Wideband Probe Research Articles

High Resolution Backscattering Acoustic Tomography Method Based on Reverse Time Migration for Arbitrary Wideband Sounding Signal

Backscattered wave acoustic tomography using wideband probing signals makes it possible to obtain three-dimensional (3D) images of scattering inhomogeneities. Signal processing based on the reverse time migration (RTM) method allows one to take into account the influence of background refractive obstacles of the medium to minimize distortions of reconstructed tomographic images. We propose a noniterative method of acoustic tomography in an immersion medium based on RTM approach supplemented with linear signal preprocessing to enhance resolution of reconstructing tomography images. The visualization of scattering objects is based on wave inversion from the measurement area considering the probing wave field specially distorted to perform regularized back convolution. The applicability of the proposed method for visualizing scattering objects in water is shown analytically, numerically and experimentally. The proposed method is resistant to noise according to regularization. The results obtained show the agreement between the numerical and analytical solution. Using the example of sounding with linear frequency modulation signals, it is demonstrated that the proposed method allows increasing the resolution of tomographic images in comparison with conventional RTM. The novelty of the proposed method is the preliminary filtration of the forward propagation wave in the course of solving the inverse problem. This approach improves the resolution of tomographic images and allows considering the influence of obstacles.

Radar imaging complex with SAR and ASR for aerospace vechicle

The subject of study in the article is the algorithms for radio monitoring of the Earth in a wide field of view from aerospace transport. The goal is to design a structural diagram of a radio complex that can operate simultaneously in two modes: modified synthetic aperture (SAR) and aperture synthesis (ASR), in accordance with algorithms synthesized by the maximum likelihood method. The modified SAR mode allows obtaining high-resolution radio images in the observation angle range ±(20°...50°) from the direction to the nadir. A method of combining a modified SAR algorithm is used, which differs from the classical imaging algorithm by the possibility of obtaining a higher spatial resolution, the payment for this is the complication of the signal processing algorithm associated with the implementation of decorrelating filters that expand the spectrum of received signals in each receiving path, and the ASR mode, which allows imaging using passive or active radar principles. The passive ASR mode provides for the imaging in the observation angle range of ±20° from the nadir based on the results of processing signals of its own broadband radio-thermal radiation, and the active mode – in the same observation angle range, but using the broadband noise signal of the backlight. An important result in the formation of a radio image in the specified viewing area when using the active mode of the ASR is that the images are close in physical content, namely, proportional to the specific effective reflection surface of the underlying surface. In addition, a distinctive feature of the synthesized algorithms is the use of wideband probing signals and, accordingly, the same input paths of receivers, which makes it possible to increase the signal-to-noise ratio of the output effect. Conclusions. The scientific novelty of the results obtained is as follows: a structural diagram of the radio complex was developed on the basis of algorithms synthesized by the maximum likelihood method. For the formation of a radio image in the radio complex, a combination of SAR and ASR (with two modes of operation) is implemented. This implementation is important, since it allows obtaining high-resolution images in the observation angle range of ±50° from the direction to the nadir. It is advisable to place the complex on airplanes, helicopters and spacecraft (preferably those that move in low orbits).

High-order probe compensation algorithm for ultra-wide-band probe in spherical near-field measurement

In order to increase the precision of spherical near-field antenna measurement systems based on wide-band probes, probe compensation algorithms supporting high-order azimuth mode (HOPC) are needed to process the near-field measurement data. In this study, an HOPC algorithm is realized based on the iterative strategy in the reference [ 3 ] for solving the spherical-mode transmission equation with high-order probes. This algorithm is applied to a dual-ridged wide-band horn probe that works in the frequency range of 2–18 GHz. Using dipoles array antennas as examples, the higher precision of the high-order algorithm is illustrated compared with that of the low-order algorithm. The convergence of the algorithm under different conditions is also systematically tested. These results indicate, firstly, the higher-order effects are more remarkable for higher frequency and secondly, when the antenna under test can totally be covered by the 6 dB domain of the main lobe, the iterative process can converge to satisfactory precision within several iterations. Therefore, the algorithm in this paper for HOPC can increase the precision of the spherical near-field system while still preserves high computational efficiency.

