Hong Siang Chua

Left-Handed Metamaterial Coplanar Waveguide Components and Circuits in GaAs MMIC Technology

A set of novel left-handed LH) basic block monolithic-microwave integrated-circuit (MMIC) components (transmission line, open and short stubs) are presented with applications to the RF/microwave filter and power divider. These new open and short LH MMIC resonators have compact sizes of 0.11 and 0.22 mm2, respectively. The prototypes of an LH bandpass filter and LH power divider constructed from these basic components have been designed, fabricated, and characterized. The LH filter consisting of an LH transmission line and four LH open resonators exhibits transmission zeros at both sides of the passband from 1.02 to 1.42 GHz with 33.3% fractional bandwidth. The LH power divider including two LH branches shows equal power split from 2.8 to 3.72 GHz. The filter and power divider benefit from the miniaturized LH MMIC components and have compact sizes of 2.85 and 2.3 mm2, respectively. Loss issues of these LH structures and, more importantly, the effect of skin depth at low frequency are investigated. Full-wave simulations for conductor thicknesses of 0.2, 1.4, and 5 mum are presented for the proposed LH MMIC components and circuits. There is a good agreement between the full-wave simulations, equivalent-circuit model, and measurement results with 1.4-mum metal thickness demonstrating the effectiveness of the models.

Integrated miniature fluorescent probe to leverage the sensing potential of ZnO quantum dots for the detection of copper (II) ions

Quantum dots are fluorescent semiconductor nanoparticles that can be utilised for sensing applications. This paper evaluates the ability to leverage their analytical potential using an integrated fluorescent sensing probe that is portable, cost effective and simple to handle. ZnO quantum dots were prepared using the simple sol-gel hydrolysis method at ambient conditions and found to be significantly and specifically quenched by copper (II) ions. This ZnO quantum dots system has been incorporated into an in-house developed miniature fluorescent probe for the detection of copper (II) ions in aqueous medium. The probe was developed using a low power handheld black light as excitation source and three photo-detectors as sensor. The sensing chamber placed between the light source and detectors was made of 4-sided clear quartz windows. The chamber was housed within a dark compartment to avoid stray light interference. The probe was operated using a microcontroller (Arduino Uno Revision 3) that has been programmed with the analytical response and the working algorithm of the electronics. The probe was sourced with a 12 V rechargeable battery pack and the analytical readouts were given directly using a LCD display panel. Analytical optimisations of the ZnO quantum dots system and the probe have been performed and further described. The probe was found to have a linear response range up to 0.45 mM (R(2)=0.9930) towards copper (II) ion with a limit of detection of 7.68×10(-7) M. The probe has high repeatable and reliable performance.

Terahertz time-domain spectroscopy of crushed wheat grain

The terahertz time-domain spectroscopy (THz-TDS) is used to measure absorption spectra in crushed wheat grain over the frequency range of 0.1-2.0 THz. A number of well resolved absorption peaks are observed for dry, 12%, 14% and 18% moisture content levels. Subtracting the transmission signal spectra of the dry flour from that of the wetted flour provides a calibrated result which relates attenuation to moisture content level.

Terahertz time-domain spectroscopy of wheat grain

In this paper, we used the terahertz time-domain spectroscopy (THz-TDS) system to measure spatially-resolved absorption spectra in crushed wheat grain over the frequency range 0.1-4.0 THz. PTFE sheet was used as a suitable material for the sample holder to measure the absorption spectra of whole-wheat grain and crushed wheat grain with 8%, 12% and 18% moisture content.

Medical Image Authentication Using DPT Watermarking: A Preliminary Attempt

Secure authentication of digital medical image content provides great value to the e-Health community and medical insurance industries. Fragile Watermarking has been proposed to provide the mechanism to authenticate digital medical image securely. Transform Domain based Watermarking are typically slower than spatial domain watermarking owing to the overhead in calculation of coefficients. In this paper, we propose a new Discrete Pascal Transform based watermarking technique. Preliminary experiment result shows authentication capability. Possible improvements on the proposed scheme are also presented before conclusions.

Fully Integrated Broadband CPW Left-Handed Metamaterials Based on GaAs Technology for RF/MMIC Applications

A fully integrated broadband coplanar waveguide left-handed metamaterial medium using GaAs technology for radio frequency/monolithic microwave integrated circuit (RF/MMIC) applications is reported and validated by the full wave simulation and measured results. The unit cell of the fabricated structures has a size of 0.09 mm2. The left handedness of the integrated left-handed structure extends from 2.3 to 17.5 GHz. The compactness and broad left-handed operating bandwidth make the presented left-handed metamaterial be well incorporated with RF/MMIC applications.

An Instrument to Measure the Characteristics of Single Wheat Grain Kernels

This paper describes an instrument, based on microwave techniques and a gas displacement method, to measure the wet mass, moisture content, volume and hence the density of single wheat grain kernels. A low-cost microwave source and detector is designed to drive a microwave cavity to determine the wet mass and moisture content of the grain. The microwave cavity is compactly integrated with the volume meter to combine the measurements into a single assembly with one loading cycle. The loading mechanism is separated from two novel gas compression bellows to improve the accuracy and stability of this measurement. All of the results are processed using a microcontroller. The measured wet mass, moisture content, volume and density of the grain are shown on an LCD display

An Overview of Microwave Techniques for the Efficient Measurement of Food Materials

There is critical demand for rapid, low-cost methods to determine food composition to provide a responsive control mechanism and an efficient quality control system in food processes. Four non-destructive microwave techniques used to measure the relative complex permittivity (e*) of food components are reviewed. The open-ended coaxial probe is found to be quick and effective for broadband measurements of liquids and pastes. Narrowband waveguide cells require careful sample preparation but they provide accurate permittivity measurements for solids, particulates and liquids. The resonant cavity method provides a high Q measurement at a single frequency and is suitable for low loss samples that can be inserted into the resonator. For scanning and conveyer belts we describe a horn antenna, free-space transmission line method. Each method is described and real examples are demonstrated for the characterisation of a range of foodstuffs.

Microwave based wheat grain kernel characterisation

A low-cost microwave source and detector is designed to drive a microwave cylindrical cavity to determine the wet mass and moisture content of single wheat grain kernels. Differences in wet mass and moisture content can be distinguished from the changes in resonant frequency and attenuation. Moisture content (8% to 16%) of single wheat grain kernels was measured. Experimental results are presented and the calibration equations are implemented in a microcontroller. Wet mass and moisture content are shown on an LCD display on the microcontroller. The measurement procedure and evaluation of the system are presented in the proposed paper.

Event recognition in parking lot surveillance system

This paper presents a novel event recognition framework in video surveillance system, particularly for parking lot environment. An event is represented by feature vector that contains dynamic information and the contextual information of the motion trajectory is incorporated into the recognition process. Experimental results have demonstrated great accuracy of the proposed event recognition algorithm.