Biopotential Recording Research Articles

Performance Evaluation of Woven Conductive Dry Textile Electrodes for Continuous ECG Signals Acquisition

Electrocardiogram (ECG) signal monitoring is one of the essential techniques for determining the physiological state of human beings. Long-term ECG monitoring is very much essential for the diagnosis and treatment of infrequent arrhythmic episodes. Although, most of the wearable microelectronic ECG implementations employ the well-established surface electrodes technology for bio-potential recordings; they are found to be susceptible to skin irritation and influence the skin-contact impedance to larger extent in long-term monitoring applications. Integration of such sensors into wearable intelligent biomedical clothing is not feasible. This specific research study determines the application of two different conductive textile fabric materials, namely, the woven conductive silver and conductive knitted jersey as dry textile electrodes for ECG biopotential acquisition. The skin-electrode contact impedance measurements for both electrodes presented reduced skin-contact impedance of less than 1 $\text{M}\Omega $ /cm2 compared to 1–5 $\text{M}\Omega $ /cm2 as reported in literature. The performance of the proposed textile sensors is evaluated qualitatively through visual inspection and quantitatively using metrics such as power spectral density, kurtosis, baseline wander analysis, and signal-to-noise ratio (SNR). The obtained quantitative measures were compared with standard clinical grade conductive-gel based disposable Ag/AgCl surface electrodes. The simulation and comparison studies showed that, the proposed textile electrodes exhibit acceptable performance for ECG acquisition and in some instances improved performance than the traditional commercial disposable gel-based surface electrodes.

Noise Optimization of CMOS Front-End Amplifier for Embedded Biomedical Recording

This paper deals with the noise optimization of a low-power front-end amplifier (FEA) integrating a band-pass filter for EEG signal recording. The AC-coupled and capacitive feedback structures have been adopted in order to reject the large DC offset generated at the electrode–skin interface. A high open-loop gain with acceptable phase margin was obtained with the proposed operational transconductance amplifier architecture. The methodology to reach a low noise-to-power trade-off is based on selecting the suitable operation region of each transistor, especially the input differential pair by considering the gm/ID parameter. The proposed amplifier was implemented in both 0.13 μm and 0.18 μm CMOS processes with a supply voltage set to ± 1 V. For both technologies, the obtained gain and bandwidth are practically similar, while the phase margin obtained in the first process (0.13 μm) is higher than the one obtained in the second process (0.18 μm); however, both values insure system stability. A lower total input-referred noise of 1.7 µVrms with a noise efficiency factor of 3.4 was obtained in 0.18 µm CMOS process. The designed FEA has been found suitable for ECG biopotential recording.

An Integrated Multi-Channel Biopotential Recording Analog Front-End IC With Area-Efficient Driven-Right-Leg Circuit.

A multi-channel biopotential recording analog front-end (AFE) with a fully integrated area-efficient driven-right-leg (DRL) circuit is presented in this paper. The proposed AFE includes 10 channels of low-noise capacitive coupled instrumentation amplifier (CCIA), one shared 10-bit SAR ADC and a fully integrated DRL to enhance the system-level common-mode rejection ratio (CMRR). The proposed DRL circuit senses the common-mode at the CCIA output so that the AFE gain is reused as the DRL loop gain. Therefore, area efficient unit-gain buffer with small averaging capacitors can be used in DRL circuit to reduce the circuit area significantly. The proposed AFE has been implemented in a standard 0.18-μm CMOS process. The DRL circuit achieved more than 85% chip area reduction compared to the state-of-art on-chip DRL circuits and maximum 60 dB enhancement to system-level CMRR. Measurement results show high/low AFE gain of 60 dB/54dB respectively with 1 μA/channel current consumption under 1.0 V power supply. The measured AFE input-referred noise in 1 Hz - 10k Hz range is 4.2 μVrms and the maximum system-level CMRR is 110 dB.

Wireless, Skin-Like Membrane Electronics With Multifunctional Ergonomic Sensors for Enhanced Pediatric Care.

Continuous cardiac monitoring using electrocardiograms (ECG) provides a range of patient information, essential for making clinical decisions, to healthcare providers. Unfortunately, the clinical standard of ECG recording requires the use of rigid metal electrodes, conductive gels, and wired electronic devices, which often cause skin injuries and health risks for pediatric patients with underdeveloped, fragile skin. Here, we introduce a wireless, soft, comfortable electronic system that obviates the need for skin preparation, electrolyte gels, or aggressive tapes. The low-profile device incorporates a thin-film circuit and nanomembrane sensors, encapsulated in a hyperelastic elastomer. The soft elastomeric membrane offers an optimized adhesion that ensures a conformal lamination of stretchable electrodes on the skin for recording of high-fidelity biopotentials. The combined set of on-board Bluetooth module, front-end amplifier, and voltage regulator enables a real-time, long-range, wireless monitoring of physiological data, including ECG, heart rate (HR) and respiratory rate (RR). A pilot study with pediatric patients demonstrates the clinical feasibility of the device as a comfortable, reliable biopotential monitor, suggesting a new standard for safe and effective pediatric care.

