Usable Frequency Research Articles

Target density estimation of mesopelagic fish using a towed, broadband, split-beam, acoustic scattering system

The ocean mesopelagic zone (200–1000 m) features a complex temporal and spatial distribution of organisms which may play an important role in ocean biogeochemical cycles. Yet a quantitative account of the abundance, biomass and migration behaviors of mesopelagic inhabitants is still lacking. Shipboard echosounders are limited by acoustic attenuation at higher frequencies constraining the usable frequency band for investigating deep sound scattering layers, as well as large acoustic sampling volumes, a result of the large depths associated with the deep scattering layers, combined with the inherent complexity of mesopelagic communities. Deep-See, a towed platform carrying multiple broadband sonars, focuses on individual targets in the deep scattering layers, to help interpret shipboard data. Target density estimation is the first step towards determining biomass in the mesopelagic zone. Two methods are investigated and applied to a summer 2019 dataset collected using two broadband split-beam echosounders (5.5–18.5 kHz, 18–47 kHz) on Deep-See in the slope waters off the New England Continental Shelf. The echo-counting method utilizes echo magnitude and phase information to determine singe targets while echo-statistics involves comparison of data to a physics-based numerical simulation to predict the statistics of broadband echoes from which target density can be extracted.

The Influence of Space Weather on the Relationship Between the Parameters TEC and foF2 of the Ionosphere

The critical frequency foF2 is an important parameter of the ionosphere, but its measurement data are often absent, especially during disturbances caused by the impact of space weather. The aim of this paper is to use the total electron content TEC to obtain foF2, which is necessary in such tasks as forecasting the maximum useable frequencies on HF paths, assimilation in the ionospheric models used in satellite wireless communication systems and for positioning. Formally, these parameters are linearly related through the equivalent slab thickness τ of the ionosphere, however, this relationship has not been practically studied for the southern hemisphere, since the thickness τ(IRI) of the International Reference Ionosphere IRI model can be used. This paper compares the efficiency of using τ(IRI) and various proposed options for determining experimental τ. The results are presented using the example of the March 2012-2017 disturbances and three stations in the southern hemisphere. Experimental medians τ(med) for a specific station in the current year and for other years, the median of another station, are used as τ. It is shown that the IRI model reacts only to negative disturbances. The use of various options for determining τ provides a 1.5-2 times better agreement with the real foF2. Especially, it concerns the long periods of enhancements of TEC (5-7 days), not connected in magnetic storms.

An Arrangement for Four-Element MIMO DRA With Complementary CP Diversity

An integrated four-element dielectric resonator-based multiple-input-multiple-output (MIMO) polarization diversity antenna is proposed in this letter. The MIMO antenna comprises two microstrip-slot fed dielectric resonator antenna (DRA) elements and two conformal open-loop fed DRA elements. These two different types of antenna elements are intended to radiate in two opposite directions to reduce the field components' interference. This aspect can offer a reliable wireless connection. Also, circular polarization diversity is implemented between the diagonally placed antenna elements to improve the isolation and diversity performance. The measured overlapping impedance bandwidth (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ii</sub> <; -10 dB) of 500 MHz (3.22-3.72 GHz) is attained for the proposed MIMO antenna with interport isolations of more than 15 dB throughout the usable frequency band. The proposed MIMO antenna acquires a measured overlapping axial ratio (AR) bandwidth (AR <; 3 dB) of 200 MHz (3.34-3.54 GHz), which covers the 3.4 GHz carrier frequency for the vehicle-to-vehicle and vehicle-to-infrastructure applications.

