The quality control of 3D printed structures is significant for the reliability of additively manufactured objects. A novel remote sensing technique for characterizing 3D printed structures was developed by non-destructive ultrasonic imaging of a commonly used thermoplastic object such as acrylonitrile butadiene syrene (ABS). The quality of the additively manufactured ABS slab printed by fused deposition modeling (FDM) technique was evaluated by imaging effective density technique. The infill density of the FDM printed structures were modified by varying the motor speed of the printing extruder. An ultrasonic raster scan of the 3D printed structure using the novel effective density imaging technique distinguished the contrast in density with a very high resolution in the density variation. In addition to the lateral scanning, the density characterization was also effective when applied axially and can probe deep inside the additively manufactured object. The experimentally measured density variation agrees well with the theoretically calculated density values as a function of flow rate. The combined lateral and axial capabilities of the imaging technique make it a promising diagnostic tool for an in situ inspection method of optimizing FDM printing and quality control of 3D printed objects.
The temperature dependence of the mechanical properties of polyvinyl alcohol-based poly n-isopropyl acrylamide (PVA-PNIPAm) hydrogel was studied from the static and dynamic bulk modulus of the material. The effect of the temperature-induced volumetric phase transition on Young’s Modulus, Poisson’s ratio, and the density of PVA-PNIPAm was experimentally measured and compared with a non-thermo-responsive Alginate hydrogel as a reference. An increase in the temperature from 27.5 to 32 °C results in the conventional temperature-dependent de-swelling of the PVA-PNIPAm hydrogel volume of up to 70% at the lower critical solution temperature (LCST). However, with the increase in temperature, the PVA-PNIPAm hydrogel showed a drastic increase in Young’s Modulus and density of PVA-PNIPAm and a corresponding decrease in the Poisson’s ratio and the static bulk modulus around the LCST temperature. The dynamic bulk modulus of the PVA-PNIPAm hydrogel is highly frequency-dependent before the LCST and highly temperature-sensitive after the LCST. The dynamic elastic properties of the thermo-responsive PVA-PNIPAm hydrogel were compared and observed to be significantly different from the thermally insensitive Alginate hydrogel.
Practically applied techniques for ultrasonic biomedical imaging employ delay-and-sum (DAS) beamforming which can resolve two objects down to 2.1λ within the acoustic Fresnel zone. Here, we demonstrate a phononic metamaterial lens (ML) for detection of laterally subwavelength object features in tissue-like phantoms beyond the phononic crystal evanescent zone and Fresnel zone of the emitter. The ML produces metamaterial collimation that spreads 8x less than the emitting transducer. Utilizing collimation, 3.6x greater lateral resolution beyond the Fresnel zone limit was achieved. Both hard objects and tissue approximating masses were examined in gelatin tissue phantoms near the Fresnel zone limit. Lateral dimensions and separation were resolved down to 0.50λ for hard objects, with tissue approximating masses slightly higher at 0.73λ. The work represents the application of a metamaterial for spatial characterization, and subwavelength resolution in a biosystem beyond the Fresnel zone limit.
Solid
phononic crystal (PnC) lenses were made active on infiltration with
thermosensitive polymers to produce a thermoactuated hybrid solid
lens with variable focusing. Acoustic lenses, both solid state and
PnCbased, are passive elements with a fixed focal length. Their focal
characteristics are functions of the lens structure or the arrangement
of the PnC unit cell. Dispersion effects, liquid-filled membranes,
and phase delay in a multi-element emitter have been used for variable
focusing. The high thermal, electric, and electromagnetic sensitivity
of the elastic properties of poly(vinyl alcohol) (PVA) poly(N-isopropylacrylamide) (PNIPAm)-based hydrogels enable them
to operate as tunable solids. However, these solids do not have strong
enough contrast with water or well-controlled shape parameters to
function as standalone lenses. Here, a tunable hybrid solid ultrasonic
lens is realized by combining a PnC lens with PVA-PNIPAm thermoacoustic
hydrogel to modify the transmission and dispersion properties of transient
acoustic waves. Variable focusing is demonstrated from 40 to 50 mm
using the anomalous thermosensitivity of the elasticity and speed
of sound of the hydrogel.
The development of ultrasonic imaging techniques is optimized using artificial tissue phantoms before the practical applications. However, due to the strong attenuation and dispersion, accumulated fatty tissues can significantly impact the resolution and even feasibility of certain ultrasonic imaging modalities. An appropriate characterization of the acoustic properties on fatty phantoms can help the community to overcome the limitations. Some of the existing methods heavily overestimate attenuation coefficients by including the reflection loss and dispersion effects. Hence, in this study, we use numerical simulation-based comparison between two major attenuation measurement configurations. We further pointed out the pulse dispersion in viscoelastic tissue phantoms by simulations, which barely attracted attention in the existing studies. Using the selected attenuation and dispersion testing methods that were selected from the numerical simulation, we experimentally characterized the acoustic properties of common fatty tissue phantoms and compared the acoustic properties with the natural porcine fatty tissue samples. Furthermore, we selected one of the tissue phantoms to construct ultrasound imaging samples with some biomasses. With the known attenuation and dispersion of the tissue phantom, we showed the clarity enhancement of ultrasound imaging by signal post-processing to weaken the attenuation and dispersion effects.
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