Peak Resonance Frequency Research Articles

Modeling and performance analysis of single fiber ring incorporated with fiber Bragg grating

The mathematical model of an optical ring resonator (RR) configuration using a single directional optical coupler (DOC) with a uniform fiber Bragg grating (FBG) incorporated and an RR configuration using two DOCs with an FBG incorporated is developed in the Z-domain. The developed mathematical model is used for the evaluation of transmission response. Spectral characteristics in terms of peak transmittance, resonant frequency, and free spectral range are determined for a single fiber ring configuration using two DOCs with an FBG incorporated. The results are found to be in very close agreement with measured values. The transmission characteristic of the single waveguide structure comprising a ring of length 2 mm enclosing a Bragg grating is analyzed. By properly optimizing the grating reflectivity and power coupling ratios of the coupler, a narrow full width at half maximum of 4.72 GHz that is around 78 times sharper than the normal FBG resonance is obtained. Further narrowing of the spectral width is achieved by increasing the RR length. The grating lengths are chosen judiciously to minimize the side peaks. The group delay and dispersion characteristics are addressed.

Mechano-Vibrational Spectroscopy of Tissues and Materials Using Vibrational Optical Coherence Tomography: A New Non-Invasive and Non-Destructive Technique

Elastic moduli of tissues and synthetic polymeric materials are important design properties needed to develop new implants. In this paper we report the use of vibrational optical coherence tomography (VOCT) to measure the resonant frequency and calculate the modulus of tissues and synthetic polymers non-invasively and non-destructively in vitro and in vivo. Values of tissue and polymer moduli were obtained by applying an audible sinusoidal sound wave to the surface of each specimen. The sound wave travels to the interior of the material and is reflected back to the surface from underlying layers. A spectrum of resonant frequencies and moduli are then obtained. By analyzing the frequencies at which the maximum displacements are observed the resonant frequencies are determined of the material components and the moduli can then be calculated from calibration equations. The characteristic spectrum of resonant frequencies measured is a finger print by which the composition of the underlying tissue components can be determined using VOCT. The resonant frequencies of cells and tissues range from about 40 Hz for fat to about 990 Hz for lamellar bone. The modulus for these tissues ranges from about 1 MPa (cells) to that for extracellular matrix components that range from 2 to 173 MPa (tissue macromolecular components). Measurements reported on synthetic polymers indicate that the resonant frequency ranges from 80 Hz (silicone rubber) to 2800 Hz (acrylonitrile butadiene styrene) and values of the modulus are found to be between 2 MPa and 2120 MPa, respectively. The resonant frequency and modulus are shown to decrease as a result of fatigue in Viton rubber. It is concluded that the width of the resonant frequency peak is related to the molecular weight distribution and that VOCT may serve as method to rapidly determine molecular weight distributions and properties after cyclic loading of uncrosslinked and crosslinked polymers.

Dual band metamaterial absorber: Combination of plasmon and Mie resonances

A dual band metamaterial absorber composed of dielectric and metallic atoms with high symmetry was numerically designed and experimentally verified. Due to simultaneously generated electric and magnetic resonances of both plasmon and Mie resonators, two absorption peaks with near unity absorptivity were obtained at 9.45 and 9.80 GHz. The loss of the electromagnetic wave at the first resonance frequency was mainly caused by ohmic loss based on plasmon resonance. For the second absorption peak resonance frequency, the incident wave was trapped inside the dielectric cube and the main loss of the electromagnetic wave was caused by dielectric loss based on Mie resonance. Most of the proposed dual band metamaterial absorbers were sensitive to the polarization direction hindering its potential applications in scientific and technological areas. Combing both plasmon and Mie resonances provides a new and simple way to build dual band isotropic metamaterial perfect absorbers eliminating polarization effect.

