Jiawen Yin

Lithium-ion batteries (LIBs) in energy storage systems often show rapid temperature and internal pressure increases before thermal runaway, posing safety risks. Thus, synchronized in-situ monitoring of both parameters is crucial for achieving early warning. However, conventional wired sensors lack pressure information, active wireless sensors need battery energy, and LC passive sensors suffer low quality factors and cross-coupling, limiting practical deployment. This article presents a battery-free, passive wireless sensor system based on Parity-Time (PT) symmetry for simultaneous temperature and pressure detection at the LIB explosion-proof valve. It consists of an active gain-side reader and a passive loss-side resonator. The loss side integrates a flexible capacitive temperature sensor. Both sides inductively couple through the same planar circular coil. Temperature modulates sensor capacitance, while pressure from the valve modulates the inter-coil coupling coefficient. The system decouples the two parameters using three zero-phase points of the S11 parameter. For practical deployment, a low-cost readout terminal based on a resistance bridge directional coupler is developed, with adaptive frequency tracking to replace the expensive vector network analyzer (VNA). Compared with a commercial VNA, maximum deviations are 5.21 dB and 7.23°. In single-parameter mode, maximum temperature and pressure sensitivities are 15.01 kHz/℃ and 95.66 kHz/kPa; in dual-parameter mode, maximum measurement errors are 1.93 ℃ and 1.99 kPa. The proposed system provides a deployable, low-cost solution for in-situ safety monitoring of lithium-ion energy storage systems.

Free chlorine is one of the key water quality parameters in tap water. However, a free chlorine sensor with the characteristics of batch processing, durability, antibiofouling/antiorganic passivation and in situ monitoring of free chlorine in tap water continues to be a challenging issue. In this paper, a novel silicon-based electrochemical sensor for free chlorine that can self-clean and be mass produced via microfabrication technique/MEMS (Micro-Electro-Mechanical System) is proposed. A liquid-conjugated Ag/AgCl reference electrode is fabricated, and electrochemically stable BDD/Pt is employed as the working/counter electrode to verify the effectiveness of the as-fabricated sensor for free chlorine detection. The sensor demonstrates an acceptable limit of detection (0.056 mg/L) and desirable linearity (R² = 0.998). Particularly, at a potential of +2.5 V, hydroxyl radicals are generated on the BBD electrode by electrolyzing water, which then remove the organic matter attached to the surface of the sensor though an electrochemical digestion process. The performance of the fouled sensor recovers from 50.2 to 94.1% compared with the initial state after self-cleaning for 30 min. In addition, by employing the MEMS technique, favorable response consistency and high reproducibility (RSD < 4.05%) are observed, offering the opportunity to mass produce the proposed sensor in the future. A desirable linear dependency between the pH, temperature, and flow rate and the detection of free chlorine is observed, ensuring the accuracy of the sensor with any hydrologic parameter. The interesting sensing and self-cleaning behavior of the as-proposed sensor indicate that this study of the mass production of free chlorine sensors by MEMS is successful in developing a competitive device for the online monitoring of free chlorine in tap water.

Chemical oxygen demand (COD) is one of the key water quality parameters in environmental monitoring. However, fabricating a COD sensor with the characteristic of batch-processing and rapid measurement is always a challenging issue. This paper reports a microfluidic electrochemical sensor for the organic matter measurement based on advanced oxidization within a fixed microvolume detection chamber by a microfabrication technique/MEMS. By fabricating a silicon-based Ag/AgCl reference electrode and employing PbO₂ as the working electrode with Pt as the counter electrode, we verified the superiority of the as-fabricated sensor by continuous potassium acid phthalate detection; an acceptable limit of detection (4.17 mg L⁻¹–200 mg L⁻¹), a low limit of detection (2.05 mg L⁻¹), a desirable linearity (R² = 0.982) and relative stability at different pH values and Cl⁻ concentrations was witnessed. Particularly, a shorter detection time (2 s) was witnessed for the as-proposed sensor compared with traditional organic matter measurement methods. Each sensing process takes only 2 seconds for sensing because a micro-cavity with a volume of 2.5 μL was fabricated and used as a detection pool. Moreover, as the sensor was fabricated by a mass-production technique, potential response consistency of multiple sensors was expected and was verified via a series of parallel experiments. In this paper, a miniaturized (8 mm × 10 mm), low-cost and reliable COD sensor was designed and fabricated by MEMS, and it provided a core sensor component for construction of an online water environment monitoring network to meet the substantial demand for COD sensors in the Internet of Things (IOT) era.