High Sensitivity Frequency Research Articles

High frequency sensitivity to interaural onset time differences in the bat inferior colliculus

Many neurons in the auditory midbrain are tuned to binaural cues. Two prominent binaural cues are the interaural level difference (ILD) and the interaural time difference (ITD). The ITD cue can further be subdivided into the ongoing envelope ITD cues and transient onset ITD cues. More is known about the sensitivity of single neurons to ongoing envelope ITDs compared to transient onset ITDs in the mammalian auditory system, particularly in bats. The current study examines the response properties of single neurons in the inferior colliculus (IC) of the big brown bat, Eptesicus fuscus, to onset ITDs in response to high frequency pure tones. Measures of neurons’ dynamic ITD response revealed an average change of 36% of its maximum response within the behaviorally relevant range of ITDs (±50 µs). Across all IC neurons, we measured an average time-intensity trading ratio of 30 µs/dB in the sensitivity of the ITD response function to changing ILDs. Minimum and maximum ITD responses were clustered within a narrow range of ITDs. The average peak in the ITD response function was at 268 µs, a finding that is consistent with other non-echolocating mammals. Some ITD-sensitive neurons also showed weak facilitation of maximum response during binaural stimulation, compared to monaural stimulation. These results suggest that echolocating bats possess the potential to use onset ITD cues to assist in the azimuthal sound localization of ultrasonic frequencies.

Design and analysis of high-frequency fiber Bragg grating vibration sensor

The fiber Bragg grating vibration sensor has received a lot of attention due to its unique performance. However, the natural frequency of the sensor limits its development and application. This paper presents an acceleration sensor with an isosceles triangular cantilever and mass block structure, which has high natural frequency and high sensitivity. The optical fiber sensing system consists of two fiber gratings. One section of the fiber grating is pasted on the cantilever and serves as an accelerometer; the other is used as a reference grating. The first-order natural frequency of the accelerometer is 8356 Hz, and its sensitivity is 0.46 pm g−1. A vibration test confirms the reliability of the sensor, and the resonant frequency of the sensor is 8193 Hz. The principle of light intensity demodulation is adopted in the sensor system and its sensitivity is 45.82 mV g−1 with a linearity of 0.997. The sensor has the advantages of high frequency and sensitivity, and thus can be applied to the rail transit bearing systems

Mode-mismatching enhanced disbond detection using material nonlinearity in guided waves at low frequency

Disbond defect is a critical concern for the integrity of adhesively bonded engineering structures, and its characterization using ultrasonic guided waves (UGW)-based methods, suffers from the contradiction of multiple wave modes co-excitation at high frequency and poor sensitivity at low frequency. With this concern, this study addresses an investigation of disbond-disturbed nonlinearity in ultrasonic guided waves (UGWs) at low frequency, and on this basis, a novel disbond detection method is developed featuring enhancement by the mode-mismatching between fundamental and second-order harmonic wave (SOHW) at a specific mode-frequency combination. First, when the probing UGWs at low frequency are excited in adhesive bonded waveguide (aluminum-epoxy-aluminum), the SOHW in intact waveguides and the disbond region are scrutinized from analytical and numerical perspectives. It is observed that in the case of mode-mismatching for UGW of a specific mode-frequency combination, SOHW is remarkably suppressed in intact regions, whereby leading to the predominance of the disbond-induced SOHW. Then, on this basis, a nonlinearity-based method using the UGW with specific mode-frequency combination is developed to outstand the disbond defect. Finally, the experimental evaluation of disbonds well validates the effectiveness of the proposed method, in which three disbond defects with various lengths (10 mm, 20 mm, and 40 mm) are identified and quantitatively evaluated using the optimal UGW mode-frequency combination.

