Can you please explain the working of modern electric ADF recievers
A modern ADF antenna is made either of 4 individual antennas or off two crossed loops.
ADF array, source
The signal strength is the same on all elements, however the distance between elements introduces a delay, which translates into a phase difference on antennas.
The principle is based on comparing the phase on two diametrically opposite elements (or in a loop).
With 2 pairs the system is able to determine the U and V amplitudes of a vector. By combining U and V it is possible to determine the direction of arrival. The accuracy is a few degrees, depending on the size of the array.
Sensing the phase difference (the dark green sine is the phase of the top-left element
This principle is not new, but is now very simple due to modern comparison techniques. It is known as Watson-Watt direction finder:
Original Watson-Watt direction finder using a Lissajous pattern, source