Function Of Vibration Frequency Research Articles

Effects of hand vibration on reflex behaviors and pain perception – A pilot study

This research investigated the effects of hand vibration on the protective reflex responses and perception of the stimulus intensity. Electrical pulses were applied to the wrist to elicit the reflex responses. Changes of the reflex response were measured using the surface electromyographic activities from the hand flexor muscles, and were analyzed as a function of vibration frequency and initial level of grip force. Psychophysical experiment was also performed to assess the effects of hand vibration on perception of the electrical stimulus. The reflex responses were stronger during vibration, and were more visible at lower vibration frequencies and higher muscle contraction level. During vibration, a poor correlation was found between the reflex responses and stimulus perception. Relevance to Industry Results suggesting to adopt low level of grip exertion (light-weighted tool) and high vibration frequency to minimize the vibration-induced change of the protective reflex behaviors are useful to tool manufacturers and related workers.

Untangling the physical contributions to instantaneous normal mode approximations: Inhomogeneous broadening, motional narrowing, and energy relaxation

An instantaneous normal mode (INM) approach to vibrational lineshapes, including motional narrowing, is presented. Simulations and calculations are carried out for a diatomic in Lennard-Jones solvent as a function of vibrational frequency, with an emphasis on determining the contributions of different physical relaxation mechanisms. The velocity correlation of a bond is easily related to a bond-weighted INM density of states, containing both resonant energy relaxation (ER) and unnarrowed inhomogeneous broadening. An effective weighted density of states or static spectrum, the distribution of an effective time-dependent frequency Ω(t), is introduced and proposed as a measure of the inhomogeneous linewidth only. It is found that the vibrational INM are in the motionally narrowed or fast modulation limit; motional narrowing of INM cannot be ignored. A dynamic spectrum containing only the motionally narrowed inhomogeneous spectrum and corresponding pure dephasing relaxation is isolated. Reintroducing energy relaxation results in excellent agreement with simulation. The validity of INM approximations and the relative importance of different relaxation mechanisms as a function of vibrational frequency is analyzed. It is suggested that, through INM, a role may be found for motional narrowing in intermolecular dynamics.

Temperature effects on vibrotactile sensitivity threshold measurements: Implications for carpal tunnel screening tests

This study examines the effect of skin temperature on fingertip vibrotactile sensitivity measurements and the resulting implications for carpal tunnel syndrome screening tests. Twenty subjects (11 men, 9 women) were tested for fingertip vibrotactile thresholds using the method of limits at four different frequencies (31.5, 125, 250, and 500 Hz) and six temperature categories (17 degrees-20 degrees C, 20 degrees-23 degrees C, 23 degrees-26 degrees C, 26 degrees-29 degrees C, 29 degrees-32 degrees C, 32 degrees-35 degrees C). Vibrotactile sensitivity thresholds increased with decreasing fingertip skin temperature. Furthermore, the relationship was a function of vibration frequency. Higher frequencies were more affected by temperature than lower frequencies, with significant effects beginning at 29 degrees C. These temperature-related effects may lead to possible false positive results in screening for carpal tunnel syndrome or other neuropathies. To minimize potential temperature-induced misclassification errors during these screening tests, fingertip skin temperature should be recorded before measurement and probably maintained above 29 degrees C during the measurement.

High-damping metals and alloys

High-Damping Metals (HIDAMETS) are the physical metallurgist’s answer to unwanted noise and vibrations. However, the characterization of the damping properties of metals and alloys is neither simple nor straightforward. This is mainly because the damping mechanisms involved depend upon the stress-induced movement of defects in the metal in question which, in turn, implies a dependence upon the microstructure (thermomechanical history) of the sample. To properly characterize the damping performance of a HIDAMET in a well-defined structural state, one must measure the mechanical damping as a function of vibration frequency, temperature, vibration strain amplitude, and static bias load over the ranges of these variables to be encountered in the application in question. This requires the use of a variety of equipment adapted to different modes of vibration and their overtones, especially when the damping is nonlinear (amplitude-dependent). Our approach to this problem is described and illustrated by test results obtained on several HIDAMETS.

