Objective: Cochlear implants are traditionally programmed to stimulate according to a generalized frequency map, where individual anatomic variability is not considered when selecting the centre ...frequency of stimulation of each implant electrode. However, high variability in cochlear size and spatial frequency distributions exist among individuals. Generalized cochlear implant frequency maps can result in large pitch perception errors and reduced hearing outcomes for cochlear implant recipients. The objective of this work was to develop an individualized frequency mapping technique for the human cochlea to allow for patient-specific cochlear implant stimulation. Methods: Ten cadaveric human cochleae were scanned using synchrotron radiation phase-contrast imaging (SR-PCI) combined with computed tomography (CT). For each cochlea, ground truth angle-frequency measurements were obtained in three-dimensions using the SR-PCI CT data. Using an approach designed to minimize perceptual error in frequency estimation, an individualized frequency function was determined to relate angular depth to frequency within the cochlea. Results: The individualized frequency mapping function significantly reduced pitch errors in comparison to the current gold standard generalized approach. Conclusion and Significance: This paper presents for the first time a cochlear frequency map which can be individualized using only the angular length of cochleae. This approach can be applied in the clinical setting and has the potential to revolutionize cochlear implant programming for patients worldwide.
The recently proposed orthogonal time-frequency-space (OTFS) modulation technique was shown to provide significant error performance advantages over orthogonal frequency division multiplexing (OFDM) ...over delay-Doppler channels. In this paper, we first derive the explicit input-output relation describing OTFS modulation and demodulation (mod/demod). We then analyze the cases of: 1) ideal pulse-shaping waveforms that satisfy the bi-orthogonality conditions and 2) rectangular waveforms which do not. We show that while only inter-Doppler interference (IDI) is present in the former case, additional inter-carrier interference (ICI) and inter-symbol interference (ISI) occur in the latter case. We next characterize the interferences and develop a novel low-complexity yet efficient message passing (MP) algorithm for joint interference cancellation (IC) and symbol detection. While ICI and ISI are eliminated through appropriate phase shifting, IDI can be mitigated by adapting the MP algorithm to account for only the largest interference terms. The MP algorithm can effectively compensate for a wide range of channel Doppler spreads. Our results indicate that OTFS using practical rectangular waveforms can achieve the performance of OTFS using ideal but non-realizable pulse-shaping waveforms. Finally, simulation results demonstrate the superior error performance gains of the proposed uncoded OTFS schemes over OFDM under various channel conditions.
This paper presents a fast and autonomous injection frequency tracking and locking technique. In the present injection-locking system, a quadrature injection-locked oscillator (QILO) is third ...harmonically locked to a quadrature voltage-controlled oscillator (QVCO). In the frequency tracking loop, the frequency difference between QVCO and QILO is extracted using the QILO's amplitude modulated (AM) envelope waveform. The AM frequency of the envelope signal bears frequency difference between the two oscillators. The envelope signal is further converted to pulse signal which subsequently drives digital feedback control circuitry to update the QILO's output frequency so that it can track the third harmonic of the injection QVCO. The frequency calibration process is purely autonomous, self-initiating whenever the AM modulated envelope waveform is generated. The feedback signal is primarily processed in the digital domain, resulting in a compact, fast, and power-efficient injection frequency-locked loop (IFLL). By incorporating a phase noise (PN) calibration routine after completing the frequency calibration, the presented IFLL resolves the intractable issue of PN degradation at the edge of the slave oscillator's injection locking range. This results in a large injection frequency tracking range of 26.5-29.7 GHz which is only limited by the QILO's LC tank tuning range. The IFLL realized in 0.13-μm CMOS consumes 2.4 mW with a negligible area penalty. Overall chip size including QVCO, QILO, and IFLL is 1 × 1 mm 2 .
Increasing penetration of renewable energy sources based on power electronic interfaces in traditional power systems reduces the inertia constant and damping coefficient. It also increases ...uncertainty and the sensitivity of the system to disturbances. The concept of the virtual synchronous generator (VSG) is used to emulate the inertia constant and damping property like a synchronous generator. It can be shown that all given VSG structures have the same dynamics as the proportional-integral-derivative (PID) controller. In this paper, the quantitative feedback theory (QFT) is used to tune the VSG parameters such that robust system stability and performance are guaranteed. Moreover, the desired disturbance attenuation is also taken into account. Through frequency response analysis and time-domain simulations, it is shown that the proposed strategy can be successfully used to solve the load-frequency control problem in islanded microgrids (MGs). In addition, the proposed QFT-based VSG is compared with another robust VSG designed by the well-known <inline-formula><tex-math notation="LaTeX">H_\infty</tex-math></inline-formula> technique to illustrate its better performance against disturbances.
