Miniature Coplanar Implantable Antenna on Thin and Flexible Platform for Fully Wireless Intracranial Pressure Monitoring System

Abstract

Minimally invasive approach to intracranial pressure monitoring is desired for long-term diagnostics. The monitored pressure is transmitted outside the skull through an implant antenna. We present a new miniature (6 mm × 5 mm) coplanar implant antenna and its integration on a sensor platform to establish a far-field data link for the sensor readout at distances of 0.5 to 1 meter. The implant antenna was developed using full-wave electromagnetic simulator and measured in a liquid phantom mimicking the dielectric properties of the human head. It achieved impedance reflection coefficient better than −10 dB from 2.38 GHz to 2.54 GHz which covers the targeted industrial, scientific, and medical band. Experiments resulted in an acceptable peak gain of approximately −23 dBi. The implant antenna was submerged in the liquid phantom and interfaced to a 0.5 mW voltage controlled oscillator. To verify the implant antenna performance as a part of the ICP monitoring system, we recorded the radiated signal strength using a spectrum analyzer. Using a half-wavelength dipole as the receiving antenna, we captured approximately −58.7 dBm signal at a distance of 1 m from the implant antenna which is well above for the reader with sensitivity of −80 dBm.

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“…The measured bandwidth is about 30MHz for the first band and 45MHz for the second band. The simulated radiation efficiency is about 10 percent for both bands, which is acceptable for such an ultra-miniature antenna, e.g., compare to [15,17].…”

“…High demand in (ultra-)miniature antennas for IoT [15,16], medical [17], and mobile phone [18,19] applications stimulated the recent progress in antenna miniaturization. In this concern, the challenges towards decreasing the maximal size below 20 0 / λ should be mentioned.…”

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“…Moreover, the Archimedean spiral shape of the top plate can end up in overall size reduction. This is because the horizontal arm of the PIFA has been compacted by its spiral shape which is a quite efficient structure to attain maximum achievable bandwidth and the effective current path length [20] has increased. It has been shown that spiral structure provides lower resonance frequency and higher radiation efficiency than its meander counterpart [20].…”

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“…However, double-sided structures (patch on one side and ground another side) are sometimes not suitable for easy mount ability on IC devices. This can be avoided with the use of single-sided co-planar structures, respectively [17].…”