Propagation Path Length Research Articles

Acceleration Estimation of Signal Propagation Path Length Changes for Wireless Sensing

Acceleration Estimation of Signal Propagation Path Length Changes for Wireless Sensing

Multi-angle speed-of-sound imaging with sparse sampling to characterize medical tissue properties

Medical Speed-of-sound (SoS) imaging, which can characterize medical tissue properties better by quantifying their different SoS, is an effective imaging method compared with conventional B-mode ultrasound imaging. As a commonly used diagnostic instrument, a hand-held array probe features convenient and quick inspection. However, artifacts will occur in the single-angle SoS imaging, resulting in indistinguishable tissue boundaries. In order to build a high-quality SoS image, a number of raw data are needed, which will bring difficulties to data storage and processing. Compressed sensing (CS) theory offers theoretical support to the feasibility that a sparse signal can be rebuilt with random but less sampling data. In this study, we proposed an SoS reconstruction method based on CS theory to process signals obtained from a hand-held linear array probe with a passive reflector positioned on the opposite side. The SoS reconstruction method consists of three parts. Firstly, a sparse transform basis is selected appropriately for a sparse representation of the original signal. Then, considering the mathematical principles of SoS imaging, the ray-length matrix is used as a sparse measurement matrix to observe the original signal, which represents the length of the acoustic propagation path. Finally, the orthogonal matching pursuit algorithm is introduced for image reconstruction. The experimental result of the phantom proves that SoS imaging can clearly distinguish tissues that show similar echogenicity in B-mode ultrasound imaging. The simulation and experimental results show that our proposed method holds promising potential for reconstructing precision SoS images with fewer signal samplings, transmission, and storage.

Microwave photonics demodulation based on a fiber loop and a virtual Fabry-Perot interferometer for sapphire fiber temperature sensors.

The interferometric optical path difference (OPD) induced by changes in the measurand within the microwave band is comparatively smaller than that observed in the realm of lightwave, thereby leading to diminished sensitivity in sapphire fiber Fabry-Perot interferometers (FPIs) within the microwave band. In order to enhance sensitivity, we propose a microwave photonics sensing system predicated on a fiber loop and a virtual FPI. By employing a constructed fiber loop, the propagation path length of the modulated signal can be extended with an increase in the number of loops. The correlation between the number of loops and sensitivities is examined both theoretically and experimentally. Our findings illustrate a direct relationship between sensitivity and the number of loops, demonstrating an increment sensitivity with each additional loop. Specifically, the FPI frequency domain temperature sensitivity in the 5th loop measures approximately 4652.95 kHz/°C, marking an enhancement of around 9.24 times compared to the 1st loop.

Semi-analytical simulation of ultrasound wave propagation in large plate-like structures

The ultrasonic guided wave (UGW) has gained considerable popularity among NDE methods for damage detection and structural health monitoring (SHM) due to its high frequency and low attenuation. Lamb waves are reflected or diffracted by structure boundaries, discontinuities, and damages. It is possible to determine a structure's health, defects, and locations based on its UGW propagation characteristics. In this study, we propose an efficient modeling method for UGW propagation through damaged and scattering plates by combining the Modal Pencil method with Wave Finite Element (WFE) and Hybrid FE/WFE methods and verifying the results with a high-precision elastic finite element model (FEM). With this approach, the transducer-excited ultrasonic field can be modeled, as well as its steady-state and transient propagation, scattering, and reflections at defects and boundaries. Long-range propagation configurations can be efficiently addressed by this method because its computation efficiency is independent of propagation path lengths. As part of the case study, we study the propagation of Lamb waves through a joint metal thin-walled structure with embedded damage. In the case study, different sensor locations are used to validate the received UGW signals quantitatively. Our findings will contribute to the development of a digital twin for monitoring structural health by providing an efficient and robust approach to modeling ultrasound propagation in damaged and large plate-like structures.

Toughening effect and mechanism of rice straw Fiber-reinforced lime soil

Lime-stabilized soil used for subgrade is prone to brittle damage under loading because of low toughness. Based on this phenomenon, the toughening effects of anticorrosive rice straw fibers on the lime-stabilized soil and its internal mechanism have been studied in this paper. Different fiber contents (0.2 wt%, 0.6 wt%, 1.0 wt%) and fiber lengths (0–10 mm, 10–20 mm, 20–30 mm) were studied. Three-point bending tests, unconfined compressive strength tests and triaxial compression tests were conducted on the rice straw fiber-reinforced lime soil. Energy absorption, deformation index, and brittleness index were evaluated under flexure, compression, and shear. The toughness change from energy, deformation, and strength was studied based on these. The toughening mechanism of fiber reinforcement was analyzed from the mechanism of fiber-soil interaction, the energy absorption threshold of the damage process, the damage pattern of specimens and the length of the crack propagation path. The results showed that with the increase in fiber content and fiber length, the energy absorption and deformation index of the damage process increased while the brittleness index decreased. The brittle damage pattern was improved, and the toughness increased. The fibers connect the soil particles on both sides of the fracture surface through the bridging effect, form a three-dimensional reinforcement network to restrict the soil particle movement and consume a lot of energy during the interaction with soil, which causes the increase in the energy absorption threshold of soil. Thus, the toughness of the lime-stabilized soil is improved.

Effect of annealing temperature on mechanical properties of TC21 titanium alloy with multilevel lamellar microstructure

The purpose of the present work is to reveal the effect of annealing temperature on the microstructure and mechanical properties of multilevel lamellar microstructure of TC21 titanium alloy in triple heat treatments, where the annealing temperatures are 760, 800 and 840 °C, respectively. The multilevel microstructure consists of β grain, α colony (αc), α plates (αp) and aged α plates (αs). The strength, plasticity, impact toughness and fracture toughness of the material were tested. The microstructure was characterized by using optical microscopy (OM), scanning electron microscopy (SEM), laser scanning confocal microscope (LSCM) and electron backscatter diffraction (EBSD). Results show that the size of αc increases and the widths of αp and βt increase gradually with the increase in annealing temperature. The number of αs precipitated on β matrix increases sharply and their size becomes smaller after aging treatment. The strength of TC21 titanium alloy increases as increasing annealing temperature while plasticity decreases. The αs is a critical unit which plays an important role in controlling strength of the alloy through Hall-Petch fitting. Furthermore, increasing the size of αc and decreasing the size of αp and αs are beneficial to increase the strength of the alloy. The impact toughness and fracture toughness of the alloy increase firstly then decrease with the increase in annealing temperature. The synergistic effect originating from different level α phase determine the toughness of the alloy. Massive cleavage and intergranular fractures in the fracture contribute to the increased length of crack propagation path so as to the decrease of toughness of the alloy. Meanwhile, it is confirmed found the toughness is also related to the change of size of αc after annealing treatment. And too large or too small size of αc is not conducive to the improvement of the toughness of the alloy.

First Detection of Global Ionospheric Disturbances Associated with the Most Powerful Gamma Ray Burst GRB221009A

We present the first report of global ionospheric disturbances due to the most powerful Gamma Ray Burst GRB221009A occurred on 9 October 2022. Very Low Frequency (VLF) and Low Frequency (LF) sub-ionospheric radio signals are used to diagnose the effect of the GRB on the lower ionosphere. Both daytime and nighttime effects are analyzed in VLF and LF bands. The magnitude of VLF signal perturbations varied with the propagation condition (day/night), path length, and frequency of the signal. The recovery times for the VLF/LF signals to get back to their pre-GRB levels varied from 2–60 min. Radio signals reflected from the E-region ionosphere for nighttime VLF signals and daytime LF signals showed greater effects compared to the daytime VLF signals reflected from the lower parts of the D-region.

Time-Lapse Cross-Well Monitoring of CO2 Sequestration Using Coda Wave Interferometry

In this study, we explored the capability of coda wave interferometry (CWI) for monitoring CO2 storage by estimating the seismic velocity changes caused by CO2 injection. Given that the CWI method is highly efficient, the primary aim of this study was to provide a quick detection tool for the long-term monitoring of CO2 storage safety. In particular, we looked at monitoring with a cross-well geometry. We also expected that CWI could help to reduce the inversion errors of existing methods. Time-lapse upgoing waves and downgoing waves from two-component datasets were utilized to efficiently monitor the area between the wells and provide a quick indication of possible CO2 leakage. The resulting mean velocity changes versus the depth indicated the depth where velocity changes occurred. Combining the upgoing and downgoing wavefields provided a more specific indication of the depth range for changes. The calculated velocity changes were determined using the time shift between the time-lapse wavefields caused by CO2 injection/leakage. Hence, the resulting velocity changes were closely related to the ratio of propagation path length through the CO2 injection/leakage layer over the length of the entire travel path. The results indicated that the noise level and repeatability of the time-lapse datasets significantly influenced the results generated using CWI. Therefore, denoising and time-lapse processing were very important for improving the detectability of any change. Applying CWI to time-lapse cross-well surveys can be an effective tool for monitoring CO2 in the subsurface at a relatively low computational cost. As a highly efficient monitoring method, it is sensitive to changes in the seismic response caused by velocity changes in the subsurface and provides additional constraints on the inversion results from conventional travel time tomography and full waveform inversion.

