kHz Signal Research Articles

Construction of an effective telephone bandwidth specifically for speaker recognition  

Although the telephone bandwidth is 0-4 kHz, the speaker specific information is not evenly distributed within this range but extends beyond 4 kHz. This is because the hypopharynx, especially the piriform fossa, affects the higher frequency region and contributes more to inter-speaker variation. By effectively shifting the higher bands to a lower frequency region, where speaker specific information is reduced, an effective 4 kHz bandwidth can be constructed to enhance speaker recognition performance. To achieve this a method was already proposed, which is extended in this paper to experimentally demonstrate and validate with more experiments. Furthermore, this paper defines the theoretically possible frequency space for which the frequency shifting method can be applied. To validate the method for different combinations of bands, possible bands were shifted in various directions in small steps. Speaker recognition experiments were conducted at each step to compare the performance against the baseband without any frequency shifting. Using the results of these extensive experiments, an approximate frequency space was defined where this frequency shifting performed better than the conventional baseband of 0-4 kHz signal. A simplified frequency shifting method was also investigated. Finally, the speech intelligibility of the frequency shifted narrow band speech signal was analysed using objective speech quality measures. This showed that intelligibility was not significantly affected by the frequency shifting method.

Comparative Study of the Anxiolytic Activity of Songorine in Elevated Plus Maze Test and by Recording Ultrasonic Vocalizations.

It was found that the diterpene alkaloid songorine administered per os to mice at a dose of 25 μg/kg provides a pronounced anxiolytic effect during elevated plus maze testing comparable to the effect of the benzodiazepine anxiolytic phenazepam. Recording of ultrasonic vocalizations of animals revealed an increase in the number of short high-frequency (50 kHz) signals under the action of songorine and the reference drug, which confirms their anti-anxiety properties.

High-performance MIM-type aluminum electrolytic capacitors with durable waterproof and wide temperature window

Capacitors are indispensable components of electronic circuits. Filter capacitors, mainly dominated by electrolytic capacitors, are critical for the accurate power supply of integrated circuits for central processors and storage devices, affecting the performance of advanced and sophisticated electronic equipment. However, electrolytic capacitors are restricted in working temperatures (<150 °C) and humidity conditions due to the inherent characteristics of MnO2 or polymer cathodes that tend to deteriorate at high temperatures and moisture. Here, high temperature resistant and conductivity SnO2 cathode and MIM-like (SnO2/AAO/Al) structures are introduced into aluminum electrolytic capacitors via ALD technology. First achieved in a higher temperature window (-60 °C∼330 °C), the capacitor maintains a stable capacity (114.5 ± 3.6 μF/cm2) and phase angles (-89.5 ± 0.2°) at 120 Hz. The tight stacking and conformability of ALD even allows unencapsulated devices to exhibit durable waterproof, showing stable performance for immersion in water within 90 days. Moreover, a thin amorphous Al2O3 (A) as buffer layer is introduced at electrode/dielectric interface, aiming to barrier the interfacial atomic diffusion at the SnO2/AAO. A stable vdW SnO2/A/AAO interfaces is obtained, proven by MD and DFT calculations. Impressively, the capacitor exhibits high reliability with high breakdown field strength (5.5 MV/cm), low leakage current (7.2 × 10–7 A/cm2 at 1 V) and low loss (2% at 120 Hz). Applied in circuits, the capacitor filters 100 kHz signal with a Vripple of only 15 mV and shows excellent charging and discharging behaviors. The work may pave the way for the practical application of electrolytic capacitors in harsh working environments.

Coherence of the frequency-difference autoproduct deduced from high-frequency acoustic fields scattered from a rough sea surfacea).