Real-Time Estimation of the Tip-Sample Interactions in Tapping Mode Atomic Force Microscopy With a Regularized Kalman Filter

The real-time and accurate measurement of tip-sample interaction forces in Tapping Mode Atomic Force Microscopy (TM-AFM) is a remaining challenge. This obstruction fundamentally stems from the causality of the physical systems. Since i) the input of the dynamic systems propagates to the output with some delay, and ii) , multiple different inputs can generate the same output, there exist no measurement or estimation technique that can estimate the force input of the systems in real-time without phase and amplitude distortion. However, an approximate and delayed estimation can still be possible. This article presents a general-purpose algorithm which aims to estimate an approximation of the force input of TM-AFM with minimum delay and error. For this reason, first, the input estimation problem is converted to an ill-posed state observation problem. Then, a Tikhonov-like regularization technique is applied to eliminate the ill-conditioning and estimate the force input using a linear Kalman filter. The proposed input observer is remarkably robust, real-time in the order of the sampling frequency, and applicable for any Linear Time Invariant (LTI) system with a (semi-) periodic process. Simulation and experimental results show that using the proposed algorithm with a wide-band AFM probe; one can determine the tip-sample forces with only a few percent error and a delay in the order of sampling time. Unlike the existing force estimation techniques for AFM, this algorithm does not require any prior knowledge of the force-distance relationship which can be very beneficial for the closed-loop control of AFM.

Immersion laser-induced ultrasound imaging of solids with complex macroscopic geometry of surface

In this paper a real-time experimental system and algorithms for immersion two-dimensional laser ultrasonic imaging of solids with complex geometry of surface are presented. Wideband probe ultrasonic pulse is generated photoacoustically in an opaque plate, which absorbs pulsed laser radiation. The back-scattered acoustic field is recorded by a multi-element piezoelectric array. The signals are used to reconstruct refraction-corrected ultrasonic images, which are post-processed to determine positions of the external and internal boundaries of the object. The numerical simulations are carried out to verify the developed algorithms. The proposed approach allowed measuring the positions of the boundaries of the polymethyl methacrylate (PMMA) sample with accuracy of ∼0.1 mm in the direction of the probe beam propagation, and ~0.2-0.3 mm in the perpendicular direction.

Method of estimating linear dimensions of object by subsurface radar sounding

The methods for recognizing subsurface objects by the length of radar range portraits in a georadar with wideband probing signals, optimized for the maximum likelihood criterion for complex hypotheses, for the case of a known internal noise power, have been developed. It is shown that, using the optimal method, an energy gain is achieved when the threshold value of the probability of correct recognition is reached.

Comparison of wideband and clinical acoustic reflex thresholds in patients with normal hearing and sensorineural hearing loss

Acoustic reflex thresholds (ARTs) obtained with a wideband (WB) probe and an adaptive threshold detection procedure were compared to ARTs using a clinical system. Ipsilateral and contralateral ARTs were elicited in a group of 79 adults with normal hearing (NH) and 51 adults with sensorineural hearing loss (SNHL). ARTs were obtained for both methods using activator tones of 0.5, 1.0, and 2.0 kHz and broadband noise (BBN) with a bandwidth extending to 4.0 kHz for the clinical and 8.0 kHz for the WB ART. Results were similar for ipsilateral and contralateral ARTs. Tonal ARTs with the clinical method were slightly elevated for the SNHL group for all three activator tones, but for the WB method were elevated at 2.0 kHz where the average hearing loss was greatest (47 dB HL). ARTs for BBN were higher for the clinical method than the WB method for both groups, and the difference between groups was around 5 dB for the clinical method but 12 dB for the WB method. This suggests that ARTs with the WB method and BBN activator extending to 8 kHz are a more sensitive indicator of high-frequency SNHL than the clinical method. Individual reflex patterns will also be presented.

