Frequency Shift Research Articles

Vibration analysis of a partially submerged structure using the DIC technique

The continuous expansion of offshore wind turbine sites has been garnering increasing attention, particularly in countries where available land is limited. Nevertheless, efficiently allocating resources for the maintenance and repair of offshore wind turbines presents a formidable challenge. This challenge is compounded by the complex and often unpredictable weather conditions, as well as various business-related issues specific to the offshore environment. To tackle these challenges, one effective solution is to implement vibration analysis through the use of digital image correlation (DIC) methods. This approach has a well-established theoretic background dating back to approximately 2008 and has demonstrated its effectiveness in the realm of structural health monitoring for large structures like bridges and towers. Relevant information on the upper structure of the wind turbines has been obtained using numerical models in our previous work. Changes in the structural feature frequencies of wind turbines are the primary focus in vibration analysis. However, changes in feature frequencies can occur for various reasons, and relying solely on frequency shifts can make it challenging to pinpoint the precise areas of damage within wind turbine structures, especially without the benefit of long-term observations. In this study, the DIC method is employed on scaled cylindrical models to gain insights into the frequency variations stemming from the erosion of non-cohesive soils beneath offshore wind turbine foundations. Changes in modal curvature within the upper structure of the wind turbine will also be analyzed. This additional investigation will enable a clear differentiation between defects in the upper structure and frequency shifts resulting from erosion or problems with the underwater foundation.

Low-power body-coupled transceiver for miniaturized body area networks

As wearable devices continue to proliferate, seamlessly integrating them into wireless body-area networks (WBANs) becomes increasingly crucial. Body-coupled communication (BCC) emerges as a promising WBAN technology, utilizing the human body itself as a transmission channel. This paper presents a novel BCC transceiver designed for efficiency and miniaturization. The proposed transceiver prioritizes reliable data transmission with a convolutional encoder. It leverages a simple direct digital synthesizer (DDS) for frequency shift keying (FSK) modulation, minimizing chip area. At the receiver, a Viterbi decoder (VD) ensures accurate data recovery. This design shines in its resource efficiency. It occupies less than 1% of an Artix-7 FPGA, operates at 268.77 MHz with a mere 111 mW power consumption, and achieves a remarkable data rate of 13.78 Mbps. This translates to a hardware efficiency of 44.46 Kbps/slice, surpassing existing transceivers. Moreover, the BCC transceiver exhibits a stellar bit error rate (BER) of over 10⁻⁷ under realistic body channel conditions. Overall, this work presents a highly efficient BCC transceiver with significant improvements in chip area, power consumption, and data rate compared to existing designs. This paves the way for practical and miniaturized WBAN solutions for future wearable applications.

Analyzing coherent and incoherent optical susceptibilities in four-wave mixing: stochasticity, symmetry, and intramolecular coupling

The nonlinear optical susceptibilities are analyzed in their optical propagation length considering the incoherent-coherent contributions with the dependence on the relaxation times. In addition, some symmetry properties of the Four-Wave mixing (FWM) signal concerning the frequency detuning exchange are used in the study, without restricting ourselves to the maxima of population oscillations. We analyze the behaviors of these optical responses in a vibronic coupling scheme using a molecule model consisting of two coupled harmonic curves of electronic energies with displaced minima in position and nuclear energies. The solvent effect in our model is treated through the natural Bohr frequency shift to a time-dependent function, with explicit manifestations in its comparison as if the upper state were broadened. Our results for both FWM signal propagation and nonlinear optical susceptibilities are sensitive to the intramolecular coupling parameters, solvent stochasticity, and perturbation order for the treatment of the weak probe beam. The consideration of a second-order probe beam in FWM would not represent a significant contribution to the predicted results, since its percentage contribution is negligible within the model development framework; however, this contribution becomes important when increasing the ratio between longitudinal and transverse relaxation times.

