Center Resonant Frequency Research Articles

A Fluidics-Based Double Flexural Membrane Piezoelectric Micromachined Ultrasonic Transducer (PMUT) for Wide-Bandwidth Underwater Acoustic Applications.

In acoustic receiver design, the receiving sensitivity and bandwidth are two primary parameters that determine the performance of a device. The trade-off between sensitivity and bandwidth makes the design very challenging, meaning it needs to be fine-tuned to suit specific applications. The ability to design a PMUT with high receiving sensitivity and a wide bandwidth is crucial to allow a wide spectrum of transmitted frequencies to be efficiently received. This paper presents a novel structure involving a double flexural membrane with a fluidic backing layer based on an in-plane polarization mode to optimize both the receiving sensitivity and frequency bandwidth for medium-range underwater acoustic applications. In this structure, the membrane material and electrode configuration are optimized to produce good receiving sensitivity. Simultaneously, a fluidic backing layer is introduced into the double flexural membrane to increase the bandwidth. Several piezoelectric membrane materials and various electrode dimensions were simulated using finite element analysis (FEA) techniques to study the receiving performance of the proposed structure. The final structure was then fabricated based on the findings from the simulation work. The pulse–echo experimental method was used to characterize and verify the performance of the proposed device. The proposed structure was found to have an improved bandwidth of 56.6% with a receiving sensitivity of −1.8864 dB rel 1 V µPa. For the proposed device, the resonance frequency and center frequency were 600 and 662.5 kHz, respectively, indicating its suitability for the targeted frequency range.

Boosting of NO2 gas sensing performances using GO-PEDOT:PSS nanocomposite chemical interface coated on langasite-based surface acoustic wave sensor

Although the physicochemical properties of graphene oxide-Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (GO-PEDOT:PSS) nanocomposite has widely reported, the urgency of this nanocomposite in the surface acoustic wave (SAW) technology still remains at the infancy stage. In this work, a high response SAW NO2 gas sensor was developed by depositing the GO-PEDOT:PSS nanocomposite on piezoelectric LGS substrate. The pristine LGS SAW sensor has showed a resonant center frequency of 136.10 MHz and it was shifted to 135.78 MHz for the GO-PEDOT:PSS coated LGS SAW sensor. The observed shift in resonance frequency likely due to the mass loading effect of GO-PEDOT:PSS nanocomposite interface. However, under the gas ambient the GO-PEDOT:PSS/LGS SAW sensor exhibited a significant negative differential frequency shift (Δf) of 5.89 kHz to100 ppm of NO2 gas with a good cycling stability, excellent sensitivity and a low detection limit (∼175 ppb) at room temperature (RT), while the pristine GO/LGS and PEDOT:PSS/LGS SAW sensors showed the Δf of about 0.9 kHz and 2.1 kHz, respectively. In addition, under the various relative humidity conditions at RT for 100 ppm of NO2, the GO-PEDOT:PSS/LGS SAW device showed a dominant Δf. Our experimental results divulged that the effect of mass loading is the responsible underlying mechanism for the superior NO2 gas sensing performances. In turn, the predominant mechanism between the chemical interface and NO2 gas molecules on GO-PEDOT:PSS/LGS SAW device has been deliberately discussed in detailed by comparing with chemo-resistive type gas sensing properties These intriguing results indicate that the significance of GO-PEDOT:PSS has a synergetic effect in SAW sensor applications.

Characters of frequency response in a coaxial Bragg structure with tapered-double-sinusoidal grooves operating at 0.35 THz frequency

On the basis of ordinary sinusoidal groove structures, an auxiliary sinusoidal distribution with a smaller etching period is superimposed, and a negative-taper is added, on the inner and outer conductor walls to form a coaxial Bragg structure with tapered-double-sinusoidal grooves. Through the FORTRAN software programming simulation experiments, we can see that compared with the ordinary sinusoidal grooves, the bandwidth of the working mode and competition mode gets narrower, the quality factor Q gets greater, the residual side-lobes are also suppressed, and the selectivity of frequency is enhanced when the coaxial Bragg structure adopts the tapered-double-sinusoidal grooves. At the same time, the center resonance frequency point of the competition mode is far away from the working mode, and the bandgap overlap is further separated. However, the reflectivity of the working mode decreases and the reflectivity of the competing mode increases with the increase in the gradient angle. These peculiarities of the negative-tapered-double-sinusoidal groove structure are favorable to construct a cavity with a narrower bandwidth and high quality factor and also are favorable to the mode selectivity.

Adaptive Response Behavior in the Pursuit of Unpredictably Moving Sounds.

