Developing an acoustic tag with bidirectional communications capabilities

Martech 2021. Marine Technology Workshop 16,18th June. Vigo, Spain Developing an acoustic tag with bidirectional communications capabilities I. Masmitja1,3, S. Gomariz1 , P.J. Bouvet2, J. Aguzzi3 and J. Del Rio1 1SARTI Research Group. Electronics Department, Universitat Politècnica de Catalunya, Vilanova i la Geltrú, Spain 2Underwater Acoustics Lab. ISEN Brest Yncrea Ouest, France 3Marine Science Institute (ICM). Consejo Superior de Investigaciones Científica (CSIC). Barcelona, Spain. Abstract—. The study of marine animal behaviour is crucial to manage fisheries stocks and to understand the climate change effect on them, especially their moving patterns. In order to achieve that, different methods have been developed during the last years, specially using acoustic tags. However, all the tags available nowadays are transmitters, and therefore, can only be used as a “listen method”. Here, we present a new acoustic tag with bidirectional communications capabilities (i.e. can transmit and also receive acoustic signals). This approach will allow the possibility to use new techniques to study marine animals (e.g. range-only and singe-beacon methods with autonomous vehicles), and therefore, increase the knowledge of their behaviour. Keywords— acoustic tag, tagged animals, underwater target localization, autonomous vehicle, acoustics I. INTRODUCTION In this paper, we present a new acoustic tag with bidirectional communications capabilities (i.e. can transmit and also receive acoustic signals). This approach will allow the possibility to use new techniques to study the marine animals and their movement patterns, for example the Range-Only and Singe-Beacon (ROSB) target tracking method with autonomous vehicles. The ROSB method can be used when the range between the target and the tracker is known, as shown in [1]. Those range measurements are usually conducted by acoustic modems which have bidirectional communication capabilities, and therefore, the range can be computed through the Time Of Flight (TOF) of exchanged messages. Nonetheless, the commercially available acoustic modems have important dimensions, and cannot be fitted in small objectives (e.g. marine animals such as jelly fish or Norway lobsters). One alternative to track small targets could be the method developed in [2,3] which uses small acoustic tags instead of modems. However, these tags do not have bidirectional communication capabilities, and therefore, the range between the target and the tracker cannot be measured, and therefore the overall performance is reduced. II. FIRST IMPLEMENTATION USING COMPACTRIO The platform used to design and test the acoustic modem was the CompactRIO (cRIO), which is programmed through the LabView language. The main parts of the cRIO system are: a real-time computer, a Field-Programmable Gate Array (FPGA) module, and a slots' bus to connect either analog or digital modules. Consequently, this versatile platform is useful to implement and test different parts of the designed acoustic modem. In this case, two cRIO model NI cRIO-9024 were used. Both equipped with a Digital-to-Analog Converter (DAC) and Analog-to-Digital Converter (ADC) modules, the NI-9263 and the NI-9215 respectively. These cRIO were controlled with a Personal Computer (PC) and the corresponding LabView software. The signals generated were amplified with a power amplifier and then transmitted using an acoustic transducer into a test tank. Then, the signal received with another transducer was conditioned and processed with a second cRIO. a) Block Diagram The main parts of the software developed, which has been used to implement all the aspects of an acoustic communication between two devices, are represented in Fig. 1. In this case, one modem was used as a master and a second modem was used as a slave. The master started the communication sending a waveform signal (TX) through the channel (in this case, the channel could be real or simulated). Then, the signal was received by the slave modem (RX). Fig. 1. Bloc diagram of the communication scheme used to measure the slant range between two acoustic devices. The signal generated had two main parts: a wake up tone and