Hall effect sensors are some of the most common magnetic sensors used for detect
ID: 2249937 • Letter: H
Question
Hall effect sensors are some of the most common magnetic sensors used for detecting position, current, magnetic field, liquid level and motion detection etc. Please answer the questions below about the design and operation of Hall effect sensors. Figure 1. Hall effect sensor operation mechanism. output (V) output (V null voltage -200 -100 100 200 100 200 300 400 500 Figure 2. Output behavior of Hall effect sensors, when the semiconductor layer is magnetized along its (a) hard axis and (b) easy axis. a) How does a magnetic Hall sensor work? What is the output and the input? (40 points). b) What are the noise sources in a Hall effect sensor? Please be specific. (20 points) c) Now imagine you deposit a piezoelectric layer (PZT, lead zirconium titanate) on top of the magnetic Co2FeAl layer to harvest vibration energy to power your sensor circuit. When the piezoelectric layer is exposed to force (or stress and strain), voltage drop across the PZT changes and causes current to floww Propose a mechanism such that when the chip is not biased (replace Up source with a resistive load), the oscillations from the environment can be converted to current and voltage. How much power can we expect from this power harvester? (40 points) Co FeAl [110] strain PZTExplanation / Answer
a) Hall-effect sensors are simple, inexpensive, electronic chips which are used in widely available gadgets and products. These sensors work by measuring the Hall voltage across two of their faces when you place them in a magnetic field.
Hall Effect Sensors are made up of a thin piece of rectangular p-type semiconductor material such as gallium arsenide (GaAs), indium antimonide (InSb) or indium arsenide (InAs) passing a continuous current through itself. When the device is placed within a magnetic field, the magnetic flux lines will be exerting a force on the semiconductor material which deflects the charge carriers, electrons, and holes, to either side of the semiconductor slab. This movement of charge carriers is basically because of the magnetic force they experience passing through the semiconductor material.
As these electrons and holes move sidewards a potential difference is created between the two sides of the semiconductor material by the build-up of these charge carriers. Then the movement of electrons through the semiconductor material is affected by the presence of an external magnetic field which is at right angles to it and this effect is greater in a flat rectangular shaped material.
The output voltage, called the Hall voltage, (VH) of the basic Hall Element is directly proportional to the strength of the magnetic field passing through the semiconductor material (output H). This output voltage can be quite small, only a few microvolts even when subjected to strong magnetic fields so most commercially available Hall effect devices are manufactured with built-in DC amplifiers, logic switching circuits, and voltage regulators to improve the sensors sensitivity, hysteresis, and output voltage. This also allows the Hall effect sensor to operate over a wider range of power supplies and magnetic field conditions.
VH=RH(I*B/T)
b) A low-frequency noise of a Hall sensor is also an important issue of concern. The small leakage currents from the sensor output are the main cause of the noise.
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