Wide bandwidth fiber-optic ultrasound probe in MOMS technology: Preliminary signal processing results

An ultrasonic probe consisting of two optical fiber-based miniaturized transducers for wideband ultrasound emission and detection is employed for the characterization of in vitro biological tissues. In the probe, ultrasound generation is obtained by thermoelastic emission from patterned carbon films in Micro-Opto-Mechanical-System (MOMS) devices mounted on the tip of an optical fiber, whereas acousto-optical detection is performed in a similar way by a miniaturized polymeric interferometer. The microprobe presents a wide, flat bandwidth that is a very attractive feature for ultrasonic investigation, especially for tissue characterization. Thanks to the very high ultrasonic frequencies obtained, the probe is able to reveal different details of the object under investigation by analyzing the ultrasonic signal within different frequencies ranges, as shown by specific experiments performed on a patterned cornstarch flour sample in vitro. This is confirmed by measurements executed to determine the lateral resolution of the microprobe at different frequencies of about 70μm at 120MHz. Moreover, measurements performed with the wideband probe in pulsed-echo mode on a histological finding of porcine kidney are presented, on which two different spectral signal processing algorithms are applied. After processing, the ultrasonic spectral features show a peculiar spatial distribution on the sample, which is expected to depend on different ultrasonic backscattering properties of the analyzed tissues.

A statistical assessment of ambient electromagnetic field using body-worn multiaxial sensors

The electromagnetic field exposure of the population due to wireless communications originates from both down-link and up-link emissions. Although the main contribution comes generally from the latter (e.g., higher by three to five orders of magnitude for the 2G), the former must be considered as well, because they are continual, and as contributions can be competitive for some cases (e.g., in femtocells). Sensor and exposimeter networks (NW) can be deployed by the operators themselves (to enrich feedback information from their own NW) or by independent external stakeholders such as regulatory agencies or local authorities. When sensors are directly worn by a user, body proximity effects – notably the masking effect – can introduce significant errors in the ambient field measurement. A methodology of the statistical assessment of this harmful effect is proposed in this article. It is mainly based on electromagnetic simulations (and partly on measurements) of a triaxial sensor – composed of three orthogonal wideband probes devoted to the evaluation of the field components – placed at different positions of a set of whole body phantoms. The main original contribution of the proposed approach is that both the isolated sensor calibration procedure and the assessment of the measurement errors are based on statistical analyses accounting for the propagation environment. The quantitative results are obtained using statistical channel models for polarimetric and non-polarimetric measurements in various propagation scenarios. Some quantitative results examples are presented. Eventually, preliminary corrections schemes are proposed. L'exposition de la population aux ondes électromagnétiques dues aux communications radio émane tant des émissions descendantes que montantes. Bien que la contribution dominante provienne généralement de ces dernières (supérieures de trois à cinq ordres de grandeur pour la 2G par exemple), les premières doivent également être prises en compte, notamment parce qu'elles sont permanentes, mais aussi parce que les deux contributions peuvent être compétitives dans certains cas (par exemple dans les femtocells ). Des réseaux de capteurs et d'exposimètres peuvent être déployés par les opérateurs eux-mêmes (leur permettant d'enrichir les informations remontées par leur propre réseau) ou par des acteurs extérieurs indépendants, tels que des organismes de contrôle réglementaire ou des collectivités locales. Si les capteurs sont directement portés par l'utilisateur, les effets de proximité du corps – notamment l'effet de masquage – peuvent introduire des erreurs très significatives dans la mesure du champ ambiant. Nous proposons dans cet article une méthodologie d'estimation statistique de cet effet néfaste. L'approche est majoritairement fondée sur des simulations électromagnétiques (et partiellement sur des mesures) d'un capteur triaxial – constitué de trois sondes large bande placées orthogonalement dédiées à la mesure des composantes du champ – placé à différentes positions de fantômes « corps entier ». L'originalité principale de cette contribution est qu'elle repose sur des analyses statistiques prenant en compte les conditions de propagation, que ce soit dans la procédure de calibration du capteur isolé ou dans l'évaluation des erreurs de mesure. Les résultats quantitatifs sont obtenus à partir de modèles statistiques de canaux, pour des mesures polarimétriques ou non, pour différents scénarios de propagation. Quelques résultats quantitatifs sont présentés. Pour terminer, des méthodes envisageables de correction encore à l'étude sont présentées.

