A Batteryless Sensor ASIC for Implantable Bio-Impedance Applications.

Area of Science:

• Biomedical Engineering
• Electrical Engineering
• Materials Science

Background:

• Electrical impedance of biological tissues is crucial for medical diagnosis and monitoring.
• Measuring bio-impedance, especially in subcutaneous tissues, presents significant technical challenges.
• Existing methods often lack the miniaturization and power efficiency required for long-term implantation.

Purpose of the Study:

• To develop a miniaturized, battery-free Application-Specific Integrated Circuit (ASIC) for bio-impedance sensing.
• To enable accurate, in-situ complex impedance measurements of biological tissues.
• To facilitate wireless data transmission and power supply for implantable devices.

Main Methods:

• Designed and fabricated a 150 nm CMOS ASIC for 4-point complex impedance extraction.
• Operated the ASIC in the frequency range of 2 kHz to 2 MHz.
• Integrated the ASIC into a prototype powered and communicated with via inductive coupling.
• Validated the prototype using discrete components, physiological solutions, and ex vivo animal organs.

Main Results:

• Achieved accurate complex impedance extraction with approximately 1 Ω resolution.
• The ASIC measures 1.22 mm × 1.22 mm and consumes 165 μA at 1.8 V.
• Demonstrated successful ex vivo measurements, validating the sensor's performance.
• Enabled wireless, accurate tissue impedance measurements through the external reader.

Conclusions:

• The developed bio-impedance sensor ASIC is suitable for miniature, battery-free, implantable devices.
• The technology enables accurate wireless bio-impedance measurements for medical applications.
• This work addresses key challenges in in-vivo tissue impedance sensing.