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Here, we report a new method using combined magnetic resonance (MR)–Photoacoustic (PA)–Thermoacoustic (TA) imaging techniques, and demonstrate its unique ability for in vivo cancer detection using tumor-bearing mice. Circular scanning TA and PA imaging systems were used to recover the dielectric and optical property distributions of three colon carcinoma bearing mice While a 7.0-T magnetic resonance imaging (MRI) unit with a mouse body volume coil was utilized for high resolution structural imaging of the same mice. Three plastic tubes filled with soybean sauce were used as fiducial markers for the co-registration of MR, PA and TA images. The resulting fused images provided both enhanced tumor margin and contrast relative to the surrounding normal tissues. In particular, some finger-like protrusions extending into the surrounding tissues were revealed in the MR/TA infused images. These results show that the tissue functional optical and dielectric properties provided by PA and TA images along with the anatomical structure by MRI in one picture make accurate tumor identification easier. This combined MR–PA–TA-imaging strategy has the potential to offer a clinically useful triple-modality tool for accurate cancer detection and for intraoperative surgical navigation.

This paper deals with the design and analysis of a quarter-wavelength, 10 W capacity, thermoacoustic refrigerator using short stack boundary layer approximation assumptions. The effect of operating frequency on the performance of the refrigerator is studied using dimensional normalization technique. The variation of stack diameter with average gas pressure and cooling power is discussed. The resonator optimization is discussed and the calculation results show a 9% improvement in the coefficient of performance and 201% improvement in power density for the optimized quarter-wavelength resonator compared to published optimization studies. The optimized resonator design is tested with DeltaEC software and the results show better performance compared to past established resonator designs.

This paper presents a design of moving coil loudspeaker for a 10 W cooling power thermoacoustic refrigerator. An electrical model is presented which simulates the behavior of the loudspeaker. The gas spring system for matching the frequency of the commercially available loudspeaker with the frequency of the acoustic resonator tube for maximizing electro-acoustical efficiency of the loudspeaker is discussed. The optimum back volume for the gas spring system is found to be 59.7 cc, which is about 1.9% of the total resonator volume when the loudspeaker frequency and the acoustic resonator frequency is made equal at 400 Hz with a moving mass of 20 g. The effect of force factor Bl on loudspeaker performance is discussed. Analysis results shows that for better performance of a refrigerator, the loudspeaker should be chosen to have a large force factor and small values for electrical and mechanical resistances. The refrigerator system is tested with DeltaEC software and its results are in good agreement with an electrical model results.

The design and optimization procedure for a loudspeaker driven 10-W cooling power thermoacoustic refrigerator components with a temperature difference of 120 K has been discussed using the linear thermoacoustic theory. The resonator losses are proportional to surface area and the optimum diameter ratio of small and large resonator tubes for minimum heat loss for a quarter-wavelength hemispherical ended resonator design is discussed. The hemispherical ended resonator design is further analytically optimized to increase COP, cooling effect at cold heat exchanger and power density by decreasing total resonator surface area and volume. An alternate convergent-divergent resonator design is proposed which is found to be more efficient compared to previous published designs. Resonator designs are tested with DeltaEC software, which predicts a lowest temperature of -48°C and -47°C for the improved hemispherical and convergent-divergent resonator designs, respectively. Theoretical results are in good agreement with DeltaEC results.

In this paper, the construction and performance of the 10W cooling power thermoacoustic refrigerators designed for a temperature difference of 120 K at 3% drive ratio are discussed. The construction and assembly procedure of the optimized thermoacoustic refrigerator components viz. spiral stack, heat exchangers, 0.28$\lambda$-taper, small diameter tube and divergent section with hemispherical end (TSDH) and 0.24$\lambda$-taper and divergent section with hemispherical end (TDH) resonator designs and loudspeaker found in the published literature, and instrumentation are discussed. The performance of the 0.28$\lambda$-TSDH, and 0.24$\lambda$-TDH resonator designs, and the uncertainties involved in the experimental measurements are discussed. Both the resonator designs show good behavior. A decent low temperature of $-$11.3${}^{\circ }$C and $-$8.7${}^{\circ }$C at 10W cooling power is achieved at the cold heat exchanger for the 0.28$\lambda$-TSDH and 0.24$\lambda$-TDH resonator designs, respectively. The comparative analysis of the experimental results with the theoretical and DeltaEC results is discussed.

In this paper, the design of 50 W thermoacoustic refrigerators operating with air as working substance at 10 bar pressure and 3% drive ratio for a temperature difference of 28 K is described. The design strategies discussed in this paper help in design and development of low cost thermoacoustic coolers compared to helium as the working substance. The design and optimization of spiral stack and heat exchangers, and the promising 0.2$\lambda$ and 0.15$\lambda$ resonator design with taper and divergent section with hemispherical end are discussed. The surface area, volume, length and power density of the hemispherical end design with air as working substance is found better compared to the published 10 and 50 W coolers using helium as the working substance. The theoretical design results are validated using DeltaEC software simulation results. The DeltaEC predicts 51.4% improvement in COP (1.273) at the cold heat exchanger temperature of $-2.7^{\circ }$C with air as working substance for the 50W 0.15$\lambda$TDH resonator design compared to the published 50W 0.25$\lambda$TDH resonator design with helium as working substance.

Although the thermoacoustic refrigeration (TAR) system has been recognized as a potential alternative environmentally cooling system, the low coefficient of performance (COP) has yet to make it marketable. One major factor contributing towards the low COP is the fabrication method applied to the stack component which is the most important component in the TAR. In this paper, comparison of the performance of a (i) 3D printed stack, (ii) a hand fabricated Mylar stack and (iii) an off-the-shelf Celcor substrates stack has been done; these being based on optimized design parameters using Multi-Objective Genetic Algorithm (MOGA). The performance is determined from the temperature attained at the cold end of the stack and the temperature difference across the stack. Experimental results showed that the 3D printed stack has the best performance by achieving a temperature, $T_c=18.9^{\circ }$C at the cold end and a temperature difference of $\mathrm{\Delta }T=18.1^{\circ }$C across the stack, about 60% of the designed temperature difference even though the fabricated 3D printed stack deviated from the optimal design due to fabrication constraint as compared to that of the Mylar stack which was closer to the optimal design. This 3D printing of the stack promises a big potential in the improvement of the TAR performance because of the consistency achievable with the precise dimensions of the stack.

The acoustic transmissions and reflections of plane waves at duct singularities can be represented with so-called scattering matrices. This paper shows how to extract scattering matrices utilizing linearized compressible flow equations and provides a comparative study of different governing equations, namely the Helmholtz, linearized Euler and linearized Navier–Stokes equations. A discontinuous Galerkin finite element method together with a two-source forcing is employed. With this method, the scattering matrix for a radial swirler of a combustion test-rig is computed and validated against the results of a fully compressible Large-Eddy-Simulation. Analogously, the scattering behavior of an axial swirler is investigated. The influence of acoustic-hydrodynamic interactions, viscous effects as well as unsteady boundary layers on the results is investigated for both configurations. A thermoacoustic stability analysis of the combustion test-rig housing the axial swirler is carried out, utilizing the scattering matrix of the swirler. Major influence of the reflections coming from the swirler on the thermoacoustic eigenfrequencies is found.