Abstract
The characteristics and applications of the “cable sensor, ” a new type of vibration sensor, are considered in this paper. Previous studies by the authors on the practical use of cable sensors in rockfall detection are reviewed. The mechanism of output voltage generation by the sensor is discussed. Methods for analyzing static electricity and molecular dynamics are applied toward elucidating the sensor's measurement principles. The following results were obtained:
1) Alternating output voltage of cable sensor occurs when an external vibration source causes multiple contacts between the conductor part of the sensor and its dielectric material (FEP). 2) The above fact is demonstrated experimentally through a vibration test using an audio speaker and an acceleration sensor. Output waveforms of the cable sensor are similar to those of the acceleration sensor. 3) From molecular dynamics analysis, it was supposed that FEP with a higher electron affinity might be produced by adding a -CF2CF3 group to the main chain of FEP in order to increase the output voltage of the sensor. 4) Output voltage of the sensor decreases with increase in capacitance of the circuit. This means that the output voltage decreases both with an increase in the length of the cable sensor and with the introduction of an extension signal transmission cable. The signal decrement could be compensated by amplification. A transfer function of the measurement circuit is derived, which enables evaluation of the necessary amplification gain. The results of the analysis of material combination for the sensor components and the proposed solutions to the equation describing the measurement circuit have deepened the understanding of the voltage output mechanism and measurement principles of cable sensors.