A no-tune no-match wideband probe for nuclear quadrupole resonance spectroscopy in the VHF range

Nuclear quadrupole resonance (NQR) spectroscopy is a method for the characterization of chemical compounds containing so-called quadrupolar nuclei. Similar to nuclear magnetic resonance (NMR), the sample under investigation is irradiated with strong radiofrequency (RF) pulses, which stimulate the emission of weak RF signals from the quadrupolar nuclei. The signals are then amplified and Fourier transformed so as to obtain a spectrum. In principle, narrowband NQR spectra can be measured with NMR spectrometers. However, pure NQR signals require the absence of a static magnetic field and several special applications require the characterization of a substance over a large bandwidth, e.g. 50–100% of the central frequency, which is hardly possible with standard NMR equipment. Dedicated zero-field NQR equipment is not widespread and current concepts employ resonating probes which are tuned and matched over a wide range by using mechanical capacitors driven by stepper motors. While providing the highest signal to noise ratio (SNR) such probes are slow in operation and can only be operated from dedicated NMR consoles. We developed a low-cost NQR wideband probe without tuning and matching for applications in the very high frequency (VHF) range below 300 MHz. The probe coil was realized as part of a reactive network which approximates an exponential transmission line. The input reflection coefficient of the two developed prototype probe coils is ≤ 20 dB between 90–145 MHz and 74.5–99.5 MHz, respectively. Two wideband NQR spectra of published test substances were acquired with an SNR of better than 20 dB after sufficient averaging. The measured signals and the SNR correspond very well to the theoretically expected values and demonstrate the feasibility of the method. Because there is no need for tuning and matching, our probes can be operated easily from any available NMR console.

Wideband Probe for Magnetic Quadrupole Resonance Spectroscopy

Article Wideband Probe for Magnetic Quadrupole Resonance Spectroscopy was published on September 7, 2013 in the journal Biomedical Engineering / Biomedizinische Technik (volume 58, issue SI-1-Track-L).

An approach to expansion of the scanning sector of active phased antenna arrays with linear-frequency-modulated wideband probe signal

The process of construction of the directional pattern of active phased antenna arrays with emission of wideband linear-frequency-modulated signals is analyzed. Factors responsible for the appearance of distortions in the directional pattern are established and an approach to elimination of these distortions is proposed.

Dual-Polarized Corrugated Horns for Advanced Measurement Applications

Recent advances in the design of orthomode junctions (OMJs) have created new devices capable of achieving as much as a 1:4 bandwidth, while maintaining the high performance of traditional OMJ designs. The new OMJ technology is based on an inverted-ridge structure, with four symmetrical feeding points for external balanced feeding, stabilizing the frequency dependence of the OMJ. This paper discusses the achievable performance and limitations of wideband probes with multiple corrugated apertures. It shows measured and predicted design examples of apertures covering up to 1:2 bandwidth in the L- to Ka-band range.

VOLUME CLUTTER ELIMINATION, ROUGH INTERFACE REVERBERATION SUPPRESSION, AND TARGET RESONANCE CONVERGENCE IN HETEROGENEOUS MEDIA USING AN ITERATIVE TIME REVERSAL MIRROR

The presence of the clutter of volume scattering and the echo return from rough interface hinders the detection of target in heterogeneous media. This work investigates the application of an iterative time reversal mirror to mitigate the difficulties. Numerical simulations based on pseudospectral finite-difference time-domain method are performed in one and two layered media. A wideband probe pulse is launched to initiate the process, and the time-reversed echo received at the same position is retransmitted as the renewed input signal for next iteration, and repeat the procedures iteratively. The results illustrate as the number of iteration increases, small volume clutter is eliminated, interface reverberation is suppressed relatively, and the echoes will converge to a time-harmonic waveform that corresponds to an object's dominant resonance mode. The detection of target is achieved by extracting this important acoustic signature.

Wideband ipsilateral measurements of middle-ear muscle reflex thresholds in children and adults

The goals of the current study were to: 1) evaluate the feasibility of a new wideband approach to measuring middle-ear muscle reflex (MEMR) status, and 2) to test the hypothesis that ipsilateral thresholds elicited with 1 or 2 kHz tones and broadband noise activators on a wideband acoustic transfer function (WATF) system are lower than thresholds elicited on a clinical system. Clinical MEMR tests have limitations, including the need for high activator levels to elicit a shift in a narrowband probe (e.g., a 0.226 or 1 kHz tone). Wideband MEMR tests using WATFs may elicit the reflex at lower levels because a wideband probe (click) is used and the threshold detection criterion can be wideband. Mean wideband MEMR thresholds across 40 normal-hearing adult ears were 2.2-4.0 dB lower than clinical MEMR thresholds, depending on the activator and specific WATF test used (admittance magnitude or energy reflectance). Wideband MEMR has potential clinical utility beyond the adult population, including use in newborn and preschool hearing screenings. In a newborn hearing screening, for example, wideband MEMR could be completed with the same system as otoacoustic emissions. However, further investigations in infants and young children are needed.

