The Touchdown Magnet

NC State researchers are developing a system to better determine a touchdown in football using low frequency magnets.

RALEIGH — Whether you're watching on television or in person in a stadium, football fans know that keeping track of a football isn’t easy. The game is fast, the players are big and the ball can get lost in the shuffle. Coaches and even referees know that too. 

The trouble is, inches matter in football. The exact location of the football can determine whether a player gained enough yardage for a third-down conversion. The exact location also can show if the ball crossed the goal line for a touchdown. The spot where the ball is can affect who wins the game. 

How many times have you seen a player diving for the goal line, trying to get even just a tiny part of the ball across the goal line for a score? Sometimes, even a multitude of video angles on instant replay do not reveal how much of the ball did cross the line, with perfect clarity. 

Now, engineers at North Carolina State University may have a way to know for sure. 

“What we do is turn the football into a small electromagnet,” says Daniel Stancil, Ph.D., head of the Electrical and Computer Engineering Department at North Carolina State University. Stancil adds that researchers worked with scientists at Carnegie Mellon University and Disney Research to create a way to track a football in three-dimensional space. 

“You could almost call it five dimensions,” says David Ricketts, Ph.D., associate professor of electrical and computer engineering at NC State. Ricketts holds up a football and begins to move it around. 

“You can do left-right, forward-back, up and down and then the ball can also be moved diagonally like this,” Ricketts adds. “So you can actually track the football in any orientation around.” 

And it’s done using a low-frequency transmitter that is integrated into the football. The process is actually fairly simple. 

The ball is first deflated and then un-laced. The rubber bladder inside the ball is removed, and then a wire is wrapped around the bladder several times. The bladder is put back in the football and then the antenna and transmitter are hooked up to the wires and epoxyed together to make them more durable. The battery is attached, and then everything is packed into the football, which is laced back up and then inflated. 

The transmitter creates a current in the wire, which turns the ball into a pretty simple electromagnet. The weight is within the standard deviation of accepted professional footballs weights. The ball is carefully balanced. 

“It’s similar to the school experiment where you wrapped a coil of wire and then connected the wire to a battery, and then looked at what happened to a compass; you’re measuring the same thing you measured with the iron filings and the permanent magnet,” explains Stancil. “On one hand it’s a permanent magnet, in the other case it’s created by currents, but in both cases the electromagnet fields are very similar.” 

The football looks completely normal on the outside. And if you toss it around, it also seems to handle in the same way as a normal football. But the unusual package on the inside makes the game anything but normal. Dr. Ricketts looks at what the high-tech football can do on a television screen in his lab at NC State’s Centennial Campus. 

“Watch the player and then watch the arrow on the side of the screen,” says Ricketts, as a player runs out onto the field between the goal line and the ten-yard line. He then runs back to the goal line and out to the 20-yard-line, then back again and out to the 30. 

Each step of the play corresponds to the movement of a yellow arrow on the side of the screen. The arrow is projected over a football field. The edge of the yellow arrow changes to red as the angle of the ball becomes more severe. Dr. Ricketts explains how the projection works.

“As the player runs down the field, the ball is changing direction as he moves it in his arms, so you can see the orientation of the ball as well as its position," Ricketts says, as he uses a small pointer to highlight the colors on the arrow. “You can see there’s a red and yellow line, and that’s telling you the orientation, so when the ball is flat to the field, the line is all yellow, but when it tips the line gets shorter and shorter. So you can tell whether the ball is straight to the field.” 

There’s a series of antennas placed around the field to track the signal produced by the transmitter inside the ball. A computer uses the data to place the ball on the field. 

And remember, the football is producing a low-frequency signal. That’s important, because low frequency signals pass through the human body. This means the ball won’t get lost in a pile up of players. 

“We use magnetic waves, which may not mean much to most people, but typical radio waves get absorbed by our bodies, or by shoulder pads, helmets and other things,” adds Ricketts. “So because we are transparent to magnet waves, when the players huddle around the ball the waves propagate through and we can see the ball just fine.” 

Multiple studies have also shown that magnetic waves are safe to use in a project like this. 

“Everybody likes to do something cool, everybody likes to do something entertaining, but I think the best part of this project was the application of science to something really tangible that people can look at and say, ‘I get that,’” says Ricketts. 

Researchers admit the system needs fine-tuning, but the NFL and several other sports leagues are reviewing the technology. 

“Who knows where this goes from here, if anywhere,” admits Stancil. “But it was fun to interact with a sports team and work on a project that was just fun to do and could add to people’s enjoyment of the game.”


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