Magneto-Inductive Powering and Uplink of In-Body Microsensors: Feasibility and High-Density Effects

Abstract

This paper studies magnetic induction for wireless powering and the data uplink of microsensors, in particular for future medical in-body applications. We consider an external massive coil array as power source (1 W) and data sink. For sensor devices at 12 cm distance from the array, e.g. beneath the human skin, we compute a minimum coil size of 150 µm assuming 50 nW required chip activation power and operation at 750 MHz. A 275 µm coil at the sensor allows for 1 Mbit/s uplink rate. Moreover, we study resonant sensor nodes in dense swarms, a key aspect of envisioned biomedical applications. In particular, we investigate the occurring passive relaying effect and cooperative transmit beamforming in the uplink. We show that the frequency-and location-dependent signal fluctuations in such swarms allow for significant performance gains when utilized with adaptive matching, spectrally-aware signaling and node cooperation. The work is based on a general magnetoinductive MIMO system model, which is introduced first.

Practical Accuracy Limits of Radiation-Aware Magneto-Inductive 3D Localization

“…Instead of acquiring h meas i by measurement, we synthesize it with a simulation that would be exact between thin-wire spiderweb coils in free space. In particular, we solve the double line integral [13,Eq. 11] numerically based on a 3D model of the coil geometry and the feed wire seen in Fig.…”

“…2] picked up by the anchors at f c = 500 kHz. The assumed spatial correlation model uses a Bessel function of kd times the inner product of the two associated anchor orientations (same as in [13]). We suspect that the significant differences between cases 2 and 3 are caused by the way the network analyzer adapts the probing signal to the link, e.g.…”

“…2] picked up by the anchors at f c = 500 kHz. The assumed spatial correlation model uses a Bessel function of kd times the inner product of the two associated anchor orientations (same as in [13]).…”

“…The formula follows from the fields of a circular loop antenna in free space [12, Eq. 5-18], a reformulation of the trigonometric expressions with projective geometry, and assuming a spatially constant field across the receive coil, cf [13,. Eq.…”