Patent ID: 7203609
Filing Date: 2007-04-10
Classification: G04F

Abstract:
1. A magnetic field generating apparatus configured to be used in an athletic time measuring system, in which an electromagnetic field is generated, a magnetic field detection coil held by an athlete detects the generated electromagnetic field, and in which thereby the arrival, at a time measuring position, of a player is detected, the magnetic field generating apparatus generating at least one electromagnetic field so that a first intensity, a second intensity that is lower than the first intensity, and a third intensity that is higher than the second intensity, are provided along the direction of travel of an athlete, and the magnetic field generating apparatus comprising: a loop coil provided on a course and generating the electromagnetic field so that the measuring position is in a location of the second intensity; a resonant capacitor, having a variable capacitance, and being connected to said loop coil; a capacitance changing section that changes the capacitance of said resonant capacitor; a sine wave supplying section that supplies a sine wave current with a predetermined frequency to said loop coil through said resonant capacitor; an intensity detecting section that detects intensity of an electromagnetic field excited by said loop coil in a state that the sine wave current is supplied by said sine wave supplying section; and a control section that controls said capacitance changing section based on the intensity of the electromagnetic field detected by said intensity detecting section to change the capacitance of said resonant capacitor.