Conditions for CNT - Coated Textile Sensors Applied to Wearable Platforms to Monitor Limb Joint Motion.

Despite recent research on joint motion measurement to monitor human body movement, current measurement techniques and tools have significant limitations, including requiring large space for measurement and causing discomfort in test subjects wearing motion sensors. Our study aims, first, to develop carbon nanotube (CNT)-based textile joint motion sensors. Second, ours study aims to identify the most suitable CNT-based sensor structure and attachment method for use on a wearable platform during general exercise speeds. Lastly, we used these sensors on the human body, using sleeves and legs to find the most stable location, and we used the CNT-based sensor condition to monitor joint motions. We utilized our CNT-based sensor, which has proper elasticity as well as conductivity, and applied it to the elbow and knee joints. Based on the strain gauge principle, we monitored the variance of electric resistance that occurred when the CNT-based sensor was stretched due to limb motion. Our study tested 48 types of sensors. These sensors were applied to the CNT using different base knit textiles as well as different attachment methods, layers, sensor lengths, and sensor widths. The four most successful sensor types, which showed superior efficacy over the others in joint motion measurement, were selected for further study. These four sensors were then used to measure the elbow and knee joint motions of human subjects by placing them on different locations on sleeves and legs. The CNT knit textile sensors best suited to measuring joint motions are those with a double-layered CNT knit and 5 cm long × 0.5 cm or 1 cm wide sensors attached to a polyester¬-based knit using a welding method. The best position for the sensor to more stably monitor joint motions was the "below hinge position" from the elbow or knee hinge joint. Our study suggests an alternative strategy for joint-motion measurement that could contribute to the development of more comfortable and human-friendly methods of human limb motion measurement.

The Effect of Electrode Designs Based on the Anatomical Heart Location for the Non-Contact Heart Activity Measurement.

This research is an extension of a previous research [1] on the different effects of sensor location that is relatively suitable for heart rate sensing. This research aimed to elucidate the causes of wide variations in heart rate measurements from the same sensor position among subjects, as observed in previous research [1], and to enhance designs of the inductive textile electrode to overcome these variations. To achieve this, this study comprised two parts: In part 1, X-ray examinations were performed to determine the cause of the wide variations noted in the findings from previous research [1], and we found that at the same sensor position, the heart activity signal differed with slight differences in the positions of the heart of each subject owing to individual differences in the anatomical heart location. In part 2, three types of dual-loop-type textile electrodes were devised to overcome variations in heart location that were confirmed in part 1 of the study. The variations with three types of sensor designs were compared with that with a single-round type of electrode design, by using computer simulation and by performing a t-test on the data obtained from the experiments. We found that the oval-oval shaped, dual-loop-type textile electrode was more suitable than the single round type for determining morphological characteristics as well as for measuring appropriate heart activity signals. Based on these results, the oval-oval, dual-loop-type was a better inductive textile electrode that more effectively overcomes individual differences in heart location during heart activity sensing based on the magnetic-induced conductivity principle.

Measurement of high-resolution mechanical contraction of cardiac muscle by induced eddy current.

There are many types of devices which help to manage a personal health conditions such as heartbeat chest belt, pedometer and smart watch. And the most common device has the relationship with heart rate or ECG data. However, users have to attach some electrode or fasten the belt on the bare skin to measure bio-signal information. Therefore, most of people want more convenient and short-ready-time and no-need to attach electrode. In this paper, we proposed the high-resolution measuring system of mechanical activity of cardiac muscle and thereby measure heartbeat. The principle of the proposed measuring method is that the alternating current generate alternating magnetic field around coil. This primary magnetic field induces eddy current which makes magnetic field against primary coil in the nearby objects. To measure high-resolution changes of the induced secondary magnetic fields, we used digital Phase-locked loop(PLL) circuit which provides more high-resolution traces of frequency changes than the previous studies based on digital frequency counter method. As a result of our preliminary experiment, peak-peak intervals of the proposed method showed high correlation with R-R intervals of clinical ECG signals(r=0.9249). Also, from signal traces of the proposed method, we might make a conjecture that the contraction of atrium or ventricle is reflected by changing conductivity of cardiac muscle which is beating ceaselessly.

Heart monitoring garments using textile electrodes for healthcare applications.

We measured the electrical activity signals of the heart through vital signs monitoring garments that have textile electrodes in conductive yarns while the subject is in stable and dynamic motion conditions. To measure the electrical activity signals of the heart during daily activities, four types of monitoring garment were proposed. Two experiments were carried out as follows: the first experiment sought to discover which garment led to the least displacement of the textile electrode from its originally intended location on the wearer's body. In the second, we measured and compared the electrical activity signals of the heart between the wearer's stable and dynamic motion states. The results indicated that the most appropriate type of garment sensing-wise was the "cross-type", and it seems to stabilize the electrode's position more effectively. The value of SNR of ECG signals for the "cross-type" garment is the highest. Compared to the "chest-belt-type" garment, which has already been marketed commercially, the "cross-type" garment was more efficient and suitable for heart activity monitoring.

