Coplanar Electrode Fluidic-Based Acoustic Sensing Method For Underwater Applications

Tesis ini mencadangkan kaedah penderiaan akustik berasaskan cecair untuk aplikasi bawah air. Mekanisme penderiaan yang dipilih adalah berdasarkan konsep kemuatan yang terhasil daripada elektrod koplanar. Struktur tersebut dicadangkan untuk mengatasi beberapa permasalahan yang timbul daripada peranti sediada iaitu Pemuat Mikromesin Transduser Ultrasonik. Isu kebolehbergantungan, disebabkan lengkungan membran yang berlebihan diatasi dengan menyuntik cecair di bawah lapisan membran bagi menambah nilai redaman ketika beroperasi di bawah tekanan luaran dan voltan yang tinggi. Penggunaan teknik litografi lembut untuk fabrikasi memberi kelebihan disebabkan proses yang lebih ringkas. Kaedah penderiaan ini dibuktikan melalui kitaran lengkap yang terdiri daripada proses pemodelan, fabrikasi dan pengujian. Dimensi struktur mematuhi kriteria yang ditetapkan seperti teori lengkungan membran dan teori penembusan kedalaman. Ujian akhir menunjukkan kebolehan peranti untuk mengesan isyarat akustik 200kHz yang dipancarkan melalui peranti bawah air dengan bacaan sensitiviti sebanyak 0.67pF/Pa. Kesan persekitaran seperti getaran pada frekuensi rendah (10Hz to 100Hz) dan perubahan suhu (-20 ̊C to 30 ̊C) juga didapati tidak memberi kesan terhadap operasi peranti. Ini menujukkan kestabilan peranti untuk berfungsi pada keadaan tertentu. ________________________________________________________________________________________________________________________ The thesis proposed a novel fluidic-based acoustic sensing method for underwater applications. The capacitive principles based on coplanar electrodes configuration is selected as the sensing mechanism. The new structure device was proposed to overcome several issues faced by the conventional device based on Capacitive Micromachined Ultrasonic Transducer (CMUT) by adapting the microfluidic technology. Reliability issues caused by the over deflected membrane was overcame by introducing the liquid backing material underneath the membrane which increases the damping at high operating voltage and high external pressure. The use of softlitography technique for fabrication also gave an advantage due to its process simplicity. The sensing concept was proven through a development cycle which consists of modelling, fabricating and testing. The structural design had satisfied several design rules such as membrane deflection theory as well as penetration depth theory. The final testing showed the ability of the device to detect 200kHz acoustic signal transmitted from the underwater acoustic projector with capacitive pressure sensitivity of 0.4 fF/Pa. It was also found that the constant frequency vibration (10Hz to 100Hz) and change of temperature (-20 ̊C to 30 ̊C) has minimal effect on the sensing performance, thus showcased the stability of the sensor

Low-cost colorimetric setup for concentration measurement of manganese ions based on optical absorbance

This study presents a cost-effective setup for measuring the concentration of Mn2+ ions using colorimetry. The current method involves a calibration curve created with expensive and large commercial laboratory-based instruments, limiting its use in financially constrained situations. To address this issue, the study proposes a low-cost setup consisting of a light-emitting diode and photodiode that utilizes colorimetric and absorbance effects for Mn2+ concentration measurement. Mn2+ colorimetric samples were prepared using the 1-(2-pyridylazo)-2-naphthol (PAN) method with concentrations ranging from 0.2 to 1.0 mg/L. The samples were tested using the proposed setup, followed by a spectrophotometry test to determine the optimal configuration for the setup. The validity of the setup was confirmed by measuring the voltage and calculating the optical absorbance, which exhibited a good correlation with the concentration, consistent with the initial expectation. The correlation coefficient for voltage and absorbance against Mn2+ concentration was found to be 0.9976 and 0.9987, respectively, indicating good linearity and suitability as a calibration curve for Mn2+ detection and measurement. Consequently, the study’s objectives were successfully achieved, and the proposed setup is considered a viable platform for more complex applications, such as real-time monitoring activities

Analytical Analysis of Flexible Microfluidic Based Pressure Sensor Based on Triple-Channel Design

