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Technical Report: Vibration Damping Materials and Their Performance Measurement 14

31. Supplementary Materials

3. Excitation force response and linearity of electromagnetic vibrators

A measurement block diagram is shown in Figure 8.

  • Figure 8

The added mass was pre-mass-canceled using a vibration exciter, and the mechanical system was configured as shown in the diagram. The same type of electromagnetic detector was used. The output of the impedance head and the current flowing through the electromagnetic detector were measured. The generated "force" differs because the gaps of the MP-910 and MP-912 are different. Therefore, the horizontal axis was normalized by the maximum applied voltage. It is normalized by the maximum output of the impedance head.

Frequency response

Figure 9 shows the force response of the two types of vibrators, Figure 10 shows the current response, and Figure 11 shows the current/force frequency response function.

The MP-910, with a DC resistance of 1 kΩ, is affected by its own impedance and exhibits a dip in its force response at approximately 8 kHz. Therefore, the current/force frequency response function has a peak at this frequency. In comparison, the MP-912, with a DC resistance of 100 Ω, exhibits relatively smooth characteristics in the 10 kHz range. This indicates that the electromagnetic exciter current versus response voltage yields better symmetry of the resonant frequency than the conventional method of comparing input voltage versus response voltage. (Figure 12)

The excitation force cannot be read from the figure because it has been normalized, but the excitation force is approximately 0.05 N/W (att 1 mm GAP, 1 kHz) in all cases. However, to obtain a practical force of 0.5 N, a voltage of approximately 100 V is required for the MP-910 and approximately 38 V for the MP-912.

  • Figure 9
  • Figure 10
  • Figure 11
  • Figure 12

Excitation linearity

The voltage applied to the electromagnetic vibrator was gradually changed, and the excitation linearity was measured. The resulting characteristics are shown in Figures 13 to 16. It can be seen that the linearity is quite high.

  • Figure 13
  • Figure 14
  • Figure 15
  • Figure 16

4. conclusion

  • The characteristics of electromagnetic detectors and exciters have not been measured much in the past. Although they are frequently used in the cantilever beam method, this measurement was conducted out of concern that the force is truly being measured by using the input to the electromagnetic exciter as a quotient. As a result, it was found that measuring the input current to the electromagnetic exciter is closer to measuring "force" than measuring the voltage.

  • The accuracy of speed detection and speed generation was found to be higher than expected.

  • We measured two types of electromagnetic detectors and vibrators manufactured by our company, and we plan to measure those manufactured by other companies in the future.

  • While it might seem that winding many turns on a coil would yield a large excitation force in an electromagnetic vibrator, this increases the impedance and has the opposite effect. It was found that winding a moderate amount of thick wire (around 1000 turns) to achieve a DC resistance of several tens of ohms is sufficient.