S. Y. Zhang

Quantitative theory for laser-generated Lamb waves in orthotropic thin plates

A quantitative theory for modeling the laser-generated transient ultrasonic Lamb waves propagating along arbitrary directions in orthotropic thin plates is presented by employing an expansion method of the generalized Lamb wave modes. The displacement is expressed by a summation of the symmetric and antisymmetric modes in the surface stress-free orthotropic plate, and it is particularly appropriate for wave form analyses of Lamb wave in thin plates because one needs only to evaluate a few of the lowest order modes. The transient wave forms are analyzed in the thermoelastic regime and the oil coating generation method for a transversely isotropic plate. The results show that the theory provides a quantitative analysis to characterize anisotropic properties and elastic stiffness properties of the orthotropic plates by the laser-generated Lamb wave detection.

A three-beam path photonic crystal fiber modal interferometer and its sensing applications

Photonic crystal fiber (PCF) modal interferometer is studied for sensing applications. There is a trade-off between high sensitivity and wide sensing range due to the intrinsic two-beam interference. We propose and experimentally demonstrate a three-beam path reflective interferometer by exciting mode conversion at the end surface of a dual-mode PCF. Approximately 5% mode conversion is taken place at the PCF end surface according to our model. In comparison with the normal dual-mode interference in a PCF, the mode conversion induced three-beam interference generates sharper spectrum and expanded sensing range. Gas sensing experiment is implemented with a sensitivity of 3019 nm/RIU. The advantage of expanded sensing range is also experimentally demonstrated.

Study on GMR in CoAg thin granular films

Abstract Giant magnetoresistance has been observed in CoxAg1−x(8⩽ x ⩽ 46 at%) thin granular films. The samples were prepared on glass substrates using ion-beam consputtering technique. It is shown that GMR depends on x, substrate temperature, and annealing treatment. For x = 22 at% film after annealing 0.5 at 500 K, the maximum of δϱ/ϱ is ∼ 13.4% at room temperature.

Anisotropy and Faraday effect in Co spinel ferrite films

Crystalline Co spinel ferrite films were prepared by rf sputtering on glass substrates without buffer layer and annealed at temperatures from 400 to 600u2009°C for 2 h in air. (100) texture was obtained in these films. The anisotropy constant, magnetic hysteresis loops, and magneto‐optical Faraday spectra of the films were measured. The texture became poor when the films were annealed below 500u2009°C, but the perpendicular anisotropy constant Ku, squareness ratio R=(Mr/Ms)⊥/(Mr/Ms)∥ increased and showed peak values of 2.2×105 ergs/cm3 and 0.94, respectively, at an annealing temperature Ta=500u2009°C. For the film annealed at 600u2009°C (higher than the Curie temperature, 520u2009°C, of Co spinel ferrite), the texture recovered, but Ku and R dropped. The Faraday rotation spectra of Co spinel ferrite films showed a broad peak centered around 720 nm. The peak value increased monotonically with increasing annealing temperature. These results may be related to the Co ion‐induced anisotropy and Co ion distribution in tetrahedral ...

New technique of photodisplacement imaging using one laser for both excitation and detection

A new interferometry technique has been developed that uses only a single laser for both exciting and detecting photothermal displacement, which greatly simplifies the system and the optical alignment. The minimum detectable displacement 10−2 A/(Hz)1/2 is obtained. To examine this setup, we have performed a simulated experiment. And also, we have succeeded in imaging the subsurface flaw in a copper block. The preliminary results demonstrate that this new method is very promising for nondestructive evaluation and other applications.

Dynamic behavior of cobalt granules with annealing treatment in ion‐beam cosputtered Co22Ag78 granular film

The dynamic behavior of ferromagnetic cobalt granules in ion‐beam cosputtered Co22Ag78 samples under annealing treatment was examined by transmission electron microscopy (TEM), using a real‐time video recording system. Cobalt granules about 10 nm in average size were embedded in a nonmagnetic silver matrix. It was observed that, in situ, the cobalt granules changed continually in shape and size with annealing temperature and time. We have estimated the changes of cobalt granule size from the results of TEM. The ferromagnetic resonance method was employed to study the evolution of the shapes of cobalt granules. It shows that cobalt granule shapes and sizes change mainly along the plane of the film during the process of annealing.

Reconstruction theory of thermal conductivity depth profiles by the modulated photoreflectance technique

A reconstruction theory of thermal conductivity depth profiles from modulated photoreflectance data has been reported. This theory is based on the pulsed spectrum technique and a regularization method. The performance of this approach is illustrated by numerical simulations.

Simulation of the flow induced by acoustic streaming in noncontact ultrasonic motors

In order to overcome many shortcomings of the traditional contact-type rotors, noncontact ultrasonic motors, which are driven by acoustic streaming, have been proposed. Recently, an analytical solution based on the second order approximation has been presented, but it gives a revolution speed five times smaller than the experimental value. In order to reconcile the discrepancy, the authors perform numerical simulations of the gas motion between the stator and the rotor driven by the acoustic streaming. With the same parameters used in the experiment, it is found that the acoustic streaming can account for the observed fast rotation.

On the Faraday rotation in FeSiO2 granular films

Abstract Large Faraday rotation (10 5 deg/cm) in Feue5f8SiO 2 granular films made by ion-beam sputtering method has been observed at room temperature. Our results show that Faraday rotation (FR) increases with Fe volume fraction f v and peaks at f v ≈0.55. This indicates that Fe granules play an important role in FR of granular materials.

Temperature dependence of the magnetostriction in polycrystalline PrFe1.9 and TbFe2 alloys: Experiment and theory

A remarkable magnetostriction λ111 as large as 6700u2009ppm was found at 70u2009K in PrFe1.9 alloy. This value is even larger than the theoretical maximum of 5600u2009ppm estimated by the Stevens equivalent operator method. The temperature dependence of λ111 for PrFe1.9 and TbFe2 alloys follows well with the single-ion theory rule, which yields giant estimated λ111 values of about 8000 and 4200u2009ppm for PrFe1.9 and TbFe2 alloys, respectively, at 0u2009K. The easy magnetization direction of PrFe1.9 changes from [111] to [100] as temperature decreases, which leads to the abnormal decrease of the magnetostriction λ. The rare earth sublattice moment increases sharply in PrFe1.9 alloy with decreasing temperature, resulting in the remarkably largest estimated value of λ111 at 0u2009K according to the single-ion theory.