The Tavis Variable Reluctance (VR) Sensing Technique is based on a magnetic coupling between sensor elements and a pressure diaphragm.  In the Tavis transducer, a metallic diaphragm is used to sense pressure (refer to the simplified Figure 1).  The diaphragm is welded and suspended between the L1 and L2 sensor elements (without contact or physical linkages of any kind).  There is an air gap (or pressure media gap) between the sensor elements and the diaphragm.  As applied pressure is increased or decreased, the diaphragm will move (deflect) toward one element, and away from the other element, changing their respective air gaps.  This changes the reluctance of the circuit, generating a voltage change proportional to the applied pressure. 

For additional details/theory regarding Tavis VR sensing, see Tavis Technical Bulletin #102.