Integration of Carbon Nanotube Bio Potential Sensors
The wireless monitoring of patients employing biosensors is an emergent field of research. Historically it was required to couple the patient to an array of sensors attached to a processing and display unit. Presently, we have devices which allow patients to be free of cumbersome wired technologies. Most of these devices require a power source and complicated circuitry to transfer the captured data to an interrogator. The complexity and powering requirement increases cost and functionality of the process. Here we have proposed a wireless, low component count, Surface Acoustic Wave (SAW), bio sensing transponder. Due to the interrogation mechanism this sensor is passive by nature, but allows interrogation distances in the region of a few metres. The above mentioned SAW integration coupled with state-of-the-art MWNT bio sensors foresees a dramatic shift in the future of bio potential sensing paradigm.
An Inter Digital Transducer (IDT) will be coupled to the MWNT bio sensors via a LC phase modulator. A second IDT will be used to couple an antenna in to the acoustic wave substrate. The LC circuit & the IDTs are matched to a predefined centre frequency. Variations in the bio sensor will induce a phase variation on the incident wave of the sensing IDT, when the incident pulse is reflected back to the IDT connected to the antenna, the phase variation will be back scattered to the interrogator. Thus the change of bio potentials can be calculated by the comparison of transmission and receive waves and their phase variations.
The results taken so far indicate the ability of a high Q, LC phase modulator to be sensitive to the potential differences for ECG & EEG requirements. Calculations for the SAW devices at a frequency of 2.4 GHz signify devices less than 1cm in diameter. Subsequent investigations will yield the integration of the LC circuitry with the SAW device. SAW models which have predominantly been used in the areas of industrial sensing applications have been adapted for the current bio sensing requirement. An instrumentation amplifier capable of characterising MWNT bio sensors has been built.
