Energy Transmission for Long-Range Passive Sensor Transponders

Drahtlose Energieübertragung ermöglicht den Betrieb von mikroelektronischen Transpondern (sog. „Tags“) ohne Batterie oder Solarzellen. Eine Basisstation sendet ein elektromagnetisches Feld zur Übertragung von Energie und Daten an einen oder mehrere Transponder. Diese bestehen in der Regel aus einer integrierten Schaltung und einer Antenne. Passive Sensor Transponder ermöglichen die Erfassung von physikalischen Umgebungsgrößen wie z.B. Druck oder Temperatur. Da induktive Systeme in ihrer Reichweite stark beschränkt sind, wird in dieser Arbeit der Ansatz der Energieübertragung über elektromagnetische Wellen im UHF Bereich betrachtet. Das Antennensignal wird im Chip in eine Gleichspannung zur Versorgung der integrierten Schaltungen umgewandelt. Die Effizienz des Systems wird im Wesentlichen von der unvermeidlichen Freiraumdämpfung und der Effizienz des Gleichrichters bestimmt. In großem Abstand zur Basisstation hat die Antennenspannung eine geringe Amplitude, und die Implementierung eines effizienten Gleichrichters stellt weiterhin eine Herausforderung dar. Die Modellierung und Analyse dieser Schaltung, sowie die Erarbeitung neuartiger Topologien, bilden den Kern dieser Arbeit. Das erste Ziel ist in diesem Zusammenhang die analytische Beschreibung des Gleichrichters unter Berücksichtigung der parasitären Eigenschaften realer Bauelemente in einem standard CMOS Prozess. In existierenden Arbeiten wurden Schaltungsmodelle für die Villard-Schaltung mit Schottky Dioden erstellt. Diese Arbeit erweitert diese Modelle um eine Berechnung des Gleichrichters mit Transistoren und Arbeitspunkt-Einstellung zur dynamischen Kompensation der Schwellenspannung. Speziell wird der komplexe Zusammenhang zwischen Eingangsleistung, Ausgangsspannung und Laststrom des Gleichrichters mathematisch beschrieben. Das aufgestellte Modell beschreibt den Einfluss der Parameter der verwendeten Bauelemente auf das eingangs- und ausgangsseitige Verhalten der Schaltung und erleichtert somit den systematischen Schaltungsentwurf. Es werden neue Schaltungstopologien erarbeitet. Diese Gleichrichter benötigen keine zusätzlichen Prozessschritte und erreichen dennoch eine hohe Ansprechempfindlichkeit. Im verwendeten 0,35µm Prozess wird die Sensitivität gegenüber der herkömmlichen Villard Schaltung um bis zu 5 dBm verbessert. Im Rahmen der Arbeit wurde ein ASIC (Application Specific Integrated Circuit) mit einem vollständigen analogen Front End für einen Sensor Transponder mit einer Reichweite von über 4 Metern entwickelt. Neben der Funktionalität zur Spannungsversorgung, Takterzeugung und Datenübertragung werden außerdem temperatur- und prozessstabile Referenzspannungen und eine temperaturabhängige Spannung erzeugt.Wireless energy transmission is frequently used as a power supply for transponder systems without batteries or solar cells. A base station transmits an electromagnetic field to send data and energy to one or several transponders (“tags”). Each tag typically comprises an integrated circuit and an antenna. Passive sensor transponders detect physical values such as temperature or pressure. Inductive energy transmission systems achieve only a limited range of less than one meter. In this work, UHF (Ultra High Frequency) electromagnetic waves are used for energy- and data transmission. The antenna signal is rectified to serve as a voltage supply for the chip. The power efficiency of the system is mainly determined by the free-space transmission as well as rectification losses. The amplitude of the antenna signal is very low at a large distance from the base station. Therefore, the rectifier is the critical circuit block concerning power efficiency. This work focuses on the analysis and the modelling, as well as the design of novel topologies for this circuit block. The first goal is to derive a rectifier analysis that takes into account the properties and parasitics of CMOS (Complementary Metal Oxide Semiconductor) devices. The Villard circuit with Schottky diodes has been modelled in several previous works. These models and analyses are extended to include rectifier circuits with dynamic threshold-voltage cancellation techniques. The mathematical relation between input power, output voltage and load current is derived analytically. The resulting model predicts the influence of device parameters on the input and output behaviour of the circuit. This leads to a systematic circuit design approach. Two novel circuits are presented. These rectifiers achieve a high sensitivity and not require additional masks or process modifications. All circuits were fabricated in a 0.35µm CMOS process. The sensitivity is improved by 5 dBm compared to the conventional Villard Circuit. The complete analog front-end of a passive UHF sensor transponder with a range of more than 4 m was designed and fabricated. The ASIC (Application Specific Integrated Circuit) manages data transmission, supply voltage, and clock generation. In addition to this functionality, the chip also generates temperature- and process-independent supply and reference voltages, as well as a temperature dependent sensor signal