Experimental Study on the Sloshing of a Rectangular Tank under Pitch Excitations

Fluid sloshing within containers subjected to external motion is a crucial yet intricate phenomenon with implications across various industries. This study investigates sloshing in a rectangular liquid tank through a series of experiments examining pitch excitations with diverse excitation frequencies and amplitudes across different liquid carrying rates. By analyzing pressure data and imagery of the free liquid surface, statistical trends in peak pressure at measurement points within the tank are identified, revealing the nonlinear behavior of the fluid. Spectral analysis generates power spectrum curves that delineate frequency components and energy distribution within the sloshing dynamics. Key findings include the identification of resonance-induced violent sloshing at a 20% liquid-carrying rate and a resonant frequency shift at a 70% liquid-carrying rate due to nonlinearity, displaying a “soft spring” characteristic in the frequency response. The free liquid surface exhibits four distinct waveforms depending on frequency. Notably, at a 70% liquid-carrying rate and resonant frequency excitation, three-dimensional vortex waves emerge, highlighting a complex three-dimensional effect within the tank. The power spectrum shows that the dominant response frequency aligns with the excitation frequency and its multiples. This investigation enhances our understanding of the intricate nature of sloshing in various liquid-carrying conditions, offering insights valuable for diverse industrial applications.

Strong coupling-induced frequency shifts of highly detuned photonic modes in multimode cavities.

Strong coupling between light and molecules is a fascinating topic exploring the implications of the hybridization of photonic and molecular states. For example, many recent experiments have explored the possibility that strong coupling of photonic and vibrational modes might modify chemical reaction rates. In these experiments, reactants are introduced into a planar cavity, and the vibrational mode of a chemical bond strongly couples to one of the many photonic modes supported by the cavity. Some experiments quantify reaction rates by tracking the spectral shift of higher-order cavity modes that are highly detuned from the vibrational mode of the reactant. Here, we show that the spectral position of these cavity modes, even though they are highly detuned, can still be influenced by strong coupling. We highlight the need to consider this strong coupling-induced frequency shift of cavity modes if one is to avoid underestimating cavity-induced reaction rate changes. We anticipate that our work will assist in the re-analysis of several high-profile results and has implications for the design of future strong coupling experiments.

Parameter Extraction of Accelerated Moving Targets under Non-Quasi-Axial Incidence Conditions Based on Vortex Electromagnetic Wave Radar

Vortex electromagnetic wave radar carrying orbital angular momentum can compensate for the deficiency of planar electromagnetic wave radar in detecting motion parameters perpendicular to the direction of electromagnetic wave propagation, thus providing more information for target recognition, which has become a hot research field in recent years. However, existing research makes it difficult to obtain the acceleration and rotation centers of targets under non-quasi-axial incidence conditions of vortex electromagnetic waves. Based on this, this article proposes a variable speed motion target parameter extraction method that combines single element and total element echoes. This method can achieve three-dimensional information extraction of radar targets based on a uniform circular array (UCA). Firstly, we establish a non-quasi-axis detection echo model for variable-speed moving targets and extract echoes from different array elements. Then, a single element echo is used to extract the target’s range slow time profile and obtain the target’s rotation center z coordinate. We further utilize the target linear, angular Doppler frequency shift extremum, and median information to extract parameters such as target acceleration, tilt angle, rotation radius, and rotation center x and y coordinates. We analyzed the impact of different signal-to-noise ratios and motion states on parameter extraction. The simulation results have verified the effectiveness of the proposed algorithm.

Mathematical modeling of water waves interaction with trapezoidal-shaped breakwater in the presence of current

In this study, an investigation is conducted into the interaction between water waves and a bottom-standing, thick, porous, and trapezoidal-shaped breakwater under the influence of an uniform current. This investigation has been conducted using several effect factors, such as the friction coefficient and porosity of the breakwater and ocean currents, to comprehend various phenomena related to wave energy dissipation, wave load, wave transmission, and wave reflection, etc. The boundary element method-based numerical technique is used to solve the associated boundary value problem. The modeling of the porosity of the breakwater structure is done using the Sollit and cross model [CK Sollitt, RH Cross. Wave transmission through permeable breakwaters. Coast Eng. 1972; 1972: 1827–1846.] of water wave passes through thick porous structures. In the presence of the following and opposite currents, the ‘Doppler-shift’ effect is observed in wave transformation characteristics due to the shift in wave frequencies. The wave-blocking phenomenon in open water and porous regions has been demonstrated. The results show that the following and opposing currents shift the frequencies for which optima in wave reflection occurs.

