[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:03.30,Default,,0000,0000,0000,,>> This is Dr. Cynthia Furse\Nof the University of Utah.
Dialogue: 0,0:00:03.30,0:00:05.86,Default,,0000,0000,0000,,Today, I'd like to talk about inductors.
Dialogue: 0,0:00:05.86,0:00:08.40,Default,,0000,0000,0000,,We're going to talk about\Nwhat is inductance and how
Dialogue: 0,0:00:08.40,0:00:10.54,Default,,0000,0000,0000,,does it relate to\Nthe magnetic field and current?
Dialogue: 0,0:00:10.54,0:00:13.28,Default,,0000,0000,0000,,We'll explain the effect of\Ndifferent inductor parameters,
Dialogue: 0,0:00:13.28,0:00:16.36,Default,,0000,0000,0000,,and finally what it does to a voltage\Nand current in the circuit.
Dialogue: 0,0:00:16.36,0:00:20.24,Default,,0000,0000,0000,,An inductor is a passive element that\Nstores energy in the magnetic field.
Dialogue: 0,0:00:20.24,0:00:23.43,Default,,0000,0000,0000,,Passive means that whether or not\Nit's connected to a voltage source,
Dialogue: 0,0:00:23.43,0:00:24.69,Default,,0000,0000,0000,,it's still an inductor.
Dialogue: 0,0:00:24.69,0:00:26.82,Default,,0000,0000,0000,,An inductor is basically a coil of wire.
Dialogue: 0,0:00:26.82,0:00:29.04,Default,,0000,0000,0000,,You can just take a wire
Dialogue: 0,0:00:29.04,0:00:31.41,Default,,0000,0000,0000,,and wrap it around your pencil\Nand you have an inductor.
Dialogue: 0,0:00:31.41,0:00:33.63,Default,,0000,0000,0000,,When you drive current\Nthrough it as shown here,
Dialogue: 0,0:00:33.63,0:00:36.75,Default,,0000,0000,0000,,you have the effect of the inductance.
Dialogue: 0,0:00:36.75,0:00:39.90,Default,,0000,0000,0000,,The inductance is given in\NHenries and its N squared.
Dialogue: 0,0:00:39.90,0:00:41.19,Default,,0000,0000,0000,,That's the number of turns,
Dialogue: 0,0:00:41.19,0:00:45.74,Default,,0000,0000,0000,,the number of coil squared times\Nthe magnetic permeability times the area,
Dialogue: 0,0:00:45.74,0:00:47.68,Default,,0000,0000,0000,,that's the surface area of this core,
Dialogue: 0,0:00:47.68,0:00:49.14,Default,,0000,0000,0000,,divided by the total length.
Dialogue: 0,0:00:49.14,0:00:50.70,Default,,0000,0000,0000,,Again, it is given in Henries.
Dialogue: 0,0:00:50.70,0:00:54.94,Default,,0000,0000,0000,,The magnetic permeability is a property\Nof the material of the core.
Dialogue: 0,0:00:54.94,0:00:58.10,Default,,0000,0000,0000,,It's given by the magnetic permeability
Dialogue: 0,0:00:58.10,0:01:00.84,Default,,0000,0000,0000,,constant times the relative permeability.
Dialogue: 0,0:01:00.84,0:01:02.90,Default,,0000,0000,0000,,For air mu.R is one.
Dialogue: 0,0:01:02.90,0:01:06.62,Default,,0000,0000,0000,,The core is generally made out\Nof ferrite or magnetic material,
Dialogue: 0,0:01:06.62,0:01:09.08,Default,,0000,0000,0000,,and that's because it increases\Nthe total inductance.
Dialogue: 0,0:01:09.08,0:01:12.84,Default,,0000,0000,0000,,So ferrite is typically the material\Nthat's used in this core.
Dialogue: 0,0:01:12.84,0:01:16.38,Default,,0000,0000,0000,,This is how you can tell which direction\Nthe magnetic field goes.
