Yung-Hua Kao

Optimizing a new blood pressure sensor for maximum performance based on finite element model

A new non-invasive, cuff-less, low-cost blood pressure (BP) sensor capable of continuous detection is optimized by this study for maximum performance. This blood pressure sensor module encapsulates specially-designed electrodes as a strain sensor to be attached to a flexible plate. In operations, the strain sensor is held stable with top surface contacting tightly with the human skin while the bottom surface under a low pressure exerted by a pressurizing wrist belt. The electrodes and plate are expected to vibrate in a synchronized fashion with artery pulsations as vibrations transmitted to the sensor through the module to vary the net (average) strain of electrodes, thus also varying its resistance. Employing a readout circuit of Wheatstone bridge, an amplifier, a filter, and a digital signal processor, the artery pulsations could be successfully converted to temporal voltage variations for calculating blood pressures via known algorithms. However, due to the small diameter of the artery, around 3 mm, mis-positioning (MP) of the sensor electrode area relative to the artery beneath is inevitable, which may lower sensor sensitivity due to smaller average strains. To remedy the problem, efforts are paid to conduct finite element modeling (FEM) and simulations on the electrodes, sensor module and the wrist including bone, tissue and other bio-structures to predict sensor output variations with respect to varied mis-positionings. Based on the predictions, the sensor optimal length is successfully found as 5 mm, which maximizes average strain, the sensitivity of the sensor.

A new cuffless optical sensor for blood pressure measuring with self-adaptive signal processing

A new cuffless, wireless optical blood pressure (BP) sensor is successfully developed by this study. This device employs the technique of photoplethysmograph (PPG) to read out in real time the intravascular blood volume change and then to calculate BP. The system utilizes a red-light LED with a wavelengths of 660 nm. The readout circuit includes a pre-amplifier, a band-pass filter, a programmable gain amplifier (PGA), an Arduino unit for calculation and a Bluetooth module for wireless communication. A notebook or a mobile phone is also used to display continuous BPs and conducts statistical analysis/results. The passband is from 0.3 to 3.4 Hz. The range of adjustable gain are from 60 to 80 dB. Measured PPGs of different subjects can be auto-adjusted with varied gain by a PGA with a pre-designed digital circuit. In results, the signal-to-noise ratio (SNR) is improved for accurate estimates on BPs. 8 subjects participated in the experimental validation, in which the obtained BPs are compared with the results from a commercial blood pressure monitor by OMRON. The maximum error of experimental results is ± 6 mmHg, which is less than 8 mmHg conforming to the requirement by the Advancement of Medical Instrumentation (AAMI). This study pioneers to report stable, accurate estimates on BPs by a cuffless optical hand-held device.

A new adaptive front-end circuit for high-resolution magnetic scales

A new front-end readout circuit design using an adaptive amplifier is proposed by this study for magnetic and optical scales. The purpose of the integrated chip (IC) designed herein is to provide the magnetic/optical scales the capability of sensing translational or angular positions of an object in largely-varying amplitudes with high resolutions. Toward this end, a new front-end readout circuit is designed with two adaptive programmable gain amplifiers (PGAs) and two analog-to-digital converters (ADCs). The PGA is particularly designed to accept signals up to 1 MHz from MR sensor signals, which could be one of three voltage levels: 120 mVp-p, 250 mVp-p, 330 mVp-p. The resulted power consumption is 56 mW. The chip also includes a successive approximation register (SAR) ADC having two 12-bit channels for sine-to-digital conversions. The linearity of ADC achieve satisfactory performance (±1LSB) in the input range of 0.5~2.5V in Vp-p. The chip was fabricated by the TSMC 0.35-micron 2P4M CMOS technology for verification.