Although moving sound-sources abound in natural auditory scenes, it is not clear how the human brain processes auditory motion. Previous studies have indicated that, although ocular localization responses to stationary sounds are quite accurate, ocular smooth pursuit of moving sounds is very poor. We here demonstrate that human subjects faithfully track a sound’s unpredictable movements in the horizontal plane with smooth-pursuit responses of the head. Our analysis revealed that the stimulus–response relation was well described by an under-damped passive, second-order low-pass filter in series with an idiosyncratic, fixed, pure delay. The model contained only two free parameters: the system’s damping coefficient, and its central (resonance) frequency. We found that the latter remained constant at ∼0.6 Hz throughout the experiment for all subjects. Interestingly, the damping coefficient systematically increased with trial number, suggesting the presence of an adaptive mechanism in the auditory pursuit system (APS). This mechanism functions even for unpredictable sound-motion trajectories endowed with fixed, but covert, frequency characteristics in open-loop tracking conditions. We conjecture that the APS optimizes a trade-off between response speed and effort. Taken together, our data support the existence of a pursuit system for auditory head-tracking, which would suggest the presence of a neural representation of a spatial auditory fovea (AF).

Characterization of magnetic interference and image artefacts during simultaneous in-beam MR imaging and proton pencil beam scanning

For the first time, a low-field open magnetic resonance (MR) scanner was combined with a proton pencil beam scanning (PBS) research beamline. The aim of this study was to characterize the magnetic fringe fields produced by the PBS system and measure their effects on MR image quality during simultaneous PBS irradiation and image acquisition. A magnetic field camera measured the change in central resonance frequency (Δf res) and magnetic field homogeneity (ΔMFH) of the B0 field of the MR scanner during operation of the beam transport and scanning magnets. The beam energy was varied between 70 − 220 MeV and beam scanning was performed along the central horizontal and vertical axis of a 48 × 24 cm2 radiation field. The time structure of the scanning magnets’ fringe fields was simultaneously recorded by a tri-axial Hall probe. MR imaging experiments were conducted using the ACR (American College of Radiology) Small MRI Phantom and a spoiled gradient echo pulse sequence during simultaneous volumetric irradiation. Computer simulations were performed to predict the effects of B 0 field perturbations due to PBS irradiation on MR image formation in k-space. Setting the beam transport magnets, horizontal and vertical scanning magnets resulted in a maximum Δf res of 50, 235 and 4 Hz, respectively. The ΔMFH was less than 3 parts per million for all measurements. MR images acquired during beam energy variation and vertical beam scanning showed no visual loss in image quality. However, MR images acquired during horizontal beam scanning showed severe coherent ghosting artefacts in phase encoding direction. Both simulated and measured k-space phase maps prove that these artefacts are caused by phase-offsets. This study shows first experimental evidence that simultaneous in-beam MR imaging during proton PBS irradiation is subject to severe loss of image quality in the absence of magnetic decoupling between the PBS and MR system.

Glycine sensor based on 1D defective phononic crystal structure

Phononic crystals (PnCs) provide an innovative platform for sensing biomaterials. In this work, we introduce a defective 1D-PnC from lead-epoxy multilayer with a central defect layer filled with glycine. The transmission spectra of the incident acoustic wave are calculated numerically by the transfer matrix method. The working principle of this sensor is to sense how much change occurs in the concentration of glycine. Any change in glycine concentration affects the acoustic properties of glycine directly. Thereby the central resonance frequency in the transmission spectrum shifted. In this study, we firstly made optimization for the type of the structure (symmetric/asymmetric), the number of periods, the glycine layer thickness, and glycine concentration to get the best sensor performance. The proposed sensor provided high sensitivity (S = 969.973 kHz) over just a molar ratio range 0–0.383 mol/L. Moreover, we calculated other performance parameters such as the quality factor, which reached a maximum value of 13,497, sensor resolution of 3.49 × 105 Hz, and figure of merit of 4.2. Based on the obtained results, this sensor has many merits such as it is designed from low cost materials, the ease of fabrication, high sensitivity, and absence of any electronic component in its design.

