Technical Report: Vibration Damping Materials and Their Performance Measurement 13

Two types of electromagnetic detectors were measured: the MP-910 with a nominal DC resistance of 850-950Ω and the MP-912 with a nominal DC resistance of 85-105Ω. A 1Ω cement resistor was inserted in series with each detector, current was detected, and the frequency response function with respect to voltage was measured. See Figure 1.

This result shows that the impedance changes quite significantly. While the MP-910 and MP-912 are almost parallel, when using the MP-910, the impedance is high, so care must be taken with the impedance of the connected instrument. When used as an electromagnetic exciter, insufficient excitation force is expected with a normal power amplifier. The decrease in impedance at high frequencies in both cases is thought to be due to the capacitance component of the coil.

Figure 3 shows the frequency response of the velocity detection. (Frequency response function with laser vibro) The frequency characteristics are quite flat, but this is because it is the sensor performance and (since it was not used as a vibrator) it was assumed that no reaction force would occur, so a weak mounting jig was used.
The linearity with respect to vibration velocity is shown in Figures 4 to 7. Both the MP-910 and MP-912 were found to have sufficient performance for measuring the loss coefficient. The normalized velocity is calculated by normalizing the maximum output measured by each detector to 100% for comparison purposes, because the detector's output voltage is very sensitive to the detection distance from the iron piece.