Query: Janus-Helmholtz underwater transducer

title: Design and fabrication of a piezoelectric micromachined ultrasound transducer (pMUT) array for underwater communication
abstract: This paper presents the design, fabrication, and characterization of a pMUT array to be used in underwater sensor networks. A 1 mm Lead Zirconate Titanate (PZT) layer was used as the piezoelectric material. The array consists of 8x8 pMUT elements with a diameter of 410 mm and Si thickness of 6 mm. The fabricated array generates 1360 Pa/V 1 cm underwater with a resonance frequency of 204 kHz, which has a transient response time of 100 ms, after which the ringing amplitude decays to 5% of the maximum value. This makes it possible to transmit 17.8 kbit/s by OOK modulation.

title: A Compact Array Transducer for Full Calibration of Underwater Acoustic Detection Neutrino Telescopes
abstract: KM3NeT, the underwater neutrino telescope in the Mediterranean Sea, is a detector under construction. KM3NeT uses Digital Optical Modules (DOMs) to detect neutrinos but there will be a study about the viability to acoustic detection of neutrinos using mainly the acoustic sensors the telescope has for positioning purposes. For this, it is necessary to calibrate and test the acoustic response of the receivers in the detector to determine the sensitivity to detect the neutrino acoustic signal and discriminate it from the environmental background. In this work, the strategy for the calibration of the sensor system using a compact array using three steps (frequency, directivity and neutrino signal like) is described. Moreover, some R D activities and results about the second step (long parametric directive signals) are shown.

title: Obtaining 3D High Resolution Underwater Acoustic Images by Synthesizing Virtual Aperture on the 2D Transducer Array of Multibeam Echo Sounder
abstract: In recent decades, imaging sonar has been the most widely employed remote sensing instruments in the field of underwater detection. The multibeam echo sounder (MBES) plays an important role in obtaining high accuracy seabed topography. However, the resolution of the MBES substantially decreases with the increasing distance. Synthetic aperture sonar (SAS) achieves constant resolution on the along track, improving the fineness of the image. However, conventional side scan SAS usually only achieves 2D images, and gaps always exist. In this modeling and experimental research paper, we propose a novel underwater acoustic imaging scheme to improve the imaging performance of MBES, based on the complementarity of MBES and SAS systems. We design a 2D transducer array to increase the detection efficiency and obtain spatial gain. Moreover, the processing scheme is analyzed to design the working parameters in actual engineering applications. We exploit a target echo simulation approach to establish the research basics of the imaging algorithms, which also reflects the shapes and shadows of targets to match actual situations as realistically as possible. The proposed imaging algorithm synthesizes a virtual aperture receiving array on the along track and reserves the multi element manifold on the across track. This helps to improve the imaging quality of the MBES and achieves high resolution 3D detection with no gaps. Simulation and tank experimental results demonstrate that the proposed scheme can significantly improve the detection ability of the MBES, especially for small 3D target detection, thus making it suitable for 3D high resolution underwater detection applications.

title: Erratum: Martins, M.S. et al. Wideband and Wide Beam Polyvinylidene Difluoride (PVDF) Acoustic Transducer for Broadband Underwater. Sensors 2019, 19, 3991
abstract: The authors wish to make the following erratum to this paper

title: A Fluidics Based Double Flexural Membrane Piezoelectric Micromachined Ultrasonic Transducer (PMUT) for Wide Bandwidth Underwater Acoustic Applications
abstract: In acoustic receiver design, the receiving sensitivity and bandwidth are two primary parameters that determine the performance of a device. The trade off between sensitivity and bandwidth makes the design very challenging, meaning it needs to be fine tuned to suit specific applications. The ability to design a PMUT with high receiving sensitivity and a wide bandwidth is crucial to allow a wide spectrum of transmitted frequencies to be efficiently received. This paper presents a novel structure involving a double flexural membrane with a fluidic backing layer based on an in plane polarization mode to optimize both the receiving sensitivity and frequency bandwidth for medium range underwater acoustic applications. In this structure, the membrane material and electrode configuration are optimized to produce good receiving sensitivity. Simultaneously, a fluidic backing layer is introduced into the double flexural membrane to increase the bandwidth. Several piezoelectric membrane materials and various electrode dimensions were simulated using finite element analysis (FEA) techniques to study the receiving performance of the proposed structure. The final structure was then fabricated based on the findings from the simulation work. The pulse echo experimental method was used to characterize and verify the performance of the proposed device. The proposed structure was found to have an improved bandwidth of 56.6% with a receiving sensitivity of 1.8864 dB rel 1 V uPa. For the proposed device, the resonance frequency and center frequency were 600 and 662.5 kHz, respectively, indicating its suitability for the targeted frequency range.

