8 research outputs found

    A Low-Power Passive UHF Tag With High-Precision Temperature Sensor for Human Body Application

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    Radio frequency identification (RFID) tags are widely used in various electronic devices due to their low cost, simple structure, and convenient data reading. This topic aims to study the key technologies of ultra-high frequency (UHF) RFID tags and high-precision temperature sensors, and how to reduce the power consumption of the temperature sensor and the overall circuits while maintaining minimal loss of performance. Combined with the biomedicine, an innovative high-precision human UHF RFID chip for body temperature monitoring is designed. In this study, a ring oscillator whose output frequency is linearly related to temperature is designed and proposed as a temperature-sensing circuit by innovatively combining auxiliary calibration technology. Then, a binary counter is used to count the pulses, and the temperature is ultimately calculated. This topic designed a relaxation oscillator independent of voltage and current. The various types of resistors were used to offset the temperature deviation. A current mirror array calibration circuit is used to calibrate the process corner deviation of the clock circuit with a self-calibration algorithm. This study mainly contributes to reducing power consumption and improving accuracy. The total power consumption of the RF/analog front-end and temperature sensor is 7.65µW. The measurement error of the temperature sensor in the range of 0 to 60◦C is less than ±0.1%, and the accuracy of the output frequency of the clock circuit is ±2.5%

    Parasitics Impact on the Performance of Rectifier Circuits in Sensing RF Energy Harvesting

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    This work presents some accurate guidelines for the design of rectifier circuits in radiofrequency (RF) energy harvesting. New light is shed on the design process, paying special attention to the nonlinearity of the circuits and the modeling of the parasitic elements. Two different configurations are tested: a Cockcroft–Walton multiplier and a half-wave rectifier. Several combinations of diodes, capacitors, inductors and loads were studied. Furthermore, the parasitics that are part of the circuits were modeled. Thus, the most harmful parasitics were identified and studied in depth in order to improve the conversion e ciency and enhance the performance of self-sustaining sensing systems. The experimental results show that the parasitics associated with the diode package and the via holes in the PCB (Printed Circuit Board) can leave the circuits inoperative. As an example, the rectifier e ciency is below 5% without considering the influence of the parasitics. On the other hand, it increases to over 30% in both circuits after considering them, twice the value of typical passive rectifiers.This work was supported in part by the Spanish Research and Development National Program under projects TIN2016-75097-P, TEC2017-85529-C3-1-R and RTI2018-102002-A-I00

    RF Energy Harvesting System Based on an Archimedean Spiral Antenna for Low-Power Sensor Applications

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    This paper presents a radiofrequency (RF) energy harvesting system based on an ultrawideband Archimedean spiral antenna and a half-wave Cockcroft-Walton multiplier circuit. The antenna was proved to operate from 350 MHz to 16 GHz with an outstanding performance. With its use, radio spectrum measurements were carried out at the Telecommunication Engineering School (Universidad Politécnica de Madrid) to determine the power level of the ambient signals in two different scenarios: indoors and outdoors. Based on these measurements, a Cockcroft-Walton multiplier and a lumped element matching network are designed to operate at 800 MHz and 900 MHz frequency bands. To correct the frequency displacement in the circuit, a circuit model is presented that takes into account the different parasitic elements of the components and the PCB. With an input power of 0 dBm, the manufactured circuit shows a rectifying efficiency of 30%. Finally, a test is carried out with the full RF energy harvesting system to check its correct operation. Thus, the RF system is placed in front of a transmitting Vivaldi antenna at a distance of 50 cm. The storage capacitor has a charge of over 1.25 V, which is enough to run a temperature sensor placed as the load to be supplied. This demonstrates the validity of the RF energy harvesting system for low-power practical applications.This research was funded in part by the project TIN2016-75097-P of the Spanish Research and Development National Program, and in part by the project TEC2017-85529-C3-1-R of the Ministerio de Economía y Empresa

    UHF Energy Harvesting and Power Management

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    As we are entering the era of Internet of Things (i.e. IoT), the physical devices become increasingly connected with each other than ever before. The connection between devices is achieved through wireless communication schemes, which unfortunately consume a significant amount of energy. This is undesirable for devices which are not directly connected to power. This is because these devices will essentially carry batteries to supply the needed energy for these operations and the batteries will eventually be depleted. This motivates the need to operate these devices off harvested energy. UHF energy harvesting, as an enabling technology for the UHF RFID, stands out amongst other energy harvesting approaches as it does not heavily rely on the natural surrounding environment and also offers a very good wireless operating range from its radiating energy source. Unlike the RFID, the power consumption and the operational range requirement of these IoT devices can vary significantly. Thus, the design of the RF energy harvesting front-end and the power management need to be re-thought for specific applications. To that end, in this thesis, discussions mainly evolve around the design of UHF energy harvesters and their associated power management units using lower power analog approaches. First, we present the background of the low power UHF energy harvesting, specially threshold-compensated rectifiers will be presented as a key technology in this area and this will be used as a build practical harvester for the UHF RFID application. Secondly, key issues with the threshold compensation will be identified and this is exploited either (i) to improve the dynamic power conversion efficiency of the harvester, (ii) to improve dynamic settling behaviour of the harvester. To exploit the ”left-over” harvested energy, an intelligent integrated power management solution has been proposed. Finally, the charge-burst approach is exploited to implement an energy harvester with -40 dBm input power sensitivity.Thesis (Ph.D.) -- University of Adelaide, School of Electrical & Electronic Engineering, 201