Updates to global empirical models for infrasonic signal celerity and backazimuth from ground truth data

Global empirical models for infrasonic signal celerity (the epicentral distance divided by the total travel time) and backazimuth deviation (the difference between the measured and predicted backazimuth assuming great circle propagation), are used for the association of infrasound automatic detections, event location and acoustic propagation simulation validation. Following a previous methodology to develop a regional celerity-range model (Nippress et al., 2014), we developed a software suite for consistent analysis of a global ground truth database, allowing estimation of empirical models for celerity and backazimuth. We observe 304 detections in the 0.32–1.28 Hz passband, with propagation path lengths of between 25 and 6280 km. Models derived from these observations suggest the backazimuth deviation distribution is range-independent, 92% of the detections studied have a deviation ≤ ±5º. However, the celerity model, produced through fitting the travel-times with a linear regression model, is range-dependent. The celerity model bounds are determined using a quantile regression fit to the travel-time residuals, and are consistent with the current understanding of infrasound propagation. At 10 + years since the publication of the last global celerity-range model, this study provides a timely update.UK Ministry of Defence © Crown Owned Copyright 2022/AWE

Modelling and characterisation ultrasonic phased array transducers for pipe inspections

Nuclear pipes require regular inspection to prevent critical damage and extend their safe working lifetime. Ultrasonic inspection using phased array transducers is a Non-Destructive Testing (NDT) method used to monitor the condition of pipes, providing internal integrity information using multiple small transducer elements. This grants a controllable ultrasonic beam that provides more detail than a conventional single element transducer. This paper presents a hybrid simulation model to characterise phased array ultrasonic transducers for pressure pipe inspections. The paper focuses on identifying defects on pipe surfaces, which have total propagation path lengths in the order of 170 ultrasound wavelengths. Simulating inspections with such large path lengths is challenging due to unreliable results from numerical dispersion errors in large finite element models. The model presented here combines the benefits of finite element modelling with analytical extrapolation to overcome the issue of large propagation distances. A practical experiment demonstrates and verifies that the hybrid simulation model matches real world inspections. Inspection accuracy was quantified using the hybrid simulation model over frequency (5, 7.5 and 10 MHz) and number of elements (8, 16 and 32) to inspect two defect shapes (rectangular and V-shape). The 10 MHz transducer showed the highest resolution for the depth measurement, while the 5 MHz transducer presented the strongest penetration to inspect the defects on the pipe's outer surface. The largest aperture transducer, 32 elements, brought about the most accurate defect size measurement. This work serves to inexpensively guide the selection and later deployment of phased array inspection tools in nuclear pipe defect detection and monitoring.

Non-Markov behavior of acoustic phase variance in the atmospheric boundary layer

The Markov approximation is widely used in wave propagation in random media. This approximation is valid if the propagation path length is greater than the scale of the medium inhomogeneities affecting a particular statistical moment of a wave field and the moment changes insignificantly over this scale. These conditions might be violated for the variance of the phase fluctuations and other statistical moments of acoustic signals that have propagated through atmospheric turbulence: the scale of the largest eddies can be hundreds of meters, and fluctuations in the acoustic refractive index are relatively strong. In the current article, the phase variance of a spherical sound wave in statistically inhomogeneous turbulence is formulated without the Markov approximation. For propagation ranges smaller than the scale of the largest eddies, the phase variance without the Markov approximation is significantly smaller than when this approximation is employed. As the range increases, the difference between the two results tends toward a constant value (a ‘memory’ effect), which might be significant in many applications. The phase variance without the Markov approximation agrees better with the experimental data on sound propagation through the atmosphere, while the variance calculated with this approximation significantly overpredicts the data.

Research on Control Strategy of Design Change Cross-Module Propagation

In the process of product design, design changes are unavoidable due to the diversification of customer requirements and the advancement of key technologies. Although modules are supposed to be functionally independent and “low-coupling” in modular products, the design change in a module can still propagate into other modules due to the interfaces among them, and this propagation increases the product development lead-time and costs. This study aims to solve the problem of cross-module propagation in design change. First, the dependence of modules on interfaces is analyzed from the perspectives of complex network characteristics, change propagation characteristics, and cost dependence, and then the correlation between modules is determined. Second, the cross-module change propagation impact is evaluated considering node importance, change cost, and propagation path length. The control strategies of cross-module design change propagation are proposed from the aspects of increasing the tolerance of interface and reducing the dependence of modules on interface, etc. Finally, a certain type of sanitation vehicle cab is utilized as an example to demonstrate the assessment process of the cross-module propagation impact of design change and to verify the feasibility of the proposed method and control strategies.

