Next generation IMPAQT miniaturized underwater transmitter system design

In recent years, terrestrial wireless sensor networks and Internet of Things (IoT) technologies have developed rapidly. However, due to the limitations of Electromagnetic (EM) signal propagation in water, there is less development and advancement in the underwater wireless sensor networks domain. As part of the IMPAQT project, a novel wireless underwater telemetry platform using acoustics has been proposed. This telemetry platform has the potential to replace the underwater sensors cables and provide a wireless method to collect and transmit a variety of environmental sensor data under water. The proposed platform system architecture consists of several ultrasonic transmitter nodes and a gateway buoy as a data aggregator node to transmit the data from the sensors to the cloud for analytics to be carried out. Transmitter nodes will read the attached sensor data and transmit it to the gateway buoy. The gateway buoy will send the collected data to a data management system using a Long Range (LoRa) communication link. The next generation IMPAQT Transmitter node developed is a compact, low-cost, low-power acoustic transmitter node that has an external sensor interface to receive data from attached sensors is described in detail in this paper. In addition, the potential for short-range EM-based underwater LoRa communication is evaluated and described

IMPAQT Miniaturized Underwater Acoustic Telemetry Platform: Transmitter Node System Design

The marine environment and its natural resources are an essential part of the geographical ecosystem and a great food source for humans. In recent years, terrestrial wireless sensor networks and Internet of Things (IoT) technologies have developed rapidly; however, due to the limitation of signal propagation in water, there is less development and advancement in the underwater sensors network domain. IMPAQT is a European research project aiming at the development of the technologies and methods to promote and support inland, coastal zone and offshore Integrated Multi-Trophic Aquaculture (IMTA) sites. As part of the IMPAQT project, a novel underwater acoustic telemetry platform has been proposed and is under development, to provide a method to collect and transmit sensors data underwater. The proposed platform architecture consists of several ultrasonic transmitter sensor nodes and a gateway buoy as a data aggregator interface. Transmitter nodes will collect and log underwater sensor data and transmit it at regular intervals to the gateway buoy and the gateway buoy will send the collected data to a data management system using a Long Range (LoRa) communication link. The IMPAQT Transmitter node has an integrated accelerometer sensor, a temperature sensor, and a pressure sensor onboard. There is also an Infrared Data Association protocol (IrDA) interface that can be used to attach any external auxiliary sensor module to the transmitter node and configure the transmitter node to collect the external module’s data. The current version of the transmitter node under development can be attached to seaweed, or it can be used as a floating sensor node in the water and due to its small size and weight design it almost has no impact on the working environment. In this paper, the background of the miniaturized underwater sensors is studied, and design method of the transmitter node is discussed. Future work will focus on the test and deployment of the transmitter and gateway in marine deployments

Ultraminiature Piezoelectric Implantable Acoustic Transducers for Biomedical Applications