A non-invasive blood glucose detection using a slotted microstrip antenna sensor

A novel highly sensitive and compact slotted microstrip antenna sensor consisting of slots with defected ground structure is designed. The substrate used in the design of antenna is FR-4 of concise dimensions 30 × 30 × 1.6 mm3 and the developed antenna resonates at 3 GHz. The human finger consisting of several layers namely bone, blood, fat and skin is modelled in the electromagnetic simulation (Computer Simulation Technology) environment resulting in finger phantom. The finger phantom is situated at different locations on proposed antenna for evaluating the concentrations of glucose from 0 to 1000 (mg/dL) and the corresponding shift in frequencies are estimated. For detection of glucose concentration in human blood, the obtained frequency shifts in the proposed work are used. In this proposed work, at the top side of proposed antenna, the finger phantom is situated, an uttermost shift in frequency of 48 MHz, sensitivity of 48 KHz/(mg/dL) and a least possible shift in frequency of 24 MHz, sensitivity of 24 KHz/(mg/dL) are obtained.

P.051 Parkinson’s disease tremor can show entrainment and distractibility with tapping test

Background: Electrophysiological tests such as the tapping test are used to distinguish functional and organic tremors, in which patients with functional tremor commonly show entrainment and amplitude reduction (>50% decrease relative to baseline) of contralateral tremor during tapping. While these features are suggested to be specific to functional tremor, the tapping test in Parkinson’s disease (PD) tremor has not been tested. Methods: We evaluated 18 PD patients (2F, age 64.17±7.30 [mean±SD] years) with rest and postural tremors using surface electromyography and triaxial accelerometry. Patients were recorded while tapping at 1, 3 and 5 Hz with the contralateral arm at rest or outstretched. Tremor amplitude and frequency were calculated using power spectrum analysis from accelerometer recordings. Results: Reduction of rest tremor amplitude was observed in 3/18 patients during 1 and 3 Hz tapping. Reduction was seen in 3/16 and 1/16 patients with postural tremors at 1 and 3 Hz tapping, respectively. Frequency shifts (>1.5 Hz) were observed in 3/18 rest tremors and 6/16 postural tremors. Seven patients exhibited rest and/or postural tremor entrainment during 3 or 5 Hz tapping. Conclusions: Distractibility and entrainment can be found in PD tremor. The tapping test may not reliably distinguish between PD tremor and functional tremor.

Frequency multiplexed dual-pulse fiber-optic Φ-OTDR for a fading-free distributed fiber sound sensor

Distributed fiber-optic sensor utilizing optical interference signal detection of the Rayleigh backscattering (RBS) light along the fiber under test (FUT) has greatly progressed over the past 20 years. It can now realize real-time sound signal recovery along the FUT with a good fidelity and high sensitivity. However, the performance of the practical distributed fiber-optic sound sensor is still limited by the fading problem, as invalid spatial channels at unknown positions arise due to the low signal intensity at these positions and the resulting near-zero signal-to-noise ratio (SNR). In this paper, we propose a novel, to the best of our knowledge, fading-free fiber sensor structure by incorporating an acousto-optic frequency shift (AOFS) loop into the light source in a dual-pulse phase optical time domain reflectometry (Φ-OTDR). As a result of stable frequency shifting and feedback within the loop, the loop source can output a high-repetition-rate narrow pulse train consisting of multiple separated frequencies. This pulse train is further shaped into two pulse bursts by an acousto-optic modulator (AOM) and an in-balanced fiber-optic Mach–Zehnder interferometer (MZI). The pulse bursts are then sent into the sensing fiber, while the RBS light is detected using an Avalanche photodiode after an erbium-doped fiber amplifier. The experimental results show that the proposed structure is capable of vibration signal recovery with a good SNR all along the FUT. The fading-free performance is evaluated under different AOFS loop gains, showing significant potential in practical fiber sensor network applications.

