Sergio J. Sanabria

Air-coupled ultrasound inspection of glued laminated timber

Abstract A novel air-coupled ultrasound (ACU) 120 kHz normal transmission system enabled successful imaging of bonding and saw cut defects in multilayered glulam beams up to 280 mm in height with a signal-to-noise ratio (SNR) of 40 dB. The main wave propagation paths were modeled; quasi-longitudinal and quasi-transverse modes were coupled in each lamella and the sound field was found to be shifted from the insonification axis as a function of the ring angle, leading to interference of wave paths in the receiver and to 15 dB amplitude variability in defect-free glulam. The assessment was improved with spatial processing algorithms that profited from the arbitrary scanning resolution and high reproducibility of ACU. Overlapped averaging reduced in-band noise by 15 dB, amplitude tracking captured only the first incoming oscillation, thus minimizing diffraction around defect regions, and image normalization compensated 6 dB of systematic amplitude variability across the fiber direction. The application of ACU to in situ defect monitoring was demonstrated by using multiparameter difference imaging of measurements of the same sample with and without saw cut defects. The segmentation of the defect geometry was improved significantly and the amplitude variability was reduced by 10 dB. Further work is planned to model additional insonification setups and grain and density heterogeneities.

Damage evolution in wood: synchrotron radiation micro-computed tomography (SRμCT) as a complementary tool for interpreting acoustic emission (AE) behavior

Abstract Tensile tests of miniature spruce wood specimens have been performed to investigate the damage evolution in wood at the microscopic scale. For this purpose, the samples were stepwise tensile loaded in the longitudinal (L) and radial (R) directions and the damage evolution was monitored in real-time by acoustic emission (AE) and synchrotron radiation micro-computed tomography (SRμCT). This combination is of outstanding benefit as SRμCT monitoring provides an insight on the crack evolution and the final fracture at microscopic scale, whereas AE permits the detection of the associated accumulation and interaction of single damage events on all length scales with high time resolution. A significant drawback of the AE testing of wood has been overcome by means of calibrating the AE amplitudes with the underlying crack length development. Thus, a setup-dependent and wood species-dependent calibration value was estimated, which associates 1 μm2 crack area generating of 0.0038 mV in the detected AE amplitude. Furthermore, for both L and R specimens, AE signals were classified into two clusters by using a frequency-based approach of unsupervised pattern recognition. The shares of AE signals of both clusters correlate with the ratio of the relative crack area of the interwall and transwall cracks gained from the fractographic analysis of SRμCT scans.

Economical sponge phantom for teaching, understanding, and researching A- and B-Line reverberation artifacts in lung ultrasound

This project evaluated a low‐cost sponge phantom setup for its capability to teach and study A‐ and B‐line reverberation artifacts known from lung ultrasound and to numerically simulate sound wave interaction with the phantom using a finite‐difference time‐domain (FDTD) model. Both A‐ and B‐line artifacts were reproducible on B‐mode ultrasound imaging as well as in the FDTD‐based simulation. The phantom was found to be an easy‐to‐set up and economical tool for understanding, teaching, and researching A‐ and B‐line artifacts occurring in lung ultrasound. The FDTD method–based simulation was able to reproduce the artifacts and provides intuitive insight into the underlying physics.

Analytical modeling, finite-difference simulation and experimental validation of air-coupled ultrasound beam refraction and damping through timber laminates, with application to non-destructive testing.

Reliable non-destructive testing (NDT) ultrasound systems for timber composite structures require quantitative understanding of the propagation of ultrasound beams in wood. A finite-difference time-domain (FDTD) model is described, which incorporates local anisotropy variations of stiffness, damping and density in timber elements. The propagation of pulsed air-coupled ultrasound (ACU) beams in normal and slanted incidence configurations is reproduced by direct definition of material properties (gas, solid) at each model pixel. First, the model was quantitatively validated against analytical derivations. Time-varying wavefronts in unbounded timber with curved growth rings were accurately reproduced, as well as the acoustic properties (velocity, attenuation, beam skewing) of ACU beams transmitted through timber lamellas. An experimental sound field imaging (SFI) setup was implemented at NDT frequencies (120 kHz), which for specific beam incidence positions allows spatially resolved ACU field characterization at the receiver side. The good agreement of experimental and modeled beam shifts across timber laminates allowed extrapolation of the inner propagation paths. The modeling base is an orthotropic stiffness dataset for the desired wood species. In cross-grain planes, beam skewing leads to position-dependent wave paths. They are well-described in terms of the growth ring curvature, which is obtained by visual observation of the laminate. Extraordinary refraction phenomena were observed, which lead to well-collimated quasi-shear wave coupling at grazing beam incidence angles. The anisotropic damping in cross-grain planes is satisfactorily explained in terms of the known anisotropic stiffness dataset and a constant loss tangent. The incorporation of high-resolution density maps (X-ray computed tomography) provided insight into ultrasound scattering effects in the layered growth ring structure. Finally, the combined potential of the FDTD model and the SFI setup for material property and defect inversion in anisotropic materials was demonstrated. A portable SFI demonstrator was implemented with a multi-sensor MEMs receiver array that captures and compensates for variable wave propagation paths in glued laminated timber, and improves the imaging of lamination defects.

