Wearable Biomedical Systems Research Articles

A power-aware task scheduler for energy harvesting-based wearable biomedical systems using snake optimizer

There is an increasing interest in energy harvesting for wearable biomedical devices. This requires power conservation and management to ensure long-term and steady operation. Hence, task scheduling algorithms will be used throughout this work to provide a reliable solution to minimize energy consumption while considering the system operation constraints. This study proposes a novel power-aware task scheduler to manage system operations. For example, we used the scheduler to handle system operations, including heart rate and temperature sensors. Two optimization techniques have been used to illustrate the impact of task scheduling on energy consumption. The first is based on Snake Optimizer (SO), and the second is a greedy approach to compute the Hamming-based Tikhonov regularization. The FPA approach showed 50% improvement in the convergence time for the scheduler.

Efficient logic cell design for ultralow-energy subthreshold operation in wearable biomedical systems

This paper explores efficient logic cell design strategies for ultralow-energy subthreshold operation in wearable biomedical systems. Traditional logic cell design approaches often lead to suboptimal efficiency due to unbalanced Pull-Up (PU) and Pull-Down (PD) networks. Various techniques are examined, including balanced PU/PD network design using body biasing and statistical distribution analysis of drain-source current. Moreover, the reverse channel (RSC) effect is investigated for device optimization. Single-stage gates such as inverters, NAND, and NOR gates are designed with Mentor Graphics tools to minimize power dissipation and area. Multistage gates like XOR and XNOR gates are also optimized for reduced signal propagation delay. A detailed analysis of D-flip-flop designs with varying transistor counts is presented. Power dissipation, delay, rise time, and fall time characteristics are compared for flip-flop configurations comprising 18, 10, and 5 transistors. The results indicate significant energy optimization with the proposed designs, particularly with the 5-transistor configuration, demonstrating the effectiveness of the proposed methodologies in achieving superior energy efficiency and reduced signal noise in biomedical systems.

Recent Advances in Materials for Wearable Thermoelectric Generators and Biosensing Devices.

Recently, self-powered health monitoring systems using a wearable thermoelectric generator (WTEG) have been rapidly developed since no battery is needed for continuous signal monitoring, and there is no need to worry about battery leakage. However, the existing materials and devices have limitations in rigid form factors and small-scale manufacturing. Moreover, the conventional bulky WTEG is not compatible with soft and deformable tissues, including human skins or internal organs. These limitations restrict the WTEG from stabilizing the thermoelectric gradient that is necessary to harvest the maximum body heat and generate valuable electrical energy. This paper summarizes recent advances in soft, flexible materials and device designs to overcome the existing challenges. Specifically, we discuss various organic and inorganic thermoelectric materials with their properties for manufacturing flexible devices. In addition, this review discusses energy budgets required for effective integration of WTEGs with wearable biomedical systems, which is the main contribution of this article compared to previous articles. Lastly, the key challenges of the existing WTEGs are discussed, followed by describing future perspectives for self-powered health monitoring systems.

ECG Arrhythmia Classification on an Ultra-Low-Power Microcontroller.

Wearable biomedical systems allow doctors to continuously monitor their patients over longer periods, which is especially useful to detect rarely occurring events such as cardiac arrhythmias. Recent monitoring systems often embed signal processing capabilities to directly identify events and reduce the amount of data. This work is the first to document a complete beat-to-beat arrhythmia classification system implemented on a custom ultra-low-power microcontroller. It includes a single-channel analog front-end (AFE) circuit for electrocardiogram (ECG) signal acquisition, and a digital back-end (DBE) processor to execute the support vector machine (SVM) classification software with a Cortex-M4 CPU. The low-noise instrumentation amplifier in the AFE consumes 1.4 μW and has an input-referred noise of 0.9 μV RMS. The all-digital time-based ADC achieves 10-bit effective resolution over a 250-Hz bandwidth with an area of only 900 μm 2. The classification software reaches a sensitivity of 82.6% and 88.9% for supraventricular and ventricular arrhythmias respectively on the MIT-BIH arrhythmia database. The proposed system has been prototyped on the SleepRider SoC, a 28-nm fully-depleted silicon on insulator (FD-SOI) 3.1-mm 2 chip. It consumes 13.1 μW on average from a 1.8-V supply.

