Mohd Norzaidi Mat Nawi

Characterization of Microfluidic-Based Acoustic Sensor for Immersion Application

This paper reported the characterization study on a new type of acoustic microsensor meant for immersion or underwater application. The new proposed device is based on microfluidic technology that is found to be able to overcome the fabrication issues associated with conventional capacitive micromachined ultrasonic transducer device. The design parameters have been explained in detail as well as their design justification. In this paper, two experiments have been setup to characterize the device performance. First, the pulse catch technique was used to investigate the devices response toward acoustic pulse or burst signal. The result shows that different number of burst cycles affects the capacitive response of the device. Providing the acoustic projector with suitable burst cycle parameter had yielded capacitive response with resolution of 1.16 pF, which is useful to be deployed in any suitable application such as for control or communication purposes. Second, the vibration effect had been studied between the ranges of 10-100 Hz of vibration. For rapid transition of the vibration frequency, the fall transition has a comparable error compared with the rise transition with an error ratio of 37:1. In terms of fluctuation behavior of the response, operating the device at static or constant frequency vibration does not have significant differences on the response, indicating its stability at single-frequency operation.

One-Side-Electrode-Type Fluidic-Based Capacitive Pressure Sensor

This paper presents the development of a novel one-side-electrode-type fluidic-based capacitive pressure sensor. A pressure sensor using a one-side-electrode and an implementation of electrical double layer capacitance concept was proposed. Mechanical analysis of the membrane was carried out using the finite-element analysis in terms of deflection and Mises stress. A sensor with a circular membrane radius of 3.2 mm, membrane thickness of 0.8 mm, microchannel thickness of 0.5 mm, and microchannel width of 0.5 mm was fabricated using polydimethylsiloxane. The validation was made between the analytical and experimental results for fluid mechanisms inside the sensor. This showed that the displacement for all types of liquid, including methanol, ethanol, and silicon oil was linearly aligned. Methanol was chosen as an electrolyte due to its liquid properties, such as low surface tension and dielectric permittivity. From the experimental results, the operating frequency, response time, and sensitivity of the sensor were 1.2 kHz, 0.12 s, and 0.77 pF/kPa, respectively. The effects of vibration, temperature, and lifetime were also discussed in this paper.

Validation of Finite Element Model (FEM) of Coplanar Electrodes Capacitive Sensing Using Microfluidic-based Sensor Device

This work aims to validate the 2D Finite Element Model (FEM) for estimating the capacitance changes across a microchannel with coplanar electrodes configuration employed. Such electrodes configuration becomes popular in microfluidic-based application where the sensing activity occurs inside a microchannel. ANSYS 12.1 is used to built the 2D model of the structure. The work begin by building the FEM model to find the capacitance per unit length, C/l or C* of different combination of coplanar structures. The variation yields an error of less than 17% as compared to analytical equation with both models having the same trend of capacitance changes. Then, based on the theory of capacitance in parallel, both models are further verified experimentally using a fabricated sensor device that employs a selected structure combination. Comparing the FEM and analytical model to the experimental measurement, the result shows the error of 5% and 24% for both models, respectively.

Numerical simulation of the microchannel for the microfluidic based flow sensor

Microfluidic technology has given major contribution to the advancement of the sensor especially in the development of microchannel. Previously, we proposed the design structure consist of microchannel which is integrated with dome-shaped container and electrode. The underwater flow sensor generally used in aqua robotic and underwater vehicle for the monitoring and surveillance. The fluid flow gives drag force to the dome-shaped which resulting some displacement and causes the liquid inside the microchannel moving. In this paper, the performance of microchannel had been simulated and discussed in order to optimize the microchannel based on the variation of height and the selection of liquid. The computational fluid dynamic (CFD) FLUENT software was used for the simulation of microchannel. From the CFD, the velocity profile has been analyzed for under and fully develop region to study the fluid flow behavior. The velocity for variation microchannel height 300μm until 1100μm was plotted where the channel with large dimension has an advantage in order to make the fluid flow smooth. In order to achieve the small scale of sensor, we limited the channel size to 400μm. Another factor that influences the fluid flow inside the microchannel is properties of liquid. A few liquids such as methanol, ethanol, water and propylene carbonate were selected. The important property we consider in selection of the right liquid is the surface tension where is it related to the kinematic viscosity. From the simulation, we prove that the liquid that having lowest kinematic viscosity and low surface tension such as methanol is have better performance than another liquid for sensing purpose.

