A long-range UHF RF identification (RFID) sensor has been designed using a 0.35- ¿m CMOS standard process. The power-optimized tag, combined with the ultralow-power temperature sensor, allows an ID and a temperature reading range of 2 m from a 2-W effective radiated power output power reader. The temperature sensor is based on a ring oscillator, where the temperature dependence of the oscillation frequency is used for thermal sensing. The temperature sensor exhibits a resolution of 0.035°C and an inaccuracy value lower than 0.1°C in the range from 35°C to 45°C after two-point calibration. The average power consumption of the temperature sensor is only 110 nW at ten conversions per second while keeping a high resolution and accuracy. These properties allow the use of the RFID as a batteryless sensor in a wireless human body temperature monitoring system.

The number of wireless medical wearables has increased in recent years and is revolutionizing the current healthcare system. However, the state-of-the-art systems still need to be improved, as they are bulky, battery powered, and so require maintenance. On the contrary, battery-free wearables have unlimited lifetimes, are smaller, and are cheaper. This paper describes a design of a battery free wearable system that measures the skin temperature of the human body while at the same time collects energy from body heat. The system is composed of an UHF RFID temperature sensor tag located on the arm of the patient. It is assisted with extra power supply from a power harvesting module that stores the thermal energy dissipated from the neck of the patient. This paper presents the experimental results of the stored thermal energy, and characterizes the module in different conditions, e.g., still, walking indoors, and walking outdoors. Finally, the tag is tested in a fully passive condition and when it is power assisted. Our experimental results show that the communication range of the RFID sensor is improved by 100% when measurements are done every 750 ms and by 75% when measurements are done every 1000 ms when the sensor is assisted with the power harvesting module.

This article presents a wireless temperature sensor tag able to work in both fully passive mode and in semi-passive mode when assisted by a flexible thermoelectric generator (TEG). The sensor tag consists of an EPC C1G2/ISO 18000-6C ultrahigh-frequency (UHF) radio frequency identification (RFID) integrated circuit (IC) connected to a low-power microcontroller unit (MCU) that samples and collects the temperature from a digital temperature sensor. With a temperature gradient as low as 2.5 °C, the test results show that the TEG provides an output power of 400 $\mu$ W with an output voltage of 40mV. Bymeans of an up-converter in order to boost the TEG output voltage, this harvester supplies the power required to the sensor tag for a 2-conv/s data rate in semi-passive mode. Moreover, when the tag operates in semi-passive mode, a communication range of 22.2 m is measured for a 2-W effective radiated power (ERP) reader. To the best of our knowledge, the proposed TEG-assisted sensor tag shows the longest communication range and the only one that provides stable external power at low-temperature gradients. The measured performance and the chosen architecture allow using the wireless sensor in multiple industrial or biomedical applications.

This paper presents a comprehensive overview and analysis of the state-of-the-art (SoA) in semi-passive or Battery-Assisted (BAP) Ultra-High Frequency (UHF) Radio Frequency Identification (RFID) sensor tags compliant with EPC Global G2/ISO-18000C. These tags operate on the same communication principle as fully passive sensor tags but incorporate a battery or an energy harvesting module. This additional power source extends communication ranges and enables power demanding applications using low power microcontrollers (MCUs) and higher-end sensors. This article also analyzes various key features, including tag integrated circuit (IC) architecture, types of energy harvesting modules, and communication range. The main conclusions are threefold. Firstly, selecting the appropriate tag IC requires a careful analysis its features such as sensitivity, sensor interfaces or data logging capabilities. For instance, among the solutions examined in the SoA, half of them opted for a tag IC capable of MCU communication via SPI or I2C buses. Secondly, it is essential to assess both the forward and backward communication links to leverage the sensitivity of the tag IC in BAP mode. Interestingly, only one third of the solutions in the SoA achieved the theoretical communication range anticipated by the tag IC sensitivity. Finally, an energy budget analysis is required to ensure that the energy generation suffices to meet the energy requirements of the tag. While most solutions rely on batteries as the energy source and analyze battery lifespan, only a few studies employing energy harvesters conduct an energy budget analysis due to the additional complexity involved.

A fully integrated power amplifier (PA) for 5 GHz 802.11a standard is implemented using a 0.18 mum CMOS process. In this paper we present the new concept of "power inductors". These on-chip inductors are implemented on the transistor drains and the output network and they can withstand the high level current signals that go through them while presenting low DC-resistance and high Q characteristics. The two stage differential power amplifier is fully integrated including the input and output networks. Measurement results show that the power amplifier achieves a power gain of 25.5 dB, 1 dB compression point (P _1dB ) of 20.8 dBm and power added efficiency of 26.7 %. The saturated output power is 26.5 dBm, achieving the highest reported output power among CMOS PAs for 5-GHz WLAN applications