Fiber optic link for detecting mechanical vibration in the presence of an electromagnetic field

Abstract

An apparatus for detecting mechanical vibration in the presence of an electromagnetic pulse, which is of particular use in the testing of land mines. An optical fiber link is provided between the device under test and a remote data collection station. A vibration sensor and optical transmitter are secured to the device under test, while an optical receiver and event latch are present at the other end of the fiber link at the data collection station.

I claim: 
     
       1. An apparatus for detecting the mechanical vibration of an explosive device in the presence of an electromagnetic field, comprising, an explosive device which is capable of producing mechanical vibration upon arming,   means located in proximity to said explosive device for sensing said vibration while being subjected to an electromagnetic field, and for generating an electric signal corresponding thereto,   optical transmitter means located in proximity to said explosive device for generating a light wave signal corresponding to said electrical signal,   optical receiver means disposed at a location remote from said explosive device for receiving said light wave signal and generating an electrical signal corresponding thereto,   an optical fiber link connecting said optical transmitter means and optical receiver means, and   means responsive to said electrical signal generated by said optical receiver means for indicating information about said mechanical vibration which is produced by said explosive device, whereby said optical fiber link prevents the coupling of energy produced by the electromagnetic field from interfering with said indicating means and said explosive device.   
     
     
       2. The apparatus of claim 1 wherein said device comprises a land mine. 
     
     
       3. The apparatus of claim 1 wherein said means for indicating information about said mechanical vibration comprises means for indicating whether the magnitude of the electrical signal generated by said optical receiver means exceeds a preset threshold value. 
     
     
       4. The apparatus of claim 1 wherein said means for indicating comprises means for displaying the electrical signal generating by said optical receiver means. 
     
     
       5. The apparatus of claim 1 wherein said means for generating an electrical signal corresponding to said vibration comprises a piezoelectric accelerometer. 
     
     
       6. The apparatus of claim 1 wherein said optical transmitter means comprises means for generating a light wave signal in the infrared frequency range. 
     
     
       7. The apparatus of claim 3 wherein said means for indicating whether the magnitude of the electrical signal exceeds a preset threshold value, comprises, means for amplifying the signal provided by the optical receiver means,   means for providing inverted and non-inverted versions of the amplified signal,   two comparator means for comparing the inverted signal and the non-inverted signal with the present threshold value,   means for feeding the inverted signal to an input of one comparator means and the non-inverted signal to an input of the other comparator means,   OR gate means for receiving the outputs of both comparator means, and   means responsive to the output of the OR gate means for providing an indication of whether the magnitude of the signal provided by said optical receiver means exceeds a preset minimum.