Narrow-band System Research Articles

Open-loop narrowband magnetic particle imaging based on mixed-frequency harmonic magnetization response

IntroductionMagnetic particle imaging (MPI), a radiation-free, dynamic, and targeted imaging technique, has gained significant traction in both research and clinical settings worldwide. Signal-to-noise ratio (SNR) is a crucial factor influencing MPI image quality and detection sensitivity, and it is affected by ambient noise, system thermal noise, and the magnetization response of superparamagnetic nanoparticles. Therefore to address the high amplitude system and inherent thermal noise present in conventional MPI systems is essential to improve detection sensitivity and imaging resolution.MethodThis study introduces a novel open-loop, narrow-band MPI signal acquisition system based on mixed-frequency harmonic magnetization response. Allowing superparamagnetic nanoparticles to be excited by low frequency, high amplitude magnetic fields and high frequency, low amplitude magnetic fields, the excitation coil generates a mixed excitation magnetic field at a mixed frequency of 8.664 kHz (fH + 2fL), and the tracer of superparamagnetic nanoparticles can generate a locatable superparamagnetic magnetization signal with rich harmonic components in the mixed excitation magnetic field and positioning magnetic field. The third harmonic signal is detected by a Gradiometer coil with high signal-to-noise ratio, and the voltage cloud image is formed.ResultThe experimental results show that the external noise caused by the excitation coil can be effectively reduced from 12 to about 1.5 μV in the imaging area of 30 mm × 30 mm, which improves the stability of the detection signal of the Gradiometer coil, realizes the detection of high SNR, and makes the detection sensitivity reach 10 μg Fe. By mixing excitation, the total intensity of the excitation field is reduced, resulting in a slight improvement of the resolution under the same gradient field, and the spatial resolution of the image reconstruction is increased from 2 mm under the single frequency excitation (20.7 kHz) in the previous experiment to 1.5 mm under the mixed excitation (8.664 kHz).ConclusionsThese experimental results highlight the effectiveness of the proposed open-loop narrowband MPI technique in improving signal detection sensitivity, achieving high signal-to-noise ratio detection and improving the quality of reconstructed images by changing the excitation magnetic field frequency of the excitation coil, providing novel design ideas and technical pathways for future MPI systems.

Enhanced visible light responsive piezoelectric photocatalysis based on Bi2S3 coated BaTiO3 nanorods heterostructures

Although the presence of the built-in electric field will solve the problem of carrier complexation in photocatalytic systems to some extent. However, free carriers will quickly shield the stabilized electric field and lose its effect. Therefore, how to introduce the dynamic piezoelectric field into the photocatalytic system has become an imminent problem. Herein, we developed an overcoated, visible light responsive, piezoelectric-assisted photocatalytic system by depositing Bi2S3 photocatalysts with a narrow-band system onto the surface of highly piezo-responsive BaTiO3 nanorods (BTO NRs). The heterojunction structure, bound by Bi-O chemical bonding, enhances carrier transport efficiency under the influence of the piezoelectric field. In the degradation experiments, the first-order rate constant for the degradation of chlortetracycline hydrochloride (CTC) in the BTO NRs/Bi2S3 system with the optimal complex ratio was 0.0276 min−1, which was 3.1 and 7.8 times higher than that of BTO NRs and Bi2S3, respectively. Additionally, we deduced the degradation pathways of CTC through a combination of Density functional theory (DFT) calculations and Liquid Chromatograph Mass Spectrometer (LC-MS), evaluating the toxicity of the intermediates. This complex system, featuring a highly photo-responsive semiconductor as a photo-acceptor deposited on a piezoelectric semiconductor surface providing a dynamic built-in electric field, enhances carrier separation efficiency under optimal light energy utilization conditions. These findings present novel and effective strategies for addressing two primary challenges in photocatalytic systems: low spectral utilization and significant photogenerated carrier complexation.

Application of the Heavy-Atom Effect for (Sub)microsecond Thermally Activated Delayed Fluorescence and an All-Organic Light-Emitting Device with Low-Efficiency Roll-off.

