Abstract
This paper describes a magnetoelastic strain sensor based on the ∆E effect and discusses some materials used in its construction. A polycrystalline Fe–Al–B alloy with good quality magnetoelastic properties was used as the transducer and glued to the test object, either brass plates or rods of SAE 1010 steel. The strain-dependent magnetic field of the transducer changes the operating point of the resonator, a strip of field-annealed Metglas 2826MB3, resulting in a modification of its resonant frequency. A model was developed to simulate the strain-dependent magnetic field acting on the resonator and thus to calculate curves of resonant frequency vs. deformation. With the help of this model, differences in the shape of the frequency vs. strain curve can be understood. For a sensor with resonant frequency of 60.5 kHz glued to a rod of SAE 1010 steel, a total resonant frequency variation ∆f ~7 kHz was observed for a deformation of 1100 ppm. The geometry of this sensor is especially favorable for the remote monitoring of a steel surface, such as the wires of the tensile armor of a marine riser.
Highlights
This paper is an extension of work originally presented at the 12th International Conference on Sensing Technology [1] in Limerick, Ireland
The Fe–Al–B transducer was glued to the steel rod with a cyanoacrylate adhesive, and the sample deformation was determined from the advance of the testing machine
This work has shown that the wireless magnetoelastic sensor functions with a steel substrate, the relation between the resonant frequency of the resonator and the strain is not linear, but rather sigmoidal in shape, or even more complex
Summary
This paper is an extension of work originally presented at the 12th International Conference on Sensing Technology [1] in Limerick, Ireland. The goal here is to develop a model for the strain-dependent magnetic field of wireless magnetoelastic strain sensors on different surfaces, for example, on the tensile armor of a marine riser. Monitoring the structural health of large structures such as bridges frequently makes use of a wireless strain sensor. Magnetoelastic stress sensors on large steel cables of Qiangjiang No 4 Bridge in China [2] are examples of noncontact stress monitoring for steel cables and prestressed tendons on suspension bridges, cable-stayed bridges, and other ferromagnetic structures. The measurement of torques on the steering column of an automobile for the purpose of servo control can be performed with strain gauges, which must, be controlled in a noncontact manner by a rotary transformer, which surrounds the steering column [3]
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