Wireless, passive inductor-capacitor sensors for biomedical applications

In contemporary medical technologies, the necessity for efficient, precise, and real-time health monitoring and management is becoming increasingly critical with the prevalence of chronic diseases and the aging population. Traditional wired sensors and active wireless sensors continue to present numerous problems in practical applications, including complex structures, substantial size, frequent battery replacements, and an elevated risk of infection. Passive and wireless inductor-capacitor (LC) sensors are emerging as significant candidates to address these challenges. These sensors are typically constructed with a simple structure comprising a capacitor and an inductor, operating through magnetic coupling with external reading devices, thereby eliminating the necessity for batteries, connection wires, and peripheral circuits. This review commences with a succinct overview of the theoretical foundations, analyzing equivalent components and operational modes. It subsequently investigates sensor technologies by examining various types of sensors, including pressure, strain, humidity, temperature, and chemical sensors. Through the introduction of two primary scenarios-wearable and implantable-the review elucidates diverse advancements and requirements pertinent to biomedical applications. It concludes with a discussion of challenges and potential solutions to facilitate future developments in this field.