The feature of abundant and environmentally friendly heavy atoms (HAs) like bromine to accelerate spin-forbidden transitions in organic molecules has been known for years. In combination with the easiness of incorporation, bromine derivatives of organic emitters showing thermally activated delayed fluorescence (TADF) emerge as a cheap and efficient solution for the slow reverse intersystem crossing (rISC) problem in such emitters and strong efficiency roll-off of all-organic light-emitting diodes (OLEDs). Here, we present a comprehensive photophysical study of a tri-PXZ-TRZ emitter reported previously and its hexabromo derivative showing a remarkable enhancement of rISC of up to 9 times and a short lifetime of delayed fluorescence of 2 μs. Analysis of the key molecular vibrations and TADF mechanism indicates almost compete blockage of the spin-flip transition between the charge-transfer states of different multiplicity 3CT → 1CT. In such a case, rISC as well as its enhancement by the HA is realized via the 3LE → 1CT transition, where 3LE is the triplet state localized on the same brominated phenoxazine donor involved in the formation of the 1CT state. Interestingly, the spin-orbit coupling (SOC) with two other 3LE states is negligible because they are localized on different donors and not involved in 1CT. We consider this as an example of an additional "localization" criterion that completes the well-known El Sayed rule on the different nature of states for nonzero SOC. The applicative potential of such a hexabromo emitter is tested in a "hyperfluorescent" system containing a red fluorescent dopant (tetraphenyldibenzoperiflanthene, DBP) as an acceptor of Förster resonance energy transfer, affording a narrow-band red-emitting system, with most of the emission in the submicrosecond domain. In fact, the fabricated red OLED devices show remarkable improvement of efficiency roll-off from 2-4 times depending on the luminance, mostly because of the increase of the rISC constant rate and the decrease of the overall delayed fluorescence lifetime thanks to the HA effect.

Seasonal Variation in the Mesospheric Ca Layer and Ca+ Layer Simultaneously Observed over Beijing (40.41°N, 116.01°E)

In March 2020, an all-solid-state dual-wavelength narrow-band lidar system was deployed. A total of 226 nights spanning from March 2020 to July 2022 were employed in order to investigate the seasonal variations of calcium atoms and ions in the mesosphere over Beijing (40.41°N, 116.01°E). The Ca+ layer shows general annual variation, while a semiannual variation is observed on the Ca layer. The calcium atomic column densities ranged from 2.0 × 106 to 1.1 × 108 cm−2, and the calcium ion column densities ranged from 1.6 × 106 to 4.2 × 108 cm−2. The mean centroid heights of Ca+ and Ca are 98.6 km and 93.0 km, respectively, and the centroid heights of Ca+ and Ca are mostly influenced by annual variations. The seasonal variation in the Ca+ and Ca layers in Beijing exhibits similarities to that of Kühlungsborn (54°N). While the peak density of Ca+ in Beijing are similar to those observed in Kühlungsborn, the peak density of the Ca layer in Beijing is about half of that reported in the Ca layer at 54°N. We provide an explanation for the disparities in the column abundance and centroid altitude of the Ca layer between Yanqing and Kühlungsborn, discussing variations in neutralization among different metal ions.

Ambient RF Energy Harvesting

In this paper, we present a study of ambient RF energy harvesting techniques. The measurement of the ambient RF power density is presented. The average of the density in broadband (1GHz- 3.5GHz) is in the order of -12dBm/m² (63µW/m²). Two systems have been studied to recover the RF energy. The first is a broadband system without matching circuit. The second is a narrow band system (1.8-1.9GHz) with a matching circuit. The rectifier circuit RF / DC and the choice of the load to optimize the DC power recovered are presented. The preliminary results indicate that the recovered energy is not sufficient to directly power devices but could be stored in a super-capacity or micro-batteries.

Study of Interference Detection of Rail Transit Wireless Communication System Based on Fourth-Order Cyclic Cumulant.

