All articles A–Z

Acoustic Chern insulator

An acoustic Chern insulator is a two-dimensional acoustic metamaterial whose sound bands carry a nonzero Chern number, so sound propagates unidirectionally along edges, immune to backscattering from defects.

Acoustic cloaking

Acoustic cloaking is the rendering of an object undetectable to sound waves, typically by a metamaterial shell that redirects sound around it; passive cloaks are limited to narrow frequency ranges.

Acoustic coupler

An acoustic coupler is an early modem that connects a computer to a phone line by sound through a handset seated in rubber cups, with no wired connection.

Acoustic detection of neutrinos

Acoustic detection of neutrinos is a proposed technique for finding ultra-high-energy neutrinos by listening for the sound pulse their particle showers emit in water or ice.

Acoustic diffuser

An acoustic diffuser is a surface that scatters sound over many directions instead of reflecting it like a flat wall, used in concert halls and control rooms.

Acoustic Doppler current profiler

An acoustic Doppler current profiler (ADCP) is a sonar instrument that measures current speed and direction at many depths by analyzing the Doppler shift of sound echoes.

Acoustic Doppler velocimetry

Acoustic Doppler velocimetry is a technique that measures fluid velocity from the Doppler shift of sound echoed by particles moving with the flow, used in turbulence and current studies.

Acoustic double-zero metamaterial

An acoustic double-zero metamaterial is an artificially structured medium in which effective density and bulk modulus both reach zero at one frequency, letting sound pass with no phase change.

Oct 15, 2026

Acoustic droplet ejection

Acoustic droplet ejection (ADE) is a contact-free liquid-handling technique that uses focused sound pulses to eject nanoliter droplets through air, widely used in high-throughput screening and crystallography.

Acoustic emission

Acoustic emission is a passive nondestructive testing method in which sensors detect stress waves a material emits under stress, revealing active damage such as crack growth or corrosion, used in bridge and pressure vessel monitoring.

Acoustic fingerprint

An acoustic fingerprint is a compact, content-based signature extracted from an audio signal, used to identify recordings against a database even when the query audio is noisy or degraded.

Acoustic force spectroscopy

Acoustic force spectroscopy (AFS) is a single-molecule micromanipulation method in which acoustic standing waves stretch DNA and other biomolecules tethered to beads, introduced at VU University Amsterdam in 2014.

Acoustic guitar

Acoustic guitar: a hollow-body plucked string instrument whose soundboard radiates string vibration acoustically. Covers steel-string and nylon-string classical types, tensions, Martin X-bracing history, sizes, woods, and pickups.

Acoustic higher-order topological insulators

Acoustic higher-order topological insulators are artificial acoustic crystals that confine sound to boundaries of lower dimension than the bulk, first demonstrated in 2018 with a breathing Kagome lattice whose corner states act as reconfigurable local resonances.

Acoustic holography

Acoustic holography is an imaging technique that reconstructs a 3D sound field from pressure measurements on a single surface, used to locate and visualize noise sources.

Acoustic imaging

Acoustic imaging forms images of underwater objects and environments from sound-wave echoes, and it is the dominant technique for mapping the seafloor and inspecting submerged structures.

Acoustic impedance

Acoustic impedance, also called sound impedance, is the ratio of sound pressure to the flow it produces, governing how much sound energy crosses a boundary between media.

Oct 15, 2026

Acoustic impedance mismatch

An acoustic impedance mismatch is a difference in acoustic impedance between two media meeting at a boundary, causing part of a sound wave to reflect rather than transmit.

Acoustic Kitty

Acoustic Kitty (also Acoustikitty) was a 1960s CIA Directorate of Science and Technology project implanting a microphone, transmitter, and antenna in a cat to eavesdrop on Soviet targets; it ended in 1967 because the cat could not be controlled.

Acoustic levitation

Acoustic levitation is a technique that suspends small particles, droplets, and solids in air at the pressure nodes of standing ultrasonic waves, enabling contact-free measurement.

Acoustic metamaterial

An acoustic metamaterial is an artificial periodic structure whose effective acoustic properties, including negative density and refractive index, are set by design rather than composition.

Acoustic metamaterial with negative dynamic mass density

An acoustic metamaterial with negative dynamic mass density is an engineered periodic structure whose effective mass density turns negative in frequency bands near local resonances of subwavelength unit cells.

Acoustic microscopy

Acoustic microscopy, also called scanning acoustic microscopy (SAM), images the interior of opaque materials and biological specimens by focusing high-frequency ultrasound, detecting delaminations, voids, and cracks with micrometer resolution.

Acoustic mirror

Acoustic mirrors, also known as sound mirrors, are large concave concrete structures that focus distant aircraft engine sound onto a listener, forming Britain's early warning system before radar.

Acoustic monitoring

Acoustic monitoring, also known as passive acoustic monitoring (PAM), surveys wildlife by deploying unattended sound recorders for days or months, supporting estimates of species occupancy, abundance, and biodiversity.