The monitoring of magnetic fields is extremely important in many industrial environments, e.g., power grids. Despite of its importance, the existing monitoring methods either are large in size, require high power consumptions and manual observation, or although integrated in small wireless devices, need the use of batteries, increasing maintenance costs. This paper proposes an intermittent magnetic field monitoring system based on passive ultra-high frequency (UHF) radio frequency identification (RFID) technology. A magnetic field magnitude sensor has been integrated into a micro-controller unit (MCU) based tag, and the standard RFID communication protocol ISO/IEC 18000-6 Type C has been partially modified to allow faster sensed data transfer, especially for multiple tag situations rarely considered in the open literature. Static or 50 Hz magnetic field sensing accuracy lower than 3% have been experimentally measured with reasonable tag charging times and read distances, making possible for example to monitor magnetic fields on more than 10 locations simultaneously with a 60 s of updating time with a tag read range of 3 m.

An ultrahigh-frequency (UHF) radio frequency identification (RFID) tag structure which includes both received signal demodulation and reflected signal amplification abilities for standard compatibility is described in this letter. To let demodulation and reflected signal amplification features coexist, a simple RF switch is used to separate the reception and reflection signal paths, and a reflection amplifier (RA) is connected to one of the two RF switch paths to realize the amplified reflection state. The RF switch can guarantee good impedance matching under reception/reflection conditions; moreover, by selecting it judiciously, i.e., with a low insertion loss, it is possible to simultaneously achieve high tag sensitivity and reflection amplification. Measurement on a tag prototype has revealed a maximum read range of 96 m (with a tag sensitivity of $-$ 42 dBm) and an average power consumption of 1.134 mW.

This article describes the design of a hydrogen concentration monitoring system based on ultrahigh-frequency radio-frequency identification (RFID) passive tags, which adopts ISO/IEC 18000-6 Type C standard. Tag devices have been designed by employing a microcontrol unit, making the proposed solution very suitable for low-cost hydrogen concentration measurement in wireless sensor networks. Furthermore, anti-collision capability has been realized by implementing a new true random number generator based on the hydrogen concentration sensing circuit and analog-to-digital converter, without employing any additional device. The correctness of all operations of the RFID system has been experimentally verified in a multiple-tag environment, as well as the hydrogen concentration monitoring capability. Particularly, measurement on an RFID tag prototype developed for the bandwidth 920-925 MHz has revealed that when the ambient temperature is 25 °C and humidity 80%, a maximum error of 9.8% is found within a hydrogen concentration range from 0.24% to 2.4%.

Cable current detection plays a vital role in power grids toward improving transmission efficiency, relieving power congestion, and ensuring grid reliability. However, the sensors in existing current detection systems either are wired with measurement instruments or are wireless yet require batteries, which is inconvenient for monitoring overhead powerlines. Inspired by RF sensing tags, which are widely used for applications such as temperature and humidity measurements, in this article, we propose a distinctive cable current detection system that can avoid the constraint of wires and batteries. By detecting the ambient magnetic field produced by ac current flowing through a cable, the proposed system realizes a minimal measurement range of 5–17.5 A at 50/60 Hz with a maximum wireless distance of 5.2 m. This prototype can detect cable current with an extendable measurement range, providing a promising strategy for passive and wireless current detection.

With the development and popularization of the Beidou-3 navigation satellite system (BDS-3), to ensure its unique short message function, it is necessary to integrate a radio frequency (RF) transmitting circuit with high performance in the BDS-3 terminal. As the key device in an RF transmitting circuit, the RF power amplifier (PA) largely determines the comprehensive performance of the circuit with its transmission power, efficiency, linearity, and integration. Therefore, in this paper, an L-band highly integrated PA chip compatible with 3 W and 5 W output power is designed in InGaP/GaAs heterojunction bipolar transistor (HBT) technology combined with temperature-insensitive adaptive bias technology, class-F harmonic suppression technology, analog pre-distortion technology, temperature-insensitive adaptive power detection technology, and land grid array (LGA) packaging technology. Additionally, three auxiliary platforms are proposed, dedicated to the simulation and optimization of the same type of PA designs. The simulation results show that at the supply voltage of 5 V and 3.5 V, the linear gain of the PA chip reaches 39.4 dB and 38.7 dB, respectively; the output power at 1 dB compression point (P1dB) reaches 37.5 dBm and 35.1 dBm, respectively; the saturated output power (Psat) reaches 38.2 dBm and 36.2 dBm, respectively; the power added efficiency (PAE) reaches 51.7% and 48.2%, respectively; and the higher harmonic suppression ratios are less than −62 dBc and −65 dBc, respectively. The size of the PA chip is only 6 × 4 × 1 mm³. The results also show that the PA chip has high gain, high efficiency, and high linearity under both output power conditions, which has obvious advantages over similar PA chip designs and can meet the short message function of the BDS-3 terminal in various application scenarios.