‘Silent’ Dome Emplacement into a Wet Volcano: Observations from an Effusive Eruption at White Island (Whakaari), New Zealand in Late 2012

The 2012–2016 White Island (Whakaari) eruption sequence encompassed six small explosive events that included one steam driven and five explosive phreato-magmatic eruptions. More enigmatic, a dome was observed at the back of the vent and crater lake in November 2012. Its emplacement date could not be easily determined due to persistent steam from the evaporating crater lake and because of the very low levels of discrete volcanic earthquakes associated with its growth. During this period, seismicity also included persistent tremor with dominant frequencies in the 2–5 Hz range. Detailed assessment of the tremor reveals a very slow evolution of the spectral peaks from low to higher frequencies. These gliding spectral lines evolved over a three-month time period beginning in late September 2012 and persisting until early January 2013, when the tremor stabilised. As part of the dome emplacement episode, the crater lake progressively dried, leaving isolated pools which then promoted persistent mud/sulphur eruption activity starting in mid-January 2013. We interpret the emplacement of the dome as a non-explosive process where the hot, mostly degassed, magma intruded slowly through the hydrothermal system in late September 2012 and cooled in a relatively quiet state. The tremor evolution might reflect the slow contraction of subsurface resonant cavities, which increased the pitch of the peak resonant frequency through time. Alternatively, spectral evolution might reflect a ‘comb function’ due to clockwork beating of the slowly cooling dome, although direct evidence of clockwork beats is not seen in the waveform data. Finally, it might represent frothing of the hydrothermal system ahead of the slowly propagating magma.

Local Ultrasonic Resonance Spectroscopy: A Demonstration on Plate Inspection

Local ultrasonic resonance spectroscopy (LURS) is a new approach to ultrasound signal analysis, which was necessitated by a novel inspection method capable of the contact-free, localized, broadband generation and detection of ultrasound. By performing a LURS scan, it is possible to detect local mechanical resonances of various features and of the specimen itself. They are highly sensitive to local mechanical properties. By observing different parameters in the frequency spectrum (e.g., resonance amplitude and resonance peak frequency), geometrical, material and condition properties can be visualized for all of the scanning positions. We demonstrate LURS for inspection of a carbon fiber reinforced polymer plate. Local defect resonances of delaminations and a flat-bottom hole were detected in the frequency range from 25 to 110 kHz. Analyzing the higher frequency range (0.3 MHz to 1.5 MHz) of the same scan, the shift of the thickness resonance frequency of the plate and its higher-order resonance frequencies carry the information about the aluminum inclusions. LURS shows an advantage in characterizing the localized features of the specimens via contact-free ultrasonic inspection.

Selective excitation of multipolar surface plasmon in a graphene-coated dielectric particle by Laguerre Gaussian beam

Localized surface plasmonic resonance has attracted extensive attention since it allows for great enhancement of local field intensity on the nanoparticle surface. In this paper, we make a systematic study on the excitation of localized surface plasmons of a graphene coated dielectric particle. Theoretical results show that both the intensity and frequency of the plasmonic resonant peak can be tuned effectively through modifying the graphene layer. Furthermore, high order localized surface plasmons could be excited and tuned selectively by the Laguerre Gaussian beam, which is induced by the optical angular orbital momentum transfer through the mutual interaction between the particle and the helical wavefront. Moreover, the profiles of the multipolar localized surface plasmons are illustrated in detail. The study provides rich potential applications in the plasmonic devices and the wavefront engineering nano-optics.

Variations of global thunderstorm activity derived from the long-term Schumann resonance monitoring in the Antarctic and in the Arctic

