A 21 m Operation Range RFID Tag for “Pick to Light” Applications with a Photovoltaic Harvester

In this paper, a novel Radio-Frequency Identification (RFID) tag for “pick to light” applications is presented. The proposed tag architecture shows the implementation of a novel voltage limiter and a supply voltage (VDD) monitoring circuit to guarantee a correct operation between the tag and the reader for the “pick to light” application. The feasibility to power the tag with different photovoltaic cells is also analyzed, showing the influence of the illuminance level (lx), type of source light (fluorescent, LED or halogen) and type of photovoltaic cell (photodiode or solar cell) on the amount of harvested energy. Measurements show that the photodiodes present a power per unit package area for low illuminance levels (500 lx) of around 0.08 µW/mm2 , which is slightly higher than the measured one for a solar cell of 0.06 µW/mm2 . However, solar cells present a more compact design for the same absolute harvested power due to the large number of required photodiodes in parallel. Finally, an RFID tag prototype for “pick to light” applications is implemented, showing an operation range of 3.7 m in fully passive mode. This operation range can be significantly increased to 21 m when the tag is powered by a solar cell with an illuminance level as low as 100 lx and a halogen bulb as source light

A wirelessly-powered sensor platform using a novel textile antenna

This thesis describes the design and analysis of a novel wideband circularly-polarized textile antenna to power up a wearable wirelessly-powered sensor system operating in the 2.45 GHz ISM band (2.4-2.5 GHz) and the building of the whole system. The system is constructed using off-the-shelf components and it is shown that the wirelessly-powered sensor system is able to operate when just a few mW are transmitted from a base station at a distance over a metre. Initially, standard linearly-polarized patch antennas are used for power transmission. However, the antennas have to be aligned perfectly for the best efficiency. Subsequently, a circularly-polarized antenna is proposed for enhanced wireless-power transfer due to the freedom of orientation. A wide-slot antenna without a ground plane has been chosen for its simplicity and wide impedance band. The geometry is firstly optimized for wide impedance and 3-dB axial ratio bandwidth on FR-4. The experimental and simulation results have been studied to analyse the characteristics of such an antenna. The wideband circularly-polarized antenna is then constructed using a conductive textile and re-optimized for on-body applications. With a simple antenna geometry and only a single layer of conductive textile layer, the axial ratio and impedance bandwidths are wide enough to cover the whole 2.45 GHz ISM band with plenty of margin and are significantly wider than any other on-body circularly-polarized textile patch antennas which have been reported. The characteristics of this wideband circularly-polarized antenna under different conditions on the human body have been measured and then connected to the wirelessly-powered sensor system to demonstrate the effectiveness of power transfer to the human body

Dense and long-term monitoring of Earth surface processes with passive RFID -- a review

Billions of Radio-Frequency Identification (RFID) passive tags are produced yearly to identify goods remotely. New research and business applications are continuously arising, including recently localization and sensing to monitor earth surface processes. Indeed, passive tags can cost 10 to 100 times less than wireless sensors networks and require little maintenance, facilitating years-long monitoring with ten's to thousands of tags. This study reviews the existing and potential applications of RFID in geosciences. The most mature application today is the study of coarse sediment transport in rivers or coastal environments, using tags placed into pebbles. More recently, tag localization was used to monitor landslide displacement, with a centimetric accuracy. Sensing tags were used to detect a displacement threshold on unstable rocks, to monitor the soil moisture or temperature, and to monitor the snowpack temperature and snow water equivalent. RFID sensors, available today, could monitor other parameters, such as the vibration of structures, the tilt of unstable boulders, the strain of a material, or the salinity of water. Key challenges for using RFID monitoring more broadly in geosciences include the use of ground and aerial vehicles to collect data or localize tags, the increase in reading range and duration, the ability to use tags placed under ground, snow, water or vegetation, and the optimization of economical and environmental cost. As a pattern, passive RFID could fill a gap between wireless sensor networks and manual measurements, to collect data efficiently over large areas, during several years, at high spatial density and moderate cost.Comment: Invited paper for Earth Science Reviews. 50 pages without references. 31 figures. 8 table

An Implantable Low Pressure, Low Drift, Dual BioPressure Sensor and In-Vivo Calibration Methods Thereof

