode is excited at resonance using a phase-locked loop (PLL) containing a voltage-controlled oscillator (VCO). The high mode is driven off-resonance at a frequency derived from computer control of a second VCO. Amplitudes are corrected, and common frequency signals derived from the two motions using divide-by-N circuits are synchronised using additional PLLs. Programmable generation of Lissajous figures and imaging with dynamically variable scan density are demonstrated.

Detection of infrasound sources using three-years array data in 2019-2021 deployed at the Lützow-Holm Bay region, Antarctica

Time-space variations of infrasound source locations for three years, 2019-2021, were studied byusing a combination of two local arrays in the Lützow-Holm Bay region (LHB), Antarctica. The local arrays deployed at two coastal outcrops clearly detected temporal variations in signal frequency content as well as propagating directions during the three years. A large number of infrasound sources were detected with many located to the north and north-west directions from the arrays. These events were generated within the Southern Indian Ocean and the northern part of LHB with frequency-content of a few seconds; these “microbaroms” are believed to originate from oceanic swells. From austral summer to fall additional infrasound sources are determined to be located to the north-east. These sources might be related to the effects of katabatic winds across the continental coastal area. Furthermore, several impulsive infrasound events during the winter had higher predominant frequencies of a few Hz, higher than the microbaroms. On the basis of a comparison of source locations with sea-ice and glacier distribution form MODIS satellite images, these high-frequency sporadic sources may be cryo-seismic signals associated with cryosphere dynamics near the local arrays. These results suggest that infrasound waves can be used to monitor surface environments in the coastal area of Antarctica.

Seizure quantification in sunflower syndrome by a wrist-worn device.

Sunflower syndrome is a rare photosensitive childhood-onset epilepsy, featuring repetitive handwaving events (HWE) triggered by light. Objective documentation of these HWE can be difficult due to the numerous events occurring daily and/or caregivers who document the seizures but are not always present. Hence, seizure diaries can be underreporting. We performed a feasibility study in three Belgian Sunflower syndrome individuals to assess the possibility to quantify the HWEby a wrist-worn wearable device (Axivity AX6). We conducted a structured exercise aiming to capture patterns of possible confounders in a controlled environment. Subsequently, patients wore the device for three to six consecutive days and nights at home. Spectral power analyses were performed to characterize the frequency signature of the different movements. The HWE of patient A and B showed homogeneity and narrow-band frequencies. Patient C did not experience any HWE at the start of the study due to proper seizure control. Regarding HWE, there was a higher spectral power for Gyroscope Z (Gz) compared to Gy. The inter-subject variability for HWE frequency peaks was in the 3-6 Hz range. Computer analysis by visual annotation, without checking the seizure diary, detected 71% of the HWE if the HWE lasted for longer than 5 s (sensitivity 64%). For shorter HWE duration, the detection rate was 50% but seemed to be higher if there was a concordant change of eye movement (63%) (sensitivity 36%). The most obvious confounder was toothbrushing (TB). However, TB showed a different pattern: that is, higher or comparable spectral power for Gy compared to Gz. There was also a higher or comparable spectral power for Gy compared to Gz for "waving hello". We show that the wearable movement sensor Axivity AX6 can detect HWE in Sunflower syndrome individuals and distinguish them from confounders in a real-world setting.

Frequency-doubling optoelectronic oscillator with fundamental frequency signal cancellation

A frequency-doubling optoelectronic oscillator (OEO) with fundamental frequency signal cancellation based on a dual-polarization Mach–Zehnder modulator (DPol-MZM) is proposed and experimentally demonstrated. In the proposed structure, two different modulation modes can be utilized to realize the frequency-doubling OEO. One is the carrier-suppressed double-sideband (CS-DSB) modulation, and the other is double-sideband (DSB) modulation. In both cases, one path is used to achieve the fundamental frequency oscillation in the OEO loop through the utilization of an equivalent or conventional DSB modulation, and the other path is employed to realize the frequency-doubled signal. In the realization of the frequency-doubled signal, the fundamental frequency signal can be cancelled by introducing an additional pure optical carrier with proper power and its polarization direction opposite to that of the modulated optical signal. A high sideband suppression ratio of the frequency-doubled signal up to 40 dB is achieved.