Analgesic Effect of Dizocine Combined with Ropivacaine on Recurrent Neuropathic Pain in Peripheral Nerve Compression Rats

To explore the analgesic effect of dizocine combined with ropivacaine on recurrent neuropathic pain in rat model of peripheral nerve compression. Rats were randomly divided into 5 groups: sham control group (S), peripheral nerve compression model group (M), dizocine group (D), ropivacaine group (R), and combined drug group (DR). Rat peripheral nerve compression model was constructed to observe the symptoms of the rats before and after surgery. Mechanical withdrawal threshold was measured on the 21st day after surgery. The electrophysiological changes of rat peripheral nerve were measured by biopotential recording system, including proximal latency, distal latency, and compound muscle action potential. The incubation period and nerve conduction velocity were further obtained. Histological changes were observed by HE staining and toluidine blue staining. Axon number and myelin damage grade were performed, and the ultrastructure was observed by transmission electron microscopy (TEM). The mechanical withdrawal threshold, nerve conduction velocity, and compound muscle action potential were effectively increased in combination group. However, the proximal latency, distal latency, and incubation period were significantly reduced. Furthermore, dizocine combined with ropivacaine can effectively reduce the degree of myelination. TEM shown that the DR group had the best therapeutic effect, and the histological appearance of the cross section was quite similar to that of the S group. Dizocine combined with ropivacaine has a significant analgesic effect in rat model of peripheral nerve compression.

Enhanced ICMR amplifier for high CMRR biopotential recordings.

This paper presents an integrated biopotential preamplifier architecture targeting applications that simultaneously require high common-mode rejection ratio (CMRR), low noise, high input common-mode range (ICMR), and current-efficiency (low Noise Efficiency Factor or NEF). A biopotential preamplifier, which performs well in line with the state-of-the-art of the field while providing enhanced ICMR and CMRR performance, was fabricated in a 0.5 μm CMOS process. Results from measurements show that the gain is 47 dB, the bandwidth ranges from 1 Hz to 7.7 kHz, the equivalent input noise is 1.8 μVrms, the CMRR is 100.5 dB, the ICMR is 1.7 V and the NEF is 3.2.

Novel multiwalled carbon nanotube (MWCNT) modified metal oxide semiconductor field effect transistor (MOSFET) based electrode for electrophysiological measurements on human skin

Standard electrodes for electrophysiological signal acquisition in clinical applications such as electrocardiography or electromyography require the use of electrolytic gel and skin abrasion for better electrical interface between electrode and skin. Since gel dries out over a period of time, signal deterioration takes place on long duration with wet electrodes. Dry electrodes are promising alternative for long duration recording; nevertheless, they suffer from high contact impedance and motion artifacts. The proposed work introduces a novel multi-walled carbon nanotube (MWCNT) modified metal oxide semiconductor field effect transistor (MOSFET) based electrode for electrophysiological measurements on human skin. Vertically aligned metallic MWCNTs grown on the gate of MOSFETs form the contact surface of the electrode. MWCNTs penetrate the outer layer of skin for stable and improved electrical contact without the gel. The proposed electrode utilizes advantages of the MOSFET such as direct charge–current conversion, insulation between skin and instrumentation unit, and low noise pre-amplification of electrophysiological signals. Electrical equivalent of MWCNTs, design, and microfabrication of convenient MOSFET are reported. MOSFET parameters are obtained from technology computer-aided design simulation environment and combined with MWCNT parameters in the simulation program for integrated circuits emphasis. Simulated results of the proposed electrode exhibited lower contact impedance and high quality signal capture with respect to wet electrodes. The results show that the proposed electrode can be used for long duration recording of biopotentials with very high stable performance.

