Goniometer
Encyclopedia
Angle
In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...
, and metron, meaning measure
Measurement
Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature etc., to a unit of measurement, such as the metre, second or degree Celsius...
.
Communications
Goniometers are used for direction findingDirection finding
Direction finding refers to the establishment of the direction from which a received signal was transmitted. This can refer to radio or other forms of wireless communication...
in signals intelligence applications for military and civil purposes, e.g. interception of satellite and naval communications as performed on the French warship Dupuy de Lôme
Dupuy de Lôme (A759)
The Dupuy de Lôme , named after the 19th century engineer Dupuy de Lôme, is a ship designed for the collection of signals and communications beyond enemy lines, which entered the service of the French Navy in April 2006...
uses multiple goniometers.
Crystallography
Crystallography
Crystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.Before the development of...
, goniometers are used for measuring angles between crystal faces. They are also used in X-ray diffraction to rotate the samples. The groundbreaking investigations of physicist Max von Laue
Max von Laue
Max Theodor Felix von Laue was a German physicist who won the Nobel Prize in Physics in 1914 for his discovery of the diffraction of X-rays by crystals...
and cohorts into the atomic structure of crystals
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
in 1912 involved a goniometer.
Light measurement
Goniophotometers measure the spatial distribution of light visible to the human eye at a specific angular position.In Medicine
Medical practitioners, (Physicians, Physician Assistants, Physical Therapists, Athletic Trainers, Chiropractors and Nurse Practitioners) use a goniometer to document initial and subsequent range of motion, at the visits for Occupational injuries, and by disabilityDisability
A disability may be physical, cognitive, mental, sensory, emotional, developmental or some combination of these.Many people would rather be referred to as a person with a disability instead of handicapped...
evaluators to determine a permanent disability. This is to evaluate progress, and also for medico-legal purposes. It is a tool to evaluate Waddell's signs
Waddell's signs
Waddell's signs are a group of physical signs, first described in a 1980 article in Spine, and named for the article's principal author, Gordon Waddell. Waddell's signs may indicate non-organic or psychological component to chronic low back pain. Historically they have also been used to detect...
(findings that may indicate symptom magnification.)
Physical therapy
In physical therapyPhysical therapy
Physical therapy , often abbreviated PT, is a health care profession. Physical therapy is concerned with identifying and maximizing quality of life and movement potential within the spheres of promotion, prevention, diagnosis, treatment/intervention,and rehabilitation...
and occupational therapy
Occupational therapy
Occupational therapy is a discipline that aims to promote health by enabling people to perform meaningful and purposeful activities. Occupational therapists work with individuals who suffer from a mentally, physically, developmentally, and/or emotionally disabling condition by utilizing treatments...
, a goniometer is an instrument which measures an axis and range of motion. If a patient or client experiences decreased range of motion in a joint (e.g. a knee or elbow), the therapist can use a goniometer to assess what the range of motion is prior to intervention, and then make sure the intervention is working by using the goniometer in subsequent interventions.
Surface science
In surface scienceSurface science
Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including solid–liquid interfaces, solid–gas interfaces, solid–vacuum interfaces, and liquid-gas interfaces. It includes the fields of surface chemistry and surface physics. Some related...
, an instrument generally called a contact angle goniometer is used to measure the static contact angle
Contact angle
The contact angle is the angle at which a liquid/vapor interface meets a solid surface. The contact angle is specific for any given system and is determined by the interactions across the three interfaces. Most often the concept is illustrated with a small liquid droplet resting on a flat...
, advancing & receding contact angles, and surface tension. The first contact angle goniometer was designed by Dr. William Zisman
William Zisman
Dr. William Albert Zisman was an American chemist and geophysicist.He was born in Albany, NY and spent his youth in Providence, RI up to the age of 14 when his family moved to Washington, DC. He earned his BS and MS degrees in physics from Massachusetts Institute of Technology. He began his career...
of the United States Naval Research Laboratory
United States Naval Research Laboratory
The United States Naval Research Laboratory is the corporate research laboratory for the United States Navy and the United States Marine Corps and conducts a program of scientific research and development. NRL opened in 1923 at the instigation of Thomas Edison...
in Washington, DC and manufactured by ramé-hart (now ramé-hart instrument company), New Jersey, USA. The original manual contact angle goniometer used an eyepiece with microscope. The current generation of contact angle instruments uses cameras and software to capture and analyze the drop shape and are better suited for dynamic and advanced studies.
A Gonioreflectometer
Gonioreflectometer
A gonioreflectometer is a device for measuring a bidirectional reflectance distribution function .The device consists of a light source illuminating the material to be measured and a sensor that captures light reflected from that material. The light source should be able to illuminate and the...
is used to measure the reflectivity of a surface at a variety of angles.
