Sweep Duration Research Articles

Influence of sweep duration on debonding detection of honeycomb structures based on acoustic band gap

Abstract Honeycomb structure is widely used in many fields, and its bond quality needs to be tested during manufacture process and in service. However, the efficiency, sensitivity, and feasibility can hardly be achieved simultaneously for traditional non-destructive testing methods. In the previous work, we have proposed a new debonding detection method using the acoustic band gap of honeycomb structures. Nevertheless, the influence of the detection parameters on the testing result has not been thoroughly investigated. In this paper, the effect of duration variation of the sweep signal used for exciting on the results is studied. Experimental results demonstrate that the transmission frequency response (TFR) of both the intact and the debonding area almost keep unchanged as the sweep duration varies from 1 s to 0.001 s. Theoretical analysis shows that the upper limit of the sweep rate is about 500 MHz/s, i.e., the minimum sweep duration is about 1.2 × 10−5 s to detect a bandgap with a bandwidth of about 6 kHz. Therefore, a shorter sweep duration can be used to further improve the detection efficiency.

Barely visible impact damage detection in CFRP composite using vibrothermography with narrowband sweep excitation

The extensive use of carbon fiber-reinforced plastic (CFRP) composite materials in various industries has posed new challenges for conducting effective structural health monitoring and nondestructive evaluation techniques. Based on local defect resonance (LDR), the vibrothermography with narrowband sweep excitation is proposed to detect BVIDs in the CFRP composite. The response spectrum of displacement at the impact crater was collected by a laser Doppler vibrometer, which was used to determine the frequency range of narrowband sweep excitation. The frequency range was further validated by the analysis of local defect resonance for thermal responses, and the sweep duration was also optimized. Subsequently, the proposed vibrothermography was employed to detect BVIDs with varying severity. The impact damage could be efficiently activated and a significant temperature rise was generated in the defective areas, which enhances the temperature contrast of the thermal images and facilitates the quantification of defects.

297 Impact of Navigated Intraoperative Ultrasound on Brain Shift and Gross Tumor Resection

INTRODUCTION: Intraoperative imaging and neuronavigation aid in achieving maximum tumor resection. However, tissue removal during surgery can cause brain shift, which alters the relative anatomy and “de-calibrates” the standard approaches. While intraoperative MRI (iMRI) is the gold-standard to correct for brain shift, it is expensive, time-consuming, and logistically difficult. As an alternative, we investigated an approach which combines intraoperative ultrasound (ioUS) technology with preoperative imaging to allow for real-time compensation of brain shift and assessment of extent of resection (EOR). METHODS: We prospectively enrolled patients undergoing neurosurgical tumor resection at Massachusetts General Hospital beginning April 2023. Patients were registered with Brainlab Ultrasound Navigation prior to surgery. ioUS sweeps were acquired before cortex incision, mid-resection, and post-resection with bkActiv and fused to preoperative MRIs. Four points around the tumor were longitudinally tracked to assess brain shift. Data included sweep duration, image processing speed, extent of brain shift as determined by intraoperative markers, and EOR assessed from the ioUS compared with postoperative MRIs. RESULTS: Seven patients were enrolled (average age 62 ± 15, 75% male) with frontal (n = 5), temporal (n = 1), and occipital (n = 1) gliomas (n = 4) and metastases (n = 3). All patients exhibiting total resection as determined by ioUS also demonstrated total resection on post-operative MRI, evaluated independently by a neuroradiologist. The average time of scan and image processing (n = 19) was 5.7 ± 1.9 and 27.8 ± 6.5 seconds respectively. CONCLUSIONS: Navigated ioUS offers accurate and efficient assessment of EOR during surgery for tumor resections. Furthermore, when brain shift is detected, navigated ioUS can allow for compensation and continued utilization of navigation via the acquisition of a brand new, navigable, intraoperatively acquired dataset.

