ABSTRACT
The natural frequency of traditional velocity sensors such as moving coil geophones limits their measurable low-frequency range, and the damping ratio affects the flatness of the sensor in the amplitude and frequency curves, resulting in variations in sensitivity over the available frequency range. In this paper, the structure and working principle of the geophone are analyzed and its dynamics are modeled. After synthesizing the negative resistance method and zero-pole compensation, two commonly adopted low-frequency extension methods, a method for improving low-frequency response, which is a series filter and a subtraction circuit to increase the damping ratio, is proposed. Applying this method to improve the low-frequency response of the JF-20DX geophone, which has a natural frequency of 10 Hz, results in a flat response to acceleration in the frequency range from 1 to 100 Hz. Both the PSpice simulation and actual measurement show a much lower noise level via the new method. Testing the vibration at 10 Hz, the new method has a 17.52 dB higher signal-to-noise ratio than the traditional zero-pole method. Both theoretical analysis and actual measurement results show that this method has a simple circuit structure, introduces less circuit noise, and has a low-frequency response improvement effect, which provides an approach for the low-frequency extension of moving coil geophones.
ABSTRACT
A series of benzo[a]pyrano[2,3-c]phenazine derivatives with a wide range of substitutions at ring C of the benzophenazine were designed and synthesized using the one-pot, four-component domino reactions. The targeted compounds were evaluated for their antitumor activities against HCT116, MCF7, HepG2 and A549 cancer cell lines in vitro. The most active compound 6{1,2,1,9} featured the CN and p-dimethylamino phenyl substituents on γ-pyran structure on ring C. Significantly, compound 6{1,2,1,9} was found to have the highest growth inhibitory activity against the HepG2 cell line with IC50 values of 6.71 µM, which was 1.6-fold more potent than positive control anticancer drug Hydroxycamptothecine (HCPT). Furthermore, structure-activity relationship (SAR) studies on the substitutions at ring C were discussed in details.
