A Wireless and Passive Implantable Pressure Sensor

A wireless and passive implantable sensor was fabricated for monitoring pressures in a liquid-flowing conduit such as blood vessels. The implantable pressure sensor, referred to as the magneto-harmonic sensor, consisted of a pressure chamber, as well as a permanent magnetic film attached to a thin membrane and a magnetically soft film at the bottom of the chamber. When excited by an external AC magnetic field, the magnetically soft film generated magnetic higher-order harmonic fields that were remotely detected with a detection coil. The presence of a permanent magnetic film generated a biasing magnetic field, causing these higher-order harmonic signals to change. An increase in the ambient pressure pushed the membrane closer to the bottom of the chamber, reducing the separation distance between the permanent magnetic film and the magnetically soft film. This increased the biasing field experienced by the magnetically soft film, which increased the change in harmonic fields. This study demonstrated that the magneto-harmonic pressure sensor exhibited good repeatability and stability within the pressure range of interest. In addition, it was shown that the temperature of the surrounding medium only had a minimal effect on the sensor's response. The wireless and passive nature of this sensor is favorable for continuous and long-term in vivo pressure monitoring, thus this sensor will be applicable for chronic patients who suffer from cardiovascular diseases.