The human body’s intracranial pressure (ICP) is a critical component in sustaining healthy blood flow to the brain while allowing adequate volume for brain tissue within the rigid structures of the cranium. Disruptions in the body’s autoregulation of intracranial pressure are often caused by hemorrhage, tumors, edema, or excess cerebral spinal fluid resulting in treatments that are estimated to globally cost up to approximately five billion dollars annually. A critical element in the contemporary management of acute head injury, intracranial hemorrhage, stroke, or other conditions resulting in intracranial hypertension, is the real-time monitoring of ICP. Currently, such mainstream clinical monitoring can only take place short-term within an acute care hospital. The monitoring is prone to measurement drift and is comprised of externally tethered pressure sensors that are temporarily implanted into the brain, thus carrying a significant risk of infection. To date, reliable, low drift, completely internalized, long-term ICP monitoring devices remain elusive. The successful development of such a device would not only be safer and more reliable in the short-term but would expand the use of ICP monitoring for the management of chronic intracranial hypertension and enable further clinical research into these disorders. The research herein reviews the current challenges of existing ICP monitoring systems, develops a new novel sensing technology, and evaluates the same for potentially facilitating long-term implantable ICP sensing. Based upon the findings of this research, this dissertation proposes and evaluates a dual matched-die piezo-resistive strain sensing device, with a novel in-vivo calibration system and method thereof, for application to long-term implantable ICP sensing

Nanopower CMOS transponders for UHF and microwave RFID systems

At first, we present an analysis and a discussion of the design options and tradeoffs for a passive microwave transponder. We derive a set of criteria for the optimization of the voltage multiplier, the power matching network and the backscatter modulator in order to optimize the operating range. In order to match the strictly power requirements, the communication protocol between transponder and reader has been chosen in a convenient way, in order to make the architecture of the passive transponder very simple and then ultra-low-power. From the circuital point of view, the digital section has been implemented in subthreshold CMOS logic with very low supply voltage and clock frequency. We present different solutions to supply power to the transponder, in order to keep the power consumption in the deep sub-µW regime and to drastically reduce the huge sensitivity of the subthreshold logic to temperature and process variations. Moreover, a low-voltage and low-power EEPROM in a standard CMOS process has been implemented. Finally, we have presented the implementation of the entire passive transponder, operating in the UHF or microwave frequency range

Variability-aware design of CMOS nanopower reference circuits

Questo lavoro è inserito nell'ambito della progettazione di circuiti microelettronici analogici con l'uso di tecnologie scalate, per le quali ha sempre maggiore importanza il problema della sensibilità delle grandezze alle variazioni di processo. Viene affrontata la progettazione di generatori di quantità di riferimento molto precisi, basati sull’uso di dispositivi che sono disponibili anche in tecnologie CMOS standard e che sono “intrinsecamente” più robusti rispetto alle variazioni di processo. Questo ha permesso di ottenere una bassa sensibilità al processo insieme ad un consumo di potenza estremamente ridotto, con il principale svantaggio di una elevata occupazione di area. Tutti i risultati sono stati ottenuti in una tecnologia 0.18μm CMOS. In particolare, abbiamo progettato un riferimento di tensione, ottenendo una deviazione standard relativa della tensione di riferimento dello 0.18% e un consumo di potenza inferiore a 70 nW, sulla base di misure su un set di 20 campioni di un singolo batch. Sono anche disponibili risultati relativi alla variabilità inter batch, che mostrano una deviazione standard relativa cumulativa della tensione di riferimento dello 0.35%. Abbiamo quindi progettato un riferimento di corrente, ottenendo anche in questo caso una sensibilità al processo della corrente di riferimento dell’1.4% con un consumo di potenza inferiore a 300 nW (questi sono risultati sperimentali ottenuti dalle misure su 20 campioni di un singolo batch). I riferimenti di tensione e di corrente proposti sono stati quindi utilizzati per la progettazione di un oscillatore a rilassamento a bassa frequenza, che unisce una ridotta sensibilità al processo, inferiore al 2%, con un basso consumo di potenza, circa 300 nW, ottenuto sulla base di simulazioni circuitali. Infine, nella progettazione dei blocchi sopra menzionati, abbiamo applicato un metodo per la determinazione della stabilità dei punti di riposo, basato sull’uso dei CAD standard utilizzati per la progettazione microelettronica. Questo approccio ci ha permesso di determinare la stabilità dei punti di riposo desiderati, e ci ha anche permesso di stabilire che i circuiti di start up spesso non sono necessari