High Isolation and Low Cross-Polarization of Low-Profile Dual-Polarized Antennas via Metasurface Mode Optimization

A low-profile dual-polarized metasurface antenna with high isolation and low cross-polarization is proposed in this communication. The proposed metasurface consists of an array of $4\times 4$ patches. Through characteristic mode analysis (CMA), a pair of degenerate modes is identified to achieve the desired radiation features. By modifying the patches of the metasurface, the strongest mode current distributions of the two modes are moved from the center to the edge of the metasurface. One feed port can efficiently excite only one particular mode, and the other mode cannot be excited simultaneously. Each of the modes are differentially fed using two Y-shaped microstrip lines via two slots. As a result, both high isolation and low cross-polarization can be obtained. The simulation and experimental results show that the proposed antenna achieves not only a low profile of $0.05\lambda _{0}$ (where $\lambda _{0}$ is the free-space wavelength at the center resonant frequency) but also a broad impedance bandwidth of 36% and a high isolation of 53 dB. In particular, the enhanced cross-polarization discrimination (XPD) is lower than −40 dB at the broadside, lower than −33 dB within ±30° of the main lobe, and lower than −28 dB within ±60° of the main lobe.

The Use of Dynamic Environment Library to Achieve Controlling of Atomic Spontaneous Emission Process

The regulation of the spontaneous emission process of the two-level atom in the excited state is studied by using the dynamic environmental library. The central resonant frequency is dynamically modulated, resulting in a dynamic environment library. In the ideal photonic band-gap environment reservoir, we researched the influence of dynamic pulse modulation forms on the evolution of atomic population. The pulse modulation forms are: single rectangular pulse modulation, continuous rectangular pulse modulation, and combined rectangular pulse modulation. The results shown that adjusting the modulation time width effectively suppressed energy dissipation, the system coherence evolution was protected, and the amplitude of atomic population oscillation became larger. The coherence evolution of the system is effectively protected under short-length combined rectangular pulse modulation. The regulation of atomic spontaneous emission can provide a theoretical basis for technical applications in the field of quantum information.

On Quantized Analog Compressive Sensing Methods for Efficient Resonator Frequency Estimation

In many applications such as gravimetric sensing, there is a need to rapidly estimate the center resonant frequency of the sensor system. This paper proposes and compares different quantized analog compressive sensing approaches for rapid frequency estimation. In particular, we discuss (a) Atomic norm Soft Thresholding - Semidefinite Programming (AST-SDP), (b) Atomic norm Soft Thresholding - Alternating Direction Method of Multipliers (AST-ADMM) and (c) Superfast Line Spectral Estimation (LSE) algorithms. As a result of this comparison we report that Superfast LSE achieves a good trade-off between computational speed, quantization, and error in frequency estimation among the three approaches. We further compare the compressive sensing approaches to several classical methods such as the Prony's algorithm and the Pisarenko's algorithm and show that compressive sensing based approaches remain robust to higher quantization errors. Finally, experimental results are shown for a quartz crystal and a MEMS based gravimetric sensor. Frequency measurement results with the quartz crystal show that a resolution of 0.1 ppm RMSE is achieved with the compressed sensing approach.

Effect of Dielectric Substrate Parameters Which Dimensions of Lens and Distance From Antenna on The Gain Enhancement of Microstrip Antenna with Metamaterial

In this study, it was aimed to determine the effect of dielectric substrate parameters which dimensions of lens and distance from antenna used as lens layer in front of antenna on antenna gain for the 2.45 GHz Wifi frequency band and calculate the effect of dielectric substrate on increasing the gain of classical microstrip antenna by using metamaterial lens layer (Square split ring resonator). For this purpose, a conventional microstrip antenna with a center resonant frequency of 2.45 GHz was first designed with the help of an electromagnetic simulation program. Then, the dielectric lens layer's size and distance from the antenna parameters were optimized and a maximum gain of 16% was obtained. In addition, it was determined that the dielectric lens layer size had more effect on increase of gain than the distance between antenna and lens layers. Then, the dielectric lens layer, 5λ / 16 antenna size and λ / 4 antenna distance which selected randomly, was designed and placed as a lens in front of the antenna (without using metamaterial). It was observed that the dielectric lens layer had an effect of antenna gain of about 7% for the single layer and 22% for the double layer. A square split ring resonator-shaped metamaterial lens layer with the same parameters as the resulting dielectric lens layer was then designed and placed in front of the conventional microstrip patch antenna for the 2.45 GHz Wifi frequency. It was observed that the lens layer with metamaterial increased the gain of the antenna by about 22% by placing it in single layer and 87% by placing it in double layer in front of the conventional microstrip amenna.

Bistable active spectral tuning of one-dimensional nanophotonic crystal by phase change.

Active spectral tuning of nanophotonic devices offers many fascinating prospects for the realization of novel optical function. Here, switchable spectral response is enabled by the architecture of one-dimensional (1D) photonic crystal (PC) integrated with phase change material of the germanium antimony telluride (GST). Active and precise tuning of the bistable passband and central resonant frequency is demonstrated in the 1D PC composed of alternate SiN and GST nanofilms. An analytical model is derived to specify the tunable spectral features, including the band gap and resonant frequencies. Both the measured and calculated results show distinct red shifts of passband and the resonant minima (or maxima), well confirming theoretical predictions. This work demonstrates a route to construct active photonic devices with the electrically or thermally tunable spectra via 1D PC and potentially extends diverse applications based on the PC platform.

