Removal of Motion Artifacts in Capacitive Electrocardiogram Acquisition: A Review.

Capacitive electrocardiogram (cECG) systems are increasingly used for the monitoring of cardiac activity. They can operate within the presence of a small layer of air, hair or cloth and do not require a qualified technician. They can be integrated into wearables, clothing or objects of daily life, such as beds or chairs. While they offer many advantages over conventional electrocardiogram systems (ECG) that rely on wet electrodes, they are more prone to be affected by motion artifacts (MAs). These effects, which are due to the relative movement of the electrode in relation to the skin, are several orders of magnitude higher than ECG signal amplitudes, they occur in frequencies that might overlap with the ECG signal, and they may saturate the electronics in the most severe cases. In this paper, we provide a detailed description of MA mechanisms that translate into capacitance variations due to electrode-skin geometric changes or into triboelectric effects due to electrostatic charge redistribution. A state-of-the-art overview of the different approaches based on materials and construction, analog circuits and digital signal processing is provided as well as the trade-offs to be made using these techniques, to mitigate MAs efficiently.

Contactless Capacitive Electrocardiography Using Hybrid Flexible Printed Electrodes.

Traditional capacitive electrocardiogram (cECG) electrodes suffer from limited patient comfort, difficulty of disinfection and low signal-to-noise ratio in addition to the challenge of integrating them in wearables. A novel hybrid flexible cECG electrode was developed that offers high versatility in the integration method, is well suited for large-scale manufacturing, is easy to disinfect in clinical settings and exhibits better performance over a comparable rigid contactless electrode. The novel flexible electrode meets the frequency requirement for clinically important QRS complex detection (0.67-5 Hz) and its performance is improved over rigid contactless electrode across all measured metrics as it maintains lower cut-off frequency, higher source capacitance and higher pass-band gain when characterized over a wide spectrum of patient morphologies. The results presented in this article suggest that the novel flexible electrode could be used in a medical device for cECG acquisition and medical diagnosis. The novel design proves also to be less sensitive to motion than a reference rigid electrode. We therefore anticipate it can represent an important step towards improving the repeatability of cECG methods while requiring less post-processing. This would help making cECG a viable method for remote cardiac health monitoring.

Modal crosstalk in Silicon photonic multimode interconnects.

We investigate modal crosstalk in silicon photonic MDM-based interconnects using tapered multiplexers. Crosstalk from coherent optical interference originates from variation in the physical structure and alters the transmission link performance. Through simulations and experimental work, optical crosstalk as a function of wavelength is analyzed to understand its impact in MDM and MDM-WDM dual-multiplexing applications. The detrimental effects are validated in the frequency and time domains through fabricated MDM interconnects of various lengths. Results indicate modal crosstalk must be < -22 dB to maintain a BER of 10-12. The experimental methodology assesses the optical modal crosstalk's impact on the data, towards a mitigation approach to improve the payload signal integrity and enable system-level optimization such as channel wavelength allocation.

High-speed grating-assisted all-silicon photodetectors for 850 nm applications.

This paper presents the design, fabrication, and measurement results of a novel lateral p-i-n silicon photodetector (Si-PD) for 850 nm in a silicon-on-insulator (SOI) platform. In the proposed photodetector, the incident light is directed horizontally using a grating coupler, significantly increasing optical absorption in the depletion area thereby increasing the PD's responsivity. The measurement results show that the grating coupler increases the responsivity by 40 times compared with the Si-PD without a grating coupler. The grating-assisted Si-PD with 5µm intrinsic width has a responsivity of 0.32 A/W and a dark current of 1 nA at 20 V reverse-bias voltage. Further, it shows an open eye diagram for 10 Gb/s PRBS­31 non-return-to-zero on-off keying (NRZ-OOK) data and has a 3-dB bandwidth of 4.7 GHz at this bias voltage. In addition, the design parameters of three variations of the grating-assisted Si-PD for high-speed applications (>25 Gb/s) are presented. The optimized grating-assisted Si-PD uses a focusing grating coupler and its p-i-n diode has a 0.3 µm intrinsic width. It has a responsivity of 0.3 A/W, an avalanche gain of 6, a dark current of 2 µA, and a 3-dB bandwidth of 16.4 GHz at 14 V reverse-bias voltage that, to the best of our knowledge, is the largest 3-dB bandwidth reported for a Si-PD. As a result, it has a figure of merit (FoM) of 4920 GHz×mA/W. Further, it shows an open eye diagram of 35 Gb/s PRBS­31 NRZ-OOK data.

Responsivity optimization of a high-speed germanium-on-silicon photodetector.

This paper experimentally demonstrates a design optimization of an evanescently-coupled waveguide germanium-on-silicon photodetector (PD) towards high-speed (> 30 Gb/s) applications. The resulting PD provides a responsivity of 1.09 A/W at 1550 nm, a dark current of 3.5 µA and bandwidth of 42.5 GHz at 2 V reverse-bias voltage. To optimize the PD, the impact of various design parameters on performance is investigated. A novel optimization methodology for the PD's responsivity based on the required bandwidth is developed. The responsivity of the PD is enhanced by enlarging its geometry and using off-centered contacts on top of the germanium, while an integrated peaking inductor mitigates the inherent bandwidth reduction from the responsivity optimization. The performance of the optimized PD and the conventional, smaller size non-optimized PD is compared to validate the optimization methodology. The sensitivity of the optimized PD improves by 3.2 dB over a smaller size non-optimized PD. The paper further discusses the impact of top metal contacts on the photodetector's performance.