Combination of neutron imaging (NI) and digital image correlation (DIC) to determine intra-ring moisture variation in Norway spruce

Abstract The hygroscopic behavior of wood has a strong influence on its mechanical performance, yet the moisture gradients within the growth ring structure have not been sufficiently investigated. The main challenge is that moisture variations are coupled with strong sample deformation, which complicates the spatial referencing of moist and dry states. In this work, neutron imaging (NI) for the detection of water and digital image correlation (DIC) for the detection of local deformation were combined to calculate the local gravimetric moisture content (MCgrav) and the volumetric moisture content (MCvol) within single growth rings. Specimens of Norway spruce [Picea abies (L.) Karst.] were exposed to an adsorption-desorption cycle, with relative humidity (RH) steps varying from 0% (oven dry) up to 95% RH. After each acclimatization step, neutron transmission and DIC images were acquired. The local deformations determined by DIC were used to assign the corresponding dry density in the undeformed state to the compartment in a moist state and thus to calculate its MC by NI. No significant MC gradients could be found between earlywood (EW) and latewood (LW) within ±0.5% accuracy. However, strong density gradients between EW and LW can be directly correlated with MCvol. It appears that the MC in the cell wall is constant regardless of the particular growth ring position.

Water vapour diffusion through historically relevant glutin-based wood adhesives with sorption measurements and neutron radiography

In this work, the sorption and moisture diffusion behaviour of historically relevant glutin-based adhesives (i.e. bone glue, hide glue, fish glue) is characterized. The adhesive’s sorption isotherms were assessed on thin film samples revealing fundamental differences between the glutin-based adhesives and the synthetic reference adhesive (polyurethane). Furthermore, the water vapour diffusion parallel to the fibre was examined by means of neutron imaging on bonded two-layer samples of Norway spruce wood. In contrast to previous studies using neutron imaging, a new evaluation approach is presented, which allows for nonzero initial moisture conditions and takes into account and compensates for the geometry changes in the sample caused by swelling and shrinkage, thus allowing for a characterization of the diffusion behaviour within the glue line. The diffusion coefficients determined with neutron imaging were interpreted in terms of a theoretical model which takes into account the glue line microstructure. Although the diffusion coefficients were on average larger values for the glutin-based adhesives compared to the reference polyurethane adhesive, the significant variation observed in the sorption measurement is not reflected. This can partially be ascribed to excessive penetration of the adhesives into the wood substrate in fibre direction, which impedes a continuous adhesive layer. Furthermore, deformation and densification of the wood structure was assessed in the vicinity of the adhesive joint. This effect can be ascribed to the surface roughness, which results in very high local stresses leading to buckling and deformation of the tracheids. This situation is similar to that found for adhesive joints in or close to the fibre direction such as finger or butt joints.

Delamination detection in a 90-year-old glulam block with scanning dry point-contact ultrasound

Abstract Glued laminated timber (glulam) is known in timber constructions since more than 100 years. Glulam members can delaminate due to aging and excessive changes of temperature and humidity. This results in significantly reduced load bearing capability of the affected structural members. This contribution focuses on the ultrasonic point-contact inspection of gluing plane delamination as a nondestructive method. Ultrasonic measurements on a section of a 90-year-old roofing glulam member are presented. The results are compared with manual detection and evaluation of delamination with a feeler gauge, with X-ray computed tomography analyses, and with numerical simulations. Appropriate data evaluation of the mechanized ultrasonic results allows the determination of material separation that are deeper than 20 mm in the signature of the surface wave and large-scale delamination (>80% of the complete bonding width) in the back-wall echo. Numerical simulations based on the finite-difference time-domain method shed light into the details of the wave propagation and support the experimental findings.

Breast-density assessment with hand-held ultrasound: A novel biomarker to assess breast cancer risk and to tailor screening?

ObjectivesTo assess feasibility and diagnostic accuracy of a novel hand-held ultrasound (US) method for breast density assessment that measures the speed of sound (SoS), in comparison to the ACR mammographic (MG) categories.MethodsACR-MG density (a=fatty to d=extremely dense) and SoS-US were assessed in the retromamillary, inner and outer segments of 106 women by two radiographers. A conventional US system was used for SoS-US. A reflector served as timing reference for US signals transmitted through the breasts. Four blinded readers assessed average SoS (m/s), ΔSoS (segment-variation SoS; m/s) and the ACR-MG density. The highest SoS and ΔSoS values of the three segments were used for MG-ACR whole breast comparison.ResultsSoS-US breasts were examined in <2 min. Mean SoS values of densities a-d were 1,421 m/s (SD 14), 1,432 m/s (SD 17), 1,448 m/s (SD 20) and 1,500 m/s (SD 31), with significant differences between all groups (p<0.001). The SoS-US comfort scores and inter-reader agreement were significantly better than those for MG (1.05 vs. 2.05 and 0.982 vs. 0.774; respectively). A strong segment correlation between SoS and ACR-MG breast density was evident (rs=0.622, p=<0.001) and increased for full breast classification (rs=0.746, p=<0.001). SoS-US allowed diagnosis of dense breasts (ACR c and d) with sensitivity 86.2 %, specificity 85.2 % and AUC 0.887.ConclusionsUsing hand-held SoS-US, radiographers measured breast density without discomfort, readers evaluated measurements with high inter-reader agreement, and SoS-US correlated significantly with ACR-MG breast-density categories.Key Points• The novel speed-of-sound ultrasound correlated significantly with mammographic ACR breast density categories.• Radiographers measured breast density without women discomfort or radiation.• SoS-US can be implemented on a standard US machine.• SoS-US shows potential for a quantifiable, cost-effective assessment of breast density.

Hand-Held Sound-Speed Imaging Based on Ultrasound Reflector Delineation

A novel hand-held speed-of-sound (SoS) imaging method is proposed, which requires only minor hardware extensions to conventional ultrasound (US) B-mode systems. A hand-held reflector is used as a timing reference for US signals. A robust reflector-detection algorithm, based on dynamic programming (DP), achieves unambiguous timing even with 10 dB signal-to-noise ratio in real tissues, successfully detecting delays 300 % to <15 %. Experiments with breast-mimicking phantoms and ex-vivo liver samples showed, for hard hypoechogenic inclusions not visible in B-mode US, a high SoS contrast (2.6 %) with respect to cystic inclusions (0.9 %) and the background SoS noise (0.6 %). We also tested our method on a healthy volunteer in a preliminary in-vivo test. The proposed technique demonstrates potential for low-cost and non-ionizing screening, as well as for diagnostics in daily clinical routine.

Mobile Ultrasound Imaging on Heterogeneous Multi-Core Platforms

Ultrasound imaging is one of the most important medical diagnostic methods. The bulkiness of state-of-the-art high-quality ultrasound devices, however, drastically limits their usability in important application scenarios. In this paper, we show how a portable medical ultrasound device can be built using many-core technology and programmable logic, combining low power consumption with high flexibility. We discuss a typical ultrasound image reconstruction algorithm and howit can be parallelized using a pipelined design that efficiently partitions theworkload among heterogeneous processing elements. A special focus lies on the limited memory resources and data bandwidth between components. To tackle both problems, we use floating windowbuffers and approximate computations, and we minimize lookup table sizes using on-the-fly calculations. We evaluate the design on the Adapteva Parallella platform, which contains a power-efficient 16-core Epiphany coprocessor and a Zynq SoC including a dual-core ARM A9 processor and programmable logic. Experimental results show that parallel beamforming of 128 input channels to a 288x128 pixel ultrasound image can be achieved on the Parallella at a rate of 5.3 frames per second consuming only 2watt of dynamic power.