Fabrication of PDMS Dome-Shaped Membrane and its Performance Analysis Using FEA for Fluidic Based Flow Sensor

The dome-shaped membrane was designed for the fluidic based flow sensor for the underwater sensing. It has the diameter of 5mm and thickness within 0.2mm. The simple fabrication process for the dome shaped structure was demonstrated using casting and molding processes. The effect of the fabrication process was investigated by measuring the thickness of the dome-shaped membrane for different sample. For the performance analysis, the actual shape which was the same with the fabricated shaped was simulated and compared with the ideal shape using finite element analysis for the same input flow rate. The membrane sensitivity of the actual shape decreased from 163.4 μm/ms-1 to 133.33 μm/ms-1 compared to the ideal shape based on the displacement of the membrane over input fluid velocity.

Fluidic based multidirectional flow sensor inspired from artificial cupula

The fluidic based multidirectional flow sensor inspired from artificial cupula was presented in this paper. It is consists of dome-shaped membrane, microchannel and one-side electrode with implementation of electrical double layer capacitor as a sensing element. The PDMS with ratio 20:1 was selected as a material because it is suitable to be implemented as a membrane. The micro-stamping technique for fabrication of dome-shaped membrane was proposed where the uniform thickness of membrane can be achieved. The operating frequency of the sensor using methanol was 1.5 kHz. The flow measurement was done by using water channel which flow rate 10 to 40 cm/s was applied with the resolution of 5 cm/s. The directionality tests for flow direction and angle also were carried out and it is proved that the sensor was able to detect the flow in omnidirectional directions.

Fabrication Techniques for PDMS Dome-Shaped Membrane Using Soft Lithography Process

The dome-shaped membrane is very important part of the micro/nano devices. The dome-shaped with the thickness of 150 μm and a radius of 3.2 mm was fabricated using the soft lithography process. The Polydimethylsiloxane (PDMS) was selected as a material because it deformable and suitable to implement as a membrane. Soft lithography is based on pattern transfer using a mold that is patterning the substrate material. In this paper, two techniques were suggested to fabricate the dome-shaped membrane which are reflow technique and stamping technique. The comparison was made for both techniques using a Scanning Electron Microscope (SEM) and it seems the stamping technique has an advantage where the uniform thickness of the dome-shaped membrane can be achieved. The discussion on the temperature effect of a stamping technique shows that the suitable temperature to harden the PDMS is in temperature room where the bubbles can be eliminated under this temperature.

A novel of fluidic based one side electrode type pressure sensor

This paper presents the development of the novel fluidic based one side electrode pressure sensor. The structure of the sensor consists of container and an electrode. For the container, the membrane and microchannel were combined in one structure. Meanwhile, the design of the electrode was extended from the pattern of coplanar electrode based on the previous study. The microfluidic technology by using a small amount of liquid as a sensing element was proposed to measure the external pressure. When the external pressure was applied to the sensor, the membrane was deflected and the liquid displaced inside the microchannel. The sensing electrode measured the changes using electrical double layer concepts and gave the output in capacitance. The sensor was successfully fabricated for electrode using printed circuit board (PCB) process and the container using polymer fabrication process. The polymer such as PDMS was chosen because it was suitable to be implemented as a membrane. The methanol was used as a liquid due to its dielectric constant. The data experiment was recorded and measured using LCR meter for different applied pressure. The capacitance response was demonstrated for pressure 2kPa until 30kPa. The sensitivity of the sensor was 0.06pF/kPa. Also, the standard deviation of output capacitance equaled to 0.04.

Finite element analysis of characteristic array SU-8 based hair cell and cantilever beam for artificial lateral line flow sensor

This paper presents the analysis of modeling for artificial lateral line flow sensor. An artificial hair cell sensor is the current technology that based on a biological inspiration and widely used in underwater applications including glider, robotic and autonomous surface vehicle (ASV). The structure of the lateral line flow sensor is consisting of cantilever beam and four hair cells attached perpendicular to the cantilever beam at the free end. The lateral line sensor with different height of hair cells are modeled and simulated with water flow rate 0 m/s to 1 m/s. High sensitivity is achieved by increasing a hair cells length and use low young modulus material for a cantilever beam. The maximum stress was analyzed in order to identify the limitation of the sensor.