Search

We present a simple-structured strain sensor based on a low-cost ionic liquid. The ionic liquid was made of sodium chloride/propylene glycol solution and was embedded in a linear microfluidic channel fabricated using Ecoflex. The proposed sensor is capable of measuring strain up to 100% with excellent repeatability. The highest gauge factor is obtained as 6.19 under direct current excitation and 3.40 under alternating current excitation at 1 kHz. The sensor shows negligible hysteresis and overshoot, and survived 10,000 rapid stretch-release cycles of a 100% peak strain with a minor deviation in the response signal. The sensor can be mounted to different locations on the human body and suits a variety of applications in the field of motion detection, human–machine interface and healthcare monitoring.

Recent advances in hemodynamic monitoring have seen the advent of non-invasive methods which offer ease of application and improve patient comfort. Bioimpedance Analysis or BIA is one of the currently employed non-invasive techniques for hemodynamic monitoring. Impedance Cardiography (ICG), one of the implementations of BIA, is widely used as a non-invasive procedure for estimating hemodynamic parameters such as stroke volume (SV) and cardiac output (CO). Even though BIA is not a new diagnostic technique, it has failed to gain consensus as a reliable measure of hemodynamic parameters. Several devices have emerged for estimating CO using ICG which are based on evolving methodologies and techniques to calculate SV. However, the calculations are generally dependent on the electrode configurations (whole body, segmental or localised) as well as the accuracy of different techniques in tracking blood flow changes. Blood volume changes, concentration of red blood cells, pulsatile velocity profile and ambient temperature contribute to the overall conductivity of blood and hence its impedance response during flow. There is a growing interest in investigating limbs for localised BIA to estimate hemodynamic parameters such as pulse wave velocity. As such, this paper summarises the current state of hemodynamic monitoring through BIA in terms of different configurations and devices in the market. The conductivity of blood flow has been emphasized with contributions from both volume and velocity changes during flow. Recommendations for using BIA in hemodynamic monitoring have been mentioned highlighting the suitable range of frequencies (1 kHz–1 MHz) as well as safety considerations for a BIA setup. Finally, current challenges in using BIA such as geometry assumption and inaccuracies have been discussed while mentioning potential advantages of a multi-frequency analysis to cover all the major contributors to blood’s impedance response during flow.

Tissue-mimicking materials for phantoms are fabricated for research purposes to simulate the mechanical or electrical properties of real human tissues and promote better understanding of their properties. This research investigated the dielectric properties (from 20 Hz to 100 kHz) of five promising muscle mimicking materials including matrix materials (gelatin powder and agar powder), and fillers (sodium chloride, glycine and aluminum powder) for the development of muscle phantoms. The mechanical behaviors were verified as well. This research determined the effects of electrode polarization (EP) on the dielectric properties of each material and then used a mathematical model to reduce these unwanted effects. Additionally, the results indicated the very low dielectric properties of gels-only samples. Both electrical conductivity and relative permittivity increased with increasing concentrations of fillers. Moreover, all fillers had their own capabilities to alter the levels and trends in the increments of dielectric values, which provide a wider selection to muscle-mimicking materials. Theoretically, it is feasible to achieve desired dielectric properties by mixing these fillers together with certain ratios. In this way, low-cost muscle phantoms can be produced and used as experimental subjects for biopotential sensing application.

Motion artefact is the biggest concern in Electrocardiogram signals, especially when recording long-term measurements. Current studies fail to address the major source of motion artefact, which is skin stretch. This study utilizes two-dimensional strain fields as motion information in two advanced algorithms- Principal Component Analysis (PCA) and Independent Component Analysis (ICA). The strain fields were computed using point tracking and infinitesimal strain theory and a comparison of mean and median strains as motion information was made. The highest improvement in Signal to Noise ratio (SNR) was observed when the mean values of strain fields over a region of interest per ECG sample were taken as motion information in ICA. The lowest SNRs were obtained when PCA and ICA were implemented without any motion information.

Tissue phantoms are widely used as substitute materials for real tissue validation of various newly emerging biomedical technologies such as ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI). However, there is no specific recipe for fabricating skin-mimicking phantoms which can mimic both the mechanical and dielectric properties of human skin at lower frequency ranges. The objective of this paper is to present a variety of tissue-mimicking materials for filling this research gap in the lower frequency range from 20 Hz to 300 kHz. The starting point of our experiments is based on the oil-in-gelatin based tissue-mimicking materials (TMMs) that have shown to mimic the dielectric properties of human skin in higher frequency ranges. This paper examines the mechanical and dielectric performance of five major classes of tissue-mimicking materials (1) Oil-in-gelatin, (2) lignin and graphene nanopowder in gelatin, (3) gelatin and distilled water, (4) mixed oil in gelatin and distilled water, and (5) lignin in gelatin and distilled water. Mechanical and electrical testing was performed using compression testing and parallel plate method respectively. The effect of electrode polarization was considered in the measured data and the intrinsic impedance values were found to be following the Cole-Cole equation. The Young's modulus range of all tissue-mimicking materials was within the range of skin.

This work aims to compile various measurement and calibration techniques for Electroencephalogram (EEG). The objective is to provide an assessment of different components of an EEG and their significance in understanding different types of responses to stimuli. This review provides an overview of recommended electrode positions and lead systems for EEG with calibration and activation procedures. The different components of an EEG according to frequency bands – Gamma, Beta, Alpha, Theta and Delta have been discussed with emphasis on their interpretation and their role in several applications. The motivation behind this study is to provide a basic understanding of the composition of EEG, understanding the significance of each brain wave and the locations at which they are most prominent.

