Technical Report on Vibration-Damping Materials and Their Performance Measurement 7

First, we will verify whether there is amplitude dependence using the attenuation method.
If there is, all measurements will be conducted using the attenuation rate method. When there is amplitude dependence, the frequency response function often deforms and does not become symmetric.
The input signal to the shaker should ideally be a synchronized sin sweep.
It is desirable to have an auto-ranging function that automates the FFT voltage range, optimizes the input and output voltage ranges, and reflects that voltage range in the calculation of the gain of the frequency response function. Additionally, it would be even better to have a function that changes the signal output level based on the gain of the frequency response function.
If measuring with a sin sweep takes a long time, it is advisable to use a signal with characteristics like those shown in the next figure.

It is a high-speed sine wave signal. The crest factor (maximum value / RMS value) is very low at 1.4, indicating a very high degree of concentration of the signal.
The FFT analysis frame is synchronized, and since a rectangular window function can be used, leakage errors do not occur.
Due to the constant signal, there is no additive effect; however, it allows for accurate measurement of the frequency response function in a short time, which has led to its increased use in recent years.
In devices that allow for signal synchronization, bandwidth limitation, and resolution changes through frequency zooming, the result is an apparently narrow bandwidth limited signal, and it is expected that S/N improvement can be achieved through zoom analysis.

The signal is a multiple sine wave with equal levels at all resolution points. The crest factor is approximately 3. The degree of concentration of the signal is moderate.
The FFT analysis frame is synchronized, and since a rectangular window function can be used, leakage errors do not occur.
Due to the constant signal, there is no additive effect; however, it allows for accurate measurement of the frequency response function in a short time, which has led to its increased use in recent years.
Devices that can perform signal synchronization, bandwidth limitation, and resolution changes through frequency zoom can expect an improvement in the signal-to-noise ratio (S/N) through zoom analysis.
By arranging sine waves in logarithmic intervals, logarithmic resolution is obtained, and by selecting and displaying logarithmic resolution frequencies on the FFT side, it becomes possible to perform logarithmic resolution measurements.

This is a signal synthesized from one sine wave aligned at the peak position. The crest factor is approximately 30.
It has the characteristic of being easy to respond to zoom analysis compared to a normal impulse.
Naturally, the beginning and end are 'zero', the FFT analysis frame is synchronized, and a rectangular window function can be used, thus preventing leakage errors.
Can be used as an input signal for the exciter in the damping rate method.

Typically, M series signals are used, and the crest factor is about 3. The degree of concentration of the signal is low.
It can be used for zoom analysis because it has signals of all frequencies.
Due to the inability to synchronize with the FFT analysis frame, the Hann window is usually used; however, the rectangular window is preferable only when measuring loss coefficients, as mentioned later. When using the Hann window, one must be cautious of leakage errors and also note that, as mentioned later, there is a lower limit for measuring loss coefficients with the Hann window.
It is also possible to impose bandwidth limitations, so during zoom analysis, it is desirable to be able to limit the bandwidth for zoom.
The effect of addition is very significant, and as shown in the figure above, there are many missing frequencies at any given moment, so it is necessary to perform addition sufficiently.
For measuring equipment with nonlinear elements, burst random is used.