The wireless communication system is used to provide dispatching, control, communication and other services for rail transit operations. In practice, interference from other wireless communication systems will affect the normal operation of trains, so it is an urgent problem to study the interference detection algorithms for rail transit applications. In this paper, the fourth-order cyclic cumulant (FOCC) of signals with different modulation modes is analyzed for the narrow-band wireless communications system of rail transit. Based on the analysis results, an adjacent-frequency interference detection algorithm is proposed according to the FOCC of the received signal within the predetermined cyclic frequency range. To detect interference with the same carrier frequency, a same-frequency interference detection algorithm using the relationship between the FOCC and the received power is proposed. The performance of the proposed detection algorithms in terms of correct rate and computational complexity is analyzed and compared with the traditional second-order statistical methods. Simulation results show that when an interference signal coexists with the expected signal, the correct rates of the adjacent-frequency and the same-frequency interference detection algorithms are greater than 90% when the signal-to-noise ratio (SNR) is higher than 2 dB and -4 dB, respectively. Under the practical rail transit wireless channel with multipath propagation and the Doppler effect, the correct rates of the adjacent-frequency and the same-frequency interference detection algorithms are greater than 90% when the SNR is higher than 3 dB and 7 dB, respectively. Compared with the existing second-order statistical methods, the proposed method can detect both the adjacent-frequency and the same-frequency interference when the interference signals coexist with the expected signal. Although the computational complexity of the proposed method is increased, it is acceptable in the application of rail transit wireless communication interference detection.

The All-Solid-State Narrowband Lidar Developed by Optical Parametric Oscillator/Amplifier (OPO/OPA) Technology for Simultaneous Detection of the Ca and Ca+ Layers

We report an all-solid-state narrowband lidar system for the simultaneous detection of Ca and Ca+ layers over Yanqing (40.41°N, 116.01°E). The uniqueness of this lidar lies in its transmitter, which is based on optical parametric oscillation (OPO) and optical parametric amplification (OPA) techniques. The injection seeded OPO and the OPA are pumped by the second harmonic of an injection-seeded Nd:YAG laser, which can generate coherent light at the wavelength of 786 nm or 846 nm lasers, whose second harmonics in turn generate the 393 nm or 423 nm pulses, respectively, for the detection of thermospheric and ionospheric Ca+ and Ca layers. Compared to the conventional dye-based system, this lidar transmitter is a narrowband system (bandwidth < 200 MHz), which has produced a factor of two more output power with higher stability and reliability. The lidar system in Yingqing demonstrated Ca+ detection sensitivity of 0.1 atoms-cm−3 for long-term observation and reached a height of ~300 km. Potential applications and further improvements in this lidar technique are also discussed in this paper.

Multichannel narrowband active noise control system with a frequency estimator based on DFT coefficients

The narrowband active noise control system (NANC) is an active control system that cancels periodic noise. The ability of the system to suppress noise is affected by the accuracy of the frequency estimator. The frequency estimator in the existing narrowband system has difficulty balancing the estimation accuracy and computational complexity. In this paper, a filtered-x discrete Fourier transform coefficients estimator least mean square (Fx-DFTCE-LMS) algorithm is proposed to enhance the noise reduction capability of multichannel NANC system. This system can handle any degree of frequency mismatch without increasing the complexity. Compared with most existing estimation methods, the proposed method does not need set initial frequency or estimator step size. Numerous simulations demonstrate that the proposed NANC system can track multiple frequencies more quickly and accurately, and effectively reduce noise.

Weak-Field Hall Resistivity and Spin-Valley Flavor Symmetry Breaking in Magic-Angle Twisted Bilayer Graphene.

Near a magic twist angle, the lowest energy conduction and valence bands of bilayer graphene moiré superlattices become extremely narrow. The band dispersion that remains is sensitive to the moiré's strain pattern, nonlocal tunneling between layers, and filling-factor-dependent Hartree and exchange band renormalizations. In this Letter, we analyze the influence of these band-structure details on the pattern of flavor symmetry breaking observed in this narrow band system and on the associated pattern of Fermi surface reconstructions revealed by weak-field Hall and Shubnikov-de Haas magnetotransport measurements.