Effect of aging temperature on mechanical properties of TC21 alloy with multi-level lamellar microstructure

This paper aims to reveal the effect of aging temperature on strength, impact toughness and fracture toughness of TC21 alloy with multi-level lamellar microstructure. The multi-level lamellar microstructures of TC21 alloy were prepared by solid solution at 1000 °C, annealing at 800 °C and respectively aging at 550 °C, 600 °C and 650 °C. The multi-level structures include β grains, α colony (αc), primary α phase (αp) and aged α plates (αs). The microstructures were performed on using optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), laser scanning confocal microscope (LSCM) and image analysis software. Results show that as aging temperature goes up, the size of αs increases and the segregation of alloy elements increases, while the β grain, grain boundary α phase (Gα) and αc almost remain unchanged. Hall-Petch formula is used to reveal that αs phase is the minimum control unit of strength. Fine grain strengthening, volume fraction of α phase (Vα) and element segregation have great influence on mechanical properties. In the impact experiment, microstructure deformation and secondary cracks consume more energy, while cleavage fracture consumes less energy. The TEM analysis found that the coordination of microstructure deformation became worse after aging. Fracture analysis shows that the size of αc plays an important role in crack propagation, and the crack propagation path always tends to cut αc vertically and pass through it. Whether the size of αc is large or small, it is not conducive to the increase of crack propagation path. Crack propagation path length and the interface energy consumed by different fracture mechanisms should be taken into consideration when there are more crack propagation paths and the fracture toughness decreases in the multi-level lamellar microstructure of TC21 alloy.

Experimental evaluation of pseudo-sound in a parametric array.

Parametric arrays have been widely investigated due to their high directivity in the low-frequency region when measuring the acoustic characteristics of materials, such as sound transmission and reflection properties, in the limited space of acoustic water tanks. Because a parametric array utilizes nonlinear interaction across the frequency components, nonlinear phenomena arise in both the acoustic medium and the hydrophone system. The unwanted nonlinear sound generated in the hydrophone and instrumentation is termed pseudo-sound. This study devised an experiment to measure the pseudo-sound without a truncator to assess the effect of the pseudo-sound in the near field. In order to separately measure the pseudo-sound, the hydrophone was placed close to the projector so that the pseudo-sound was dominantly generated. The method is based on the fact that, if we can suppress a parametric signal by minimizing the propagation path length in the medium, the resulting measured signal can be attributed to the pseudo-sound. The resultant signal levels were matched to the levels at corresponding distances based on the primary levels of a (separately conducted) distance-varying experiment. Finally, the suitability of the proposed technique was evaluated by comparing its results with the pseudo-sound levels measured using a truncator.

Towards Exploring the Influence of Community Structures on Information Dissemination in Sina Weibo Networks

The power of online social networks to propagate information within communities and from one community to the next is undeniable. Both network structure and information propagation affect each other; they restrict and cooperate with each other. However, they can also dynamically reshape the network topology of user’s social relationship in this process. The above process ultimately forms a feedback loop: the network structure affects how information spreads, while information propagation reshapes network topologies, so both evolve in concert over time. Using information propagation trees (IPT) of posts from the Sina Weibo microblogging site, we conducted a null model-based analysis to determine the influence of community structures on information propagation. We first generated randomized copies of the IPTs and then mined community structures from the originals and copies for comparison. An in-depth examination of the results in terms of improved significant profile, the length of information propagation path, and the relevance of the nodes in the propagation path indirectly reveals the inhibitory effect of community structures on information propagation.

Surface Electric Field Variations Due to Different Human Postures for Wireless Endoscopy Applications

Radio signal strength indicator (RSSI)-based localization methods for wireless capsule endoscopy (WCE) application require a patient to wear on-body sensors detecting the RF signals from the capsule. The main advantage of WCE is to allow the patient to live normally and to move freely during the natural transit time, which could take up to 73 hours. Changes in posture can be accompanied by the movement of soft tissues in the abdominal region. This will affect the propagation path length between on-body receiving sensors and the ingested wireless capsule, and consequently the received signal strength (RSS). This article explores potential variations in RSSI measurements created by postural change. Retroreflective markers placed in direct contact with the skin of a participant were used to represent appropriate locations of the on-body slot antennas, which could be used for WCE localization. Optical motion capture technology was used to determine an estimate of the location of the markers and corresponding skin position for different postures. The relative displacement of the markers from their initial location (the standing posture) was a maximum of 24 mm for the lying posture (supine position) for the participant with a BMI of 29 kg/m2. The maximum variation of the surface electric field of 13.77 dB was calculated using the attenuation path loss (PL) model for the human abdominal region propagation environment at 2.45 GHz. If not anticipated, posture-induced variations in RSSI can produce misleading interpretations and will require adjustments of WCE localization algorithms.