AN ARCHITECTURAL APPROACH FOR REDUCINGPOWER AND INCREASING SECURITY OF RFID TAGS

Radio Frequency Identification (RFID) technology is currently employed for a variety of applications such as RFID-based wireless payment, healthcare, homeland security, asset management,etc. Due to newer privacy requirements and increasingly secure applications, typical RFID tags are required to expand security features such as data encryption and safe transactions. However, RFID tags have extremely strict low-power consumption requirements. Thus, reduced power consumption and secure data transactions are two main problems for the next generation RFID tags.This dissertation presents an architectural approach to address these two main problems.This dissertation provides a multi-domain solution to improve the power consumption andsecurity, while also reducing design time and verification time of the system. In particular, Idescribe (1)a smart buffering technique to allow a tag to remain in a standby mode until addressed,(2)a multi-layer, low-power technique that transcends the passive-transaction, physical, and data layers to provide secure transactions, (3) an FPGA-based traffic profiler system to generate traces of RFID communications for both tag verification and power analysis without the need of actual hardware, and (4) a design automation technique to create physical layer encoding and decoding blocks in hardware suitable for RFID tags.This dissertation presents four contributions: (1) As a result, based on a Markov Process energymodel, the smart buffering technique is shown to reduce power consumption by 85% over a traditionalactive tag; (2) The multi-layer, low-power security technique provides protection againstmalicious reader attacks to disable the tag, to steal the information stored in or communicatedto the device. The power consumption overhead for implementing these layers of security is increased approximately 13% over the basic tag controller; (3) In addition, the FPGA-based traffic profiler system has been able to generate traces for ISO 18000 part 6C (EPC Gen2) protocol; and (4) The designs of endocing/decoding blocks are generated automatically by the Physical LayerSynthesis tool for five protocols used in or related to RFID. Consequently, any power consumption of five designs is less than 5 £gW. Furthermore, compared with five designs implemented by hand, the difference of the power consumption between two of them is less than 7% at most

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

Battery-less near field communications (nfc) sensors for internet of things (iot) applications

L’ implementació de la tecnologia de comunicació de camp proper (NFC) en els telèfons intel·ligents no para de créixer degut a l’ús d’aquesta per fer pagaments, això, junt amb el fet de poder aprofitar l’energia generada pel mòbil no només per la comunicació, sinó també per transmetre energia, el baix cost dels xips NFC, i el fet de que els telèfons tinguin connectivitat amb internet, possibilita i fa molt interesant el disseny d’etiquetes sense bateria incorporant-hi sensors i poder enviar la informació al núvol, dins del creixent escenari de l’internet de les coses (IoT). La present Tesi estudia la viabilitat d’aquests sensors, analitzant la màxima distància entre lector i sensor per proveir la potència necessària, presenta tècniques per augmentar el rang d’operació, i analitza els efectes de certs materials quan aquests estan propers a les antenes. Diversos sensors han estat dissenyats i analitzats i son presentats en aquest treball. Aquests son: Una etiqueta que mesura la humitat de la terra, la temperatura i la humitat relativa de l’aire per controlar les condicions de plantes. Un sensor per detectar la humitat en bolquers, imprès en material flexible que s’adapta a la forma del bolquer. Dues aplicacions, una per estimació de pH i una altre per avaluar el grau de maduració de fruites, basats en un sensor de color. I, per últim, s’estudia la viabilitat de sensors en implants per aplicacions mèdiques, analitzant l’efecte del cos i proposant un sistema per augmentar la profunditat a la que aquests es poden llegir utilitzant un telèfon mòbil. Tots aquests sensors poden ser alimentats i llegits per qualsevol dispositiu que disposin de connexió NFC.La implementación de la tecnología de comunicaciones de campo cercano (NFC) en los teléfonos inteligentes no para de crecer debido al uso de esta para llevar a cabo pagos, esto, junto con el hecho de poder aprovechar la energía generada por el móvil no sólo para la comunicación, sino también para transmitir energía, el bajo coste de los chips NFC, i el hecho que los teléfonos tengan conectividad a internet, posibilita y hace muy interesante el diseño de etiquetas sin batería que incorporen sensores i poder enviar la información a la nube, enmarcado en el creciente escenario del internet de las cosas (IoT). La presente Tesis estudia la viabilidad de estos sensores, analizando la máxima distancia entre lector i sensor para proveer la potencia necesaria, presenta técnicas para aumentar el rango de operación, y analiza los efectos de ciertos materiales cuando estos están cerca de las antenas. Varios sensores han sido diseñados y analizados y son presentados en este trabajo. Estos son: Una etiqueta que mide la humedad de la tierra, la temperatura y la humedad relativa del aire para controlar las condiciones de plantas. Un sensor para detectar la humedad en pañales, impreso en material flexible que se adapta a la forma del pañal. Dos aplicaciones, una para estimación de pH y otra para evaluar el grado de maduración de frutas, basados en un sensor de color. Y, por último, se estudia la viabilidad de sensores en implantes para aplicaciones médicas, analizando el efecto del cuerpo y proponiendo un sistema para aumentar la profundidad a la que estos se pueden leer usando un teléfono móvil. Todos estos sensores pueden ser alimentados y leídos por cualquier dispositivo que disponga de conexión NFC.The implementation of near field communication (NFC) technology into smartphones grows rapidly due the use of this technology as a payment system. This, altogether with the fact that the energy generated by the phone can be used not only to communicate but for power transfer as well, the low-cost of the NFC chips, and the fact that the smartphones have connectivity to internet, makes possible and very interesting the design of battery-less sensing tags which information can be sent to the cloud, within the growing internet of things (IoT) scenario. This Thesis studies the feasibility of these sensors, analysing the maximum distance between reader and sensor to provide the necessary power, presents techniques to increase the range of operation, and analyses the effects of certain materials when they are near to the antennas. Several sensors have been designed and analysed and are presented in this work. These are: a tag that measures the soil moisture, the temperature and the relative humidity of the air to control the conditions of plants. A moisture sensor for diapers, printed on flexible material that adapts to the diaper shape. Two applications, one for pH estimation and another for assessing the degree of fruit ripening, based on a colour sensor. And finally, the feasibility of sensors in implants for medical applications is studied, analysing the effect of the body and proposing a system to increase the depth at which they can be read using a mobile phone. All of these sensors can be powered and read by any NFC enabled device