Devices and methods for the measurement and control of fluid using one or two capacitors are described. The devices use Micro-Electro-Mechanical-Systems (MEMS) and radio-frequency inductive coupling to sense the properties of a fluid in a tube. The single and double capacitor devices may be coupled to shunts implantable in a patient and operable to be interrogated non-invasively. The shunts employing the novel capacitor devices are insensitive to stray signals such as the orientation of a patient's head. The devices are operable to employ a wireless external spectrometer to measure passive subcutaneous components.