Compact, Programmable, Two-Stage Configuration for Implantable Biopotential Recording Amplifiers

This paper proposes an area-efficient CMOS amplifier for neural recording applications. The proposed neural amplifier takes advantage of indirect negative feedback to realize a rather low upper [Formula: see text]3-dB cutoff frequency. As a result, the capacitance needed to realize the cutoff frequency is so small that can be easily implemented on-chip. Moreover, the proposed circuit also employs attenuators in the same feedback loop in order to further reduce the silicon area consumed by the capacitors and at the same time to increase the input impedance of the circuit. Designed based on a two-stage configuration, the amplifier provides tunable lower cutoff frequency and digitally-programmable upper cutoff frequency and voltage gain. The circuit is designed in a 0.18-[Formula: see text]m technology, and consumes 0.022[Formula: see text]mm2 and 0.27[Formula: see text]mm2 of chip areas for single- and eight-channel designs, respectively. Operated with a supply voltage of 1.8[Formula: see text]V, power consumption of the proposed amplifier is 36.7[Formula: see text][Formula: see text]W with the simulated input-referred noise of 4[Formula: see text][Formula: see text] over 1[Formula: see text]Hz–10[Formula: see text]kHz for each channel. The amplifier also provides an output swing of 0.95 Vpp with a total harmonic distortion of [Formula: see text]50[Formula: see text]dB at the frequency of 1[Formula: see text]kHz.

Correction: An automated system for the objective evaluation of human gustatory sensitivity using tongue biopotential recordings.

[This corrects the article DOI: 10.1371/journal.pone.0177246.].

Conductively coupled flexible silicon electronic systems for chronic neural electrophysiology

Materials and structures that enable long-term, intimate coupling of flexible electronic devices to biological systems are critically important to the development of advanced biomedical implants for biological research and for clinical medicine. By comparison with simple interfaces based on arrays of passive electrodes, the active electronics in such systems provide powerful and sometimes essential levels of functionality; they also demand long-lived, perfect biofluid barriers to prevent corrosive degradation of the active materials and electrical damage to the adjacent tissues. Recent reports describe strategies that enable relevant capabilities in flexible electronic systems, but only for capacitively coupled interfaces. Here, we introduce schemes that exploit patterns of highly doped silicon nanomembranes chemically bonded to thin, thermally grown layers of SiO2 as leakage-free, chronically stable, conductively coupled interfaces. The results can naturally support high-performance, flexible silicon electronic systems capable of amplified sensing and active matrix multiplexing in biopotential recording and in stimulation via Faradaic charge injection. Systematic in vitro studies highlight key considerations in the materials science and the electrical designs for high-fidelity, chronic operation. The results provide a versatile route to biointegrated forms of flexible electronics that can incorporate the most advanced silicon device technologies with broad applications in electrical interfaces to the brain and to other organ systems.

A 0.006 mm2 1.2 $\mu$ W Analog-to-Time Converter for Asynchronous Bio-Sensors

This paper presents a low-power analog-to-time converter (ATC) for integrated bio-sensors. The proposed circuit facilitates the direct conversion of electrode bio-potential recordings into time-encoded digital pulses with high efficiency without prior signal amplification. This approach reduces the circuit complexity for multi-channel instrumentation systems and allows asynchronous digital control to maximize the potential power savings during sensor inactivity. A prototype fabricated using a 65-nm CMOS technology is demonstrated with measured characteristics. Experimental results show an input-referred noise figure of 3.8 $\mu V_{\mathrm{ rms}}$ for a 11-kHz signal bandwidth while dissipating 1.2 $\mu \text{W}$ from a 0.5-V supply and occupying $60\times 80\,\,\mu \text{m}\,\,^{\mathrm{ 2}}$ silicon area. This compact configuration is enabled by the proposed asynchronous readout that shapes the mismatch components arising from the multi-bit quantizer and the use of capacitive feedback.

Self‐Adhesive and Ultra‐Conformable, Sub‐300 nm Dry Thin‐Film Electrodes for Surface Monitoring of Biopotentials

AbstractAccurate and unobtrusive monitoring of surface biopotentials is of paramount importance for physiological studies and wearable healthcare applications. Thin, light‐weight, and conformal bioelectrodes are highly desirable for biopotential monitoring. This report demonstrates the fabrication of sub‐300 nm thin, dry electrodes that are self‐adhesive and conformable to complex 3D biological surfaces and thus capable of excellent quality of biopotential (surface electromyogram and surface electrocardiogram) recordings. Measurements reveal single‐day stability of up to 10 h. In addition, the bending stiffness of the sensor is calculated to be ≈0.33 pN m2, which is comparable to stratum corneum, the uppermost layer of human skin, and this stiffness is over two orders of magnitude lower than the bending stiffness of a 3.0 µm thin sensor. Laminated on a prestretched elastomer, when relaxed, the sensor forms wrinkles with a period and amplitude equal to 17 and 4 µm, respectively, which these values agree with theoretical calculations. Finally, with skin vibrations of up to ≈15 µm, the sensor exhibits motion artifact‐less monitoring of surface biopotentials, in contrast to a wet adhesive electrode that shows much greater influence.

