# What is phase coherence?

## What is phase coherence?

coherence, a fixed relationship between the phase of waves in a beam of radiation of a single frequency. Two beams of light are coherent when the phase difference between their waves is constant; they are noncoherent if there is a random or changing phase relationship.

### What is MRI phase coherence?

Phase Coherence. A term describing the degree, to which precessing nuclear spins are synchronous.

#### What is phase coherence EEG?

Coherence is an estimate of the consistency of relative amplitude and phase between signals detected in coils or electrodes within a set frequency band. In sensor space if signals are in phase then their amplitudes will add, if they are out of phase the signals will subtract possibly reducing the coherence value.

What is phase coherence audio?

Phase is the relationship of two or more signals coming from microphones on the same sound source. Think of it as the timing of the signal. If both mics are not the same distance, a good rule is to place the far mic three times the distance from the source as the close mic. This will help eliminate phase issues.

Why do spins precess?

Nuclei precess around the magnetic field for essentially the same reasons that tops or gyroscopes precess around a gravitational field: For the gyroscope, angular momentum results from a flywheel rotating about its axis. For the nucleus, angular momentum results from an intrinsic quantum property (spin).

## What is coherence between signals?

In signal processing, the coherence is a statistic that can be used to examine the relation between two signals or data sets. It is commonly used to estimate the power transfer between input and output of a linear system.

### How do you calculate coherence of an EEG?

That is, because spectral coherence (or Magnitude Squared Coherence) is calculated |Sxy/Sxx*Syy|, i.e. the cross-spectral density divided by the product of the autospectra. There may be cases where the connectivity increases, whereas the power decreases.

#### What is phase locking factor?

(1997), Lachaux et al. (1999), Ghuman et al. (2011). Phase locking is a measure of the propensity for two time series signals to maintain constant phase separation with each other over a period of time. Phase locking values range from 0 for a random phase relationship to 1 for a fixed phase relationship.

Which is the best definition of phase coherence?

Two definitions that we like are listed below. In many ways, the term ‘Phase-coherent’ is not strictly defined. Often, it is interpreted as signals/systems operating at the same frequency with a consistent phase relationship. In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency.

What does in-phase and coherent mean in waves?

Coherent means that the phase difference between two waves is CONSTANT. They can be in phase, out of phase, or neither. This means that at any given instant the phase difference between the waves is some angle θ and the value of this angle never changes.

## When does a signal have a coherence time?

In the broad spectrum of the graph, the signals aren’t coherent. But if you look at a small time segment (a few cycles), they are close to being coherent. Looking at it this way, the signals are said to have a “coherence time”. If the phase difference of the two waves is the same, they are coherent.

### What is the relationship between coherence and correlation?

Coherence and correlation. The coherence of two waves expresses how well correlated the waves are as quantified by the cross-correlation function. The cross-correlation quantifies the ability to predict the phase of the second wave by knowing the phase of the first. As an example, consider two waves perfectly correlated for all times.