Equalization of Intensity-Modulated Fiber-Optic Voltage Sensors for Power Distribution Systems

We test fiber-optic voltage sensors based on optical reflection from a piezoelectric transducer. Our specific devices possess a 2 kHz fundamental resonance, and we verify a readily usable frequency band from approximately 10 Hz to 3 kHz, with a dynamic range of 60 dB for a detection system integrating over this entire band. Additionally, we demonstrate a digital signal processing approach to equalize the measured frequency response, enabling accurate retrieval of short-pulse inputs. Our results suggest the value and applicability of intensity-modulated fiber-optic voltage sensors for measuring both steady-state waveforms and broadband transients which, coupled with the straightforward and compact design of the sensors, should make them effective tools in electric grid monitoring.

Changes in Orientation Behavior due to Extended High-Frequency (5 to 10 kHz) Spatial Cues.

Objectives:Current hearing aids have a limited bandwidth, which limits the intelligibility and quality of their output, and inhibits their uptake. Recent advances in signal processing, as well as novel methods of transduction, allow for a greater useable frequency range. Previous studies have shown a benefit for this extended bandwidth in consonant recognition, talker-sex identification, and separating sound sources. To explore whether there would be any direct spatial benefits to extending bandwidth, we used a dynamic localization method in a realistic situation.Design:Twenty-eight adult participants with minimal hearing loss reoriented themselves as quickly and accurately as comfortable to a new, off-axis near-field talker continuing a story in a background of far-field talkers of the same overall level in a simulated large room with common building materials. All stimuli were low-pass filtered at either 5 or 10 kHz on each trial. To further simulate current hearing aids, participants wore microphones above the pinnae and insert earphones adjusted to provide a linear, zero-gain response.Results:Each individual trajectory was recorded with infra-red motion-tracking and analyzed for accuracy, duration, start time, peak velocity, peak velocity time, complexity, reversals, and misorientations. Results across listeners showed a significant increase in peak velocity and significant decrease in start and peak velocity time with greater (10 kHz) bandwidth.Conclusions:These earlier, swifter orientations demonstrate spatial benefits beyond static localization accuracy in plausible conditions; extended bandwidth without pinna cues provided more salient cues in a realistic mixture of talkers.

Bandpass NGD investigation of O-shape fully distributed structure with S-matrix modelling

PurposeThe aim of this paper is to provide the theoretical conceptualization of a bandpass (BP) negative group delay (NGD) microstrip circuit. The main objective is to provide a theorization of the particular geometry of the microstrip circuit with experimental validation of the NGD effect.Design/methodology/approachThe methodology followed in this work is organized in three steps. A theoretical model is established of equivalent S-parameters model using Y-matrix analysis. The GD analysis is also presented by showing that the circuit presents a possibility to generate NGD function around certain frequencies. To validate the theoretical model, as proof-of-concept (POC), a microstrip prototype is designed, fabricated and tested.FindingsThis work clearly highlighted the modelled (analytical design model), simulated (ADS simulation tool) and measured results are in good correlation. Relying on the proposed theoretical, numerical and experimental models, the BP NGD behaviour is validated successfully with GD responses specified by the NGD centre frequency: it is observed around 2.35 GHz, with an NGD value of about −2 ns.Research limitations/implicationsIt is to be noticed the proposed GD analysis requires limitations of the theoretical NGD model. It is depicted and validated through a POC demonstrating that the circuit presents a possibility to generate NGD function around certain frequencies (assuming constraints around usable frequency and bandwidth).Practical implicationsThe NGD O-shape topology developed in this work could be exploited in the future in the microwave and radiofrequency context. Thus, it is expected to develop GD equalization technique for radiofrequency and microwave filters, GD compensation of oscillators, filters and communication systems, design of broadband switch-less bi-directional amplifiers, efficient enhancement of feedforward amplifiers, design method of frequency independent phase shifters with negligible delay, synthesis method of arbitrary-angle beamforming antennas. The BP NGD behavior may also be successfully used for the reduction of resonance effect for the electronic compatibility (EMC) of electronic devices.Social implicationsThe non-conventional NGD O-circuit theoretical development and validation through experimental POC could be exploited by academic and industrial developers in the area of wireless communications including, but not restricted to, 5-generation communication systems. The use of the remarkable NGD effect is also useful for the mitigation of electromagnetic interferences between electronic devices and more and more complex electromagnetic environment (current development of Internet of Things[ IoT]).Originality/valueThe originality of this work relies on the new NGD design proposed in this work including the extraction of S-matrix parameters of the microstrip novel structure designed. The validation process based upon an experimental POC showed very interesting levels of NGD O-circuit (nanosecond-GD duration).