Dialogue: 0,0:01:16.38,0:01:18.89,Default,,0000,0000,0000,,Take your fingers and wrap them\Nin the direction of current,
Dialogue: 0,0:01:18.89,0:01:20.87,Default,,0000,0000,0000,,the fingers of your right\Nhand and your thumb
Dialogue: 0,0:01:20.87,0:01:23.24,Default,,0000,0000,0000,,will show you which direction\Nthe magnetic field goes.
Dialogue: 0,0:01:23.24,0:01:25.55,Default,,0000,0000,0000,,In this case, wrap your fingers\Nin the direction of
Dialogue: 0,0:01:25.55,0:01:28.70,Default,,0000,0000,0000,,the core and you'll see that\Nthe magnetic field comes out of the top,
Dialogue: 0,0:01:28.70,0:01:31.25,Default,,0000,0000,0000,,and because magnetic field lines\Nare always closed lines,
Dialogue: 0,0:01:31.25,0:01:32.80,Default,,0000,0000,0000,,it comes back in the bottom.
Dialogue: 0,0:01:32.80,0:01:38.41,Default,,0000,0000,0000,,The magnetic field for this solenoid\Ninductor, is basically doughnut-shaped.
Dialogue: 0,0:01:38.41,0:01:41.99,Default,,0000,0000,0000,,Here's an example of a wire wound inductor.
Dialogue: 0,0:01:41.99,0:01:44.50,Default,,0000,0000,0000,,The core is a non magnetic ceramic.
Dialogue: 0,0:01:44.50,0:01:46.04,Default,,0000,0000,0000,,So it's more or less like air,
Dialogue: 0,0:01:46.04,0:01:49.94,Default,,0000,0000,0000,,except the ceramic holds it\Ntogether and also dissipates heat.
Dialogue: 0,0:01:49.94,0:01:53.21,Default,,0000,0000,0000,,A very thin wire, thin like is\Nabout as thick as your hair,
Dialogue: 0,0:01:53.21,0:01:55.10,Default,,0000,0000,0000,,is wrapped around the ceramic\Nand then attached on
Dialogue: 0,0:01:55.10,0:01:58.81,Default,,0000,0000,0000,,either side to electrodes with\Na resin coating over the top.
Dialogue: 0,0:01:58.81,0:02:00.68,Default,,0000,0000,0000,,Here's a multi-layer inductor.
Dialogue: 0,0:02:00.68,0:02:03.38,Default,,0000,0000,0000,,The electrodes or connections\Nare on either side,
Dialogue: 0,0:02:03.38,0:02:05.20,Default,,0000,0000,0000,,and you can see that you can just print
Dialogue: 0,0:02:05.20,0:02:07.85,Default,,0000,0000,0000,,a series of loops and you\Nconnect them by vias.
Dialogue: 0,0:02:07.85,0:02:10.44,Default,,0000,0000,0000,,Here's an example of\Na via, here's another via.
Dialogue: 0,0:02:10.44,0:02:13.37,Default,,0000,0000,0000,,A via is where you drill a hole\Nand fill it with solder,
Dialogue: 0,0:02:13.37,0:02:17.56,Default,,0000,0000,0000,,and that basically connects two different\Nlayers of your multilayer inductor.
Dialogue: 0,0:02:17.56,0:02:21.44,Default,,0000,0000,0000,,Here's a thin-film inductor made\Na very similar way where you have
Dialogue: 0,0:02:21.44,0:02:27.42,Default,,0000,0000,0000,,several layers of coils to\Nmake the total inductance.
Dialogue: 0,0:02:27.42,0:02:31.30,Default,,0000,0000,0000,,Now, let's talk about\Nthe electrical properties of the inductor.
Dialogue: 0,0:02:31.30,0:02:34.76,Default,,0000,0000,0000,,Remember, it's a passive element that\Nstores energy in the magnetic field.
Dialogue: 0,0:02:34.76,0:02:36.48,Default,,0000,0000,0000,,Again, here's a solenoid.
