Jimmy Ching-Ming Chen

Microwave Gas Sensor based on Graphene-loaded Substrate Integrated Waveguide Cavity Resonator

In this paper, novel microwave gas sensors based on graphene-loaded substrate integrated waveguide (SIW) cavity resonators are presented. Two SIW-based cavity resonators, a ring-slot resonator and a complementary split ring resonator (CSRR), are fabricated and coated with chemical vapor deposited (CVD)-grown graphene. The fabricated graphene contains a layer of polymethyl methacrylate (PMMA) on its top. The graphene sheets exhibit high sensitivity to various kinds of polar and non-polar gases. When polar gas contacts the graphene sheet, it will donate or receive electrons, thereby changing its conductance. The SIW cavities thus perform a resonant frequency shift from the perturbation of electron exchange. In the experiment, a frequency shift of 59 MHz and 157 MHz for the SIW ring-slot resonator and CSRR, respectively, can be observed after pure ammonia gas is injected into a closed chamber filled with air at standard atmospheric pressure and temperature. This work demonstrates a very simple and efficient gas sensing scheme in the microwave regime. The proposed devices are promising to be further integrated with RF front-ends, providing a low cost and high sensitive gas sensing and environmental monitoring solution.

A novel fabrication method of carbon electrodes using 3D printing and chemical modification process

Three-dimensional (3D) printing is an emerging technique in the field of biomedical engineering and electronics. This paper presents a novel biofabrication method of implantable carbon electrodes with several advantages including fast prototyping, patient-specific and miniaturization without expensive cleanroom. The method combines stereolithography in additive manufacturing and chemical modification processes to fabricate electrically conductive carbon electrodes. The stereolithography allows the structures to be 3D printed with very fine resolution and desired shapes. The resin is then chemically modified to carbon using pyrolysis to enhance electrochemical performance. The electrochemical characteristics of 3D printing carbon electrodes are assessed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The specific capacitance of 3D printing carbon electrodes is much higher than the same sized platinum (Pt) electrode. In-vivo electromyography (EMG) recording, 3D printing carbon electrodes exhibit much higher signal-to-noise ratio (40.63 ± 7.73) than Pt electrodes (14.26 ± 6.83). The proposed biofabrication method is envisioned to enable 3D printing in many emerging applications in biomedical engineering and electronics.

In-situ monitor electrochemical processes in batteries using vibrating microcantilevers

In this paper, we propose a novel in-situ technique to characterize electrochemical processes in lithium ion batteries (LIB) by monitoring the frequency shift of microcantilevers. The fabricated cantilevers coated with battery electrodes were tested in a home made liquid cell, and their mass changes associated with SEI formation and lithium insertion were monitored by a laser vibrometer. The resonant frequency of cantilevers before cycling was 18,400Hz and shifted to 16,800Hz after lithiation. The initial mass of the cantilever before cycling was measured 45.35 μg. Therefore, the lithium stored in the silicon anode during the first lithiation was estimated 7.89μg.

Metamaterial leaky wave antenna enabled efficient 3D spectrally-encoded microwave tomography using linear sampling method

The linear sampling method (LSM) is an effective method to detect complicated structures in a short time. In this paper, we develop a novel kind of LSM by means of metamaterial (MTM) leaky wave antennas (LWAs) to conduct spectrally-encoded three-dimensional (3D) microwave tomography that can reconstruct a conductive target with coaxial multi-layer and various diameter cylinders. The unique frequency-space mapping feature of MTM LWAs enables an efficient 3D microwave imaging with a larger field of view compared with conventional LSM approaches that usually operate at one single frequency. Validated through both theoretical analysis and experimental results, the proposed MTM imaging scheme allows us to reconstruct 3D shapes effectively with minimal prior knowledge of the target and computational resources. Furthermore, the measured results verify the proposed imaging method by successfully detecting the unknown targets with different shapes and locations for the MTM LWAs operating at 1.8–3 GHz.

3D remote sensing based on frequency scanning metamaterial antenna array using linear sampling method

This paper presents a novel approach for linear sampling method (LSM) to conduct remote sensing for radar applications, such as automotive radar sensors, by incorporating frequency mapping antenna array based on metamaterial leaky wave antennas (MTM-LWAs). Unlike traditional LSM using only one single frequency to illuminate in a certain direction, the proposed approach utilizes a frequency scanning MTM antenna array to perform frequency-space mapping over the targeted three dimensional (3D) background that includes unknown objects, resulting in a significantly increased field-of-view (FOV). The information obtained from the frequency-space scanning scheme is then transferred to the LSM analysis to detect the locations and shapes of the unknown objects. The proposed novel frequency scanning scheme in combination with LSM serves as an efficient 3D remote sensing scheme without the use of any phase shifters.