MEMS Gyroscope.
So, folks, in this video, I want to talk about some of the basics and
operating principles of the MEMS gyroscope.
And let me start some of the applications that these MEMS gyroscope enable.
So, chances are, if you are driving a car today, it's equipped
with a electronic stability program or electronic stability control,
which prevents the car from rolling over or skidding,
which might happen if you're driving, especially in snow or wet condition.
And that rollover of the car or the skidding of the car is detected by
the MEMS-based gyroscope in this car, and then the electronics
in the car acts upon that information to prevent that from happening.
So this one application that is in the automotive space.
There are many applications of these MEMS-based gyroscope
in the consumer space as well.
So one of the prominent device which was one of the first device to
feature a MEMS-based gyroscope was this Nintendo Wii controller,
which was introduced around 2009.
And this device enabled you to detect the movement
of this remote, both up and down, and also sideways.
And that enabled a lot of gaming applications.
And more recently, the use of these MEMS-based gyroscope
has really exploded after they got adopted in the smartphones and tablets.
And there are now thousands and
thousands of games that you can download on these smartphones and
tablets which leverage the, both the MEMS gyroscope and
also the accelerometer together to enable very precise motion sensing,
which enables a lot of these gaming application.
So here is one of my favorite examples, which is a game I used to play as a kid,
which involved this labyrinth and a ball which you had to maneuver,
and, you know, navigate along this labyrinth to
bring it into a certain box and in a certain position.
And nowadays, you know, a lot of this functionality is mimicked in our
smartphones and tablets by using these MEMS-based accelerometers and gyroscopes.
So now let me introduce three terms which are often used in the context
of MEMS gyroscope, and they are very fun to, you know, just say.
So these three terms are pitch, roll, and yaw.
So what they represent is, they represent the angular motion or
the angular velocity along the x, y, and z axis.
So if this plane, this your paper based airplane,
was to move along this up and down direction, that would be the pitch.
If it moved sideways such that the one wing went up and
one wing wing went down, it would represent roll.
And then if it moved sideways like that, that would
represent a motion angular velocity along the z axis, which would be yaw.
For the genesis of these terms, one of the [UNKNOWN] I'm using a picture
of a plane to demonstrate it is that the genesis of these terms lies in aviation,
where movement along this axis, which is the pitch, would,
determine how far the plane would go if it was landing.
And if you ever drive a plane, a manual plane like a Cessna aircraft,
that's controlled by this elevator which is located in the tail part of the plane,
and that's associated with the pitch.
The roll is a movement of this plane sideways.
And that's controlled by these arrows which
are located on the wings of the plane.
They control the roll of the plane.
And then the third is the motion along the z axis,
which is what you know, would enable you to change directions.
And this is controlled by this rudder which is
again located towards the tail end of the plane.
So, these are these three terms, pitch, roll, and yaw.
And now that you have some some knowledge of where they come from,
you can hopefully relate to them more easily.
So if we go back to some of these applications, so when my car was
essentially moving in this direction, I would say it was rolling over.
When it was skidding on this plane,
then I would say then that was associated with a yaw.
So if I want to prevent the rollover of the car and prevent it from skidding,
I would need a MEMS based gyroscope which detects the roll and the yaw axis.
Okay?
Similarly, if I have this Nintendo Wii, if I'm holding it in my wrist like this.
Okay?
So if I move it up and down, that would be my pitch.
If I move it sideways, that would be my yaw.
And if I rotate my wrist, if I rotate my wrist, that would be the roll.
Okay? So now let's turn our attention to some of
the basics of how does MEMS space gyroscope actually work.
So, the fundamental effect which determines the operation of all
of these MEMS-based gyroscopes is this Coriolis effect,
which is in turn is based on the Newton's law of motion.
But what it states, is that, let's say I have a mass, shown in green over here,
which is moving along the x direction.
Okay.
And its subjected to I'm going to rotation along the z direction,
so it experiences a force which is a Coriolis force,
which is given by 2 times the mass of this block.
And it's proportional to both the velocity along of this mass,
and it's proportional to this angular velocity which is subjected upon it, okay?
And in terms of a vector product,
it's direction is given by the vector product of V cross Omega.
So it's perpendicular both to the velocity vector and
it's perpendicular to the angular velocity vector as well.
So in this case, if I had a mass which was moving along the x direction, and
it was subjected to a angular rotation,
with a angular velocity vector located along the z direction, okay?
It would experience a Coriolis force which is proportionate to 2 times,
which is given by 2 times the mass, the velocity, and then the angular velocity.
And its direction is given by the vector product of that velocity and
angular velocity, so if in this case the force is along the minus y direction.
Okay? An important thing to
note is that it's proportional to the mass.
So if I were to take a small amount of angular rotation, it might help to,
you know, to have a mass which is large enough.
And later we'll see that it has implications on
what process technology which we, is used to make these MEMS gyroscope.
Okay, so if we want a MEMs gyroscope which is very sensitive to detecting
small amount of angular rotation, then it might be wiser to use a process
which results in a larger proof mass, or larger mass of this vibrating body, okay?
So while I demonstrated this Coriolis effect using one of this mass,
often what is used in practice is we use two
of these masses which are vibrating in opposite direction.
Okay.
So what is used, let's say you have two of these masses.
Okay.
They're vibrating along the plus x and minus x direction.
And when they're subjected to, let's say,
angular rotation, which is located along the z direction.
And let's say these, both these masses have the same mass.
So they would experience equal Coriolis force but opposite in direction, okay?
So this would experience a Coriolis force along this direction which would be given
by 2 times the mass times the velocity times the angular velocity.
And this will also experience a Coriolis force which is same in
magnitude as the two masses are same in magnitude, but opposite in direction.
So if we are sensing the difference in the Coriolis
force experienced by these two masses, we can actually improve our sensitivity.
So for example, I was, let's say sensing the capacitance which was
associated with these two vibrating masses in, let's say, some fixed plate.
If I was actually sensing the difference in capacitance, okay?
And if I measure now these two masses which are vibrating in the opposite
direction, I would sense a larger delta, so you've got a larger change
in capacitance, and that would help increasing my sensitivity in turn as well.
Another thing, another thing why using these two masses instead
of one vibrating in the opposite direction is very important is
because it can help me negate the effect of acceleration or
unwanted acceleration on these masses, okay?
So let's add these two vibrating masses, vibrating around opposite direction.
And the whole system was subjected to acceleration along,
let's say, minus y direction, so both of these two masses would experience
force which are located along the same direction, okay?
Since both of these have the same mass and they're subjected to
the same acceleration, the forces on these two masses would be the same.
And again, if I was measuring the property which was associated with the difference
between the two, okay, so let's say I was, again, sensing the capacitance difference,
both of these will experience a change in the capacitance, but
there'll be no effective delta c between these two masses, okay?
So it helps me negate the effect of this
unwanted acceleration that can influence these two masses.
So the only thing that i will measure is the angular velocity,
which results in forces which are opposite in direction.
Remember, this will experience a Coriolis force like this.
The other one will experience a Coriolis force along the opposite direction.
Okay, so many a times the term which is used to also describe
these masses are the tuning fork based gyroscope,
which utilizes essentially a tuning fork, if you look at it.
It utilizes these two arms of the tuning fork, they move along opposite direction,
so if this fork is subjected to a rotation, it will experience,
the two parts of this fork would
experience Coriolis force which is equal in magnitude but opposite in direction.