Solid semiconductor sensors are used as detectors in
high-energy physics experiments, in medical applications, in space
missions and elsewhere. Minimal knowledge of the electric field
inside the elementary cells of these sensors is highly important for
their performance understanding. The field governs the charge
propagation processes and ultimately determines the size and quality
of the electronic signal of the cell. Hence, the simulation of
these sensors as detectors in different analyses relies strongly on
the field knowledge. For a certain voltage applied to the cell, the
field depends on the specifics of the device's growth and
fabrication. The information about these is often commercially
protected or otherwise very difficult to encode in state-of-the-art
technology computer-aided-design (TCAD) software. In this work, we
show that by taking the top-down approach, combining public
beam-test data and a very limited public TCAD knowledge, we are able
to effectively approximate the 3D electric field function in the
pixel cell of one important and widely used example, namely the
ALPIDE sensor, for simulating the charge propagation
processes. Despite its broad usage worldwide, the ALPIDE field is
not available to the community. We provide an effective field
function, that adequately describes the sensor behaviour without
trying to reconstruct further details about the device or the
details behind its processing. We comment on the process by which
the effective field function is derived with the help of the
Allpix2 software, and on how similar work can be performed for
other devices, starting from the same grounds.