Yuqiao Liu

A Multi-Disciplinary Framework for Continuous Biomedical Monitoring Using Low-Power Passive RFID-Based Wireless Wearable Sensors

We have applied passive Radio Frequency Identification (RFID), typically used for inventory management, to implement a novel knit fabric strain gauge assembly using conductive thread. As the fabric antenna is stretched, the strength of the received signal varies, yielding potential for wearable, wireless, powerless smart-garment devices based on small and inexpensive passive RFID technology. Knit fabric sensors and other RFID biosensors can enable comfortable, continuous monitoring of biofeedback, but requires an integrated framework consisting of antenna modeling and fabrication, signal processing and machine learning on the noisy wireless signal, secure HIPAA- compliant data storage, visualization and human factors, and integration with existing medical devices and electronic health records (EHR) systems. We present a multidisciplinary, end-to-end framework to study, model, develop, and deploy RFID-based biosensors.

An improved design of wearable strain sensor based on knitted RFID technology

In this study, we built a lumped component model for knit tag antennas. Comfortable, seamless, and wireless antennas were manufactured using conductive yarns and RFID technology. Knitting fabrication enabled rapid prototyping of these wearable antennas. Using the lumped component model, we optimized the geometry and knit structure of the antenna, resulting in improved radiation efficiency, reading range, and sensitivity.

Innovative propagation mechanism for inter-chip and intra-chip communication

SoC (System on chip) technology has rapidly developed in recent years, stimulating emerging research areas such as investigating the efficacy of wireless network interconnection within a single chip or between multiple chips. However the design of the on-chip antenna faces the challenge of obtaining high radiation efficiency and transmission gain due to conductive loss of the silicon substrate. A new on-chip propagation mechanism of radio waves, which takes advantage of the un-doped silicon layer, is developed in order to overcome this challenge. It was found that by properly designing the dimension of silicon wafer, the un-doped silicon layer is able to act like a waveguide. Most of the energy is directed to the approximately lossless the undoped silicon layer of high resistivity instead of attenuating in the doped silicon substrate or radiating to the air. HFSS modeling and simulation results are provided to show that efficiency, gain and directivity of the on-chip antenna are greatly improved. In addition, this type of antennas can be easily reconfigured, which as a result, makes wireless SoCs with wireless interconnects or even a wireless network on PCB (Printed Circuit Board) possible.

Wireless NoCs Using Directional and Substrate Propagation Antennas

Wireless Network-on-Chip (WNoCs) are introduced to improve the performance for long distance communication within a chip. The on-chip antennas utilized in these WNoCs can be omni-directional or bi-directional, broadcasting to every receiving antenna or directional only in a specific pairing, respectively. There are positives and negatives for both types of antennas, although bi-directional antennas that do not cross paths have the added benefit of decreasing the possibility of interference. This work analyzes the performance of a WNoC with bi-directional antennas that uses an innovative substrate propagation technique recently introduced in literature. Antennas that use substrate propagation are capable of longer distance communication compared to typical on-chip antennas that use surface propagation. It is shown that by using the substrate propagation technique, wireless NoCs with minimal bi-directional antennas can reduce the number of wireless nodes by 66% while achieving similar performance of within ±5% of throughput.

2D titanium carbide (MXene) for wireless communication

Flexible 100-nm-thick antennas are made by one-step spray coating of metallic 2D titanium carbide MXene. With the development of the Internet of Things (IoT), the demand for thin and wearable electronic devices is growing quickly. The essential part of the IoT is communication between devices, which requires radio-frequency (RF) antennas. Metals are widely used for antennas; however, their bulkiness limits the fabrication of thin, lightweight, and flexible antennas. Recently, nanomaterials such as graphene, carbon nanotubes, and conductive polymers came into play. However, poor conductivity limits their use. We show RF devices for wireless communication based on metallic two-dimensional (2D) titanium carbide (MXene) prepared by a single-step spray coating. We fabricated a ~100-nm-thick translucent MXene antenna with a reflection coefficient of less than −10 dB. By increasing the antenna thickness to 8 μm, we achieved a reflection coefficient of −65 dB. We also fabricated a 1-μm-thick MXene RF identification device tag reaching a reading distance of 8 m at 860 MHz. Our finding shows that 2D titanium carbide MXene operates below the skin depth of copper or other metals as well as offers an opportunity to produce transparent antennas. Being the most conductive, as well as water-dispersible, among solution-processed 2D materials, MXenes open new avenues for manufacturing various classes of RF and other portable, flexible, and wearable electronic devices.