Dialogue: 0,0:02:36.48,0:02:40.31,Default,,0000,0000,0000,,The voltage is given by the inductance\Ntimes the derivative of the current.
Dialogue: 0,0:02:40.31,0:02:42.22,Default,,0000,0000,0000,,That means, that at DC when there is
Dialogue: 0,0:02:42.22,0:02:44.99,Default,,0000,0000,0000,,no change in the inductance\Nthat the voltage will be zero.
Dialogue: 0,0:02:44.99,0:02:49.07,Default,,0000,0000,0000,,That effectively means that the inductor\Nlooks like a short circuit at DC.
Dialogue: 0,0:02:49.07,0:02:50.90,Default,,0000,0000,0000,,Here's the equation for the current.
Dialogue: 0,0:02:50.90,0:02:54.22,Default,,0000,0000,0000,,It's the integral of the voltage\Ndivided by the inductance.
Dialogue: 0,0:02:54.22,0:02:57.33,Default,,0000,0000,0000,,Here's the equation for the energy.
Dialogue: 0,0:02:57.94,0:03:00.78,Default,,0000,0000,0000,,This is what happens to the inductor.
Dialogue: 0,0:03:00.78,0:03:03.47,Default,,0000,0000,0000,,The current basically\Nstarts out at zero and
Dialogue: 0,0:03:03.47,0:03:06.82,Default,,0000,0000,0000,,gradually rises to\Nits full total value for current.
Dialogue: 0,0:03:06.82,0:03:08.24,Default,,0000,0000,0000,,The total value for current,
Dialogue: 0,0:03:08.24,0:03:11.50,Default,,0000,0000,0000,,remember that the inductor would\Nbe a short circuit in that case,
Dialogue: 0,0:03:11.50,0:03:16.60,Default,,0000,0000,0000,,would simply be V over\NR in its final state.
Dialogue: 0,0:03:16.60,0:03:18.77,Default,,0000,0000,0000,,The voltage on the other hand,\Ndoes change quickly.
Dialogue: 0,0:03:18.77,0:03:21.41,Default,,0000,0000,0000,,It goes from zero to all\Nof a sudden going up
Dialogue: 0,0:03:21.41,0:03:24.32,Default,,0000,0000,0000,,to a maximum value and\Nthen dropping on down.
Dialogue: 0,0:03:24.32,0:03:28.32,Default,,0000,0000,0000,,The maximum value of this voltage\Nis the source voltage.
Dialogue: 0,0:03:28.32,0:03:30.62,Default,,0000,0000,0000,,So we can see the time t equals zero,
Dialogue: 0,0:03:30.62,0:03:34.05,Default,,0000,0000,0000,,the current is zero, and the voltage\Nacross the resistor is zero.
Dialogue: 0,0:03:34.05,0:03:37.06,Default,,0000,0000,0000,,But the voltage across the inductor\Nis the source voltage.
Dialogue: 0,0:03:37.06,0:03:39.70,Default,,0000,0000,0000,,At time equal infinity or\Nlate time steady state,
Dialogue: 0,0:03:39.70,0:03:42.47,Default,,0000,0000,0000,,the current is Vb over R\Nas if the inductor were
Dialogue: 0,0:03:42.47,0:03:46.70,Default,,0000,0000,0000,,a short circuit and the voltage\Nacross the resistor goes to Vb,
Dialogue: 0,0:03:46.70,0:03:49.46,Default,,0000,0000,0000,,where as the voltage across\Nthe inductor would be zero.
Dialogue: 0,0:03:49.46,0:03:51.59,Default,,0000,0000,0000,,This is all controlled by a time constant.
Dialogue: 0,0:03:51.59,0:03:53.42,Default,,0000,0000,0000,,The time constant for this circuit,
Dialogue: 0,0:03:53.42,0:03:56.18,Default,,0000,0000,0000,,is L over R. Time constant tells us how
Dialogue: 0,0:03:56.18,0:04:00.54,Default,,0000,0000,0000,,quickly the voltage drops\Nor the current rises.