The prevalence of random scattering from a rough ocean surface increases with increasing χ=kh cos θ, where k is the acoustic wavenumber, h is the root-mean-square surface height, and θ is the incidence angle. Generally, when χ≫1, coherence between incident and surface-scattered fields is lost. However, such coherence may be recovered when χ≫1 by considering the frequency-difference autoproduct of the surface-scattered field, a quadratic product of complex fields at nearby frequencies. Herein, the autoproduct's coherent reflection coefficient for χ> 20 is determined from surface-scattered sound fields obtained from 50 independent realizations of the rough ocean surface measured in pelagic waters off the coast of California in January 1992. The recordings were made with a source at a depth of 147 m that broadcasted 30 and 40 kHz signals to a single receiver 576 m away at depth of 66 m. An analytic formula for the coherent reflection coefficient of the frequency-difference autoproduct, based on the Kirchhoff approximation and a Gaussian surface autocorrelation function, compares favorably with measurements. Improved agreement with the single-receiver measurements is possible via a minor adjustment to the surface autocorrelation length. The adjustment identified here matches that determined previously from horizontal spatial coherence estimates utilizing the experiment's eight-element receiving array.

A 1.2 V, 92 dB Dynamic-Range Delta-Sigma Modulator Based on an Output Swing-Enhanced Gain-Boost Inverter

This article presents a third-order, feedforward, single-bit Delta-Sigma analog-to-digital modulator (DSM) based on an output swing-enhanced gain-boost inverter for low-voltage low-power applications such as wearable devices, mobile health, and the Internet of Things (IoTs). The proposed output swing-enhanced structure addresses the output-swing reduction in the conventional structure while achieving high DC gain and large output swing simultaneously. Implemented in a 180 nm CMOS process, the entire chip is comprised of a delta-sigma modulator, an oscillator, and a current reference. It achieves 86.1 dB peak SNR and 92 dB dynamic range (DR) with 1.95 kHz signal bandwidth. The whole chip dissipates 54.5 μW, leading to a 167.6 dB Schreier Figure of Merit (FoMs).

High-capacity MIMO visible light communication integrated into mini-LED LCDs

Visible light communication (VLC) can be integrated into a liquid crystal display (LCD) by modulating its backlight while normally showing pictures. Received by ordinary cameras, such integrated display and communication (IDAC) systems are promising for the Internet of Things and Metaverse. However, in the premise of unaffected display function, the capacity of current IDAC systems is limited, with data rates of very few kbps. This work proposes a new architecture: multiple-input, multiple-output (MIMO) VLC integrated into a mini-LED LCD, whose many backlight segments act as multiple transmitters. A camera utilizes the rolling shutter effect with independent pixel columns to form multiple outputs. The communication capacity is thus significantly multiplied by the backlight column number. In addition, local dimming, which is favorable for an LCD’s contrast and power consumption, is exploited to achieve efficient signal modulation. We built a mini-LED LCD prototype with 8-by-20 backlight segments for experimental verification. The backlight segments multiplex a video-rate signal for local dimming and a high-frequency (∼34 kHz) signal modulated through multi-pulse position modulation (MPPM) for VLC. By taking photographs with a camera 1.1 m away from the screen, a record-high rate of 201.6 kbps (approximately ten times faster than current IDAC systems) was experimentally achieved with a bit error rate satisfying the forward error correction. Improved image contrast due to local dimming was also observed.

BRAND: a platform for closed-loop experiments with deep network models.

Objective.Artificial neural networks (ANNs) are state-of-the-art tools for modeling and decoding neural activity, but deploying them in closed-loop experiments with tight timing constraints is challenging due to their limited support in existing real-time frameworks. Researchers need a platform that fully supports high-level languages for running ANNs (e.g. Python and Julia) while maintaining support for languages that are critical for low-latency data acquisition and processing (e.g. C and C++).Approach.To address these needs, we introduce the Backend for Realtime Asynchronous Neural Decoding (BRAND). BRAND comprises Linux processes, termednodes, which communicate with each other in agraphvia streams of data. Its asynchronous design allows for acquisition, control, and analysis to be executed in parallel on streams of data that may operate at different timescales. BRAND uses Redis, an in-memory database, to send data between nodes, which enables fast inter-process communication and supports 54 different programming languages. Thus, developers can easily deploy existing ANN models in BRAND with minimal implementation changes.Main results.In our tests, BRAND achieved <600 microsecond latency between processes when sending large quantities of data (1024 channels of 30 kHz neural data in 1 ms chunks). BRAND runs a brain-computer interface with a recurrent neural network (RNN) decoder with less than 8 ms of latency from neural data input to decoder prediction. In a real-world demonstration of the system, participant T11 in the BrainGate2 clinical trial (ClinicalTrials.gov Identifier: NCT00912041) performed a standard cursor control task, in which 30 kHz signal processing, RNN decoding, task control, and graphics were all executed in BRAND. This system also supports real-time inference with complex latent variable models like Latent Factor Analysis via Dynamical Systems.Significance.By providing a framework that is fast, modular, and language-agnostic, BRAND lowers the barriers to integrating the latest tools in neuroscience and machine learning into closed-loop experiments.