The paper analyzes the records of the magnetic components of the Schumann resonance signals obtained at the Ukrainian Antarctic station “Akademik Vernadsky” (coordinates: 65.25° S, 64.25° W) from March 2002 to March 2019 and at Svalbard in the Arctic (coordinates: 78.15° N and 16.05° E) from October 2013 to June 2019. The time-course is studied of the monthly average intensities and peak frequencies of the first Schumann resonance maximum, as well as the background noise intensity at the first minimum. Both observed parameters demonstrate periodic seasonal variations. The intensities are in-phase in different hemispheres while the peak frequencies are in anti-phase. Another feature of the resonance signals is interannual trend of the resonance intensity and peak frequency observed in both hemispheres being synchronous with 11-year solar cycle. The background noise intensities demonstrate the absence of appreciable interannual variations. We propose the following interpretation of these results. Seasonal changes in peak frequencies are determined by the regular meridian drift of the world thunderstorm centers up to ±(18°–26°) in latitude from the equator. Seasonal variations of the intensity are controlled by changes of thunderstorm activity that increase of about 1.5 times during the boreal summer compared with the winter. World thunderstorm activity is practically independent on the phase of the solar cycle. The observed interannual trends in the parameters of the first Schumann mode are determined by the global changes in the lower ionosphere. They can be explained by increasing of the upper (magnetic) characteristic height by 2–3 km due to additional ionization during the years of maximum solar activity. Another explanation might be an increase of the lower (electric) characteristic height by 1–1.5 km during the years of the quiet Sun due to variation of the flux of galactic cosmic rays. Moreover, we showed that involvement of ionosphere conductivity profiles in the point source model accounting their seasonal drift provides reliable estimating the global thunderstorms’ centers activities. To explain a behavior of the intensity changes recorded in the Antarctic observatory a mechanism of additional modulation of the local resonant cavity parameters within the solar cycle is required.

Research on terahertz radiation peak control of photoconductive antenna

This paper studies the interaction effect between the micro-structure photoconductive antenna (PCA) and femtosecond laser, the control of radiated terahertz (THz) wave, and the radiation regulation mechanism of the THz wave for the photoconductive antenna (PCA). The Drude-Lorentz theory model is used to solve the photocurrent density, which is then iterated to the excitation grid by FDTD method. And then the time-varying electromagnetic fields is solved by Maxwell’s equations. The radiated THz wave from the near field to far field in the multi-layer medium is got through the Green's Function of transmission line, and the relationship between the photocurrent and impedance of the radiation is established. At the same time, the relationship between the photocurrent and the magnetic resonance model is also established. The control mechanism of THz wave radiation from micro-structure S-shaped PCA is analyzed by simulation. The results show that the radiation impedance of the equivalent model is changed after split ring resonator (SRR) is introduced into the H-shaped PCA. Meanwhile, it is known that the coupling effect exists when the coupling coefficient is not zero. With the increasing of the coupling coefficient, and the radiation intensity of the resonance frequency peak increases and shifts. The adjusting range of the center frequency between 0.50−0.80 THz, the frequency modulation degree is 75%, and the peak radiation efficiency increases by 70% after simulating the S-shaped PCA. This work lays an important foundation for the design of THz wave resonance center frequency range and structure of high-power PCA.

Enhancement of Brillouin light scattering signal with anti-reflection layers on magnetic thin films

The significant enhancement of Brillouin light scattering (BLS) spectroscopy intensity in a ferromagnetic thin film with an additional dielectric anti-reflection layer is experimentally investigated. The anti-reflection layer thickness dependent BLS measurements on ferromagnetic layers are performed systematically. Consequently, we observe that BLS signals are dramatically enhanced by more than 450% at a specific dielectric layer thickness due to the pure optical effect. Because of the large signal enhancements, the errors of the spin wave resonance peak frequencies are noticeably reduced as well. Since many magnetic properties such as the saturation magnetization, the surface anisotropy, and the exchange stiffness constant are determined by the spin wave resonance frequencies from the BLS spectra, the additional anti-reflection layer can help to improve the reliability of BLS experiments. Especially, the BLS signal improvement plays a crucial role in the precise determination of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) energy density, since the iDMI energy density is calculated from the difference of Stokes and anti-Stokes resonance frequencies, which is typically order of 1 GHz.

X-band metamaterial absorbers based on reduced graphene oxide-silicon carbide-linear low density polyethylene composite

Graphene oxide obtained by Hummer's method is used to synthesize reduced graphene oxide (RGO) using chemical and thermal treatment method. Flexible composites of RGO-Silicon carbide (SiC)-Low density polyethylene (LLDPE) in different wt.% ratios of fillers are characterized for complex permittivity and permeability in X-band. A metamaterial design of ring shaped with four stripe structure is designed on developed substrate as well as standard FR4 substrate and simulated using EM simulator, CST Microwave Studio. Simulated results showed shifting of resonant peak frequency from C-band frequency for FR4 substrate to X-band for developed substrates signifying a role of microwave constitutive properties of the dielectric spacer. The fabricated metamaterial structure on RGO-SiC-LLDPE composite of thickness 0.7 mm shows a S11 ∼ −25 dB at 10.7 GHz with maximum absorption of 96.7%. Thus, the developed meta-material design showing a potential application in microwave applications.