Rotating target detection model under arbitrary incidence of the vortex beam based on optical RDE

Abstract The optical rotational Doppler effect (RDE) related to orbital angular momentum has attracted extensive attention in rotating targets detection. In this paper, we present a novel rotating target detection model based on optical RDE, where the vortex beam can be incident on the rotating target with an arbitrary case. Based on the proposed detection model, we investigated the mechanism of rotation Doppler shift and deduced the generalized formula of the Doppler frequency shift under arbitrary incidence of the vortex beam by phase modulation method. Subsequently, the model is studied under different incidence conditions, and the variation of Doppler frequency shift with different incident parameters is analyzed combining with the deduced formulas. Meanwhile, we also give the detection methods to for motion parameter estimations of the rotating target. Theoretical and simulated results verify the effectiveness of the proposed model, and more detailed motion parameters can be obtained based on RDE. This theoretical model enables us to better understand the generation of the rotational Doppler frequency and may be useful for the application of remote sensing of a rotating target.

Harmonic impedance optimization scheme for multi‐resonance systems to suppress resonance

AbstractHarmonic resonance is caused by harmonic source matching resonance frequency and presents the characteristics of decentralization and whole network in modern grids. The current resonance suppression methods mainly focus on reducing the harmonic source, and are suitable for single‐site and small‐scale grids. This paper presents a new method for suppressing parallel resonance at system level. The holistic harmonic resonance is suppressed by reducing the harmonic impedance. In addition, new resonances are prevented by weakening the coupling between resonance and non‐resonance frequencies. The resonance modal analysis and resonance frequency shift (RFS) are employed to optimize harmonic impedance. Simulation results indicate that the capacitance parameter has higher sensitivity and is theoretically more suitable for RFS. Considering the accuracy of modal frequency sensitivity, a variable‐limit genetic algorithm for iteration is proposed. The validity of the proposed method was verified using an IEEE 14‐bus test network.

Extrinsic magnetised plasma kolakoski quasicrystal

This manuscript explores the microwave transmission properties of multilayer structures that employ the Kolakoski sequence. The structures, composed of alternating layers of extrinsic magnetized plasma, are analysed under normal incidence conditions, with a focus on various parameters such as frequency, external magnetic field intensity, and electron density. At frequencies higher than the plasma frequency, consistent bandgaps are observed across different layer counts, indicating strong transmission characteristics. Conversely, at frequencies lower than the plasma frequency, the thickness of the bandgap fluctuates due to the inherent nature of the Kolakoski sequence, suggesting potential applications in multi-channel filtering. The study demonstrates the ability to adjust the significant bandgap above the plasma frequency through manipulation of the external magnetic field. By increasing the strength of the magnetic field, the bandgap undergoes a shift and narrows, highlighting the tunability of the transmission properties. On the other hand, increasing the number of layers widens the bandgap below the plasma frequency, resulting in the emergence of narrow transmission peaks. Moreover, the influence of electron density on the transmission spectra is examined, showing that higher electron density leads to wider bandgaps, although with minimal frequency shifts. The intricate interplay between structural parameters, external factors, and transmission characteristics provides valuable insights for optimizing multi-channel microwave reflectors and related devices.

Stiffness calibration of qPlus sensors at low temperature through thermal noise measurements

