Index of content:
Volume 85, Issue 8, 15 April 1999
- MAGNETIC SENSORS (NOT RECORDING)
85(1999); http://dx.doi.org/10.1063/1.369975View Description Hide Description
This article demonstrates spin valve (sv) sensor applications as rotational speed control devices, in a Wheatstone bridge configuration. The sensor architecture uses two active self-biased sv elements (dimensions ) in a CoZrNb flux guide. The other two spin valves are inactivated for external fields inferior to 150 Oe. Inactivation is achieved by increasing the ferromagnetic coupling of the inactive spin valves above 200 Oe, by roughening the surface of the underlying oxide layer (12 Å average roughness). When excited by a magnetized wheel with 60 N-S poles rotating at 360 rpm, the sensor yields a 400 mV pp square wave output with rise/fall times corresponding to an angular resolution of 0.17°. Amplitude is independent of speed (0–3000 rpm), and of sensor to wheel separation Bridge output decreases 26% when temperature is increased to 150 °C. Bridge offset of 350 mV is caused by the resistance differences between the active and inactive sv elements.
85(1999); http://dx.doi.org/10.1063/1.369976View Description Hide Description
Magnetic bar codes can be used in dirty environments instead of optical bar codes or as invisible codes in order to enhance the security of prepaid cards. In this article, we propose a high density magnetic bar code system in which the existence or nonexistence of a bar element is detected by a magnetic bridge. A micro head constituting a magnetic bridge is fabricated with thin amorphous cores and thin copper wire coils. The magnetic bar elements are printed with magnetic ink. The basic characteristics, such as signal separation from neighboring bar elements, are discussed in terms of the element width and the space between two adjacent elements.
85(1999); http://dx.doi.org/10.1063/1.369977View Description Hide Description
Strain sensitivity of amorphoussputteredfilm was studied in detail, so as to examine the potential of film for highly sensitive microstrain gauges. The film exhibited the figure of merit (change in film permeability μ per unit strain ε) of the value of which is comparable to that of amorphous ribbons. Reflecting the large value of F, the high-frequency impedance of the film was also subjected to change due to strain: the change in impedance of 46% was observed at 100 MHz applying a strain of It is also demonstrated that utilizing the strain-dependent impedance, a small strain of can be detected with the film.
A torque transducer based on local bands of naturally stabilized remanent circumferential magnetization85(1999); http://dx.doi.org/10.1063/1.369978View Description Hide Description
A simple construction for “polarized ring”-type torquetransducers is described. Instead of residing within a separate magnetoelastically active ring, bands of circumferential remanent magnetization are established in the shaft itself. Coercivity, crystal anisotropy, and the closed circumferential configuration combine to stabilize the polarization. Symmetry precludes the appearance of magnetic fields from an untorqued shaft. Stress anisotropy associated with applied torque tilts the average easy axis into a helical orientation with chirality and helix angle proportional to torque direction and amplitude. Fields, associated with the divergence of the axial component of this magnetization, then arise in the space around each such band. Suitable shaft materials have high enough anisotropy and coercivity, and low enough magnetostriction to prevent these fields from significantly magnetizing proximate shaft regions. Experimental transducers, using heat treated alloy steel shafts, perform adequately for many industrial applications.
85(1999); http://dx.doi.org/10.1063/1.369865View Description Hide Description
An experimental technique for measuring the distribution of the normal and planar components of the magnetic induction near the surface of a superconducting sample is described. This technique utilizes a design of a double-layered Hall sensor array fabricated from a GaAs/AlGaAs heterostructure containing two parallel layers of a two-dimensional electron gas. Applications of this technique are demonstrated in measuring the current density distribution and in characterizing the flux creep process in a thin crystal.