Critical implementation issues of excitation signals for embedded wearable bioimpedance spectroscopy systems with limited resources

Wideband excitation signals are essential in bioimpedance spectroscopy for measurements in a time ensuring a quasi-stable measurement condition. In particular, for wearable biomedical systems, due to limited system resources, several aspects regarding measurement time, crest factor, slew rate requirements, frequency distribution, amplitude spectrum, and energy efficiency need to be thoroughly investigated. In this paper, we present an investigation of excitation signals, which includes not only the theoretical aspects but also aspects of real implementation on microcontroller-based systems. At a fixed number of samples and sampling rate, we investigate the implementability of signal frequencies and the resulting spectral efficiency. We focus on sources of signal distortion due to timer and amplitude deviations. The results show that for 4096 samples and a sampling frequency of 1 MHz, wideband signals are 2.76 times faster than a stepped frequency sweep. The multisine signal provides a better energy efficiency and has a lower slew rate requirement on hardware (around 0.3 V µs−1), but has a relatively high crest factor, even after optimization. An exemplary investigation of the distortion of the time/frequency and amplitudes following implementation on a standard industrial advanced RISC machines microcontroller has shown that a sampling rate compensation is required to overcome timer inaccuracies. Furthermore, non-return-to-zero binary signals are more sensitive to distortion due to hardware-related issues and have a lower signal-to-distortion-and-noise (SINAD) ratio than 24 dB, which is lower than the multisine signal, having a SINAD of 31 dB.

Unconventional Device and Material Approaches for Monolithic Biointegration of Implantable Sensors and Wearable Electronics

AbstractImplantable biosensors and wearable bioelectronics need to be intimately interfaced with soft human tissues for a high‐quality health diagnosis and feedback therapy. Despite the recent developments in these devices, it is essential to further enhance their performance and functionalities in order to facilitate the formation of intimate interfaces between the devices and the human body. This will help minimize the unwanted injuries to target tissues, enhance the efficiency of sensing and therapy, and achieve long‐term biocompatibility. In this regard, the physiological and mechanical properties of the target tissues need to be considered carefully when designing the materials and devices to be employed in implantable and wearable electronics. Herein, a discussion of the recent developments in implantable biosensors and wearable electronics, based on unconventional device designs and material approaches, is presented. This review particularly focuses on the design principles of devices and materials that enable an intimate integration of biosensing devices with soft tissues and target organs. In addition, recent developments of electronics employed in stand‐alone wearable biomedical systems, such as wearable displays and energy devices, are presented. Moreover, future prospects for emerging approaches that could enable further developments of implantable biosensors and wearable electronics are also discussed.

(Invited) Wearable Microfluidic and Electronic Frameworks for Biomedical Applications

