Direct Energy, 2018a

5 HALL EFFECT 91
5 Hall Eect
5.1 Introduction
In this chapter we discuss another type of inductive energy conversion device,
the Hall eect device. While these devices may be made from conductors,
they are more often made from semiconductors, like silicon, which
are easily integrated into microelectronics. The Hall eect was discovered
using gold by Edwin Hall in 1879 [57]. The rst practical devices were
produced in the 1950s and 1960s when uniform semiconductor materials
were rst manufactured [57].
Hall eect sensors are used to measure some hard to observe quantities.
Without external tools, humans cannot detect magnetic eld. However, a
small, inexpensive Hall eect sensor can act as a magnetometer. Also, the
Hall eect can be used to determine if a semiconductor is n-type or p-type.
One of the rst applications of Hall eect devices was in computer keyboard
buttons [57]. Today, Hall eect devices are used to measure the rotation
speed of a motor, as ow rate sensors, in multiple types of automotive
sensors, and in many other applications.
5.2 Physics of the Hall Eect
Hall eect devices are direct energy conversion devices that convert energy
from a magnetic eld to electricity. The physics behind these devices is
described by the Lorentz force equation. This discussion follows references
[3] and [9]. If we place a charge in an external electric eld, it will feel a
force parallel to the applied electric eld. If we place a moving charge in
an external magnetic eld, it will feel a force perpendicular to the applied
magnetic eld. The Lorentz force equation
−→ F = Q
( −→E +
−→ v ×
−→ B
)
(5.1)
describes the forces on the moving charge due to the externalelectric and
magnetic elds. In the above equation, −→ F represents force in newtons on
a charge moving with velocity −→ v in units m s . The quantity −→ E represents
the electric eld intensity in units m V , and −→ B represents the magnetic ux
density in units Wb m . Charge in coulombs is denoted by Q. Notice that the
2
force on the charge due to the electrical eld points in the same direction
as the electrical eld while the force on the charge due to the magnetic eld
points perpendicularly to both the velocity of the charge and the direction
of the magnetic eld.