Qi Tang

Bio: Qi Tang is an academic researcher from University of Arizona. The author has contributed to research in topics: Metamaterial & Antenna (radio). The author has an hindex of 7, co-authored 23 publications receiving 127 citations. Previous affiliations of Qi Tang include Facebook.

Microfluidic Devices for Terahertz Spectroscopy of Live Cells Toward Lab-on-a-Chip Applications

Abstract: THz spectroscopy is an emerging technique for studying the dynamics and interactions of cells and biomolecules, but many practical challenges still remain in experimental studies. We present a prototype of simple and inexpensive cell-trapping microfluidic chip for THz spectroscopic study of live cells. Cells are transported, trapped and concentrated into the THz exposure region by applying an AC bias signal while the chip maintains a steady temperature at 37 °C by resistive heating. We conduct some preliminary experiments on E. coli and T-cell solution and compare the transmission spectra of empty channels, channels filled with aqueous media only, and channels filled with aqueous media with un-concentrated and concentrated cells.

Stability Analysis of Non-Foster Circuit Using Normalized Determinant Function

Abstract: Non-Foster elements are highly desired to overcome the bandwidth limit of electrically small antennas, cloaking, and metamaterials. However, they are prone to be unstable and thus it is quite challenging to implement non-Foster circuits in practice. Hence a rigorous and effective method of analyzing the stability should always be the priority when designing a non-Foster network. This paper applies normalized determinant function to analyze the stability of non-Foster circuits. A floating-version negative capacitor based on Linvill’s negative impedance converter is taken as the example. Factors affecting the stability in the practical design are thoroughly investigated, including device parasitics, dc biasing, distributed transmission line in the layout and load impedance. Circuit parameters are substituted with practical values to reduce the complexity of calculation. Finally, experiments are conducted to verify the analysis.

11-Gbps Broadband Modem-Agnostic Line-of-Sight MIMO Over the Range of 13 km

Abstract: A modem-agnostic Line-of-Sight (LoS) MIMO system, which performs MIMO processing in analog domain, can be retrofitted to any kind of single-input-single-output (SISO) digital modems to further increase spectral efficiency and data- rate. We show that two of the enabling technologies for broadband analog MIMO processing over several GHz bandwidth are: (1) precise signal delay compensation using continuously tunable delay line and (2) operating analog MIMO equalization at high RF intermediate frequency. Based on these two principles, we design and implement a 2×2 LoS MIMO system that supports MIMO processing of up to 1.6 Gbaud 64-QAM signal. The channel interference can be reduced lower than −25 dB over the entire signal spectrum after MIMO equalization. We demonstrate an indoor 2×2 LoS MIMO link of 16.7 Gbps with each channel carrying 1.6 Gbaud 64 QAM and an outdoor MIMO link of 11.1 Gbps over the range of 13 km with each channel carrying 1.6 Gbaud 16-QAM signal at millimeter-wave (MMW) frequency of 85 GHz.

Stability analysis and parasitic effects of negative impedance converter circuits

Abstract: Stability is a major obstacle preventing practical applications of negative impedance converters (NIC) such as electrically small antenna matching. Return ratio method with a mesh or nodal analysis in frequency domain can provide an insight of the overall stability and performance of a NIC. This paper studies the stability of two types of NICs, based on tunneling diode and cross-coupled pair MOSFET. The influence of device capacitances, load impedance, and bias network are discussed.