Circularly polarized offset-fed DRA elements & their application in compact MIMO antenna

In this work, the generation of circular polarization (CP) in two different dielectric resonator antenna (DRA) elements (one element gets energized by the offset conformal-strip and another one is by the offset microstrip-slot) is precisely explored. CP radiations from the presented DRA elements are acquired by removing a proper asymmetrical notch from the rectangular dielectric resonators (rDRs) and feeding the rDRs at an appropriate offset distance from the center. Furthermore, these two DRA elements are integrated into one antenna system, which can be used for multiple-input-multiple-output (MIMO) application. Owing to the use of two different excitation schemes, the dielectric resonators are mounted on two opposite sides of the substrate and are being radiated in two opposite directions to realize pattern diversity compact MIMO system. So, the presented MIMO design is able to diminish the intersecting spatial field components between the antenna elements, which in turn reduce the envelope correlation coefficient and improve the inter-port isolation. The proposed diversity/MIMO antenna can be utilized as a proficient contender in rich multipath environments to overcome the appearances of channel fading. Experimental outcomes convey that the proposed MIMO antenna features overlapping 3-dB axial ratio (AR) band ranging from 5.30 to 5.87 GHz and overlapping 10-dB impedance band ranging from 5.15 to 6.12 GHz with inter-port isolation of greater than 17 dB throughout the usable frequency band.

Defining the usable bandwidth of weak-motion records: application to induced seismicity in the Groningen Gas Field, the Netherlands

Seismic hazard and risk analyses are increasingly tapping into the previously underused resource of local weak-motion records. This is facilitating the development of local- or even application-specific models for the characterisation of earthquake ground motion. In turn, this offers the opportunity to derive non- or partially non-ergodic models and significantly reduce bias and uncertainty. However, weak-motion data, while carrying important information about local earthquake source, path and site effects, are susceptible to noise. We show that high-frequency noise has a record-, or region-specific, impact on pseudo-spectral acceleration (PSA). This impact depends on the shape of the records’ Fourier amplitude spectrum (FAS): PSA from moderately to highly damped ‘soil’ records (e.g. Groningen, the Netherlands) is much less susceptible to high-frequency noise than PSA from weakly damped ‘rock’ records (e.g. Eastern North America). We make use of simulated ground motion records to develop a parametric model for the lower usable period of PSA (Tmin). The model accounts for the impact of high-frequency noise on PSA, conditional on easily measured parameters characterising the shape of a record’s FAS. We then present a workflow, describing processing undertaken for records of induced seismicity from the Groningen gas field. The workflow includes the definition of maximum and minimum usable frequencies and periods of FAS and PSA, respectively. As part of the workflow, we present an approach that considers multiple estimates of Tmin. These include the parametric model and, additionally, record-specific hybrid simulations that artificially extend or modify time series’ FAS beyond the noise floor to assess subsequent impacts on PSA.

Plane wave beamforming with adaptively weighted frequency compound using bandpass filtering

We previously proposed the frequency and plane-wave compounding minimum variance distortion-free response (FPWC-MVDR) beamformer for ultrasonic reception beamforming, which weights the transmission angle and frequency band adaptively. This method required multiple subband transmissions and receptions for each transmission angle, reducing the frame rate. Here, we propose a filtered-FPWC-MVDR method that extracts and uses subband components via signal processing from the echo received after a single wideband pulse transmission. After confirming that this method provides the same performance as the original FPWC-MVDR, we experimentally investigate the subband conditions required, i.e. the bandwidth and number of subbands, when using this method. As a result, to improve the point target resolution, we find that there is an appropriate subbandwidth condition involving a trade-off between ensuring echo localization and increasing the degrees of freedom for frequency weight determination. Additionally, for improved contrast, the subbands were arranged appropriately to cover the entire usable frequency band.

