标签：
豪探测器
The Hall effect, is a magnetohydrodynamic phenomenon where an external magnetic field affects the flow of charge carriers in a semiconductor in such a way that an electric field appears directed at right angles to both the magnetic flux lines and the current-flow direction.
Magnetohydrodynamics (MHD) is the study of electrically conducting fluids in motion. In this case, the electrically conducting fluid is the ensemble of majority charge carriers in the semiconductor.
For example, in P-type semiconductor material the majority charge carriers are positively-charged holes. A Hall sensor could be made from a rectangular thin film of P-type semiconductor with aluminum contacts laid down along its edges. One pair of opposite electrodes are connected to a source of dc current. The other pair connects to a sensitive voltmeter with a very high input impedance (electrometer).
In a Hall effect sensor, a magnetic field pushes the majority charge carrier flow to one side, creating a voltage difference across the flow.
The dc current will flow uniformly from the positive electrode to the negative electrode. This flow acts as a conducting fluid moving uniformly across the film. Since charge is uniformly distributed over the film, no voltage appears across the opposite pair of electrodes connected to the electrometer.
If we now apply a magnetic field directed normal to the film’s surface, a Lorentz force appears whose magnitude and direction are everywhere given by the vector cross product of the local charge-carrier velocity and the local magnetic field. In other words, the moving holes are pushed across the film at right angles to the dc current flow.
The holes therefore pile up along the edge next to one electrometer electrode (which sees a relative positive voltage), and away from the other (negative). The electrometer registers a potential difference proportional to the dc current and the magnetic field strength.
Since such Hall effect sensors can be manufactured from virtually any semiconductor by ordinary semiconductor fabrication processes, they are ideal sensors for magnetic fields. All of the circuitry can easily be integrated along with the sensor, so very small, highly stable, and extremely sensitive sensors can be made. The chips need only four connections: two raw dc power leads (the regulation can be integrated on the chip along with the rest of the electronics), and two analog output leads. Depending on the application, it is possible to integrate a Hall sensor into virtually any semiconductor device that needs one.
Note that the Hall sensor reports only the component of the magnetic field vector normal to the thin-film’s surface. It is quite insensitive to any other components. To report the field’s complete magnitude and direction requires three sensors oriented along three orthonormal axes.
Three Hall sensors oriented along three orthonormal axes determine the magnetic field’s magnitude and direction.
系统分类:
仪表传感器 | 用户分类:
无分类 | 来源:
原创