A Survey on Millimeter-Wave Beamforming Enabled UAV Communications and Networking

Abstract: Unmanned aerial vehicles (UAVs) have found widespread commercial, civilian, and military applications. Wireless communication has always been one of the core technologies for UAV. However, the communication capacity is becoming a bottleneck for UAV to support more challenging application scenarios. The heavily-occupied sub-6 GHz frequency band is not sufficient to meet the ultra high-data-traffic requirements. The utilization of the millimeter-wave (mmWave) frequency bands is a promising direction for UAV communications, where large antenna arrays can be packed in a small area on the UAV to perform three-dimensional (3D) beamforming. On the other hand, UAVs serving as aerial access points or relays can significantly enhance the coverage and quality of service of the terrestrial mmWave cellular networks. In this paper, we provide a comprehensive survey on mmWave beamforming enabled UAV communications and networking. The technical potential of and challenges for mmWave-UAV communications are presented first. Then, we provide an overview on relevant mmWave antenna structures and channel modeling. Subsequently, the technologies and solutions for UAV-connected mmWave cellular networks and mmWave-UAV ad hoc networks are reviewed, respectively. Finally, we present open issues and promising directions for future research in mmWave beamforming enabled UAV communications and networking.

A Techno-Economic Framework for Satellite Networks Applied to Low Earth Orbit Constellations: Assessing Starlink, OneWeb and Kuiper

Abstract: The emergence of Low Earth Orbit (LEO) satellite systems has been seen as a potential solution for connecting remote areas where engineering terrestrial infrastructure is prohibitively expensive. Despite the hype, we still lack an open-source modeling framework for assessing the techno-economics of satellite broadband connectivity which is therefore the purpose of this paper. Firstly, a generalizable techno-economic model is presented to assess the engineering-economics of satellite constellations. Secondly, the approach is applied to assess the three main competing LEO constellations which include Starlink, OneWeb and Kuiper. This involves simulating the impact on coverage, capacity and cost, as both the number of satellites and quantity of subscribers increases. Finally, a global assessment is undertaken visualizing the potential capacity and cost per user via different subscriber scenarios. The results demonstrate how limited the capacity will be once resources are spread across users in each satellite coverage area. For example, for 0.1 users per km2 (so 1 user per 10 km2), we estimate a mean per user capacity of 24.94 Mbps, 1.01 Mbps and 10.30 Mbps for Starlink, OneWeb and Kuiper, respectively, in the busiest hour of the day. But if the subscriber density increases to 1 user per km2, then the mean per user capacity drops significantly to 2.49 Mbps, 0.10 Mbps and 1.02 Mbps. LEO broadband will be an essential part of the connectivity toolkit, but the results reveal that these mega-constellations will most likely have to operate below 0.1 users per km2 to provide a service that out-competes other broadband connectivity options.

Terahertz Microfluidic Metamaterial Biosensor for Sensitive Detection of Small-Volume Liquid Samples

Abstract: Metamaterial (MM) assisted terahertz (THz) label-free biosensing has promising applications. However, the sensitive THz detection of highly absorptive liquid samples remains challenging. Here, we present a novel multi-microfluidic-channel MM biosensor for highly sensitive THz sensing of small-volume liquid samples. The multichannels are set mostly in the strong electric field enhancement area of the MM, which significantly decreases the liquid's amount and enhances the interaction between the sensing targets and the THz wave (thus increasing the sensitivity). The sensing results of isopropyl-alcohol–water mixtures and bovine serum albumin solutions based on the bow-tie array MM with multichannels demonstrate the effectiveness of the proposed design and the great potential in THz biosensing. This design has the advantages of being highly sensitive, label-free, cost-effective, easy to operate, and only needing a tiny liquid volume. Thus, our device provides a robust route for MM-assisted THz label-free biosensing of liquid-based substances.

Microfluidic Devices for Terahertz Spectroscopy of Live Cells Toward Lab-on-a-Chip Applications

Abstract: THz spectroscopy is an emerging technique for studying the dynamics and interactions of cells and biomolecules, but many practical challenges still remain in experimental studies. We present a prototype of simple and inexpensive cell-trapping microfluidic chip for THz spectroscopic study of live cells. Cells are transported, trapped and concentrated into the THz exposure region by applying an AC bias signal while the chip maintains a steady temperature at 37 °C by resistive heating. We conduct some preliminary experiments on E. coli and T-cell solution and compare the transmission spectra of empty channels, channels filled with aqueous media only, and channels filled with aqueous media with un-concentrated and concentrated cells.