Frequency Measurement Technique Research Articles

Combined Fourier and Zero Crossing Technique for Frequency Measurement in Power Networks in the Presence of Harmonics.

A new approach to the design of a digital algorithm for network frequency estimation is proposed. The algorithm is derived using Fourier and zero crossing technique. The Fourier method is used as digital filter and zero crosing technique is applied to the cosine and sine components of the original signal which can be corrupted by higher harmonics. The algorithm showed a very high level of robustness as well as high measurement accuracy over a wide range of frequency changes and it can be used for frequncy tracking in power networks when the higher harmonics are presented in voltage or current signals. The theoretical basis and practical implementation of the technique are discribed. To demonstrate the performance of the developed algorithm, computer simulated, as well as real life data records, are processed.

Vision-Based Monitoring and Frequency analysis for Structural beams

Real-time assessment presents a significant challenge in Structural Health Monitoring (SHM), where the timely detection of structural defects and determination of in-service strength are crucial. In the developing field of SHM, the integration of diverse technologies is becoming increasingly essential, especially given the different challenges brought on by climate change and the complex nature of civil engineering structures. Traditional approaches, such as vibration analysis, acoustic emission, ultrasonic testing, and thermal imaging, despite their widespread use, face challenges in accurately pinpointing structural damage due to their reliance on a single technology. Meanwhile, dynamic response measurements of structures present a promising method for gaining internal insights into structures. Additionally, the advent of Unmanned Aerial Vehicles (UAVs) has enhanced the viability of vision-based techniques, such as digital image correlation (DIC), for surface assessment. This paper investigates damage in lightly reinforced concrete beams using a dual-technique approach that exploits the strengths of the DIC technique and frequency measurement technique, aiming to enhance the detection and analysis of damage in reinforced concrete beams. This integration signifies a step forward in SHM especially if integrated with other advancements leading to a better monitoring of structures.

An Equal Precision Programmed Cymometer Design Using Low-Power Technique

Based on equal precision frequency measurement and pulse counting technique, a multi-period synchronous frequency measurement method is proposed in this paper. A programmed cymometer is designed with a full frequency band with equal precision measurement and improved measurement accuracy. In addition to adopting a low-power gate-control clock technique, the strong stability of our design is also carried out through the filtering of interference signals. Finally, the designed circuit is implemented with FPGA. The experimental results show that the static power consumption of the programmable frequency meter testing platform designed after continuous operation for 100 h is only 0.56 W, and the input impedance is 1 M Ω/40 pF. At the same time, the errors of frequency, cycle measurement, duty cycle measurement, and time interval are within a reasonable range. In addition, the measurement accuracy requirements for various indicators can also be met at a maximum frequency of 100 MHz. Therefore, this work can provide a feasible design method for low-power consumption electrical systems that are easy to replicate.

Study of Ultra High Frequency Measurement Techniques for Online Monitoring of Partial Discharges in High Voltage Systems

Partial Discharge (PD) activity is a pre-cursor for insulation degradation which may eventually lead to catastrophic failure of the electrical equipment with severe social and economic consequences. It is therefore imperative that PD is detected at its early stages to permit repair or replacement, prior to total failure. The bulky non-planar construction of existing ultra-high frequency (UHF) sensors coupled with the lack of proper feeding techniques and the ultrawide signal bandwidth of PD signals which necessitates the use of digital storage oscilloscope have restricted field deployment of UHF technique for online PD detection. In this work, we present a compact ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.58 \boldsymbol {\lambda } $ </tex-math></inline-formula> ) wideband (0.5-3 GHz) dual arm Archimedean slot spiral with coplanar waveguide feed for PD detection, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\lambda } $ </tex-math></inline-formula> is the wavelength at center frequency. Numerical simulations of the antenna were compared with the measurements of the fabricated antenna. The fabricated wideband antenna was used to detect PD emissions from a mineral oil test cell connected to 10 kVA 50 Hz transformer. We also present different UHF signal measurement techniques ranging from PD pulse detection to reconstruction of the bandlimited PD signal in the digital domain for online structural health monitoring of high voltage systems. The proposed UHF PD measurement techniques are low cost compared to the conventional approach and indicate the feasibility of an embedded system for online PD monitoring using the fabricated UHF sensor.

