Passive solid-state magnetic field sensors and applications therefor

A system for detecting rate of flow of a fluid, the system comprising:

• a sensor having at least one multilayer material located adjacent to, but separated from, a circumference of a rotor wheel of a rotor, the multilayer material comprising a layer of a first selected thickness of a selected magnetostrictive material connected across an interface to a layer of a second selected thickness of a selected piezoelectric material and configured so that, when the magnetostrictive material is subjected to a change in magnetic field from rotation of the rotor, a change in at least one dimension of the magnetostrictive material induces a strain in, and produces a detectable non-zero voltage signal in, the piezoelectric material, where at least a portion of the rotor wheel is in a flow path of, and is turned by flow of, a fluid, and where the rotor comprises one or more selected magnetic materials located at N locations (N≧1) on the rotor circumference, and the N locations are approximately equally spaced along the circumference;
• voltage sensing means, connected to the piezoelectric material layer, to sense and count a number of times the voltage signal attains or exceeds a selected value in a selected time interval as the rotor wheel rotates;
• and
• conversion means for receiving and converting the voltage sensing count to a value that is a measure of fluid flow rate of the fluid.