Issues in mid-frequency sound intensity fluctuation on the Washington Shelf

Strong mid-frequency sound intensity fluctuations were found on the Washington shelf during an experiment in the summer of 2022. The Scintillation Index (SI) of integrated sound energy on single channels at 20 km range was near unity for both 3.5 kHz and 6.0 kHz signals. Accompanying oceanographic measurements from moorings and a towed profiling system revealed sound field variability at multiple time and spatial scales caused by linear and nonlinear internal waves, internal tides, and coastal trapped waves. While the 2022 dataset provides valuable information for addressing issues on intensity fluctuation, additional experimental data are needed to understand the impacts on active and passive mid-frequency sonar systems. To that end, a second Washington Shelf experiment is being planned for the summer of 2025. This talk will discuss the planned measurements and the range of issues to be addressed. These include the frequency-dependence of SI over 1–10 kHz, broadband fading, vertical and horizontal coherence, and the impacts of variability on propagation in subsurface ducts. These measurements are important for investigating fundamental oceanographic causes of sound fluctuation as well as for the design of appropriate signal processing methods. (Work supported by the Office of Naval Research.)

The use of Navy range bottom-mounted, bi-directional transducers for long-term, deep-ocean prey mapping

Beaked whales have been shown to be particularly sensitive to mid-frequency active sonar but continue to spend considerable time on Navy training ranges, where exposure to sonar is frequent. Understanding the underlying movements of their prey could help to explain the distribution and abundance patterns seen for beaked whales. Beaked whales are among the deepest diving marine mammals and have been shown to feed near the ocean bottom, at depths up to 3000 m. Typical surface-deployed prey mapping technology is not suitable for probing these deep foraging depths. This pilot study aims to us the bi-directional nodes on Navy hydrophone ranges that were developed for underwater communications as a rudimentary prey mapping system. A 1 ms 2 kHz signal was broadcast on an 8 kHz carrier signal and resulting returns were processed to estimate depths of the reflectors. Data are presented from three different time periods on the Southern California Anti-Submarine Warfare Range.

A New Kilohertz Gravitational-wave Feature from Rapidly Rotating Core-collapse Supernovae

We present self-consistent three-dimensional core-collapse supernova simulations of a rotating 20M ⊙ progenitor model with various initial angular velocities from 0.0 to 4.0 rad s−1 using the smoothed particle hydrodynamics code SPHYNX and the grid-based hydrodynamics code FLASH. We identify two strong gravitational-wave features with peak frequencies of ∼300 Hz and ∼1.3 kHz in the first 100 ms postbounce. We demonstrate that these two features are associated with the m = 1 deformation from the proto-neutron star (PNS) modulation induced by the low-T/∣W∣ instability, regardless of the simulation code. The 300 Hz feature is present in models with an initial angular velocity between 1.0 and 4.0 rad s−1, while the 1.3 kHz feature is only present in a narrower range, from 1.5 to 3.5 rad s−1. We show that the 1.3 kHz signal originates from the high-density inner core of the PNS, and the m = 1 deformation triggers a strong asymmetric distribution of electron antineutrinos. In addition to the 300 Hz and 1.3 kHz features, we also observe one weaker but noticeable gravitational-wave feature from higher-order modes in the range between 1.5 and 3.5 rad s−1. Its initial peak frequency is around 800 Hz, and it gradually increases to 900–1000 Hz. Therefore, in addition to the gravitational bounce signal, the detection of the 300 Hz, 1.3 kHz, the higher-order mode, and even the related asymmetric emission of neutrinos could provide additional diagnostics for estimating the initial angular velocity of a collapsing core.

