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.

This letter presents the design of a 140-160 GHz vector-modulator-type phase shifter, integrated in a 55-nm BiCMOS technology. The circuit is optimized to minimize the occupied area and maximize the linearity, facilitating its integration in D-band phased arrays. Test results show an average insertion loss of 4.5 dB, an OP 1 dB of -3.7 dBm, and rms gain/phase errors lower than 1.4 dB and 7.5°. The circuit core occupies 0.05 mm², consuming less than 66 mW of dc power.

A self-healing two-stage millimeter-wave broadband power amplifier (PA) with on-chip amplitude/phase compensation is realized in 65-nm CMOS. The amplitude and phase compensations are accomplished by using feedback bias/capacitive schemes to extend the linear operation region and optimize the PA efficiency. Tunable control knobs are inserted in the linearization block to enhance the PA performance yield against process/temperature variations and device ageing effects. This prototype shows a 5.5-dB improvement of the output 1-dB compression point (P_1dB) and a less than 2% chip-to-chip gain variation. At a 1-V supply, the differential PA achieves a saturation output power (P_sat) of 14.85 dBm with a peak power-added-efficiency (PAE) of 16.2%. With the amplitude compensation, P_1dB is increased to 13.7 dBm. With the phase compensation, the output phase variation is decreased to less than 0.5°. To the best of our knowledge, this prototype provides the highest P_sat and P_1dB with simultaneously high PAE from a single PA reported to date. The PA delivers a linear gain of 9.7 dB and has a 7-GHz 3-dB bandwidth from 55.5 to 62.5 GHz with a compact total area of 0.042 mm².

This work provides an overview of the current state-of-the-art of the RFID technology in the Wireless Sensor Network (WSN) field. The different RFID alternatives are described with their pros and cons. The benefits and limitations of battery-free wireless sensors based on RFID technology are presented. Subsequently, the paper describes the design of an UHF RFID integrated circuit (IC) designed to harvest and store the power from an incoming RF signal in order to supply low power analog or digital sensors. The IC has been implemented using a low cost 0.35 μm CMOS process and it incorporates a serial peripheral interface (SPI) in order to communicate with the sensor. Battery-free wireless operation for industrial monitoring using the designed IC has been demonstrated by implementing two wireless sensors that monitor both temperature, using a thermistor, and pressure, using a commercial digital sensor. The wireless temperature sensor shows an error below ±1°C from -25°C to 105°C, whereas the pressure sensor error is below ±2 mbar from 325 to 1000 mbar. A battery free communication range of 1.5 meters is demonstrated for both sensors using a 2-W effective radiated output power reader.

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.