Efficient General Reflectarray Design and Direct Layout Optimization with a Simple and Accurate Database Using Multilinear Interpolation

In this work, a simple, efficient and accurate database in the form of a lookup table to use in reflectarray design and direct layout optimization is presented. The database uses N-linear interpolation internally to estimate the reflection coefficients at coordinates that are not stored within it. The speed and accuracy of this approach were measured against the use of the full-wave technique based on local periodicity to populate the database. In addition, it was also compared with a machine learning technique, namely, support vector machines applied to regression in the same conditions, to elucidate the advantages and disadvantages of each one of these techniques. The results obtained from the application to the layout design, analysis and crosspolar optimization of a very large reflectarray for space applications show that, despite using a simple N-linear interpolation, the database offers sufficient accuracy, while considerably accelerating the overall design process as long as it is conveniently populated.

Strength Development Monitoring of Cemented Paste Backfill Using Guided Waves

The strength of cemented paste backfill (CPB) directly affects mining safety and progress. At present, in-situ backfill strength is obtained by conducting uniaxial compression tests on backfill core samples. At the same time, it is time-consuming, and the integrity of samples cannot be guaranteed. Therefore guided wave technique as a nondestructive inspection method is proposed for the strength development monitoring of cemented paste backfill. In this paper, the acoustic parameters of guided wave propagation in the different cement-tailings ratios (1:4, 1:8) and different curing times (within 42 d) of CPBs were measured. Combined with the uniaxial compression strength of CPB, relationships between CPB strength and the guided wave acoustic parameters were established. Results indicate that with the increase of backfill curing time, the guided wave velocity decreases sharply at first; on the contrary, attenuation of guided waves increases dramatically. Finally, both velocity and attenuation tend to be stable. When the CPB strength increases with curing time, guided wave velocity shows an exponentially decreasing trend, while the guided wave attenuation shows an exponentially increasing trend with the increase of the CPB strength. Based on the relationship curves between CPB strength and guided wave velocity and attenuation, the guided wave technique in monitoring the strength development of CPB proves feasible.

Fast Evaluation of Caprock Strength Sensitivity to Different CO2 Solutions Using Small Sample Techniques

The Draupne shale is a rock formation functioning as overburden for gas reservoirs in the Norwegian Sea and potentially as caprock for future CO2 storage locations as well. In this paper, the Draupne shale was exposed to several fluids: CO2 gas, supercritical CO2, CO2 gas dissolved in brine, supercritical CO2 dissolved in brine, as well as brine and dry air. The motivation for the exposure tests was to investigate whether injected CO2 in a reservoir coming into contact with the caprock could change the caprock’s mechanical properties and increase the risk for leakage of the stored CO2. In addition, a systematic exposure study will provide more insight into the various processes susceptible of altering the shale’s shear strength and acoustic velocity, such as clay hydration, mineral dissolution, and capillary forces. Due to the low permeability of the shale, experiments were conducted on mm-sized disk samples, reducing fluid diffusion into the shale, and allowing for many repeated tests on disks close by in the original core. The punch method, where a small circle is punched out of the shale, was used to assess shear strength, while continuous wave technique was used to assess ultrasonic velocity. Results show that the shale is not noticeably sensitive to CO2, in the sense that no additional weakening is observed in the presence of CO2 as compared to brine exposure. This last weakening effect is probably due to poor matching between pore fluid salinity and exposure brine strength.

Comparative Analysis of the Filling Capacity of Simulated Lateral Canals of Two Bioactive Root Canal Sealers Using Warm Gutta-Percha Technique

The aim of this study was to evaluate ex vivo the sealing achieved at simulated lateral canals (SLC) and the quality of filling according to their position in the root canal after using the same filling technique. SLC were created at three levels in 55 teeth and divided into two groups depending on the root canal sealer used (1: BioRoot® RCS, 2: GuttaFlow® bioseal). They filled them with the continuous wave technique and submitted to a diaphanization technique. The samples were analyzed using a magnifying lens (20×), pictures were taken, which proceeded to linear measurement with the ImageJ® program and used a filling score system with five grades (0 to 4, 0 and 1 not acceptable, 2 to 4 acceptable); BioRoot® RCS has got a greater proportion than GuttaFlow® bioseal for SLC filled acceptably at 10 mm from the apex (p < 0.05). The highest proportion of SLC filled acceptably was found in the middle third (6 mm) (p < 0.05), followed by the apical third (3 mm) and the coronal third (10 mm). The difference between apical and coronal third could be significant; BioRoot® RCS has been better than GuttaFlow® bioseal for filling SLC in the coronal third of the teeth. Studies on the characteristics of these cements are missing to explain these differences.

Soft Mango Firmness Assessment Based on Rayleigh Waves Generated by a Laser-Induced Plasma Shock Wave Technique

Many methods based on acoustic vibration characteristics have been studied to indirectly assess fruit ripeness via fruit firmness. Among these, the frequency of the 0S2 vibration mode measured on the equator has been examined, but soft-flesh fruit do not show the 0S2 vibration mode. In this study, a Rayleigh wave is generated on a soft mango fruit using the impulse excitation force generated by a laser-induced plasma shock wave technique. Then, the flesh firmness of mangoes is assessed in a non-contact and non-destructive manner by observing the Rayleigh wave propagation velocity because it is correlated with the firmness (shear elasticity), density, and Poisson’s ratio of an object. If the changes in the density and Poisson’s ratio are small enough to be ignored during storage, then the Rayleigh wave propagation velocity is strongly correlated to fruit firmness. Here, we measure the Rayleigh wave propagation velocity and investigate the effect of storage time. Specifically, we investigate the changes in firmness caused by ripening. The Rayleigh wave propagation velocity on the equator of Kent mangoes tended to decrease by over 4% in 96 h. The Rayleigh wave measured on two different lines propagated independent distance and showed a different change rate of propagation velocity during 96-h storage. Furthermore, we consider the reliability of our method by investigating the interaction of a mango seed on the Rayleigh wave propagation velocity.

Influence of Different Crack Factors on Acoustic Wave Signals Using Orthogonal Analysis

The existence of cracks in key components of engineering equipment is a huge threat to the safe operation of the equipment. The influence of four factors (length, location, orientation, and width of the crack) on the attenuation characteristic of signal propagation is studied through simulation and experiment. The orthogonal experimental design is applied to design the simulation scheme, and the signal affected by the four factors is simulated by the finite-difference time-domain method. The degree of influence of the different factors is evaluated by conducting an analysis of range and an analysis of variance. The results show that the influence of crack length and location on signal relative attenuation is more remarkable according to the significance level α = 0.05, followed by crack orientation and crack width. The attenuation trend in the experimental results is similar to the simulation. Therefore, the longer the crack length is, the easier it is to be detected by the acoustic wave technique, while the effect of crack orientation and crack width on identifying cracks is limited. The study successfully establishes the relationship between signal parameters and crack factors and offers a theoretical foundation for evaluating the status of cracks in key components.