EMF meter

EMF measurements are measurements of ambient (surrounding) electromagnetic fields that are performed using particular sensors or probes, such as EMF meters. These probes can be generally considered as antennas although with different characteristics. In fact probes should not perturb the electromagnetic field and must prevent coupling and reflection as much as possible in order to obtain precise results. There are two main types of EMF measurements:

EMF probes may respond to fields only on one axis, or may be tri-axial, showing components of the field in three directions at once. Amplified, active, probes can improve measurement precision and sensitivity but their active components may limit their speed of response.

Measurements of the EMF are obtained using an E-field sensor or H-field sensor which can be isotropic or mono-axial, active or passive. A mono-axial, omnidirectional probe is a device which senses the Electric (short dipole) or Magnetic field linearly polarized in a given direction.

Using a mono-axial probe implies the need for three measurements taken with the sensor axis set up along three mutually orthogonal directions, in a X, Y, Z configuration. As an example, it can be used as a probe which senses the Electric field component parallel to the direction of its axis of symmetry. In these conditions, where E is the amplitude of incident electric field, and θ is the amplitude of the angle between sensor axis and direction of electric field E, the signal detected is proportional to |E|cos θ (right). This allows obtainment of the correct total amplitude of the field in the form of

or, in case of the magnetic field

An isotropic (tri-axial) probe simplifies the measurement procedure because the total field value is determined with three measures taken without changing sensor position: this results from the geometry of the device which is made by three independent broadband sensing elements placed orthogonal to each other. In practice, each element’s output is measured in three consecutive time intervals supposing field components being time stationary .

An EMF meter is a scientific instrument for measuring electromagnetic fields (abbreviated as EMF). Most meters measure the electromagnetic radiation flux density (DC fields) or the change in an electromagnetic field over time (AC fields), essentially the same as a radio antenna, but with quite different detection characteristics.

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Wikipedia