Absolute calibration of a streaked optical pyrometer at nanosecond time scale with a luminescent concentrator

The Streaked Optical Pyrometer (SOP) is a visible diagnostic widely used to study the warm dense matter regime at high energy laser facilities, gas guns, or ion accelerators. It is usually coupled with a Velocity Interferometer System for Any Reflector (VISAR) diagnostic for simultaneous shock wave velocity, reflectivity, and temperature measurements to study the Equation of State (EOS) of materials. While VISAR is a well-mastered technology that provides velocity measurements with low relative uncertainties (close to percent), SOP diagnostics still suffer from high imprecision. In this article, we present a new calibration method in order to obtain absolute temperature measurements with reduced uncertainties. This approach is based on a novel light source: a Ce:YAG luminescent concentrator pumped by LEDs. This device produces enough optical power for calibration at the nanosecond sweep duration of the streak camera. As a demonstration, it has first been installed at the LULI facility and tested on quartz samples shocked at temperatures above 4000 K.

Simulation of Chorus Wave Excitation in the Compressed/Stretched Dipole Magnetic Field

AbstractThe properties of chorus waves have been extensively studied, which are important to understand chorus generation and wave‐particle interactions between chorus and energetic electrons. Observations reveal that there exists a distinct day‐night asymmetry for the properties of chorus waves, such as the sweep rate and duration, which is predicted to be relevant to the asymmetric configuration of Earth's background magnetic field. In this paper, using the one‐dimensional (1‐D) particle‐in‐cell (PIC) simulation model with a compressed/stretched dipole magnetic field, we study the dependences of the properties of rising‐tone chorus waves on the background magnetic field. It is demonstrated that the saturated amplitude and the chorus sweep rate increase while the chorus duration decreases with an increase of the compression factor ξ, which represents the compression/stretch degree of the field line. Moreover, the threshold of exciting chorus waves in the compressed dipole field is generally lower than that in the stretched dipole field. These results are useful to understand the chorus excitation and the day‐night asymmetry of chorus properties.

Efficient electron transfer in quantum dot chains controlled by a cubic detuning profile via shortcuts to adiabaticity

Long-distance fast and precise transfer of charge in semiconductor nanostructures is one of the goals for scalable electronic devices. We study theoretically the control of shuttling of an electron along a linear chain of semiconductor electrostatically defined quantum dots by an electric field pulse with nonlinear time-dependent profile. We show that this essential nonlinearity along with shortcuts to adiabaticity techniques speed up the electron transfer with high fidelity, while still holding great robustness under spin-flip interactions and inhomogeneities in the couplings of the chain. A given fidelity can be set experimentally by controlling the maximum sweep energy and duration of the control pulse.

Non-invasive auditory brainstem responses to FM sweeps in awake big brown bats

We introduce two EEG techniques, one based on conventional monopolar electrodes and one based on a novel tripolar electrode, to record for the first time auditory brainstem responses (ABRs) from the scalp of unanesthetized, unrestrained big brown bats. Stimuli were frequency-modulated (FM) sweeps varying in sweep direction, sweep duration, and harmonic structure. As expected from previous invasive ABR recordings, upward-sweeping FM signals evoked larger amplitude responses (peak-to-trough amplitude in the latency range of 3–5 ms post-stimulus onset) than downward-sweeping FM signals. Scalp-recorded responses displayed amplitude-latency trading effects as expected from invasive recordings. These two findings validate the reliability of our noninvasive recording techniques. The feasibility of recording noninvasively in unanesthetized, unrestrained bats will energize future research uncovering electrophysiological signatures of perceptual and cognitive processing of biosonar signals in these animals, and allows for better comparison with ABR data from echolocating cetaceans, where invasive experiments are heavily restricted.

Roles of wing flexibility and kinematics in flapping wing aerodynamics

Insects are excellent fliers because of their ability to generate precise wing kinematics and deform their wings for the sufficient production of unsteady aerodynamic forces. Most of the previous studies on the effects of wing kinematics on the aerodynamics have been limited to the use of rigid wings, and leaves the contribution of wing flexibility unknown. Here, an experiment was conducted to investigate the effect of varied sweep duration and timing of rotation on the unsteady aerodynamic characteristics of hovering flexible and rigid wings at Re of 104. This study found that the forces generated by the flexible wing showed a conspicuous phase delay, which was more sensitive to the change in sweep duration than the timing of rotation. The transient negative lift associated with rigid wings undergoing delayed and advanced wing rotations totally disappeared in the flexible case. A digital particle image velocimetry (DPIV) measurement at the middle of stroke revealed a slight difference in the vortical structures surrounding the two wings in terms of proximity to the shed trailing-edge vortices (TEVs). Also, the linearly twisted nature of the flexible wing caused the coherent leading-edge vortex (LEV) to be stabilized throughout the wingspan. This increased the radial limit of the delayed stall from 3.6c in the rigid wing to 4.8c in the flexible wing. In general, the flexible wing with symmetric and delayed wing rotations generated the higher efficiency. The corresponding net force vectors were tilted in an almost vertical direction in comparison to the rigid wing. This is an indication that natural fliers adopt specific wing kinematics in addition to their wing deformation for the upward titling of their net force vector, which will significantly enhance their aerodynamic performance.