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.

SiP-Based SSBI Cancellation for OFDM

We propose for the first time to use a silicon photonics (SiP) solution for a passive optical network to both reduce signal-signal beat interference (SSBI) and recuperate a part of the downlink carrier for use in the uplink. The Kramers-Kronig (KK) receiver for direct detection of advanced modulation formats overcomes SSBI at the cost of a moderate carrier to signal ratio (>6 dB) and high oversampling (4×). We propose an optical SSBI solution that achieves better performance than KK and requires only standard sampling and low (3 dB) carrier to signal power ratio. The receiver is conceived for the downlink in passive optical networks, where carrier signal must be husbanded for re-use in the uplink. Using cost effective and power efficient SiP, the receiver filters the incoming signal, suppresses SSBI, and routes a portion of the carrier for use in the uplink. We experimentally examine the SSBI suppression in this paper. While previous demonstrations used bulky, discrete components, we achieve significant Q-factor improvement with a simple SiP solution. We examine the optimal frequency offset between the carrier and the microring resonator center frequency. The robustness to frequency drift, as well as the impact of imperfect filtering, is discussed and quantified.

Residual intensity modulation-induced error in resonator fiber optic gyroscopes with triangular phase modulation.

The residual intensity modulation (RIM) is one of the major sources of instability in optical detection based on phase modulation. In resonator fiber optic gyroscopes (RFOGs), the RIM leads to a nonzero output signal at the resonance center frequency, which degrades the bias stability of the RFOG. While the origins of the RIM are not fully understood, we present experimental results of the RIM in the Y-branch waveguide modulator with triangular phase modulation. We establish a model to analyze the RIM-induced error in the RFOG with triangular phase modulation and pointed out that symmetrical acquisition in a triangular wave period can reduce the RIM-induced error. We experimentally study the equivalent modulation depth of the RIM with different acquisition times in a triangular wave period and symmetrical acquisition in a triangular wave period. The results show that symmetrical acquisition in a triangular wave period can eliminate the RIM-induced error.

A Compact Plus Shaped Carpet Fractal Antenna with an I-Shaped DGS for C-band/X-band/UWB/WIBAN applications

This article presents the design and development of a compact broadband “+” shaped aperture coupled carpet fractal antenna with a defected ground structure (I shaped slot in the ground) for broadband/ultra wideband (UWB) and a multiband characteristics. The antenna has overall dimensions of 8.4 cm × 5.5 cm × 3.2 mm and is fed using aperture coupled feeding mechanism. It shows an impedance bandwidth (< 10 dB) of 4460 MHz from 6.93 to 11.39 GHz with fractional bandwidth of 0.48 at the center resonant frequency of 9.16 GHz. A multiband behavior is also exhibited by this antenna from 3.9–4.08 GHz, 4.8–5.06 GHz and 6.1–6.4 GHz with impedance bandwidths of 180 MHz, 260 MHz and 300 MHz respectively. It therefore supports the wireless applications of Wi-MAX (3.8–4.1 GHz), Wi-BAN/long distance radio telecommunication (4.8–5.06 GHz), wireless sensor networks (6.1–6.4 GHz), satellite (7.4–7.8 GHz) and UWB (6.9–11.03 GHz). The antenna is designed as a ‘+’ shaped patch with fractal rectangular slots cut out from it up to iterations of second order that allow the antenna to support multiband characteristics. The bandwidth at these bands is improved by using I shaped defected ground structure (DGS) and a parasitic feeding method i.e. aperture coupled feeding (Karur et al., in: ICMARS (IEEE), Jodhpur, India, pp. 266–270, 2014).The antenna has a compact structure with two layers of FR4 substrate, the ‘+’ shaped carpet fractal printed on the upper substrate layer and the lower substrate has a ground layer printed on its top and feed line on its bottom layer respectively. It shows a simulated peak gain of 4 dB at an operation frequency of 7.95 GHz. The antenna design and simulations are done using CST MWS V14. The Simulation results in terms of impedance bandwidth, smith chart, gain are presented in this article. To validate the impedance bandwidth results, the proposed carpet fractal antenna is experimentally tested using a vector network analyzer and the measured results are found to be closely matching with the simulated ones, allowing the antenna to be practically suitable for the afore mentioned wireless applications.