Modern electricity grids throughout the world, particularly in islands such as Great Britain, face a major problem on the road to decarbonisation: the significantly reduced level of system inertia ...due to integration of Renewable Energy Sources (RES). Given that most RES such as wind and solar are decoupled from the grid through power electronics converters, they do not naturally contribute to system inertia. However, RES could support grid stability through appropriately controlling the converters, but currently no market incentives exist for RES to provide this support. In this paper we develop a methodology to optimally clear a market of ancillary services for frequency control, while explicitly considering the participation of grid-forming and grid-following inverter-based technologies. We propose a mathematical framework that allows to compute shadow prices for ancillary services offered by a pool of diverse providers: synchronous and synthetic inertia, enhanced frequency response (e.g. from curtailed RES) and traditional primary frequency response (e.g. by thermal generators). Several case studies are run on a simplified Great Britain system, to illustrate the applicability and benefits of this pricing scheme.
This brief presents a comprehensive tutorial on the recent advances of injection-locking techniques used for millimeter-wave (mm-Wave) and terahertz (THz) signal generation systems. Injection locking ...has the potential to significantly improve the system performance in terms of low phase noise and low power consumption. The focus will be on the state-of-the-art injection-locking techniques to effectively widen the locking range and reduce the phase noise, including injection-locked frequency dividers (ILFDs), injection-locked frequency multipliers (ILFMs), and sub-harmonic injection-locked phase-locked loops (IL-PLLs).
Power system operators are increasingly procuring frequency regulation reserves from distributed energy resources via aggregators. Provision of the frequency regulation services by the aggregators ...can be studied from different aspects and by using different models, ranging from very-short-run to long-term scheduling models. By developing a methodology for ensuring the operational model's compliance with the dynamic constraints, this article bridges the gap between economic studies of the aggregator's frequency containment reserve market participation on the one hand and the distributed energy resources' dynamic response on the other. The article presents a mixed-integer linear program for the aggregator's portfolio management that incorporates constraints of individual units' fast dynamics, and validates them via dynamic simulations. The results demonstrate the importance of including reserve activation constraints when modelling storage technologies and settling time constraints when modelling conventional units.
Laser frequency drift (LFD) restricts the low-frequency vibration sensing ability of phase-sensitive optical time-domain reflectometer (<inline-formula> <tex-math notation="LaTeX">\Phi ...</tex-math></inline-formula>-OTDR). In this study, we propose a self-diagnosis structure combining Mach-Zehnder interference and <inline-formula> <tex-math notation="LaTeX">\Phi </tex-math></inline-formula>-OTDR is first designed to realize LFD measurement and vibration sensing simultaneously. A multiscale variational mode decomposition (VMD) with the judgment at different amplitude scales, time scales, and modal scales is proposed to suppress the influence of LFD at low-frequency vibration demodulation. Experimental results show a long-time continuous LFD measurement and vibration sensing along the sensing fiber of 10040 m. After the parameter optimization of iteration and mode decomposition with multiscale VMD, infrasonic and sub-Hertz vibration signals can be detected with improved SNR. The ultralow-frequency vibration signal as low as 0.04 Hz is also demodulated under a long-time continuous detection of more than 40 min. The fitting coefficient between the recovered vibration frequency and the actual vibration frequency is 0.99966. This self-diagnostic structure, based on multiscale VMD, effectively suppresses the influence of LFD on <inline-formula> <tex-math notation="LaTeX">\Phi </tex-math></inline-formula>-OTDR and reliably recovers ultralow-frequency vibrations during long-term detection.
Abstract
Optical frequency combs in the terahertz frequency range are long-awaited frequency standards for spectroscopy of molecules and high-speed wireless communications. However, a terahertz ...frequency comb based on a low-cost, energy-efficient, and room-temperature-operating device remains unavailable especially in the frequency range of 0.1 to 3 THz. In this paper, we show that the resonant-tunneling-diode (RTD) oscillator can be passively mode-locked by optical feedback and generate a terahertz frequency comb. The standard deviation of the spacing between the comb lines, i.e., the repetition frequency, is reduced to less than 420 mHz by applying external bias modulation. A simulation model successfully reproduces the mode-locking behavior by including the nonlinear capacitance of RTD and multiple optical feedback. Since the mode-locked RTD oscillator is a simple semiconductor device that operates at room temperature and covers the frequency range of 0.1 to 2 THz (potentially up to 3 THz), it can be used as a frequency standard for future terahertz sensing and wireless communications.
This paper describes a highly sensitive sensing system for remote sensing applications. Typically, a resonant sensor based on film bulk acoustic resonator (FBAR) requires a frequency counter, ...impedance analyzer, or network analyzer to measure the shift of the resonant frequency. This paper presents a hand-held, low-cost but highly sensitive sensing system built with an FBAR-based oscillator and a phase-locked-loop for ppm-level detection of frequency shift as well as signal processing. The achieved voltage-frequency sensitivity is 1.035 V/kHz with the minimum detectable frequency shift of 4.81 ppm (5.21 kHz) and the dynamic range of 134 ppm (145 kHz). Also, the output of the sensing system is purposely designed to be a DC voltage that is linearly related to the frequency shift. To our knowledge, it is the first FBAR-based sensing system that converts the frequency shift to DC voltage.
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