Dialogue: 0,0:04:00.65,0:04:02.72,Default,,0000,0000,0000,,So the way this works,
Dialogue: 0,0:04:02.72,0:04:04.49,Default,,0000,0000,0000,,is current begins to flow in the inductor
Dialogue: 0,0:04:04.49,0:04:07.04,Default,,0000,0000,0000,,and it starts to create a magnetic field.
Dialogue: 0,0:04:07.04,0:04:08.79,Default,,0000,0000,0000,,At time t equals zero,
Dialogue: 0,0:04:08.79,0:04:09.96,Default,,0000,0000,0000,,this acts like an open circuit.
Dialogue: 0,0:04:09.96,0:04:12.04,Default,,0000,0000,0000,,The voltage is high and the current is low.
Dialogue: 0,0:04:12.04,0:04:15.04,Default,,0000,0000,0000,,But very quickly as soon as\Nthe magnetic field is established,
Dialogue: 0,0:04:15.04,0:04:16.37,Default,,0000,0000,0000,,the current flows freely.
Dialogue: 0,0:04:16.37,0:04:17.75,Default,,0000,0000,0000,,So at time t equal infinity,
Dialogue: 0,0:04:17.75,0:04:21.73,Default,,0000,0000,0000,,it acts like a short circuit where the\Nvoltage is low and the current is high.
Dialogue: 0,0:04:21.73,0:04:24.75,Default,,0000,0000,0000,,So what does the inductor do in a circuit?
Dialogue: 0,0:04:24.75,0:04:28.50,Default,,0000,0000,0000,,Here basically is the equation for\Nthe voltage considering the time constant.
Dialogue: 0,0:04:28.50,0:04:32.15,Default,,0000,0000,0000,,This is a picture of the current\Nfor this particular example,
Dialogue: 0,0:04:32.15,0:04:35.74,Default,,0000,0000,0000,,where we have a 1K resistor\Nand a one millihenry inductor.
Dialogue: 0,0:04:35.74,0:04:42.46,Default,,0000,0000,0000,,The current rises reaching\N66 percent of its value at time tau.
Dialogue: 0,0:04:42.95,0:04:45.32,Default,,0000,0000,0000,,This is what happens to the voltage,
Dialogue: 0,0:04:45.32,0:04:46.37,Default,,0000,0000,0000,,it starts at zero,
Dialogue: 0,0:04:46.37,0:04:48.29,Default,,0000,0000,0000,,it jumps up to the source voltage,
Dialogue: 0,0:04:48.29,0:04:52.48,Default,,0000,0000,0000,,and at tau it's 36 percent\Nof its original value.
Dialogue: 0,0:04:52.48,0:04:57.33,Default,,0000,0000,0000,,So this is what the inductor does to\Nthe voltage and current in the circuit.
Dialogue: 0,0:04:57.74,0:05:02.15,Default,,0000,0000,0000,,This is what it would look like if you\Nhit an inductor with a square wave.
Dialogue: 0,0:05:02.15,0:05:04.72,Default,,0000,0000,0000,,The voltage would rise and fall,
Dialogue: 0,0:05:04.72,0:05:06.35,Default,,0000,0000,0000,,and then when the square wave drop,
Dialogue: 0,0:05:06.35,0:05:08.76,Default,,0000,0000,0000,,it would fall and rise.
Dialogue: 0,0:05:09.25,0:05:13.40,Default,,0000,0000,0000,,This is basically acting\Nlike a device that gives you
Dialogue: 0,0:05:13.40,0:05:17.64,Default,,0000,0000,0000,,the derivative of the voltage that\Nwas initially put on the inductor.
Dialogue: 0,0:05:17.64,0:05:20.02,Default,,0000,0000,0000,,Inductors in series and parallel.
Dialogue: 0,0:05:20.02,0:05:23.72,Default,,0000,0000,0000,,Inductors that are in series add just\Nlike they did if they were resistors,
Dialogue: 0,0:05:23.72,0:05:26.57,Default,,0000,0000,0000,,and inductors in parallel add\Nas if they were resistors.