Diurnal measurements of sound attenuation (100 Hz—10 kHz) in a shallow (1-2 m), seagrass (Zostera marina) meadow are impacted by photosynthetic activity and water column height

Seagrass meadows are important habitats that provide a variety of ecosystem services. As the seagrasses photosynthesize, they fill their vascular tissues with oxygen which is also released as bubbles into the water column. Measurements of sound attenuation were made in August 2022 in a shallow (1–2 m water depth) Zostera marina meadow in Shinnecock Bay, New York. Sound sources included tones (100 Hz–2 kHz) transmitted over an 8hour period (0800–1600 local time) and a 10 kHz Fishtek pinger operating over a 3 day period. Hydrophones were placed in the seagrass meadow at ranges of 1, 3, and 7 m from the source to determine attenuation. Vertical profiles of temperature, salinity, and dissolved oxygen were measured at the study site during the 8 hour tonal source experiment, and solar irradiance and tide level for Shinnecock Bay were obtained for the 3 day study period. Peak to peak sound pressure levels varied by more than 31 dB over a diurnal period for the 10 kHz signals. Sound attenuation of lower frequency tones varied from 9 to 30 dB both with dissolved oxygen (a proxy for photosynthetic activity of the seagrass) as well as water column height.

Energy‐efficient selection of relay for UWSNs in the Internet of underwater things

SummaryInternet of underwater things (IoUT) for underwater monitoring is known worldwide for smart interlinked underwater things that exhibit the capacity to monitor the vast unexplored waters of the oceans. Concept of IoUT has been derived from Internet of Things (IoT) in order to acquire the exquisite benefits of networking in underwater environment. IOT standards and technologies do not work well in underwater environment, such as infrared, Wi‐Fi, and radio frequency (RF) due to high channel errors and limited range up to few meters. Acoustic waves, however, can be used to communicate both in shallow and deep oceans due to their low frequency (kHZ) signal. In context of IoUT, communication based on acoustic links enables different applications such as underwater exploration, environmental monitoring, and disaster prevention even without availability of GPS facility like free space environment. In unpredictable and changing underwater environment, energy efficiency becomes a major challenge during data routing along multiple devices. Batteries of the sensor nodes, autonomous underwater vehicle (AUV), and remotely operated vehicle (ROV) cannot be removed with easiness and difficult to recharge, and the only way out is efficient sensor node selection for relaying to save massive amount of energy. Energy aware channel routing protocol (ECARP) does not consider the depth of the node while selecting the relay nodes to forward the data. Relay node selection in underwater Internet of things (IOUT) is a primary problem addressed in this research based on channel state information (CSI) for establishing best path to relay information among IOUT devices. Our major focus was to develop better technique for the relay node selection using a CSI and select relay node by looking at its depth from ocean surface and residual energy in the proposed ED‐CARP. Simulation results validate that proposed ED‐CARP can decrease the communication cost and increase the network lifetime.

Ultracompact Microinterferometer-Based Fiber Bragg Grating Interrogator on a Silicon Chip

We report an interferometer-based multiplexed fiber Bragg grating (FBG) interrogator using silicon photonic technology. The photonic-integrated system includes the grating coupler, active and passive interferometers, interferometers, a 12-channel wavelength-division-multiplexing (WDM) filter, and Ge photodiodes, all integrated on a 6x8 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> silicon chip. The system also includes optical and electric interfaces to a printed board, which is connected to a real-time electronic board that actively performs the phase demodulation processing using a multitone mixing (MTM) technique. The device with active demodulation, which uses thermally-based phase shifters, features a noise figure of σ = 0.13 pm at a bandwidth of 700 Hz, which corresponds to a dynamic spectral resolution of 4.9 fm/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . On the other hand, the passive version of the system, based on a 90º-hybrid coupler, features a noise figure of σ = 2.55 pm at a bandwidth of 10 kHz, also showing successful detection of a 42 kHz signal when setting the bandwidth to 50 kHz. These results demonstrate the advantage of integrated photonics, which allows the integration of several systems with different demodulation schemes in the same chip and guarantees easy scalability to a higher number of ports without increasing the dimensions or the cost.