Miniature piezoelectric acoustic transducers have been developed for numerous applications. Compared to other transduction mechanisms like capacitive or piezoresistive, piezoelectric transducers do not need direct current (DC) bias voltage and can work directly exposed to fluid. Hence, they are good candidates for biomedical applications that often require the transducer to work in water based fluid. Among all piezoelectric materials, aluminum nitride (AlN) is a great choice for implantable sensors because of the high electrical resistance, low dielectric loss, and biocompatibility for in vivo study. This thesis presents the design, modeling, fabrication, and testing of the AlN acoustic transducers, miniaturized to be implantable for biomedical applications like hearing or cardiovascular devices. To design and model the transducer in air and in water, a 3D finite element analysis (FEA) model was built to study the transducer in a viscous fluid environment. An array of AlN bimorph cantilevers were designed to create a multi-resonance transducer to increase the sensitivity in a broad band frequency range. A two-wafer process using microelectricalmechanical systems (MEMS) techniques was used to fabricate the xylophone transducer with flexible cable. Benchtop testing confirmed the transducer functionality and verified the FEA model experimentally. The transducer was then implanted inside a living cochlea of a guinea pig and tested in vivo. The piezoelectric voltage output from the transducer was measured in response to 80-95 dB sound pressure level (SPL) sinusoidal excitation spanning 1-14 kHz. The phases showed clear acoustic delay. The measured voltage responses were linear and above the noise level. These results demonstrated that the transducer can work as a sensor for a fully implantable cochlear implant. The second generation device, an ultraminiature diaphragm transducer, was designed to be smaller, and yet with an even lower noise floor. The transducer was designed and optimized using a 2D axial-symmetric FEA model for a better figure of merit (FOM), which considered both minimal detectable pressure (MDP) and the diaphragm area. The low-frequency sensitivity was increased significantly, because of the encapsulated back cavity. Because of this merit, cardiovascular applications, which focus on low frequency signals, were also investigated. The diaphragm transducers were fabricated using MEMS techniques. Benchtop tests for both actuating and sensing confirmed the transducer functionality, and verified the design and model experimentally. The transducer had a better FOM than other existing piezoelectric diaphragm transducers, and it had a much lower MDP than the other intracochlear acoustic sensors.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147673/1/chumingz_1.pd

Ultrasonic transducer tuning using wafer bonding method

954-959This study demonstrates the wafer bonding method for performance tuning of piezoelectric Micromachined Ultrasonic Transducer (pMUT) from on-the-shelf piezoelectric disc (PZT). Polydimethylsiloxane (PDMS) and Epoxy were studied as adhesive materials. A thick bonding layer was deposited using the spin coating technique. Wafer bonding was carried out at room temperature to simulate in-situ pMUT repairing scenario. Bonding integrity is analyzed using Field Emission Scanning Electron Microscope (FESEM) images, while electrical characterization of pMUT is carried out using impedance analysis. Fabricated pMUTs have been calibrated using the pulse-echo technique in a freshwater tank. This study found that PDMS at the minimum thickness of 28 μm is preferably compatible for in-situ wafer bonding of pMUT compared to the Epoxy. PDMS has significantly reduced device impedance at 62.4 % reduction compared to 58.9 % reduction for Epoxy. Both pMUTs were able to transmit and receive short acoustic ping with the calibrated speed of sound of 1333.3 m/s. PDMS has successfully contributed to a broader operating frequency between 30 – 150 kHz for transmission and 75 – 140 kHz for the reception

Ultrasonic transducer tuning using wafer bonding method

This study demonstrates the wafer bonding method for performance tuning of piezoelectric Micromachined Ultrasonic Transducer (pMUT) from on-the-shelf piezoelectric disc (PZT). Polydimethylsiloxane (PDMS) and Epoxy were studied as adhesive materials. A thick bonding layer was deposited using the spin coating technique. Wafer bonding was carried out at room temperature to simulate in-situ pMUT repairing scenario. Bonding integrity is analyzed using Field Emission Scanning Electron Microscope (FESEM) images, while electrical characterization of pMUT is carried out using impedance analysis. Fabricated pMUTs have been calibrated using the pulse-echo technique in a freshwater tank. This study found that PDMS at the minimum thickness of 28 µm is preferably compatible for in-situ wafer bonding of pMUT compared to the Epoxy. PDMS has significantly reduced device impedance at 62.4 % reduction compared to 58.9 % reduction for Epoxy. Both pMUTs were able to transmit and receive short acoustic ping with the calibrated speed of sound of 1333.3 m/s. PDMS has successfully contributed to a broader operating frequency between 30 – 150 kHz for transmission and 75 – 140 kHz for the reception