Assessment of bridge natural frequency as an indicator of scour using centrifuge modelling

One of the most prevalent causes of bridge failure around the world is “scour”—the gradual erosion of soil around a bridge foundation due to fast-flowing water. A reliable technique for monitoring scour would help bridge engineers take timely countermeasures to safeguard against failure. Although vibration-based techniques for monitoring structural damage have had limited success, primarily due to insufficient sensitivity, these have tended to focus on the detection of local damage. High natural frequency sensitivity has recently been reported for scour damage. Previous experiments to investigate this have been limited as a result of the cost of full-scale testing and the fact that scaled-down soil-structure models tested outside a centrifuge do not adequately simulate full-scale behaviour. This paper describes the development of what is believed to be the first-ever centrifuge-testing programme to establish the sensitivity of bridge natural frequency to scour. A 1/60 scale model of a two-span integral bridge with 15 m spans was tested at varying levels of scour. For the fundamental mode of vibration, these tests found up to a 40% variation in natural frequency for 30% loss of embedment. Models of three other types of foundation, which represent a shallow pad foundation, a deep pile bent and a deep monopile, were also tested in the centrifuge at different scour levels. The shallow foundation model showed lower frequency sensitivity to scour than the deep foundation models. Another important finding is that the frequency sensitivity to “global scour” is slightly higher than the sensitivity to “local scour”, for all foundation types. The level of frequency sensitivity (3.1–44% per scour depth equivalent to 30% of embedment of scour) detected in this experiment demonstrates the potential for using natural frequency as an indicator of both local and global scour of bridges, particularly those with deep foundations.

Optimized inspection of upstream oil and gas methane emissions using airborne LiDAR surveillance

Methane is a short-lived climate pollutant responsible for approximately 20% of anthropogenic global warming, and reducing methane emissions from the oil and gas (O&G) industry is considered among the most urgent and actionable measures to mitigate climate change. Recent reports suggest a large fraction of upstream O&G methane emissions result from a small number of super-emitter facilities, emphasizing the value of novel methods that inspect O&G facilities with greater frequency than is practical using existing techniques. Here we describe an optimized method wherein O&G facilities are inspected for emissions at high frequency and high sensitivity using active laser (LiDAR) sensors mounted to aircraft. The method relies on a hierarchical clustering and routing procedure to establish optimal routes to be flown by aircraft departing from local airports and equipped with LiDAR methane sensors. Routes are optimized to inspect all well sites subject to emissions regulation in three O&G intensive regions: the Permian basin, the state of Colorado, and the state of Pennsylvania. While some cost estimates require additional field data, these modeling results suggest the optimized inspections can be performed with comparable effectiveness and up to a factor of six lower cost per inspection compared to current detection methods. The cost per inspection required to achieve equivalent emissions reduction depends on factors such as the weather conditions during inspection (which impacts the limit of detection and therefore the inspection frequency required to achieve equivalency) and the well density (which impacts the flying distance), and the advantage of this program over traditional inspection will be reduced under unfavorable conditions. These modeling results suggest that optimized routing may enable frequent inspection of upstream O&G facilities at large scale and potentially lead to a substantial decrease in both oilfield methane emissions and compliance costs borne by industry.

A double-side electrically-actuated arch microbeam for pressure sensing applications

In this study, we consider a pressure sensor whose main component is a clamped-clamped shallow arched microbeam. Two fixed electrodes are used to actuate the microbeam in the transverse direction. The lower electrode is powered by a combination of DC and AC voltages sources to excite the microbeam (drive mode). The upper electrode is polarized with a DC voltage and used to detect the change in the capacitance resulting from the transverse vibrations of the microbeam (sense mode). We formulate a fully-coupled multi-physics model of the electrically-actuated shallow arch microbeam combining the nonlinear Euler-Bernoulli beam theory with the nonlinear Reynolds equation governing the surrounding fluid domains (drive and sense zones). The model captures the inherent nonlinear physical aspects including the mid-plane stretching, the squeeze film damping, and fringing field effect. We validate the developed model by quantitatively comparing our nonlinear frequency-response against existing experimental results. We conduct static analysis to identify the occurrence of snap-through and pull-in instability for different initial midpoint rises. The coupled eigenvalue problem is also solved to compute the damped natural frequencies along with their corresponding beam and fluid mode shapes. The obtained natural frequencies are in good agreement with those reported in the literature. High sensitivity of the natural frequency to pressure variations is observed when decreasing the gap distance separating the microbeam from the fixed electrodes and reducing the initial midpoint rise of the curved microbeam.We also investigate the effect of breaking the symmetry of the microstructure on its dynamic response by introducing a slight perturbation in the mass distribution. The stability analysis reveals the occurrence of a new period doubling bifurcation point. Of interest, the location of this bifurcation point is observed to be sensitive to the pressure of the surrounding fluid medium. As such, we propose to exploit this nonlinear feature for design enhancement of the pressure sensor.

