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Nonreciprocity in space-time modulated photonic crystals has been investigated in the context of nonreciprocal propagation and polarization. Here, we investigate a reconfigurable nonreciprocal wave growth in space-time modulated crystals. Imposing an adaptable progressive phase shift between successive time-modulated cells results in blue and red shifts of the forward and backward momentum band gaps around the typical 0.5 growth normalized frequency. We applied this spatiotemporal scheme to engineering the dispersion relation of a loaded transmission line$-$a 1D periodic structure$-$in the microwave regime.

When an electromagnetic (EM) wave is propagating in a medium whose properties are varied abruptly in time, the wave experiences refractions and reflections known as "time-refractions" and "time-reflections", both manifesting spectral translation as a consequence of the abrupt change of the medium and the conservation of momentum. However, while the time-refracted wave continues to propagate with the same wave-vector, the time-reflected wave is propagating backward with a conjugate phase, despite the lack of any spatial interface. Importantly, while time-refraction is always significant, observing time-reflection poses a major challenge - because it requires a large change in the medium occurring within a single cycle. For that reason, time-reflection of EM waves was observed only recently. Here, we present the observation of microwave pulses at the highest frequency ever observed (0.59 GHz), and the experimental evidence of the phase-conjugation nature of time-reflected waves. Our experiments are carried out in a periodically-loaded microstrip line with optically-controlled picosecond-switchable photodiodes. Our system paves the way to the experimental realization of Photonic Time-Crystals at GHz frequencies.

We investigate and simulate signal amplification in a transmission line (TL) with time-modulated characteristic impedance Zo. Periodically varying $Z_o$ is achieved by loading TL with a sinusoidally time-modulated capacitor (TMC). For a detailed study, three models are considered: a lossless L-C TL lumped model loaded with shunt infinite quality factor (Q) TMC, a TL loaded with a shunt infinite Q TMC, and finite Q TMC. By solving the eigenvalue problem in all models, dispersion diagrams (DD) are plotted with a created momentum band gap (MBG) at a modulation frequency double the signal frequency. Within MBG, only imaginary frequencies are found and correlated to MBG width and signal growth level. Using Harmonics Balance (HB) and Transient Simulation (TS), signal amplification is confirmed, and the obtained results are consistent with the DD outcomes. In the second model, the effect of TL length on amplification is investigated and explained by studying the unit cell's Bloch impedance. The loss effect is considered by adding a series resistance (Rc) to the third model's TMC (finite Q). Decreasing amplification levels, confirmed by circuit modeling, due to the increase of Rc value is explained by studying real and imaginary DDs and the attenuation constant.

High-power interferers are one of the main hurdles in wideband communication channels. To that end, this paper presents a wideband interferer detection method. The presented technique operates by sampling the incoming signal as an input, and produces the frequency and the power readings of the detected interferer. The detection method relies on driving an open circuit stub, where the voltage is proportional to the power of the interferer, and the standing wave pattern is an indicator of its frequency. This approach is feasible over multi-octave bandwidth with a wide power dynamic range. The concept is analyzed for design and optimization, and a prototype is built for a proof-of-concept. The measured results demonstrate the ability to detect an interferer within the 1--16 GHz frequency range, with a power dynamic range between -20 to 20 dBm. The detection concept is also fitted with different types of tunable bandstop filters (BSFs) for automatic detection and suppression of the interferer if its power exceeds a programmable threshold. With a measured response time of 500 ns, the presented method is a technology enabler for wideband receivers.

This paper presents a low-loss optically-controlled inline RF switch suitable for L- and S-band applications. Under 1.5 W laser power, the switch exhibits a measured ON-state insertion loss of less than 0.33 dB and return loss better than 20 dB across the band. The measured OFF-state isolation ranges from 27 dB at 1 GHz to 17 dB at 4 GHz. The switch comprises a single silicon chiplet excited by a 915-nm laser fiber which creates electron-hole pairs, thereby exciting the ON-state silicon plasma. An optical fiber is guided through the bottom of the RF substrate to illuminate the chiplet, which bridges a 1.075-mm microstrip line gap. To the best of our knowledge, this is the lowest-loss silicon plasma switch demonstrated today., Comment: 4 pages, 5 figures, to be published in IEEE Wireless and Microwave Technology Conference (WAMICON), 2021

This paper introduces a new technology for a high-speed, high-power mobile form-factor tuner utilizing gas discharge tube plasma cells as switching components. To the best of our knowledge, this represents the first plasma-enabled RF matching network. Technology development is reviewed, the fabrication and measurement of a proof-of-concept switched stub impedance tuner are presented, and techniques for improvement are discussed. The proof-of-concept impedance tuner functions with a 27% bandwidth from 3 to almost 4 GHz and shows a power gain better than -2.5 dB across all switching state-frequency combinations at a 50 W input power level with spread coverage of the Smith chart. State change transient timing is measured to be on the order of 500 ns. This technology demonstration highlights the potential of miniaturized, rapidly-tunable, high-power, plasma-based RF devices., Comment: 4 pages, 7 figures, published in IEEE Wireless and Microwave Technology Conference (WAMICON), 2021