Determination of the Annual Optimal Reliable Frequency for Different Transmitter/Receiver Stations Distributed over the Iraqi Territory

This paper aimed to determine the Optimal Reliable Frequency (ORF) that can maintain certain connection link between different transmitter/receiver stations laid over the Iraqi territory. Three different transmitting sites were chosen as tested stations located in the northern, central, and southern regions of Iraq. These sites are Mosul, Baghdad, and Basra, respectively. In this study, the years 2009 and 2014, which represent the minimum and maximum years of solar cycle 24, were chosen to examine the effect of low and high solar activity on the determined ORF. The datasets of the Best Usable Frequency (BUF) were calculated using the ASAPS international communication model. An analytical study was made on the generated BUF parameter dataset of the annual time for the adopted years. Also, an analytical simulation was made for the suggested ORF parameter depending on the BUF parameter datasets. The results of this simulation showed that the suggested ORF parameter can be represented by polynomial equation of different orders. The suggested formula was determined depending on different tested parameters (path length, bearing, time (day) and BUF values). For this purpose, a certain program was built using a visual basic programing language (VB6). The suggested ORF parameter was investigated for the annual time for the three sites of the years 2009 and 2014.

Comparison of speech recognition in cochlear implant patients with and without residual hearing: A review of indications

Objective This study evaluated existing guidelines for cochlear implantation (CI) according to the residual hearing of the patient. Speech recognition performance of adults implanted according to their degree of residual hearing was retrospectively evaluated. Methods Speech recognition results of 174 adult cochlear implant recipients were analyzed. All participants had pure tone thresholds of >75 dB at 2 and 4 kHz and were divided into three groups based on differing levels of low-frequency residual hearing. Results Findings indicate that CI was of benefit for all patients with bilateral severe hearing loss and patients with nonfunctional residual hearing both in quiet and noisy conditions. Patients with residual low-frequency hearing could benefit from combined electro-acoustic stimulation compared to CI alone or to hearing aids alone preoperatively. The speech recognition performance of all CI recipients with different levels of residual hearing in the low frequencies was similar except that superior performance was observed in the group using electro-acoustic stimulation compared to electrical stimulation alone. Discussion and conclusions Study results demonstrate the success of CI in accordance with current guidelines and also support expanding implantation guidelines to include patients who have severe-to-profound high-frequency sensorineural hearing loss and usable residual low frequency hearing.

Towards soft x-ray fluorescence measurements in the laboratory using a laser-produced plasma source and a complementary metal-oxide semiconductor detector

With the advent of commercially available CMOS technology suitable for direct detection of photons in the soft X-ray range, new possibilities are opening up for the improvement and optimization of experiments requiring energy discrimination capabilities in this energy range. SDDs are widely used as energy-dispersive detectors, but they cannot be used with pulsed sources due to the overwhelming temporal photon density. Wavelength-dispersive solutions offer unmatched energy resolution, but suffer from low detection efficiency and a limited energy bandwidth which can be monitored. The use of common CCDs as energy-dispersive detectors in this energy range is limited by their energy resolution and especially their readout speed, which can result in significant experimental dead time and limits the usable frequency of pulsed sources. Therewhile, CMOS detectors with high energy resolution and high frame rates are an efficient, versatile and cost-effective alternative as detectors for pulsed sources. In this work we present the characterization of a commercially available, backside-illuminated CMOS detector regarding its energy resolution and quantum efficiency at the BESSY II synchrotron radiation facility with a well-known soft X-ray radiation source. Furthermore it is used in a proof of principle XRF measurement with a laboratory-based laser-plasma source.