A new single inductor bipolar multiple output (SIBMO) boost converter using pulse frequency modulation (PFM) control for OLED drivers and optical transducers

This study proposes a single-inductor bipolar multiple-output (SIBMO) boost converter utilizing pulse frequency (PFM) control for organic light-emitting diode (OLED) drivers and optical transducers. The purpose of the converter designed herein is to provide multiple voltage sources with opposite polarities to meet the requirements of various applications such as OLEDs or optical transducers. The bipolar voltage sources are essential for offering alternating driving voltages to extend the lifetime of OLEDs. The converter boosts the input of 2.8 V to two positive and two negative outputs, i.e., +12 V, +6 V, -12 V, and -6 V. Different from the commonly-used pulse width modulation (PWM), the constant on-time (COT) approach is adopted herein with a dynamic charging algorithm to automatically adjust the operating frequency, thus profiting from less circuit complexity, improvement of cross regulation, and high transfer efficiency in unbalanced load cases. The total maximum output power is 320 mW, as the switching frequency varies from 650 kHz to 0 Hz, and the maximum efficiency reaches 83.1% by simulation. The converter was fabricated by TSMC 0.25μm 1P3M high voltage CMOS technology for verification.

A PPG sensor for continuous cuffless blood pressure monitoring with self-adaptive signal processing

A new portable PPG-BP device designed for continuously measuring blood pressure (BP) without a cuff is proposed in this study. This continuous and long-time BP monitoring enabled herein by the proposed portable cuffless BP sensor. Towards the aforementioned goal, the sensor is designed capable of detecting in real time, non-invasively and continuously the temporal intravascular blood volume change based on the principle of photoplethysmograph (PPG) for estimating BP. The hardware of the sensor consists mainly of light emitting diodes (LEDs) in wavelengths of 660 nm, a photo detectors (PD), and also signal processing chips to read output signals of the PD. The PD readout circuit includes a PD pre-amplifier, a band-pass filter, a programmable gain amplifier (PGA), a microcontroller unit for calculation and a wireless module for communication. A laptop is also used to display continuous BPs and conducts statistical analysis and displaying results. 27 subjects participated in the experimental validation, in which the obtained BPs are calibrated by and then compared with the results from a commercial blood pressure monitor by OMRON. The resultant signal-to-noise ratio (SNR) is capable of rising more than 15%, correlation coefficient, R2, for systolic blood pressure (SBP) and diastolic blood pressure (DBP) are 0.89 and 0.98, respectively.

Live demonstration: A new adaptive front-end readout circuit for high-resolution magnetic scales

Summary form only given. This study proposed an adaptive front-end readout circuit design for high resolution magnetic scales. The demonstration will provide the operation of magnetic scales, that can show the amount of displacement of magnetic scales by FPGA module. The adaptive front-end circuit can be sense three kind of input gain with FPGA module via magnetic scales movement. In the further, the visitors can experience and understand working principles of high resolution magnetic scales. The paper submit was accepted from 2015 IEEE Sensors conference, that paper ID is 1201.

Effects of Mis-Positioning a New Cuffless Blood Pressure Sensor and Optimal Design via a 3D Fluid-Solid-Electric Finite Element Model

