  We present the concept of a passive spin-wave device which is able to
distinguish different radio-frequency pulse trains and validate its
functionality using micromagnetic simulations. The information is coded in the
phase of the individual pulses which are transformed into spin-wave packets.
The device splits every incoming packet into two arms, one of which is coupled
to a magnonic ring which introduces a well-defined time delay and phase shift.
Since the time delay is matched to the pulse repetition rate, adjacent packets
interfere in a combiner which makes it possible to distinguish simple pulse
train patterns by the read-out of the time-integrated spin-wave intensity in
the output. Due to its passive construction, this device may serve as an
energy-efficient wake-up receiver used to activate the main receiver circuit in
power critical IoT applications.