a chirp signal. The slave modem was waiting for a wake up tone. When this was detected, it started the decoding and correlation procedure. Each time a correlated signal was detected, the slave computed the time between the start acquisition time and the correlated signal detection. Then this time was used to compute a constant time between the slave signal detection and the acknowledgement signal transmitted by the slave. This is an important step, because the master cannot know a priory the time required by the slave to process the signal, and therefore, this time must always be the same. Finally, the master computed the range between both modems using the TOF elapsed. NINTH INTERNATIONAL WORKSHOP ON MARINE TECHNOLOGY, Martech 2021 Vigo, Juny 16th, 18th - ISBN: 978-84-09-31270-2 Page 5 Martech 2020. Marine Technology Workshop 17,19th June. Vigo, Spain b) Laboratory tests The experimental results were conducted at Institut Supérieur De L'electronique Et Du Numérique (ISEN) - Brest (France) (isenbrest.fr), using the L@bISEN research laboratory testing facilities. There, they have a water tank for underwater acoustics with all the required acoustic instrumentation. The photographs presented in Fig. 2 show the water tank as a test-tank, the cRIO modules, and all the set used. Moreover, some of the results obtained are also shown, where we can observe the correlation signal between the received and the transmitted signal (left) and the range computed (right). The separation between transducer where 2 m. Fig. 2. Images taken during a laboratory experiment (left), correlation between RX and TX signal (center) and the computed slant range (right). III. TAG PROTOTYPE SCHEMATIC DESIGN After the first implementation using the cRIO an initial acoustic tag prototype has been developed. The bloc diagram of the designed schematic is shown in Fig. 3, where the main elements of this design are: a) Piezoelectric driver, using a boosted class D amplifier with bridge-tied load configuration; b) Analog switch, to select between transmission and reception; c) Signal conditioning, using a pre-amplifier, an automatic gain control amplifier, and a band-pass filter; and d) Micro Controller, based on ARM Cortex M4 with sleep mode and wake-up for ultralow power consumption. IV. PRINTED CIRCUIT BOARD DESIGN Finally, the Printed Circuit Board (PCB) designed can be observed on Fig. 3. One of the main challenges is to reduce the size and weight of the whole system. Therefore, small packages have been used such as Wafer-Level Packaging (WLP) and 0201 components. With that, the initial acoustic tag PCB size is 21 mm x 8.9 mm (with components in both sides). Fig. 3. Bloc diagram of the schematic design (left), and PCB design (right). V. CONCLUSIONS This work describes the first approach to design and build an acoustic tag with bidirectional communications capabilities, where an initial cRIO implementation, laboratory tests and schematic/PCB prototype are presented. ACKNOWLEDGMENT This work received financial support from the Spanish Ministerio de Economia y Competitividad (contract TEC2017-87861-R project RESBIO, and RTI2018-095112-B-I00 project SASES), and from the Generalitat de Catalunya "Sistemas de Adquisición Remota de datos y Tratamiento de la Información en el Medio Marino (SARTI-MAR)" 2017 SGR 371. This work has been directed and carried out by members of the Tecnoterra-associated unit of the Scientific Research Council through the Universitat Politècnica de Catalunya, the Jaume Almera Earth Sciences Institute and the Marine Science Institute. IM was funded by a MSCA-IF-GF (ID:893089, H2020-EU.1.3.2, European Commission) REFERENCES [1] I. Masmitja et al., "Range-Only Single-Beacon Tracking of Underwater Targets From an Autonomous Vehicle: From Theory to Practice," in IEEE Access, 2019. [2] I. Masmitja et al., "Area-only method for underwater object tracking using autonomous vehicles," OCEANS 2019 - Marseille, Marseille, France, 2019, pp. 1-10. [3] I. Masmitja et al., “Mobile robotic platforms for the acoustic tracking of deep-sea demersal fishery resources,” Sci. Robot., vol. 5, no. eabc3701, 2020. NINTH INTERNATIONAL WORKSHOP ON MARINE TECHNOLOGY, Martech 2021 Vigo, Juny 16th, 18th - ISBN: 978-84-09-31270-2 Page 6