Simple fabrication method of an ultrasensitive gold micro-structured dry skin sensor for biopotential recording

Fast advancement of dry biopotential electrode has driven to the reduction of using Ag/AgCl (wet electrode). There is a necessity for development of flexible and eco-friendly micro-structured (MSE) dry biopotential electrode utilizing biodegradable and non-toxic materials for a better life and sustainable future. It is very difficult to create micro-structure without using any solvents or high-end equipment. Here, a novel micro-structured electrode coated with Ti/Au film is fabricated using a sandpaper template and is proposed for biopotential signal monitoring applications. We used sandpaper, which is recyclable and biodegradable. The proposed MSE is a flexible, stretchable, and biocompatible dry micro-structured electrode. The sheet resistance of the proposed MSE is 2.5 Ω/sq. The area of MSE was only 4 cm × 4 cm (l × w), and the sweat of the epidermis layer of human skin could be utilized as the electrolyte for the flexible MSE during the electrocardiography (ECG) and electromyography (EMG) recording. The fabricated MSE was enough thin and flexible to be well attached onto the skin. The contact impedance of the flexible MSE was stable and suitable for long-term biopotential recording. The main advantage of the electrodes is simple fabrication, which can be used in wearable electrode systems to monitor human health. The results of the experiment show that the proposed electrode can operate in dry conditions when the subject is resting, and it shows fewer motion artifacts during movement.

A 790 nW Low-Noise Instrumentation Amplifier for Bio-Sensing Based On Gm-RSC Structure

This paper presents a low-power low-noise instrumentation amplifier (IA) for bio-potential recording. The proposed IA is based on a novel Gm-RSC structure, whose gain is determined by the transconductance (Gm) and the equivalent resistance ([Formula: see text]) of the switched-capacitor (SC) load. The transconductance amplifier stage is based on the current-reuse telescope topology to achieve low noise at low-power dissipation. A resistor-controlled oscillator is designed to generate desirable operational frequency for SC load and to continuously tune the mid-band gain of the IA for different biomedical applications. Measurement results show that the input referred noise of the proposed IA is about 1.27[Formula: see text][Formula: see text]VRMS ([Formula: see text][Formula: see text]Hz) and the noise efficiency factor is 3.3. The range of tunable gain is from 28 to 40[Formula: see text]dB. The common mode rejection ratio and power supply rejection ratio at 50[Formula: see text]Hz are 72 and 78[Formula: see text]dB, respectively. The IA consumes only 660[Formula: see text]nA current at 1.2[Formula: see text]V supply and the active area of the IA is only 0.035[Formula: see text]mm2.

Effective Biopotential Signal Acquisition: Comparison of Different Shielded Drive Technologies

Biopotential signals are mainly characterized by low amplitude and thus often distorted by extraneous interferences, such as power line interference in the recording environment and movement artifacts during the acquisition process. With the presence of such large-amplitude interferences, subsequent processing and analysis of the acquired signals becomes quite a challenging task that has been reported by many previous studies. A number of software-based filtering techniques have been proposed, with most of them being able to minimize the interferences but at the expense of distorting the useful components of the target signal. Therefore, this study proposes a hardware-based method that utilizes a shielded drive circuit to eliminate extraneous interferences on biopotential signal recordings, while also preserving all useful components of the target signal. The performance of the proposed method was evaluated by comparing the results with conventional hardware and software filtering methods in three different biopotential signal recording experiments (electrocardiogram (ECG), electro-oculogram (EOG), and electromyography (EMG)) on an ADS1299EEG-FE platform. The results showed that the proposed method could effectively suppress power line interference as well as its harmonic components, and it could also significantly eliminate the influence of unwanted electrode lead jitter interference. Findings from this study suggest that the proposed method may provide potential insight into high quality acquisition of different biopotential signals to greatly ease subsequent processing in various biomedical applications.

Skin Conformal Polymer Electrodes for Clinical ECG and EEG Recordings.

