Existing measurement is simple when you can break the circuit or clip a clamp around the current carrying conductor, but in the case of a multi-layer PCB this may not be always practical or possible.
Aim-TTi have come up with a means to00 this problem with the I-prober 520, which can measure current (dc upwards to 5MHz) simply by positioning the insulated suggestion onto the existing carrying conductor without making any power contact.
The I-prober measures the magnetic field that results from current flowing through the conductor, when the insulated tip is located on the PCB's track (above the conductor), the same way as an established current loop übung does, by surrounding the conductor with high Mu material (like ferrite).
The positioning of the I-prober on the pcb is critical, as the signal is effected relative to the conductor, as the I-prober measures the permanent magnet field at a accurate point on the board, so moving it away from conductor reduces the scored signal, this is why the I-prober is known as a positional current probe.
Positional current vertueux aren't new, however they were initially physically large and only ideal for computing high current at low bandwidths, however Aim-TTi have come up with a patented miniaturised Fluxgate Magnetometer which is at the center of the probe and is capable of measuring area at a accurate position, it also has a much lower noise and wider bandwidth when compared to a regular Fluxgate Magnetometer.