Department of Electrical and Electronics Engineering

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    Flexible and Wearable Sensors for Health Monitoring Applications
    (CRC Press, 2023) Gupta, Navneet
    Over the past decade, flexible electronics have attracted much interest as conventional semiconductors are not competent to provide new product paradigms. The flexible devices are bendable, stretched, and can be folded without losing functionality. Flexible electronics devices are used in various fields, such as consumer electronics, medical, health care, and security devices, because they are generally lightweight, non-breakable, and involve a relatively simple manufacturing process. The use of wearable electronics for non-invasive real-time health monitoring has also gained popularity. The continuous monitoring of body locomotion, biophysical parameters, and biomarkers is valuable in quantifying human performance and off-site patient care. Flexible electronics provide a natural interaction between the human body and wearable devices because of their high flexibility and conformity. So, in this chapter, we shall discuss the flexible substrate, active material, transduction mechanism, and fabrication processes of different flexible sensors with a special focus on temperature, pressure, and strain sensors.
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    Realization of ppb-level acetone detection using noble metals (Au, Pd, Pt) nanoparticles loaded GO FET sensors with simultaneous back-gate effect
    (Elsevier, 2022-02) Hazra, Arnab
    In the current study, graphene oxide (GO), uniformly loaded with different noble metal nanoparticles (Au, Pd and Pt) were synthesized by spray coating technique and implemented in field effect transistor (FET) sensors. The morphology, structure, composition and electronic properties of the synthesized materials were characterized. The sensing results indicated that the incorporation of noble metals can greatly enhance the VOC sensing properties of a few layers of GO by using their chemical and electrical sensitization effect. At optimized gate potential, GO FET exhibited outstanding sensing properties at low operating temperature i.e. 50 °C. Specifically, the FET sensor based on Pd loaded GO exhibited the highest response, quickest response/recovery (37 s/91 s) characteristics, best selectivity and low operating temperature towards low concentration of acetone. Almost five times higher sensitivity towards acetone (400 ppb) was achieved in Pd/GO as compared to the pure GO channel nanoparticles under a suitable back gate bias.
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    Synthesis and characterization of hybrid NiO/CeO2 p-n heterojunction nanofibers for room temperature ammonia sensing application
    (Elsevier, 2024-08) Hazra, Arnab
    The development of room temperature chemiresistive NH3 gas sensors with superior selectivity and stability is always an uphill task to solve. This work describes the synthesis and characterization of NiO/CeO2 p-n heterojunction nanofiber assembly using a facile electrospinning method. Systematic studies are conducted using SEM, XRD, XPS, and TEM to examine the microstructure and morphology. The electro spun nanofibers offer high surface area of NiO/CeO2 p-n heterojunction composite sensor with an average fiber diameter of ∼125 ± 20 nm, regulated morphology, and interconnectivity through junction formation. Under ambient temperature, the sensing performance for 10–100 ppm NH3 gas is investigated. The increased specific surface areas, formations of multiple NiO/CeO2 bridging point contacts are responsible for the improved gas sensitivity. Experiments reveal that NiO/CeO2 hybrid nanofiber sensor outperforms the pure NiO NF sensor for NH3 sensing, in addition to superior selectivity, good stability and quick response/recovery time. Gas sensors based on NiO/CeO2 are anticipated to become a viable option for the detection of ammonia in breathed gas of sufferers with gastrointestinal or renal disorders in the future due to their flexibility, room temperature operation, and good reaction to ammonia.
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    Sensor tags for wireless body-centric communication: challenges and opportunities
    (IOP, 2022-09) Rano, Dinesh
    Chapter 10 gives a comprehensive overview of the devices and methods required for interfacing sensor tags for wireless body-centric communication (WBAN). The antenna is an integral part of WBAN devices and plays a vital role in establishing a link between a wearable device and a base communication station situated remotely from the body. The patch antennas used in WBAN applications are often limited by their operational bandwidth, size, reduced efficiency, strong coupling with the body, and high specific absorption rate. This chapter highlights the existing challenges and some solutions for designing an antenna for WBAN applications. An in-depth study of one promising solution related to the design of electromagnetic band-gap surfaces for interfacing the wearable devices and base station is included.