Magnitude - Delay Least Mean Squares Equalization for Accurate Estimation of Time of Arrival

Multipath signals are known to be the main source of error in localization procedures; they are generated by the reflection from different objects through non-line of sight (NLOS) paths and overlap with the line of sight (LOS) signal. The time delay and strength of the LOS signal are critical parameters for ranging which are both affected by the overlapped NLOS components. The situation is worse when the frequency bandwidth (BW) is limited that inherently leads to decrease in the resolution of system obeying the Fourier limit ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3^\ast 10^{\wedge }8$ </tex-math></inline-formula> /BW). Leveraging the classical super-resolution techniques such as Maximum Likelihood (ML), MUSIC and compressive sensing (CS), the Fourier limit can be overcome but at the cost of having higher complexity and more computational time. In this paper, the Magnitude-Delay Least Mean Squares Equalization (MD-LMSE) is proposed uniquely for super-resolution time delay estimation. The proposed estimation algorithm is based on the recursive time domain Least Mean Squares (LMS) minimization, which is established through an equalizer structure. The MD-LMSE approach provides high accuracy, super resolution and low computational time that makes it suitable for real time implementation. The proposed MDLMSE algorithms is used through an experimental setup consisting one LOS signal and one NLOS signal to improve the range resolution of a narrowband system 95% with low error of 6.66%.The obtained results verify that the proposed approach is a good candidate for accurate ranging, especially in low frequency applications (with limited bandwidth) by enabling higher penetration depths.

THE ROLE OF NARROW BAND IMAGING- MAGNIFYING ENDOSCOPY (NBI-ME) OR DETECTING GASTRIC INTESTINAL METAPLASIA IN PATIENT WITH CHRONIC GASTRITIS

Background: Atrophy gastritis and intestinal metaplasia are early phenotypic markers in gastric carcinogenesis. White light endoscopy does not allow direct biopsy of intestinal metaplasia due to a lack of contrast of the mucosa. Narrow-band imaging system with magnifying endoscopy (NBI-ME) in the gastric mucosa suggested that the appearance of a light blue crest (LBC) on the epithelial surface may be a distinctive endoscopic finding associated with the presence of intestinal metaplasia. Objective: The aim of the present study was to clarify the value of NBI-ME for diagnosing gastric intestinal metaplasia. Methods: The research was designed as a cross-sectional descriptive study, studied on 52 patients with chronic gastritis in Hospital of Hue University of Medicine and Pharmacy. Results: Gastric intestinal metaplasia was found in 26.9% patients with WLE. LBCs specific for IM were found in 51.9% patients with NBI-ME. The sensitivity, specificity and accuracy of narrow-band imaging were 88%, 81.5%, and 84.6%, respectively. Conclusion: In narrow-band imaging with magnifying endoscopy (NBI-ME), observation of a light blue crest on the epithelial surface in the gastric mucosa is a highly accurate sign of the presence of histological intestinal metaplasia. Key words: gastric intestinal metaplasia, NBI-ME

Optical Expediency of Back Electrode Materials for Organic Near-Infrared Photodiodes.

Organic semiconductor devices, including organic photodetectors (OPDs) and organic photovoltaics (OPVs), have undergone vast improvements, thanks to the development of non-fullerene acceptors. The absorption range of such NFA-based systems is typically shifted toward the near-infrared (near-IR) region compared to early-generation fullerene-based systems, rendering organic semiconductor devices suitable for near-IR sensing applications. While most efforts are concentrated on the photoactive materials, less attention is paid to the impact of the back electrodes on the device performance. Therefore, this work focuses on the optical expediency of gold (Au), silver (Ag), aluminum (Al), and graphite as back electrode materials in organic optoelectronics. This work shows that the "one size fits all" methodology is not a valid approach for choosing the back electrode material. Instead, considering the active layer absorption, the active layer thickness, and the intended application is necessary. A traditional polymer/fullerene-based system, poly(3-hexylthiophene) with [6,6]-phenyl C61 butyric acid methyl ester (P3HT:PC60BM), and a state-of-the-art narrow-band gap non-fullerene-based system, poly[4,8bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b; 4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethy-lhexyl)3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-(2-6-diyl)] and 2,2'-((2Z,2'Z)-((5,5'-(4,4-bis(2-ethylhexyl)4H-cyclopenta[1,2-b:5,4-b']dithiophene-2,6-diyl)bis(4-((2ethylhexyl)oxy)thiophene-5,2-diyl))bis(methanylylidene)) bis(5,6-difluoro3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (PCE10:COTIC-4F), are investigated by combining optical transfer matrix modeling simulations with experimentally determined recombination and extraction losses. We find that the narrow-band gap system shows performance gains when employing Au as the back electrode. Furthermore, we show that these performance gains are dependent on active layer thickness, yielding the most significance for thin active layers (<100 nm). Such thin, ultra-narrow-band gap devices are the focus of near-IR sensing applications, highlighting the importance of methodically choosing the back electrode. Lastly, the impact of the back electrode on the OPV device performance is outlined.

