A Study On The Mechanism Of Ultralow Frequency Absolute Vibration Detection Based On The Magnetic Damping

Ultralow frequency absolute vibration means the vibration which has no static reference point (i.e. datum) relative to inertial space under the vibration frequency below1Hz, such as aviation aircrafts, marine warships and large-span bridges. In actual engineering applications, for the measurement of the ultralow frequency absolute frequency, it is always difficult to find a desirable method. Because existing inertial vibration transducers have their amplitude-frequency response presenting high-pass properties, and their natural frequencies are generally within5Hz to12Hz, and during the ultralow frequency measurements, their output signals are almost overwhelmed by the noise. Started with the mechanical model of the currently most popular piezoelectric acceleration transducers, this paper has analyzed and demonstrated their structural characteristics, frequency characteristics and S/N ratio, and found such model being severely congenitally deficient, that is to say, it is difficult to turn to the design of the mechanical structure to reduce the natural frequency of the transducer fn=(1/2π)(?)k/m (where, k is for the spring stiffness coefficient, m is for the mass of the inertial mass) and if the spring stiffness coefficient k is decreased, the transducer will easily shake to be self excited, and if the inertial mass m is increased, it will be bound to increase the mass and volume of the transducer, thereby affecting the precision of the vibration detection and extent of the applicability.In this connection, this paper is proposed with a new concept utilizing the repulsive force between ends of the same polarity of two pieces of permanent magnet instead of the mechanical spring force of conventional transducers. We call the damping formed utilizing the magnetic force as "magnetic damping". Based on the new mechanism of the magnetic damping, the author has made efforts as below:(1)Mathematical model of the transducer based on the new mechanism of the magnetic damping and its analysis;(2)Signal conditioning circuit supporting the transducer based on the new mechanism of the magnetic damping;(3)Developing a transducer prototype based on the new mechanism of the magnetic damping;(4)Independently developed a simple ultralow frequency vibration test exciting bench for the transducer prototype;(5)Obtained test waveform with better S/N below0.25Hz of the prototype.The experimental waveform demonstrates that such transducer can obtain effective signal in the ultralow frequency range and have better S/N, which can provide good reference for further study of the ultralow frequency absolute vibration transducer.Finally, this paper has summed up and made a prospect of the subsequent further work, nailed down the contents and orientation for the future work.