A 24-kHz BW 90.5-dB SNDR 96-dB DR continuous-time delta-sigma modulator using FIR DAC feedback

This paper presents a single bit continuous time delta-sigma modulator (CTDSM) with finite impulse response (FIR) feedback DAC designed for audio applications. By using FIR feedback in the input stage, the linearity requirements of the first integrator are relaxed, and the clock jitter sensitivity is reduced, as seen in a multi-bit quantizers. The choppers, working in conjunction with the FIR DAC, effectively suppresses in-band aliasing noise generated by the chopper in the first integrator. A fast comparator serves as a single-bit quantizer, and the 9.2% TS loop delay eliminates the need for excess loop delay compensation in the modulator. Energy efficient integrators are implemented using the current-starved OTA. The CTDSM prototype was fabricated using a 180-nm CMOS process, achieving a 90.5 dB SNDR and 96 dB DR with a 24 kHz signal bandwidth. The power consumption is 210 μ W, corresponding to a Schreier figure-of-merit value of 171.1 dB.

A 14-Bit Oversampled SAR ADC With Mismatch Error Shaping and Analog Range Compensation

DAC mismatch is a major challenge for high-resolution ADCs. This paper proposes an analog-detection-based input range compensation technique for high-resolution ADCs with mismatch error shaping (MES). By applying a pre-comparison and suitably switching the DAC MSB, the input loss caused by MES is compensated. By adopting a flying-capacitor sampling technique, the prediction errors found in prior solutions are avoided. The prototype 14-bit SAR ADC achieves 80.4 dB SNDR and 93 dB SFDR in a 4 kHz signal bandwidth with an OSR of 16. It only occupies 0.0034 mm and consumes 0.656 μW under a 0.8 V supply, leading to a Schreier figure-of-merit of 178.3 dB. These features make it suitable for miniaturized high-performance IoT and biomedical systems.

Experimental demonstration of spatial division multiplexing multiple-input/multiple-output underwater acoustic communication using a time-reversal method at the depth of the continental shelf: a consideration of optimization of signal length and number of transmission channels

In this paper, the performance of the adaptive passive time-reversal method is investigated for an at-sea experiment of multiple-input/multiple-output underwater acoustic communication over a range of 13.5 km. The experiment was conducted at a depth of 200 m utilizing up to five transmitters with 4–8.5 kHz signal bandwidth for spatial division multiplexing. It was confirmed that the performance depends on the delay time from the timing of the channel response estimation to the communication signal reception, and the optimal signal length and the number of transmission channels can be determined according to the required bit error rate (BER) for the system. As a result, using the optimal signal length and a number of transmission channels, effective data rates of 30.21 and 37.53 kbps are achieved with BER ranges of less than 0.1% and 1%, respectively, with more than 90% of received communication signal packets.

Lower-ionosphere electron density and effective recombination coefficients from multi-instrument space observations and ground VLF measurements during solar flares

A new model to predict the electron density and effective recombination coefficient of the lower ionosphere under solar flare conditions is presented. This model relies on space-borne solar irradiance measurements in coincidence with ground recorded active transmissions of Very Low Frequency (VLF), (<30 kHz) signals. Use is made of the irradiance measured by broad-band radiometers onboard the satellites: GOES, SDO, and PROBA2. Measurements are made over succeeding and partly overlapping wavelength intervals of the instrument bandpass ranges altogether covering the range 0.1–20 nm. The aim is to determine the effectiveness of the particular instrument bandpass in producing changes in the ionization of the lower ionosphere (D-region) during solar X-ray flares. Ionization efficiency is evaluated using modelled Solar Spectral Irradiance for each flare separately and for each instrument as a function of its bandpass.The new model is based on coupling of the continuity equation with the Appleton relation and uses the concept of time delay – the time lag of the extreme VLF amplitude and phase behind the flare irradiance maximum. The solution of the continuity equation predicts the electron density time - height profile for 55–100 km altitude.An analysis of M to X class flares shows the flare-enhanced electron densities due to a particular ionizing wavelength domain are in good agreement for the case where irradiance is taken over the bandpass of (1) either GOES (0.1–0.8 nm) or SDO/ESP (0.1–7 nm) for up to 90 km (2) either SDO/ESP or PROBA2/LYRA (1–2 +6–20 nm) at heights above 90 km. The results agree within 22% for heights up to 90 km, and differ by at most a factor of 2 for heights above 90 km. Remarkable agreement is shown between measured and evaluated time delay; discrepancies are generally less than 8%. The effective recombination coefficient is deduced from the model itself and is found to be consistent with other independent estimates.