Lung-to-ear sound transmission does not improve directional hearing in green treefrogs (Hyla cinerea).

Amphibians are unique among extant vertebrates in having middle ear cavities that are internally coupled to each other and to the lungs. In frogs, the lung-to-ear sound transmission pathway can influence the tympanum's inherent directionality, but what role such effects might play in directional hearing remains unclear. In this study of the American green treefrog (Hyla cinerea), we tested the hypothesis that the lung-to-ear sound transmission pathway functions to improve directional hearing, particularly in the context of intraspecific sexual communication. Using laser vibrometry, we measured the tympanum's vibration amplitude in females in response to a frequency modulated sweep presented from 12 sound incidence angles in azimuth. Tympanum directionality was determined across three states of lung inflation (inflated, deflated, reinflated) both for a single tympanum in the form of the vibration amplitude difference (VAD) and for binaural comparisons in the form of the interaural vibration amplitude difference (IVAD). The state of lung inflation had negligible effects (typically less than 0.5 dB) on both VADs and IVADs at frequencies emphasized in the advertisement calls produced by conspecific males (834 and 2730 Hz). Directionality at the peak resonance frequency of the lungs (1558 Hz) was improved by ∼3 dB for a single tympanum when the lungs were inflated versus deflated, but IVADs were not impacted by the state of lung inflation. Based on these results, we reject the hypothesis that the lung-to-ear sound transmission pathway functions to improve directional hearing in frogs.

Design and simulation of a photonic crystal resonator as a biosensor for point-of-care applications

Abstract Point-of-care (POC) devices are essential for rapid testing of samples for early diagnosis of diseases. The accuracy and the sensitivity of the POC device depend mainly on the biosensors. The currently used POC devices require specialized operating personnel, long sample preparation time and high equipment costs. We aim to explain a bio-sensing concept using a photonic crystal (PC) resonator that would mitigate the drawbacks of the present sensing techniques. Photonic crystals consist of spatially arranged dielectric materials presenting a band gap that prevents electromagnetic waves of certain frequency range to propagate through it. PC resonators have shown to have very high sensitivities for bio-sensing applications at THz frequencies. A PC resonator with a high Q-factor is designed and simulated to detect the changes in the surrounding dielectric permittivity. As an application for detecting specific biomolecules, a protocol for surface functionalization has been explained. This will enable the selective binding of biomolecules from the sample. Shift in resonant frequency and attenuation in magnitude at the peak resonant frequency can be observed from the simulation results. These changes in the resonator properties can be indicative of the presence of a particular biomolecule or pathogen and its concentration within the sample.

Multiple Fano resonances with flexible tunablity based on symmetry-breaking resonators

A symmetry-breaking nanostructure is proposed to achieve multiple Fano resonances. The nanostructure consists of an asymmetric ring resonator coupled to a plasmonic waveguide. The broken symmetry is introduced by deviating the centers of regular ring. New resonant modes that are not accessible through a regular symmetric ring cavity are excited. Thus, one asymmetric cavity can provide more than one resonant mode with the same mode order. As a result, the interval of Fano resonances is greatly reduced. By combining different rings with different degrees of asymmetry, multiple Fano resonances are generated. Those Fano resonances have different dependences on structural parameters due to their different physical origin. The resonance frequency and resonance peak number can be arbitrarily adjusted by changing the degree of asymmetry. This research may provide new opportunities to design on-chip optical devices with great tuning performance.