Noise as a Factor of Useful Signal Amplification Based on the Effect of Stochastic Resonance

Abstract The effect of stochastic resonance is investigated. The principles of the effect are considered on the basis of a Brownian particle moving in a system with a symmetric bistable potential. Different from the widely existing noise elimination methods, stochastic resonance enables a new method to utilize the energy of noises, nonlinear system, and signal frequency to reach certain weak signal enhancement effects that noise elimination cannot perform well. The presence of noise at the input of nonlinear systems possessing the effect of the stochastic resonance allows to stand out a weak signal from an additive mixture with white Gaussian noise. The equation and structural scheme of stochastic resonance are considered The conditions for the occurrence of stochastic resonance are formulated and the determining role of noise variance in the realization of this effect is shown. For the first time, a numerical calculation of standing out of harmonic oscillation from an additive mixture with white Gaussian noise based on the stochastic resonance effect is carried out. The output signal-to-noise ratio dependence of the stochastic resonator on the intensity of input noise and the input signal frequency is investigated. The frequency dependencies of the output signal are investigated and the components of this signal are analysed. It is shown that the stochastic resonator acts as a low-pass filter and reduces the output noise level. Numerical modelling of the stochastic resonance effect also shows that the output signal of the stochastic resonator contains odd harmonics of the input oscillation, which is characteristic of nonlinear systems. It is shown that the stochastic resonance effect can be widely used in radio engineering and telecommunications to amplify the useful signal.

DiffSph: a Python tool to compute diffuse signals from dwarf spheroidal galaxies

So far no diffuse emissions in dwarf spheroidal satellites of the Milky Way have ever been observed. Given that dwarf galaxies are predominantly composed of Dark Matter, the discovery of these signals could offer valuable insights into understanding the nature of Dark Matter. We present “diffSph”, a Python tool which in its present version provides fast predictions of such diffuse signals in radio frequencies. It also features a very comprehensive module for the computation of “J” and “D” factors that are relevant for indirect Dark Matter detection using gamma rays. Routines are coupled to parton-shower algorithms and Dark Matter halo mass functions from state-of-the-art kinematic fits. This code is also useful for testing generic hypotheses (not necessarily associated with any Dark Matter candidate) about the cosmic-ray electron/positron sources in the dwarf galaxies. The diffSph tool has already been employed in searches for diffuse signals from dwarf spheroidal galaxies using the LOw Frequency ARray (LOFAR).

Effects of ttk on development and courtship of male Nilaparvata lugens.

The transcription product of tramtrack (ttk) is an important transcription factor which plays many roles in the regulation of the development, differentiation and chromosome recombination of organisms. Few studies have been reported on the specific functions of ttk in other insects except Drosophila melanogaster. Our aims are to reveal the ttk effects on development and courtship of male rice pest brown planthopper (BPH), Nilaparvata lugens. In this study, we first assayed spatiotemporal expression of ttk in BPH, then treated the fourth nymphs of BPH with dsttk. We found most individuals died before emerging to adults, the adult eclosion rate was only 18.89%. No courtship behavior was found in individuals injected with dsttk. Further research showed that the main frequency of courtship vibration signal (CVS) 431.3 Hz in the individuals injected with dsttk was significantly higher than 223 Hz in the individuals injected with dsGFP, and female adults nearly had no response to the 431.3 Hz CVS. We found that about 81% of the 4-instar nymphs of BPH treated with dsttk died before they emerged as adults, the successfully emerged adults emitted the 431.3 Hz CVS to which female adults did not respond and lost the ability of courtship. This was first finding about the functions of ttk in rice planthopper and illustrated the potential of ttk as target for RNAi to control rice planthopper. © 2024 Society of Chemical Industry.

