Smart Bandage with Inductor‐Capacitor Resonant Tank Based Printed Wireless Pressure Sensor on Electrospun Poly‐L‐Lactide Nanofibers

Abstract

in many ways advantageous compared to the matured silicon-based technology. For example, high temperature process steps are incompatible with flexible substrates (e.g., polyethylene terephthalate (PET), polyethylene naphtholate (PEN), and Polydimethylsiloxane (PDMS), etc.), which are typically needed in emerging applications such as electronic skin, [1,5] and smart packages. [6] Several flexible wearable sensors have been developed on such substrates for biomedical applications to monitor parameters, such as sweat pH, [7] temperature, [8] humidity, [9] etc. Likewise, various force and pressure sensors have been developed to monitor physiological parameters such as blood pressure, respiration, and heart rate, etc. [10][11][12][13][14] It is preferable to have wireless data transmission from such sensors, as commonly employed hard wired approach does not consider user comfort. Therefore, the advanced technologies in this field aim to develop biocompatible and light weight wearable sensors with fully integrated wireless system capable of continuous monitoring of physiological parameters. In this regard, Radiofrequency Identification (RFID) sensor tags are attractive as they eliminate the use of battery and the complexity of wired electronics. [15,16] These tags are generally designed for highfrequency range (HF) 13.56 MHz band and ultrahigh frequency (UHF) range (860-960 MHz band depending on local regulations). However, with human body acting as a lossy medium with a high dielectric constant, the performance of RFID tags deteriorates when they are used for wireless epidermal sensing.In contrast to far field-based systems, the HF band (3-30 MHz) allows devices to communicate through an inductive coupling in the near field region without emitting energy in far field. This short-range system is a promising alternative to transmit power and data where the medium is highly lossy for instance, human tissue. Most commercial sensing tags include a chip to store and process the RF signal, whereas in chipless tags no electronic components are included. [16,17] LC circuit working in HF region can be used as a nondestructive sensing platform in biomedical applications, especially as an implant. [18,19] Motivated by the above challenges, herein we have used the LC tank-based approach for wireless sensing. Easy to use multifunctional wearable devices, with no wires hanging around, are needed for real time health monitoring at user's comfort. Herein, an inductor-capacitor (LC) resonant tank-based wireless pressure sensor, screenprinted on an electrospun Poly-L-lactide (PLLA) nanofibers-based flexible, biocompatible, and piezoelectric substrate is presented. The printed resonant tank (resonant frequency of ≈13.56 MHz) consists of a planar inductor connected in parallel with an interdigitated capacitor. The capacitance, of the interdigitated capacitor present on the piezoelectric substrate varies in response to applied pressure. As a result, the resonant frequency changes and the LC tank works as a wireless pressure sensor. The sen...

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