Active Noise Cancellation for Underwater Environments
Noise can interfere activities both on land and in the underwater environment. In this research we propose a noise cancellation system using ANC (Active Noise Control) techniques to reduce acoustic noise signal using Raspberry Pi, to receive an amplitude and phase of the noise signal, calculate each sampled signal using normalised least means square (NLMS), and finally it will produce a replica of the transmitled noise by shifting the phase noise at 180°, through the speaker in real-time environment so that the signal noise can be reduced and decrease.
The system is designed using Matlab and Simulink, the model is compiled for Raspberry Pi board as the hardware target. Raspberry Pi is a small computer so it make a system more efficient. The experimentation results shows that ANC can work in an optimal mode in delay=5 and filter length=64 and can reduce noise level until 0,894 dB in underwater environment and maximal reduction level in 2 Khz frequency. The system can influence in around the system and reduce the signal level about 1,97 dB in 10 cm depth, and 1,02 dB in 40 cm depth.
Autonomous Underwater Vehicle
The problem of power and communication limitation in underwater environment makes it more challenge to increase the degree of autonomy and intelligence for an autonomous underwater vehicle (AUV).
In this research, we propose a new approach of decentralized system environment for AUV simulation using Matlab and CORBA event channel coexistence on several machines, we believe it will emerge more investigation how the real-time control system performance could be reconfigured easily both in semi-automatically or manually interventions by a remote station.
Despite a number of results presented here, we believe it will emerge more investigation in the current trends of real-time control system or bilateral control system area, with GA to adding the system intelligent processing to find out the proper weighting matrices.
Upcoming research in this fields should be directed to considering the problems in implemented system modeling and developing appropriate methodologies to uncover the effective CORBA programming to support Matlab and CORBA event channel coexistence that will be affected to increase the degree of real-time reconfigurable control significantly.
Furthermore, in this research we will design an AUV hull with a specific shape with the intention that can deflect and absorb high-frequency electromagnetic waves emitted from RADAR uses RAM from polymer composite materials reinforced with carbon fiber reinforcement polymeric (CFRP). Furthermore, RAM is used to make composite materials with electromagnetic wave absorbent powder is added, the mixture composition can be effectively adjusted by adjusting the percentage of absorbent powders are tailored to the nature and characteristics of the electromagnetic wave frequency to be absorbed. All ingredients and materials used in making this RAM comes from domestic materials and materiality, which sought to obtain results with acceptable tolerances.
AUV body structure is composed of two parts, namely the hull inner hull and outer hull, with a structure using materials RAM, RAS, and AAM. The hull is composed of a material of RAM that works not only as a bearing structure and sustain the system, but also has an important role in absorbing the electromagnetic waves coming from an ASW tracking system at high frequencies. While the outer hull is a RAS that functions as a protective wall aerodynamically shaped angled to deflect and absorb electromagnetic waves from RADAR. While the AAM has an important role in absorbing acoustic wave ASW tracking system at low frequencies.
The NRL Arch is the industry standard for testing the reflectivity of materials. Originally designed at the Naval Research Laboratory, the NRL Arch allows for quick, repeatable non-destructive testing of microwave absorbent materials over a wide frequency range.
Reflectivity is defined as the reduction in reflected power caused by the introduction of an absorbent material. This reduction in power is compared to a ‘perfect’ reflection which is approximated very well by the reflection off a flat metallic plate.
As seen in the figure above, a customized NRL arch consists of a transmit and receive antenna which are oriented towards a metal plate. To measure normal incidence reflectivity the antennas are located as close to each other as physically possible. Absorbent material is often used to minimize antenna cross talk. The antennas can be located anywhere on the arch to allow measurements of performance at off normal angles of incidence with the practical limitation of the ability to separate the signal from the material under test from the direct antenna to antenna cross talk.
In the figure above shows the measurement results of electromagnetic wave reflection from several type of RAM, include the 1 mm thick of Aluminum plate as reference.
Absorbers are used to eliminate electromagnetic energy. In free space they do so by presenting an impedance to an incoming wave equal to the impedance of free space (377 Ω). At a material interface, the incident, reflected and refracted waves must obey the boundary condition that the sum of E and H fields of the waves must be continuous.
From the test results showed that the RAM with multilayer configurations is able to absorb an electromagnetic wave around 10 dB, and it reflect completely over 30degree.
We measure several type of RAMs, which are R157TL900, R157DL900, R157SL1000, R157SL900, include the 1 mm thick of Aluminum plate as reference. From measurement results, absorption of R157TL900 has highest absorptions result compare with others, because we use 3 layer of absorber. For a single layer absorber comparison, a characteristic of R157SL1000 is better than R157SL900.