This paper presents the design and analysis of a wearable CMOS biosensor with three different designs of energy-resolution scalable time-based resistance to digital converters (RDC), targeted towards either minimizing the energy/conversion step or maximizing bit-resolution. The implemented RDCs consist of a 3-stage differential ring oscillator which is current starved with the resistive sensor, a differential to single ended amplifier, an off-chip counter and serial interface. The first design RDC included the basic structure of time-based RDC and targeted low energy/conversion step. The second design RDC aimed to improve the rms jitter/phase noise of the oscillator with help of speed-up latches, to achieve higher bit-resolution as compared to the first design RDC. The third design RDC reduced the power consumption by scaling the technology with the improved phase-noise design, achieving 1-bit better resolution as that of the second design RDC. Using a time-based implementation, the RDCs exhibit energy-resolution scalablity, and consume 861nW with 18-bit resolution in design 1 in TSMC 0.35um technology. Design 2 and 3 consume 19.1uW with 20-bit resolution using TSMC 0.35um, and 17.6uW with 20-bit resolutions using TSMC 0.18um, respectively (both with 10ms read-time, repeated every second). With 30ms read-time, design 3 achieves 21-bit resolution, which is the highest resolution reported for a time-based ADC. The 0.35um time-based RDC is the lowest-power time-based ADC reported, while the 0.18um time-based RDC with speed-up latch offers the highest resolution. The active chip-area for all 3-designs are less than 1.1 mm^2., Comment: 12 pages, 16 figures

Kapton HN films, adopted worldwide due to their superior thermal durability (up to 400 {\deg}C), allow the high temperature sintering of nanoparticle based metal inks. By carefully selecting inks and Kapton substrates, outstanding thermal stability and anti-delaminating features are obtained in both aqueous and organic solutions and were applied to four novel devices: a solid state ion selective nitrate sensor, an ssDNA based mercury aptasensor, a low cost protein sensor, and a long lasting organic thin film transistor (OTFT). Many experimental studies on parameter combinations were conducted during the development of the above devices. The results showed that the ion selective nitrate sensor displayed a linear sensitivity range with a limit of detection of 2 ppm. The mercury sensor exhibited a linear correlation between the RCT values and the increasing concentrations of mercury. The protein printed circuit board (PCB) sensor provided a much simpler method of protein detection. Finally, the OTFT demonstrated a stable performance with mobility values for the linear and saturation regimes, and the threshold voltage. These devices have shown their value and reveal possibilities that could be pursued.

The recent advancement of the Internet of Things (IoT) enables the possibility of data collection from diverse environments using IoT devices. However, despite the rapid advancement of low-power communication technologies, the deployment of IoT networks still faces many challenges. In this paper, we propose a hybrid, low-power, wide-area network (LPWAN) structure that can achieve wide-area communication coverage and low power consumption on IoT devices by utilizing both sub-GHz long-range radio and 2.4 GHz short-range radio. Specifically, we constructed a low-power mesh network with LoRa, a physical-layer standard that can provide long-range (kilometers) point-to-point communication using custom time-division multiple access (TDMA). Furthermore, we extended the capabilities of the mesh network by enabling ANT, an ultra-low-power, short-range communication protocol to satisfy data collection in dense device deployments. Third, we demonstrate the performance of the hybrid network with two real-world deployments at the Purdue University campus and at the university-owned farm. The results suggest that both networks have superior advantages in terms of cost, coverage, and power consumption vis-\`a-vis other IoT solutions, like LoRaWAN.

Decades of continuous scaling has reduced the energy of unit computing to virtually zero, while energy-efficient communication has remained the primary bottleneck in achieving fully energy-autonomous IoT nodes. This paper presents and analyzes the trade-offs between the energies required for communication and computation in a wireless sensor network, deployed in a mesh architecture over a 2400-acre university campus, and is targeted towards multi-sensor measurement of temperature, humidity and water nitrate concentration for smart agriculture. Several scenarios involving In-Sensor-Analytics (ISA), Collaborative Intelligence (CI) and Context-Aware-Switching (CAS) of the cluster-head during CI has been considered. A real-time co-optimization algorithm has been developed for minimizing the energy consumption in the network, hence maximizing the overall battery lifetime of individual nodes. Measurement results show that the proposed ISA consumes ~467X lower energy as compared to traditional Bluetooth Low Energy (BLE) communication, and ~69,500X lower energy as compared with Long Range (LoRa) communication. When the ISA is implemented in conjunction with LoRa, the lifetime of the node increases from a mere 4.3 hours to 66.6 days with a 230 mAh coin cell battery, while preserving more than 98% of the total information. The CI and CAS algorithms help in extending the worst-case node lifetime by an additional 50%, thereby exhibiting an overall network lifetime of ~104 days, which is >90% of the theoretical limits as posed by the leakage currents present in the system, while effectively transferring information sampled every second. A web-based monitoring system was developed to archive the measured data in a continuous manner, and to report anomalies in the measured data., Comment: 15 pages with author info, 18 figures