Jeong-Whan Lee

Portable Activity Monitoring System for Temporal Parameters of Gait Cycles

A portable and wireless activity monitoring system was developed for the estimation of temporal gait parameters. The new system was built using three-axis accelerometers to automatically detect walking steps with various walking speeds. The accuracy of walking step-peak detection algorithm was assessed by using a running machine with variable speeds. To assess the consistency of gait parameter analysis system, estimated parameters, such as heel-contact and toe-off time based on accelerometers and footswitches were compared for consecutive 20 steps from 19 individual healthy subjects. Accelerometers and footswitches had high consistency in the temporal gait parameters. The stance, swing, single-limb support, and double-limb 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. And the walking step-peak detection accuracy was 99.15% (±0.007) for the proposed method compared to 87.48% (±0.033) for a pedometer. Therefore, the proposed activity monitoring system proved to be a reliable and useful tool for identification of temporal gait parameters and walking pattern classification.

Textile electrodes of jacquard woven fabrics for biosignal measurement

In the last few years, textile electrodes have become an interesting topic for physiological monitoring, steadily developing to be applied in innovative wearable sensing systems. The structure of textile electrodes can be fabricated by weaving, knitting, or embroidering conductive yarn and is now commercially available. The upgraded textile electrode is used in biosignal sensing and was designed in the form of a jacquard woven structure to measure the ECG. In the case of knit fabric, which has piezo‐resistive properties, the textile electrodes were developed by using the fabric’s flexible strain gauges in a bio‐monitoring system. However, the piezo‐resistive sensing fabrics have some shortcomings such as low dynamic range, poor repeatability, and performance deterioration after washing or repeated folding. Woven fabric, which is cloth woven in the warp and weft directions, has less strain properties and can be constructed more uniformly than knit fabric. Therefore, due to their more consistent woven structure, jacquard woven fabrics made with conductive yarn can be manufactured evenly on a large scale and consistently maintain their properties. The woven structure of jacquard electrodes consists of a double‐faced weave and is woven with a silver covering yarn in the weft direction. The proposed textile electrodes were composed of two groups made up of warps with either the unremoved 100% warps or the half‐removed 50% warps of jacquard woven electrodes that were convex or flat and were either with or without conductive paste. The ECG measurements for the textile electrodes were repeated three times in resting conditions. The convex jacquard electrodes of the half‐removed 50% warps with the conductive paste resulted in the most significant SNR improvement (33.67 dB). The purpose of this paper was to investigate a method to design jacquard woven electrodes uniformly on a large scale and to apply it feasibly to ECG measurement.

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.

The Effect of Textile-Based Inductive Coil Sensor Positions for Heart Rate Monitoring

In the research related to heart rate measurement, few studies have been done using magnetic-induced conductivity sensing methods to measure the heart rate. The aim of this study was to analyze the effect of the position of a textile-based inductive coil sensor on the measurement of the heart rate. In order to assess the capability of the textile-based inductive coil sensor and the repeatability of measured cardiac muscle contractions, we proposed a new quality index based on the morphology of measured signals using a textile-based inductive coil sensor. We initially explored eight potential positions of the inductive sensor in a pilot experiment, followed by three sensor positions in the main experiment. A simultaneously measured electrocardiography (ECG) signal (Lead II) which was used as a reference signal for a comparison of the R-peak location with signals obtained from selected positions of the textile-based inductive coil sensor. The result of the main experiment indicated that the total quality index obtained from the sensor position ‘P3’, which was located 3xa0cm away from the left side from the center front line on the chest circumference line, was the highest (QI value = 1.30) among the three positions across all the subjects. This finding led us to conclude that (1) the position of the textile-based inductive coil sensor significantly affected the quality of the measurement results, and that (2) P3 would be the most appropriate position for the textile-based inductive coil sensor for heart rate measurements based on the magnetic-induced conductivity sensing principle.

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.

Interactive toothbrushing education by a smart toothbrush system via 3D visualization

The very first step for keeping good dental hygiene is to employ the correct toothbrushing style. Due to the possible occurrence of periodontal disease at an early age, it is critical to begin correct toothbrushing patterns as early as possible. With this aim, we proposed a novel toothbrush monitoring and training system to interactively educate on toothbrushing behavior in terms of the correct brushing motion and grip axis orientation. Our intelligent toothbrush monitoring system first senses a users brushing pattern by analyzing the waveforms acquired from a built-in accelerometer and magnetic sensor. To discern the inappropriate toothbrushing style, a real-time interactive three dimensional display system, based on an OpenGL 3D surface rendering scheme, is applied to visualize a subjects brushing patterns and subsequently advise on the correct brushing method.

A Simple Optical Angular Sensors to Measure the Human Joint Angle

Medical practioners usually measure dorsiflection of the human joint angle for medical assessment purpose. In order to measure the joint angle, a more or less standard mechanical or electro-mechanical goniometer is used. But mechanical construction has many problems. This research is originated from the lack of user-friendly, versatile and not expensive apparatus which are commercially available. In this paper, we present new design concepts of goniometer utilizing the light refraction characteristics of optical fiber in order to measure angular displacement of the human joints. In order to form an asymmetrical beam profile at the end of fiber tips, we cut the end of fiber tip at an angle of 35 degrees. Phototransistor is used to measure beam intensity as a function of optical fiber angle with respect to optical axis of fiber. Thus the sensed signal represented an indirect measure of curvature angle. The result showed that asymmetrical beam profile provide wider linear relationship than symmetrical one. Eventually, overall performance of the proposed sensor is quite suitable for measurement of the human joint angle

Toothbrushing Region Detection Using Three-Axis Accelerometer and Magnetic Sensor

Due to the possible occurrence of periodontal disease at an early age, it is important to have proper toothbrushing habits as early as possible. With this aim, the feasibility and concept of a smart toothbrush (ST) capable of tracing toothbrushing motion and orientation information was suggested. In this study, we proposed the advanced ST system and brushing region classification algorithm. In order to trace the brushing region and the orientation of a toothbrush in the mouth, we required the absolute coordinate information of ST. By using tilt-compensated azimuth (heading) algorithm, we found the inclination and orientation information of the toothbrush, and the orientation information while brushing inner tooth surfaces showed specific heading features that could be reliably discriminated from other brushing patterns. In order to evaluate the feasibility of clinical usage of the proposed ST, 16 brushing regions were investigated by 15 individual healthy subjects. The proposed ST system demonstrated 97.1%(±0.91) of the region detection accuracy and 15 brushing regions could be classified. This study also showed that the proposed ST system may be helpful for dental care personnel in patient education and instruction for oral hygiene regarding brushing habits.

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.

Magneto-Plethysmographic Sensor for Peripheral Blood Flow Velocity

In order to detect blood volume changes, we proposed the new magnetic plethysmographic sensor using time-varying magnetic fields, and thereby, measuring the change of impedance of exciting coil. The change of coil impedance was proportional to the change of blood volume passing through a volume-of-interests, which inductively coupled with exciting coil. In order to verify the feasibility of the proposed method, photo-plethysmographic and magneto-plethysmographic (MPG) signals were recorded from the index and middle finger of the left hand simultaneously. Comparison of the proposed sensor signals with ultrasound Doppler blood flow velocity recordings shows the excellent correlation (r = 0.9355, p <; 0.01) and the RR intervals derived from electrocardiograph and MPG signals showed a very high degree of correlation (r = 0.9823, p <; 0.01).