In designing a flexible microfluidic-based pressure sensor, the microchannel plays an important role in maximizing the sensor's performance. Similarly, the material used for the sensor's membrane is crucial in achieving optimal performance. This study presents an analytical analysis and FEA simulation of the membrane and microchannel of the flexible pressure sensor, aimed at optimizing it design and material selection. Different types of materials, including two commonly used polymers, Polyimide (PI) and Polydimethylsiloxane (PDMS) were evaluated. Moreover, different designs of the microchannel, including single-channel, double-channel, and triple-channel, were analyzed. The applied pressure, width of the microchannel, and length of the microchannel were varied to study the normalized resistance of the microchannel and maximize the performance of the pressure sensor. The results showed that the triple-channel design produced the highest normalized resistance. To achieve maximum performance, it is found that using a membrane with a large area facing the applied pressure was optimal in terms of dimensions. In conclusion, optimizing the microchannel and membrane design and material selection is crucial in improving the overall performance of flexible microfluidic-based pressure sensors

The potential of shear wave velocity as an erosion risk index

Soil erosion is a captious environmental problem in regions of hot tropical climates, causing loss of land and natural disasters such as river sedimentation, flooding, and slope failures. Based on soil properties and their response to erosion agents, efforts have been made to develop simplified models and indices for the estimation of erosion. ROM scale is proven to be effective in forecasting risk levels for erosion assessment. However, the method requires soil sampling and laboratory experimentation, which is time-consuming and laborious, especially when analyzing huge areas. Therefore, this study aims to develop a relation between ROM scale and shear wave velocity estimated by the spectral-analysis-of-surface-waves (SASW) method. For this purpose, 36 soil samples were extracted, and twelve SASW tests were conducted at twelve sites identified along Sungai Langat. Soil particle distribution was carried out to calculate the ROM erosion index value for all the extracted soil samples. The fast Fourier Transform (FFT) algorithm was used to transform the time-recorded signals into the frequency domain, and the dispersion curves were generated after the masking process. The shear wave velocity erosion risk ranged from 10 m/s to 120 m/s, indicating critical risk and low risk, respectively. Low erosion risk levels were observed for high shear wave velocity values, representing a decaying pattern in exponential relation. The resulting correlation between ROM scale and shear wave velocity produced a coefficient of determination value of 0.71, indicating a strong relation. This study indicated the potential of shear wave velocity as an erosion risk index

Alteration in the functional organization of the default mode network following closed non-severe traumatic brain injury

The debilitating effect of traumatic brain injury (TBI) extends years after the initial injury and hampers the recovery process and quality of life. In this study, we explore the functional reorganization of the default mode network (DMN) of those affected with non-severe TBI. Traumatic brain injury (TBI) is a wide-spectrum disease that has heterogeneous effects on its victims and impacts everyday functioning. The functional disruption of the default mode network (DMN) after TBI has been established, but its link to causal effective connectivity remains to be explored. This study investigated the differences in the DMN between healthy participants and mild and moderate TBI, in terms of functional and effective connectivity using resting-state functional magnetic resonance imaging (fMRI). Nineteen non-severe TBI (mean age 30.84 ± 14.56) and twenty-two healthy (HC; mean age 27.23 ± 6.32) participants were recruited for this study. Resting-state fMRI data were obtained at the subacute phase (mean days 40.63 ± 10.14) and analyzed for functional activation and connectivity, independent component analysis, and effective connectivity within and between the DMN. Neuropsychological tests were also performed to assess the cognitive and memory domains. Compared to the HC, the TBI group exhibited lower activation in the thalamus, as well as significant functional hypoconnectivity between DMN and LN. Within the DMN nodes, decreased activations were detected in the left inferior parietal lobule, precuneus, and right superior frontal gyrus. Altered effective connectivities were also observed in the TBI group and were linked to the diminished activation in the left parietal region and precuneus. With regard to intra-DMN connectivity within the TBI group, positive correlations were found in verbal and visual memory with the language network, while a negative correlation was found in the cognitive domain with the visual network. Our results suggested that aberrant activities and functional connectivities within the DMN and with other RSNs were accompanied by the altered effective connectivities in the TBI group. These alterations were associated with impaired cognitive and memory domains in the TBI group, in particular within the language domain. These findings may provide insight for future TBI observational and interventional research

