Technical Notes

We have collected general purpose technical information here for your reference, including technical notes, presentations and webinars. For product specific technical notes, please see the Technical Support section under the appropriate Product Page.

Magnetic Units (Gauss and Tesla)

Conversion of Gauss to Tesla:
1µG = 0.1nT, 1mG = 100nT, 1G = 100µT, 10G = 1mT, 10,000G = 1T

Relationship between Magnetic Flux Density (B) and Magnetic Field Strength (H):

In vacuum (or air) B=µoH. For SI units µo = 4pi x 10-7H/m, B is expressed in Tesla and H in Ampere turn/m or A/m. Hence in vacuum or air a flux density of 1T = 796kA/m.
For cgs units µo = 1, B is expressed in gauss and H in oersted. Hence in vacuum or air a flux density of 1 gauss = 1 oersted.
For further information visit the NIST Reference on Constants, Units, and Uncertainty

Magnetic Field Vectors and Components

The magnetic field at any point in space is a vector quantity. This means there is a direction associated with the field as well as a field strength. Consider the arrow below:
Formula

The direction of the arrow can be thought of as the direction of the magnetic field. The length of the arrow can be thought of as the strength of the field, i.e. the longer the arrow, the stronger the field. Call this length B.

If I place set of axes on the arrow I can divide the field into two components of the field, namely the x component and the y component. Call these lengths Bx and By.
Formula

I can now describe the length of the arrow, or the strength of the magnetic field, in terms of the x and y components. Using the Pythagorean Theorem:
Pythagorean Theorem Formula

Now imagine that there exists a third direction, so that the arrow, B can be pointing out of (or into) the plane of the page. There is now a third component, namely Bz, which in our example is the length of the component stretching from the page outward to the tip of the arrow.
Formula

By exactly the same mathematics, I can now describe B as:
Formula

The value B, is the strength of the magnetic field. Bx, By, and Bz are the three components measured by a three axis teslameter (gaussmeter). A single axis measuring device will change its reading depending on which way the sensitive axis is oriented with respect to the direction of the magnetic field. To obtain a complete representation of magnetic field at any point in space, one needs not only the value of B, but the direction, which can be expressed as the three components, Bx, By and Bz.

Some magnetic field sensors measure only one component of the magnetic field (Fluxgates and Hall effect instruments). These are referred to as single axis devices.

Other instruments measure only the total field amplitude (NMR, ESR). This is the quantity B above.

It is possible to combine three axis sensors to give three field measurements in a single probe package. These are referred to as three-axis devices.

Occupational Magnetic Fields Guidelines for DC Fields

The biological effects of AC fields are detectable at much lower levels than for DC fields. It is therefore inappropriate to use the AC field Guidelines for DC fields.

The International Commission on Non-Ionizing Radiation Protection (ICNIRP) Guidelines for Occupational Static Magnetic Fields are 200mT for continuous exposure, 2000mT for short-term whole-body and 5000mT for exposure to arms & legs. These field levels are high and indicate the lack of evidence for biological effects from DC fields. The ICNIRP level for persons with pacemakers and other implanted devices is set at the much lower level 0.5mT (5gauss). This level is apparently not related to biological effects but rather to possible effects on electrical or electronic devices (particularly reed-relays) or metal prosthesis.

Adoption of the 0.5mT (5gauss) level and installing shielding or access restrictions avoids potential problems with operators or visitors having implanted devices and also avoids malfunction of most electronic control & test equipment used in the vicinity of magnets. Setting DC Field exposure levels at less than 0.5mT seems unnecessary except for special, magnetically sensitive processes. (Some electron beam equipment such as display devices or electron lithography systems require lower fields.)

The US Food and Drug Administration (USFDA) in “Guidance for the Submission of Premarket Notifications for Magnetic Resonance Devices” requires iso-field contours at 0.5mT (5gauss), 1mT, 10mT, 20mT, 40mT, and 200mT (see Section 4, Site Planning) in planes parallel and perpendicular to the magnetic field. Entry into regions where the magnetic field is in excess of 0.5mT is only allowed for authorized personnel.

The earth’s geomagnetic field is about 0.05mT (50µT or 0.5gauss). Inside buildings there can be variations due to steel in the building construction. GMW has measured DC fields to about 0.1mT in the open space of buildings and to 0.5mT at the corners of large steel components such as machine tools.

In measuring the actual fringing magnetic field it is necessary to remember that the magnetic field (magnetic flux density, B) is a vector quantity with three components. The typical Hall effect Gaussmeter or Teslameter only measures one component of the field. To measure the total field it is necessary to measure the three components Bx, By & Bz and then calculate the vector total (square root of the sum of the squares:

Formula The three component measurement can be difficult and time consuming with a standard Hall gaussmeter or teslameter. The Metrolab THM 7025 Three Axis Hall Effect Teslameter measures the three components simultaneously & provides the vector total with a resolution down to 0.01mT (0.1gauss). Senis Three Axis Magnetic Field Transducers provide three analog components with a frequency response from dc to approximately 1kHz and can be used with a data logger to map or monitor magnetic fields in the range 0.01mT to 2T. For high resolution measurement or mapping of magnetic fields of less than 1mT, the Bartington Mag-03 range provides very high resolution with frequency response from dc to 3kHz. Acquisition and spectral analysis in a portable instrument is provided by the Bartington Spectramag-6.

For more details, please refer to:

Ian J. Walker, August 2000, revised October 2015.

RoHS and WEEE Compliance

The EU’s Restriction of Hazardous Substances (ROHS) Directive 2002/95/EC, often referred to as the “lead free” directive, restricts the use of certain hazardous substances in the design and production of electrical and electronic equipment. It is closely linked with the Waste Electrical and Electronic Equipment (WEEE) Directive 2002/96/EC which sets collection, recycling and recovery targets for electrical goods and is part of a legislative initiative to solve the problem of huge amounts of toxic waste.

Substances restricted by the RoHS Directive include: lead, mercury, cadmium, chromium VI (also known as hexavalent chromium or Cr6+), polybrominated biphenyl (PBB), and polybrominated diphenyl ether (PBDE). This RoHS Directive adopted by the Member States of the Euoropean Union is effective July 1, 2006, each Member State will adopt its own enforcement and implementation policies using the Directive as a guide. Whether products are made in the EU or imported to the EU the RoHS Directive still applies to all equipment specified in the WEEE Directive, certain exemptions do apply.

Beginning with Japan’s adoption of the Law for Promotion of Effective Utilization of Resources (PEUR) in 1991, recycling laws have encouraged Japanese manufacturers to limit the use of hazardous materials. Although Japan does not have any legislation directly dealing with the RoHS Directive, starting July 1, 2006Japanese manufacturers began limiting the use of hazardous substances, similar to the RoHS guidelines, to meet the PEUR Amendment Obligation to provide information on chemical substances in home appliances and PCs. A content marking standard J-Moss was established by (Japanese Industrial Standard) JIS C 0950 to certify the presence of a specific chemical or substance for target products. The target electrical and electronic products of Japanese manufacturers and import sellers restricted by J-Moss include: personal computers, unit-type air conditioners, television sets, refrigerators, washing machines, microwave ovens, and clothes dryers.

For more information refer to:

Webinar: Integrated Probe Card Solutions for Magnetic Testing

We discuss combining GMW’s expertise in Electromagnets & Magnetic Modeling with Celadon expertise in Probe Cards & Testing for complete integrated solutions compatible with all Probers. The fully integrated probe card is typically used for on-wafer parametric tests, modeling, characterization and wafer level reliability as well as functional tests.

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