The ball & the system

The Ball

The basis of the system is an electronic technique for detecting the proximity of a tennis ball which has particular magnetic properties. This requires the standard ball to be modified by replacing a few grams of the inorganic filler normally present in the rubber (e.g. clay) with a powder which has suitable magnetic permeability. The TEL balls are fully approved by the ITF for tournament use and have been produced by Penn, Slazenger and Wilson.

The System

Sensors, consisting of transmit and receive antennas are embedded in the court below the surface under the lines. The layout is such that the system becomes a close approach tracking system which provides ball approach trajectory angle (in elevation) information. In addition, the position of the center of the ball contact area (footprints) is obtained. This information can then be used to calculate the position of the boundary of the footprint relative to the outer edge of the line. The Mark III system also recognizes ball arrival (before impact), court impact and launch (after impact) which provides even more and consistent accuracy.