Author Archives: Arvind Krishnan

Capacitance calculation using EMS for SolidWorks


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


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


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

The concept of air region in EM Simulation


In all EM simulation, the empty spaces (or volumes) within a model and around a model are important. This is because we are interested in computing and plotting the magnetic and electric fields in these regions. Imagine a magnet lying on a table, there is magnetic field inside the magnet (of course) but there is also a magnetic field in the air region surrounding the magnet and also in the table. In order to capture these fields, one must model these empty spaces as 3D geometry along with the components of interest.

If you are using EMS for SolidWorks, creating air geometry inside SolidWorks is extremely easy (see video linked below). You first have to create a new part in the assembly you want to simulate. Remember that all EMS models have to be SolidWorks assembly to be simulated. In the new part, you can sketch and extrude any arbitrary shape as long as you make sure that this shape sufficiently encloses all the other parts of the assembly. Next you must use the Cavity feature in SolidWorks to subtract out all the inner components. Now your model is ready for EM simulation (see Figure 1). Please note that you are not just limited to a box region as shown in the figure. For some designs which are cylindrical in nature, it is more appropriate to create a cylindrical air geometry (see Figure 2).Air region in EM Simulation

Figure 1- Air region created around a C core inductor using SolidWorks cavity feature

Air region cylindrical in EM Simulation

Figure 2- One can create a cylindrical air region as well for models that are cylindrical in nature

Video explaining how to create air region in SolidWorks:

When you create the air region, make sure that it is sufficiently big so that the results at the extremities of the air region is negligible compared to the ones closer to the model. For example, plot the magnetic flux density on the boundary faces of the air region and compare those values to the maximum value of the magnetic flux density. Also the magnetic flux density should be fairly uniform in these boundary faces.

This blog post is a part of Learn EMS for SolidWorks series. To learn more about EMS, visit

Embedded Electro-mechanical/ Electro-magnetic (EM) simulation inside Autodesk Inventor


by Arvind Krishnan, Director of Product Management, EMWorks

What is EM simulation?

Electro-magnetic or EM simulation is the use of computational techniques to determine the electric and magnetic fields in an electric machine or device. EM simulation can give valuable insight to an engineer about his designs. She can obtain engineering parameters like inductance, flux linkage, impedance, Back EMF, Induced voltage, Capacitance, Forces and Torques etc. So engineers who design electrical devices like motors, generators, linear transducers, inductors, actuators, transformers, voice coils, sensors, resistors, insulators, induction heaters etc can benefit largely from EM simulation. Without EM simulation, one would have to resort to costly prototype testing to validate their designs leaving little or no room to optimize and improve the products.

Benefits of EM simulation

EM simulation fits very well into the design process. Companies who use EM simulation are able to create high quality optimized products which make them hypercompetitive in todays market. The rise in popularity of simulation tools have ensured that companies all around the world from industrialized nations of the west to the developing nations of the east have a level playing field. What is more important is that the seamless integration of EM simulation into the product development process have accelerated this trend. Now an engineer can quickly put his concepts and inventions to life my modeling them in 3D CAD packages like Autodesk Inventor. CAD embedded EM simulation packages like EMS for Autodesk Inventor enables them to validate, improve and optimize their design quickly without ever entering a testing laboratory or engaging in a prototype. Further more, EM simulation can be coupled to mechanical and thermal simulations to accurately predict the thermal and mechanical performance of electrical devices. Once the design is accepted, 3D printers bring life to these digital products which can then be tested before they are sent for mass manufacturing. This 3D digital engineering product development process has revolutionized the electrical machines and devices industry. Figure 1 shows a typical product development workflow using Autodesk Inventor and EMS for Inventor.


Figure 1 – The product development workflow inside Autodesk Inventor

Benefits of integration inside Autodesk Inventor

Autodesk Inventor is a very popular 3D CAD platform for engineers in the field of electrical machines and devices. EMS for Autodesk Inventor enables engineers to incorporate EM simulation into their product development process. Integration inside Autodesk Inventor brings in the following advantages –

  1. Direct use of 3D CAD model for simulation. No need to export CAD geometry for simulation purpose thereby maintaining the integrity of the design.
  2. Enable simulation based product development where simulation feeds into the 3D design allowing engineers to make drastic changes to their initial design concept. All of these are possible without ever leaving Autodesk Inventor platform.
  3. The learning curve for engineers to learn and use simulation is shortened because they don’t have to learn a new program and a new interface. They can work inside their familiar Autodesk Inventor interface to perform their EM simulations.