title: Analysis of the crosstalk in an underwater planar array transducer by the equivalent circuit method
abstract: A planar array transducer consists of several transducers arranged on an acoustic window, which causes crosstalk. The crosstalk is a phenomenon in which the acoustic pressure generated by a projector is transferred to adjacent hydrophones through the acoustic window and the transferred pressure generates noise signals in the hydrophones. The performance of the planar array transducer is deteriorated due to this acoustic interaction, which should be minimized for maximum array performance. Analysis of the crosstalk has been carried out with sophisticated numerical methods, which motivated the need to develop a simpler and accurate analysis method. In this work, an equivalent circuit has been developed to analyze the crosstalk level of the planar array transducer, and the validity of the developed method has been verified by comparing the result from the equivalent circuit analysis with that from finite element analysis.

title: Design and development of D33 mode piezoelectric acoustic transducer array using PVDF for underwater application
abstract: An acoustic transducer arrays is well known applied in acoustic imaging system. This acoustic imaging system is applied in many areas for example medical imaging and underwater imaging system. D33 mode based piezoelectric acoustic transducer array is designed and developed for underwater applications. The previous researchers have a problem with sensitivity of transducer. The transducer array is used d33 mode concept to increase the sensitivity of transducer. The transducer array is fabricated on Printed Circuit Board (PCB) with sensing element, polyvinylidene fluoride (PVDF) and polydimethylsiloxane (PDMS) as a matching layer. The transducer array is characterized using Pulse Echo experimental method. This method is normally used to characterize the transducer in underwater applications. The calibration for hydrophone is made to ensure that the capability and performance of reference transducer is followed the given specification. The hydrophone and PAT linear array are tested in test tank. Three pin, Pin A, Pin B, and Pin C are being tested. The result is shows that Pin B has highest sensitivity, followed by Pin A and Pin C is the lowest. All pins have resonance frequency at 1250 kHz. The fractional bandwidth for Pin B is at 34%

title: Determination of the calibration error of a reciprocal underwater acoustic transducer from standard data obtained in a two way comparison calibration process using the acoustic reciprocity parameter
abstract: Hydrophones are more commonly calibrated using the two way comparison method than the three way reciprocity method. The comparison method is the most frequent chosen technique for hydrophone calibration due to the time consuming nature of conducting the free field three way reciprocity technique. This method is chosen despite the three way reciprocity method resulting in a more accurate calibration than that of the comparison method due to it being an absolute method of calibration. This paper illustrates how to derive the indeterminate error in a twoway comparison calibration using the reciprocity parameter with the limited data supplied from a standard commercial calibration process if the transducer under test is reciprocal. The proposed simple method demonstrates that the determination of this error can be derived whilst examining the reciprocity of the transducer under test and can be performed post calibration using the supplied data consisting of complex impedance (Z) and the measured receive (M) and transmit (S) sensitivities of the transducer under test. This method is advantageous as one does not have to break the measuring circuit to observe other variables such as voltage and current at the transducer terminals to prove reciprocity which is difficult to do during an automated comparison calibration process. It is shown that from this proposed method the actual error ~0.3 dB) of the two way calibration process was substantially less than the calibration error stated by the manufacturer (1 dB)

title: Caracterizacao de um Transdutor de Pressao para Instrumentos Submarinos Characterization of a Submersible Pressure Transducer for Underwater Instruments
abstract: Ate o presente momento nao ha uma regulamentacao reconhecida pelos fabricantes de sensores de pressao submersiveis referente a especificacoes minimas e procedimentos de calibracao e teste. Uma metodologia para verificar a performance do sensor MS5803 foi elaborada com base em trabalhos realizados pela British Geological Survey Uma plataforma, que futuramente podera ser adaptada para medidas de campo, foi construida para permitir o levantamento das especificacoes do transdutor. Este trabalho foca no sensor MS5803 01 devido a sua popularidade em projetos de " hardware aberto" como por exemplo robos submarinos, maregrafos/ondografos e computadores de mergulho, entre outros. Os resultados deste trabalho tem a itencao de ser uma fonte independente de dados de caracterizacao de forma a estender as informacoes providas pelo fabricante. Palavras chave: sensor de pressao, instrumentacao submarina, transdutor de pressao submarino, sensor de profundidade, sensor piezoeletrico, calibracao.  At this moment there is not any regulations adopted industry wide for minimum specifications and calibration procedures to be used on submersible pressure transducers. A methodology was elaborated to verify performance characteristics of the MS5803 sensor following the guidelines of the British Geological Survey. A test platform, that can be easily adapted for field tests, was built to measure the transducer specifications. This work focus on the MS5803 01 sensor, since it's becoming popular in open projects ranging from underwater robotics (AUV and ROVs) wave/tide gauges and diving computers among many others. The results from this work intends to be an independent source of characterization data extending the information provided by the manufacturer.  pressure sensor, underwater instrumentation, submersible pressure transducer, depth sensor, piezoelectric sensor, calibration.

title: 3 Dimensional mapping of underwater surface for navigation using underwater ultrasonic piezoelectric transducer