Electromagnetic Vibration Exciter Research Articles

Force distortion in a coil/magnet vibration exciter for shallow structures subjected to large displacements

An electromagnetic noncontact vibration exciter has been designed for investigating nonlinear vibrations of shallow structures such as gongs, cymbals, and spherical shells. It is composed of two devices: a coil driven by a current and a small magnet glued on the structure. One interest of this system is that the mass of the magnet is small compared to the mass of the structure, so that its dynamic properties are only slightly modified. The magnitude of the force applied to the structure via the magnet depends on the relative position of magnet and coil. As a consequence, an harmonic distortion appears in the force wave form as the magnitude of the magnet displacement increases. A theoretical study is first carried out in order to find an optimal geometry for the coil that minimizes the force distortion. In a second step, a simple degree-of-freedom model is used to evaluate the distortion rate. It is found that this rate not only depends on the exciter properties, but also on the dynamics of the system under testing. A multiple-scale technique is used for the resolution of the nonlinear model that governs the distortion. Experimental results will be presented which confirm the theoretical predictions.

Reversibility and irreversibility in the packing of vibrated granular material

Abstract We report on the settling of loosely packed, cohesionless granular material under mechanical vibrations. Monodisperse spherical beads were confined to a long vertical cylinder that was driven by an electromagnetic vibration exciter. Under vibrations the bead packing evolves from an initial, low-density configuration towards higher density. Ramping the vibration intensity repeatedly up and back down again reveals the existence of both an irreversible and a reversible branch in the response. The reversible branch represents a steady state in which the packing density depends monotinically on the vibration intensity. We have investigated the bead size, depth, and ramp rate dependence of the compaction process. Our results indicate how the occupied volume fraction can be optimized by slowly reducing the vibration intensity along the reversible branch.

Research on the dynamic test method for force-balance accelerometers (FBAs) with electric stimulation Part 2. An improved test method for voltage-source type FBAs

This paper presents a novel dynamic test method for voltage-source output type force-balance accelerometers (VFBAs) with electric stimulation. The paper researches the equivalence the electrical and mechanical stimulation methods for VFBAs and analyses the principle errors. Experimental results obtained from the two stimulation methods are compared. The test method for VFBAs with electrcal stimulation is feasible and may be used instead of the common electromagnetic vibration exciter under certain conditions. Equipment for this test method is simple and can be utilized in on-line application environments.

Research on the dynamic test method for force-balance accelerometers (FBAs) with electric stimulation

Abstract At present, an electromagnetic vibration exciter is the equipment commonly used for the dynamic testing of force-balance accelerometers (FBAs), which is a mechanical stimulation method. This paper researches a method with electric stimulation, which is based on the electromechanical reciprocity of current-output type FBAS (IFBAs). The equivalence between the electrical and mechanical stimulation methods and the test errors are analysed. Experimental results obtained from the two stimulation methods are compared. The test method for IFBAs with electrical stimulation is feasible and may be used instead of the commonly used electromagnetic vibration exciter under certain conditions. Equipment for this test method is inexpensive and can be utilized in on-line application environments.

Experimental and theoretical study of power flow between randomly vibrating welded plates

The authors have previously described [J. Acoust. Soc. Am. Suppl. 1 72, S77 (1982)] a modal analysis technique for estimating power flow between welded plates in a form compatible with statistical energy analysis (SEA) formulations. The theory is here extended to point excitation of simply supported and freely suspended welded thin plates. This is used to assess various theoretical hypotheses concerning the dependence of the power flow between the plates on internal damping, excitation position, and structural dimensions. The general formulation allows a study of contributions from cross-correlation between modes of the two plates and other effects that are customarily neglected in SEA studies. The accompanying experimental study is with an L-shaped aluminum plate suspended by strings and driven by an electromagnetic vibration exciter, successively attached at a number of points on the plate. Measurements are reported for power input and vibrational energy in each plate and subsequently used to calculate apparent coupling loss factors. The latter are compared with the theoretical estimates. [Work supported by Whirlpool Corporation.]

Cyclic strength of magnesium-base reinforced composites

Fatigue tests on the CMs were conducted in the UNV apparatus [5] with an electromagnetic vibration exciter under conditions of bending of a flat cantilever-type specimen. The stress in the critical specimen section was determined from the vibration amplitude of the specimen end, using curves constructed in calibration tests. Calibration was performed by means of strain gauges bonded to specimens in their critical section zones [3].

Vibration Exciters with Interchangeable Heads

A new concept in electromagnetic vibration exciter design, in which the entire dynamic portion of the vibration exciter can be quickly changed, provides optimization of performance characteristics for specific applications. Since a head with the specific performance characteristics needed for the job can be selected, it is no longer necessary to use a compromise design. The performance characteristics discussed include those applicable to 200g testing, the testing of large objects where high side load capability and a rigid table are essential, the measurement of structural modes, impedances, and transfer functions, and confirmation calibration of accelerometers and other transducers. The design objectives and solutions are presented for the stiff highly damped suspension systems that make interchangeable heads possible. The moving element skeletons of five different heads are described in detail, showing how the different performance criteria for various applications are achieved. Included in the program are three different vibration exciter sizes with four or five heads for each.