Electromagnetically induced transparency in novel dual-band metamaterial excited by toroidal dipolar response

We demonstrated a novel metamaterial with dual-band electromagnetically induced transparency (EIT) via simulation, experiment and numerical analysis, with resonance frequencies of the transparency peaks of 7.60 and 10.27 GHz. The E-e metamaterial unit cells were composed of E-shaped and e-shaped patterns. By analyzing the surface current distribution and the magnetic field, we qualitatively verified the toroidal dipole response in the E-e metamaterial at 10.27 GHz. Meanwhile, by calculating the multipole’s radiated power, we found that the two transparency peaks were due to the excitation of the electric and toroidal dipole responses. By changing the incident angle from 0° to 60°, we observed changes in transmission spectra, and the quality factors (Q-factors) of the two transparency peaks increased. In addition, the proposed E-e metamaterial can be designed to act as a refractive index sensor or other electronic equipment for the control of electromagnetic waves.

Laser Resonance Frequency Analysis: A Novel Measurement Approach to Evaluate Acetabular Cup Stability During Surgery.

Artificial joint acetabular cup stability is essential for successful total hip arthroplasty. However, a quantitative evaluation approach for clinical use is lacking. We developed a resonance frequency analysis (RFA) system involving a laser system that is fully contactless. This study aimed to investigate the usefulness of laser RFA for evaluating acetabular cup stability. First, the finite element method was performed to determine the vibration mode for analysis. Second, the acetabular cup was press-fitted into a reamed polyurethane cavity that replicated the human acetabular roof. The implanted acetabular cup was vibrated with pulse laser irradiation and the induced vibration was detected with a laser Doppler vibrometer. The time domain signal from the vibrometer was analyzed by fast Fourier transform to obtain the vibration frequency spectrum. After laser RFA, the pull-down force of the acetabular cup was measured as conventional implant fixation strength. The frequency of the first highest amplitude between 2 kHz and 6 kHz was considered as the resonance peak frequency, and its relationship with the pull-down force was assessed. The peak frequency could predict the pull-down force (R2 = 0.859, p < 0.000). Our findings suggest that laser RFA might be useful to measure acetabular cup stability during surgery.

Theoretical Resonance Analysis of Langevin Transducers with Equivalent Circuit Models for Therapeutic Ultrasound

In this paper, the resonance characteristics of Langevin ultrasonic transducers is analyzed with equivalent circuit models. Transducer configuration is devised by half-wavelength principle and material properties used. Both resonance peak frequency and effective electromechanical coupling coefficient are simulated by calculating the transducer’s input electrical impedance at given center frequencies, 30 kHz, 40 kHz, and 50 kHz. In case of a bare transducer, the relative errors derived from its expected resonance peaks are equal to be 0.3% at 30 kHz, 0.8% at 40 kHz, and 0.6% at 50 kHz. The corresponding coupling coefficients are found to be 0.20, 0.17, and 0.20, respectively. For a transducer coupled with a titanium rod, similar simulations are also carried out at the same frequencies. The model errors become 0.8%, 1.1%, and 0.7%, while their coupling coefficients are estimated to be 0.10, 0.07, and 0.10. The model is thus shown to be capable of predicting those resonance signatures within narrow margin under a variety of conditions. The results indicate that this approach may be taken advantage of to determine the design criteria of Langevin transducers for therapeutic procedures.

A Study of Wideband Energy Reflectance in Patients with Otosclerosis: Data from a Chinese Population.

Objective(s) The purpose of this study was to explore the effectiveness of wideband acoustic immittance (WAI) in the diagnosis of otosclerosis by comparing the differences in the energy reflectance (ER) of WAI between patients with otosclerosis and age- and gender-matched normal hearing controls in the Chinese population. Methods Twenty surgically confirmed otosclerotic ears were included in the otosclerotic group. The ER of WAI at ambient and peak pressures, resonance frequency, and 226-Hz tympanogram were collected prior to surgery using a Titan hearing test platform (Interacoustics A/S, Middelfart, Denmark). All diagnoses of otosclerosis in the tested ear were confirmed by surgery after the measurements. Thirteen normal adults (26 ears) who were age- and gender-matched with the otosclerotic patients were included as the control group. Results At peak pressure, the ERs of otosclerotic patients were higher than those of the control group for frequencies less than 4,000Hz and were lower for frequencies greater than 4,000Hz. In addition, within the analyzed frequencies, the differences observed at 2,520Hz was statistically significant (p<0.05/16=0.003, Bonferroni corrected). At ambient pressure, the differences observed at 1,260 and 6,350Hz were statistically significant (p<0.05/16=0.003, Bonferroni corrected). Although the differences between the otosclerotic and control groups exhibited similar trends to those in studies implemented in Caucasian populations, the norms in the present study in the control group were different from those in the Caucasian populations, suggesting racial differences in WAI test results. Regarding the middle ear resonance frequency, no significant difference was observed between the two groups (P>0.05). Conclusion WAI can provide valuable information for the diagnosis of otosclerosis in the Chinese population. Norms and diagnostic criteria corresponding to the patient's racial group are necessary to improve the efficiency of WAI in the diagnosis of otosclerosis.

