Resumen de Analysis of wireless body-centric medical applications for remote healthcare
The combination of a fast increase in elderly population, rising cost of healthcare, and the prevalence of chronic diseases paves the way for a new shape of healthcare systems, migrating from an hospital-centred system to a futuristic user-centred environment, improving citizen's life quality and wellbeing. Many of the common diseases develop from a lousy day-life behaviour, which gradually degenerates to a certain degree of significant pathology. Monitoring daily parameters and connecting them to a remote infrastructure some lousy patient's habit can be avoided, allowing a substantial increase in treatment outcomes’ efficacy and effectiveness. With the new generation of connectivity technology, likewise, the IoT, body parameters measured from the skin can be easily shared on an expanded network. Indeed, the concept of Internet-of-things (IoT) provides a robust framework for interconnecting edge computing devices, wearable sensors and smartphones and cloud computing platforms for seamless interactions. Therefore, these improvements are going to generate a high demand for creating a wearable IoT technology (wIoT) to deploy large-scale wearable sensors networked with remote medical infrastructure. Nevertheless, a substantial changing in electronics, materials and telecommunications methodology has to be done to achieve such a futuristic goal. Three essential concepts must be taken into account to design new wearable IoT: Mimetism, robustness, and connectivity. Planar and rigid electronics does not fit requirements for medical on body device, which need to be soft, flexible and biocompatible to shape the body with comfort for the users. Also, usability studies have changed the design of new wearable devices making them always invisible in day life (e.g., wrist accelerometer in the form of jewellery) allowing to create integrated and hidden sensors. As the information managed by wIoT is directly related to the users' life, any mistake caused for a weak measurement or an incorrect calculation must be remarkably reduced to accept wIoT technology as an alternative to the traditional medicine approach. A reliable network allows to quickly deliver data to health care centres, elaborate them and realize new aggregative analysis to boost the quality of diagnosis and therapies.
Among the requirements and the technologies considered, appear essential to shaping the design on the specific target, avoiding a generic solution by using a single restricted choice. For this reason, after having chosen a narrow range of medical application, it can be more straightforward to address the problem by investigating different options. After an introduction about the technologies that have been considered for addressing the requirements for wearable health devices (WHD), the first part of this thesis has the aim to analyze, modify and test a variety of sensors for specific WHD applications. This thesis discusses advantages and limitations of three different communication technologies for on body measurement and methods to choose and reshape sensors for optimum body-centric assessments. The RFID technology is considered one of the most influential solutions to overcome the limited power consumption due to the presence of many sensors connected. Further, the Bluetooth low energy has been studied to solve security problems and reading distance that overall represent the bottleneck of the RFID for the body-worn sensors. However, this technology is more complicated and, consequently, the battery life is sharply decreased. Analog devices can drastically reduce the energy needs due to the sensors and the communications, considering few elements and a simple transmitting method. An entirely passive communication method, based on FSS is studied, enabling a reasonable reading distance with precise and reliable sensing capabilities, which has been discussed in this thesis.
The objective of this thesis is to investigate multiple wireless technologies for wearable devices to identify suitable solutions for particular applications in the medical field. The first objective is to demonstrate the usability of the inexpensive battery-less technologies as a useful indicator of such physio-pathological parameters by investigating the properties of the RFID tags. Furthermore, a more complex aspect regards the use of small passive components as wireless sensors for sleep diseases.
Lastly, an outcome of the thesis is to develop an entirely autonomous system using the BLE technology to obtain advanced properties keeping low power and a low price.
Concretely, these are the primary goals of the thesis:
1. Desing, prototype and test an epidermal RFID tag, which can measure body temperature to demonstrate the employment of low-power, low cost and disposable technology for specific medical applications. Its performances are explored considering the variability of the human body. Also, biocompatible materials are examined to identify their conformability with the human body. Finally, sensing capability are investigated to define a proper field of applications.
2. Analyse, prototyping and test a wearable and flexible breathing sensor based on the FSS transmitting method to demonstrate practical uses of this approach for a simple, low-power and reliable medical sensor. Its performance is investigated considering various frequency ranges, different substrate materials and different places on the body to validate its compatibility with the human body.
