Passive Cooperative Targets for Subsurface Physical and Chemical Measurements: A Systems Perspective

International audienceWe investigate the use of a commercially available ground-penetrating radar (GPR) for probing the response of subsurface sensors designed as passive cooperative targets. Such sensors must meet two design criteria: introduce a signature unique to the sensor which will hence be differentiated from clutter, and introduce in this signature a response characteristic allowing for recovering the physical quantity under investigation. Using piezoelectric substrates for converting the incoming electromagnetic pulse to an acoustic wave confined to the sensor surface (surface acoustic wave transducer) allows for shrinking the sensor dimensions while providing sensing capability through the piezoelectric substrate acoustic wave velocity dependence with the physical quantity under investigation. Two broad ranges of sensing mechanisms are discussed: intrinsic piezoelectric substrate velocity dependence with a quantity—restricted to the measurement of temperature or strain and, hence, torque or pressure—and extrinsic load dependence on the sensor, allowing for the measurement of variable capacitive or resistive loads. In all cases, the delay introduced by the physical quantity variation induces a phase rotation of the returned signal of a few periods at most, to be measured with a resolution of a fraction of a period: the GPR receiver sampling time reference must exhibit a long term stability at least as good as the targeted phase measurement needed to recover the physical quantity. We show that the commercial GPR exhibits excessive time-base drift, yielding a loss in the sensing capability, while a quartz-oscillator-based alternative implementation of the classical stroboscopic sampling receiver compensates for such a drawback

Analysis of Wireless Body-Centric Medical Sensors for Remote Healthcare

Aquesta tesi aborda el problema de trobar solucions confortables, de baixa potència i sense fils per aplicacions mèdiques. La tesi tracta els avantatges i les limitacions de tres tecnologies de comunicació diferents per la mesura de paràmetres del cos i mètodes per redissenyar sensors per avaluacions òptimes centrades en el cos. La tecnologia RFID es considera una de les solucions més influents per superar el problema del consum d'energia limitat, a causa de la presència de molts sensors connectats. També s'ha estudiat la tecnologia Bluetooth de baixa energia per resoldre els problemes de seguretat i la distància de lectura que, en general, representen el coll d'ampolla de RFID pels sensors de cos. Els dispositius analògics poden reduir dràsticament les necessitats d'energia a causa dels sensors i les comunicacions, considerant pocs elements i un mètode de transmissió simple. S'estudia un mètode de comunicació completament passiu, basat en FSS, que permet una distància de lectura raonable amb capacitats de detecció precises i confiables, que s'ha discutit en aquesta tesi. L'objectiu d'aquesta tesi és investigar múltiples tecnologies sense fils per dispositius portàtils per identificar solucions adequades per aplicacions particulars en el camp mèdic. El primer objectiu és demostrar la facilitat d'ús de les tecnologies econòmiques sense bateria com un indicador útil de paràmetres fisiopatològics mitjançant la investigació de les propietats de les etiquetes RFID. A més a més, s'ha abordat un aspecte més complex respecte a l'ús de petits components passius com sensors sense fils per trastorns del son. Per últim, un altre objectiu de la tesi és el desenvolupament d'un sistema completament autònom que utilitzi tecnologia BLE per obtenir propietats avançades mantenint baix tant el consum com el preuEsta tesis aborda el problema de encontrar soluciones confortables, inalámbricas y de baja potencia para aplicaciones médicas. La tesis discute las ventajas y limitaciones de tres tecnologías de comunicación diferentes para la medición en el cuerpo y los métodos para elegir y remodelar los sensores para evaluaciones óptimas centradas en el cuerpo. La tecnología RFID se considera una de las soluciones más influyentes para superar el consumo de energía limitado debido a la presencia de muchos sensores conectados. Además, la baja energía de Bluetooth se ha estudiado se ha estudiado la tecnologia Bluetooth de baja energia para resolver los problemas de seguridad y la distancia de lectura que, en general, representan el cuello de botella de la RFID para los sensores de cuerpo. Los dispositivos analógicos pueden reducir drásticamente las necesidades de energía debido a los sensores y las comunicaciones, considerando pocos elementos y un método de transmisión simple. Se estudia un método de comunicación completamente pasivo, basado en FSS, que permite una distancia de lectura razonable con capacidades de detección precisas y confiables, que se ha discutido en esta tesis. El objetivo de esta tesis es investigar múltiples tecnologías inalámbricas para dispositivos portátiles para identificar soluciones adecuadas para aplicaciones particulares en campos médicos. El primer objetivo es demostrar la facilidad de uso de las tecnologías económicas sin batería como un indicador útil de dichos parámetros fisiopatológicos mediante la investigación de las propiedades de las etiquetas RFID. Además, se ha abordado un aspecto más complejo con respecto al uso de pequeños componentes pasivos como sensores inalámbricos para enfermedades del sueño. Por último, un resultado de la tesis es desarrollar un sistema completamente autónomo que utilice la tecnología BLE para obtener propiedades avanzadas que mantengan la baja potencia y un precio bajo.This thesis addresses the problem of comfortable, low powered and, wireless solutions for specific body-worn sensing. The thesis discusses advantages and limitations of three different communication technologies for on body measurement and investigate methods to reshape sensors for optimum body-centric assessments. The RFID technology is considered one of the most influential solutions to overcome the limitated 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. 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 medical fields. The first objective is to demonstrate the usability of the inexpensive battery-less technologies as a useful indicator of such a 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 has been addressed. 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

