Systems, methods, and mechanisms for sound beam focal point determination within an acoustic medium may include propagating a first sound beam to intersect a second sound beam, where the second sound beam converges at a focal point. The first and second sound beams may originate from known locations. A direction of the first sound beam within the acoustic medium may be adjusted to produce a maximum amplitude of signals generated from nonlinear mixing of the first sound beam and the second sound beam, where the maximum amplitude may correspond to the intersection of the first sound beam with the focal point of the second sound beam. A location of the intersection may be determined, at least in some instances, based on the known locations, the adjusted direction of the first sound beam, and a direction of the second sound beam.

A system is provided for communication through or along a barrier. The system includes a transmitter unit for transmitting a signal comprising a transmitter housing, a transmitter fixation element for fixing a first side of the transmitter housing against a barrier, an exciter embedded in or protruding from the first side of the transmitter housing, such that the exciter is applied against the barrier by the fixation element, and an audio input. The transmitter further includes circuitry for driving the exciter based on a signal received at the audio input. The system further includes a receiver unit for receiving a signal comprising a receiver housing, a receiver fixation element for fixing a first side of the receiver housing against the barrier, a vibration sensor for detecting vibrations generated by the exciter, an audio output, and circuitry for driving the audio output based on a signal detected by the vibration sensor.

A system is provided for communication through or along a barrier. The system includes a transmitter unit for transmitting a signal comprising a transmitter housing, a transmitter fixation element for fixing a first side of the transmitter housing against a barrier, an exciter embedded in or protruding from the first side of the transmitter housing, such that the exciter is applied against the barrier by the fixation element, and an audio input. The transmitter further includes circuitry for driving the exciter based on a signal received at the audio input. The system further includes a receiver unit for receiving a signal comprising a receiver housing, a receiver fixation element for fixing a first side of the receiver housing against the barrier, a vibration sensor for detecting vibrations generated by the exciter, an audio output, and circuitry for driving the audio output based on a signal detected by the vibration sensor.

A system includes a first structure, wherein the first structure lacks space inversion symmetry, and wherein the first structure includes a first elastic lattice. The system further includes a second structure, wherein the second structure lacks space inversion symmetry, and wherein the second structure includes a second elastic lattice. Additionally, the system includes the first structure coupled to the second structure such that the first structure and the second structure have a mirror symmetry to each other.

A system includes a first structure, wherein the first structure lacks space inversion symmetry, and wherein the first structure includes a first elastic lattice. The system further includes a second structure, wherein the second structure lacks space inversion symmetry, and wherein the second structure includes a second elastic lattice. Additionally, the system includes the first structure coupled to the second structure such that the first structure and the second structure have a mirror symmetry to each other.

A gradient-index phononic crystal flat lens which controls the behavior of an acoustic wave having a designated frequency. The gradient-index phononic crystal flat lens may include one or more super cells each having a plurality of layers stacked in a vertical direction according to a target gradient index profile, wherein each of the layers is composed of an aggregate in which unit cells having scatterers formed with the same size in the centers thereof are arranged in a horizontal direction. The one or more super cells may each include a divider provided between the neighboring layers, and configured to force the acoustic wave to propagate in the horizontal direction within the gradient-index phononic crystal flat lens.

A gradient-index phononic crystal flat lens which controls the behavior of an acoustic wave having a designated frequency. The gradient-index phononic crystal flat lens may include one or more super cells each having a plurality of layers stacked in a vertical direction according to a target gradient index profile, wherein each of the layers is composed of an aggregate in which unit cells having scatterers formed with the same size in the centers thereof are arranged in a horizontal direction. The one or more super cells may each include a divider provided between the neighboring layers, and configured to force the acoustic wave to propagate in the horizontal direction within the gradient-index phononic crystal flat lens.

A method, an equipment, and a computer readable medium for evaluating structural strength of fiber and nanosized materials reinforced concrete are provided. The method includes: obtaining a sound velocity of a fiber and nanosized materials reinforced concrete test block; deriving a structural compressive strength of the fiber and nanosized materials reinforced concrete test block according to the sound velocity and a relation between fiber and nanosized materials reinforced concrete structural compressive strength and fiber and nanosized materials reinforced concrete sound velocity; determining strengths of various parts of the fiber and nanosized materials reinforced concrete test block based on measured parameters and recorded design parameters of the test fiber and nanosized materials reinforced concrete, and evaluating deviations of the strengths of the respective parts from the structural compressive strength. The partial design strengths and the deviations from the structural compressive strength may be evaluated and corrective measures may be given.

A method, an equipment, and a computer readable medium for evaluating structural strength of fiber and nanosized materials reinforced concrete are provided. The method includes: obtaining a sound velocity of a fiber and nanosized materials reinforced concrete test block; deriving a structural compressive strength of the fiber and nanosized materials reinforced concrete test block according to the sound velocity and a relation between fiber and nanosized materials reinforced concrete structural compressive strength and fiber and nanosized materials reinforced concrete sound velocity; determining strengths of various parts of the fiber and nanosized materials reinforced concrete test block based on measured parameters and recorded design parameters of the test fiber and nanosized materials reinforced concrete, and evaluating deviations of the strengths of the respective parts from the structural compressive strength. The partial design strengths and the deviations from the structural compressive strength may be evaluated and corrective measures may be given.

An apparatus for determining a suitability of a frequency band for data communication with a node by way of a communication channel may be provided. The apparatus may comprise a receiver configured to receive first and second signals from the node by way of the communication channel, the first and second signals having frequencies within the frequency band. The apparatus may comprise processing circuitry communicatively coupled to the receiver, the processing circuitry being configured to determine a calibration function depending on the first signal, process the second signal depending on the calibration function, determine the suitability of the frequency band for data communication with the node by way of the communication channel depending on the processed second signal and output an indication of the said suitability. The processing circuitry may be configured to determine the suitability of the frequency band for data communication with the node depending on the processed second signal by comparison of the processed second signal to predetermined reference data.