Jiehui Liu

Influence of Ru3+ ions on anisotropy of PbFe12O19 single crystals

A remarkable influence of Ru3+ ions on the anisotropy of single crystals of PbFe12O19 was found. Single crystals of PbFe12−xRuxO19 were grown by flux method. For small addition of Ru ions, the uniaxial anisotropy constant K1 increases sharply, and reaches a maximum at x = 0.05. Then, the K1 tends to decrease with further increasing x. A maximum relative increment of 27% in K1 was obtained at 273°K. Also, the variation of K1 and Ha with T in a range of 100–273°K was investigated. For the crystals with x = 0.35, the phenomenon of spin reorientation was observed with the change of easy direction from c axis to basal plane at the temperature around 200°K. Below 200°K, K1 becomes negative. In addition, K2 increases monotonously with decreasing temperature.

Acoustic radiation force on a double-layer microsphere by a Gaussian focused beam

A new model for calculating the radiation force on double-layer microsphere is proposed based on the ray acoustics approach. The axial acoustic radiation force resulting from a focused Gaussian beam incident on spherical shells immersed in water is examined theoretically in relation to its thickness and the contents of its double-layer. The attenuation both in the water and inside the sphere is considered in this method, which cannot be ignored while the high frequency ultrasonic is used. Results of numerical calculations are presented for fat and low density polyethylene materials, with the hollow region filled with animal oil, water, or air. These results show how the acoustic impedance and the sound velocity of both layers, together with the thickness of the shell, affect the acoustic radiation force.

Non-reciprocal wave propagation in one-dimensional nonlinear periodic structures

We study a one-dimensional nonlinear periodic structure which contains two different spring stiffness and an identical mass in each period. The linear dispersion relationship we obtain indicates that our periodic structure has obvious advantages compared to other kinds of periodic structures (i.e. those with the same spring stiffness but two different mass), including its increased flexibility for manipulating the band gap. Theoretically, the optical cutoff frequency remains unchanged while the acoustic cutoff frequency shifts to a lower or higher frequency. A numerical simulation verifies the dispersion relationship and the effect of the amplitude-dependent signal filter. Based upon this, we design a device which contains both a linear periodic structure and a nonlinear periodic structure. When incident waves with the same, large amplitude pass through it from opposite directions, the output amplitude of the forward input is one order magnitude larger than that of the reverse input. Our devised, non-reci...

Broadband underwater acoustic carpet cloak based on pentamode materials under normal incidence

Acoustic carpet cloak in air has become an attractive topic in the past few years and has been realized in many feasible ways. However, underwater acoustic carpet cloak still suffers from lacking operator flexibility. Inspired by those works before, we design an impedance matching underwater acoustic carpet cloak using pentamode materials under normal incidence. The carpet cloak employs an effective velocity lower than water to restore the distorted reflected waves and its effective density is tuned to guarantee impedance matching with water. It is also demonstrated that a cloaked area with a higher height can be formed by simply using more microstructures in the cloak. Simulation results depict that the proposed carpet cloak has a great performance in a wide range of frequency. Our investigation may have potential applications in simplifying the underwater acoustic carpet cloak design.

Acoustic radiation force on a sphere in a progressive and standing zero-order quasi-Bessel-Gauss beam

HighlightsThe beam coefficients of the zero‐order quasi‐Bessel‐Gauss beam are proposed.The quasi‐Bessel‐Gauss beam can perform negative axial radiation forces.Beam width significantly influences the radiation force on sphere of bigger radius for quasi‐Bessel‐Gauss beam. Abstract By means of series expansion theory, the incident quasi‐Bessel‐Gauss beam is expanded using spherical harmonic functions, and the beam coefficients of the quasi‐Bessel‐Gauss beam are calculated. According to the theory, the acoustic radiation force function, which is the radiation force per unit energy on a unit cross‐sectional surface on a sphere made of diverse materials and immersed in an ideal fluid along the propagation axis of zero‐order quasi‐Bessel‐Gauss progressive and standing beams, is investigated. The acoustic radiation force function is calculated as a function of the spherical radius parameter Symbol and the half‐cone angle Symbol with different beam widths in a progressive and standing zero‐order Bessel‐Gauss beam. Simulation results indicate that the acoustic radiation forces with different waist radii demonstrate remarkably different features from those found in previous studies. The results are expected to be useful in potential applications such as acoustic tweezers. Symbol. No caption available. Symbol. No caption available.