Observation of biological and emulsion samples by newly developed three-dimensional impedance scanning electron microscopy

Imaging at nanometre-scale resolution is indispensable for many scientific fields such as biology, chemistry, material science and nanotechnology. Scanning electron microscopes (SEM) are widely used as important tools for the nanometre-scale analysis of various samples. However, because of the vacuum inside the SEM, a typical analysis requires fixation of samples, a drying process, and staining with heavy metals. Therefore, there is a need for convenient and minimally invasive methods of observing samples in solution. Recently, we have developed a new type of impedance microscopy, multi-frequency impedance SEM (IP-SEM), which allows nanoscale imaging of various specimens in water with minimal radiation damage. Here, we report a new IP-SEM system equipped with a linear-array terminal, which allows eight tilted images to be observed in a single capture by applying eight frequencies of input signals to each electrode. Furthermore, we developed a three-dimensional (3D) reconstruction method based on the Simulated Annealing (SA) algorithm, which enables us to construct a high-precision 3D model from the 8 tilted images. The method reported here can be easily used for 3D structural analysis of various biological samples, organic materials, and nanoparticles.

Linear prediction on Cent scale for fundamental frequency analysis

Understanding the fundamental frequency and harmonic content of audio signals is crucial for many applications in music analysis, including music transcription, audio synthesis, and genre identification. This study formulates a signal processing approach combining Linear Prediction (LP) analysis and the Cent scale to accurately characterize the pitch and harmonic structure of the audio signals. Pitch tracking on the LP spectrum in the Cent scale provides more accurate and reliable pitch estimation, especially in the presence of noise or overlapping harmonics. The Cent scale aligns the harmonics of different notes more closely, making it easier to discern the correct pitch.

Formation tracking control for networked heterogeneous MSV systems with actuator faults: A distributed optimal event-triggered fixed-time sliding mode fault-tolerant control approach

This paper studies the formation tracking problem in networked heterogeneous marine surface vessel systems (NHMSVs) subject to model perturbations, marine environmental disturbances, and actuator faults. A distributed optimal event-triggered fixed-time sliding mode fault-tolerant control (EFSMFC) method is proposed, which can achieve formation tracking within a fixed time that is only related to the control parameters. At the same time, a distance-based Floyd distributed optimization method is used to reduce the high communication cost caused by the redundancy of the network communication topology. In addition, an event-triggered strategy is integrated into the design of the controller to reduce the update frequency of control signals and reduce waste of communication resources. Finally, using Lyapunov stability theory, the global fixed-time convergence of system errors is proved. The simulation results demonstrate the feasibility of the proposed method, exhibiting superior robustness and speed compared to existing control methods.

A Denoising Method for Partial Discharge Ultrasonic Signals in GIS Based on Ultra-High Frequency Signal Synchronization

A Denoising Method for Partial Discharge Ultrasonic Signals in GIS Based on Ultra-High Frequency Signal Synchronization

Thickness monitoring of threshing mixture on the oscillating plate of corn grain harvester