A Reconfigurable Architecture for Continuous Double-Sided Swept-Laser Linearization

This paper reports a reconfigurable architecture to generate and maintain the linearity of frequency-swept semiconductor lasers for both current rising (up-sweep) and falling (down-sweep) edges, respectively. This method combines both passive and active controls to achieve a high frequency-sweep linearity using an integrated digital architecture. Both the passive and active control utilize the same feedback—the interferometric signal of the laser's output—which has a frequency proportional to laser frequency-sweep velocity. This architecture is highly reconfigurable, allowing key parameters to be changed, including sweep velocity, tuning range, and sweep duration, making it a highly versatile and flexible approach suitable for a range of semiconductor lasers and a variety of applications. This architecture was implemented on an FPGA to validate the concept and evaluate its performance. By precisely tracking the interferometric feedback signal, it was found that this approach allowed a semiconductor laser to generate and maintain a phase error of less than $\frac{\pi }{2}$ within the regions of interest at different sweep velocities for both up-sweep and down-sweep cycles. Given that the delay length of the interferometer is 226 ns, the instantaneous optical frequency error is within 0.12% at 1552 nm.

Interfacial Charge Dynamics in Metal-Oxide–Semiconductor Structures: The Effect of Deep Traps and Acceptor Levels in GaN

Using numerical simulations, we investigate the effects of deep traps and deep acceptor levels in magnesium-doped $\mathrm{Ga}\mathrm{N}$ on interface charges in the semiconductor-oxide interface. Specifically, in this work we address two open issues observed in experimental studies on $\mathrm{Ga}\mathrm{N}$ trench metal-oxide-semiconductor field-effect transistors. (i) We investigate the observed clockwise hysteresis in the transfer characteristics and elucidate the underlying physical mechanism causing it. By employing appropriate models for substitutional carbon at nitrogen sites (${C}_{N}$) and nitrogen vacancies (${V}_{N}$), we calculate the hysteresis dependence on the trap concentrations and the measurement sweep duration ${T}_{s}$. We show that ${C}_{N}$ acceptor traps in $p$-$\mathrm{Ga}\mathrm{N}$ are likely responsible for this phenomenon and the largest hysteresis is predicted for a sweep duration of ${T}_{s}\ensuremath{\approx}30\phantom{\rule{0.2em}{0ex}}\mathrm{s}$. (ii) We also address the apparent inconsistency between the experimental and theoretically predicted magnesium-ionization levels and the variations of the measured transfer characteristics, specifically the threshold voltage. We show that the bands bending in the channel area creates a layer in which magnesium is completely ionized. As a result, the magnesium partial ionization does not have an effect and, while the threshold voltage decreases, nor does the breakdown voltage, as observed experimentally. The measured threshold voltage, which is lower than the theoretically predicted value, is caused by fixed and trapped charges at the interface, in agreement with values reported in the literature.

Comparison of time and frequency domain features’ immunity against lift-off in pulse-compression eddy current imaging

