Technical Report: Vibration Damping Materials and Their Performance Measurement 7

First, we will use the damping method to verify whether there is any amplitude dependence.
If present, all measurements should be performed using the attenuation method. When amplitude dependence is present, the frequency response function is often deformed and not symmetrical.
The input signal to the vibrator should be a synchronized sine sweep for optimal performance.
It is desirable to have an auto-ranging function that automates the voltage range of the FFT, optimizes the input and output voltage ranges, and reflects that voltage range in the calculation of the frequency response function gain. Furthermore, it would be even better if there was a function to change the signal output level based on the gain of the frequency response function.
If the sine sweep measurement takes too long, it is recommended to use a signal with the characteristics shown in the following figure.

This is a high-speed sinusoidal sweep signal. The crest factor (maximum value / RMS value) is very low at 1.4, indicating a very high degree of signal concentration.
Because it can be synchronized with the FFT analysis frame and a rectangular window can be used as the window function, leakage errors do not occur.
Although there is no additive effect because the same signal is always used, it is widely used in recent years because it allows for accurate measurement of the frequency response function in a short time.
In devices that allow signal synchronization, bandwidth limiting, and resolution changes via frequency zoom, the signal becomes a limited and filtered signal with an apparent narrow bandwidth, and zoom analysis can be expected to improve the signal-to-noise ratio (S/N).

This is a multiplexed sine wave with equal levels at all resolution points. The crest factor is approximately 3. The degree of signal concentration is moderate.
Because it can be synchronized with the FFT analysis frame and a rectangular window can be used as the window function, leakage errors do not occur.
Although there is no additive effect because the same signal is always used, it is widely used in recent years because it allows for accurate measurement of the frequency response function in a short time.
In devices that allow signal synchronization, bandwidth limiting, and resolution changes via frequency zoom, zoom analysis can be expected to improve the signal-to-noise ratio (S/N).
By arranging sine waves at logarithmic intervals, logarithmic resolution can be obtained, and by selecting and displaying the logarithmic resolution frequency on the FFT side, logarithmic resolution measurement becomes possible.

This signal is created by combining two sine waves with their peak positions aligned. The crest factor is approximately 30.
Compared to conventional impulses, it has the advantage of being easier to handle with zoom analysis.
Naturally, the beginning and end are "zero," it is synchronized with the FFT analysis frame, and a rectangular window can be used as the window function, so no leakage error occurs.
It can be used as an input signal to the exciter in the damping ratio method.

Typically, M-sequence signals are used, with a crest factor of approximately 3. The degree of signal concentration is small.
Because it has signals of all frequencies, it can also be used for zoom analysis.
Because it cannot be synchronized with the FFT analysis frame, the Hanning window is usually used, but as described later, the rectangular window is better only when measuring the loss coefficient. When using the Hanning window, attention must be paid to leakage error, and as described later, attention must be paid to the lower limit of measurement of the loss coefficient with the Hanning window.
Bandwidth limiting is possible for this as well, so when performing zoom analysis, it is desirable to be able to limit bandwidth by the zoom bandwidth.
The summing effect is very significant, and as shown in the diagram above, there are many frequencies that are missing at each instant, so summing is necessary.
Burst random is used for measuring instruments with nonlinear elements.