    Harnessing energy for wearables: a review of radio frequency energy harvesting technologies

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    Wireless energy harvesting enables the conversion of ambient energy into electrical power for small wireless electronic devices. This technology offers numerous advantages, including availability, ease of implementation, wireless functionality, and cost-effectiveness. Radio frequency energy harvesting (RFEH) is a specific type of wireless energy harvesting that enables wireless power transfer by utilizing RF signals. RFEH holds immense potential for extending the lifespan of wireless sensors and wearable electronics that require low-power operation. However, despite significant advancements in RFEH technology for self-sustainable wearable devices, numerous challenges persist. This literature review focuses on three key areas: materials, antenna design, and power management, to delve into the research challenges of RFEH comprehensively. By providing an up-to-date review of research findings on RFEH, this review aims to shed light on the critical challenges, potential opportunities, and existing limitations. Moreover, it emphasizes the importance of further research and development in RFEH to advance its state-of-the-art and offer a vision for future trends in this technology

    Inductively Coupled CMOS Power Receiver For Embedded Microsensors

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    Inductively coupled power transfer can extend the lifetime of embedded microsensors that save costs, energy, and lives. To expand the microsensors' functionality, the transferred power needs to be maximized. Plus, the power receiver needs to handle wide coupling variations in real applications. Therefore, the objective of this research is to design a power receiver that outputs the highest power for the widest coupling range. This research proposes a switched resonant half-bridge power stage that adjusts both energy transfer frequency and duration so the output power is maximally high. A maximum power point (MPP) theory is also developed to predict the optimal settings of the power stage with 98.6% accuracy. Finally, this research addresses the system integration challenges such as synchronization and over-voltage protection. The fabricated self-synchronized prototype outputs up to 89% of the available power across 0.067%~7.9% coupling range. The output power (in percentage of available power) and coupling range are 1.3× and 13× higher than the comparable state of the arts.Ph.D

    Q-learning Channel Access Methods for Wireless Powered Internet of Things Networks

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    The Internet of Things (IoT) is becoming critical in our daily life. A key technology of interest in this thesis is Radio Frequency (RF) charging. The ability to charge devices wirelessly creates so called RF-energy harvesting IoT networks. In particular, there is a hybrid access point (HAP) that provides energy in an on-demand manner to RF-energy harvesting devices. These devices then collect data and transmit it to the HAP. In this respect, a key issue is ensuring devices have a high number of successful transmissions. There are a number of issues to consider when scheduling the transmissions of devices in the said network. First, the channel gain to/from devices varies over time. This means the efficiency to deliver energy to devices and to transmit the same amount of data is different over time. Second, during channel access, devices are not aware of the energy level of other devices nor whether they will transmit data. Third, devices have non-causal knowledge of their energy arrivals and channel gain information. Consequently, they do not know whether they should delay their transmissions in hope of better channel conditions or less contention in future time slots or doing so would result in energy overflow

    Ultra low power CMOS rectifier design for radio frequency energy harvesting systems using self-body-biasing techniques / Amin Khalili Moghaddam

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    The internet of things (IoT) technology has recently gone through a significant evolution and the obsession in this field is due to its ability to simultaneously connect and remotely control any physical objects. The IoT usually incorporates radio frequency identification (RFID) systems and other schemes which enable automated object identification in numerous applications such as environmental monitoring, object tracking, contact-less identification, and implantable medical device (IMD). Such systems commonly use wireless power transfer techniques for the purpose of operation. An integrated radio frequency energy harvesting (RFEH), which adopts a viable and efficient technique, is responsible for capturing sufficient power for the above-mentioned applications. The performance of the RFEH system relies on the performance of the integrated rectifier in order to operate with high efficiency. In this work, a symmetric differential-drive cross-coupled bridge (DDCCB) rectifier structure is proposed for far-field RFEH systems with the capability of capturing radio frequency (RF) signals and converting into a positive and a negative direct current (DC) voltage at the output. Four self-body-biasing techniques are proposed without requiring any additional or auxiliary circuits using local nodes in the structure. Only one of the proposed techniques illustrates a significant improvement in simulations which is referred to as lower dc feeding (LDCF) technique in this work. The proposed self-body-biasing technique has been implemented in a double-rail three-stage configuration with identical design parameters with the conventional self-body-biasing technique which is referred to as source-to-body (SB) biasing technique in this work. The SB and the LDCF rectifiers were fabricated in a standard 130 nm CMOS process and compared at the operation frequency of 500 MHz, 953 MHz and 2 GHz along with a corresponding load of 2 k, 10 k and 50 k. The LDCF technique allows the p-type transistors to operate with a dynamic threshold voltage (Vth) which improves the power conversion efficiency (PCE) when the rectifier is operating at a smaller received power. A 9.5% of maximum improvement is achieved at the peak PCE when the rectifier is operating at 953 MHz, and driving a 10 k load. A maximum PCE of 73.9% is measured at 2 GHz when the rectifier is driving a 2 k load. The LDCF technique also offers a self-limiting capability for its output voltage, by reducing the PCE at larger received power. A limiting voltage level of 3.5 V is measured irrespective to the operating frequency and load. This capability aids the protection of the subsequent circuits in a wireless sensor from being overpowered
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