Research about Miniature Vibration Sensor based on Hall Effect

Abstract

When we move the Hall component in a uniform gradient magnetic field under the constant current, the Hall electromotive force it outputs depends only on the amount of its displacement in the magnetic field. According to this characteristic, this paper analyses the basic principles, the selection of uniform gradient magnetic field and the output of displacement expression data. This paper makes a research from the four aspects. With improvement and innovation, we try to design a sensor which can measure miniature vibration. Introduction Nowadays, as the deepening of the scientific research, we have become increasingly demanding for the accuracy of measurements. That, how to measure small vibrations conveniently and quickly, is a research aspect that receives much concern. Hall displacement sensor, compared with other displacement sensors, has features such as quick response, simple structure and low cost, and some disadvantages about the measurement as well. To achieve the effect small vibrations to be measured, we will improve and research the sensor, based on its disadvantages. Fundamental principles Hall effect When a magnetic field is present to the semiconductor that is perpendicular to the direction of the current, the electrons and holes inside the semiconductor will experience a force, which is called the Lorentz force, and the electrons and holes will accumulate on one face of the material, establishing an electric field. The force from the electric field opposes the Lorentz force. When the electric field reaches a certain value, the electric force and the Lorentz force experienced by the holes and electrons are balance. The electric field opposes the migration of further charge, so a steady electrical potential is established, making the subsequent electron and holes can pass without deflection. This is called the Hall effect. As is shown in the Fig.1. Suppose the conductor is a cuboid, whose length, width and height are a, b, and c respectively, the electricity flows in from surface cd vertically, and that the magnetic field intensity is B vertical to surface ab, the voltage between the two boards front and back is therefore Hall voltage Fig.1: Hall effec International Power, Electronics and Materials Engineering Conference (IPEMEC 2015) © 2015. The authors Published by Atlantis Press 969 According to the formula of Hall voltage U, with a fixed electric current I, as long as the magnetic field gradient is constant, the value of Hall voltage across the Hall element will show a positive liner relationship with its displacement within the Hall element. Hall element. Produce Hall element using the principle of Hall Effect. The performance curve of Hall element is as follows: The purpose is to find appropriate electric current and magnetic field, so that with a fixed electric current and constant magnetic field gradient, the Hall element will work with in interval AB in the phase diagram. The working status of Hall element is also associated with temperature. For the sake of measuring accuracy, SS495A1 Hall element is chosen, whose working temperature is between -40C and 150C with strong flexibility, matching the requirement of measurement and design. . Fig.2: Characteristic Choosing the magnetic field As is shown in the first step, in order to make the instrument reflect tiny vibration, a liner relationship between Hall voltage and displacement is in need. Thus, we need to select a magnetic field with constant gradient. This essay develops the study according to an experiment – correction verify procedure, fitting Hall voltage and displacement of Hall elements in magnetic field of various shapes, through which we find that magnetic field of bar magnet is pretty close. Consequently, we made further improvement based on this idea, and finally choose to fix two angel-shaped iron on the two sides of the bar. The specific measuring method is as follows: Fig.3 Measuring method Fitting this set of data using MATlAB, we have Fig.4: