Abstract
We propose a novel double-layered insulator configuration for a human-brain-implanted impulse radio ultra-wideband (IR-UWB) antenna. The dimension of the antenna is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10.0\times 11.0\times0.954$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , including the dual-layer insulator. The insulator provides a dielectric loading effect of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r}~\approx ~50$ </tex-math></inline-formula> (lossless) for obtaining an improved radiating power and the broadband-impedance-matching characteristic in brain tissues. The outer layer is made of biocompatible 3-D printing material, and the inner insulator is filled with deionized water with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r}~\approx ~80$ </tex-math></inline-formula> and loss tangent (tan <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta$ </tex-math></inline-formula> ) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx ~0.25$ </tex-math></inline-formula> at 4 GHz. A slotted UWB antenna with the proposed insulator is located between the emulated dura and CSF tissues inside the skull for brain signal detection. The design uses a multilayer phantom, mimicking the seven tissue layers of the brain. The impedance and radiation performance of the proposed antenna configuration are also discussed using the commercial high-precision human phantom model. The designed IR-UWB antenna shows a boresight radiation characteristic toward the top of the head with a proper high gain in the target frequency of 3–5 GHz. The computed expectations are verified experimentally. Furthermore, it is demonstrated that the UWB spectrum generated from a UWB radio-frequency (RF) transmitter can be transmitted stably using the proposed antenna as a transmitting antenna. In addition, the link budget of the system setup is analyzed. The improved gain characteristic of the antenna from the proposed dual-layer insulator can be utilized to retain the link margins while satisfying the UWB communication regulation and average specific absorption rate (SAR) limitation.
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