The localization of low- and high-frequency vibrotactile stimuli

Four experiments were conducted to determine whether spatial localization on the skin varied in acuity as a function of frequency of vibratory stimulation. The glabrous skin of the palm over the hypothenar eminence was selected as the site for stimulation by two frequencies, one at 25 Hz to stimulate non-Pacinian receptors, and one at 250 Hz to excite Pacinian receptors. Because the Pacinian receptors have larger receptive fields than the non-Pacinians, it was thought that the subjects' ability to localize would be poorer when the Pacinians were the class of receptor stimulated. In addition to frequency of vibration, the presence of a surround, the site of stimulation, the separation of the stimulator pair used in the 2AFC method, and the use of an impulse stimulus were all conditions varied to determine whether a simple direct correlation exists between receptor category and spatial acuity for vibratory stimuli. A significant difference in acuity was found as a function of vibration frequency at a proximal locus on the palm, but this vanished at a distal locus. The results have been interpreted to suggest that receptor density and its gradient across the skin areas involved may be as important as receptor type in the determination of spatial acuity.

Experimental and analytical determinations of the mechanical impedance response of animals to vertical vibration

The mechanical impedance of sitting, unanesthetized rhesus monkeys and dogs is determined for vertical, sinusoidal vibration. The animals were briefly (30 sec) exposed at discrete frequencies from 2 to 30 Hz at acceleration amplitudes of 0·5 and 1·0 g. The experimental data were applied to a two-mass, single-degree-of-freedom model to determine the whole body coefficients of elasticity and damping as a function of frequency and body mass. The coefficients were obtained for each test at each frequency by requiring the impedance of the model to match that measured from the animals. A part of the model is an empirical equation defining the ratio of non-reactive to reactive animal mass as a function of vibration frequency and intensity. The impedance response of the model for the monkey and also that for the dog closely matched the experimental results throughout the 2–30 Hz range at 0·5 and also at 1·0 g.

An analysis of acoustic power radiated into a reverberation chamber by a transversely vibrating slender bar

The acoustic power radiated by a transversely vibrating bar of circular cross section into a rectangular reverberation chamber is calculated by consideration of the total power absorbed by the chamber walls. A normal mode approach is used. The bar, which extends over the entire room length, lies parallel to four room edges and vibrates in a standing wave. The acoustic power radiated when averaged over all possible bar positions closely approximates the free field value. An expression for the corresponding normalized spatial standard deviation is obtained as a function of vibration frequency, chamber volume, chamber reverberation time, bar length and direction of vibration of the bar. The results have been confirmed experimentally. The radiated acoustic power has also been computed for a bar vibrating near a wall or an edge in the chamber. The main object of the study has been to provide a basis for the calculation of the stress induced in heat exchanger tubes by fan and flow noise via the reciprocal relationship between modal radiated power and response. The large number of tubes necessitates an estimate of the variation of tube response with position within the exchanger casing.

Mechanical Tuning of the Acoustic Receptor Organ of the Noctuid Moth

Mechanical characteristics of the auditory organ of Noctuid moths (Prodenia eridania, Cramer) have been investigated in an effort to define the stimulus at the receptor organ. This organ contains two receptor cells of unequal sensitivity and is suspended from the tympanic membrane. The neural spike rates produced by the more sensitive of the two cells have been recorded as a function of vibration frequency while mechanically stimulating the tympanic membrane. The frequency characteristic obtained in this way is determined by the mechanical properties of the receptor organ itself and is not affected by the system of air-filled cavities surrounding it. The resulting characteristic shows a primary resonance near 2 kHz, an antiresonance near 10 kHz, and one or more higher order resonances above 10 kHz. When the tympanic membrane is exposed to acoustic waves so that the intratympanic cavities become effective, the hearing organ is most sensitive to sound frequencies between 25 and 60 kHz [K. D. Roeder, J. Insect Physiol. 12, 843 (1966)]. Thus it appears that the primary mechanical resonance at 2 kHz is attenuated by the acoustic cavity system. The remaining high-frequency response is adapted to the frequency range of the sonar signals of bats.