Dialogue: 0,0:05:26.57,0:05:28.64,Default,,0000,0000,0000,,So here's how we can use inductors.
Dialogue: 0,0:05:28.64,0:05:31.38,Default,,0000,0000,0000,,There are many applications for inductors.
Dialogue: 0,0:05:31.38,0:05:34.10,Default,,0000,0000,0000,,Inductive coupling is\Na very cool thing where you
Dialogue: 0,0:05:34.10,0:05:36.100,Default,,0000,0000,0000,,use the current to\Nproduce a magnetic field,
Dialogue: 0,0:05:36.100,0:05:40.91,Default,,0000,0000,0000,,the magnetic field moves to another coil\Nright here where it is picked up,
Dialogue: 0,0:05:40.91,0:05:43.96,Default,,0000,0000,0000,,and a current comes out of this coil.
Dialogue: 0,0:05:43.96,0:05:47.87,Default,,0000,0000,0000,,Here's an example of inductive coupling\Non the University of Utah campus.
Dialogue: 0,0:05:47.87,0:05:50.27,Default,,0000,0000,0000,,Wave has created an electric powered bus.
Dialogue: 0,0:05:50.27,0:05:53.03,Default,,0000,0000,0000,,Underneath, there's a coil\Nof wire in the bottom of
Dialogue: 0,0:05:53.03,0:05:56.48,Default,,0000,0000,0000,,the Wave bus and then in the concrete\Nunderneath is another coil.
Dialogue: 0,0:05:56.48,0:05:59.57,Default,,0000,0000,0000,,The current is induced in\Nthe coil on the concrete,
Dialogue: 0,0:05:59.57,0:06:01.13,Default,,0000,0000,0000,,which is picked up in\Nthe coil of the bus in
Dialogue: 0,0:06:01.13,0:06:03.72,Default,,0000,0000,0000,,order to charge its batteries at a stop.
Dialogue: 0,0:06:03.72,0:06:06.37,Default,,0000,0000,0000,,Blackrock Microsystems has created
Dialogue: 0,0:06:06.37,0:06:09.79,Default,,0000,0000,0000,,an inductively coupled brain stimulator
Dialogue: 0,0:06:09.79,0:06:11.92,Default,,0000,0000,0000,,where you have a 100 electrodes\Nshown right here,
Dialogue: 0,0:06:11.92,0:06:13.63,Default,,0000,0000,0000,,very small needle electrodes,
Dialogue: 0,0:06:13.63,0:06:16.93,Default,,0000,0000,0000,,and this coil right here with\Na lot of different turns,
Dialogue: 0,0:06:16.93,0:06:20.62,Default,,0000,0000,0000,,is used to couple to power\Noutside through the skin.
Dialogue: 0,0:06:20.62,0:06:23.26,Default,,0000,0000,0000,,Here's a picture of a passive ID chip.
Dialogue: 0,0:06:23.26,0:06:29.96,Default,,0000,0000,0000,,This is often used in theft detection\Ndevices in commercial sales.
Dialogue: 0,0:06:29.96,0:06:31.96,Default,,0000,0000,0000,,Here's a little circuit right there,
Dialogue: 0,0:06:31.96,0:06:35.92,Default,,0000,0000,0000,,and here's the inductor that\Nis picking up the current,
Dialogue: 0,0:06:35.92,0:06:40.75,Default,,0000,0000,0000,,that's picking up the magnetic field\Nfrom an externally generated source.
Dialogue: 0,0:06:40.75,0:06:45.30,Default,,0000,0000,0000,,Here's a picture of the passive ID\Nthat's normally used to tag animals,
Dialogue: 0,0:06:45.30,0:06:47.44,Default,,0000,0000,0000,,and there's the coil inside.
Dialogue: 0,0:06:47.44,0:06:50.14,Default,,0000,0000,0000,,Here's an application of a transformer.
