IEEE Circuits and Systems Magazine - Q3 2022 - 1

Circuits
and Systems
IEEE
MAGAZINE
Volume 22, Number 3
Third Quarter 2022
Features
6 The 21st Century Systems: An Updated
Vision of Discrete-Time Fractional Models
Manuel Duarte Ortigueira and J.A. Tenreiro Machado
Two different approaches for describing discrete-time fractional linear systems
are presented. The first is based on the nabla and delta discrete-time derivatives.
In this case, suitable exponentials are introduced and used to define discrete
Laplace transforms. The second approach is based on the bilinear (Tustin) transformations.
For both cases, appropriate algorithms for obtaining the impulse,
step, and frequency responses are presented. The state-variable representation
is also analysed.
22 System Design of a Closed-Loop
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Vagus Nerve Stimulator Comprising
a Wearable EEG Recorder and an
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Implantable Pulse Generator
Xiaolong Li Member, IEEE, Ming Yu, Jin Zhu, Wei Zheng, Guojun Ma,
Xiaoqiao Deng, Weijia Huang, and Wouter A. Serdijn Fellow, IEEE
Closed-loop vagus nerve stimulators (VNSs) are used to treat refractory
epilepsy (RE) and provide an alternative treatment modality with fewer side
effects for RE. This work proposes a closed-loop VNS that senses the scalp
EEG via a wearable EEG recorder (WER) and stimulates the vagus nerve
via an implantable VNS (IVNS), the combination of which is referred to as
a " HybridVNS " . First, the architecture and system control (by an App) of the
HybridVNS are presented. Next, discrete component implementations of its
key building blocks including the multichannel preamplifier, pulse generator
and wireless power link are provided. Further, a 4-channel preamplifier magnifies
the recorded EEG signals, and each channel consists of a capacitively
coupled instrumentation amplifier (CCIA) cascaded by a 2nd-order low pass
filter. The measured gain and the input-referred noise (IRN) of the preamplifier
are 45.8 dB and 4.9 μVrms
(1 Hz-200 Hz), respectively. We propose a
switched-resistor array pulse generator for constant-current stimulation, and
a novel distance-frequency adaptive inductive coupling link (DFAICL) to automatically
tune the resonance frequency. A maximum wireless power transmission
efficiency of 17% is achieved in the DFAICL when the supply power is
30dBm and the distance is 20 mm at 2 MHz. Finally, we demonstrate that in
the WER, the onset of an epileptic seizure can be detected by a threshold
of coastline length (294 μV) combined with a threshold of slope (7.3 μV/ms)
within a unit time segment (780 ms), which provides an average accuracy
of 88.2%. The feasibility of the IVNS was tested in an acute rodent epilepsy
experiment. However, the closed-loop experiment was not conducted.
Digital Object Identifier 10.1109/MCAS.2022.3189929
THIRD QUARTER 2022
IEEE CIRCUITS AND SYSTEMS MAGAZINE
1

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IEEE Circuits and Systems Magazine - Q3 2022

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