Micromachined Scanning Devices for 3D Acoustic Imaging

Acoustic imaging (including ultrasound and photoacoustic imaging) refers to a class of imaging methods that use high-frequency sound (ultrasound) waves to generate contrast images for the interrogated media. It provides 3D spatial distribution of structural, mechanical, and even compositional properties in different materials. To conduct 3D ultrasound imaging, 2D ultrasound transducer arrays followed by multi-channel high-frequency data acquisition (DAQ) systems are frequently used. However, as the quantity and density of the transducer elements and also the DAQ channels increase, the acoustic imaging system becomes complex, bulky, expensive, and also power consuming. This situation is especially true for 3D imaging systems, where a 2D transducer array with hundreds or even thousands of elements could be involved. To address this issue, the objective of this research is to achieve new micromachined scanning devices to enable fast and versatile 2D ultrasound signal acquisition for 3D image reconstruction without involving complex physical transducer arrays and DAQ electronics. The new micromachined scanning devices studied in this research include 1) a water-immersible scanning mirror microsystem, 2) a micromechanical scanning transducer, and 3) a multi-layer linear transducer array. Especially, the water-immersible scanning mirror microsystem is capable of scanning focused ultrasound beam (from a single-element transducer) in two dimensions for 3D high-resolution acoustic microscopy. The micromechanical scanning transducer is capable of sending and receiving ultrasound signal from a single-element transducer to a 2D array of locations for 3D acoustic tomography. The multi-layer linear transducer array allows a unique electronic scanning scheme to simulate the functioning of a much larger 2D transducer array for 3D acoustic tomography. The design, fabrication and testing of the above three devices have been successfully accomplished and their applications in 3D acoustic microscopy and tomography have been demonstrated

Micromachined Scanning Devices for 3D Acoustic Imaging

Acoustic imaging (including ultrasound and photoacoustic imaging) refers to a class of imaging methods that use high-frequency sound (ultrasound) waves to generate contrast images for the interrogated media. It provides 3D spatial distribution of structural, mechanical, and even compositional properties in different materials. To conduct 3D ultrasound imaging, 2D ultrasound transducer arrays followed by multi-channel high-frequency data acquisition (DAQ) systems are frequently used. However, as the quantity and density of the transducer elements and also the DAQ channels increase, the acoustic imaging system becomes complex, bulky, expensive, and also power consuming. This situation is especially true for 3D imaging systems, where a 2D transducer array with hundreds or even thousands of elements could be involved. To address this issue, the objective of this research is to achieve new micromachined scanning devices to enable fast and versatile 2D ultrasound signal acquisition for 3D image reconstruction without involving complex physical transducer arrays and DAQ electronics. The new micromachined scanning devices studied in this research include 1) a water-immersible scanning mirror microsystem, 2) a micromechanical scanning transducer, and 3) a multi-layer linear transducer array. Especially, the water-immersible scanning mirror microsystem is capable of scanning focused ultrasound beam (from a single-element transducer) in two dimensions for 3D high-resolution acoustic microscopy. The micromechanical scanning transducer is capable of sending and receiving ultrasound signal from a single-element transducer to a 2D array of locations for 3D acoustic tomography. The multi-layer linear transducer array allows a unique electronic scanning scheme to simulate the functioning of a much larger 2D transducer array for 3D acoustic tomography. The design, fabrication and testing of the above three devices have been successfully accomplished and their applications in 3D acoustic microscopy and tomography have been demonstrated

Envisioning the future of aquatic animal tracking: Technology, science, and application

Electronic tags are significantly improving our understanding of aquatic animal behavior and are emerging as key sources of information for conservation and management practices. Future aquatic integrative biology and ecology studies will increasingly rely on data from electronic tagging. Continued advances in tracking hardware and software are needed to provide the knowledge required by managers and policymakers to address the challenges posed by the world's changing aquatic ecosystems. We foresee multiplatform tracking systems for simultaneously monitoring the position, activity, and physiology of animals and the environment through which they are moving. Improved data collection will be accompanied by greater data accessibility and analytical tools for processing data, enabled by new infrastructure and cyberinfrastructure. To operationalize advances and facilitate integration into policy, there must be parallel developments in the accessibility of education and training, as well as solutions to key governance and legal issues