coil detection chart

[green]

I've seen detection shape charts for DD and round coils. Not sure what the Y axis scale is. Was playing the other day and noticed the detection range was way outside the coil for shallow targets. Thought I would chart some data. Thinking three targets(40x40mm 1 layer)(20x20mm 2 layers)(10x10mm 4 layers) heavy duty aluminum foil. Should be same decay time constant for each target. Have charted signal strength at offset and target distance points in the past. Tried something different this time. Charted target offset that caused a 500uv change at integrator out at different target distances. A 500uv change is an easy signal to detect and gives some resolution vs trying to repeat a 100 or 200uv change. Charted the 20x20mm 2 layer target. Target was parallel to coil for all data points, offset measured from center of target. At lower target distances the null in the center is very narrow. Charted one end of the figure eight coil only, other end should be a mirror image. Any suggestions on how to chart detection shape better? Could chart the other targets if anyone is interested.

[green]

I've seen detection shape charts for DD and round coils. Not sure what the Y axis scale is. Was playing the other day and noticed the detection range was way outside the coil for shallow targets. Thought I would chart some data. Thinking three targets(40x40mm 1 layer)(20x20mm 2 layers)(10x10mm 4 layers) heavy duty aluminum foil. Should be same decay time constant for each target. Have charted signal strength at offset and target distance points in the past. Tried something different this time. Charted target offset that caused a 500uv change at integrator out at different target distances. A 500uv change is an easy signal to detect and gives some resolution vs trying to repeat a 100 or 200uv change. Charted the 20x20mm 2 layer target. Target was parallel to coil for all data points, offset measured from center of target. At lower target distances the null in the center is very narrow. Charted one end of the figure eight coil only, other end should be a mirror image. Any suggestions on how to chart detection shape better? Could chart the other targets if anyone is interested.

Decided I was interested. Charted all three targets(all 3.5usec TC). Hung target from a pendulum centered over test coil, adjusted target distance while target swung in test plane for a good indication. Included pendulum target distance on each chart.