9.9 µW, 140 dB DR, and 93.27 dB SNDR, Double Sampling ΔΣ Modulator Using High Swing Inverter-Based Amplifier for Digital Hearing Aids

In this paper, an ultra-low-power second-order, single-bit discrete-time (DT) double sampling ΔΣ modulator was proposed for hearing aid applications. In portable biomedical devices that are permanently used such as hearing aids, short battery lifetime and power dissipation are considerable issues. In a typical delta–sigma modulator, the most power-consuming parts are the operational transconductance amplifiers (OTAs), and their elimination without loss of efficiency is now challenging. This proposed modulator includes an ultra-low-power self-biased inverter-based amplifier with swing enhancement instead of power-hungry OTAs. Low voltage amplifier design reduces output swing voltage, affecting delta–sigma modulator efficiency and decreasing the signal-to-noise and distortion ratio (SNDR) and dynamic range (DR) values. In this article, the proposed amplifier’s source and tail transistors were biased in the sub-threshold region, increasing the output swing voltage significantly and leading to desired properties for a hearing aid modulator. The proposed amplifier peak-to-peak swing voltage was approximately 1.01 V at a 1 V power supply. In addition, the proposed modulator design used a standard 180 nm CMOS technology, which obtained 140 dB DR and 93.27 dB SNDR for a 10 kHz signal bandwidth with an oversampling ratio (OSR) of 128. Finally, the modulator’s effective chip area was 0.02 mm2 and consumed only about 9.9 µW, while the figure of merit (FOMW) and FOMs achieved 1.31 fJ/step and 183.31, respectively.

Behavioral Modeling and Circuit Design of High Precision Low Power Dynamic Zoom ADC

In this paper, a high-precision, energy-saving dynamic zoom ADC consisting of a 6-bit SAR ADC and a second-level Σ − ∆ modulator (SDM) is proposed. Non-ideal factors, including slew rate (SR), limited bandwidth and DC gain of the op-amp, and kT/C noise, mismatch of DAC capacitors, are analyzed with a behavioral model in Simulink to guide actual circuit design more accurately. The ADC parameters are adjusted and optimized by model simulation. Because the DAC capacitors mismatch produces harmonic distortion, the DWA technique is used. A new digital combined circuit is proposed to minimize power consumption. To further improve its energy efficiency, a gain enhancement current mirror OTA is designed and the SAR ADC adopts upper plate sampling technique. The layout of zoom ADC occupies 0.856 mm2 in 65 nm techniques. It achieves 109.2 dB SNDR, 17.84 bits ENOB at 1 kHz signal bandwidth and consumes only 0.233 mW.

A Σ-Δ Modulator Based on an Inverter-based Integrator with Dynamic Current Switch

This paper presents a low-power high-resolution 3rd-order 1-bit Σ-Δ modulator based on an inverter-based integrator with a dynamic current switch. To reduce the power consumption of the modulator circuit, a dynamic current switch branch is added to form a low-power inverter-based integrator. A 3rd-order 1-bit Σ-Δ modulator is designed in a TSMC 65 nm CMOS technology to verify the effectiveness of the proposed integrator circuit. The prototype Σ-Δ modulator achieves 102.4 dB SNDR, 16.71 Bit ENOB in a 2 KHz signal BW at an Over Sampling Ratio (OSR) of 160, while consuming only 29.5-μW. And the FOMSNDR is 180.7 dB.