Non-contact atomic force microscopy (nc-AFM) offers a unique experimental framework for topographical imaging of surfaces with atomic and/or sub-molecular resolution. The technique also permits to perform frequency shift spectroscopy to quantitatively evaluate the tip–sample interaction forces and potentials above individual atoms or molecules. The stiffness of the probe, k, is then required to perform the frequency shift-to-force conversion. However, this quantity is generally known with little precision. An accurate stiffness calibration is therefore mandatory if accurate force measurements are targeted. In nc-AFM, the probe may either be a silicon cantilever, a quartz tuning fork (QTF), or a length extensional resonator (LER). When used in ultrahigh vacuum (UHV) and at low temperature, the technique mostly employs QTFs, based on the so-called qPlus design, which actually covers different types of sensors in terms of size and design of the electrodes. They all have in common a QTF featuring a metallic tip glued at the free end of one of its prongs. In this study, we report the stiffness calibration of a particular type of qPlus sensor in UHV and at 9.8 K by means of thermal noise measurements. The stiffness calibration of such high-k sensors, featuring high quality factors (Q) as well, requires to master both the acquisition parameters and the data post-processing. Our approach relies both on numerical simulations and experimental results. A thorough analysis of the thermal noise power spectral density of the qPlus fluctuations leads to an estimated stiffness of the first flexural eigenmode of ≃2000 N/m, with a maximum uncertainty of 10%, whereas the static stiffness of the sensor without tip is expected to be ≃3300 N/m. The former value must not be considered as being representative of a generic value for any qPlus, as our study stresses the influence of the tip on the estimated stiffness and points towards the need for the individual calibration of these probes. Although the framework focuses on a particular kind of sensor, it may be adapted to any high-k, high-Q nc-AFM probe used under similar conditions, such as silicon cantilevers and LERs.

Heuristic approach to trajectory correlation functions in bounded regions with Lambert scattering walls

The behavior of spins undergoing Larmor precession in the presence of time varying fields is of interest to many research fields. The frequency shifts and relaxation resulting from these fields are related to their power spectrum, determined from the Fourier Transform of the auto-correlation functions of the time varying field. Using the method of images C. M. Swank, A. K. Petukhov, and R. Golub (2012 and 2016) calculated the position-position auto-correlation function for particles moving in a rectangular cell with specular scattering walls. In this work we present a heuristic model that applies the method of images to the case of Lambert scattering walls. The results of this model are compared to simulation and show remarkably good agreement from the ballistic to diffusive regime of gas collisions, for both square and general rectangular cells.

Strain-invariant stretchable radio-frequency electronics.

Wireless modules that provide telecommunications and power-harvesting capabilities enabled by radio-frequency (RF) electronics are vital components of skin-interfaced stretchable electronics1-7. However, recent studies on stretchable RF components have demonstrated that substantial changes in electrical properties, such as a shift in the antenna resonance frequency, occur even under relatively low elastic strains8-15. Such changes lead directly to greatly reduced wireless signal strength or power-transfer efficiency in stretchable systems, particularly in physically dynamic environments such as the surface of the skin. Here we present strain-invariant stretchable RF electronics capable of completely maintaining the original RF properties under various elastic strains using a 'dielectro-elastic' material as the substrate. Dielectro-elastic materials have physically tunable dielectric properties that effectively avert frequency shifts arising in interfacing RF electronics. Compared with conventional stretchable substrate materials, our material has superior electrical, mechanical and thermal properties that are suitable for high-performance stretchable RF electronics. In this paper, we describe the materials, fabrication and design strategies that serve as the foundation for enabling the strain-invariant behaviour of key RF components based on experimental and computational studies. Finally, we present a set of skin-interfaced wireless healthcare monitors based on strain-invariant stretchable RF electronics with a wireless operational distance of up to 30 m under strain.

Simulation of a Radio-Frequency Wave Based Bacterial Biofilm Detection Method in Dairy Processing Facilities