A graphene‐based tunable miniaturized‐element frequency selective surface in terahertz band and its application in high‐isolation multiple‐input multiple‐output system

AbstractGraphene is a promising material for terahertz (THz) reconfigurable devices due to the tunability of the surface conductivity. Here, a graphene‐based THz miniaturized‐element tunable band‐stop frequency selective surface (FSS) is demonstrated. The proposed FSS unit cell consists of convoluted metallic strips with graphene embedded between adjacent metallic strips. The center resonance frequency of the stop band shows an obvious blue shift from 1.76 to 2.56 THz when increasing the chemical potential of the graphene from 0 to 0.5 eV. Particularly, the convoluted design leads to an ultra‐small cell dimension of 11.73% of the free space wavelength at resonance frequency (1.76 THz). In addition, the positive role of the proposed FSS in enhancing the isolation of the multiple‐input multiple‐output (MIMO) system has been verified through two simple models. This work provides an effective method to design miniaturized‐element graphene‐based tunable FSSs, and gives a simple way to realize high‐isolation MIMO systems.

Multirate Resonant Controllers for Grid-Connected Inverters With Harmonic Compensation Function

Resonant controller (RSC) is one of the most popular approaches for ac current/voltage control due to the high performance of zero steady-state tracking error. However, it suffers from heavy computational burden issue when multiple RSCs are demanded to control multiple harmonics. To alleviate this issue, a down-sampled multirate RSCs (MRRSCs) scheme is proposed for controlling power inverters, e.g., grid-connected inverters and active power filters. The proposed control scheme is composed of an inner control loop with a fast sampling rate, which is identical to the switching frequency, and an array of paralleled MRRSCs-based external control loop with a reduced sampling rate. With the reduced sample rate, the MRRSCs can be executed alternatively in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -frame, such that the computational burden can be significantly reduced per cycle. Moreover, to reinforce the wide frequency adaptability of the MRRSC, its central resonant frequency is online updated according to the output of the phase-locked loop. In the paper, the equivalent single-rate closed-loop model of the overall system is developed, based on which the controller parameters are designed employing the Nyquist diagram and root locus. Finally, experiments are performed on a grid-connected inverter to validate the superiority of the proposed scheme.

Low Profile Microsrip Antenna with Broadside Radiation Patterns and Low Cross Polarizations

A low profile microstrip antenna with adjustable bandwidth around 3 GHz is proposed. The compact antenna consists of a square patch with a square aperture to tune the resonance center frequency. The input impedance bandwidth is about 2.67% with stable gain around 3.2 dBi. Besides, the 3-dB beam width is about 100°. Both the side-fed and bottom-fed modes are analyzed. According to the simulation, good broadside radiation patterns with low cross polarizations are observed in the two principal planes. The detailed design considerations are described and discussed while the surface current distribution and radiation characteristics are analyzed. This design is suitable for mobile wireless communication.

Control of the Atomic Population of an Excited Atom by Using the Double Lorentzian Reservior

The evolution of two-level atomic system, in which the initial state is excited state, is investigated by adjusting the structural parameters of the dynamic and static double Lorentzian environment reservoir. In a static state (no modulation), we studied the effects of half width, center resonant frequency, and specific gravity on the evolution of energy level population. Under dynamic modulation, we used the dynamic cavity environment to control the evolution of spontaneous emission from an excited two-level atom. The dynamic modulation form for the half width of the double Lorentzian environment reservoir includes the rectangular single pulse, rectangular periodic pulse, and slowly continuous pulse. These conclusions make the idea of using the environmental change to modulate the coherent evolution of atomic system become true.

Development of energy harvesting MEMS vibration device sensor with wideband response function in low-frequency domain

An aluminum-nitride (AlN) based microelectromechanical system (MEMS) vibration device sensor with a power-harvesting function is developed. We aimed at realizing a vibration sensor with wideband response in a low-frequency vibration domain, owing to the high-power density of vibration sources energy normally in a particular low frequency with several hertz deviations. A special design was implemented in this work, for the first time, to realize the sensor structure with a wideband response function. The given sensor has a disk-shaped proof mass attached to three sandwiched AlN spring flexures and a supporting beam system. Using MEMS techniques, the sensors were fabricated with the single die size of 7 × 7 mm and observed via scanning electron microscopy comprehensively. The functional feature of the electrical performance of the sensors was evaluated. The results demonstrated that with the given sensor, which has a low center resonant frequency of 57.5 Hz with a response feature of a half-voltage bandwidth of > 10 Hz, an output voltage of 2.4–4 mV at an acceleration of 0.1–0.6 g can be typically achieved. The low-frequency vibration sensor with a wideband response function can be used for many industrial and civilian applications to eliminate the restrictions on power sources.