This paper reports a comparison between imaging procedures based on time- and frequency-domain features applied to eddy current data collected on an Aluminium alloy benchmark sample. Both the defect detection capability and the immunity against lift-off are analysed. Historically, the pulsed eddy current method was introduced to improve the performance of eddy current testing both in terms of increased penetration depth and lift-off invariance by exploiting time-domain features analysis, commonly precluded when using single- or multi-tone excitations. In this work, such analysis is instead accomplished by using a swept-frequency excitation signal along with an optimized pulse-compression procedure. This approach allows the user to easily tune the energy delivered to the system by increasing the sweep duration to improve on demand the resultant Signal-to-Noise Ratio (SNR) without losing the capability of time-domain feature extraction. The imaging procedure makes use of amplitude and phase features of both frequency- and time-domain data where time-phase is defined through the Hilbert transform of the pulse-compression output. The detection capability of various imaging strategies, namely A-, B- and C-scans, are compared in terms of inspection depth and lift-off robustness by using the SNR merit factor. It is shown that time-domain features outperform frequency-based ones in terms of SNR for the case of deeper defects and that phase features are robust against lift-off variations for both time and frequency domains. In addition, the analysis of time-amplitude images clearly shows the presence of lift-off invariant points. To our knowledge, this is the first experimental evidence of the lift-off invariance points retrieved after applying pulse-compression in combination with coded excitation instead of using directly pulsed, multi-tone or single-tone sinusoidal signals. This not only confirms previous results achieved by the authors but also demonstrates that pulse-compression eddy current can represent a solution to combine the advantages of pulsed and sinusoidal excitation strategies.

Model evaluation of rapid 4-dimensional lung tomosynthesis

PurposeThis is an investigation of a lung motion digital tomosynthesis (DTS) model using combined stationary detector and stationary cold cathode x-ray sources at projection acquisition rates that exceed the present norms. The intent is to reduce anatomical uncertainties from artifacts inherent in thoracic 4-dimensional computed tomography (CT). Methods and materialsParameters necessary to perform rapid lung 4-dimensional DTS were studied using a conventional radiographic system with linear motion of the x-ray source and a simple hypothetical hardware performance model. Hypothetical rapid imaging parameters of sweep duration, projections per second, pulse duration, and tube current (mA) were derived on the basis of 0.5 mm and 1 mm motion captures per phase, 10 and 15 breaths per minute (bpm), 10 to 40 mm breathing amplitude, and 2 signal-to-noise ratio (SNR) levels. Anterior-posterior and lateral projection images of a normal size anthropomorphic thorax phantom with iodine contrast inserts were collected and reconstructed with an algebraic algorithm to study the effects of reduced x-ray output associated with field emission cold cathodes composed of carbon nanotubes or metal Spindt-type. Radiographic projections were collected at 3 SNR levels that were set at standard clinical DTS milliampere-seconds (mAs) and reduced corresponding to 50% and 25% standard DTS mAs to simulate a reduced x-ray output. ResultsThe DTS SNR of the inserts was superior in all reconstructions at clinical mAs versus automatic exposure-control radiographs and superior in 3 of 4 at the 50% and 25% mAs levels. The most demanding performance parameters corresponding to 40 mm amplitude, 15 bpm, 0.5 mm motion capture limit, and 61 projections were sweep duration (10.4 msec), projection rate (5862 projections per second), pulse duration (0.161 msec), current 189 mA anterior-posterior, and 653 mA lateral. ConclusionsFeasibility depends on the output performance of stationary cold cathode hardware being developed for DTS. Present image receptor technology can accommodate frame acquisition rates.

Dynamic Measurement of Arterial Liver Perfusion With an Interventional C-Arm System.

Objective intraprocedural measurement of hepatic blood flow could provide a quantitative treatment end point for locoregional liver procedures. This study aims to validate the accuracy and reproducibility of cone-beam computed tomography perfusion (CBCTp) measurements of arterial liver perfusion (ALP) against clinically available computed tomography perfusion (CTp) measurements in a swine embolization model. Triplicate CBCTp measurements using a selective arterial contrast injection were performed before and after complete embolization of the left lobe of the liver in 5 swine. Two CBCTp protocols were evaluated that differed in sweep duration (3.3 vs 4.5 seconds) and the number of acquired projection images (166 vs 248). The mean ALP was measured within identical volumes of interest selected in the embolized and nonembolized regions of the perfusion map generated from each scan. Postembolization CBCTp values were also compared with CTp measurements. The 2 CBCTp protocols demonstrated high concordance correlation (0.90, P < 0.001). Both CBCTp protocols showed higher reproducibility than CTp in the nontarget lobe, with an intraclass correlation of 0.90 or greater for CBCTp and 0.83 for CTp (P < 0.001 for all correlations). The ALP in the embolized lobe was nearly zero and hence excluded for reproducibility. High concordance correlation was observed between the CTp and each CBCTp protocol, with the shorter CBCTp protocol reaching a concordance correlation of 0.75 and the longer achieving 0.87 (P < 0.001 for both correlations). Dynamic blood flow measurement using an angiographic C-arm system is feasible and produces quantitative results comparable to CTp.