High resolution channel sounder with narrowband low interference characteristics

Channel impulse response (CIR) measurements typically require the transmission of high power wideband probing signals to characterise channels. These signals are potentially harmful to users of the spectrum under assessment This paper presents a method of high resolution channel sounding causing only low levels of wideband interference and details a measurement system developed to characterise the band currently used for global navigation satellite systems (GNSS), where high levels of probing signal would have safety of life implications.

Design and Study of Wide-Band Patch Antenna Fed by Meandering Probe

A wide-band probe fed patch antenna with low cross polarization and symmetrical broadside radiation pattern is proposed and studied. By employing a novel meandering probe feed and locating a patch about 0.1/spl lambda//sub 0/ above a ground plane, a patch antenna with 30% impedance bandwidth (SWR<2) and 9 dBi gain is designed. The far field radiation pattern of the antenna is stable across the operating bandwidth. Parametric studies and design guidelines of the proposed feeding structure are provided.

Signal processing techniques for inverse problems in stochastic propagation and scattering channels

The basic signal processing techniques associated with inverse problems are signal extraction, deconvolution, signal and signal parameter estimation, channel modeling and characterization. Maximum entropy, minimum cross-entropy, Kullback-Liebler divergence and other information theoretic criteria have been widely used for regularization of underdetermined inversion. We show how maximum entropy and continuous wavelet transforms can be used for spreading function (reflection density function) estimation. If the signal source or receivers are in motion through heterogeneous medium with randomly rough boundaries, propagation and scattering channels are stochastic. Stochastic channels can be characterized by stochastic Greens functions and spreading functions. If the medium probing signals are narrow band, spreading functions are random functions that show how the received signal is spread in delay and Doppler. For wideband probing signals, spreading function spread the received echo in time and time-scale dilation. If the probing signal satisfies admissibility conditions for CWT, wideband spreading functions can be estimated by inverting CWT. Rebollo-Neira and Fernandez-Rubio have shown that the continuous wavelet transform is an optimal solution of the inverse problem, estimation of the spreading function, in a maximum entropy sense. [Work supported by Office of Naval Research Code 333 and Code 321 US.]

Exposure measuring techniques for wide band mobile radiocommunications

The paper illustrates the limits and performances of different experimental monitoring techniques, which are applied to digitally modulated radiofrequency electromagnetic fields used for mobile telecommunications. Different experimental set-ups have been developed, verified and applied for the analysis and characterisation of wide band probes and narrow band measuring procedures.

Wideband Reflectance Measures of the Ipsilateral Acoustic Stapedius Reflex Threshold

The purpose of this study was to develop a method for acoustically measuring the ipsilateral acoustic stapedius reflex threshold by using wideband shifts in energy reflectance and admittance. A group of 27 young adult subjects with normal hearing participated in the study. Contralateral reflex thresholds were first measured for a 4000 Hz activator tone (maximum level, 92 dB SPL), using a clinical method with a 226 Hz probe tone. Ipsilateral and contralateral reflex thresholds were then measured by using an experimental wideband reflectance and admittance system that used a band-filtered click (200 to 2000 Hz) as the probe stimulus, presented simultaneously with the 4000 Hz activator tone. Reflex thresholds for the wideband system were determined by using statistical tests of the magnitude of the reflex responses as well as their correlation with other reflex responses. Clinical and experimental reflex thresholds were obtained for 9 of the 27 subjects for all conditions. Clinical reflex thresholds were absent for 8 subjects for whom experimental reflex thresholds were present and were present for 5 subjects who had absent experimental reflex thresholds for one or more conditions. An additional 5 subjects had absent reflex thresholds in all conditions, consistent with the low maximum level of the activator. Wideband measures of contralateral reflex thresholds were approximately 3 dB lower than those obtained with the clinical system. The magnitudes of the group means of the reflex responses were similar for ipsilateral and contralateral stimulations. Wideband measures of reflectance and admittance may be used to estimate the ipsilateral acoustic stapedius reflex threshold by separating in frequency the spectral energies of the wideband probe stimulus from the activator stimulus. This technique holds promise for measuring reflex thresholds for individuals with absent reflex thresholds through the use of standard clinical methods.