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In viscous fluid-saturated elastic porous media, the spherical dilatational wave displacement equations are developed on Biot's theory and the spherical shear wave displacement equations are developed based on a modified wave frame. Analytical forms of the solutions are introduced by considering the wave magnitude dispersion due to the viscosity of Newtonian fluids. The attenuation of dilatational wave and shear wave are separately studied. Due to the high attenuation of the shear wave, the superposition characteristic is only considered for dilatational waves under the multiple energy source models. Many advantages of the multiple sources over the single source have been theoretically or numerically demonstrated, such as multiple energy sources can produce a larger relative displacement than single source, the wave direction is controllable and the magnitude of the relative displacement can be adjusted as required under the multiple source. [ABSTRACT FROM AUTHOR]

An asymmetric multiple-information cryptosystem based on spherical wave and chaotic random phase mask (CRPM) is proposed. In this security system, each secret color image is decomposed into R, G, and B channels and then independently phase-only encoded. The resulting channel is first illuminated by spherical wave and then modulated by CRPM to obtain an encoded channel. Similarly, each encoded channel of n secret images is obtained and then individually multiplied together to produce a corresponding encoded channel. The final encoded image R, G, and B channels of n secret images are digitally concatenated. The proposed method has mainly three advantages over reported methods. First, extremely sensitive and robust parameters of CRPM and spherical wave are exploited as decryption keys to enhance the security levels. Second, the different secret images are encrypted by different decryption keys, which cannot be accessed by unauthorized users. Moreover, fewer optical components are employed in the proposed scheme. The extracted secret images are free from crosstalk noise effects. The load of the key's management and transmission is lightened by using CRPM. The encryption and decryption processes can be implemented by opto-electronic setup. Numerical simulation results show the viability and security of the proposed method. [ABSTRACT FROM AUTHOR]

We analyse a scattering problem of electromagnetic waves by a bounded chiral conductive obstacle, which is surrounded by a dielectric, via the quasi-stationary approximation for the Maxwell equations. We prove the reciprocity relations for incident plane and spherical electric waves upon the scatterer. Mixed reciprocity relations have also been proved for a plane wave and a spherical wave. In the case of spherical waves, the point sources are located either inside or outside the scatterer. These relations are used to study the inverse scattering problems. [ABSTRACT FROM AUTHOR]

This paper presents an active cancellation method based on repeater jamming to weaken the incident wave rather than to weaken the scattered wave in conventional method. The method works well on chirp-subpulse stepped frequency (CSSF) signal. The incident plane wave is interfered by a spherical wave which is generated by a horizontal electric dipole. The analysis and simulation show that the plane wave can be reduced obviously via this method. By incorporating frequency and phase modulation, the backscattering of the target is reduced significantly. Numerical experiments also show that with greater wavelength, the cancellation performance gets better. [ABSTRACT FROM AUTHOR]

Plane-wave-based ultrafast imaging has become the prevalent technique for non-conventional ultrasound imaging. The image quality, especially in terms of the suppression of artifacts, is generally compromised by reducing the number of transmissions for a higher frame rate. We hereby propose a new ultrafast imaging framework that reduces not only the side lobe artifacts but also the axial lobe artifacts using combined transmissions with a new coherence-based factor. The results from simulations, in vitro wire phantoms, the ex vivo porcine artery, and the in vivo porcine heart show that our proposed methodology greatly reduced the axial lobe artifact by 25±5 dB compared with coherent plane-wave compounding (CPWC), which was considered as the ultrafast imaging standard, and suppressed side lobe artifacts by 15 ± 5 dB compared with CPWC and coherent spherical-wave compounding. The reduction of artifacts in our proposed ultrafast imaging framework led to a better boundary delineation of soft tissues than CPWC. [ABSTRACT FROM PUBLISHER]

This paper presents a beamforming-based acoustic imaging (BBAI) method employing a two-dimensional (2D) microphone array that not only can locate an acoustic source in the XY plane parallel to the array, but can also identify the distance between the source and array in the Z direction, denoted as the source depth, and thus provides three-dimensional (3D) localization ability. In this method, the acoustic field is reconstructed on virtual XY planes at different distances along the Z direction. The source depth is then determined according to the virtual plane providing the maximum response of the acoustic field. The location of the source in the X and Y directions of the identified virtual plane can then be easily determined based on the standard beamforming principles of a planar array. The proposed BBAI method is evaluated based on simulations involving single- and multiple-point sources, and corresponding experimental evaluations are similarly conducted in an anechoic chamber. Both simulation and experimental results demonstrate that the proposed method is capable of locating acoustic sources in 3D space.

A physical-geometrical model for a possible early universe is proposed. One considers an initial singularity containing the energy of the whole universe. The singularity expands as a spherical wave at the speed of light generating space and time. The relations of the special theory of relativity, quantum mechanics and gas kinetics are considered applicable. A structuring of the primary wave is adopted on reasons of geometrical simplicity as well as on satisfying the conservation laws. The evolution is able to lead to particles very close to neutrons as mass and radius. The actually admitted values for the radius and mass of the universe as well as the temperature of the ground radiation (3-5 K) can be obtained by using the proposed model.

Holographic data storage is a promising technology that provides very large data storage capacity, and the multiplexing method plays a significant role in increasing this capacity. Various multiplexing methods have been previously researched. In the present study, we propose a shift-peristrophic multiplexing technique that uses spherical reference waves, and experimentally verify that this method efficiently increases the data capacity. In the proposed method, a series of holograms is recorded with shift multiplexing, in which the recording material is rotated with its axis perpendicular to the material’s surface. By iterating this procedure, multiplicity is shown to improve. This method achieves more than 1 Tbits/inch2 data density recording. Furthermore, a capacity increase of several TB per disk is expected by maximizing the recording medium performance.

We derived a closed-form expression of the maximum power transfer efficiency (MPTE) between a transmitting antenna inside the brain and a receiving antenna outside the head using spherical wave expansion. The derived expression was validated using a FEKO simulation. The properties of the insulator and radiation mode were analyzed in each available medical implant communications service (MICS) and industrial, scientific and medical (ISM) band as a means of increasing the reliability of wireless biotelemetry implementation. Some interesting preceding results in the literature were revisited with the figure-of-merit MPTE. It was also newly found that the effect on MPTE by the physical size and material properties of the insulator in both transverse magnetic (TM) and transverse electric (TE) mode decreases for 2.4 GHz and 5.8 GHz and the loss of the insulator does not have a severe impact on MPTE once the dielectric constant is greater than a certain value. This work can be used as an implanted-antenna design guide for building reliable biotelemetry communication.