Performance of Free-space Optical Communication Systems using Optical Amplifiers under Amplify-forward and Amplify-received Configurations

: In concerning the growth of era digital technology that has on the stage of indutrial revolution 4.0, the demand for broadcasting the information in huge ammount is mandatory and reaching the user into the last mile as well. This urgent demand must be supported with reliable communications platform that meet those growth and development. Free-space optical (FSO) communications is one of the platform that has some potentials to be implemented to meet this demand. In this paper, Wavelength Division Multiplexing (WDM) on FSO that carrying data rate on 80 Gbps is investigated through simulation. The configuration of FSO is setup on the scheme of amplify-forward and amplify-received which each of one is using an optical amplifier. The investigation is seeking the best performance of optical signal amplification between EDFA and SOA under the atmospheric channel. From the simulation, we find that EDFA has better performance than SOA as the optical signal amplification for 8 channels of C-band in order to carry huge information and reaching the last mile user. The maximum of propagation path length under the FSO channel for scheme of amplify-forward and amplify received using EDFA is 1.7 Km where the performance of BER can be achieved at 10-6.

Design and Validation of an Adaptive Cubesat Transmitter System using a Thermal Vacuum Chamber (TVAC)

CubeSat in a low earth orbit primarily uses a UHF transmitter with a fixed RF output power. In this paper, the design of the CubeSat transmitter with adaptive power control ability is presented. The design drive is to optimise the SNR and overcome the variability of the propagation path length due to different ground station elevation angles by adjusting its transmitting power. The TVAC test is conducted to validate the performance of the adaptive function in the transmitter. The TVAC is used to emulate the satellite condition in an outer space environment. Four thermal cycles starting from +60°C to -20°C with less than 10-5Pa pressure condition are employed, which was conducted at the KIT CeNT, Japan. The transmitter was integrated inside the satellite structure as a complete CubeSat system. The output power of the transmitter is tested from 0.5W to 2W based on the proposed satellite adaptive mode. The frequency stability of the transmitter is monitored and complies with an average of 70% below requirement, which is less than 2ppm. The results indicate that the RF output power is adjustable to operate as the proposed CubeSat adaptive transmitter in a thermal vacuum condition, which was first developed in Malaysia.

Transformation of an ultra-wideband electromagnetic pulse in the process of its propagation through a large laboratory plasma

The transformation of a subnanosecond ultrawideband electromagnetic pulse (UWB EMP) in a large-volume transparent plasma has been demonstrated experimentally using a large-scale KROT plasma device. The column of the plasma generated in the device chamber has a length of more than 4 m and a diameter of more than 1 m. This allows one to implement the regime of quasiuniform ionization, which is necessary to simulate UWB EMP propagation through the ionosphere. It is shown that the length of the wave propagation path in the plasma is sufficient for dispersion transformation of the pulse retaining the envelope of its frequency spectrum.

Design and validation of an adaptive CubeSat transmitter system

CubeSat in low earth orbit (LEO) primarily uses an amateur radio-band transmitter with a fixed specification. Nevertheless, the LEO satellite does not have an orbital velocity that equates to one sidereal day. Therefore, the ground station antenna views the satellite at different elevation angles which result in varied propagation path lengths. In this paper, an adaptive transmitter is designed to optimise the LEO satellite communication link and overcome the variability of the propagation path length issue due to different ground station elevation angles. A satellite communication link and operation analyses are performed to identify the relationship between the variation of the elevation angle so as to determine the optimum signal-to-noise ratio (SNR), improve data rate and increase the power efficiency of an adaptive link. Based on the results, a model is developed to control the adaptive configuration. The SNR and power consumption performance of the developed transmitter is compared with commercial transmitters. The results indicate that the transmitter output power is adjustable from 0.5 W to 1 W, and the data rate is selectable between 9600 bps and 19,200 bps. Compared to other CubeSat transmitters, the developed adaptive transmitter demonstrates more than 20% improvement in terms of SNR optimisation, additional throughput and power reduction.