Cleaning is a critical operation in the corn grain harvesting process, and the operation is seriously affected by the uneven distribution of the threshing mixture on the oscillating plate. To monitor the thickness of the threshing mixture on the oscillating plate of the corn grain harvester, in this study, we adopted the lever principle to design a corn threshing mixture thickness monitoring device based on the piezoresistive effect and theoretically analyzed the lever impact mechanics. The factors affecting the force on the sensor of the monitoring device are the vibration frequency of the oscillating plate, the thickness of the threshing mixture, and grain moisture content, which were obtained through theoretical analysis. The operational performance of the corn threshing mixture thickness monitoring device was assessed through a set of single-factor experiments, revealing the influence laws of three factors on the impact voltage: vibration frequency, thickness of the threshing mixture, and grain moisture content. A back-propagation (BP)11Back-propagation (BP) neural network prediction model was established using an orthogonal experiment with impact voltage, vibration frequency, and grain moisture content as input layers and the thickness of the corn threshing mixture as the output layer. An STM32 microcontroller was used as the primary control unit to build a thickness monitoring data acquisition and processing system that could process and operate the impact voltage collected by the pressure sensor and the vibration frequency signal collected by a Hall sensor. The data were wirelessly transmitted to a PC to predict the thickness of the threshing mixture by using the trained BP neural network. The experimental results of monitoring the variation in corn threshing mixture thickness demonstrated that the device could effectively monitor changes in thickness. The monitoring accuracy of the monitoring device was found to be over 90%, and the system can be used for monitoring the threshing mixture thickness on the oscillating plate of the corn grain harvester.

Low-boiling-point perfluorocarbon nanodroplets for adaptable ultrasound-induced blood-brain barrier opening

Low-boiling point perfluorocarbon nanodroplets (NDs) are valued as effective sonosensitive agents, encapsulating a liquid perfluorocarbon that would instantaneously vaporize at body temperature without the NDs shell. Those NDs have been explored for both therapeutic and diagnostic purposes. Here, phospholipid-shelled nanodroplets containing octafluoropropane (C3F8) or decafluorobutane (C4F10) formed by condensation of microbubbles were thoroughly characterized before blood-brain (BBB) permeabilization. Transmission electron microscopy (TEM) and cryo-TEM were employed to confirm droplet formation while providing high-resolution insights into the droplet surface and lipid arrangement assessed from electron density observation after condensation. The vaporization threshold of NDs was determined with a high-speed camera, and the frequency signal emitted by the freshly vaporized bubbles was analyzed using cavitation detection. C3F8 NDs exhibited vaporization at 0.3 MPa (f0 = 1.5 MHz, 50 cycles), and emitted signals at 2 f0 and 1.5 f0 from 0.45 MPa onwards (f0 = 1.5 MHz, 50 cycles), while broadband noise was measured starting from 0.55 MPa. NDs with the higher boiling point C4F10 vaporized at 1.15 MPa and emitted signals at 2 f0 from 0.65 MPa and 1.5 f0 from 0.9 MPa, while broadband noise was detected starting from 0.95 MPa. Both ND formulations were used to permeabilize the BBB in healthy mice using tailored ultrasound sequences, allowing for the identification of optimal applications for each NDs type. C3F8 NDs proved suitable and safe for permeabilizing a large area, potentially the entire brain, at low acoustic pressure. Meanwhile, C4F10 droplets facilitated very localized (400 μm isotropic) permeabilization at higher pressure. This study prompts a closer examination of the structural rearrangements occurring during the condensation of microbubbles into NDs and highlight the potential to tailor solutions for different brain pathologies by choosing the composition of the NDs and adjusting the ultrasound sequence.

Low-Cost Embedded System Design for Smart Home Automation Using RF Technology

Abstract Applications for smart home technologies can be described as the adaptation of control systems used in industrial areas to modern living environment of people. Home automation systems are the systematic and seamless adaptation of smart home technologies to the individual’s personal needs and desires. Smart homes encompass a range of technologies designed to cater to the needs of residents, simplifying their daily routines and contributing to a more comfortable and secure way of life. Nowadays, most buildings are constructed with expensive, builtin smart home technology. However, when it comes to old buildings without smart home technology, integrating this technology into those structures can be challenging due to the requirement for intrusive overhead wall modifications necessary for installing the technological infrastructure. In this study, a radio frequency based low-cost embedded system is designed to bring intelligent technology to existing homes or old buildings. Various sub-units have been designed and established to be situated in different places of the house. Physical events and situations that occur in the house are sensed by the sub-units and transmitted to the main control unit by means of a specially developed communication protocol via radio frequency signals. This removes the cable clutter and creates a more flexible and easy installation environment.