Issues of electromagnetic interference can cause malfunctions or degrading effects to the device’s output signal or complete failure of the electronic devices. In order to shield these components from this interference, the popular and commonly known EMI gasket is used to contribute to the formation of an electromagnetic shield. However, to prove if the EMI gasket has done its job of offering the right level of protection against emissions, it has to be tested. In this article, we will discuss on how you can test your EMI gaskets in your devices in various ways for better performance.
- Visual Inspection
It is recommended that a first check to assess the effectiveness of an EMI gasket involves a visual check. Although this method does not quantify the performance of the gasket it might be useful in determining potential problems that might hinder performance of the gasket in shielding against EMI. Set your focus on signs of physical abuse or excessive use by looking for related signs such as cracks, rags, or what is caused by compression. Further, ensure that the surface of the gasket is clean of debris, dirt or any other contaminant that may affect the ability of the gasket to have a correct seal. Any signs of damage or wear must be taken seriously and the organization may have to order a new EMI gasket for the SDRAM or SIMM board assembly.
- Contact Resistance Testing
The effectiveness of an EMI gasket is determined by its capability of making a conductive contact between the two mating surfaces. Among the easy ways to check this conductive connection is by doing a contact resistance test. This test involves taking an electrical measure of resistance between the EMI gasket, and the surfaces it is sealing. A low reading will confirm that the gasket is electrically conducting as planned and to the level where it also provides shielding from EMI. On the other hand low resistance may be accompanied by low conductivity of the material and therefore low effectiveness of the shield. Usually, to measure contact resistance of the gasket, specific tools like a multimeter or low resistance ohmmeter are incorporated.
- Test & Measurement Techniques: Shielding Effectiveness
A slightly more complicated technique for evaluating EMI gaskets is to test the shielding effectiveness of the gasket. SE is the measure of EMI gasket’s efficiency to prevent the flow of electromagnetic interference. This test can be done using signal generator and spectrum analyzer generally to perform the test. The signal generator sends out a known electromagnetic signal that the spectrum analyzer then records the amount of EMI permeating the gasket. Shielding effectiveness is simply derived by performing an interference comparison before and after utilizing the EMI gasket. High attenuation means that the amount of EMI that is reduced by the gasket is high, while low attenuation means that improvement was needed.
- Time-domain reflectometry (TDR) testing.
Another innovative technique used to evaluate effectiveness of EMI gaskets is time domain reflectometry (TDR). TDR testing is where a pulse signal is run through a test cable and the reflected signal monitored to look for any spikes which will show up any impedance mismatches that may suggest a problem with the gasket’s seal. The use of TDR during EMI gasket testing means that it can show how effectively the gasket fits against the mating surfaces and if there are breaches in shielding or variations in the shielding. Usually, this method is applied in complicated apparatus in which differential testing of EMI shielding is essential.
- Environmental Testing
Temperature cycles, fluctuations in humidity and exposure to chemicals will have an impact on the performance of EMI gaskets. For the purpose of evaluating serviceability of the gasket it is necessary to test it under different conditions which are created in the given device. For instance, in temperatures, carrying out a test where the device is exposed to the chamber with high temperatures or low temperatures show how the EMI gasket will perform under pressure. Likewise, conditions that involve specific exposure to moisture, dust or chemicals will indicate to what extent, the gasket continues to remain protective despite the harsh conditions. EMI gasket testing under environmental conditions is acceptable since it provides an indication of these gasket’s behaviour in the real world after a given period of usage.
- EMI Field Probing
The second way of examining the efficiency of EMI gaskets is with the help of EMI field probes to measure the electromagnetic field within the device. This method enables one to observe areas in which EMI leakage might be occurring, and the effectiveness of an EMI gasket in minimizing interference. Using field probe, it is possible to investigate the behavior of the electromagnetic field density when the gasket is pressed to the components of the device. When high amounts of EMI are measured internally this indicate that the gasket might not be offering adequate shielding to protect the device.
- Comparative Testing
Comparative testing includes the use of devices with the EMI gasket installed and without to assess the effectiveness of an EMI gasket. Therefore, when the signals’ strength is compared before and after inserting the gasket, a direct proof of the gasket’s efficiency is obtained. If the best performance of the device changes drastically with the use of the gasket, then the conclusion that should be made is that the EMI gasket is preventing electromagnetic interference.
Conclusion
EMI gaskets contribute highly in providing protection for the sensitive electronic devices and it is critical to design ways of testing them in order to confirm that they can effectively shield every device from EMI. Namely, to confirm that your EMI gasket is performing as it should, you can use simple means of visual inspection, contact resistance test, shielding effectiveness test, TDR, environmental test, field probing and comparative test. This ensures that if there is any problem, it will most likely be detected during testing rather than it causing a complete breakdown of a device.