Linear Ultrasound Transmitter Based on Transformer with Improved Saturation Performance

Ultrasound methods are currently employed in a wide range of applications. They are integrated in complex electronics systems, like clinical echographs, but also in small and compact boards, like industrial sensors, embedded systems, and portable devices. Ultrasound waves are typically generated by energizing a piezoelectric transducer through a high-voltage sequence of small sinusoidal bursts. Moreover, in several applications, the ultrasound board should work in a wide frequency range. This makes the transmitter, i.e., the electronics that drives the transducer, a key part of the circuit. The use of a small transformer simplifies the electronics and reduces the need of high-voltage power sources. Unfortunately, the transformer magnetic core, when subjected to the sequence of bursts employed in ultrasound, is particularly prone to saturation. This phenomenon limits the maximum voltage and/or the minimum frequency the transformer can be employed for. In this work, a transmitter based on a transformer is proposed. Inspired by the technique currently employed in the power network transformers, we added a prefluxing circuit, which improves the saturation performance 2-fold. The proposed transmitter was implemented in a test board and experimented with two commercial transformers at 80 Vpp. Measurements show that the proposed prefluxing circuit moves down the minimum usable frequency 2-fold: from 400 to 200 kHz for one of the two transformers, and from 2.4 to 1.2 MHz for the other.

A Search for Technosignatures around 31 Sun-like Stars with the Green Bank Telescope at 1.15–1.73 GHz

Abstract We conducted a search for technosignatures in 2018 and 2019 April with the L-band receiver (1.15–1.73 GHz) of the 100 m diameter Green Bank Telescope. These observations focused on regions surrounding 31 Sun-like stars near the plane of the Galaxy. We present the results of our search for narrowband signals in this data set, as well as improvements to our data processing pipeline. Specifically, we applied an improved candidate signal detection procedure that relies on the topographic prominence of the signal power, which nearly doubles the signal detection count of some previously analyzed data sets. We also improved the direction-of-origin filters that remove most radio frequency interference (RFI) to ensure that they uniquely link signals observed in separate scans. We performed a preliminary signal injection and recovery analysis to test the performance of our pipeline. We found that our pipeline recovers 93% of the injected signals over the usable frequency range of the receiver and 98% if we exclude regions with dense RFI. In this analysis, 99.73% of the recovered signals were correctly classified as technosignature candidates. Our improved data processing pipeline classified over 99.84% of the ∼26 million signals detected in our data as RFI. Of the remaining candidates, 4539 were detected outside of known RFI frequency regions. The remaining candidates were visually inspected and verified to be of anthropogenic nature. Our search compares favorably to other recent searches in terms of end-to-end sensitivity, frequency drift rate coverage, and signal detection count per unit bandwidth per unit integration time.

A Novel Mode-Stirred Reverberation Chamber Design for 5G Millimeter Wave Bands

A novel mode-stirred reverberation chamber (RC) is designed and analyzed for millimeter wave bands. The size of the proposed RC with dimensions of 0.9 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.9$ </tex-math></inline-formula> m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.1$ </tex-math></inline-formula> m is suitable for user equipment (UE) tests. Two Z-shaped mode-stirrers are applied to generate a uniform field. To fulfill the communication and test requirements for user equipment, reference, measurement and link antennas with a large bandwidth are utilized, which can support both the frequency range (FR) 1 and FR2 bands of the 5G spectrum. The lowest usable frequency (LUF) and mode density were first calculated and examined. Then, the power transfer function (PTF) from 2 GHz to 40 GHz was obtained to verify the path loss. Three measurement campaigns were carried out to verify the accuracy of the RC. Firstly, the transmission power of the passive antenna for a conductive test was compared with the RC over the air (OTA) total radiated power (TRP) for single-tone signals. Then, signals with bandwidths of 100 MHz and 400 MHz were applied. A maximum power difference of only 0.8 dB was found in the above two experiments. Furthermore, the TRP for the same commercial 5G UE in both RC and compact antenna test range (CATR) systems was measured and compared. To the best of the authors’ knowledge, this is the first work to provide TRP results for 5G millimeter wave bands in a RC. The test results show that the TRP values for the two systems are almost the same with a maximum deviation of 0.5 dB, while the time required to carry out tests using the RC is lower than that for the CATR system.

