Engineers at the Fraunhofer Institute for Microelectronic Circuits and Systems have developed an implantable sensor that supposedly can measure intracardiac pressures. Once delivered to the endomyocardium via catheter, the sensor can take readings 200 times a second and transmit them without using a battery. The new system will be displayed at the electronica show in Munich, Germany in November.
The rod-shaped sensor, which is 2 millimeters by 10 millimeters in size, is attached to the wall of the heart with the aid of a catheter. When the catheter is withdrawn, the sensor remains in situ. If necessary, it will deliver pressure data over a period of several months. That said, it transmits solely on demand: Just like a passive RFID transponder, the sensor only operates when its associated reader device supplies it with energy – via an inductive antenna coupling. The sensor does not require a battery, rechargeable or otherwise. An output of 90 microwatts is sufficient to take a pressure measurement and transmit the reading across a distance of up to 40 centimeters. Since the sensor and its integrated antenna can only be positioned longitudinally in the heart, it must be read laterally, on the side of the ribcage. In order to minimize attenuation of the signal by bone, body tissues and liquids, the system transmits in the 10 MHz range. It is encapsulated in a biocompatible polymer shell which, unlike metal, does not block radio waves, but allows them to pass. The Duisberg researchers have also developed a new low-loss transmission process, as vom Bögel explains: “The load modulation that is used for passive RFID transponders deliberately destroys a portion of the transmitted energy in order to encode the transmitted information. We use that portion of energy, which is usually lost, as transmission energy, and thus achieve significantly longer ranges.”
Fraunhofer-Gesellschaft press release: Radio signals from the heart