Preparation-free and skin compliant biopotential electrodes with high recording quality enable wearables for future healthcare and the Internet of Humans. Here, super-soft and self-adhesive electrodes are presented for use on dry and hairy skin without skin preparation or attachment pressure. The electrodes show a skin-contact impedance of 50 kΩ cm2 at 10 Hz that is comparable to clinical standard gel electrodes and lower than existing dry electrodes. Microstructured electrodes inspired by grasshopper feet adhere repeatedly to the skin with a force of up to 0.1 N cm-2 without further attachment even during strong movement or deformation of the skin. Skin compliance and adhesive properties of the electrodes result in reduction of noise and motion artifacts superior to other dry electrodes reaching the performance of commercial gel electrodes. The signal quality is demonstrated by recording a high-fidelity electrocardiograms of a swimmer in water. Furthermore, an electrode with soft macropillars is used to detect alpha activity in the electroencephalograms from the back of the head through dense hair. Compared to gel electrodes, the soft biopotential electrodes are nearly imperceptible to the wearer and cause no skin irritations even after hours of application. The electrodes presented here could combine unobtrusive and long-term biopotential recordings with clinical-grade signal performance.

Microelectrode array and multichannel system for recording the electrical activity of neurons in vitro

Microelectrode array and multichannel system for recording the electrical activity of neurons in vitro

An automated system for the objective evaluation of human gustatory sensitivity using tongue biopotential recordings.

The goal of this work is to develop an automatic system for the evaluation of the gustatory sensitivity of patients using an electrophysiological recording of the response of bud cells to taste stimuli. In particular, the study aims to evaluate the effectiveness and limitations of supervised classifiers in the discrimination between subjects belonging to the three 6-n-propylthiouracil (PROP) taster categories (supertasters, medium tasters, and non-tasters), exploiting features extracted from electrophysiological recordings of the tongue. Thirty-nine subjects (equally divided into the three PROP status classes by standard non-objective scaling methods) underwent a non-invasive, differential, biopotential recording of their tongues during stimulation with PROP by using a custom-made, flexible, silver electrode. Two different classifiers were trained to recognize up to seven different features extracted from the recorded depolarization signal. The classification results indicate that the identified set of features allows to distinguish between PROP tasters and non-tasters (average accuracy of 80% ± 18% and up to 94% ± 15% when only supertasters and non-tasters are considered), but medium tasters were difficult to identify. However, these apparent classification errors are related to uncertainty in the labeling procedures, which are based on non-objective tests, in which the subjects provided borderline evaluations. Thus, using the proposed method, it is possible, for the first time, to automatically achieve objective PROP taster status identification with high accuracy. The simplicity of the recording technique allows for easy reproduction of the experimental setting; thus the technique can be used in future studies to evaluate other gustatory stimuli. The proposed approach represents the first objective and automatic method to directly measure human gustatory responses and a milestone for physiological taste studies, with applications ranging from basic science to food tasting evaluations.

A 64-channels neural interface for biopotentials recording and PNS stimulation.

A biomedical interface that combines into a single and compact device the recording of biopotentials and the electrical stimulation of neural fibres is presented. It is intended for enabling the control over a robotic hand and for restoring the sensory feedback in amputees by directly interfacing the peripheral nervous system (PNS) in closed-loop. A modular system consisting in one or more independent 16-channels bidirectional units was conceived. Each module is based on three 0.35μm bulk-CMOS integrated circuits (ICs): a recording unit, a High-Voltage (HV) stimulator and a HV booster. A tunable bandwidth (10Hz-8kHz) allows the recording IC to acquire both electroneurographyc (ENG) and electromiographyc (EMG) signals with a programmable gain up to 43.5dB. The signals are then converted into a digital domain by means of a ΣΔ converter. Due to the typical high impedance at the electrode-tissue interface, a programmable HV booster that increases the stimulation voltage up to 19V was designed. It is directly controlled by the stimulation module that generates current-based pulses with a programmable amplitude and pulse-width. The whole system was validated by means of in-vivo experiments in rats.

A Precision Pseudo Resistor Bias Scheme for the Design of Very Large Time Constant Filters

In this brief, a novel pseudo resistor bias scheme capable of achieving improved performances against process parameter variations is presented. The use of a matched structure allows for achieving a simulated statistical variation $\sigma/\mu$ one order of magnitude better than conventional bias schemes proposed in the literature. The entire circuit was designed to be able to emulate a tunable resistor whose resistance could be digitally set in the range of 400 $\text{M}\Omega$ –90 $\text{G}\Omega$ . The design of a very low frequency bandpass filter (BPF) for biopotential recording was also covered as a suitable application. The tunability offered by the bias scheme was employed, in this case, to realize a high-pass cutoff frequency variable in the range of 10 Hz–2 kHz. An integrated circuit including eight acquisition channels, each of which is composed of the designed BPF and a conventional 10-bit analog-to-digital converter, was finally realized in a CMOS 0.35- $\mu\text{m}$ process. The chip was successfully tested showing a measured $\sigma/\mu$ variation of the high-pass cutoff frequency equal to 0.13 when different channels on the same die are considered.