Frequency spectra of various events pertinent to lightning cloud flashes obtained from wavelet transform technique and ratified by narrow band measurement technique

In the present study, frequency spectra of the electric field corresponding to the various cloud events, such as, initial breakdown process, regular pulse bursts, chaotic pulse trains and recoil streamers have been analysed. For the purpose, electric field radiated by cloud flashes were obtained simultaneously by a wide bandwidth antenna system and two narrow bandwidth antenna systems tuned at 3 MHz and 30 MHz. The frequency spectra of the broad band electric field signatures were obtained by using the wavelet transform technique and were compared with the magnitudes of the narrow band signals at the given central frequencies. To the best of our knowledge, it is the first study in which frequency spectra is obtained by transforming the time domain signal using wavelet transform technique and ratified by narrow bandwidth system for the cloud flashes. Fifteen cloud flashes pertinent to the Swedish thunderstorms were selected for the purpose. It is found that, the cloud flashes radiate at frequencies as low as 3 kHz to as high as a few tens of Mega Hertz (MHz). Electric field radiation corresponding to the initial breakdown process were found to radiate in the frequency range of 50 kHz to 5 MHz on the average, maximum energy is being radiated in the frequency range of 500 kHz to 5 MHz. Similarly, the final stage corresponding to the regular pulse bursts was found to radiate in the frequency range of 50 kHz to 5 MHz and that corresponding to the chaotic pulse trains was found to be in the range of 100 kHz to 5 MHz. Whereas, the very narrow pulses at the final stage, that can be termed as pulses corresponding recoil streamers (or Q-streamers) were found to radiate in the frequency range of 50 kHz to well above 10 MHz. Q-streamers can be considered as the strongest source of very high frequency and is justified by the simultaneous measurement of the electric fields at very high frequency (30 MHz) narrow bandwidth system. Rectification of the biasness of the conventional wavelet power spectrum has also been performed, however, no significant change in the spectrum was observed. Therefore, this study provides a strong basis for applying the wavelet transform technique without employing large number of narrowband system to acquire frequency domain information of lightning phenomena.

Sierpinski-like fractal ultra-wideband antenna with triple-band-notched characteristics

In order to avoid the interference conflict of narrow-band communication system to ultra-wideband (UWB) system, a Sierpinski-like fractal UWB antenna with triple-band-notched characteristics is proposed. The radiating patch adopts a second-order Sierpinski-like fractal structure with circular and pentagonal nested iterations, and uses the defective structure ground plate to achieve good ultra-wideband characteristics. By adding symmetrical inverted L-shaped open branches on the upper part of the fractal structure,and adding symmetrical L-shaped open branches on both sides of the microstrip feeder, and etching the inverted π-shaped narrow slit at the feeder produces notch characteristics of the 4.5–4.8 GHz, 7.2–7.8 GHz and 8.0–8.5 GHz bands. The simulation and measured results show that the antenna is effective in suppressing interference from narrow-band systems such as the international satellite frequency band, the X band satellite and the ITU-band in the 3.1–18.1 GHz band. In addition to the filtering frequency band, the antenna has relatively stable gain and omnidirectional radiation characteristics in the passband, and can be used in various ultra-wideband systems.

Two years of pulsar observations with the ultra-wide-band receiver on the Parkes radio telescope

ABSTRACT The major programme for observing young, non-recycled pulsars with the Parkes telescope has transitioned from a narrow-band system to an ultra-wide-band system capable of observing between 704 and 4032 MHz. We report here on the initial 2 yr of observations with this receiver. Results include dispersion measure (DM) and Faraday rotation measure (RM) variability with time, determined with higher precision than hitherto, flux density measurements and the discovery of several nulling and mode changing pulsars. PSR J1703−4851 is shown to be one of a small subclass of pulsars that has a weak and a strong mode which alternate rapidly in time. PSR J1114−6100 has the fourth highest |RM| of any known pulsar despite its location far from the Galactic Centre. PSR J1825−1446 shows variations in both DM and RM likely due to its motion behind a foreground supernova remnant.

