A dual frequency ultrasound transducer includes a high frequency ultrasound array and a low frequency transducer positioned behind or proximal to the high frequency ultrasound array. In one embodiment, a dampening material is positioned between a rear surface of the high frequency array and the a front surface of the low frequency array. The dampening preferably is high absorbing of signals at the frequency of the high frequency array but passes signals at the frequency of the low frequency transducer with little attenuation. In additional, or alternatively, the low frequency can angled with respect to the plane of the high frequency transducer to reduce inter-stack multipath reflections. Beamforming delays compensate for the differences in physical distances between the elements of the low frequency transducer and the plane of the high frequency transducer.

A focused ultrasonic transducer includes a piezoelectric substrate having a first face and a second face, a back metal layer disposed over the first face, and a patterned metal layer disposed over the second face. The patterned metal layer includes a first plurality of concentric ring electrodes wherein each of the first plurality of concentric ring electrodes are wired to be individually accessible. A controller actuates a subset of the concentric ring electrodes such that electrical control of focal length is achieved by selecting a group of electrodes to actuate so that acoustic waves generated from selected electrodes arrive at a desired focal length in-phase and interfere constructively to create a focal spot of high acoustic intensity. The patterned metal layer optionally includes a first central electrode that is surrounded by the first plurality of concentric ring electrodes.

A method for locating an object underwater may involve using a sound transmitter to transmit a sound pulse. The sound pulse may be reflected by the object to be located and then received by a sound receiver. The sound receiver may be spatially distant from the sound transmitter, meaning that the sound receiver is spaced apart from the sound transmitter by an amount that is of a similar order of magnitude as a distance between the sound transmitter and the object or between the sound transmitter and the seafloor. The sound pulse may contain encoded information relating to a time of transmission of the sound pulse and a transmission position of the sound transmitter. The encoded information may then be decoded by the sound receiver to determine the position of the object.

Embodiments of the present invention provide a navigation system which, on the one hand, is arranged on sides of the underwater vehicle/AUV and, on the other hand, includes a surface transmitter as a counterpart. The two units communicate with each other such that the surface transmitter emits its signal directed to the position of the underwater vehicle and/or that the surface transmitter follows the underwater vehicle to improve the position determination capability.

Embodiments of the present invention provide a navigation system which, on the one hand, is arranged on sides of the underwater vehicle/AUV and, on the other hand, includes a surface transmitter as a counterpart. The two units communicate with each other such that the surface transmitter emits its signal directed to the position of the underwater vehicle and/or that the surface transmitter follows the underwater vehicle to improve the position determination capability.

An active indoor location sensing technique is presented for smartphones and other types of mobile devices without requiring any additional sensors or pre-installed infrastructure. The main idea is to actively generate acoustic signatures by transmitting a sound signal with a phone's speakers and sensing its reflections with the phone's microphones. This active sensing achieves finer-grained control of the collected signatures than the widely-used passive sensing.

Methods and systems for the efficient determination of the direction of multiple signal sources in both near and far field using hierarchical combinations of sets of raw input signals to convert spatial input to angular output. Each increasing hierarchical combination increases angular resolution, improving image quality with low computational expenditure.

A marine sonar display device comprises a display, a sonar element, a memory element, and a processing element. The display presents sonar images. The sonar element generates a sonar beam and presents transducer signals. The processing element is in communication with the display, the sonar element, and the memory element and receives the transducer signals, calculates sonar data from the transducer signals and generates a three-dimensional view of a portion of the body of water, wherein the view includes a plurality of sonar images. Each sonar image is generated from sonar data derived from a previously-generated sonar beam and includes representations of underwater objects and a water bed. The processing element also generates a cursor plane and a cursor positioned thereon, both of which appear on the three-dimensional view. The processing element further controls the display to present the three-dimensional view, the sonar images, the cursor plane, and the cursor.

A self-contained monitor array for measuring at least one type of electromagnetic emission and at least one type of mechanical wave emission from a marine-based and/or terrestrial human activity or installation such as alternate energy sources. A multi-modal monitor system includes at least two such arrays, at least one clock, and at least one data storage unit. The monitor system is employed at the site of a turbine installation to measure at least one type of emission generated by the turbine and may comprise a controller to compare the emission signals with pre-determined acceptable value ranges and adjust the performance of the turbine accordingly.

A system and a method for determining one or more wave characteristics from a moving platform are disclosed. A sonar system, such as an Acoustic Doppler Current Profiler, can profile the water motion relative to the platform, and an earth reference can determine a measure of the platform motion relative to a fixed earth reference. Both water profile and earth reference measurements can be synergistically employed to compensate for motion of the platform. Directional wave spectra and non-directional wave spectrum can be computed and translated via linear wave theory to surface height spectra and used to calculate characteristics, such as significant wave height, peak period, and peak direction.