Error Prevention in Sensors and Sensor Systems

Achievements in all fields of engineering and fabrication methods have led towards optimization and integration of multiple sensing devices into a concise system. These advances have caused significant innovation in various commercial, industrial, and research efforts. Integrations of subsystems have important applications for sensor systems in particular. The need for reporting and real time awareness of a device’s condition and surroundings have led to sensor systems being implemented in a wide variety of fields. From environmental sensors for agriculture, to object characterization and biomedical sensing, the application for sensor systems has impacted all modern facets of innovation. With these innovations, however, additional sources of errors can occur, that can cause new but exciting challenges for such integrated devices. Such challenges range from error correction and accuracy to power optimization. Researchers have invested significant time and effort to improve the applicability and accuracy of sensors and sensor systems. Efforts to reduce inherent and external noise of sensors can range from hardware to software solutions, focusing on signal processing and exploiting the integration of multiple signals and/or sensor types. My research work throughout my career has been focused on deployable and integrated sensor systems. Their integration not only in hardware and components but also in software, machine learning, pattern recognition, and overall signal processing algorithms to aid in error correction and noise tailoring in all their hardware and software components

Photodiodes embedded within electronic textiles

A novel photodiode-embedded yarn has been presented and characterized for the first time, offering new possibilities for applications including monitoring body vital signs (including heart rate, blood oxygen and skin temperature) and environmental conditions (light, humidity and ultraviolet radiation). To create an E-Textile integrated with electronic devices that is comfortable, conformal, aesthetically pleasing and washable, electronic components are best integrated within the structure of a textile fabric in yarn form. The device is first encapsulated within a protective clear resin micro-pod before being covered in a fibrous sheath. The resin micro-pod and covering fibres have a significant effect on the nature of light received by the photoactive region of the device. This work characterised the effects of both encapsulating photodiodes within resin micro-pods and covering the micro-pod with a fibrous sheath on the opto-electronic parameters. A theoretical model is presented to provide an estimate for these effects and validated experimentally using two photodiode types and a range of different resin micro-pods. This knowledge may have wider applications to other devices with small-scale opto-electronic components. Wash tests confirmed that the yarns could survive multiple machine wash and drying cycles without deterioration in performance

In vivo investigations of photoplethysmograms and arterial oxygen saturation from the auditory canal in conditions of compromised peripheral perfusion

Pulse oximeters rely on the technique of photoplethysmography (PPG) to estimate arterial oxygen saturation (SpO2). In conditions of poor peripheral perfusion such as hypotension, hypothermia, and vasoconstriction, the PPG signals detected are often small and noisy, or in some cases unobtainable. Hence, pulse oximeters produce erroneous SpO2 readings in these circumstances. The problem arises as most commercial pulse oximeter probes are designed to be attached to peripheral sites such as the finger or toes, which are easily affected by vasoconstriction. In order to overcome this problem, the ear canal was investigated as an alternative site for measuring reliable SpO2 on the hypothesis that blood flow to this central site is preferentially preserved. Novel miniature ear canal PPG sensors were developed along with a state of the art PPG processing unit and a data acquisition system to allow for PPG measurements from different depths and surfaces of the ear canal. A preliminary in vivo investigation on seven healthy volunteers has revealed that good quality PPG signals with high amplitude can be obtained from the posterior surface of the outer ear canal. Based on these observations, a second prototype probe suitable for acquisition of PPGs from the posterior surface of the outer ear canal was developed. A pilot study was then carried out on 15 healthy volunteers to validate the feasibility of measuring PPGs and SpO2 from the ear canal in conditions of induced local peripheral vasoconstriction (right hand immersion in ice water). The PPG signals acquired from the ear canal probe were compared with those obtained simultaneously from finger probes attached to the left and the right index fingers. Significant drop (p 45%) and right (> 50%) index fingers during the ice water immersion, while good quality PPG signals with relatively constant amplitude were obtained from the ear canal. Also, the SpO2 values showed that the ear canal pulse oximeter performed better than the two finger pulse oximeters (mean failure rate 30%). A second in vivo investigation was carried out in 15 healthy volunteers, where hypoperfusion was induced more naturally by exposing the volunteer to cold temperatures of 10C for 10min. Normalised Pulse Amplitude (NPA) and SpO2 was calculated from the PPG signals acquired from the ear canal, the finger and the earlobe. By the end of the cold exposure, a mean drop of > 80% was found in the NPA of finger PPGs. The % drop in the NPA of red and infrared earlobe PPG signals was 20% and 26% respectively. Contrarily to both these sites, the NPA of the ear canal PPGs had only dropped by 0.2% and 13% respectively. The SpO2 estimated from the finger sensor was below 90% in 5 volunteers (failure) by the end of the cold exposure. The earlobe pulse oximeter failed in 3 volunteers. The ear canal sensor on the other hand had only failed in 1 volunteer. These results strongly suggest that the ear canal may be used as a suitable alternative site for reliable monitoring of PPGs and SpO2 in cases of compromised peripheral perfusion

