Fig. 1. Schematic of the parallelepiped and the heat-pulse needles used in the model: (a) three-dimensional view [the heater needle is at (x, y) = (a/2, b/2), the sensor is at (x, y) = (a/2 + rcos[], b/2 + rsin[])] and (b) top view in polar coordinate [the heater needle is at (0, 0), the sensor is at (r, )]. For illustration purpose, the radius of heater probe and temperature probe are exaggerated and are not to scale.