Quantification of a Low-Cost Stretchable Conductive Sensor Using an Expansion/Contraction Simulator Machine: A Step towards Validation of a Noninvasive Cardiac and Respiration Monitoring Prototype

Abstract

Abstract:The use of wearable sensors in health monitoring is increasing dramatically, largely due to their convenience and low-cost. Understanding the accuracy of any given sensor is paramount to avoid potential misdiagnosis. Commercially available electro-resistive band (ERB) sensors have been integrated into several newly developed wearable devices with a view to using these sensors to monitor a range of respiratory and cardiovascular metrics. Quantification of the ERBs is a necessary to step towards validation of these prototypes, as it provides valuable information, which could be exploited for compensation and ultimately, for improvement of their performance. Here, we present an analysis of the ERB sensors using an expansion/contraction simulator machine. Using the developed rig, the characteristics of four ERBs were compared with a linear displacement sensor (string potentiometer) during continuous use over the course of four-and-a-half days to investigate the error and nonlinearity of the ERBs. The analysis of the recorded data includes calculation and comparison of the total harmonic distortions of the two sensors to quantify ERB nonlinearity. Moreover, comparisons between the peak-to-peak voltages and signal-to-noise ratios of the ERB and string potentiometer demonstrate the effect nonlinearity on these factors. This paper demonstrates the nonlinearity of ERBs and highlights the implications for their use in practice.

Continuous Vital Monitoring During Sleep and Light Activity Using Carbon-Black Elastomer Sensors

“…There are a number of varieties of conductive polymers/fabrics available in the current market; however, the majority of these materials are not available commercially and are still in the research stage. Stretchable electroresistive sensors incorporate two main components, the conductive component (e.g., carbon black, graphene, nanowires, or metal elements such as silver, gold, nickel, and copper) with flexible support material (e.g., silicon-based elastomers, rubber-based elastomers) [30]. Graphene-based material shows better dynamic characteristics and performance but is in the early stage of research with limited availability.…”

“…The patches rely only on passive pressure applied to the fabric (such as during sleep, where at least one patch is compressed against the body), so the device is unusable in sitting and standing positions due to the lack of passive pressure against the T-shirt. In our experience with polymer-based resistive elements or conductive fabric [30][31][32], resistive change has a non-linear relationship where the highest sensitivity is obtained within the low strain region, <2% stretch. Therefore, when conductive fabric or carbon black elastomers are used, the sensors are not particularly tight in use, requiring less compressive force either from the T-shirt material or substrate layer to follow the body movement closely and accurately.…”

Morphic Sensors for Respiratory Parameters Estimation: Validation against Overnight Polysomnography

“…To avoid the overstretching and ripping of the ERB, a thin safety line matching the maximum permitted stretching for the ERB is affixed to the printed circuit board and a holding clasp on the other side (Figure 1). The maximum permitted elongation for the ERB sensor was determined using a bespoke stress testing device [22,29,30]. The stress testing device enabled the determination of the sensor breaking point and was also employed to characterise the sensor and fine-tune the circuit parameters leading to this new front end.…”

Towards Ultra Low-Cost Myoactivated Prostheses

“…The concept of ERBs is on the principle that, as the length of cord changes, its resistance will also change somewhat proportionally [ 22 ]. Although a nonperfect linear change of resistance with stretch has been demonstrated [ 23 ] for this sensor, nevertheless, it can be employed to acquire Analogous of Surface Electromyography (ASEMG) signals, where a change in ERB resistance is relatively proportional to the variations in muscle tension produced by the voluntary flexion. The volume shifts detected by the ERBs are more tolerant to changes in sensor location than conventional SEMG.…”

“…In this paper, we are proposing the design and mechanism of a simple, low-cost alternative to the existing ULPs [ 19 ] that uses ERBs and can achieve some hand basic tasks. The ASEMG signals acquired from ERBs reduce the computational power requested for the embedded system; hence, this can be replaced with an inexpensive control platform like Arduino [ 23 , 24 ].…”