Oblique Chirp Sounding and Prediction of the Maximum Usable Frequency on the Middle- and Long-Distance Paths

Oblique Chirp Sounding and Prediction of the Maximum Usable Frequency on the Middle- and Long-Distance Paths

Comparing Ionospheric MUF using IRI16 Model with Mid-Latitude Ionosonde Observations and Associated with Strong Geomagnetic Storms

High frequency (HF) radio wave propagation depends on the ionosphere status which is changed with the time of day, season, and solar activity conditions. In this research, ionosonde observations were used to calculate the values of maximum usable frequency (MUF) the ionospheric F2- layer during strong geomagnetic storms (Dst ≤ -100 nT) which were compared with the predicted MUF for the same layer by using IRI-16 model. Data from years 2015 and 2017, during which five strong geomagnetic storms occurred, were selected from two Japanese ionosonde stations (Kokubunji and Wakkanai) located at the mid-latitude region. The results of the present work do not show a good correlation between the observed and predicted MUF values for F2- layer during the selected events of strong geomagnetic storms at these stations. Thus, there is a further need to improve the IRI-16 model for better matching with the observations during strong geomagnetic storms.

Design, analysis, and validation of Radio Research Agency reverberation chamber

SummaryThis study presents the electromagnetic (EM) field uniformity analysis of the Korean National Radio Research Agency (RRA) reverberation chamber (RC). The analysis is performed using the normative procedure of International Electrotechnical Commission (IEC) 61000‐4‐21 for the estimation of the lowest usable frequency (LUF) of the RRA RC based on the field uniformity characterization. A full‐wave EM model of the RRA RC is designed using the method‐of‐moments (MOM) technique. The triaxial electric fields at the eight corners of the defined working volume are measured using electric field probes for the complete revolution of the mechanical stirrer. The experimental data are obtained for the frequency range of 80–1,000 MHz through the designed data acquisition software. The post‐processing of the experimental and simulation data in terms of calculation of standard deviation of recorded E‐field data, and its comparison with the defined standard deviation limit in IEC 61000‐4‐21 standard is performed to obtain the LUF of the RRA RC. A good degree of agreement was observed between the simulated and measured results of the RC field uniformity.

ESTIMATION OF THE ERROR IN PREDICTING&#x0D; THE MAXIMUM OBSERVED FREQUENCY IN CONDITIONS&#x0D; OF MINIMAL SOLAR ACTIVITY

The results of experimental studies of variations in the maximum observed fre-quency in 2016–2019 are presented on the mid-latitude route Cyprus – Rostov-on-Don. The accuracy of forecasting the maximum usable frequency when setting the state of the ionosphere using the IRI-2016 model is estimated. It is shown that in calm geophysical conditions, the typical values of the root-mean-square deviations of the maximum usable frequency from the maximum observed frequency reach 2,6 MHz.

Synthetic Inductance Standards Made Up of Capacitances and Gyrators

Inductance standards currently available are made up of toroidal inductors, i.e., coils of wire wound around a toroidal nonmagnetic core. The maximum inductance achievable is 10 H, while modern LCR meters offer measurement ranges up to more than 10 kH. Due to their winding capacitance and wire resistance, toroidal inductors exhibit quite large parasitic elements that restrict the operating frequency due to resonances. Using a gyrator in conjunction with a capacitance standard creates a synthesized inductance, which can exhibit values up to hundreds of kilohenries. Optimizing the gyrator's parameters leads to much lower parasitics and thus an extended usable frequency range even for inductances available as toroidal inductors. Furthermore, the physical size of a gyrator circuit is much smaller than that of a toroid, which simplifies thermoregulation and transportation.