Papers by Keyword: Multimode

Abstract: Time-resolved photoluminescence spectra of vertical cavity surface emitting laser (VCSEL) structures under different excitation intensity are investigated. The effect of the distributed Bragg reflectors (DBR) on the laser emission and the mechanism of multi-longitudinal-mode are analysed. A broad peak around 2.80eV is observed from the structure without DBR cavity when pumped under low excitation intensity. At higher excitation density up to 21.4kW/cm², a lasing peak appears at 2.86eV, and exhibits a rapid growth and red shift with the increase of the excitation density. The decay time of the peak is about 66ps. When the spectrum is measured after the deposition of DBR on the top side of the grown nitride structure, the number of peaks increases to 7, and the free spectral range 0.21×10¹⁴ Hz is close to the value that calculated by the Fabry-Perot cavity length. After depositing the second DBR, multi PL peaks around 2.87eV are observed. The relationship of laser emission intensity and angle of the polarizer shows nearly a cosine square variation. However, the polarization characteristics of the four main peaks are different, which indicates that these peaks occurr by the oscillation of different optical cavities.

Abstract: Aiming at the problems such as switch impulsion, insurmountability for influence caused by nonlinearity in one tank gun control system which adopts double PID controller to realize the multimode switch control between high speed and low speed movement, the system math model is built up; And then, Model Reference Adaptive Control (MRAC) method based on nonroutine reference model is brought in and the adaptive gun controller is designed. Consequently, the compensation of nonlinearity and multimode control are implemented. Furthermore, the Tracking Differentiator (TD) is affiliated to the front of controller in order to restrain the impulsion caused by mode switch. Finally, the validity of control method in this paper is verified by simulation.

Abstract: Most of the ultrasonic surgical or therapeutic devices apply the outside body designs with only the vibration tip contacting and delivering energy to the tissue. For inside body applications, a miniaturized 421 kHz piezoelectric transducer with OD 2 mm and length 10.35 mm based on longitudinal vibration mode was developed in this paper. The transducer is a one-wavelength design with a stepped horn to focus the energy. The theoretical analyses on mechanical, electrical and acoustic properties were performed using finite element analysis (FEA) and equivalent circuit (EC) model, which showed consistent results. The Qm and keff were found to be 393 and 0.21, respectively. The maximum acoustic output power was observed to be 27 mW at 10 V input when the depth of immersion is 1/4 wavelength. Ultrasonic streaming was also observed when the whole transducer was immersed in the water and the input power level was in the order of 0.6 W.