A Miniaturized Reconfigurable CRLH Leaky-Wave Antenna Using Complementary Split-Ring Resonators

Composite Right-/Left-Handed (CRLH) Leaky-Wave Antennas (LWAs) are a class of radiating elements characterized by an electronically steerable radiation pattern. The design is comprised of a cascade of CRLH unit cells populated with varactor diodes. By varying the voltage across the varactor diodes, the antenna can steer its directional beam from broadside to backward and forward end-fire directions. In this paper, we discuss the design and experimental analysis of a miniaturized CRLH Leaky-Wave Antenna for the 2.4 GHz WiFi band. The miniaturization is achieved by etching Complementary Split-Ring Resonator (CSRR) underneath each CRLH unit cell. As opposed to the conventional LWA designs, we take advantage of a LWA layout that does not require thin interdigital capacitors; thus we significantly reduce the PCB manufacturing constraints required to achieve size reduction. The experimental results were compared with a nonminiaturized prototype in order to evaluate the differences in impedance and radiation characteristics. The proposed antenna is a significant achievement because it will enable CRLH LWAs to be a viable technology not only for wireless access points, but also potentially for mobile devices.

Computational electromagnetic simulation and performance analysis of reconfigurable antennas for outdoor 60 GHz applications

A number of measurement based studies have demonstrated that adaptive steering of highly directional antenna beams can overcome higher path loss of signals at millimeter wave (mmW) frequencies. In this paper, we present a novel 60 GHz pattern reconfigurable antenna capable of steering its beams in both the azimuth and the elevation directions. The performance of this steerable antenna is evaluated via ray tracing simulations of an urban city model. In both the line of sight (LOS) and non line of sight (NLOS) scenarios, the proposed antenna outperforms a conventional omni-directional antenna in terms of received power and delay spread characteristics.

Design and implementation of the Secondary User-Enhanced Spectrum Sharing (SUESS) radio

This paper describes our design and proof-of-concept implementation of the Secondary User-Enhanced Spectrum Sharing (SUESS) radio that dynamically observes, understands, learns, plans, and adapts its spectrum sharing behaviors in an operating band that is shared with a noncooperative Primary User (PU) radio link. The SUESS radio leverages awareness of the PUs performance to drive the selection and adaptation of three spectrum coexistence mechanisms that include the Electromagnetic (EM), Physical (PHY), and Medium Access Control (MAC) protocol layers. Our goal is to design and build a prototype of a software-defined cognitive radio that maximizes throughput of the SUESS radio link while minimizing performance impact to a PU link in a shared RF operating band at short separation distances.

Wireless Network-on-Chip analysis of propagation technique for on-chip communication

Network-on-Chip (NoC) is a communication paradigm capable of facilitating a scalable interconnection infrastructure for multi core processors. Wireless NoCs have been introduced to improve the communication performance over long-distance processing nodes. Current on-chip antennas used in wireless NoCs communicate predominantly through surface waves, where the efficacy of the wireless nodes is partially determined by the radiation efficiency and transmission gain limited due to the conductivity loss of the silicon substrate. Recently, an on-chip propagation technique of radio waves was introduced, through the un-doped silicon layer as opposed to surface-waves prevalent in literature. The through-substrate propagation waves provide a unique solution to overcome the challenge of long-distance communication between processing nodes. In this work, overall improvements are shown compared to traditional wireless NoCs with the placement of antennas on undoped silicon (i.e. communicating through surface waves), simulated in NoC architectures across performance metrics of area, power consumption and latency.