Bistability phenomena based on frequency-sensitive self-collimation in nonlinear photonic crystals

By introducing the change of beam behavior near the frequency sensitive self-collimation point, a new kind of bistability is observed in a finite nonlinear photonic crystal (PhC). The mechanism of such a PhC bistability is from the complex interplay between cavity resonance, nonlinearity and beam behavior. Additionally, it has unique properties, including: high frequency sensitivity, small volume, short switching time, robustness and position flexibility. With the consideration of beam behavior, a new theory based on the coupled-mode equation has been constructed, whose result agrees with the numerical one very well. The new PhC bistability could be widely used to design various optical devices, as a bistable all-optical switch has also been demonstrated.

Frequency Scanning Single-Ridge Serpentine Dual-Slot-Waveguide Array Antenna

This paper presents a novel one-dimensional (1D) frequency scanning dual-slot-waveguide array antenna with versatile advantages such as large scan volume, high frequency sensitivity, low cross-polarization and low sidelobe. Electromagnetic waves radiate through the leaky-wave dual slots, machined on the side chambers of the single-ridge serpentine waveguide. By properly designing the serpentine waveguide, which plays the role of delay line, such 1D frequency scanning array antenna can achieve 39° scanning over a frequency range from 9.7 GHz to 10.3 GHz, and high frequency sensitivity of 65°/GHz. The dual slots with all the adjacent monomers inclined in same direction are designed to acquire low cross-polarization and avoid high-order mode radiation. The cross-polarization is 45 dB lower than the corresponding co-polarization over the whole working band. Taylor aperture distribution is employed to achieve a low sidelobe (−21 dB). The nonresonance VSWR is below 1.2, and meanwhile the resonance VSWR remains a low level, around 2.5. Furthermore, our proposed 1D array as a building block can compose a novel 2D electric scanning array, with frequency scanning in one dimension and phase scanning in the orthogonal dimension. A 2D array consisting of three waveguide elements is simulated to predict the phase scanning performance, and the results indicate that a 120° scanning performance can be obtained. At last, a 1D serpentine dual-slot-waveguide array antenna is fabricated, whose measurements show good agreement with simulations.

Auditory evoked potentials of utricular hair cells in the plainfin midshipman, Porichthys notatus.

The plainfin midshipman, Porichthys notatus, is a soniferous marine teleost fish that generates acoustic signals for intraspecific social communication. Nocturnally active males and females rely on their auditory sense to detect and locate vocally active conspecifics during social behaviors. Previous work showed that the midshipman inner ear saccule and lagena are highly adapted to detect and encode socially relevant acoustic stimuli, but the auditory sensitivity and function of the midshipman utricle remain largely unknown. Here, we characterized the auditory evoked potentials from hair cells in the utricle of non-reproductive type I males and tested the hypothesis that the midshipman utricle is sensitive to behaviorally relevant acoustic stimuli. Hair cell potentials were recorded from the rostral, medial and caudal regions of the utricle in response to pure tone stimuli presented by an underwater speaker. We show that the utricle is highly sensitive to particle motion stimuli produced by an underwater speaker positioned in the horizontal plane. Utricular potentials were recorded across a broad range of frequencies with lowest particle acceleration (dB re. 1 m s-2) thresholds occurring at 105 Hz (lowest frequency tested; mean threshold -32 dB re. 1 m s-2) and highest thresholds at 605-1005 Hz (mean threshold range -5 to -4 dB re. 1 m s-2). The high gain and broadband frequency sensitivity of the utricle suggest that it likely serves a primary auditory function and is well suited to detect conspecific vocalizations including broadband agonistic signals and the multiharmonic advertisement calls produced by reproductive type I males.

