Research

^{Nanomaterials-Sensor Laboratory}

Flexible Antennas and Devices for IoT application, Gas sensors and biosensors targeting environmental pollution, national security and energy security; microfabrication and materials characterization.

Google Scholar link: Dr. Praveen Sekhar

CPW Fed Wideband Bowtie Slot Antenna on PET Substrate

**Figure**: (a) Photograph of the printed antenna (b)Magnified SEM image. (c)Surface morphology (d) cross-section image of the printed pattern (obtained with 20μmscale)

The above antenna is a new wideband bowtie-shaped slot antenna is realized on a flexible polyethylene terephthalate (PET). The slotted bowtie design is implemented with an asymmetric bowtie flare angle and a larger feeding neck with a metal strip inside the bowtie slot to achieve a wider bandwidth and a higher gain. The designed free space antenna is fabricated using inkjet printing and tested. The fabricated antenna operates over 2.1–4.35 GHz frequency range (69.77% fractional bandwidth) which covers WLAN, WiMax, and most of the 3G and 4G frequency bands.

Flexible Antennas: A Review

The figure above shows various substrates for antenna prototypes on (a) polyethylene terephthalate (PET), (b) polyethylene naphthalate (PEN), (c) Polyimide, (d) liquid crystal polymer (LCP), and (e) paper substrates. used for recent flexible antenna research. Flexible antennas are fabricated using various conductive materials and substrates. The substrate is chosen based on its dielectric properties, tolerance to mechanical deformations (bending, twisting, and wrapping), susceptibility to miniaturization, and endurance in the external environment. In contrast, the selection of conductive material (based on electrical conductivity) dictates the antenna performance, such as radiation efficiency.

Inkjet Printing on a New Flexible Ceramic Substrate for Internet of Things (IoT) Applications
The image of the printed capacitor pattern on the ceramic substrate for high-temperature testing is shown in Figure below (a). After sintering the printed IDT capacitor, the measured capacitance value was found to be 46.5 pF (Figure below-b), indicating the electrical integrity of the IDT pattern. , the capacitance value was found to be 52.9 pF after the substrate cooled down, indicating the absence of any degradation when subjected to high temperatures. The increase in capacitance after the substrate was cooled is attributed to the temperature-dependent dielectric properties of the ceramic. The temperature was limited to 500 °C due to the presence of Ag ink. Device testing at higher temperatures is possible when high-temperature tolerant inks such as Pt is used.

**Figure:** High-temperature stability test results (a) Interdigitated capacitive pattern after sintering, (b) Measuring capacitance using LCR meter, (c) Heating on the hotplate at 500 °C, (d) Capacitive pattern after one-hour heating, and (e) Measuring capacitance using LCR meter after heating.

An Ink-jet Printed Flexible Monopole Antenna for Super Wideband Applications. This Circular flexible antenna is fabricated on a low cost and flexible PET substrate that makes this antenna suitable for SWB communication that includes ISM band, WiMAX, WLAN, UWB applications. It operates in a broad frequency bandwidth of 1.6 GHz to 56.1 GHz with a VSWR≤ 2. Due to the compact size and flexibility, this antenna can be used for medical applications, wearables, vehicular navigation system.

Electrochemical Gas Sensor Integrated with Vanadium Monoxide Nanowires for Monitoring Low Concentrations of Ammonia Emission. This flexible electrochemical sensor for the detection of extremely low concentration of ammonia (1 part per billion, ppb) was fabricated by integrating vanadium monoxide (VOx; x = 0.8–1.2) nanowires on the platinum electrodes. The nanowire-based sensor responds at room temperature non-linearly to a staircase sequence of ammonia from 1 ppb to 100 ppb. The picture shows the sensor during a bending test.

Early Brain Stroke Detection Using Flexible Monopole Antenna. The inkjet printed slotted disc monopole antenna is designed, printed, and analyzed at 2.45 GHz ISM band on a polyethylene terephthalate (PET) substrate for early detection of brain stroke. It exhibits 480 MHz (19.55%) bandwidth ranging from 2.25 GHz to 2.73 GHz frequency. This antenna can be placed on the head, and the reflected signals will be collated and processed by digital signal processing algorithms.

A CPW-fed flexible UWB antenna for IoT applications. This inkjet ultra-wideband (UWB) flexible antenna is printed on photo paper with silver nanoparticles ink. It operates over 3.2–30 GHz (161% fractional bandwidth, FBW) range with a return loss of – 10 dB or less and a voltage standing wave ratio (VSWR) < 2. Picture below was taken during printing utilizing Fujifilm’s Dimatix 2831 inkjet printer.

Trace Detection pf Pentaerythritol Tetranitrate Using Electrochemical Gas Sensors.