Physiological Parameter Sensing with Wearable Devices and Non-Contact Dopper Radar.

M.S. Thesis. University of Hawaiʻi at Mānoa 2017

Ground, Proximal, and Satellite Remote Sensing of Soil Moisture

Soil moisture (SM) is a key hydrologic state variable that is of significant importance for numerous Earth and environmental science applications that directly impact the global environment and human society. Potential applications include, but are not limited to, forecasting of weather and climate variability; prediction and monitoring of drought conditions; management and allocation of water resources; agricultural plant production and alleviation of famine; prevention of natural disasters such as wild fires, landslides, floods, and dust storms; or monitoring of ecosystem response to climate change. Because of the importance and wide‐ranging applicability of highly variable spatial and temporal SM information that links the water, energy, and carbon cycles, significant efforts and resources have been devoted in recent years to advance SM measurement and monitoring capabilities from the point to the global scales. This review encompasses recent advances and the state‐of‐the‐art of ground, proximal, and novel SM remote sensing techniques at various spatial and temporal scales and identifies critical future research needs and directions to further advance and optimize technology, analysis and retrieval methods, and the application of SM information to improve the understanding of critical zone moisture dynamics. Despite the impressive progress over the last decade, there are still many opportunities and needs to, for example, improve SM retrieval from remotely sensed optical, thermal, and microwave data and opportunities for novel applications of SM information for water resources management, sustainable environmental development, and food security

Doppler Radar Techniques for Distinct Respiratory Pattern Recognition and Subject Identification.

Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017

Techniques, Circuits and Devices for Noncontact Sensing through Wireless Coupling