Dialogue: 0,0:06:50.14,0:06:52.10,Default,,0000,0000,0000,,On one side on the primary winding,
Dialogue: 0,0:06:52.10,0:06:55.38,Default,,0000,0000,0000,,you'll have a number of windings N1,
Dialogue: 0,0:06:55.38,0:06:57.56,Default,,0000,0000,0000,,and they will generate\Na magnetic field which is
Dialogue: 0,0:06:57.56,0:06:59.70,Default,,0000,0000,0000,,going to go through\Nthis transformer core shown here.
Dialogue: 0,0:06:59.70,0:07:02.27,Default,,0000,0000,0000,,This doughnut-shaped thing.\NThen on the other side,
Dialogue: 0,0:07:02.27,0:07:05.34,Default,,0000,0000,0000,,you can have a different number\Nof windings and two,
Dialogue: 0,0:07:05.34,0:07:09.47,Default,,0000,0000,0000,,to pick up the magnetic flux\Nthat's going through there.
Dialogue: 0,0:07:09.47,0:07:11.57,Default,,0000,0000,0000,,What will happen, is you will change
Dialogue: 0,0:07:11.57,0:07:12.86,Default,,0000,0000,0000,,the current on this side and you'll get
Dialogue: 0,0:07:12.86,0:07:14.39,Default,,0000,0000,0000,,out actually less current on this side,
Dialogue: 0,0:07:14.39,0:07:18.86,Default,,0000,0000,0000,,less voltage so that you're able to change\Nthe voltage across the transformer.
Dialogue: 0,0:07:18.86,0:07:22.02,Default,,0000,0000,0000,,Here are several places that you\Nmight have seen transformers;
Dialogue: 0,0:07:22.02,0:07:23.33,Default,,0000,0000,0000,,upon a power pole,
Dialogue: 0,0:07:23.33,0:07:25.14,Default,,0000,0000,0000,,as a charger for your devices,
Dialogue: 0,0:07:25.14,0:07:28.84,Default,,0000,0000,0000,,as a taser or on top of\Nan electric power system.
Dialogue: 0,0:07:28.84,0:07:32.84,Default,,0000,0000,0000,,Inductors can be used as\Nboth high and low pass filters.
Dialogue: 0,0:07:32.84,0:07:34.91,Default,,0000,0000,0000,,Here's a picture of a low pass filter,
Dialogue: 0,0:07:34.91,0:07:36.92,Default,,0000,0000,0000,,where the inductor is here\Nand we're reading the voltage
Dialogue: 0,0:07:36.92,0:07:39.32,Default,,0000,0000,0000,,across the resistor. So what happens?
Dialogue: 0,0:07:39.32,0:07:41.96,Default,,0000,0000,0000,,If a DC signal goes through,
Dialogue: 0,0:07:41.96,0:07:45.19,Default,,0000,0000,0000,,the inductor acts like a short-circuit,
Dialogue: 0,0:07:45.19,0:07:48.70,Default,,0000,0000,0000,,and so a large voltage is\Nread across the resistor.
Dialogue: 0,0:07:48.70,0:07:50.66,Default,,0000,0000,0000,,But if a high frequency goes through,
Dialogue: 0,0:07:50.66,0:07:52.20,Default,,0000,0000,0000,,the inductor acts like
Dialogue: 0,0:07:52.20,0:07:55.72,Default,,0000,0000,0000,,an open circuit and so no voltage\Nmakes it through to the resistor.
Dialogue: 0,0:07:55.72,0:07:58.05,Default,,0000,0000,0000,,Here is the high pass configuration,
Dialogue: 0,0:07:58.05,0:08:00.31,Default,,0000,0000,0000,,and that's just the opposite.
Dialogue: 0,0:08:01.03,0:08:03.86,Default,,0000,0000,0000,,So I'm sure you're very curious\Nabout where the picture
Dialogue: 0,0:08:03.86,0:08:07.25,Default,,0000,0000,0000,,was from the introductory slide.
Dialogue: 0,0:08:07.25,0:08:10.80,Default,,0000,0000,0000,,This is in White Canyon, in American Fork.