Multi-Domain Entropy-Random Forest Method for the Fusion Diagnosis of Inter-Shaft Bearing Faults with Acoustic Emission Signals.

Inter-shaft bearing as a key component of turbomachinery is a major source of catastrophic accidents. Due to the requirement of high sampling frequency and high sensitivity to impact signals, AE (Acoustic Emission) signals are widely applied to monitor and diagnose inter-shaft bearing faults. With respect to the nonstationary and nonlinear of inter-shaft bearing AE signals, this paper presents a novel fault diagnosis method of inter-shaft bearing called the multi-domain entropy-random forest (MDERF) method by fusing multi-domain entropy and random forest. Firstly, the simulation test of inter-shaft bearing faults is conducted to simulate the typical fault modes of inter-shaft bearing and collect the data of AE signals. Secondly, multi-domain entropy is proposed as a feature extraction approach to extract the four entropies of AE signal. Finally, the samples in the built set are divided into two subsets to train and establish the random forest model of bearing fault diagnosis, respectively. The effectiveness and generalization ability of the developed model are verified based on the other experimental data. The proposed fault diagnosis method is validated to hold good generalization ability and high diagnostic accuracy (~0.9375) without over-fitting phenomenon in the fault diagnosis of bearing shaft.

A Unidirectional Beam-Scanning Antenna Excited by Corrugated Metal–Insulator–Metal Ground Supported Spoof Surface Plasmon Polaritons

A unidirectional beam-scanning antenna is proposed. The antenna is constructed by placing a series of circular radiating elements on a 2-mm dielectric slab backed by a corrugated metal–insulator–metal (CMIM) ground. The CMIM structure is introduced not only as a ground but also as a waveguide for spoof surface plasmon polaritons (SSPPs). The beam-scanning function is realized through the phase difference of SSPPs fed to the radiating elements. In addition, the CMIM ground reflects downward radiation waves onto upward space, leading to a unidirectional pattern and enhanced radiation gain. Both the numerical simulation and experiment results demonstrate the good performance of the proposed antenna. They validate that the antenna achieves unidirectional radiation and scanning angle of 57° when the frequency varies from 6.2 to 9 GHz with the frequency sensitivity of 20.4°/GHz. The realized gains are higher than 8.11 dBi over the entire band. Compared with the published works, this paper provides a novel feed technology, a simpler structure, and higher frequency sensitivity. The high-frequency sensitivity is beneficial to reduce the bandwidth burden of the entire system. The antenna has potential applications in satellite communication.

Hybridization-induced dual-band tunable graphene metamaterials for sensing

The infrared absorption spectrum due to structural vibrations in molecules has been widely used to resolve chemical identification. However, this method is limited by the weak molecule-light interaction. Graphene plasmon, having strong confinement and large field enhancement, provides a promising way to increase their interactions. Here we propose tunable hybridization-induced graphene nanostructures for sensing application. Our results reveal that when the symmetry of the graphene disk is broken by introducing a small circular defect, dual-band resonance can be excited at mid-infrared frequencies. The dual-band resonance peaks are produced by plasmon hybridization effect between two simple structures: graphene disks and circular defects. We investigate the influence of the size and position of the circular defect on the dual-band resonance peaks. We further explore the dual-band resonance peaks for sensing, and the sensitivity can reach 550 cm−1/RIU and the FOM can reach 20.4. Compared to the original graphene disk structure, the results show stronger resonance intensity and higher frequency sensitivity. Our findings provide a new platform for sensing, and moreover the dual-band resonance structure feature enables us to promote the development of multi-substance detection.