Static contact angle
Wetting
Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting is determined by a force balance between adhesive and cohesive forces.Wetting is important in the bonding or adherence of...
expresses the contact angle analytically.
where
= Interfacial tension between the solid and gas
= Interfacial tension between the solid and liquid
= Interfacial tension between the liquid and gasContact angle goniometers measure a droplet’s contact angle by assuming the droplet fits the geometry of a sphere, ellipsoid, or the Young-Laplace equation.
Another perspective that describes contact angles uses cohesion vs. adhesion. Cohesion is the force between the liquid molecules which hold the liquid together. Adhesion is the force between the liquid molecules and the solid molecules. The contact angle is a quantitative measure that tells the user the ratio of cohesion vs. adhesion. If the contact angle is near zero, meaning the liquid droplet spreads completely on the solid surface, adhesive forces are dominating. If the contact angle is very high, meaning the liquid droplet beads up on the solid surface as water does on a freshly waxed car, cohesive forces are dominating.
Advancing and receding contact angles
While static contact angles give static information about the interfacial tensions between the solid, liquid, and gas, advancing and receding contact angles give some information about the dynamic interaction of the liquid, solid, and gas. An advancing contact angle is determined by pushing a droplet out of a pipette onto a solid. When the liquid initially meets the solid it will form some contact angle. As the pipette injects more liquid through the pipette, the droplet will increase in volume, the contact angle will increase, but its three phase boundary will remain stationary until it suddenly jumps outward. The contact angle the droplet had immediately before jumping outward is termed the advancing contact angle. The receding contact angle is now measured by sucking the liquid back out of the droplet. The droplet will decrease in volume, the contact angle will decrease, but its three phase boundary will remain stationary until it suddenly jumps inward. The contact angle the droplet had immediately before jumping inward is termed the receding contact angle. The difference between advancing and receding contact angles is termed contact angle hysteresis which can be used to characterize surface heterogeneity, roughness, and mobility. Surfaces that are not homogeneous will have domains which impede motion of the contact line.Surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
for any liquid in gas or the interfacial tension between any two liquids. If the difference in densities between the two fluids is known, the surface tension or interfacial tension can be calculated by using the pendant drop method. Surface tension quantifies the cohesive force present at the surface of a droplet. Contact angle goniometers measure surface tension by examining a drop hanging from a syringe tip in air. The balance of forces acting on the drop include the surface tension. The surface tension can be calculated using the below equation
where:
is the liquid-air surface tensionSurface tensionSurface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
(J/m² or N/m)- β is the shape factor
- Δρ is the difference in density between fluids at the interface (kg/m3)
- g is accelerationAccelerationIn physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...
due to gravity (m/s²) - R is the radiusRadiusIn classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
of the drop curvature at the drop’s apex (m)
3 dimensionless first order equations can define the shape factor
- dx/ds = cosθ
- dz/ds = sinφ
- dφ/ds = 2 + βz – sinφ/x
Iterative approximations can solve for β.
Positioning
Linear stage
A linear stage or translation stage is a component of a motion system used to restrict an object to a single axis of motion. The term linear slide is often used interchangeably with "linear stage", though technically "linear slide" refers to a linear motion bearing, which is only a component of a...
, however, rather than moving linearly with respect to its base, the stage platform rotates partially about a fixed axis above the mounting surface of the platform. Positioning goniometers typically use a worm drive
Worm drive
A worm drive is a gear arrangement in which a worm meshes with a worm gear...
with a partial worm wheel fixed to the underside of the stage platform meshing with a worm in the base. The worm may be rotated manually or by a motor as in automated positioning systems.
Knife and blade cutting edge angle measurement
The included cutting angles of all kinds of sharp edge blades is measured using a laser reflecting goniometer. Developed by CATRA in the UK, a range of devices can accurately determine the cutting edge profile including a rounding of the tip to ½°. The included angle of a blade is important in controlling its cutting ability and edge strength, i.e. a low angle makes the edge thin and optimized for cutting while a large angle makes it thick, which cuts poorly, but is very strong.See also
- InstrumentationInstrumentationInstrumentation is defined as the art and science of measurement and control of process variables within a production, or manufacturing area....
- ProtractorProtractorIn geometry, a protractor is a circular or semicircular tool for measuring an angle or a circle. The units of measurement utilized are usually degrees.Some protractors are simple half-discs; these have existed since ancient times...
- TrigonometryTrigonometryTrigonometry is a branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides. Trigonometry defines the trigonometric functions, which describe those relationships and have applicability to cyclical phenomena, such as waves...
- SCR-277SCR-277The SCR-277 was a mobile, trailer mounted radio range set for radio guidance of aircraft. It was standardized by the U.S. Army in June of 1941.-Specifications:...