This work 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. 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 to the SV, and when combined with HR, yields CO. Results from a clinical human study on 13 subjects demonstrate this proof of concept device.
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 heart's pre-ejection period during both Valsalva and whole-body tilt maneuvers.
Organic thin-film transistors (OTFTs) are promising for flexible large-area electronics. However, the bias-stress effect (BSE) in OTFTs causes operational instability that limits the usefulness of the OTFT technology in a wide range of circuit applications. Currently, most existing studies on OTFT BSE are inadequate because of one or more of the following reasons. First, they study the BSE on OTFTs with thermally grown Si0 2 , which cannot be used in flexible electronics due to its high deposition temperature. Secondly, they use devices with no encapsulation, and the devices degrade by exposure to H 2 0 and 02 in ambient air. The existence of such other degradation mechanisms complicates the interpretation of the BSE measurements on these devices. Lastly, they do not study the BSE systematically to fully identify its dependencies on various stress conditions. This work addresses these issues by systematically studying the electrical characteristics of the BSE in integrated pentacene OTFTs with polymer gate dielectric and encapsulation. Pentacene is used as the model organic semiconductor because it is the most widely used organic semiconductor for OTFTs.The measurements reveal that the BSE results from carriers that are trapped at the semiconductor/dielectric interface. The BSE can be accurately modeled by a shift in the gate voltage, AV, which equals qN/Ci, where N is the density of trapped carriers, and Ci is the channel capacitance per unit area. The BSE occurs only when both gate field and channel carriers are present and the drain current does not increase the BSE. Because the density of traps is limited, when there are more carriers induced in the channel than available number of traps, AV saturates at a constant value, which is directly proportional to the trap density in the channel. This behavior of AV saturation despite the presence of free carriers in the channel is observed for the first time in a TFT.Through the temperature measurements, we identify that the source of the long time constants for trapping is the high energy barriers for carriers to be trapped. The effective energy barrier is found to be 0.8 eV for the measured pentacene OTFTs. The time constants associated with the traps are dispersed due to the disorder in the pentacene and gate dielectric. The dependencies of the BSE to various stress conditions are modeled, which allows prediction of AV for different stress times and voltages. The model is used to estimate the implication of the BSE on circuit applications and usable lifetime.Full recovery of the original I-V characteristics occur when the bias stress is removed. The recovery is found to have time dependency and thermal activation energy that is similar to the BSE implying that the recovery mechanism is similar to that of the BSE. The application of the negative VSG accelerates recovery, which serves as evidence that the recovery is achieved by detrapping of the trapped carrier. Possible mechanisms for the BSE and its recovery are discussed based on the experimental observ...
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 x 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.
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