3. Investigate the use of the BLE as continuous monitoring of breathing to detect sleep disorder diseases by producing and test some prototypes. The primary goal is to study the trade-off between power consumption, data transmitted, conformability and reliability of the sensors.
Chapter 2 provides an overview of the leading technologies used in telecommunications for medicine and to define the boundaries of the research, the outcome and the guidelines. Later, an introduction to the RF technology and its advantages in some application are discussed in Chapter 3. In the same chapter, a manipulation to develop an entirely passive, disposable and wireless radio-thermometer is explained. Chapter 4 clarify the semi-passive technique based on the frequency selective surfaces, which can increase reading distance and resolution to get more reliable measures. Here, a breathing sensor, based on temperature changes in the respiration airflow for assisting chronic sleep disease has been discussed as a proof of concept. After that, an introduction to the Bluetooth low energy (BLE) technology and a more complex form of data analysis is shown in Chapter 5, an application that makes use of the Galvanic skin response sensor has been shown to detect sleep apneas and sleep arousals. Chapter 5 also discuss a brief correlation between sleep monitoring sensors by using the BLE technology.
Inspired by the exponential growth of the IoT in biomedical fields, this Thesis has faced overall issues on multiple technologies which are nowadays accessible in the marketplace. The primary scientific contribution regarded a broad perspective for detecting well-being parameters using a non-invasive, light-weight, low-cost, and low-energy approach. By starting with a claimed RFID technology, the best-addressed challenge has been the reshaping of tags, which are not ideated to be placed on the body. The study was directed in the electromagnetic point of view at the hardware and the system level, but also on the sensing aspect of the whole design, taking into account a real environment. A good performance regarding conformability design, reading distance and temperature reliability have been achieved. The measured reading distance for epidermal tags allows monitoring the users while they are crossing a gate or around no-contact contactless barriers. Therefore, a real-life ability has been confirmed by the experiments, and a proper matching between requirements and achievements provides a step forward for the RFID in medical uses. The effectiveness of the RFID technology depends on its wholly passive nature that reduces its cost and enables disposable applications. Their performances have been demonstrated for real-time, spotted discontinuous cases. This approach is overall indicated for tracking and monitoring a significant amount of users in public areas likewise airports and stations. One of the most exciting alternatives to the passive RFID has been the FSS-based sensors that enable a better resolution and a high accuracy regarding sensing capability, still having a low price and a semi-passive behaviour. With top performances regarding wearability, battery life and reading distances, FSS-based are also very versatile, and high adaptability has been demonstrated by fabricating and testing various prototype for many frequency ranges. Furthermore, the FSSs are robust to the human body variability thanks to their wide frequency range, and the body presence and lossy substrates do not significantly reduce their performance. It has also been demonstrated they hold a longer reading distance than the RFID, introducing new scenarios. Moreover, the most accurate efficacy of the FSS-based allows measuring more complex body parameters, such as the respiration rate, by measuring the airflow temperature, that consequently also enable a wide range of new applications. Therefore, this property makes FSS-based sensing helpful in the continuous home measurement, where a combination of long-term recording and reliability are necessary. Despite RFID and FSS-based sensing are quite similar, an objective comparison emphasizes their differences regarding the usage permitted. Finally, a stable active alternative is also discussed here to indicate its advantages and disadvantages compared with the technologies above. This thesis demonstrates the usability of the BLE as a transmission method for breathing sensors based on a simple commercial magnetometer. The main benefits here discussed regard a smart onboard computation algorithm, which reduces consistently the amount of data transmitted, consequently decreasing the energy used in connections and also, the volume of the stored data. The possibility to arrange different sensors on the same board, increases the robustness of the calculation method, obtaining more reliable information which has been proved by adding the GSR information for detecting apnea and a deep breath. Another conferred advantage depends on its high compatibility with several consumer electronics which provide to use commercial smartphones as gateways to spread real-time details on web platform with any uses of other customized infrastructures. On the other hand, this more complex and rigid structure reduces the conformability on the body, forcing a redesign/reshaping that is not always achievable. The analogue mode is however considered a preferred choice also if the strategy to save energy can be implemented with structured technology or standardized protocols. The reduced amount of on body electronics is a benefit to reduce size, weight and dimension of batteries, enabling a not-invasive conformability on the human body.
