Bidirectional parallel capacitive data links: Modeling and experimental results

We present, in this paper, a bidirectional capacitive data link. Enhancement of the spatial pulse position modulation used on the downlink is introduced, and a load-shift keying modulation is implemented for the uplink. Different grounds on the transmitter and the receiver are discussed, and a compatible solution is proposed. A human skin electrical model is extracted using the agilent impedance analyzer 4294A while doing in vivo measurements on cheek skin and then applying curve fitting to the data between 2 and 20 MHz. Multiple geometries for the link are analyzed, and a 5-mm × 5-mm plate size is used for the design of the transceiver. The signal-to-noise ratio along with the capacity of the channel is analyzed theoretically while computing the limits for the downlink and the valid operating frequency to highlight the core parameters that affect the crosstalk interference between channels. The tradeoff in using the uplink on the same channel as the downlink is also discussed and analyzed. The operating frequency is 10 MHz, a bit-rate of 20 Mb/s is demonstrated on the uplink, and 10 Mb/s is demonstrated on the downlink. An in vivo human skin model for a 5-mm × 5-mm plate size with 21.2-mm separation is extracted, and the capacity's equation of the channel is computed using the equations for the analysis of the system.

Uncontrolled Keywords

• Biomedical implants
• data link
• capacitive link
• capacitive channel
• skin impedance
• loadshift keying
• spatial pulse positioning
• resistor network