Frequency and mode measurement techniques for megawatt-class gyrotrons

Abstract State-of-the-art vacuum electron tubes such as gyrotrons, deliver RF output powers up to more than 2 MW at frequencies up to 170 GHz. In terms of the very high power levels, a proper verification of the gyrotron components itself and measurements during gyrotron operation are vital to prevent possible fatal errors. Several basic RF measurement setups, which are used at IHM/KIT, are discussed. Currently, their upper frequency limit is 175 GHz. In terms of future gyrotron operation above 200 GHz, upgrades of the measurement setups for operation up to 260–330 GHz are prepared. The experimental devices discussed herein are a quasi-optical mode generator for the verification of the quasi-optical gyrotron output system, the window measurement test stand to verify the ceramic gyrotron output window and the frequency diagnostic system to measure the operating frequency and thereby the excited mode.

High Resolution Frequency Measurement Techniques for Relaxation Oscillator Based Capacitive Sensors

This work presents high resolution and adaptable frequency measurement techniques for relaxation oscillator based capacitive sensors. The techniques rely on extremely simple hardware such as a 1-bit coarse voltage quantizer to generate a 1-bit data stream and subsequently determine frequencies with resolutions greater than 20 bits from the 1-bit data stream. The proposed readouts are based on two types of 1-bit hardware approaches with Nyquist sampling in one approach and oversampling in the other. The first approach employs a Nyquist rate sampled 1-bit comparator while the second approach relies on an oversampled 1-bit quantizer based delta-sigma modulator (DSM) as a hardware to generate the bit stream. High resolution frequency is estimated from the 1-bit data stream using parametric, non-parametric and compressed sensing approaches. We provide detailed study and measurement results comparing the performance of the proposed techniques for test inputs with different frequencies and amplitudes and multiple signal shapes including sine, square, triangular and sawtooth. We show that the 1-bit comparator along with the CS approach provides the best performance across all input amplitude, frequency and shapes. A capacitive water level sensor was implemented in a PCB and embedded in a conventional square wave relaxation oscillator to verify the proposed technique. Measurement results show that incremental SNRs can be achieved only by increasing the 1-bit data stream length without any change in the hardware thereby demonstrating the adaptability of the technique based on an application requirement.

Adaptive versus Conventional Positive Position Feedback Controller to Suppress a Nonlinear System Vibrations

The nonlinear vibration control of a nonlinear dynamical system modeled as the well-known Duffing oscillators is investigated within this article. The conventional Positive Position Feedback (PPF) controller is proposed to mitigate the considered system nonlinear vibrations. The whole system mathematical model is analyzed by applying the multiple time scales perturbation method. The slow-flow modulation equations that govern the oscillation amplitudes of both the main system and controller are derived. The stability analysis is investigated based on Lyapunov’s first method. The effects of the different control parameters on both the main system and controller are explored. The obtained analytical and numerical results illustrated that the PPF controller can eliminate the main system nonlinear vibrations once the controller natural frequency is tuned to be the same value as the external excitation frequency, otherwise, the controller adds excessive vibrational energy to the main system rather than suppressing it. In addition, the PPF controller can destabilize the main system motion when excited by strong excitation force. Therefore, a modified version of the PPF controller named the Adaptive Positive Position Feedback (APPF) controller is proposed to overcome the main drawbacks of the conventional PPF controller. The idea is to track the external excitation frequency using an adaptive frequency measurement technique to update continuously the PPF controller natural frequency to become the same value of the excitation frequency. Based on this strategy, the system mathematical model is analyzed again by making the controller’s natural frequency equal to the external excitation frequency. The obtained analytical and numerical simulations showed that the adaptive positive position feedback controller can suppress the main system nonlinear vibration close to zero regardless of the excitation force amplitude and excitation frequency.

