David Da He

A continuous, wearable, and wireless heart monitor using head ballistocardiogram (BCG) and head electrocardiogram (ECG)

Continuous and wearable heart monitoring is essential for early detection and diagnosis of cardiovascular diseases. We demonstrate a continuous, wearable, and wireless heart monitor that is worn at the ear. The device has the form factor of a hearing aid and is wirelessly connected to a PC for data recording and analysis. With the ear as an anchoring point, the heart monitor measures the ballistocardiographic (BCG) motion of the head using a MEMS tri-axial accelerometer, which is an electrode-less method to measure heart rate. Additionally, electrocardiogram (ECG) is measured locally near the ear using a single-lead configuration. The peak timing delay between the head ECG and the head BCG, or RJ interval, can be extracted in the presence of noise using cross-correlation. The RJ interval is shown to correlate to the hearts pre-ejection period during both Valsalva and whole-body tilt maneuvers.

Mixed-Signal Organic Integrated Circuits in a Fully Photolithographic Dual Threshold Voltage Technology

Analog & digital circuits implemented in a dual threshold voltage (VT) p-channel organic technology are presented. The dual VT organic technology is compatible with large-area and mechanically flexible substrates due to its low processing temperature (≤ 95°C) and scalable patterning techniques. We demonstrate the first analog & digital organic integrated circuits produced by a dual-gate metal process. The analog circuits are powered by a 5-V supply and include a differential amplifier and a two-stage uncompensated operational amplifier (op-amp). A dynamic comparator is measured to have an input offset voltage of 200 mV and latching time of 119 ms. Both the comparator and the op-amp dissipate 5 nW or less. Area-minimized digital logic is presented. Inverters powered by a 3-V supply were measured to have positive noise margins and consumed picowatts of power. An 11-stage ring oscillator, also powered by a 3-V supply, swings near rail to rail at 1.7 Hz. These results demonstrate dual threshold voltage process feasibility for large-area flexible mixed-signal organic integrated circuits.

A wearable vital signs monitor at the ear for continuous heart rate and Pulse Transit Time measurements

A continuous, wearable and wireless vital signs monitor at the ear is demonstrated. The device has the form factor of a hearing aid and is wirelessly connected to a PC for data recording and analysis. The device monitors the electrocardiogram (ECG) in a single lead configuration, the ballistocardiogram (BCG) with a MEMS triaxial accelerometer, and the photoplethysmograms (PPG) with 660nm and 940nm LED sources and a static photocurrent subtraction analog front end. Clinical tests are conducted, including Valsalva and head-up tilt maneuvers. Peak timing intervals between the ECG, BCG and PPG are extracted and are shown to relate to pre-ejection period and mean arterial blood pressure (MAP). Pulse Transit Time (PTT) extracted from cross-correlation between the PPG and BCG shows improved results compared to the pulse arrival time (PAT) method for tracking changes in MAP.

Dual Threshold Voltage Organic Thin-Film Transistor Technology

A fully photolithographic dual threshold voltage (VT) organic thin-film transistor (OTFT) process suitable for flexible large-area integrated circuits is presented. The nearroom-temperature (<; 95 °C) process produces integrated dual VT pentacene-based p-channel transistors. The two VT s are enabled by using two gate metals of low (aluminum) and high (platinum) work function. The Al and Pt gate OTFTs exhibit nominally identical current-voltage transfer curves shifted by an amount ΔVT. The availability of a high-VT device enables area-efficient zero-Vos high-output-resistance current sources, enabling high-gain inverters. We present positive noise margin inverters and rail-to-rail ring oscillators powered by a 3-V supply-one of the lowest supply voltages reported for OTFT circuits. These results show that integrating nand p-channel organic devices is not mandatory to achieve functional area-efficient low-power organic integrated circuits.

An Ear-Worn Vital Signs Monitor

This paper presents a wearable vital signs monitor at the ear. The monitor measures the electrocardiogram (ECG), ballistocardiogram (BCG), and photoplethysmogram (PPG) to obtain pre-ejection period (PEP), stroke volume (SV), cardiac output (CO), and pulse transit time (PTT). The ear is demonstrated as a natural anchoring point for the integrated sensing of physiological signals. All three signals measured can be used to obtain heart rate (HR). Combining the ECG and BCG allows for the estimation of the PEP, while combining the BCG and PPG allows for the measurement of PTT. Additionally, the J-wave amplitude of the BCG is correlated with the SV and, when combined with HR, yields CO. Results from a clinical human study on 13 subjects demonstrate this proof-of-concept device.

