Controlling thermal transport has become relevant in recent years. Traditionally, this control has been achieved by tuning the scattering of phonons by including various types of scattering centres in the material (nanoparticles, impurities, etc). Here we take another approach and demonstrate that one can also use coherent band structure effects to control phonon thermal conductance, with the help of periodically nanostructured phononic crystals. We perform the experiments at low temperatures below 1 K, which not only leads to negligible bulk phonon scattering, but also increases the wavelength of the dominant thermal phonons by more than two orders of magnitude compared to room temperature. Thus, phononic crystals with lattice constants ≥1 μm are shown to strongly reduce the thermal conduction. The observed effect is in quantitative agreement with the theoretical calculation presented, which accurately determined the ballistic thermal conductance in a phononic crystal device.

/pdf/engineering-thermal-conductance-using-a-two-dimensional-a7jak7z5xw.pdf

Engineering thermal conductance using a two-dimensional phononic crystal

A review of ultrasonic testing applications in additive manufacturing: Defect evaluation, material characterization, and process control.

The physics of ultrasound

Coarsening of martensite with multiple generations of twins in laser additively manufactured Ti6Al4V

A multibeam beam-forming network (BFN) for generating 2-D multibeam array antenna (MAA) is proposed using single-layer substrate integrated waveguide (SIW) technology. Firstly, a new topology for building $16\times 16$ BFNs is proposed, which successfully transforms the traditional topology from a 3-D configuration to a 2-D (or uniplanar) one. Two major challenges are tackled during this transformation, namely, the planarization of basic components and the reduction of excessive intersections between multiple paths. To this end, a novel design of eight-port hybrid couplers, as critical components of this BFN, is developed to transform a 3-D to a 2-D structure. Furthermore, a new design of eight-port crossover, which can address four path intersections simultaneously, is proposed to reduce the total number of path intersections from 16 to only 4. The proposed topology for $16\,\times \,16$ BFNs allows all the basic components, including eight-port hybrid couplers, eight-port crossovers, and phase shifters, to be placed within a single-layer configuration. Fed by the proposed uniplanar $16\times 16$ BFN, a 2-D MAA with 16 ( $4\,\times \,4$ ) beams, which is capable of switching the beams in both elevation and azimuth directions, is realized. Compared with the previous 2-D Butler matrix (BM) designs using multilayer technology, it is for the first time that a uniplanar design of $16\times16$ BFN is proposed and realized, which significantly simplifies the design and fabrication complexity.

Uniplanar Beam-Forming Network Employing Eight-Port Hybrid Couplers and Crossovers for 2-D Multibeam Array Antennas

In this paper, a 2-D beamforming phased array using a novel 2-D Nolen matrix network is presented. The Nolen matrix is a novel antenna feeding network composed of only couplers with dedicated coupling ratios and phase shifters. It does not require crossover and load termination compared to other networks based on Butler and Blass matrix. To be specific, the closed-form equations are derived first for uniplanar single $3 \times 3$ Nolen matrix, which is composed of three couplers and three phase delay lines. Most importantly, it is found that the proposed Nolen matrix can employ couplers with arbitrary phase differences to achieve relatively flexible progressive phase delays across the radiating elements, presenting a high degree of freedom on circuit topology and beamforming performance. Then, a 2-D antenna feeding network is designed by stacking and cascading six $3 \times 3$ Nolen matrices, and a 2-D patch antenna array is integrated with the proposed feeding network to generate nine radiation beams with unique directions on azimuth and elevation planes, realizing the 2-D beamforming function. To verify the proposed design concept, a prototype of 2-D beamforming phased array operating at 5.8 GHz is designed, fabricated, and measured, and the experimental results agree well with simulation and theoretical analysis.

A Novel 2-D $3\times3$ Nolen Matrix for 2-D Beamforming Applications

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.

Nondestructive ultrasonic evaluation of fused deposition modeling based additively manufactured 3D-printed structures

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 275 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

https://www.mdpi.com/2073-4360/12/7/1462/pdf

Thermally Tunable Dynamic and Static Elastic Properties of Hydrogel Due to Volumetric Phase Transition.

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. Traditional methods for ultrasound detection in biomedical application suffer from limited lateral resolution. Here, the authors show that a phononic metamaterial lens can be used for spatial characterisation of subwavelength objects, even beyond the Fresnel zone of the emitting transducer.

/pdf/sub-wavelength-lateral-detection-of-tissue-approximating-3iswg4qbza.pdf

Sub-wavelength lateral detection of tissue-approximating masses using an ultrasonic metamaterial lens

The effects of temperature and frequency dispersion on sound speed in bulk poly (vinyl alcohol) poly (N-isopropylacrylamide) hydrogels caused by the phase transition.

Yuqi Jin

Papers

A Novel 2-D $3\times3$ Nolen Matrix for 2-D Beamforming Applications

Nondestructive ultrasonic evaluation of fused deposition modeling based additively manufactured 3D-printed structures

Thermally Tunable Dynamic and Static Elastic Properties of Hydrogel Due to Volumetric Phase Transition.

Sub-wavelength lateral detection of tissue-approximating masses using an ultrasonic metamaterial lens

The effects of temperature and frequency dispersion on sound speed in bulk poly (vinyl alcohol) poly (N-isopropylacrylamide) hydrogels caused by the phase transition.