A tunable local field potentials computer simulator to assess minimal requirements for phase–amplitude cross-frequency-coupling estimation

ABSTRACTThe quantitative study of cross-frequency coupling (CFC) is a relevant issue in neuroscience. In local field potentials (LFPs), measured either in the cortex or in the hippocampus, how γ-oscillation amplitude is modulated by changes in θ-rhythms-phase is thought to be important in memory formation. Several methods were proposed to quantify CFC, but reported evidence suggests that experimental parameters affect the results. Therefore, a simulation tool to support the determination of minimal requirements for CFC estimation in order to obtain reliable results is particularly useful. An approach to generate computer-simulated signals having CFC intensity, sweep duration, signal-to-noise ratio (SNR), and multiphasic-coupling tunable by the user has been developed. Its utility has been proved by a study evaluating minimal sweep duration and SNR required for reliable θ–γ CFC estimation from signals simulating LFP measured in the mouse hippocampus. A MATLAB® software was made available to facilitate methodology reproducibility. The analysis of the synthetic LFPs created by the simulator shows how the minimal sweep duration for achieving accurate θ–γ CFC estimates increases as SNR decreases and the number of CFC levels to discriminate increases. In particular, a sufficient reliability in discriminating five different predetermined CFC levels is reached with 35-s sweep with SNR = 20, while SNR = 5 requires at least 140-s sweep.

76–81-GHz CMOS Transmitter With a Phase-Locked-Loop-Based Multichirp Modulator for Automotive Radar

This paper presents the design of a linear frequency-modulated continuous-wave (FMCW) radar transmitter (TX) for automotive radar applications. The TX has a wide operating range from 76 to 81 GHz by employing a frequency-doubling architecture using an LC voltage-controlled oscillator operating at 38–40.5 GHz and a differential frequency doubler using a single transformer. A chirp generator is integrated into the TX, which provides various frequency chirp profiles with programmable chirp slope and sweep duration. The proposed CMOS FMCW TX can be applied to various modulation algorithms for multiple target detection and the avoidance of ghost targets. The TX is implemented using 65-nm CMOS technology. The chip size is 1.48 $\,\times\,$ 1.85 mm $^{2}$ . The measurement results shows a 76–81-GHz frequency range and 3-dBm output power while dissipating 320 mW. The phase-noise density of the TX is ${-}{\hbox{83.33}}$ dBm/Hz at an offset frequency of 1 MHz when the output frequency is 77 GHz.

Volumetric Security Alarm Based on a Spherical Ultrasonic Transducer Array

Most of the existent alarm systems depend on physical or visual contact. The detection area is often limited depending on the type of the transducer, creating blind spots. Our proposition is a truly volumetric alarm system that can detect any movement in the intrusion area, based on monitoring the change over time of the impulse response of the room, which acts as an acoustic footprint. The device depends on an omnidirectional ultrasonic transducer array emitting sweep signals to calculate the impulse response in short intervals. Any change in the room conditions is monitored through a correlation function. The sensitivity of the alarm to different objects and different environments depends on the sweep duration, sweep bandwidth, and sweep interval. Successful detection of intrusions also depends on the size of the monitoring area and requires an adjustment of emitted ultrasound power. Strong air flow affects the performance of the alarm. A method for separating moving objects from strong air flow is devised using an adaptive thresholding on the correlation function involving a series of impulse response measurements. The alarm system can be also used for fire detection since air flow sourced from heating objects differ from random nature of the present air flow. Several measurements are made to test the integrity of the alarm in rooms sizing from 834-2080m3 with irregular geometries and various objects. The proposed system can efficiently detect intrusion whilst adequate emitting power is provided.

