1320 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1957 



of the rod will result. The effect is a consequence of the resultant helical 

 flux field causing a change in length of the rod in a helical sense. Con- 

 versely, it was also observed that a rod under torsion will produce a 

 voltage between its ends when the rod is magnetized (see Fig. 1). 



Recently, during an investigation of the magnetic properties of nickel 

 wire, it was observed that a voltage was developed across the ends of a 

 nickel wire as its magnetization state was changed. Both the amplitude 

 and the polarity of the observed signal could be varied by movements 

 of the nickel wire. Most surprising, the amplitude of the observed voltage 

 V2 of Fig. 2, was many times that which would be expected if a con- 

 ventional pickup loop were used. 



After determining experimentally that the observed voltage was 

 generated solely in the nickel wire and was not a result of air flux coupling 

 the sensing loop (nickel wire plus unavoidable copper return wire), it 

 was concluded that the flux in the nickel wire must follow a helical path. 

 This suggested that torsion was the cause of the observed effect, a con- 

 clusion verified experimentally. The direction of the applied twist de- 



APPLY I, 



TWIST 



OBSERVE V2 



Fig. 1 — Observation of an internally induced voltage V2 generated by a mag- 

 netic wire under torsion. 



TWIST 



Fig. 2 — Comparison of the internally induced voltage v-i to the voltage Vt 

 induced in the oickup loop. 



