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  • Book
    Yun Chen.
    Digital2013
    Continuous wireless monitoring of in vivo biopotential, biochemical, and biomechanical properties has the potential to yield breakthroughs in our understanding of human health and disease. In particular, current technology does not yet allow us to do so at micron (i.e., cellular) scales. We look to create a scalable system of chronically implantable passive sensors with a wireless detection platform to individually address and continuously monitor them. Scaling down the size of resonant sensors poses significant challenges for passive wireless detection. In particular, inherently higher resonant frequencies at smaller sizes push our operation into regimes where traditional approaches fail. Two schemes based on power reflection distortion (PRD) and group delay distortion (GDD) are proposed to operate over a wide range of frequencies. They are shown to be capable of operating in high frequency regimes near and above the readout circuit self-resonance. In addition, we describe a generic finite-difference time-domain (FDTD) framework for analyzing electromagnetic (EM) wave propagation and scattering in an anatomically realistic human phantom with an inhomogeneous dispersive model. Interactions with implantable resonant sensors are studied within this framework. We demonstrate a wireless real-time monitoring system with passive, flexible sensors, which scale down to unprecedented dimensions of 1x1x0.1 cubic mm. This level of scaling is enabled by the presented GDD detection scheme, which overcomes the operating frequency limits of traditional strategies and exhibits insensitivity to lossy tissue environments. We apply this system to capture human pulse waveforms in real-time as well as to continuously monitor in vivo intracranial pressures with sensors down to 2.5x2.5x0.1 cubic mm in proof-of-concept mice studies. Furthermore, printable wireless sensor arrays are introduced and their use in concurrent spatial pressure mapping is shown. Our vision is to extend the passive sensing approach and scale the resonant sensor platform down to intracellular dimensions at the intersection of intracellular delivery limits and integrated circuit fabrication capabilities. We demonstrate a family of 3D multilayer micro-Tag (uTag) structures as a potential platform for resonant tagging and sensing at the cellular level. As a stepping stone towards chronic cellular monitoring, we demonstrate the delivery of uTags into living cells and viability of internalized uTags over a 5-day period. Looking forward, this technology creates exciting opportunities to use remote physiological monitoring as a routine part of biomedical research and patient care. In the future, we foresee that such monitoring will be possible even at the cellular level.