Manipulating sound wave radiation by zero-index metamaterials

Based on previous conceptions, there is only a homogeneous field in zero-index metamaterials (ZIMs). However, in this paper, It is found that when higher modes such as dipole, quadrupole, or octopole patterns are excited in a structure through cavity of ZIMs, there will generate an inhomogeneous pressure field in the ZIMs. In addition, when the resonance of the monopole or higher mode is excited in the cavity, a very intense pressure field will develop, such that the radiation of the source in the cavity is enhanced as compared to that of a source in free space without the ZIM cavities. Compared to classic local resonances achieved by Helmholtz resonators and membranes, the resonances in such a structure are more suitable for manipulating wave radiation owing to the significantly richer resonant modes. Furthermore, the proposed structure can be used to control sound radiation patterns and obtain directive radiation.Based on previous conceptions, there is only a homogeneous field in zero-index metamaterials (ZIMs). However, in this paper, It is found that when higher modes such as dipole, quadrupole, or octopole patterns are excited in a structure through cavity of ZIMs, there will generate an inhomogeneous pressure field in the ZIMs. In addition, when the resonance of the monopole or higher mode is excited in the cavity, a very intense pressure field will develop, such that the radiation of the source in the cavity is enhanced as compared to that of a source in free space without the ZIM cavities. Compared to classic local resonances achieved by Helmholtz resonators and membranes, the resonances in such a structure are more suitable for manipulating wave radiation owing to the significantly richer resonant modes. Furthermore, the proposed structure can be used to control sound radiation patterns and obtain directive radiation.

Realization of manipulating acoustic surface waves radiation direction with rectangular-groove structure

Acoustic surface waves (ASWs) can be generated through a one-dimensional array of grooves. Sound can be collimated by ASWs. However, in previous studies, the groove period and grating period have been the same. In this work, we propose a structure where the groove period is different from the grating period, and collimates sound waves with very small side lobes. The structure can alter the acoustic wave radiation direction by manipulating ASWs and the relationship between the radiation direction and the frequency for different groove depths are investigated. Furthermore the incident direction of the sound wave, which can be coupled into ASWs, can be manipulated by changing the period of rectangular grating. We theoretically illustrate the physical mechanism of controlling the ASW radiation direction by wave-number analysis. These theoretical predictions are verified using numerical simulations. Using this proposed structure, we can manipulate the ASW radiation direction, which is very important for practi...

Study of the temperature rise induced by a focusing transducer with a wide aperture angle on biological tissue containing ribs

We used the spheroidal beam equation to calculate the sound field created by focusing a transducer with a wide aperture angle to obtain the heat deposition, and then we used the Pennes bioheat equation to calculate the temperature field in biological tissue with ribs and to ascertain the effects of rib parameters on the temperature field. The results show that the location and the gap width between the ribs have a great influence on the axial and radial temperature rise of multilayer biological tissue. With a decreasing gap width, the location of the maximum temperature rise moves forward; as the ribs are closer to the transducer surface, the sound energy that passes through the gap between the ribs at the focus decreases, the maximum temperature rise decreases, and the location of the maximum temperature rise moves forward with the ribs.

The study on the nonclassical nonlinear effect of concretes with different mix rate

The mix rate of concrete has great influence on the strength of concrete. At present, research method on different mix rate of concrete is always mechanical rather than acoustical. Different mix rates have different porosities in concretes and their linear and nonlinear acoustic properties of concrete are also different. In this paper, the porosity, the linear and nonlinear acoustic properties such as sound velocity, harmonics, nonlinear frequency shift of the concrete samples are compared. And we explore the possibility of using the linear and nonlinear parameters to characterize the strength of concrete.

The study of dissipative nonlinearity in oil sand

The acoustic waves propagating in sand have the nonlinear dissipative phenomenon that the dissipative coefficient of acoustic waves with larger amplitude is smaller than that with smaller amplitude. The results of experimental investigations on the propagation of acoustic waves in oil sand with different oil content are presented in the paper. The nonlinear dissipative phenomenon in oil sand is studied and the analytical description is given to explain the phenomenon. It is found that the relative growth coefficient and the dissipative index are dependent on the oil content in oil sand. According to the dependence relationships between the sensitive coefficients and the oil content, a new prospective approach to measure the oil content in oil sand is provided in the paper for oil exploration.