Development of Implantable Pulse Oxygen Saturation Meter for Dairy-Cattle Respiratory Monitoring

This master of science thesis introduces an implantable measurement device that can be used to measure oxygen saturation (SpO2) with pulse oximetry methods. The device is intended to be incorporated into a implantable measurement device developed earlier at Tampere University of Technology (TUT). Two prototype devices were built and tested externally on a human subject with number of different measurement setups to determine how it would function in vivo. Respiratory diseases are the cause of approximately 50 % of all mortality in cattle. They can be hard to diagnose in early stages since there are no obvious external symptoms, this can cause outbreaks in groups of cattle. SpO2 gives a good measurement on how the respiratory system is functioning in the cattle by measuring the amount of oxygenated hemoglobin versus deoxygenated hemoglobin. The developed device measures the SpO2 with a probe made out of two light emitting diodes (LED) and a photosensor. In the thesis two types of coating methods where used to seal the probe, 3.5mm layer of medical grade epoxy and 15 µm layer of Parylene-C. The effect of these coatings on the probe components and signals where determined with measurements prior to coating and after. Parylene-C coating had much less effect on the signal acquisition than the epoxy coating, where the amplitude of the non-pulsatile signal increased on average over 1V and the pulsatile part decreased in amplitude. For Parylene-C there was a minor decrease in the amplitude of the non-pulsatile part but the pulsatile part had similar amplitude to non-coated probe. This difference is partially explained with the fact that thicker layer of coating creates internal scattering of light inside the coating. This light hits the photosensor before being absorbed by tissue and thus increases the DC level. A signal processing script was written in MATLAB to calculate the uncalibrated SpO2 from the raw signal. The noise level in all measurements was estimated with the standard deviation since the signal is unambigous and it was concluded that with a moving average filter of 4- or 8-points it is possible to reduce the noise significantly. Thermal radiation of the probe was estimated with test measurement of two different LED drive currents and theoretical calculations, neither case showed any significant increase in temperature. The effect of fat tissue that will surround the implant was also tested in a practical way with cow fat from a local supermarket. According to theory, light penetrates well through fat tissue and this was confirmed with measurements where the increased thickness of fat tissue decreased the amplitude of the signal. By applying a 8-point moving average filter it was possible to acquire a signal through ∼1cm thick layer of tissue with no perfusion. Number of other minor topics were solved some theoretically and others practically. The output of the thesis is a novel device that could be easily implanted in a dairy-cow as well as other mammals. The thesis also presents new information on the effects of coating SpO2 probes and the effects of fat tissue in cattle on the SpO2 signal. Pulse oxygen saturation measurements have not been conducted with an implantable meter before in any type of animal and thus certain uncertainty of measurements can only be eliminated with an implantation of a real device

