Technical Report on Vibration-Damping Materials and Their Performance Measurement 13

Measured two types of electromagnetic detectors (nominal DC resistance values: MP-910 with 850 to 950 Ω, and Mp-912 with 85 to 105 Ω). A 1 Ω cement resistor was inserted in series with the electromagnetic detector to detect current, and the voltage frequency response function was measured. See Figure 1.

It was found that the impedance changes significantly as a result. Although MP-910 and MP-912 are nearly parallel, when using the MP-910, the impedance is higher, so care must be taken regarding the impedance of the connecting instruments. When used as an electromagnetic vibrator, it is expected that a standard power amplifier will result in insufficient excitation force. The decrease in impedance at high frequencies for both is thought to be due to the capacitive components of the coils.

The frequency response of speed detection is shown in Figure 3 (frequency response function with a laser vibrometer). The frequency characteristics are quite flat, which is considered to be due to the sensor's performance (since it was not used as an exciter), and it is thought that this is because a weak mounting fixture was used, leading to no reaction force.
The linearity with respect to the vibration speed is shown in Figures 4 to 7. It was found that both MP-910 and MP-912 have sufficient performance for loss coefficient measurement. The normalized speed refers to the maximum output measured by each detector being normalized to 100% for comparison, as the output voltage of the detector is very sensitive to the detection distance from the iron piece.