A Low-Complexity Time-Domain Method for a Fast and Accurate Measurement of Q-Factor and Resonant Frequency of RF and Microwave Resonators

A new time-domain technique for an accurate and fast measurement of the resonant frequency and Q-factor of resonators is presented. In this technique, the phase slope with respect to frequency of a resonator is characterized and used to specify its Q-factor and resonant frequency. To measure the phase slope, a slow-rate linear chirp signal is generated and passed through the resonator under test. The output signal is amplified and subsequently divided into two equal parts which are delayed by different amounts. Due to the linear time-frequency relationship of the chirp signal, the instantaneous frequencies of the two delayed signals are slightly different at any given time, and their phase difference can determine the resonator's phase slope. Detailed analysis of the proposed approach is presented and its accuracy is verified through simulations and measurements. Based on the measured results, the proposed approach characterizes the resonant frequency and Q-factor by less than 0.6% and 4% error, respectively.

Frequency Shifts Estimation for Sensors Based on Optoelectronic Oscillators

Optoelectronic oscillators (OEO) based sensors generate low-phase-noise signals, whose frequency is in the order of GHz. These sensors are highly sensitive to parameters like strain, transverse load or temperature. Particularly, an OEO transforms a wavelength change into a frequency shift in the order of MHz. This creates a particular challenge for measuring instruments used in OEO, where novel mathematical methods for advanced processing of their signals is required. The principle of rational approximations is a frequency measurement technique based on number theory, with the fundamental property of measurement time dependent on the frequency value of input signals. This means that if the frequency of input signals increases, less time for measuring is required. This is quite useful for time-frequency measurement systems, where if more accuracy is needed, more time is required for measuring. This paper shows how the principle of rational approximations can be used in OEO based sensors, this allows to estimate the frequency shifts in a bandwidth from 6 to 600 MHz, with a maximum uncertainty of 2.5 MHz. Such an accuracy is achieved in a time as short as 0.2 μs.

Radio Frequency Studies of Soot Loading and Ammonia Storage on a Diesel Particulate Filter with a SCR Catalyst Coating

In the exhaust system of some diesel vehicles, the diesel particulate filter (DPF) is loaded with a selective catalyst reduction (SCR) wash coat. This combined catalyst, referred to as a SDPF, serves two functions by trapping soot and by reducing NOx emissions. The latter is accomplished via reactions of NOx with NH3 stored on the SCR wash coat. The NH3 is dosed, as urea, upstream of the SDPF.

A de‐embedding method with matrix rectification and influences of residual errors on model parameters extraction of InP HEMTs

As the cutoff frequency of InP HEMTs enters the terahertz band, high frequency measurement and modeling techniques in hundreds of gigahertz become urgent needs for further millimeter monolithic integrated circuits design. We proposed a new de-embedding method linking device measurements and modeling based on full EM simulation data acquired from HFSS and advanced design system (ADS). The simulation results for passive dummy structures are well consistent with experiments, and the de-embedding method is proved very effective for a resistive passive device with high distributed embedding surroundings in frequency range below 40 GHz. Based on these experimental facts, the EM simulations were extended up to 300 GHz and corresponding de-embedding deviation was further investigated. Results show that the proposed de-embedding method has very high accuracy in the whole frequency region with a maximum S-parameters deviation of only 2.58%. However, further analysis proves that the small residual errors still significantly affect extracted small signal model parameters of InP HEMTs especially for transit time τ. Thus, further improvements on de-embedding accuracy or careful considerations of more error functions in modeling process are necessary for obtaining physically meaningful model parameters.

Determination of the Required Power Response of Inverters to Provide Fast Frequency Support in Power Systems with Low Synchronous Inertia

The decommissioning of conventional power plants and the installation of inverter-based renewable energy technologies decrease the overall power system inertia, increasing the rate of change of frequency of a system (RoCoF). These expected high values of RoCoF shorten the time response needed before load shedding or generation curtailment takes place. In a future scenario where renewables are predominant in power systems, the ability of synchronous machines to meet such conditions is uncertain in terms of capacity and time response. The implementation of fast power reserve and synthetic inertia from inverter-based sources was assessed through the simulation of two scenarios with different grid sizes and primary reserve responses. As main results it was obtained that the full activation time for a fast power reserve with penetration above 80% of inverter-based generation would need to be 100 ms or less for imbalances up to 40%, regardless of the synchronous response and grid size, meaning that the current frequency measurement techniques and the time for fast power reserve deployment would not ensure system stability under high unbalanced conditions. At less-unbalanced conditions, the grid in the European scale was found to become critical with imbalances starting at 3% and a non-synchronous share of 60%.