Application areas

EM simulation has many applications areas ranging from small electrical machines to large transformers. These devices can use DC, AC or other kinds of excitation. The applications of electromagnetics are so vast that it will be a great injustice to categorize them as I have attempted here for the sake of brevity. I admit that there are many devices and applications that overlap these categories.

  1. Rotary and linear actuators, Motors and Generators
  2. Transformers, Inductors
  3. Insulators, high power switches, bus bar networks, Induction heaters
  4. Sensors, motion controllers and measurement devices
  5. Permanent magnet based devices, magnet arrays, magnetic levitation

EMS for Inventor can calculate the magnetic field inside a motor and also the cogging torque

Figure 2 – EMS for Inventor can calculate the magnetic field inside a motor and also the cogging torque

EMS for Inventor can help visualize the losses in the core of a transformer

Figure 3 – EMS for Inventor can help visualize the losses in the core of a transformer


EMS for Autodesk Inventor is a 3D field simulation software that is embedded inside Autodesk Inventor. It can perform both electric and magnetic simulation with AC, DC and transient excitations. EMS has powerful Multiphysics capability to do coupled EM, mechanical and thermal simulation. EMS customers use the product to design solenoids, motors, transformers, magnet arrays, high voltage insulators, electric generators, speed sensors, induction heaters, bio-medical actuators and magnetizers. Autodesk Inventor customers can download a full trial version of EMS in the Autodesk App store. For more information on EMS, visit

Metal Detector Explained


Electromagnetics and its impact

It is amazing how many applications the theory of Electromagnetics has in today’s world. If Faraday and Maxwell have a chance to view the number of devices that makes use of their discovery, they will be simply blown away. Simply by the impact of their discovery in today’s world, many scientist believe that these two men were probably the most important people to have inhabited the Earth since 1600. You don’t have to take my word, you can read about their impact here.

In this short note, I want to explain the concept of metal detector and how it uses Electromagnetic principles for its functioning. More important we will see how an electromagnetic software like EMS can help companies that design and build Metal Detectors.

Concept of modern metal detectors

The principle of metal detector is quite simple and as the name suggest it is a device that can identify if metals are present say in hard to find places like under the soil, inside rocks etc. It finds its use in detecting things from land mines (really a wonderful use of metal detector which has saved many thousands of life and is still continuing to save) to gold mines.

Most metal detector have 2 coils – one coil carries alternating current usually at very high frequency (1-10 KHz) and other coil acts like a receiver. The excited coil generates a magnetic field and this induces a small amount of current in the receiver coil. This current (also called as Induced current or Eddy current) is known and calibrated. Now when you take this arrangement near a metallic (or ferromagnetic) substance, two things happen. First, the excited coil also induces an eddy current in the metallic (or ferromagnetic) substance. This eddy current produces its own magnetic field that opposes the magnetic field produced by the coils. This causes the eddy current in the receiver coil to drop. A sensor senses this drop in eddy current from the expected value and gives a signal indicating the presence of a metallic substance. In the figure below, the orange coil is the excited coil and the green one is the receiver coil. High frequency AC current is circulated in the orange coil and the eddy currents induced in the green coil in the absence of any metallic substance is calibrated.

Simple arrangement of coils in a metal detectorFigure1 – Simple arrangement of coils in a metal detector

Role of SolidWorks and EMS in designing a metal detector

For an engineer, several design factors need to be considered before this concept can be made into a functional product and that is where SolidWorks CAD and EMS Simulation software can play a vital role. Let us look at some of them.

  1. What is the right size of the coil?
  2. What frequency and magnitude of AC current should be applied?
  3. What is the induced current in the receiver coil under ideal (no metal in the vicinity) conditions?
  4. How can I package the entire arrangement into a product?

Together with SolidWorks, the EMS product can help a designer answer all the above questions. Once a concept coil is arrived at, it can be tested virtually using EMS to visualize all the engineering parameters. For example, engineers can visualize the magnetic flux density in the coils as shown in the figure.

Metal Detector - EMS can plot the magnetic flux density in the coils

 Figure 2 – EMS can plot the magnetic flux density in the coils

EMS product will also give you the value of the induced current in the receiver coil.