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    ZnO Nanorod Based Ultra Sensitive and Selective Explosive Sensor
    (IEEE, 2013-02) Rao, V. Ramgopal
    A small scale (20 μm), ultra sensitive (50 ppb) and highly selective sensor based on ZnO nanostructures using Micro-electro-mechanical system (MEMS) platform has been reported here for the detection of explosive and Volatile Organic Compound (VOC) vapors. Flower and rod like architectures of nanorods were used as a sensing layer. The nanorods prepared via chemical synthesis were uniform with diameters of 50-80 nm and lengths about 3-4 μm. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) reveal that the nanostructures are well oriented with the c-axis, perpendicular to the substrate. A relatively higher selectivity for 2, 4, 6-Trinitrotoluene (TNT) vapors compared to other VOCs at room temperature were observed. The intensity of deep level green emission peak associated with point defects decreases after exposure as revealed from Photoluminescence (PL) spectra.
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    Al-doped ZnO thin-film transistor embedded microcantilever as a piezoresistive sensor
    (AIP, 2013) Rao, V. Ramgopal
    In this work, an aluminium-doped zinc oxide (AZO) thin film transistor, embedded in a polymer micro-cantilever, is demonstrated for nano-mechanical sensing applications. This device senses the surface stress due to a change in the carrier mobility of the semi-conducting layer. Due to the low Young's modulus and high strain sensitivity of the AZO layer, this micro-cantilever shows a deflection sensitivity of 116 ppm per nanometer of deflection. Also, mechanical characterization of these devices shows that the resonance frequency is in the range of a few tens of kilohertz which is suitable for sensor applications.
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    Porphyrin induced changes in charge transport of graphene FET
    (IEEE, 2016) Rao, V. Ramgopal
    The transport properties of back-gated graphene field effect transistors (GFETs) can be tuned via chemical doping. In this study, we report alteration of charge transport properties of GFET via 5-(4-hydroxyphenyl)-10,15,20-tri-(p-tolyl) zinc(II) porphyrin (Zn(II)-TTPOH) and its free base counterpart. We propose that, the porphyrin induces p-type doping in graphene.
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    Application of Mono Layered Graphene Field Effect Transistors for Gamma Radiation Detection
    (IEEE, 2018-10) Rao, V. Ramgopal
    In this work, we report the application of graphene field effect transistors (GFETs) as a gamma radiation sensor. The GFETs were irradiated at room temperature by 60 Co gamma radiation source for 10 kGy and 20 kGy gamma dose. The Electrical measurements and Raman spectroscopy showed that gamma radiation induced p-doping in graphene. Large positive shifts in Dirac point and significant degradation in electron mobility were observed post-gamma irradiation. Thus modulation in transport properties of GFETs was utilized here to measure the absorbed gamma radiations. We propose, a GFET based radiation detector with high sensitivity of + 113 V for 20 kGy gamma dose operating in ambient condition.
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    MoS2 based nanomechanical bolometer for combined radiation sensing and the estimation of material properties
    (IEEE, 2023) Rao, V. Ramgopal
    Two-dimensional material-based bolometer sensors have unique optoelectronic properties. Here, a transparent and flexible bolometer and photodetector, based on MoS 2 is presented which measures radiation intensity via mechanical transduction and band gap transition. Three different cavity dimensions are fabricated to understand its effect on the bolometer performance. The fabricated devices are used to estimate the gauge factor (GF) and absorption coefficient of the material from the valley and peak data of current-time curves. The GF of 100 and absorption coefficient of 2×106 cm−1 is obtained for the MoS 2 on PDMS device. The work presented here is highly encouraging for the utilization of MoS 2 & PDMS in bolometers, thermal sensors and photodetectors.
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    Determining ionizing radiation using sensors based on organic semiconducting material
    (AIP, 2009-03) Rao, V. Ramgopal
    The use of organic semiconducting material sensors as total dose radiation detectors is proposed, wherein the change in conductivity of an organic material is measured as a function of ionizing radiation dose. The simplest sensor is a resistor made using organic semiconductor. Furthermore, for achieving higher sensitivity, organic field effect transistor (OFET) is used as a sensor. A solution processed organic semiconductor resistor and an OFET were fabricated using poly 3-hexylthiophene (P3HT), a p-type organic semiconductor material. The devices are exposed to Cobalt-60 radiation for different total dose values. The changes in electrical characteristics indicate the potential of these devices as radiation sensors.