Recycled FPGA Detection Using Exhaustive LUT Path Delay Characterization and Voltage Scaling

Field-programmable gate arrays (FPGAs) have been extensively used because of their lower nonrecurring engineering and design costs, instant availability and reduced visibility of failure, high performance, and power benefits. Reports indicate that previously used or recycled FPGAs are infiltrating the electronics’ supply chain and making the security and reliability of the critical systems and networks vulnerable. Current recycled integrated circuit (IC) detection procedures include parametric, functional, and burn-in tests that require golden or reference data. Besides, they are time consuming, require expensive equipment, and do not focus on FPGAs. In this article, we propose two recycled FPGA detection methods based on supervised and unsupervised machine learning algorithms. We develop a sophisticated ring oscillator (RO) design to exploit the degradation of lookup tables (LUTs) and use them in the proposed methods. In the supervised method, a one-class classifier is trained with RO frequencies, kurtosis, and skewness data obtained from unused FPGAs, which differentiates unused and aged FPGAs. The unsupervised method uses $k$ -means clustering and Silhouette value analysis to detect suspect recycled components with very little (if any) golden information. In addition, we introduce a voltage scaling-assisted RO frequency measurement technique that improves the classification. The proposed methods are examined for Spartan-3A and Spartan-6 FPGAs, and the result shows that both methods are effective in detecting recycled FPGAs, which experience accelerated aging for at least 12 h equivalent to 70 days in real-time age.

ON POTENTIAL OF USING WIND TURBINES WITH COAXIAL WIND ROTORS FOR AUTONOMOUS POWER SUPPLY

The paper presents the experimental research results for the horizontal-axis wind turbine with coaxial wind rotors. It is assumed that such coaxial layout of the wind turbine can be used for designing of the wind energy systems with relatively low capacity and limited location area since the coaxial systems have advantages in overall dimensions and maximum using of the swept area. Possibility of coaxial horizontal-axis wind turbines usage is determined by positive or negative effect of turbines on each other. Literature review shows that closely spaced wind turbines can generally improve flow characteristics under certain conditions and consequently increase wind energy system efficiency. We have carried out the experiments in T-5 wind tunnel with two coaxial model two-bladed wind turbines which rotate in opposite directions. The generator of the first turbine and first turbine itself are located on the same shaft in the test section of wind tunnel. The second generator is in a lower compartment of the experimental setup and is connected by the transmission. We have measured the dynamic, energy and frequency characteristics of wind energy systems based on created experimental setup. A Pitot tube and automatic metering devises have measured the dynamic parameters and energy performance respectively. A frequency counter has saved all of the data obtained with the laser frequency measurement technique. The experiment has some specific technical features so the data received need to be corrected. The coaxial wind turbine power has decreased in comparison to isolated wind turbine at low wind speed. The return flows reinforce turbulence so wind speed falls. If wind speed increases, the impact of the return flows decreases, the coaxial wind turbine capacity significantly grows and exceeds isolated turbine capacity. The possibility of using wind turbines with coaxial wind rotors for autonomous power supply is shown. Such wind turbines are perspective and require more detailed analysis.

In-situ frequency calibration of frequency modulated continuous wave reflectometry.

Frequency modulated continuous wave reflectometers have been used to measure the plasma density profiles of the KSTAR tokamak. Three reflectometers are operating in an extraordinary polarization mode in the frequency range of Q band (33-50 GHz), V band (50-75 GHz), and W band (75-110 GHz). Each full frequency band is linearly swept in 20 μs. The accuracy of the density profile measurement is dependent on how precisely the frequency is calibrated. Two new frequency measurement techniques are developed to in situ calibrate the instantaneous frequency during the sweep time of 20 μs. First the intermediate frequency (IF) of the receiver is analyzed based on wavelet transform as applying a fixed frequency signal from a synthesizer to the local oscillator (LO) port. The frequency of the transmitted microwave is simply obtained by adding or subtracting the measured IF to the given LO frequency. Once the group delay of the whole system is known, the frequency can be calibrated by measuring the IF. By measuring the reflectometer output without plasma with delay lines of different lengths and subtracting them, the frequency can be calibrated by eliminating the unknown group delay of the system except the known group delay of the delay line. These two techniques are described in detail, and the calibrated frequencies conducted by the two techniques are compared.