Le tecnologie per la misurazione di grandezze fisiche senza contatto sono diventate sempre più centrali in vari settori, che vanno dal monitoraggio industriale alle applicazioni sanitarie. In questo contesto, la tesi si concentra sullo sviluppo e l'implementazione di tecniche innovative, circuiti elettronici e dispositivi per la rilevazione senza contatto. L’analisi presentata all'interno di questa tesi considera lo scenario del rilevamento senza contatto a distanza nel campo elettromagnetico lontano (far-field) e al rilevamento senza contatto di prossimità, sfruttando le interazioni elettromagnetiche in campo vicino (near field). Nell’ambito del rilevamento senza contatto a distanza, la tesi indaga l'uso delle onde elettromagnetiche per il monitoraggio non invasivo del livello di solidi granulari all’interno di silos. Questo sistema, sviluppato impiegando un sensore radar commerciale a onda continua modulata in frequenza, dimostra il potenziale di questa tecnologia nel monitoraggio non invasivo e senza contatto in contesti agricoli e industriali. Considerando invece lo scenario del rilevamento senza contatto di prossimità, la tesi fornisce un'analisi dell'interrogazione senza contatto di sensori passivi e ne presenta diversi approcci e applicazioni. Vengono affrontate le problematiche delle misurazioni senza contatto, proponendo alcune soluzioni per migliorarne l'affidabilità e l'accuratezza, permettendo in particolare di renderle indipendenti dalla distanza di interrogazione. In particolare, la tesi presenta un sistema per la misurazione senza contatto della frequenza di risonanza di risonatori MEMS piezoelettrici. La tecnica proposta sfrutta l'accoppiamento magnetico tra un’unità di interrogazione ed un’unità sensore ed è applicata in modo innovativo per la rilevazione della temperatura, sfruttando le proprietà dei risonatori a disco in nitruro di alluminio (AlN) su silicio sottile piezoelettrico (TPoS) ed una tecnica di interrogazione senza contatto a tempo commutato. Inoltre, la tesi presenta un’etichetta flessibile per la misurazione della temperatura corporea, che combina il rilevamento a contatto della temperatura con una lettura senza contatto dell’unità sensore sfruttandone l'accoppiamento magnetico con un unità di interrogazione. L’etichetta flessibile, che costituisce l'unità sensore, è composta da una bobina induttiva che consente l'accoppiamento magnetico, un condensatore ceramico utilizzato come elemento sensibile alla temperatura, sfruttandone il coefficiente di temperatura della capacità, ed un induttore aggiuntivo utilizzato per rendere la frequenza di risonanza del circuito risonante RLC indipendente dalla flessione dell’etichetta. In modo analogo, le tecniche di interrogazione proposte sono state applicate ad un nuovo metodo per l'interrogazione senza contatto di un sensore induttivo, utilizzato per rilevare target conduttivi. Il sistema proposto presenta una bobina avvolta collegata con un condensatore per formare un circuito LC risonante, la cui frequenza di risonanza cambia quando un target conduttivo viene introdotto nel campo magnetico generato dalla bobina stessa. Attraverso una bobina di interrogazione esterna, accoppiata elettromagneticamente al sensore induttivo, è possibile interrogare senza contatto il sensore induttivo, permettendo quindi la rilevazione a distanza di target conduttivi. Infine, lo studio esposto in questa tesi introduce una tecnica avanzata per l'interrogazione senza contatto di sensori resistivi passivi, sfruttando risonatori a cristallo di quarzo come dispositivo risonante e basandosi sulla stima del fattore di qualità del circuito che costituisce l’unità sensore. Il metodo proposto supera i limiti delle tecniche basate su misure di ampiezza, legati in particolare all'influenza della distanza di interrogazioneNoncontact sensing technologies have become increasingly central in a variety of fields, ranging from industrial monitoring to healthcare applications. In this context, the thesis focuses on the development and implementation of innovative techniques, electronic circuits, and devices for contactless sensing via wireless coupling, responding to the growing interest in noncontact measurement methods. The themes treated in this thesis regard both the scenario of distant noncontact sensing in the electromagnetic far field, and proximate wireless sensing, leveraging on near-field electromagnetic interactions. Each domain is distinctly characterized by its specific technologies, applications, and methodologies, reflecting their operational ranges and fundamental principles. In the domain of distant wireless sensing, the thesis investigates the use of electromagnetic waves for unobtrusive level monitoring of granular solids in silos. This system, developed employing a commercial frequency-modulated continuous-wave radar sensor, demonstrates the potential of this technology in unobtrusive monitoring in agricultural and industrial environments. Considering the proximate wireless sensing domain, the thesis provides an analysis of noncontact interrogation of passive sensors and it presents different approaches and applications. It addresses the challenges and offers solutions for enhancing the reliability and accuracy of contactless measurements, which can be advantageously independent of the interrogation distance. This can path the way to the development of low-cost, disposable and sustainable devices for healthcare and industrial applications. In particular, the thesis presents a system for the noncontact measurement of the resonant frequency of piezoelectric MEMS resonators. The technique exploits magnetic coupling between interrogation and sensor units, and it is innovatively applied for temperature sensing exploiting a thin-film piezoelectric on silicon (TPoS) aluminium nitride (AlN) disk resonators and a contactless interrogation time-gated technique. Furthermore, the thesis presents a flexible patch for body temperature measurement, combining contact sensing with contactless readout, and exploiting magnetic coupling between interrogation and sensor units. The flexible patch, forming the sensor unit, is composed of an inductive coil for magnetic coupling, a ceramic capacitor used as the temperature sensing element exploiting its temperature coefficient of capacitance and an additional inductor to make the resonant frequency of the resulting resonant RLC circuit independent from the bending of the patch. Similarly, interrogation techniques have been applied to a novel method for contactless interrogation of an inductive sensor used for detecting conductive targets. The system features a solenoidal coil connected with a capacitor to form a resonating LC circuit, whose resonant frequency changes when a conductive target is introduced in the generated magnetic field. An external interrogation coil electromagnetically coupled to the inductive sensor enables the wireless measurement for conductive target detection. Lastly, the study introduces an advanced technique for the contactless interrogation of passive resistive sensors. The novel approach exploits the resonant frequency stability and the high quality factor of a quartz crystal resonator, used as a resonant element, with a series-connected resistor acting as the sensing element. This method overcomes the limitations of amplitude measurements techniques typically affected by the interrogation distance

