Contactless angle detection using permalloy

An overview is given of measurements on angle detectors. The detectors consist of a pair of planar-Hall elements opposite to a rotatable magnet. The measurements are performed on a number of planar-Hall elements of different shape and size, and show good agreement with a previously described theoretical mode. To increase the accuracy of the angle detector, three modifications of the original concept of the planar-Hall elements are treated: a ring-shaped element having increased output voltage; an optimized configuration of a pair of planar-Hall elements and a permanent magnet, to cancel out the effects of magnetic anisotropy in the permalloy on the accuracy of the angle detector; and an annealing step at 500 degrees C applied to the permalloy to create a magnetically isotropic film. The results of measurements on planar-Hall elements as suggested in modifications are presented and show good agreement with theory

Detection of protein concentrations using a pH-step titration method

A stimulus-response method based on the application of a pH step is proposed for the detection of protein immobilized in a membrane on top of an ion-sensitive field-effect transistor (ISFET). The ISFET response to a step-wise change in pH, applied at the interface between the membrane and the surrounding solution, depends on the concentration of protein immobilized in the membrane because proton-dissociation reactions of the protein cause a delayed diffusion of protons and hydroxyl ions through the membrane. Our theoretical description shows that the delay in ISFET response is linearly related to the concentration of protein immobilized in the membrane. Experiments performed with lysozyme as a model protein show the feasibility of this detection principle

Permalloy multilayers to reduce the effects of uniaxial anisotropy

The anisotropic magnetoresistance effect of Permalloy (Ni0.82 Fe0.18) is used in a contactless angle detector. The uniaxial magnetic anisotropy in a Permalloy thin film causes a difference between the direction of magnetization and the magnetic field direction. This leads to a systematic error in the angle detector output. The effects of uniaxial magnetic anisotropy can be reduced by using Permalloy multilayers with different orientations of their anisotropy axes. A double layer with mutually perpendicular anisotropy axes is found to be sufficient for application in an angle detector. The Stoner-Wohlfarth single-domain model is used to describe the systematic error of an angle detector using multilayer