An Optimized IR-UWB Communication System with Interference Reduction on a Narrowband System Using Genetic Algorithm

This paper proposed a new impulse radio ultra wideband (IR-UWB) signal to reduce interference on narrowband systems at high usage 5.2 GHz frequency. The combination of 4th and 5th order derivatives of Gaussian pulses were employed to generate the signal so that satisfy the US Federal Communications Commission (FCC) mask. The genetic algorithm technique was used to find the pulse optimized parameters. In this paper, spectrum was optimized by changing the shape factor (sigma) and amplitude of Gaussian pulses so that the transmitted power spectrum density was minimized at a frequency of 5.2 GHz and maximized at the other frequencies from 3.1 to 10.6 GHz according to the FCC mask. The signal was applied in an IR-UWB transceiver system with binary-phase shift keying modulation. The IR-UWB waveform is generated by a programmable digital to analog based circuit. The proposed system was compared with conventional IR-UWB systems at the same condition. The simulation results in multipath channel showed that the proposed system not only reduced interference with the narrowband system, but also this was robust against narrowband interference at 5.2 GHz frequency.

Channel Coding Based on Power Line Communication

This paper focuses on the forward error correction (FEC), the basic parameters determination of the RS convolution code, Turbo code and the LDPC code, and the corresponding encoding and decoding algorithm in power line communication (PLC) standard. Simulation experiment which is designed for narrow-band power line communication system based on OFDM is done. The coding using RS convolution code, Turbo code and LDPC code are compared, and further it is determined that which encoding method is more suitable for power line communication in China.

Field-Trial Experiments of an IoT-Based Fiber Networks Control and Management-Plane Early Disaster Recovery via Narrow-Band and Lossy Links System (FRENLL)

Field-Trial Experiments of an IoT-Based Fiber Networks Control and Management-Plane Early Disaster Recovery via Narrow-Band and Lossy Links System (FRENLL)

Honeycomb-Lattice Mott Insulator on Tantalum Disulphide.

Effects of electron many-body interactions amplify in an electronic system with a narrow bandwidth opening a way to exotic physics. A narrow band in a two-dimensional (2D) honeycomb lattice is particularly intriguing as combined with Dirac bands and topological properties but the material realization of a strongly interacting honeycomb lattice described by the Kane-Mele-Hubbard model has not been identified. Here we report a novel approach to realize a 2D honeycomb-lattice narrow-band system with strongly interacting 5d electrons. We engineer a well-known triangular lattice 2D Mott insulator 1T-TaS_{2} into a honeycomb lattice utilizing an adsorbate superstructure. Potassium (K) adatoms at an optimum coverage deplete one-third of the unpaired d electrons and the remaining electrons form a honeycomb lattice with a very small hopping. Abinitio calculations show extremely narrow Z_{2} topological bands mimicking the Kane-Mele model. Electron spectroscopy detects an order of magnitude bigger charge gap confirming the substantial electron correlation as confirmed by dynamical mean field theory. It could be the first artificial Mott insulator with a finite spin Chern number.

Parameters Uncertainty Immunization of Global Synchronous Pulsewidth Modulated VSIs With Round P&amp;O Algorithm

This letter proposes a closed-loop scheme for global synchronous pulsewidth modulated voltage source inverters with round perturbation and observation (R-P&O) algorithm to immunize the parameters uncertainty, e.g., line impedance and filter impedance variation. In specific, the rms value of measured total current harmonics at point of common coupling will be periodically sent to each inverter as feedback signal using the low-cost narrowband communication system. Then, the inverters will assume the R-P&O scheme to correct the phase shift angles among pulsewidth modulation carriers for intentionally minimizing the total current harmonics. Doing so, the closed-loop scheme can achieve the expected performance even under the severe parameters’ variation. The experimental results verified the performance of the proposed method.