Conference Agenda

MAST Med 2022 Grand Hyatt, Central Athens, Greece

Thu 3 Nov 2022

11:30 Thu 3 Nov 2022


3B: Undersea

Critical Undersea Sensors

Next Gen Synthetic Aperture Sonar for A18M AUV (UMISAS)

  • Mrs Fanie Bernard
    Communication Officer

UMISAS is a next generation Synthetic Aperture Sonar (SAS) which will equip the A18-M AUV developed for the Belgian-Netherland Mine Countermeasures Forces. The presentation will highlight the unique design features of the sonar which make it one of the best side-looking sonars available on the market, using widely accepted criteria such as image resolution, area coverage rate, signal to noise ratio etc. The sonar arrays are built using state-of-the art wideband piezo-composites. In order to minimize noise pickup, the signals from the 256 channels of the port and starboard interferometric array assemblies are digitized directly in their respective array housings, using low power consumption A/Ds driven by FPGAs. The unique feature of the sonar array design is the simultaneous use of two frequency bands, VHF and HF, in order to maximize the signal-to-noise ratio even in harsh environments, such as shallow waters characterized by high levels of multipathing, or warm waters, where the sound absorption is very high. Thus the sonar source level is 219dB which exceeds that of currently available SAS by more than 8dB (>600% power increase). Another key feature of the SAS is the real-time image formation on a Jetson Xavier GPU with a total power consumption lower than 30Watts. This performance is achieved using a very efficient and accurate proprietary SAS image formation algorithm which is massively parallelized on the GPU. This low power consumption allows the A18-M to conduct survey missions in excess of 20 hours. The accurate positioning required for SAS operation is obtained by combining the outputs of the navigation grade inertial navigator PHINS from Ixblue, which is synchronized with the SAS, with a unique 3D velocity vector estimate derived from the SAS data itself. The performance achieved with the system as well as that foreseen by planned future upgrades will be given.

Hybrid Piezoelectric Hydrophones for Underwater ISR (Intelligence, Surveillance, Reconnaissance)

  • Mr. Angelos Tsereklas
    Managing Director
    SOTIRIA Technology

In this paper the development of hydrophones able to acoustically detect underwater threats (e.g. UUVs, submarines, divers) is illustrated. At the first place, the development of hydrophones using hybrid piezoelectric films, consisting of Ba1-xPbxTiO3 on top of bronze wafers was realized. Pb was added to decrease the development of cracks. Additionally, commercially available PZT (Pb[ZrxTi1-x]O3 (0=x=1)) hybrid films on top of bronze wafers were also used as the sensing elements of the hydrophones.

These hydrophones were developed using these two different types of sensing elements. For each sensing element, cables were soldered on the wafer metal and the piezoelectric film. A Plexiglass enclosure was manufactured using additive manufacturing, allowing for the sensing elements to be hosted inside. Finally, the entire system was covered with liquid rubber sealant to secure its waterproofness.

Finally, these transducers have been tested by submerging them into a tank filled with water consisting of 3% salt, each one facing directly the other at a distance of a few centimeters. One of the devices was used as a speaker and the other one as a receiver. The voltage at the input of the speaker was kept at 10Vpp and then the response at the output of the receiver was examined through the oscilloscope, for frequencies from 0.1Hz to 200 kHz. The response of the home-made Ba1-xPbxTiO3 hydrophone offered 3db cut-off frequencies at about 1Hz and 100kHz respectively, while the response of the commercially available PZT hydrophone offered a 3db cut-off frequency at 10Hz and 90kHz respectively.

Fluxgate Magnetometers and Artificial Intelligent Algorithms for Underwater ISR (Intelligence, Surveillance, Reconnaissance)

  • Mr. Angelos Tsereklas
    Managing Director
    SOTIRIA Technology

In this paper, a fluxgate magnetometer with sensitivity and range at pTHz-1/2 and 1mT levels, respectively, is presented. It is based on the orthogonal fluxgate operation with the addition of dc bias in the periodical excitation to overcome Barkhausen and magnetostrictive noise. The sensing core is an amorphous wire, used after either thermal annealing and consequent magnetic annealing with the annealing field along the magnetization axis, or stress current annealing. Using this type of sensor, a submarine of average displacement can be captured at an extended range compared to the current state of the art magnetic and acoustic benchmarks.

Furthermore, algorithms for the detection of submarines in significantly longer distances have also been tried. For this reason, an array of fluxgates is required, set at a distance of orders of magnitude larger than the longest dimension of the submarine, that offers data usable for algorithms based on artificial intelligence. In fact, the simulated employment of orthonormal basis function (OBF) decomposition methods and the implementation of Gram-Schmidt orthonormalization method resulted in the detection of the magnetic dipole of the submarine in distances longer than 150% the sensor’s range.

The combination of such an array of fluxgates with the use of the mentioned algorithm may well be used for the development of a magnetic anomaly detection (MAD) system to detect the position and direction of submarines.

Evaluating Sonar Target Strength: Novel Approach With Asymptotic Numerical Methods

  • Mr. Giacomo Bertolotto
    System Engineer
    Fincantieri S.p.A.

Knowing the sonar Target Strength of own naval platform (ship or submarine) has always been an element of primary importance for the safe planning of the mission by the command teams.

While there are measurement sites for the electromagnetic signature (RCS) of large objects, such as ships, which allow the validation of the results obtained with Electromagnetic SW prediction methods, in the underwater environment due to the great variability of the environmental conditions it is particularly difficult perform sonar Target Strength (TS) measurements except on scale models in controlled environments.

Therefore, it is important to have reliable methods to calculate the sonar Target Strength: the equivalent of the Radar Cross Section (RCS) in the EM domain.

This paper describes a novel method to calculate the TS for objects with fully reflective acoustic characteristics, using the asymptotic solver included in the CST EM Studio Suite, highlighting which relationships between EM and the acoustic environment must be considered to obtain consistency of the results.

The results of a first phase of validation are presented and relevant points to be explored for the modeling of the acoustic characteristics of the materials used in the construction are highlighted.

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