Magnetic flux is the product of magnetic field density and a reference area. The area of interest may be the area enclosed by the loop under the pavement.
Electric current is induced by changes in magnetic flux over time. The field strength can stay the same, and you can still have a change in flux if the area changes. An expanding conductor loop in a constant field is a good example of this. I’m not saying that’s how the vehicle sensors work…but it’s an interesting point.
Your rights are the same at any intersection that has equipment that is not functioning properly. Look both ways, wait for it to clear and proceed. Notify local agency of the problem.
The local sensor-activated lights have a row of three yellow disks to show motorcyclists and bicyclists the best place to stop to ensure the sensor is activated. You might want to suggest this to your local traffic department.
I’ve always found that getting close to the cuts in the ground work best, if it works at all. Though the problem there is that you’re either getting close to or actually sitting/putting your foot down in the oil.
Besides the Tennessee law, there are a couple of other states in the last couple of years that allow motorcyclists to go through the red light if it does not activate for you. I’m sure that if you proceded with care you could get away with it in most any state unless they really wanted to give you a hard time.
Really? I was told by my physics prof. way back when that the way they detect the metal is that the metal becomes magnetized by the magnetic field of the circuit, and that the magnetic field of the car changes the magnetic flux, which therefore changes the current in the circuit, rendering it detectable. The links seemed to support this:
Since iron is so readily magnetized, and aluminum is not, I thought there might be a significant difference for a vehicle with large amounts of aluminum vs. steel.
You’re right, it’s been a while since I had to think about this stuff. Magnetic flux is not the change itself, but changes in flux will induce a current. At least I remembered the word. :smack:
There might be a difference. The sites I read indicate that they think the thing works by putting a magnetic material in proximity to the street coil thus forming a magnetic core that changes the inductance. If this is true then a car with lots of aluminum wouldn’t be as effective as one of steel and iron.
I wonder about this since the magnetic field from the current-carrying coil has to either surround the core or pass through a hole in the core (like the window in a transformer core) to make the magnetic material be a core.
It seems to me that the metallic object forms a shorted turn in the secondary of a transformer. This changes the current in the primary [the coil in the street] and because the primary coil voltage stays the same this is an effective change in the primary impedance which would unbalance the Wheatstone bridge. If this is the mechanism then any conductive material will do the job if there is enough of it.
When I had a motorcycle, I got decent results from stopping on the cut line and rocking the bike from side to side. I often got the light (very briefly) with no help from a car.
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