The ear as a location for wearable vital signs monitoring

Obtaining vital signs non-invasively and in a wearable manner is essential for personal health monitoring. We propose the site behind the ear as a location for an integrated wearable vital signs monitor. This location is ideal for both physiological and mechanical reasons. Physiologically, the reflectance photoplethysmograph (PPG) signal behind the ear shows similar signal quality when compared to traditional finger transmission PPG measurements. Ballistocardiogram (BCG) can be obtained behind the ear using 25mm×25mm differential capacitive electrodes constructed using fabric. The BCG signal is able to provide continuous heart rate and respiratory rate, and correlates to cardiac output and blood pressure. Mechanically, the ear remains in the same orientation relative to the heart when upright, thus simplifying pulse transit time calculations. Furthermore, the ear provides a discreet and natural anchoring point that reduces device visibility and the need for adhesives.

A flexible pressure monitoring system for pressure ulcer prevention

Pressure ulcers are painful sores that arise from prolonged exposure to high pressure points, which restricts blood flow and leads to tissue necrosis. This is a common occurrence among patients with impaired mobility, diabetics and the elderly. In this work, a flexible pressure monitoring system for pressure ulcer prevention has been developed. The prototype consists of 99 capacitive pressure sensors on a 17-cm×22-cm sheet which is flexible in two dimensions. Due to its low cost, the sensor sheet can be disconnected from the reusable electronics and be disposed of after use, suitable for a clinical setting. Each sensor has a resolution of better than 2-mmHg and a range of 50-mmHg and offset is calibrated in software. Realtime pressure data is displayed on a computer. A maximum sampling rate of 12-Hz allows for continuous monitoring of pressure points.

An ear-worn continuous ballistocardiogram (BCG) sensor for cardiovascular monitoring

Traditionally, ballistocardiogram (BCG) has been measured using large and stationary devices. In this work, we demonstrate a portable and continuous BCG monitor that is wearable at the ear. The device has the form factor of a hearing aid and is wirelessly connected to a PC for data recording and analysis. With the ear as an anchoring point, the device uses a MEMS tri-axial accelerometer to measure BCG at the head. Morphological differences exist between head BCG and traditional BCG, but the principal peaks (J waves) and their vectors are preserved. The frequency of J waves corresponds to heart rate, and when used in conjunction with an electrocardiograms (ECG) R wave, the timing of J waves yields the RJ interval. Results from our clinical study show linear correlation between the RJ interval and the hearts pre-ejection period during hemodynamic maneuvers, thus revealing important information about cardiac contractility and its regulation.

An integrated organic circuit array for flexible large-area temperature sensing

Traditionally, several technologies have been used for temperature sensing, including integrated silicon ^#x0394;VBE and #x0394;Vt circuits, resistance temperature detectors, and thermocouples [1]. The organic thin-film transistor (OTFT) is a new technology suitable for temperature sensing because of two key advantages. First, OTFTs have the ability to be fabricated on flexible and large-area substrates [2]. This ability allows an OTFT temperature sensor to be used for applications such as electronic skin, biomedical thermal imaging, and structural temperature monitoring [2]. Second, the OTFTs semiconductor trap states make OTFTs highly responsive to temperature. This paper presents the first integrated OTFT temperature sensing circuit array. The array is compatible with flexible and large-area substrates, and its outputs are 22 times more responsive than the MOSFET implementation while dissipating 90nW of power per cell.

Dual threshold voltage integrated organic technology for ultralow-power circuits

For the first time, we demonstrate control of organic thinfilm transistors (OTFT) threshold voltage (VT) by modifying the gate work function. We present a near-room-temperature, fully lithographic process to fabricate integrated pentacene dual VT OTFTs suitable for large-area and flexible mixed signal circuits. Platinum and aluminum are used as the gate metals for the high VT (more depletion-like) and low VT (more enhancement-like) p-channel devices, respectively. The availability of a high VT device enables area-efficient zero-VGS current source loads. We demonstrate positive noise margin inverters which use pico Watts of power and a 3 V supply. Compared to a single VT implementation, the dual VT inverter occupies an area that is 30× smaller, and is 17× faster. These results show that p-channel only organic technologies can produce functional and low-power circuits without integrating a complementary device.