RFID multiantenna systems for wireless communications and sensing

Many scientific, industrial and medical applications require the measurement of different physical parameters in order to collect information about the spatially distributed status of some process. Very often this information needs to be collected remotely, either due to the spatial dispersion of the measurement points or due to their inaccessibility. A wireless embedded self-powered sensor may be a convenient solution to be placed at these inaccessible locations. This thesis is devoted to study the analytical relation governing the electromagnetic coupling between a reader and a embeddable self-powered sensor, based on radio frequency identification (RFID) technology, which is capable of wirelessly retrieving the status of physical parameters at a remote and inaccessible location. The physical parameter to be sensed may be the electromagnetic (EM) field existing at that location (primary measurement) or the indirect measurement of other parameters such as the temperature, humidity, etc. (secondary measurement). Given the simplicity of the RFID solution (highly embeddable properties, scavenging capabilities, penetration and radio coverage characteristics, etc.) the measurement can be done at a single location, or it can be extended to a set of measuring locations (an array or grid of sensors). The analytical relation is based on a reciprocity formulation studying the modulation of the scattered field by the embedded sensor in relation with the incident field, and allows to define a set of quality parameters of interest for the optimum design of the sensors. Particular attention is given to the scavenging circuitry as well as to the antenna design relevant to the sensing objective. In RFID tags, the existence of an RF harvesting section is an improvement with respect to conventional scattering field probes since it removes the need of DC biasing lines or optical fibers to modulate the sensor. However, this harvesting section introduces non-linearities in the response of the sensor, which requires a proper correction to use them as EM-field probes, although the characterization of the non-linearities of the RFID tag cannot be directly done using a conventional vector network analyzer (VNA), due to the requirements of an RFID protocol excitation. Due to this, this thesis proposes an alternative measurement approach that allows to characterize the different scattering states used for the modulation, in particular its non-linear behavior. In addittion, and taking this characterization as the starting point, this thesis proposes a new measurement setup for EM-field measurements based on the use of multiple tones to enlarge the available dynamic range, which is experimentally demonstrated in the measurement of a radiation pattern, as well as in imaging applications. The RFID-based sensor response is electromagnetically sensitive to the dielectric properties of its close environment. However, the governing formulation for the response of the probe mixes together a set of different contributions, the path-loss, the antenna impedance, the loads impedance, etc. As a consequence, it is not possible to isolate each contribution from the others using the information available with a conventional RFID sensor. This thesis mathematically proposes and experimentally develops a modification of the modulation scheme to introduce a new set of multi-load scattering states that increases the information available in the response and properly isolate each term. Moreover, this thesis goes a step forward and introduces a new scattering state of the probe sensitive to temperature variations that do not depend on the environment characteristics. This new configuration enables robust environmental sensing in addition to EM-field measurements, and sensing variations of the dielectric properties of the environment

Edge Artificial Intelligence for Real-Time Target Monitoring

The key enabling technology for the exponentially growing cellular communications sector is location-based services. The need for location-aware services has increased along with the number of wireless and mobile devices. Estimation problems, and particularly parameter estimation, have drawn a lot of interest because of its relevance and engineers' ongoing need for higher performance. As applications expanded, a lot of interest was generated in the accurate assessment of temporal and spatial properties. In the thesis, two different approaches to subject monitoring are thoroughly addressed. For military applications, medical tracking, industrial workers, and providing location-based services to the mobile user community, which is always growing, this kind of activity is crucial. In-depth consideration is given to the viability of applying the Angle of Arrival (AoA) and Receiver Signal Strength Indication (RSSI) localization algorithms in real-world situations. We presented two prospective systems, discussed them, and presented specific assessments and tests. These systems were put to the test in diverse contexts (e.g., indoor, outdoor, in water...). The findings showed the localization capability, but because of the low-cost antenna we employed, this method is only practical up to a distance of roughly 150 meters. Consequently, depending on the use-case, this method may or may not be advantageous. An estimation algorithm that enhances the performance of the AoA technique was implemented on an edge device. Another approach was also considered. Radar sensors have shown to be durable in inclement weather and bad lighting conditions. Frequency Modulated Continuous Wave (FMCW) radars are the most frequently employed among the several sorts of radar technologies for these kinds of applications. Actually, this is because they are low-cost and can simultaneously provide range and Doppler data. In comparison to pulse and Ultra Wide Band (UWB) radar sensors, they also need a lower sample rate and a lower peak to average ratio. The system employs a cutting-edge surveillance method based on widely available FMCW radar technology. The data processing approach is built on an ad hoc-chain of different blocks that transforms data, extract features, and make a classification decision before cancelling clutters and leakage using a frame subtraction technique, applying DL algorithms to Range-Doppler (RD) maps, and adding a peak to cluster assignment step before tracking targets. In conclusion, the FMCW radar and DL technique for the RD maps performed well together for indoor use-cases. The aforementioned tests used an edge device and Infineon Technologies' Position2Go FMCW radar tool-set