Structural Analysis And Topology Optimization Design For Bandwidth Extension of Magnetoelectric Seismometer

Magnetoelectric seismometers can measure earthquake information and play an important role in earthquake monitoring. Aiming at the wider effective frequency bandwidth of magnetoelectric seismometers, a novel seismometer based on topology optimization structural pendulum is reported. The topology optimization of leaf spring structure in magnetoelectric seismometer is designed, the natural frequency and spurious frequency characteristics of the novel seismometer are analyzed. Based on variable density theory, the Solid Isotropic Material with Penalization (SIMP) model of the seismometer is established, and the Method of Moving Asymmetric (MMA) is adopted to obtain the optimal topology structure. The finite element analysis using ANSYS shows that novel seismometer after topology optimization structure is characteristic with lower natural frequency and higher spurious frequency than that of before optimization seismometer. The real vibration experimental results indicate that after topology optimization, the effective frequency bandwidth of seismometer is increased by 55.50%, improving from [1s, 51Hz] to [4s, 78Hz].

Traveling-wave control of the bending wave in a beam for high quality sound radiation

The bending wave generated by the actuator exciting a panel can be controlled to be in the traveling wave form void the structural resonances, which deteriorates the radiated sound if the panel is used as a speaker. Although such traveling-wave control method (TCM) yields a wider effective frequency range than the modal control method, the requirement of using many actuators is the practical problem yet. If a beam is employed instead of a plate as a panel speaker, the number of actuators can be reduced despite a smaller radiating surface than a plate. This study adopts three actuators for the beam control using TCM. An actuator excites the beam in the middle position, and the two actuators near the two edges are used to suppress the reflected waves from the boundaries. The control result shows that the driving-point mobility of the primary actuator is converted into that of an infinite beam, which means that the boundaries are changed into anechoic ones and the structural resonances are eliminated. Accordingly, the beam radiates a smooth sound spectrum without sharp peaks and troughs related to the resonant responses. Effects of material and dimension in determining the effective frequency range are also explored.

Extending the Frequency Limits of "Postage-Stamp PIV" to MHz Rates

The effective frequency limits of postage-stamp PIV, in which a pulse-burst laser and very small fields of view combine to achieve high repetition rates, have been extended by increasing the PIV acquisition rate to very nearly MHz rates (990 kHz) by using a faster camera. Charge leaked through the camera shift register at these framing rates but this was shown not to bias the measurements. The increased framing rate provided oversampled data and enabled use of multi-frame correlation algorithms for a lower noise floor, increasing the effective frequency response to 240 kHz where the interrogation window size begins to spatially filter the data. The velocity spectra suggest turbulence power-law scaling in the inertial subrange steeper than the theoretical -5/3 scaling, attributed to an absence of isotropy.

Application of orthogonalization methods of pseudospectra of steps for human identification

A method for processing audio signals of steps of various people in order to effectively separate pseudospectra of signals that can be further subjected to the classification procedure is proposed. The model of a human steps detector was based on the dynamic parameters of the foot position when walking. To record step signals, vibroacoustic sensors were used, sensitive to mechanical and acoustic vibrations in the frequency range from 10 to 1000 Hz. The processing of recorded step signals involved calculating their envelope and then calculating the pseudospectra of the envelope. The procedure for orthogonalization of the pseudospectra of steps for their effective frequency diversity can be used as the basis for the operation of an automated Remote Access Control System. This system can find the application in areas where for one reason or another it is impossible to install another biometric system or is extremely inconvenient, for example, to control access to a room into which the working personnel enter in a special uniform, gloves, and goggles.