D6.1 - Surface Micromachined Pressure Sensors for Medical Applications

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
D6 - Medical I
H. Trieu - Fraunhofer-Institut (IMS), Duisburg (Germany)
618 - 623


Pressure is physiologically a very interesting parameter in medical diagnostics. From blood pressure for patients suffering from hypertension to cranial pressure in hydrocephalus, intra ocular pressure in glaucoma or bladder pressure in incontinence as some examples it covers a broad range of relevance of different diseases. Facing new challenges in health care as a result of demographic change and an accompanied increase in life expectancy as well as the high incidence of widespread diseases in industrialized countries, new techniques for early diagnosis in prevention as well as novel concepts for long term monitoring using micro implants and telemedicine platforms are introduced.

For the development of micro implants with the capability of telemetric operation two requirements are essential for the technology in use: miniaturization and low power consumption. The presented technology of surface micromachined capacitive pressure sensors has successfully demonstrated to fulfil these characteristics in various research and product development projects. The micro implant transponder consists of an integrated capacitive pressure sensor and a coil including some discrete electronic components for the transmission of power and data. The pressure sensor is fabricated in CMOS technology which allows a monolithic design with high integration density. Due to the high miniaturization and the energy efficiency of capacitive pressure sensing the sensor can operate telemetrically. A magnetic field with a frequency of 133 kHz or 13.5 MHz is generated by an external coil that is connected to a handheld reader. The field transfers power to the second coil of the pressure sensor transponder located inside the implant by inductive coupling. Apart from the power, the transponder extracts its clock by the frequency of the magnetic field. The digitized pressure values of the sensor are Manchester and CRC coded. Transfer of the values is done by load modulation that causes damping of the magnetic field. The field damping is evaluated by the reader. If the CRC of the transferred data is valid pressure values are processed further.

The basis as well as some selected medical applications of the technology are presented in this lecture.