Ignacio Gil

Flexible resistive sensors are promising for wearable and ergonomic applications because they can be easily fabricated on textiles or flexible substrates and enable real-time monitoring of human movement and posture, especially in health monitoring systems. This review presents an overview of recent developments in an interdisciplinary way and summarises advances in materials, fabrication methods, and ergonomic applications. A structured literature search was conducted across major databases, including only studies focused on resistive sensing. The selected works were analysed in terms of conductive materials, fabrication techniques (e.g., direct ink writing (DIW) and textile-based methods), and their integration into wearable systems. Flexible resistive sensors are widely used for monitoring joint motion, posture, and physiological signals in healthcare and industrial environments. However, several challenges remain, including limitations in sensitivity, signal stability, material durability, and the need for reliable calibration in real-world conditions. This review highlights current progress and existing limitations and outlines future research directions toward more robust and user-friendly wearable sensing solutions for ergonomic applications.

Wearable technology has increased interest in monitoring vital signs in various medical fields, especially breathing monitoring. However, existing methods to track breathing patterns face challenges, including lack of user comfort, robustness, system reliability, and data processing issues. Therefore, it is crucial to develop user-friendly and reliable wireless methods to overcome these challenges. In this paper, we present a new wireless communication platform for real-time breathing monitoring. The platform consists of a wearable stretching belt with an embroidered loop antenna-based sensor connected to a compact Bluetooth transmitter, with dimensions of 17.145 x 11.303 mm², placed on the abdomen. The proposed antenna-based sensor was designed to transmit data over wireless networks operating at a 2.4GHz frequency. Its sensing mechanism involves detecting a received signal strength indicator (RSSI) wirelessly transmitted by the antenna sensor, which is responsive to strain. Experimental results were conducted to track different breathing patterns from a male volunteer. The system was compared with a Biopac MP36, and the obtained results showed a strong correlation with the measured values. The proposed system demonstrates the ability to detect various breathing patterns, including eupnea, hypopnea, hyperpnea, and Biot’s respiration. Furthermore, its accuracy in detecting these breathing patterns highlights its potential for clinical applications, such as monitoring respiratory health in patients with sleep disorders or chronic respiratory conditions.

A textile woven presence sensor was previously presented to demonstrate its functionality in eliminating some false positives on car seat presence sensors. After studying the functionality, the next characteristic that the textile sensor should demonstrate is its reliability. The woven sensor was prepared to be tested against ageing. The ageing cycle was prepared according to the UNE-EN ISO 17228:2015 standard. Nine woven sensors are prepared, seven of them face the aging test, and two are selected as reference sensors. The characterization of the woven sensor has been carried out through a microcontroller measurement circuit that obtains the cycles to charge the sensor. Comparison of the results obtained shows that the effects of ageing are negligible. The behavior of the aged sensors is similar to that of the reference sensors, indicating that the variations in the values of both aged and reference sensors are provoked by the environmental conditions during the measurements. To support this argument, a statistical study based on a t-Student analysis was carried out. After 4 ageing cycles, the functionality of the sensors remains unaffected. This research proves the reliability of the woven textile sensor, which encourages its use in automotive applications.

Diabetes poses a significant global health challenge, underscoring the urgent need for accurate and continuous glucose monitoring technologies. This review provides a comprehensive analysis of both invasive and non-invasive sensor technologies, with a particular focus on antenna-sensors and their working principle. Key aspects, including the selection of substrates and conductive materials, fabrication techniques, and recent advancements in rigid and flexible antenna-sensor designs, are critically evaluated. Notably, textile antenna-sensors are gaining increasing attention due to their potential for seamless integration into daily clothing. Furthermore, the influence of the human body on antenna-sensor performance is examined, emphasizing the importance of human phantom simulation and fabrication for precise modeling and validation. Finally, this review highlights the current technical challenges in the development of flexible antenna-sensors and discusses their transformative potential in enabling next-generation, non-invasive, and patient-centric glucose monitoring solutions.

This paper presents a study on the repeatability of washing effects on two antenna-based sensors for breathing monitoring. One sensor is an embroidered meander antenna-based sensor integrated into a T-shirt, and the other is a loop antenna integrated into a belt. Both sensors were subjected to five washing cycles, and their performance was assessed after each wash. The embroidered meander antenna was specifically compared before and after washing to monitor a male volunteer’s different breathing patterns, that is, eupnea, apnea, hypopnea, and hyperpnea. Stretching tests were also conducted to evaluate the impact of mechanical deformation on sensor behavior. The results highlight the changes in sensor performance across multiple washes and stretching conditions, offering insights into the durability and reliability of these embroidered and loop antennas for practical applications in wearable health monitoring. The findings emphasize the importance of considering both washing and mechanical stress in the design of robust antenna-based sensors.

This paper presents a biomechanics sensing system based on an ultra-high frequency (UHF) RFID tag coupled with a meander resonator for motion tracking and displacement sensing. The variations in their relative position alter the strength of mutual coupling, leading to impedance changes in the RFID tag antenna. These impedance variations modulate the power reflection coefficient, which in turn affects both the backscattered signal strength (RSSI) and the turn-on threshold power of the RFID tag. The performance of the system was evaluated through simulations and experimental validation, demonstrating a 14 dB reduction in RSSI and a 5 dBm increase in threshold power over a displacement range of 30 mm. The system was further validated for wearable movement sensing in knee flexion tracking, where results indicated an RSSI variation of around 12 dB as the knee angle changed from 115∘ to 175∘. Additionally, the turn-on threshold power ( Pth ) exhibited a strong correlation with knee flexion angles, achieving a coefficient of determination ( R2 = 0.973 ) based on curve-fitted data. These results validate the feasibility of the proposed system for wearable body motion monitoring in healthcare applications.