Electrocardiography (ECG) is widely used in clinical practice, for example to diagnose coronary artery disease or the cause of chest pain during a stress test, while the patient is running on a treadmill. However, artefacts due to subject’s movement are hard to identify and eliminate and can be easily mistaken for symptoms of arrhythmia, leading to misdiagnosis and false alarms. Skin stretch has been identified as a major source of motion artefacts in ECG signals. A Motion Artefact Rejection System (MARS) has been developed, where a polymer patch electrode with Young’s modulus lower than of skin was used to simultaneously measure ECG and skin stretch. Skin-stretch artefacts were induced in 7 subjects across the following age groups: 18–35 years (3 subjects), 36–55 years (2 subjects), and 56 years and above (2 subjects). The motion artefact measured using patch electrodes was used in advanced signals processing algorithms- Principal Component Analysis (PCA) and Independent Component Analysis (ICA). A novel, state-of-the-art technique to identify and eliminate motion artefacts from ECG signals has been developed which is feasible for medical implementations.

This article focusses on preparation and mechanical testing of thin-polymer electrodes to efficiently measure the biomedical signals while providing a conformal skin-contact. The method to prepare thin electrode films using Polydimethylsiloxane (PDMS) with different Young's moduli has been described. The Young's modulus was evaluated for each film by conducting tension-relaxation tests. The PDMS electrodes were made conductive by mixing them with Multi-Walled Carbon Nano Tubes (MWCNTs) and Graphene Nano Powder (GNP) using an ultrasonic mixer. The current study addresses a novel approach of preparing PDMS based sensors by doping them with CNTs and GNPs and wetting them in N-N Dimethylformamide (DMF) prior to their dispersion in PDMS. This was done to avoid their clumping in PDMS and to ensure more uniform dispersion. The conductance of the PDMS/MWCNT and PDMS/GNP electrodes were measured using an impedance spectrometer and were compared with that of standard silver-silver chloride (Ag/AgCl) and dry silver (Ag) electrodes.

Skin is the outermost layer of the human body which regulates the body temperature and protects the body from abrasion and water loss. The Young’s Modulus of skin is measured as a ratio of the stress applied to the skin in vitro or in vivo over the skin deformation. Skin is found to be highly anisotropic and Young’s Modulus is found to be dependent on orientation with respect to Langer’s lines, where highest value is seen in the parallel orientation, and can be twice the perpendicular values. Young’s Modulus decreases up to three orders of magnitude with hydration. An inverse relationship between skin’s thickness and Young’s Modulus is observed. It can be concluded that the thickness of skin increases with age until 30 years and varies inversely with age after then. This paper summarises evidence for correlation of Young’s Modulus with intramural and extraneous factors such as Langer’s lines, skin’s thickness, ageing and hydration.

Objective: The mechanical behaviour or the Young’s Modulus of the skin is measured as a ratio of the stress applied to the skin in vitro or in vivo over the skin deformation. The Young’s Modulus of skin is an important factor to estimate the characteristics of skin, to determine the course of a disease or to follow a cosmetic application. Methods: The mechanical behaviour of the skin is measured by changing the shape of skin by employing tensile, indentation, and suction and torsion tests. Results: Out of all the skin’s mechanical testing methods, suction tests are a common choice for skin testing, as they are easy to apply in vivo and consider both in-plane and normal loading conditions. Skin is found to be highly anisotropic and viscoelastic, with a range of Young’s Modulus between 5 kPa and 140 MPa. Conclusion: This paper reviews in vivo and in vitro reported values for Young’s Modulus of human skin for tensile, indentation, suction and torsion mechanical testing methods.

This work presents a 2D quantification of strain field caused due to the motion artifact in an Electrocardiogram (ECG) measurement. The objective of this work is to estimate the skin stretch induced motion artifact in an ECG signal. An ECG measurement was obtained from a subject for 10 seconds using standard Ag/AgCl electrodes by continuously moving the arm back and forth during the measurement. A Poly dimethyl siloxane (PDMS) patch of dimensions 40 mm × 45 mm × 0.254 mm was adhered to the arm during motion. The movement of the PDMS patch during the ECG measurement was recorded in a video and motion artifact was quantified in terms of normal and shear strain components ex, ey and exy. These values were derived using feature detection and Euclidean distance feature mapping. The motion artifact was eliminated from the ECG signal using Extended Kalman Filtering (EKF).

This work presents an image-processing approach to determine the 2D skin strain field caused by motion. It is expected that quantifying this strain field will help eliminate motion artifacts due to skin stretch in ECG signal acquisition. The objective of this work was to quantify the stretch induced strain in terms of normal and shear components E x , E y and E xy . These values were derived from video using feature detection and Euclidean distance feature matching. The stretching of skin has been emulated using a thin poly dimethyl siloxane (PDMS) film of dimensions 3cm × 3cm × 0.0254cm. Strain was induced using a uni-axial tensile-relaxation test. Results from the image processing algorithm were validated against a finite element simulation in SolidWorks® as well as tensile-test data. The overall values of strains- E x , E y and E xy found through point tracking and finite strain equation matched within acceptable limits of deviation. Simulation of thick films resulted in greater error, confirming expected limitations of the 2D strain model.