Rabiul Hasan

We present a new palladium-based nanogap hydrogen sensor designed for fast, low-concentration H₂ detection in environmental monitoring applications. The device consists of a long electrically-conductive low-stress palladium cantilever beam separated by a nanometer-sized air gap from a second cantilever beam of different length placed near the first beam tip thus forming a H₂-dependent capacitor. The cantilevers are anchored on top of a thermally-isolated SiN membrane with an integrated microheater that maintains the sensor at constant temperature. When exposed to H₂, the capacitor nanogap is reduced resulting in a change in capacitance with H₂ sensitivity $S_{\mathrm {H2}} =0.15$ fF/ppm. The sensor shows a consistent response up to $55~^{\circ }$ C with a thermal drift smaller than 0.22 aF/^oC and a minimum detectable signal of 10 ppm. The device repeatability was confirmed across 5 consecutive test cycles. Selectivity tests show negligible response to common interfering gases CO, CO₂, CH₄, water vapor and NH₃ ( $S_{i}\lt 5.2\times 1{0}^{-6}$ fF/ppm). The sensor exhibited a response time of approximately 390 ms upon exposure to H₂.[2025-0141]

We present a novel mid-infrared spectrometer that operates within the spectral range of 3-5 μm range for atmospheric gas measurements without the assistance of a vacuum. This spectrometer utilizes an array of silicon microbolometers, each with a different overlapping broad spectral response. Each microbolometer features a suspended silicon nitride platform, a polysilicon thermistor, and an infrared absorber layer all positioned above platinum mirror. By utilizing this membrane-based microbolometer, the device achieved a 10-fold increase in response when compared to regular substrate-based microbolometer at an average of 45,000 V/W responsivity, allowing for a heightened detectivity of 2.49 x 10 ⁸ cm√Hz/W. The spectrum of the incoming radiation is obtained computationally from the bolometer array collective response via regularization methods, thus eliminating the need for costly narrowband IR filters. Additionally, the device’s gas detection capability was validated with CO ₂ and CO gas testing, both of which exhibit significant absorption within the expected 3-5 μm mid-infrared region.

We demonstrate the realization of a very low energy, on-the-eye vergence-type distance ranger based on sensing of a locally-uniform vector field, specifically the earth’s magnetic field. This ranging method is passive, only requiring measurement of the magnetic field vector at both eyeballs utilizing magnetometer chips placed on the eye scleral regions. The eye vergence angle and range distance are calculated from these two vector quantities. The method can obtain a range reading with as little as 118 nJ of energy consumed per eye for 3.3V and 50 nJ when operated at 1.9V. This method is thus suitable for applications where energy storage is very limited such as in smart contacts vision correcting microsystems.

The field of flexible antennas is witnessing an exponential growth due to the demand for wearable devices, Internet of Things (IoT) framework, point of care devices, personalized medicine platform, 5G technology, wireless sensor networks, and communication devices with a smaller form factor to name a few. The choice of non-rigid antennas is application specific and depends on the type of substrate, materials used, processing techniques, antenna performance, and the surrounding environment. There are numerous design innovations, new materials and material properties, intriguing fabrication methods, and niche applications. This review article focuses on the need for flexible antennas, materials, and processes used for fabricating the antennas, various material properties influencing antenna performance, and specific biomedical applications accompanied by the design considerations. After a comprehensive treatment of the above-mentioned topics, the article will focus on inherent challenges and future prospects of flexible antennas. Finally, an insight into the application of flexible antenna on future wireless solutions is discussed.

This study proposes a coplanar waveguide‐fed circular monopole antenna that is designed by ink‐jetting conductive silver particle ink on photo paper. The antenna comprises a slotted circular patch and a reduced symmetrically slotted ground plane that is etched rectangularly. The slotted circular patch and ground plane provide the design flexibility with a broad bandwidth, substantial gain over 1.66–56.1 GHz frequency band, and relatively consistent radiation pattern. The fractional bandwidth (%BW) of this antenna is 188.5% that is covering industrial, scientific, and medical (ISM) bands, ultra‐wideband, wireless local area network (WLAN) band, worldwide interoperability for microwave access (WiMAX) band, and various frequencies of upcoming fifth‐generation technology. The total size of the antenna is only 34 × 25 mm ² , with an electrical dimension of 0.18 λ × 0.13 λ at 1.66 GHz. The bandwidth ratio (BR) is 33.81:1, and the bandwidth dimension ratio (BDR) is 7462, which is the highest among the flexible super‐wideband antennas reported so far. It is a low profile, lightweight, and low‐cost antenna that is accommodating a broad frequency spectrum for extended wideband communication. The measured results show good agreement with the simulations.