Measurements of ultrasonic deterrents and an acoustically branded hairdryer: Ambiguities in guideline compliance

Acoustic radiation from three commercial pest deterrents and two hair dryers were measured in an anechoic chamber. The deterrents were chosen because the frequency range at which they emit the most energy is either in the very high-frequency sound band (11.2-17.8 kHz) or the ultrasound band (greater than 17.8 kHz). These are sources that may be heard by a subset of the general population, with the young typically having better high frequency sensitivity. A hairdryer reported to increase the frequency of the motor noise above the audible hearing range was compared with a standard hairdryer. The outputs of the deterrents are compared against six international regulations and guidelines for audible and ultrasound exposure. Multiple ambiguities in the application of these guidelines are discussed. These ambiguities could lead to a device being considered as in compliance despite unconventionally high levels. Even if a device measured here meets a guideline, actual exposures can exceed those taken here and may therefore breach guidelines if the listener is closer to the device or reflections increase the exposure level.

Interference‐rejecting current measurement method with tunnel magnetoresistive magnetic sensor array

Innovative methods for wide range measurement of electric current remains an active research problem in modern power systems. Conventional methods based on magnetic field readouts have realized non-contact current measurement by interpreting magnetic flux density into electric current, such as Hall effect and Rogowski Coil arrangement. TMR magnetic sensor has spread its application for current measurement due to its miniaturization, low cost, high response frequency and high sensitivity. However, due to the superposition of unwanted magnetic field, the magnetic fieldunder measurement is strongly affected. In this paper, a four-sensor array design is proposed to solve this problem. Transcendental equations, which can not only calculate the current under measurement but also the interference current at random places, are constructed. Numerical simulations, finite element analysis (FEA) of the field and laboratory experiments were performed to verify the proposed method. It is shown that when targeted current is 100 A and interference is 820 A, the largest simulated error is 3.92 × 10−10; when targeted current is 100 A and interference is 1000 A, error with FEA is 2.3796%, when targeted current and interference are both 500 A, experimental error is 4.14%. This verifies the effectiveness of the proposed method.

Diffractive multifocal intraocular lens implantation in eyes with a small-diameter pupil

Postoperative outcome of diffractive multifocal intraocular lens (MIOL) implantation in eyes with a small-diameter pupil was evaluated. This non randomized case series involved 23 eyes of 23 patients who underwent diffractive MIOL implantation and whose preoperative photopic pupil diameter was ≤3.0 mm [small-diameter pupil (SDP) group], and 79 eyes of 79 patients implanted with the same MIOL whose pupil diameter was >3.0 mm as controls (LDP group). Contrast sensitivity of high spatial frequency (12, and 18 cycle per degree) and both 12.5% and 6% low-contrast visual acuity (VA) were significantly worse in the SDP group than in the LDP group (P = 0.04, 0.05, 0.05, 0.03). However, no significant difference was found between eyes in the SDP group with a postoperative pupil diameter greater than 3.0 mm and LDP group eyes. No significant differences were found in uncorrected and corrected distance VA (UDVA, CDVA), uncorrected and corrected near VA (UNVA, CNVA), contrast sensitivity with low spatial frequency, and defocus curve between the two groups. In conclusion, in eyes implanted with a diffractive MIOL, a pupil diameter of ≤3.0 mm deteriorates contrast sensitivity. This effect was eliminated postoperatively when pupil size was enlarged to >3.0 mm during surgery.

Enhanced magnetoelectric voltage in ferrite/PZT/ferrite composite for AC current sensor application

In this paper, we report the fabrication of a rare-earth free current sensor based on a PZT/NiCoZn-ferrite magnetoelectric (ME) trilayer composite disk. To improve the sensitivity of the sensor, the structure uses an in-plane series connection, which increases the ME voltage by two for a fixed volume. Then, we propose a full characterization of the sensor: electrical modeling, low and high frequency limits, sensitivity, linearity, distortion and resolution. The device is also evaluated under sinus, square, and triangle waveform currents, which are excitation signals commonly used in the field of electrical engineering. The current sensor shows high current sensitivity (90 mV/A), good linearity from 0.001 to 30 A and low added impedance (0.01 Ω) in a frequency range of 10 Hz–30 kHz for a very compact structure (4 cm3). It also exhibits a high resolution of 1 mA (for a 1 A peak signal) and good stability.

