The analogy
A radio with no battery.
The crystal radio produces no energy: it draws on what already crosses the air, and its only intelligence is to select a single station from it.
The circuit
What it does, what it does not do.
The distinction that matters
It is not a shield.
A passive circuit blocks nothing and protects from nothing: it has no power to set against what surrounds it.
What a passive resonant circuit can do is more modest — it selects a component already present, it does not impose one.
The link between that selection and what we observe remains an experimental hypothesis. We label it as such, everywhere.
The patent
The principle is not ours.
Patented in 1995 by Michel Marignan, extended in 1997 by Alain Baudry and Michel Marignan. Portfolio expired, principle public. A patent establishes novelty, never efficacy.
Every circuit carries its etched plaque. The name is legible on the object, not only on the invoice.
An expired patent gives you a principle. It gives you neither the grid, nor the frequencies, nor the method, nor the protocol, nor the network.
Next
The only way to know is to measure.
With a tester, calibration is individual. Without a tester, the universal signature is the only one that can be chosen without a prior determination.