Photonic Microwave Frequency Measurement Based on Frequency-Configurable Pilot Tones

A photonic technique for microwave frequency measurement with flexible range and high resolution is proposed based on frequency-configurable pilot tones. The method extracts the remote unknown microwave frequency by measuring electrical power at two known pilot frequencies, avoiding dual-channel photodetection and broadband microwave power measurement over the whole interested frequency range. Moreover, it enables flexible measurement range by configuring two pilot frequencies. A proof-of-concept experiment is successfully demonstrated with the frequency range of 6–18.9 GHz and the resolution of 0.1 GHz.

A Bayesian Estimation Model for Transient Engine Exhaust Characterization Using Fourier Transform Infrared Spectroscopy

Comprehensive emissions models extensively use engine exhaust data from vehicle experiments to represent the relationship between fuel composition and pollutants. However, the predicted emissions from these models often neglect the effects of transients and speed-load history. Fourier transform infrared (FTIR) spectroscopy is a high frequency measurement technique capable of comprehensive speciation. However, due to long residence times of exhaust within a FTIR spectrometer gas cell, FTIR measurements are contaminated by the effects of historical emissions, precluding the attainment of time-resolved engine exhaust data. This work presents a Bayesian estimation model for processing FTIR measurements to obtain accurate estimations of instantaneous engine exhaust composition. The Bayesian model utilizes a simple model of the mixing dynamics of the gas cell and measurement noise statistics to estimate the composition of exhaust entering the FTIR gas cell during a measurement period. To validate the estimation...

Note: A miniature oscillating microbalance for sampling ice and volcanic ash from a small airborne platform.

A lightweight and low power oscillating microbalance for in situ sampling of atmospheric ice and volcanic ash is described for airborne platforms. Using a freely exposed collecting wire fixed at only one end to a piezo transducer, the instrument collects airborne materials. Accumulated mass is determined from the change in natural frequency of the wire. The piezo transducer is used in a dual mode to both drive and detect the oscillation. Three independent frequency measurement techniques are implemented with an on-board microcontroller: a frequency sweep, a Fourier spectral method, and a phase-locked loop. These showed agreement to ±0.3 Hz for a 0.5 mm diameter collecting wire of 120 mm long, flown to 19 km altitude on a weather balloon. The instrument is well suited to disposable use with meteorological radiosondes, to provide high resolution vertical profiles of mass concentration.

Microwave frequency measurement based on optical phase modulation and stimulated Brillouin scattering

A photonic technique for microwave frequency measurement based on stimulated Brillouin scattering (SBS) with low measurement error and large measurement range is demonstrated. In the scheme, an optical phase modulator is employed and the intensity balance between the two sidebands of the phase-modulated signal is broken by use of SBS in a fibre. The frequency measurement is achieved by detecting the existence of a microwave signal after photoelectric detection of the phase modulated signal. The measurement error is experimentally shown to be 50 MHz in a narrow measuring range of ∼1 GHz and 100 MHz in a wide range of 20 GHz.

Broadband instantaneous frequency measurement based on stimulated Brillouin scattering.

A technique for the instantaneous frequency measurement (IFM) of broadband signals is proposed based on stimulated Brillouin scattering (SBS) in a single-mode optical fiber. The instantaneous frequency and amplitude information is obtained by the narrowband filtering of the acoustic-optic interaction in the SBS process. Through sideband management of the optical-modulation, the IFM bandwidth can be far beyond the Brillouin frequency shift (i.e. ~11 GHz in 1550 nm). Proof-of-concept experiments for both the linearly frequency modulated pulse and frequency Costas coded pulse are carried out to verify the feasibility of the IFM.