Enhanced detection of high frequency gravitational waves using optically diluted optomechanical filters

Detections of gravitational waves (GW) in the frequency band 35 Hz to 500 Hz have led to the birth of GW astronomy. Expected signals above 500 Hz, such as the quasinormal modes of lower mass black holes and neutron star mergers signatures are currently not detectable due to increasing quantum shot noise at high frequencies. Squeezed vacuum injection has been shown to allow broadband sensitivity improvement, but this technique does not change the slope of the noise at high frequency. It has been shown that white light signal recycling using negative dispersion optomechanical filter cavities with strong optical dilution for thermal noise suppression can in principle allow broadband high frequency sensitivity improvement. Here we present detailed modelling of AlGaAs/GaAs optomechanical filters to identify the available parameter space in which such filters can achieve the low thermal noise required to allow useful sensitivity improvement at high frequency. Material losses, the resolved sideband condition and internal acoustic modes dictate the need for resonators substantially smaller than previously suggested. We identify suitable resonator dimensions and show that a 30 $\mu$m scale cat-flap resonator combined with optical squeezing allows 8 fold improvement of strain sensitivity at 2 kHz compared with Advanced LIGO. This corresponds to a detection volume increase of a factor of 500 for sources in this frequency range.

Low-power integrating frequency difference-to-voltage converter with applications in injection-locked FLL

This paper presents a new integrating frequency difference-to-voltage converter (iFDVC) with applications in injection-locked frequency-locked loops (FLLs). The proposed iFDVC features low power consumption, high frequency sensitivity, a zero static frequency error, and a low sensitivity to PVT (process, voltage, and temperature) uncertainty. A detailed analysis of the time and frequency-domain behaviour of the iFDVC is presented. The effectiveness of the iFDVC is studied by embedding it in a FLL with a relaxation oscillator. To shorten locking process without sacrificing frequency accuracy, injection-locking is employed. The loop dynamics of the FLL with and without injection-locking are analyzed. The simulation results of an injection-locked FLL with the proposed iFDVC designed in an IBM 130 nm 1.2 V CMOS technology demonstrate that the injection-locked FLL has a lock time 4.5 times smaller and an acquisition range 59 times larger as compared with those of the corresponding FLL without injection-locking while consuming 60 $$\upmu$$ W only. The iFDVC was also implemented using off-shelf components and its performance was validated using measurement results.

Layout and Interconnect Optimization for Low-Power and High-Sensitivity Operation of $E$ -Band SiGe HBT Frequency Dividers

A layout and interconnect optimization techniques for low-power and high-sensitivity performance of static frequency dividers in $E$ -band is reported. The layout optimization provides optimal transistor placement and identifies critical interconnects, which allows to reduce their parasitics. These measures provide high operation frequency and good sensitivity of the divider without a need of investing additional dc current.

A high performance humidity sensor based on surface acoustic wave and graphene oxide on AlN/Si layered structure

A surface acoustic wave (SAW) humidity sensor based on AlN/Si (doped) layered structure and graphene oxide (GO) sensing layer is proposed for high sensitivity and low temperature coefficient of frequency. With the GO thin film, the sensitivity of the humidity sensor is increased to 42.08 kHz/RH% when the relative humidity is greater than 80%RH. The humidity sensor performs well even at both very low (≤10%RH) and very high (≥90%RH) detection range of humidity. The present sensor has low hysteresis, excellent short term repeatability and long term stability (variation less than ± 2%). The sensor also shows a fast response and short recovery time. Moreover, using the AlN/Si (doped) layered structure, the thermal stability of the sensor is significantly improved. After being covered with GO thin film, the temperature coefficient of frequency (TCF) of the sensor is further reduced to −22.1 ppm/°C, much smaller than the previously reported SAW humidity sensors.