KSME International Journal

, Volume 15, Issue 7, pp 866–875 | Cite as

Complex modal testing of asymmetric rotors using magnetic exciter equipped with hall sensors

  • Chong-Won Lee
  • Si-Kyoung Kim
Materials & Fracture · Solids & Structures · Dynamics & Control · Production & Design


The complex modal testing methods developed for asymmetric rotors are briefly discussed and their performances are experimentally evaluated. For the experiments, a laboratory test rotor is excited by using a newly developed, cost effective magnetic exciter equipped with Hall sensors, which measure the excitation forces. It is concluded that the exciter system is characterized by a wide bandwidth and a high resolution for both the excitation and force measurement, and that the one-exciter/two-sensor technique for complex modal testing of asymmetric rotors is superior to the standard two-exciter/two-sensor technique in terms of practicality and realization.

Key Words

Complex Modal Testing dFRFs Asymmetric Rotors Magnetic Exciter hall Sensors 



Magnetic force

fy, fz

y- and z- direction force vectors

g,\(\bar g\),\(\tilde g\)

Complex force vectors in stationary coordinate


Air gap

Gjw,\(\hat G(j\omega )\),\(\tilde G(j\omega )\)

Fourier transforms of g,\(\bar g\) and\(\tilde g\)

Hgp,\(H_{\hat g\hat p} \),\(H_{\tilde g\tilde p} \)

Normal dFRFs

\(H_{\hat gp} \),\(H_{g\hat p} \)

Reverse dFRFs of anisotropic rotors

\(H_{\tilde gp} \),\(H_{g\tilde p} \)

Reverse dFRFs of asymmetric rotors

\(\tilde H_{ik} i,k = p,g,\hat g,\tilde g\)

Estimated dFRFs using unidirectional excitation


Imaginary number\( = \sqrt { - 1} \)


Stiffness of simple rotor

p,\(\bar p\)

Complex displacement vectors in stationary coordinate

P(jw),\(\hat P(j\omega )\)

Fourier transforms ofp and\(\bar p\)

Sik,\(i,k = p,g,\hat g,\tilde g\)

Directional auto- and cross- spectral density functions


y- and z- directional displacement vectors

\(\gamma _{g\hat g}^2 (\gamma _{g\tilde g}^2 )\)

Directional coherence function between g,\(\bar g\) (g,\(\tilde g\))


Rotational speed

\(F(\bar F)\)

Forward (conjugate forward) mode

\(B(\bar B)\)

Backward (conjugate backward) mode


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Copyright information

© The Korean Society of Mechanical Engineers (KSME) 2001

Authors and Affiliations

  1. 1.Center for Noise and Vibration Control, Department of Mechanical EngineeringKAISTTaejonKorea
  2. 2.Advanced Engineering CenterSamsung SDIKyunggi-doKorea

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