Figure 4. Coil ring and magnet disc a) individually b) adjacent. Telemetry electronics positioned on big end

From

Piston Data Telemetry in Internal Combustion Engines

K. M. Ebrahimi, A. Lewalski, A. Pezouvanis, B. Mason

American Journal of Sensor Technology. 2014, 2(1), 7-12 doi:10.12691/ajst-2-1-2