Design of Common ECG/PPG Electrod

Import 03/11/2016Tématem této bakalářské práce je návrh společné EKG/PPG elektrody. První část je zaměřena na teoretický rozbor Elektrokardiografie a Fotopletysmografie. Práce dále obsahuje rešerši, která zpracovává různé studie související s těmito metodami měření biologických signálů. Praktická část je zaměřena na návrh a výrobu společné elektrody. Cílem této práce je umožnit společné snímání, jak elektrické aktivity srdce, tak objemových změn v tkáních. Snímání EKG bylo provedeno pomocí dvou kovových destiček, a pro měření PPG byl využit reflexní typ senzoru. K sloučení obou typů senzorů byl využit textilní gumový pás, díky kterému je možno umístit senzory v různých vzdálenostech na různých částech těla. Hlavním přínosem práce je otestování různých umístění snímačů na těle, výběr toho nejvhodnějšího a dále možnost snímat společně oba signály EKG i PPG pro pozdější analýzu naměřených křivek.The theme of this bachelor thesis is Design of Common ECG/PPG electrode. The first part is focused on the theoretical analysis of Electrocardiography and Photopletysmography. Next part of this thesis is a search, which handles various studies associated with these methods of measuring biological signals. The practical part is focused on design and manufacture of common electrode. The aim of this work is to enable the common sensing electrical activity of heart and volume changes in the tissue. For measuring ECG was used two little metal squares and for sensing PPG was used reflective type sensor. For merger both types of sensor was used textile rubber belt, which allow different placement of sensors on the body. The main contribution of this work is to test and evaluate different sensor location on the body, selection of the most appropriate and the chance to shoot together both ECG and PPG signals and determine their measured results.450 - Katedra kybernetiky a biomedicínského inženýrstvívýborn

Reflectance photoplethysmography for non-invasive monitoring of tissue perfusion

Monitoring blood perfusion and oxygenation changes is of vital importance and for this reason many different techniques have been developed over the decades. Photoplethysmography (PPG) is an optical technique that measures blood volume variations in vascular tissue and it is well known for its utilisation in pulse oximetry for the estimation of arterial blood oxygen saturation (SpO2). In pulse oximetry, mainly the pulsatile component of the signal (AC PPG) is used while the continuous DC component is mostly excluded. Near Infrared Spectroscopy (NIRS) is another optical technique that measures changes in the concentration of oxygenated (ΔHbO2), deoxygenated (ΔHHb), and total haemoglobin (ΔtHb) from the variations in light attenuations at different wavelengths. The main motivation of this research is to explore the capability of Photoplethysmography in assessing tissue perfusion and oxygenation similarly as NIRS. The hypothesis underlining this research is that the DC component of the PPG signal contains information on the overall absorbed light and this part of the PPG signal, acquired at least two wavelengths, may be used to obtain ΔHbO2, ΔHHb, and ΔtHb as performed in NIRS. Therefore, DC PPG attenuations may be related to haemoglobin concentrations by the modified Beer-Lambert law (MBLL). In order to investigate this, novel reflectance, custom-made PPG sensors and measurement systems, including advanced signal processing algorithms, have been developed for the acquisition and analysis of raw PPG signals (AC + DC) from different anatomical locations. Three in vivo studies on healthy volunteers were carried out in order to investigate if ΔHbO2, ΔHHb, and ΔtHb estimated from PPG could indicate changes in blood perfusion and oxygenation. The studies consisted of vascular occlusions on the forearm, negative bed tilting, and whole body cold exposure. Raw PPG signals were acquired from different locations such as the forearm, fingers, and forehead, whereas simultaneous NIRS signals were used as a reference. The results showed that ΔHbO2, ΔHHb, and ΔtHb could be effectively estimated from PPG signals. These parameters indicated the changes in blood volumes and/or oxygenation, whereas comparison with NIRS signals showed good levels of correlation and trending. These promising results showed that DC PPG signals could be used to monitor changes in blood perfusion and oxygenation, extending the range of applications of Photoplethysmography