Correction of Dechirp Distortion in Long-Distance Target Imaging with LFMCW-ISAR

The combined linear frequency modulation continuous wave (LFMCW) and inverse synthetic aperture radar (ISAR) can be used for imaging long-distance targets because of its long-distance and high resolution imaging abilities. In this paper, we find and study the dechirp distortion phenomenon (DDP) for imaging long-distance targets by a dechirp-on-receive LFMCW radar. If the targets are very far from the radar, the maximum delay-time is not much smaller than a single sweep duration, and the dechirp distortion is triggered since the distance of the target is unknown in a LFMCW-ISAR system. DDP cannot be ignored in long-distance imaging because double images of a target appear in the frequency domain, which reduces resolution and degrades image quality. A novel LFMCW-ISAR signal model is established to analyze DDP and its negative effects on long-distance target imaging. Using the proportionately distributed energy of double images, the authors propose a method to correct dechirp distortion. In addition, the applicable scope of the proposed method is also discussed. Simulation results validate the theoretical analysis and the effectiveness of the proposed method.

Common approach for compensation of axial motion artifacts in swept-source OCT and dispersion in Fourier-domain OCT

Swept-source optical coherence tomography (SS-OCT) is sensitive to sample motion during the wavelength sweep, which leads to image blurring and image artifacts. In line-field and full-field SS-OCT parallelization is achieved by using a line or area detector, respectively. Thus, approximately 1000 lines or images at different wavenumbers are acquired. The sweep duration is identically with the acquisition time of a complete B-scan or volume, rendering parallel SS-OCT more sensitive to motion artifacts than scanning OCT. The effect of axial motion on the measured spectra is similar to the effect of non-balanced group velocity dispersion (GVD) in the interferometer arms. It causes the apparent optical path lengths in the sample arm to vary with the wavenumber. Here we propose the cross-correlation of sub-bandwidth reconstructions (CCSBR) as a new algorithm that is capable of detecting and correcting the artifacts induced by axial motion in line-field or full-field SS-OCT as well as GVD mismatch in any Fourier-domain OCT (FD-OCT) setup. By cross-correlating images which were reconstructed from a limited spectral range of the interference signal, a phase error is determined which is used to correct the spectral modulation prior to the calculation of the A-scans. Performance of the algorithm is demonstrated on in vivo full-field SS-OCT images of skin and scanning FD-OCT of skin and retina.

Vocal behavior of the Mongolian gerbil in a seminatural enclosure

This study represents the first effort to obtain a comprehensive library of adult Mongolian gerbil (Meriones unguiculatus) vocalizations recorded in a variety of behavioural contexts. In Phase I of the study, a gerbil colony was introduced into a seminatural enclosure and allowed to breed naturally over an observation period of 19 months. During this period, detailed observations of gerbil social and vocal behaviour were made. In Phase II, this knowledge was used to stage natural behavioural scenarios among adult gerbils in which high-quality recordings of vocalizations could be obtained, and the spectro-temporal properties of these vocalizations analysed. Calls generally occurred in interactive social situations, such as same-sex aggression, mating, food dispute, alarm, and disturbance by conspecifics. Additionally, brief ultrasonic calls were associated with investigation of a new setting and were named ‘contact calls’. Vocalizations were classified by behavioural context and analysed with respect to spectral and temporal characteristics. Calls encompassed a broad range of frequencies (approx. 3-45 kHz); most calls possessed significant energy at two or more harmonics in addition to the fundamental frequency. Calls generally lasted approx. 4-500 ms and were emitted in sequences of 3-20 variants with silent intervals. Such natural call series had significant low-frequency AM content below 8 Hz. Calls within an individual behavioural class had substantial variability in both spectral and temporal properties, but were significantly different from all other call classes in one or more of average fundamental frequency, frequency sweep range, duration, or frequency sweep direction.

Cross-channel amplitude sweeps are crucial to speech intelligibility

Classical views of speech perception argue that the static and dynamic characteristics of spectral energy peaks (formants) are the acoustic features that underpin phoneme recognition. Here we use representations where the amplitude modulations of sub-band filtered speech are described, precisely, in terms of co-sinusoidal pulses. These pulses are parameterised in terms of their amplitude, duration and position in time across a large number of spectral channels. Coherent sweeps of energy across this parameter space are identified and the local transitions of pulse features across spectral channels are extracted. Synthesised speech based on manipulations of these local amplitude modulation features was used to explore the basis of intelligibility. The results show that removing changes in amplitude across channels has a much greater impact on intelligibility than differences in sweep transition or duration across channels. This finding has severe implications for future experimental design in the fields of psychophysics, electrophysiology and neuroimaging.