ULTRA LOW POWER FSK RECEIVER AND RF ENERGY HARVESTER

This thesis focuses on low power receiver design and energy harvesting techniques as methods for intelligently managing energy usage and energy sources. The goal is to build an inexhaustibly powered communication system that can be widely applied, such as through wireless sensor networks (WSNs). Low power circuit design and smart power management are techniques that are often used to extend the lifetime of such mobile devices. Both methods are utilized here to optimize power usage and sources. RF energy is a promising ambient energy source that is widely available in urban areas and which we investigate in detail. A harvester circuit is modeled and analyzed in detail at low power input. Based on the circuit analysis, a design procedure is given for a narrowband energy harvester. The antenna and harvester co-design methodology improves RF to DC energy conversion efficiency. The strategy of co-design of the antenna and the harvester creates opportunities to optimize the system power conversion efficiency. Previous surveys have found that ambient RF energy is spread broadly over the frequency domain; however, here it is demonstrated that it is theoretically impossible to harvest RF energy over a wide frequency band if the ambient RF energy source(s) are weak, owing to the voltage requirements. It is found that most of the ambient RF energy lies in a series of narrow bands. Two different versions of harvesters have been designed, fabricated, and tested. The simulated and measured results demonstrate a dual-band energy harvester that obtains over 9% efficiency for two different bands (900MHz and 1800MHz) at an input power as low as -19dBm. The DC output voltage of this harvester is over 1V, which can be used to recharge the battery to form an inexhaustibly powered communication system. A new phase locked loop based receiver architecture is developed to avoid the significant conversion losses associated with OOK architectures. This also helps to minimize power consumption. A new low power mixer circuit has also been designed, and a detailed analysis is provided. Based on the mixer, a low power phase locked loop (PLL) based receiver has been designed, fabricated and measured. A power management circuit and a low power transceiver system have also been co-designed to provide a system on chip solution. The low power voltage regulator is designed to handle a variety of battery voltage, environmental temperature, and load conditions. The whole system can work with a battery and an application specific integrated circuit (ASIC) as a sensor node of a WSN network

Energy autonomous systems : future trends in devices, technology, and systems

The rapid evolution of electronic devices since the beginning of the nanoelectronics era has brought about exceptional computational power in an ever shrinking system footprint. This has enabled among others the wealth of nomadic battery powered wireless systems (smart phones, mp3 players, GPS, …) that society currently enjoys. Emerging integration technologies enabling even smaller volumes and the associated increased functional density may bring about a new revolution in systems targeting wearable healthcare, wellness, lifestyle and industrial monitoring applications

Low Power Circuits for Miniature Sensor Systems.

With the development of VLSI technologies, the sensor systems of all kinds of applications have entered our everyday's life. For specific applications such as medical implants, the form factor of such systems is the crucial concern. In order to minimize of size of the power sources with a given lifetime, the ability to operate the system with low power consumption is the key. An effective way of lowering the active power dissipation is through aggressive voltage scaling. For minimal energy operation, the optimum supply voltage is typical lower than the subthreshold voltage. On the other hand, a sensor system spends most of the time idling while only actively obtaining data in a short period of time. As a result, strong power gating is needed for reducing the leakage power. We discuss the design challenges for several building blocks for the sensor system that have not been gotten much emphasis in term of power consumption. To monitor the period for idle time and to wake up the system periodically, two types of ultra low power timers are proposed. The first one utilizes the gate leakage of a MOS transistor to achieve low temperature dependency and large time constant. The second one implements a program-and-hold technique to compensate for the temperature coefficient of a one-shot oscillator with 150pW of average power. We propose a low power temperature sensor that is suitable for passive RFID transponder. To retrieve the data out of the sensor chip, two passive proximity communication schemes are presented. Capacitive coupling can be used for chips on a stack where the key challenge is misalignment. A alignment detection and microplate reconfiguration method is proposed to solve the problem. We also propose a passive inductive coupling scheme using pulse signaling. Compared to the traditional backscattering technique, the limitations on the quality factor of the inductor and the signal sensitivity of the receiver can be relaxed.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61782/1/yushiang_1.pd