Sensor LC para la medida de pequeñas deformaciones : aplicación en mallas abdominales

Abstract

Sensors based on LC type resonant passive circuits have been extensively studied mainly for use in hostile environments such as: high temperature, corrosive media or biomedical applications (especially for implant use). The low complexity, adaptability, cost-effectiveness, and the fact that they do not need batteries, neither connect to a power source nor to a specialized circuitry for transmitting energy and information are some of the most striking features of these passive sensors. While energy-harvesting, battery or wire-powered devices can be the right choice for certain applications, in the biomedical field, the wireless powered sensors offer great advantages. Wireless electronics provides mobility to the patient and avoids infections through the skin and more serious health issues especially if it's about implantable sensors. Low or zero power consumption, flexibility, small size and low cost are therefore the most important parameters to consider when designing sensors for biomedical applications. The ability of passive circuits to operate throughout the RF bands makes these sensors the ideal candidates to play a crucial role in health care and cutting-edge concepts such as IoT (Internet of Things). By means of a wireless link, using an inductively coupled transmitter/readout coil, these sensors are powered and provide data. This thesis addresses the entire process of developing a passive "zero-power" wireless sensor based on an LC-type resonant circuit to measure micro-displacements with customizable range and resolution (up to 5 microns). The sensor is made out of an interdigitated parallel plate capacitor and an air core coil. A biocompatible polymer material is chosen as the substrate. The operating principle of the sensor is based on the change in resonant frequency of the device as a consequence of the area variation shared between the plates. One of the plates is movable and responds to the physical variable of measurement, in this case a longitudinal deformation. The shift of the resonance peak has been studied in order to establish correlations between the physical variable to be measured and the electrical response of the sensor to that stimulus. Several sensors with different geometric parameters are designed, simulated, manufactured and characterized. First, the characterization of the capacitor is carried out followed by the frequency characterization of the components, coils, capacitors and the LC Tags validating the operating principle to finally characterize the sensor in surgical meshes' application, those that are used in the correction of herniated defects in the abdominal wall. During the characterization of the sensor, different ex-vivo and in-vivo tests are included to determine the mechanical response, biocompatibility and the effects of dispersive tissues such as skin, fat and muscle tissues in the powered communication between the implanted sensor and the reader device from the outside. The tests' results show the scalability of the sensor and the possibility of applying it to a biomedical environment, as well as demonstrate a valid generic technique for the real time monitoring of micro-displacements in these and other applications. The multidisciplinary work developed in this thesis has led to the manufacturing of a demonstrator constituted by a sensor system for the wireless measurement of the uniaxial deformation of surgical meshes. The validity of the principle of measurement applied, and the adaptability to other types of applications due to its scalability it is demonstrated using mechanical tests. The tests also demonstrate the validity of the decisions made regarding the materials used for their implementation as well as those related to the used packaging. A couple of samples of the first prototype have been implanted in an animal model in which the biocompatibility of the used materials, and the possibility to power the sensors as well as the wireless detection of the resonance peak have been verified.

Date of Award	5 Sept 2017
Original language	Spanish
Supervisor	Jordi Aguilo Llobet (Director)