Category Archives: Sensors

Capacitance calculation using EMS for SolidWorks

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Computing the value of capacitance for a parallel plate capacitor with multiple dielectrics

What is a capacitor?

Capacitor is an electrical device that can store electrical energy. In a way they are similar to batteries but not exactly the same. In a battery, it is the chemical reactions which produces electrons in one location (also called as a terminal in battery terminology) and the movement of these electrons from one terminal to another results in a current flow. But capacitors don’t produce electrons but only distributes them unevenly. A capacitor can be charged by connecting it to a battery. Once it is charged (and removed from the battery) it stores charges. You can now use this capacitor to say light up a small light bulb for some time. A simplest capacitor is a parallel plate capacitor (figure 1). It has 2 parallel metallic plates separated by a distance. If there is no material in between the plates, then it is filled with air. This air which is an insulator is also called as dielectric.

Parallel plate capacitor

Figure 1 – Parallel plate capacitor

How does a capacitor store charges?

Let us refer to Figure 1. When the top plate is connected to the positive terminal of a battery and the bottom plate to the negative terminal, the capacitor is being charged. Before the capacitor is connected to the battery, it is electrically neutral. The amount of positive and negative charges in the top plate are the same. This is also the case for the bottom plate. So as a unit, the capacitor is electrically neutral (a state when the quantity of positive charge is the same as the negative charge). Now when connected to the battery, the electrons from the top plate move to the bottom plate through the wire and the battery. This creates a net positive charge on the top plate and a net negative charge on the bottom plate. Still as a unit, the capacitor (the 2 plates put together) is still electrically neutral. It is just that the charges are distributed in such a way that one plate contains a net positive charge and the other a net negative charge. Now this capacitor can be connected to a load like a light bulb and there will be a flow of electrons from the bottom plate to the top plate through the light bulb. The light bulb sees a current coming in and hence it glows. This flow of electrons happens till the top and bottom plate becomes electrically neutral. So you don’t expect the light bulb to be glowing for a long period of time.

How are capacitors measured?

Capacitors are measured and rated by the amount of charge it can hold. This is measured in Capacitance and the unit for capacitance is Farads or Microfarads. Higher the capacitance, the more charge the capacitor can store.

What role does the dielectric play?

So far we haven’t looked into dielectric and what role it plays in a capacitor.  The dielectric choice is important in a capacitor because as the capacitor is charged there is an electric field generated in the dielectric. When you put more and more charge, the electric field build up. This is possible up to a point when the electric field reaches the dielectric breakdown. At this point the dielectric breaks down and hence becomes a conductor of charges. The capacitor can no longer store charge.

Our example – capacitor with multiple dielectric

Let us look at a case where there are multiple dielectrics in a capacitor. As shown in Figure 2, the parallel plates are filled with 3 dielectrics. The objective is to find the capacitance of this capacitor using EMS for SolidWorks.

Capacitor with 3 dielectrics

Figure 2 – Capacitor with 3 dielectrics

EMS for Solidworks can

  • Compute the capacitance of this capacitor
  • Compute the electric field in the dielectric region
  • Predict if any breakdown occurs

Capacitance calculation EMS results

According to EMS, the value of the capacitance is 6e-11 Farads (Figure 3). Figure 4 shows the electric field distribution in the dielectric region when the capacitor is connected to 12 V battery.

Capacitance as computed by EMS

Figure 3 – Capacitance as computed by EMS

Electric field distribution in the dielectirc - Capacitance calculation

Figure 4 – Electric field distribution in the dielectirc

Validation

Theoretical Result EMS Result
Capacitance (F) 60.08e -12 F 60.084e -12 F

 

The formula for the theoretical result is taken from the source below.

Source Capacitance

Conclusion

EMS for SolidWorks can accurately predict the capacitance and the electric field distribution of any type of capacitor. Most real life capacitors don’t have a plate area that is very very large. In fact, the length is very comparable to the thickness of the dielectric. In such cases, the analytical models don’t hold true. These are the cases where EMS for SolidWorks can be an excellent software for modeling and studying capacitors. The author wishes to express special thanks to Mr. Majdi El Fahim for the solid modeling and simulation of the capacitor presented in this article.

For more information about EMWorks and its products, visit www.emworks.com.

New article about inductive noise problems

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3D FEA Software Solves Tough Inductive Noise Problems
by Peter Markowski, Envelope Power, Ansonia, Conn.
A previous article on 3D electromagnetic finite element analysis (FEA) software explained how a new generation
of these tools, which includes EMS from EMworks, can be used for optimization of high-frequency transformer
design (see the reference.) In this article, I would like to show how the same software can help to solve difficult
layout problems in electronics, especially power electronics.
Switched-mode power supplies are notorious for hard-to-eliminate noise problems simply because we cannot
completely avoid proximity of high-power switching circuits and sensitive controls. Good engineering practices
such as minimizing high-frequency current loops and voltage surfaces, perpendicular arrangement of potential
source-target sets and using large copper planes for shielding are naturally a must. But without any way of
quantifying problematic phenomena it is impossible to know if we are pushing our luck and if we did the best we
could within the given constraints. In the end, we have to make a choice between unnecessarily conservative
designs and risking costly, time consuming (and stressful!) fixing of prototypes.

To read more, http://www.emworks.com/ckfinder/userfiles/files/design_EnvelopePower.pdf

A Spaceclaim®-embedded Multiphysics Simulation Package

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MONTREAL (September 25, 2014) – EMWorks Inc. announces the launch of its multi-physics simulation package SimClaim which is fully embedded in Ansys SpaceClaim®, formerly SpaceClaim, Engineer®.  Based on the powerful finite element method, SimClaim brings the company’s proven simulation technology to the widest base of mechanical, electrical and electromechanical designers seeking to validate and optimize their electrical, thermal, and structural designs all within the SpaceClaim environment. “We are pleased to have partnered with SpaceClaim to bring this all important multi-physics simulation technology to the SpaceClaim user community. The support we received from SpaceClaim over the last couple of years has been instrumental in accomplishing this important milestone for our company” said Dr. Ammar Kouki, Vice-President of EMWorks. He added “Ansys SpaceClaim®, is an extremely powerful 3D direct modeling software package that eliminates CAD worries for designers. Direct modeling is dramatically different from the traditional CAD software because it allows the user to directly access the model without even knowing its history. SimClaim leverages this power to enable designers and CAE specialists to carry out conceptual analysis inside SpaceClaim in record time without needing to be CAD experts. CAD experts on the other hand, will find that the SpaceClaim-SimClaim combination is hard to beat when it comes to design validation through simulation given the speed and the highly efficient workflow that this combination offers.”

Electromechanical devices in EMS?

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Electromechanical, electromagnetic, and power electronics devices can readily be studied using EMS. Electromagnetic behaviour could also be investigated with EMS. Below is sample list of devices and applications classified by areas:

Electromechanical
• Motors and generators
• Linear and rotational actuators
• Relays
• MEMS
• Magnetic recording heads
• Magnetic levitation
• Solenoids
• Loud speakers
• Electromagnetic Brakes and Clutches
• Alternators
• Magnetic bearings

Electromagnetic
• Coils
• Permanent magnets
• Sensors
• NDT, NDE
• High power
• High voltage
• PCBs
• MRI Magnets
• Induction heating
• Bushings
• Switchgear
• Cables

Power electronics
• Transformers
• Inverters
• Converters
• Bus bars
• Inductors

Electromagnetic behavior
• Insulation studies
• Electrostatic discharge
• Electromagnetic shielding
• EMI/EMC
• Electromagnetic exposure