I have read that putting loops of copper wire inside of your rims can help. Apparently the ends need to be electrically connected into loops to be effective though. I ride bikes with plenty of steel, so this has not been a problem for me. The one light that I ever really have to trigger on my own works great by just stepping off my bike and laying it down sideways on top of the sensing loop.

If you call the city and explain the problem, you should be able to get them to recalibrate the light sensors to be sensitive enough to be tripped by a steel-frame bike.

To the OP: the two round loops are the sensors. the other cuts are just troughs for wiring to run from the sensors to the control box.