Reusable electrical activity of the heart monitoring patch for mobile/ubiquitous healthcare.

In order to monitor electrical activity of the heart during daily life, we present an electrode of a medical instrument system which is able to measure the body surface potential difference by minimizing the electrode distance. The designed electrode is composed of concentric circles. It was made from the basis of the Laplacian equation, and implemented on PCB coated with gold. So that it does not cause the uncomfortable feeling of contact and possible skin troubles which are typical shortcoming of the conventional ECG measurement. The suggested method utilized three concentric circles on FR-4 substrate, so new amplifier design regarding measuring of small biological signal, is considered which has the characteristics of asymmetric input impedance since the area of concentric circular ring electrodes is not identical. Thereby, electrical activity of the heart was obtained successfully. However, its signal quality is a little bit degraded and the motion artifact still remains as a major problem as is in conventional electrocardiography measurement. Certainly stable measurement setup was needed to reduce the motion artifact originated from variation in static electricity between skin and electrode interfaces.

Application for the wearable heart activity monitoring system: analysis of the autonomic function of HRV.

The wearable patch-style heart activity monitoring system (HAMS) which was used for recording ECG signal in this study is self-developed. This electrode design helps the non-restricted, non-aware and non-invasive ECG measurement. The modified bipolar electrode is convenient in use because it is designed for easy attachment and detachment with ECG measuring module by snap button. Besides, it minimizes EMI by removing the cables. In the same subjects who were exposed under stress and non-stress, the questionnaire was given out, the amount of the stress hormone was measured by blood test and the ECG signal was recorded. Through the analysis of ECG signal which is measured with wearable patch-style HAMS, the parameter highly related with mental stress were extracted from frequency and time domain. These parameters were certified as the meaningful factor after correlation analysis on the results from questionnaire and stress hormone test. Also, it is proved that the availability of wearable patch-style heart monitoring system is efficient as health monitoring system in any places and occasion.

Wearable accelerometer system for measuring the temporal parameters of gait.

A small and wireless accelerometer system was developed for the estimation of temporal gait parameters. The new system was built using two 3-axis accelerometers. Measurement's accuracy was assessed using as a criterion standard provided by foot switches. To assess the consistency of this system, estimates of heel contact and toe off time based on accelerometers and those based on footswitches were compared for 20 steps from 8 individual healthy subjects. Accelerometers and footswitches had high consistency in the temporal gait parameters. The stance, swing, single support, and double support time of gait cycle revealed ICCs values of 0.95, 0.93, 0.86, and 0.75 on the right and 0.96, 0.86, 0.93, 0.84 on the left, respectively. Therefore, this system proved to be a reliable tool for identification of temporal gait parameters.

Tooth brushing pattern classification using three-axis accelerometer and magnetic sensor for smart toothbrush.

The concept of intelligent toothbrush, capable of monitoring brushing motion, orientation through the grip axis, during toothbrushing was suggested in our previous study. In this study, we describe a tooth brushing pattern classification algorithm using three-axis accelerometer and three-axis magnetic sensor. We have found that inappropriate tooth brushing pattern showed specific moving patterns. In order to trace the position and orientation of toothbrush in a mouth, we need to know absolute coordinate information of toothbrush. By applying tilt-compensated azimuth (heading) calculation algorithm, which is generally used in small telematics devices, we could find the inclination and orientation information of toothbrush. To assess the feasibility of the proposed algorithm, 8 brushing patterns were preformed by 6 individual healthy subjects. The proposed algorithm showed the detection ratio of 98%. This study showed that the proposed monitoring system was conceived to aid dental care personnel in patient education and instruction in oral hygiene regarding brushing style.

Development of smart toothbrush monitoring system for ubiquitous healthcare.

The design of an intelligent toothbrush, capable of monitoring brushing motion, orientation through the grip axis, during toothbrushing is described. Inappropriate tooth-brushing styles, even in adults, sometimes cause dental problems, cavities, gingivitis, etc. This smart system provides user to monitor his or her brushing pattern using accelerometer and magnetic sensors for evaluation of toothbrushing style. Directional information of toothbrush with respect to the earth's magnetic field and activity data were measured by a miniaturized low-power micro-controller, MSP430 and transmitted to personal computer by 2.4 GHz radio transmitter, nRF2401. A personal computer provides an on-line display of activity and orientation measurements during toothbrushing. The signal trace is then analyzed to extract clinically relevant information. This preliminary study showed that the proposed monitoring system was conceived to aid dental care personnel in patient education and instruction in oral hygiene regarding brushing style.