I. Introduction Advances in wearable electronics, functional nanocomposite polymers, flexible microfluidics, and commercial polymer microfluidics are reported on a daily basis. However, much of this research is field-specific, despite the enormous potential that the convergence of these research areas has for the future of health care, worker safety, food safety, consumer devices, and commercial microfluidics. We present an innovative approach of powerful, general-purpose frameworks that facilitate interfacing of nanocomposite polymer-based, microfluidic, and electronic devices on flexible polymer, textile, or industrial polymer platforms. Such approaches offer practical solutions for areas such as safety lighting and health monitors for safety vests; heart monitors and perspiration monitors for athletic clothing; and other applications in real-time wearable bioelectric and biochemical monitoring. II. Wearable Microfluidic and Electronic Frameworks A. Wearable bioelectric sensors Intense research into wearable electronics has resulted in many innovative devices and systems, e.g.: flexible polyimide or Kapton printed circuit boards (PCBs) [1]; roll-to-roll foil and other printed devices [2]; printing and weaving of textiles [3]; and special geometries for flexible interconnect between rigid components [4]. We have investigated conductive nanocomposite polymers and metal transfer processes for wearable bioelectric sensors [5, 6]. These technologies can be employed in, for example, conformable and wearable systems for electrocardiogram (ECG) [5], tissue impedance [7] and pressure [8] sensors. Unlike many other techniques, the technology and materials employed for our devices are highly compatible with clothing-based textiles. B. Wearable microfluidics Much less research has been performed in the emerging area of wearable microfluidics. Traditionally, microfluidic devices are fabricated in rigid substrates or flexible materials such as polydimethylsiloxane (PDMS) that are bonded to rigid substrates. Free-standing PDMS devices are developed for, e.g., perspiration sensors [9]; however, such processes typically require long fabrication times, equipment in a cleanroom facility, and difficulty with integration onto textiles. Other devices employ porous materials or microneedles to deliver biofluids, e.g., perspiration or interstitial fluid, by capillary forces [10]; however, such devices are limited in fluid collection or are too invasive. Wearable textile-based devices have been recently demonstrated that use the textile itself as a fluidic “channel” [11]; however, such devices are dependent on the fluidic characteristics of the fabric. To overcome these limitations and facilitate the development of fully flexible, wearable, and durable microfluidic devices that can be used for a wider variety of applications, we have developed a printing-based fabrication process that employs screen printable plastisol ink [12]. This process is demonstrated for simple multi-level microfluidic devices toward the goal of fully wearable microfluidic systems. III. Summary Many methods have been developed for microelectronic and microfluidic devices in rigid or flexible packages (e.g., [13, 14, 15]). However, such technologies suffer from difficult integration and/or limited flexibility, limited geometries, limited microfluidic sample size, and/or difficult integration, especially on textile-based substrates. The technologies we present offer simple and compatible printing-based and transfer processes for microelectronic and microfluidic frameworks that facilitate cost-effective development of durable wearable biomedical systems. References Y. Chuo, et. al., IEEE Transactions Biomedical Circuits Systems 4(5):281-94 (2010).K. Jain, et. al., Proceedings of the IEEE 93(8):15000-10 (2005).F. Carpi, et. al., IEEE Transactions Information Technology Biomedicine 9(3):295-318 (2005).M. Gonzalez, et. al., Microelectronics Reliability 51:1069-76 (2011).D. Chung, et. al. Proc. SPIE 9060, (2014); doi:10.1117/12.2046548.D. Hilbich, et. al., Proc. SPIE 98020R (2016); doi:10.1117/12.2219284.D. Chung, et. al., J Electrochemical Society 161(2):B3071-76 (2014).A. Rahbar, et. al., Proc. SPIE 90600O (2014); doi:10.1117/12.2044342.J. Choi, et. al., Adv Healthcare Mater 6:1601355 (2017).F. Benito-Lopez, et. al., Procedia Chemistry 1(1):1103-1106 (2009).A. Nilghaz, et. al., Lab Chip 12:209-218 (2012).D. Chung & B.L. Gray, J Micromech Microeng, 27(11), (2017).S. Cheng., et. al., Advanced Functional Materials 21(12):2282-90 (2011).M. Scholles, et. al., Proc. of SPIE 7593:75930C-2 (2013).A. Wu, et. al., Lab Chip 10:519-521 (2010).

Smart Textile-Based Wearable Biomedical Systems: A Transition Plan for Research to Reality

The field of smart textile-based wearable biomedical systems (ST-WBSs) has of late been generating a lot of interest in the research and business communities since its early beginnings in the mid-nineties. However, the technology is yet to enter the marketplace and realize its original goal of enhancing the quality of life for individuals through enhanced real-time biomedical monitoring. In this paper, we propose a framework for analyzing the transition of ST-WBS from research to reality. We begin with a look at the evolution of the field and describe the major components of an ST-WBS. We then analyze the key issues encompassing the technical, medical, economic, public policy, and business facets from the viewpoints of various stakeholders in the continuum. We conclude with a plan of action for transitioning ST-WBS from "research to reality."