Many sensors could be used in a passive wireless mode. These include RLC,
acoustic wave and magneto-elastic sensors. These types of sensors are
designed to exhibit a change in fundamental frequency when exposed to
environmental factors such as temperature, pressure, or chemicals. An
interrogation circuit can inductively couple to the sensor and measure
the change in fundamental frequency. The change can be used to measure
the environmental factor. Sensor sensitivity and inductive coupling
efficiency can be competing design constraints. A driver, electrically
connected to the sensor and inductively coupled to the interrogation
circuit, can relax the constraints. The driver, however, can introduce
noise into the sensor. The sensor can be shielded using physical and
geometric techniques to reduce the noise.