Plot of the eddy current density in the receiver coil

Figure 3 – Plot of the eddy current density in the receiver coil

Most importantly you can model different hypothetical situations like what happens to the induced current in the receiver coil when you come across a metallic object at a particular distance from the coil. EMS can also compare the induced eddy currents in the receiver coil when a metallic part is present and when it is not present. This way the product can be perfected before a prototype is made and tested.

Metal detactor - EMS plots with the presence of a metallic part

Figure 4 – EMS plots with the presence of a metallic part

Metal detactor - Compare the eddy currents induced in the presence of a metallic part with the ideal cas

Figure 5 – Compare the eddy currents induced in the presence of a metallic part with the ideal case

Advantages of this approach

The advantage of using Simulation in product development is well studied and many engineers have got impressive results by using this approach. First of all the time taken to bring a concept to the shelf is greatly reduced. Next, the cost of product development is lower as the number of prototypes required to perfect the product is greatly reduced. For most companies which uses this approach, their first prototype with some minor tweaks invariably becomes their final product. Finally, this approach enables innovation in product development as many what-if scenarios which an engineer conceives can be tested thoroughly and the best design can be chosen.

EMS for SolidWorks

EMS for SolidWorks is the first and only completely embedded Gold Certified software for SolidWorks which helps SolidWorks users study their magnetic, electric and electromagnetic designs seamlessly. It can utilize the geometry created using SolidWorks directly for simulation. Its user interface emulates SolidWorks and hence there is no learning curve associated with the EMS software for SolidWorks users. Please click here to try out EMS for SolidWorks and see how it can help you design better products. For more information visit




Magnetic bearings



Bearings are devices which constrains the relative motion of a moving (rotating or translating) part. They also aid in reducing friction. When we think of a bearing we often think of only a mechanical bearing (see image) as it is the most commonly used type of bearing.

Bearings have numerous applications in the field of machine design, automotive, transportation, oil & gas, medical apparatus etc. They are ubiquitous in any device that has motion. In this brief note, I will discuss a bit about a different kind of bearing, Magnetic bearing and highlight its advantages when compared to a mechanical one.

Limitations of mechanical bearings

Mechanical bearings have limited life due to wear and tear and they require lubrication. In many high speed applications they also may need special type of cooling. Nevertheless it is an exhaustible component that needs to be replaced several times during the life of its parent device.

Magnetic bearing

A magnetic bearing facilitates the same functions of a mechanical bearing by employing a magnetic array of permanent magnets. In short there are 2 sets of concentric magnetic arrays which are held in place by the magnetic forces. Since there is no contact there is no wear and tear and technically the magnetic bearing has a very long life.  In addition it can handle very high speeds and large loads with zero friction. This makes a magnetic bearing an excellent choice for machine design, marine, automotive, aerospace and medical devices industry. Recently, there has been a surge in the use of magnetic bearings across various industries. Below is an image of an axial magnetic bearing designed in SoldiWorks. In this design the outer bearing is stationary and the inner bearing is connected to a shaft and is spinning. The weight of the shaft is supported by the magnetic force exerted on the inner bearing.

A magnetic bearing design simulated using EMS for SolidWorks

EMS for SolidWorks helps bearing designers to size their magnetic arrays to support various designs of the shaft (basically different weights). This way the bearing can ensure optimum performance. Another advantage of a magnetic bearing is that it can support offset of the inner cylindrical array wrt to the stationary outer cylinder.


EMS software can predict accurately the forces acting on the inner bearing for various offset positions.

The magnetic arrangement is assembled according to the figure given below. The N-S directions of each magnet is indicated by the black arrows. This type of arrangement can be easily created in EMS and the magnetic flux distribution and the axial force acting on the inner array can be visualized and computed respectively.



Variation of axial force acting on the inner magnet array with the offset is shown below and is automatically computed by EMS. Note that as the offset increases, so does the axial force but after a point the force reduces. Beyond an offset of 18 mm, the force reverses direction and pulls back the inner array. Using these values of axial force, we can compute the axial magnetic stiffness coefficient


EMS for SolidWorks

EMS for SolidWorks is the first and only completely embedded Gold Certified software for SolidWorks which helps SolidWorks users study their magnetic, electric and electromagnetic designs seamlessly. It can utilize the geometry created using SolidWorks directly for simulation. Its user interface emulates the SolidWorks and hence there is no learning curve associated with the EMS software for SolidWorks users. Please click here to try out EMS for SolidWorks and see how it helps you design better products. For more information visit