Measurement of multiple unrelated physical quantities using a single magnetic field response sensor

This paper presents a non-contact method for powering and interrogating magnetic field response sensors that facilitates measurement of multiple unrelated physical quantities using the same sensor. The sensors are electrically passive inductive–capacitive or passive inductive–capacitive–resistive circuits that are powered using oscillating magnetic fields, and once electrically active, the sensors respond with their own oscillating magnetic fields. The sensor's magnetic field response frequency, amplitude and bandwidth are correlated to the magnitude of one or more physical quantities that each sensor measures. The magnetic field response sensors and the technique for powering and interrogation alleviate many shortcomings of traditional sensor/measurement systems. The shortcomings are having a data acquisition channel dedicated to each sensor, wiring/circuitry weight associated with measurements, electrical arcing, wire degradations due to wear or chemical decay and the logistics needed to add new sensors. Because measurements can be derived from influences upon the sensor's magnetic field or electrical field, the circuit that forms the sensor need not be in physical contact with the measurand. The method for discerning sensor response frequency, resistance and amplitude is presented herein. The method does not require the sensors to be near or physically connected to acquisition hardware or a power source. The theoretical basis for the measurement acquisition technique is discussed including the influence of key parameters on measurement acquisition. One example of a magnetic field response sensor for measuring the magnitude of three unrelated physical quantities—material phase transition, temperature and position—will be presented. A fluid-level measurement will also be presented.