The effects of mis-positioning a newly-designed noninvasive, cuffless blood pressure sensor are thoroughly investigated via simulation and analysis on a 3D fluid-solid-electric finite element model. A subsequent optimal design of this blood pressure is conducted based on the aforementioned mis-positioning effects. A highly-accurate, non-invasive, cuffless blood pressure (BP) sensor was successfully developed recently for an effective personal monitoring device on blood pressures. This new small-sized, portable blood pressure sensor is able to offer continuous BP measurements. The availability of continuous blood pressures are important for monitoring and evaluating personal cardiovascular systems. The sensor contains a strain-sensitive electrode encapsulated by flexible polymer. As the sensor placed on the position right on the top of the center of the wrist pulsation area, the deflection of the sensor induces the resistance changes of the electrode. By measuring the changes in electrode resistance, the level of pulsation is successfully quantified. Subsequent calculation based in this measurement can lead to fair estimates on blood pressures.However, as the sensor is placed on the wrist area where pulsation occurs, the mis-positioning of the sensor to the desired location, the center of the pulsation area, is inevitable. This study is dedicated to investigate the effects of the mis-positioning via a 3D finite element model. A new 3D fluid-solid-electro coupling interaction finite element model of the wrist is built for predicting the vibration of radial artery and then diastolic and systolic blood pressures. The FEM includes sensor of gel capsule and strain-sensing electrodes, radial artery, blood, radius bones, tendon, muscles and the front-end readout circuit. The FEM is the multi physics FEM with fluid, solid and electric. The section of wrist is constructed from magnetic resonance imaging (MRI) and the length of the FEM is 40mm. The complete 3D FEM model successfully simulated the vibration of skin surface and the sensor module. The diastolic and systolic blood pressures can be accurately predicted by the simulated output resistance.The pulsation levels due to varied mis-positionings are simulated by the built model, and simulation results are successfully validated by experiments. It is found that due to the unsymmetrical geometry of the wrist, the pulsation levels are also varied in an un-symmetric fashion with the mis-positionings in different directions. The maximum output of the BP sensor occurs when the sensor is placed ±3 mm away from the center of the pulsation area, while the sensor output remain valid for subsequent signal processing as the sensor is placed within ±5 mm from the pulsation center. Considering the inevitable mis-positionings by all possible users in different genders and ages, the sizes of the sensors are successfully optimized for satisfactory average signal quality over all possible users.Copyright

OPTIMAL DESIGN AND EXPERIMENTAL VALIDATION OF A NEW NO-CUFF BLOOD PRESSURE SENSOR BASED ON A NEW FINITE ELEMENT MODEL

A new multi-physics finite element model (FEM) on the vibration of the radial artery on the wrist is built by this study to predict vibration of wrist artery vessel vibration and then diastolic and systolic blood pressures. The FEM includes the sensor of gel capsule and strain-sensing electrodes, skin, bones and muscles. The vibrations of skin surface and the sensor module are successfully simulated by the established FEM. The resulted vibratory deformation of the sensor electrodes are further transformed to resistance variations to mimic realistic electronics of the front-end readout circuit via establishing a cross-discipline sub-FEM model. The established FEM can is particularly customized to varied ages, weights, heights, genders, and special cardiovascular diseases of users. The customization can be performed in a fashion of one-time calibration by medical staff and/or medical staff. With the customized FEM in high accuracy level, the diastolic and systolic pressures can be accurately predicted by the simulated output resistance variation. Based on simulation FEMs, the design of the pulse sensor is successfully optimized via the processes of Taguchi and numerical methods. The measurements are also conducted to a dozen of subjects. It shows that the designed novel blood pressure sensor is capable of sensing the blood pressure to require accuracy level of the error less than 10% as compared to commercial counterparts with a cumbersome cuff.Copyright

A New Prediction Model on the Luminance of OLEDs Subjected to Different Reverse Biases for Alleviating Degradation in AMOLED Displays

Organic light-emitting diodes (OLEDs) have drawn much attention in areas of displays and varied illumination devices due to multiple advantages, such as high brightness, high efficiency, wide viewing angle, and simple structure. However, the long-time degradation of OLED emission is a serious drawback. This degradation was investigated by past works, which pointed out that the degradation was induced by high-density currents through OLED component under the long-time operation [1][2]. Proposed by a past work [3], different reverse biases was imposed on OLED components in display frames to alleviate the long-time degradation on OLEDs. Most recently, along with the reverse bias, new pixel circuits [4][5] for AMOLED displays are designed to alleviate OLED degradation, thus successfully extending OLED life time. However, since emission luminances in different frame times during AMOLED displaying differs significantly for displaying varied images, the OLED degradation evolves in a highly unpredictable fashion. In this study, based on valid theories, the voltage across the OLED is first used as indicator for OLED degradation. Then the relation between the level of OLED degradation, in terms of OLED’s cross voltage, and the history of imposing reverse biases are precisely modeled. With the model, the degradation of the OLED under reverse bias to extend lifetime can be successfully predicted. Based on this model, engineers can then optimize the applied reverse bias on OLEDs to maximize the OLED lifetime for varied display requirement.Copyright