A weak fault feature extraction of rolling element bearing based on attenuated cosine dictionaries and sparse feature sign search

The time domain signal of bearing pitting/spalling fault always presents shock and modulation, and it is often submerged by strong noises, especially in the early stage. the conventional fault feature extraction method may have insufficient feature extraction accuracy, and even in some extreme cases, the fault feature frequency cannot be extracted because of the strong noise interference. Aiming at overcoming the noise interference problem encountered in this kind of weak fault feature extraction, a novel weak fault feature extraction algorithm termed as ACFSS of rolling bearing is proposed. The ACFSS is based on an overcomplete dictionary (or overcomplete atomic library) of Attenuated Cosines(AC) basis, which is highly matched to the bearing fault waveforms, and an improved Basis Pursuit algorithm with Feature Sign Search(FSS) is introduced into the ACFSS to improve the calculating speed. In order to select the suitable parameters of the attenuated cosine dictionary, some methods such as peak resonance frequency (PRF), power variation peak (PVK), time shift parameter (TSP), etc. are introduced. These parameters span the sparse overcomplete dictionary. Finally, the bearing fault data of Case-Western University and full life accelerated IMS bearing data are utilized to verify the validation of ACFSS. Compared with the ordinary envelope spectrum analysis(ESA) method /the ordinary Basis Pursuit Denoising(BPDN) method/ Wavelet package transform(WPT) Kurtogram method and Empirical Mode Decomposition(EMD) combining Singular Value Decomposition(SVD) method, The experiment show that the proposed method are more redundant and robust when facing strong noise interference, and it can be used to extract the weak fault feature frequency efficiently and accurately.

Dynamic Responses of Electrically Driven Quartz Tuning Fork and qPlus Sensor: A Comprehensive Electromechanical Model for Quartz Tuning Fork.

A quartz tuning fork and its qPlus configuration show different characteristics in their dynamic features, including peak amplitude, resonance frequency, and quality factor. Here, we present an electromechanical model that comprehensively describes the dynamic responses of an electrically driven tuning fork and its qPlus configuration. Based on the model, we theoretically derive and experimentally validate how the peak amplitude, resonance frequency, quality factor, and normalized capacitance are changed when transforming a tuning fork to its qPlus configuration. Furthermore, we introduce two experimentally measurable parameters that are intrinsic for a given tuning fork and not changed by the qPlus configuration. The present model and analysis allow quantitative prediction of the dynamic characteristics in tuning fork and qPlus, and thus could be useful to optimize the sensors’ performance.

Design and simulation of a temperature-tunable terahertz metamaterials based on VO2 particles

A temperature-sensitive metamaterial containing vanadium dioxide (VO2) particles is designed and simulated in the terahertz band. A near-perfect absorption peak is achieved by optimizing structural parameters at room temperature. The peak amplitude and resonance frequency can be linearly modulated through changing structural parameters. Moreover, a new absorption band and an absorption peak are achieved when the simulated temperature reaches or exceeds the phase transition point of VO2 particles. The absorption band and the absorption peak are shifted to higher resonance frequencies with the temperature increasing. Moreover, this absorption band is expanded and the peak amplitude is gradually decreased with the temperature increasing. This proposed temperature-tunable terahertz metamaterial absorber can be used in many areas, such as sensing, communication, and more.