c is the velocity of the P wave or S wave in the seismic source region, and [f.sub.c] is the corner frequency
. Its formula  is
Microphones were chosen to exhibit flat frequency response in bandwidth of respiratory sounds (i.e., 100 to 1000 Hz) and accelerometers featuring a resonant frequency well above the upper corner frequency
The active signal filter is formed by using an AC op-amp integrator with DC gain control with the corner frequency
of 15.92 kHz.
It can be realized by increasing corner frequency
of first-order inertial element so as to increase the flow-pressure coefficient of the load sensing valve or reducing the spring stiffness of the load sensing valve and the piston area of variable hydraulic cylinder.
To remove the low frequency noise caused by the motion artifact, a study has been conducted to ascertain a reasonable value for the high-pass corner frequency
The MOSFETs are biased in the subthreshold region and this will provide high output impedance and hence enhance the lower corner frequency
. All biased currents are designed using simple current mirrors.
For the 85 % of rock bursts, the corner frequency
does not exceed 23 Hz.
The highpass corner frequency
was determined from De Luca.
A corner frequency
[f.sub.injRC] is defined in (9).
The output current filter may easily be designed by choosing both a desired filter corner frequency
and a small inductor value (one freedom degree).
According to Figure 5 a pessimistic estimation of the OTA corner frequency
is around 100 kHz.
For all measurements, the highpass filter corner frequency
is set 8 % lower than the measurement frequency, and the lowpass filter corner frequency
is set 8 % higher than the measurement frequency.