This paper describes the principles behind the radio-frequency (RF) sensing of bacterial biofilms in pipes and heat exchangers in a dairy processing plant using an electromagnetic simulation. Biofilm formation in dairy processing plants is a common issue where the absence of timely detection and subsequent cleaning can cause serious illness. Biofilms are known for causing health issues and cleaning requires a large volume of water and harsh chemicals. In this work, milk transportation pipes are considered circular waveguides, and pasteurizers/heat exchangers are considered resonant cavities. Simulations were carried out using the CST studio suite high-frequency solver to determine the effectiveness of the real-time RF sensing. The respective dielectric constants and loss tangents were applied to milk and biofilm. In our simulation, it was observed that a 1 µm thick layer of biofilm in a milk-filled pipe shifted the reflection coefficient of a 10.16 cm diameter stainless steel circular waveguide from 0.229 GHz to 0.19 GHz. Further sensitivity analysis revealed a shift in frequency from 0.8 GHz to 1.2 GHz for a film thickness of 5 µm to 10 µm with the highest wave reflection (S11) peak of ≈−120 dB for a 6 µm thick biofilm. A dielectric patch antenna to launch the waves into the waveguide through a dielectric window was also designed and simulated. Simulation using the antenna demonstrated a similar S11 response, where a shift in reflection coefficient from 0.229 GHz to 0.19 GHz was observed for a 1 µm thick biofilm. For the case of the resonant cavity, the same antenna approach was used to excite the modes in a 0.751 m × 0.321 m × 170 m rectangular cavity with heat exchange fins and filled with milk and biofilm. The simulated resonance frequency shifted from 1.52 GHz to 1.54 GHz, for a film thickness varying from 1 µm to 10 µm. This result demonstrated the sensitivity of the microwave detection method. Overall, these results suggest that microwave sensing has promise in the rapid, non-invasive, and real-time detection of biofilm formation in dairy processing plants.

Daily Living Activity Recognition with Frequency-Shift WiFi Backscatter Tags

To provide diverse in-home services like elderly care, versatile activity recognition technology is essential. Radio-based methods, including WiFi CSI, RFID, and backscatter communication, are preferred due to their minimal privacy intrusion, reduced physical burden, and low maintenance costs. However, these methods face challenges, including environmental dependence, proximity limitations between the device and the user, and untested accuracy amidst various radio obstacles such as furniture, appliances, walls, and other radio waves. In this paper, we propose a frequency-shift backscatter tag-based in-home activity recognition method and test its feasibility in a near-real residential setting. Consisting of simple components such as antennas and switches, these tags facilitate ultra-low power consumption and demonstrate robustness against environmental noise because a context corresponding to a tag can be obtained by only observing frequency shifts. We implemented a sensing system consisting of SD-WiFi, a software-defined WiFi AP, and physical switches on backscatter tags tailored for detecting the movements of daily objects. Our experiments demonstrate that frequency shifts by tags can be detected within a 2 m range with 72% accuracy under the line of sight (LoS) conditions and achieve a 96.0% accuracy (F-score) in recognizing seven typical daily living activities with an appropriate receiver/transmitter layout. Furthermore, in an additional experiment, we confirmed that increasing the number of overlaying packets enables frequency shift-detection even without LoS at distances of 3–5 m.

Bidirectional large strain monitoring using a novel graphene film-based patch antenna sensor

Abstract This study proposes a rectangular microstrip patch antenna sensor based on a high-conductivity graphene film for bidirectional strain detection in structural health monitoring (SHM). By using a highly conductive graphene film instead of traditional metal foil to produce a patch antenna, the antenna possesses a higher flexibility and a larger sensing range. The mechanical, electromagnetic, and radiative properties were investigated. The strain sensing principle based on the resonant frequency offset of the graphene film antenna was proposed. The relationships between the resonant frequency shift and structural strain were quantitatively explored through theoretical deductions, finite element simulations, and experiments. According to the experimental results, the shift in the resonant frequency was linearly related to the lateral and longitudinal strains. The sensitivity coefficients for the lateral and longitudinal strains were 2.2037 kHz/με and 3.6198 kHz/με, respectively. The thermal strain can be distinguished based on the linear resonant frequency-temperature relationship. The results demonstrated the advantages and prospects of the proposed novel patch antenna for SHM.

Optimization of Mach-Zehnder interferometer of high-spectral-resolution lidar for large-scale wind measurement

The optimization design of a quadri-channel Mach–Zehnder interferometer (QMZI) of the high-spectral-resolution lidar is presented for the large-scale wind measurement. The optimized QMZI can discriminate the Doppler frequency shift generated by atmospheric wind from aerosol Mie scattering echo signals and molecular Rayleigh scattering echo signals, and then the wind information can be retrieved. The optimal optical path differences (OPDs) of QMZI are determined by theoretical and simulation analysis. The wind measurement simulation experiments prove that the designed QMZI can measure the large-scale wind with an accuracy of meter level.