Miniaturized planar capacitance tomography system using fan beam projection technique for stagnant samples visualization

Abstract

Miniaturized device is an approach by integrating the laboratory function into small platform. These miniaturized devices are equipped with sensors or actuators to perform sensing, sample preparation or analysis and is well known as lab-on-chip (LOC) since 1990. The conventional miniaturized device available in the market normally provides single dimensional (1D) data at a time in most micro analysis processes. In order to obtain images from the device, cameras and microscopes are normally used. However, the size and tubing intact on the device make it difficult for cameras or optical devices to be placed within the reaction chamber to capture images that are related to the process. Processes such as cell detection and environmental analysis sometimes require two dimensional (2D) images in order to enhance the quality of analysis and data accuracy. Therefore, this research proposes to integrate tomography technique within the miniaturized device for capturing images within the device chamber in order to replace bulky optical equipment. Tomography system has been widely used in medical and industrial processes for image reconstruction. This research integrates Electrical Capacitance Tomography (ECT) system within a miniaturized device for visualization of stagnant samples via planar electrodes. This miniaturized planar tomography system consists of electrode array for the measurement of dielectric property changes within the chamber. This miniaturized device consists of 8-planar electrodes circulating the detection chamber where the dimension of each of the electrodes are 4 mm × 2 mm (length × width) printed on the circuit board. A home-made polydimenthylsiloxane chamber is fabricated and adhered on top of the electrodes to position the sample for electrical measurement and image reconstruction. Fan beam projection technique is utilized for data measurement from the miniaturized planar capacitive tomography system. The obtained data are processed using Linear Back Projection (LBP) algorithm via Matlab package for image reconstruction. Three samples: liquid-liquid, liquid-gas and liquid-solid are studied. Electrical measurement using fan beam projection is carried out and images of the samples are successfully reconstructed via LBP. Based on the obtained results, the error percentage for multiphase sample of water and air is 25% while 14.77% for solid sample of yeast and glucose. The obtained results show that the qualities of acquired images are highly depending on the voltage differences between each measurement. The amount of volume between the two materials affects the measured voltage differences. The nearer the samples to the planar electrode, the voltage differences observed are more significant. The reconstructed images using miniaturized planar capacitive tomography system for all the samples show good similarity to the camera captured images.