Input Frequency Response Research Articles

Numerical investigation of a two-stage serial vibration isolation system using frequency response function based substructuring method

The mechanical system applied in industry and manufacturing fields is generally a complex multi-stage isolation system, which contains a lot of connection parts. In order to better analyze the effect of the connection parts, the transfer path model of a two-stage serial system is developed in this article using frequency response function based substructuring method. To verify the proposed transfer path model, a finite element model that simulates a two-stage serial vibration isolation system is built. By comparing the predicted results and exact values, the model proves to be correct. Furthermore, the random noise is introduced into the system-level frequency response functions for error sensitivity analysis and the influence on the substructure frequency response functions is quantified through comparison. Since the possible errors are unknown in the experimental measurement, 5%, 25%, and 50% random errors are introduced into all the input frequency response functions individually to analyze the influence of different noise levels on the prediction accuracy. In order to solve the ill-conditioned inverse problem involved in the model, the truncated singular value decomposition is also applied. The simulation results show that compared with the direct-inverse method, truncated singular value decomposition can decrease the prediction error caused by the introduced noise more effectively.

EFFECT OF VARIATIONS IN MICROPHONE COVER SHAPE AND WEARING POSITION ON THE PERFORMANCE OF A HEARING-SUPPORT DEVICE MOUNTED ON EAR — SIMULATION STUDY

Morphological and positional factors that can affect the actual performance of the hearing-support (HS) devices are utilized to support the damaged hearing ability of the sensorineural hearing-impaired persons. However, there have been few studies that demonstrated the effects of variations in such design factors on the frequency response of the device experimentally. In this study, the effect of design variations in the shape of the microphone cover on the housing and the wearing position of the device mounted on the ear on the input frequency response of the device and on the performance of an embedded beamforming algorithm were investigated using a human upper body model, a hearing aid housing model, and an acoustic environment model using computer simulation. Experimental results showed that the implemented simulator could simulate the actual acoustic situations (differences less than 5 dB in audible frequency range) and that both of the response patterns of the device and beamforming algorithm were varied in accordance with the variations in the shape of the microphone cover and the mounting position of the device on the ear. These results demonstrate the necessity of additional design and algorithm fine-tuning of each (HS) device to improve its actual speech enhancement performance.

Effect of input compression and input frequency response on music perception in cochlear implant users

Objective: A study was conducted to determine whether modifications to input compression and input frequency response characteristics can improve music-listening satisfaction in cochlear implant users. Design: Experiment 1 compared three pre-processed versions of music and speech stimuli in a laboratory setting: original, compressed, and flattened frequency response. Music excerpts comprised three music genres (classical, country, and jazz), and a running speech excerpt was compared. Experiment 2 implemented a flattened input frequency response in the speech processor program. In a take-home trial, participants compared unaltered and flattened frequency responses. Study sample: Ten and twelve adult Nucleus Freedom cochlear implant users participated in Experiments 1 and 2, respectively. Results: Experiment 1 revealed a significant preference for music stimuli with a flattened frequency response compared to both original and compressed stimuli, whereas there was a significant preference for the original (rising) frequency response for speech stimuli. Experiment 2 revealed no significant mean preference for the flattened frequency response, with 9 of 11 subjects preferring the rising frequency response. Conclusions: Input compression did not alter music enjoyment. Comparison of the two experiments indicated that individual frequency response preferences may depend on the genre or familiarity, and particularly whether the music contained lyrics.

Deterministic and band-limited stochastic energy harvesting from uniaxial excitation of a multilayer piezoelectric stack

Deterministic and band-limited stochastic energy harvesting scenarios using a multilayer piezoelectric stack configuration are investigated for uniaxial dynamic pressure loading. The motivation for exploring this off-resonant energy harvesting problem derives from typical civil infrastructure systems subjected to dynamic compressive forces in deterministic or stochastic forms due to vehicular or human loads, among other examples of compressive loading. Modeling of vibrational energy harvesters in the existing literature has been mostly focused on deterministic forms of mechanical vibration as in the typical case of harmonic excitation, while the efforts on stochastic energy harvesting have thus far considered second-order systems such as piezoelectric cantilevers. In this paper, we present electromechanical modeling, analytical and numerical solutions, and experimental validations of piezoelectric energy harvesting from harmonic, periodic, and band-limited stochastic excitation of a multilayer piezoelectric stack under axial compressive loading in the off-resonant low-frequency range. The deterministic problem employs the voltage output-to-pressure input frequency response function of the harvester for a given electrical load, which is also extended to periodic excitation. The analytical stochastic electromechanical solution employs the power spectral density of band-limited stochastic excitation to predict the expected value of the power output. The first one of the two numerical solution methods uses the Fourier series representation of the excitation history to solve the resulting ordinary differential equation, while the second method employs an Euler–Maruyama scheme to directly solve the governing electromechanical stochastic differential equation. The electromechanical models are validated through several experiments for a multilayer PZT-5H stack under harmonic and band-limited stochastic excitations at different pressure levels. The figure of merit is also extracted for this particular energy harvesting problem to choose the optimal material. Soft piezoelectric ceramics (e.g. PZT-5H and PZT-5A) offer larger power output as compared to hard ceramics (e.g. PZT-8), and likewise, soft single crystals (e.g. PMN-PT and PMN-PZT) produce larger power as compared to their hard counterparts (e.g. PMN-PZT-Mn); and furthermore, single crystals (e.g. PMN-PT and PMN-PZT) generate more power than standard ceramics (e.g. PZT-5H and PZT-5A) for low-frequency, off-resonant excitation of piezoelectric stacks.

Investigations of spurs and PM noise after frequency division

We show that the noise and spurious signals over the entire input frequency response of a binary digital divider contribute with equal weight to the output signal. Similar results are also obtained using non-binary digital dividers. We present a simple model that allows one to understand the mechanisms that produce these aliasing effects. Only filters at the input or intermediate stages of division can reduce these effects in digital dividers. We also show that direct-digital-synthesis, where the output of a counter is used to drive a shift register and a digital-to-analogue converter to produce a sinewave output, is largely free from these effects.

The application of actuator performance limits to aeroservoelastic compensation

An interaction between an aircraft's structural dynamics, unsteady aerodynamics and flight control system can have serious effects on the aircraft both in terms of structural integrity and rigid body stability. The effects of such an interaction, known as aeroservoelasticity, are poorly understood and as a result, very conservative flight control system design methods are used in order to achieve flight clearance. This paper demonstrates how the use of nonlinear actuation system models predicts a maximum boundary for the amplitude of the structural response as a result of the performance limits of the nonlinear actuation system. This envelope of maximum structural response can then be used to allow relaxation of the current design criteria for the structural mode filters. The procedure is demonstrated using a representative aircraft system model. Finally, the results of single input frequency response tests of a representative actuation system are presented in support of the earlier results.