# Hall Plate : AC input behavior?

Discussion in 'Electronic Basics' started by Will, Nov 17, 2005.

1. ### WillGuest

Hi All,

I have a basic question regarding Hall plates for a course I am taking. (I
understand the basic operation of a Hall plate using a constant DC current
source across the current pads to sense a perpendicular magnet field).
However, I have a task of investing what is the behavior of a typical Hall
plate if you apply AC constant current source instead of a DC constant
current.

Can anyone comment on the behavior of this say applying 10Hz or 100Hz?
Would you just see a periodic Hall voltage in response to your MF? Would it
still be a linear relationship? Would the output be usable? What would be
the typical highest input frequency this device could sustain?

Will the resulting magnetic flux from your alternating current input
interact with the magnetic field you are trying to sense?

Since you typically use high input currents to sense small magnetic fields,
I would think that any AC current input with a large magnitude would either
desensitize your sensor or possibly interact with the very device your are
trying to sense?

Are there any applications where you could use an AC input current source?
Or is this strictly a DC current driven device?

Michael.

2. ### John PopelishGuest

The Hall effect voltage is proportional to the current through the
plate, and also proportional to th perpendicular component of the
field passing through the plate, so it should work fine with AC
excitation. The output is one polarity when the current is one
polarity, and the other polarity when the current changes direction.
This should hold true till the frequency gets so high that the plate
dimensions are a significant fraction of a wavelength or the applied
frequency.
Not much, since the applied current creates a magnetic field that
wraps around the plate, and the Hall effect is dependent on the field
passing through the plate. I guess there might be some effects at the
edges where the wrapping field passes through. Are you analyzing the
effect, mathematically, or experimentally?
The excitation current is usually limited by the resistance of the
plate and the heat that resistance produces. These limits normally
keep the magnetic field from the excitation quite low.
AC excitation allows narrow band amplification and phase locked
detection, which rejects lots of noise and DC drift, so it could have
applications for low level sensing.

3. ### Jasen BettsGuest

I see no reason why it wouldn't still be linear, so long as thare's no
ssemiconductor junctions, or other non-linear devices involved to foul
things up.
if it did not there would be no hall voltage produced.
last week someome said that low AC voltages are easier to detect than low DC
voltages.