Simulasi airbumi bagi akuifer cetek pesisir pantai di Lembangan Sungai Kelantan

Penekanan terhadap teknik simulasi aliran airbumi adalah penting sebelum model simulasi digunakan dalam meramalkan perubahan turus airbumi. Teknik menjana model simulasi perlulah melalui prosedur-prosedur seperti menentukur, analisis sensitiviti dan pengesahan sebelum ia digunakan sebagai alat ramalan perubahan turus airbumi. Beberapa andaian dan permudahan perlu dibuat kerana dalam membina model simulasi seperti keadaan di lapangan adalah sukar untuk dilaksanakan. Model simulasi yang digunakan adalah “Aquifer Simulation Model for WINdows� (ASMWIN) yang menggunakan persamaan beza terhingga aliran airbumi dalam bentuk dua dimensi bagi akuifer tak terkurung. Keputusan ramalan simulasi airbumi pada tahun 2050 menunjukkan hampir kesemua paras turus airbumi di setiap loji di daerah Kota Bharu akan berada di bawah kedudukan teratas skrin terutamanya pada musim kering. Kajian ini dapat membantu pihak bertanggungjawab dalam merancang pengurusan air pada masa akan datang dengan lebih berkesan

Variance of total dissolved solids and electrical conductivity for water quality in Sabak Bernam

Water pollution is one of the most serious environmental problems in Malaysia. The most notable occurrence of pollution happened in Selangor. Currently, there are various water quality monitoring (WQM) methods to observe the quality of water. One of the methods used is the internet of things (IoT) for wireless sensor network technology to obtain real-time data measurement. In this study, the developed WQM system is equipped with a sensor that can measure total dissolved solid (TDS) and electrical conductivity (EC). Arduino UNO was used in this system as a microcontroller to interact with the sensor. The Wi-Fi module, ESP8266, was used to transfer the collected data to ThingSpeak, which acts as a cloud to store all the data. The results showed that both sample populations can be discriminated since the p-value is greater than 0.05 in the normality test, while in the paired sample t-test, the p-value is less than 0.05. In conclusion, this research provides an easier way to monitor water quality by taking up less time at less cost, as well as being reliable in giving real-time data reading

Enhancement of piezoelectric micromachined ultrasonic transducer using polymer membrane for underwater applications

533-539An effort to enhance receiving response of piezoelectric micromachined ultrasonic transducers (pMUT) at low frequency was reported. PMUTs were fabricated with the vibrating membrane formed by a layer of polydimethylsiloxane (PDMS) polymer. Lead zirconate titanate, Pd (Zt,Ti)O3 (PZT) was utilized as the piezo-active layer, sputtered with nickel electrodes. Spin coating and low temperature wafer bonding were proposed as part of the key fabrication methods. Fabricated transducers were characterized in the compact acoustic tank setup using 500 kHz and 1.25 MHz reference projectors. Analyses revealed the maximum receiving response was -36.6 dB re 1V of 200 kHz burst at 10 λ hydrophone-projector separations and 20 V peak to peak of drive voltage on reference projector. Finally, response spectrum of the transducer was plotted against two commercialized bulk hydrophones at equivalent frequency band for validation and comparison

Implementation of a Single Emulsion Mask for Three-Dimensional (3D) Microstructure Fabrication of Micromixers Using the Grayscale Photolithography Technique

Three-dimensional (3D) microstructures have been exploited in various applications of microfluidic devices. Multilevel structures in micromixers are among the essential structures in microfluidic devices that exploit 3D microstructures for different tasks. The efficiency of the micromixing process is thus crucial, as it affects the overall performance of a microfluidic device. Microstructures are currently fabricated by less effective techniques due to a slow point-to-point and layer-by-layer pattern exposure by using sophisticated and expensive equipment. In this work, a grayscale photolithography technique is proposed with the capability of simultaneous control on lateral and vertical dimensions of microstructures in a single mask implementation. Negative photoresist SU8 is used for mould realisation with structural height ranging from 163.8 to 1108.7 µm at grayscale concentration between 60% to 98%, depending on the UV exposure time. This technique is exploited in passive micromixers fabrication with multilevel structures to study the mixing performance. Based on optical absorbance analysis, it is observed that 3D serpentine structure gives the best mixing performance among other types of micromixers