Many electrical engineers would have thought that EMI only exists when you received a ‘FAIL’ report from a test house. Well, unfortunately, that is not the case. EMI is everywhere and among us. One of the least expected is during your routine shopping at your favorite grocery store.
Think about when you are walking happily along the shopping aisle with your cart full of your favorite food, of all a sudden, you received an electrical shock when your hand accidentally bumped into your friend’s. No, that is certainly not a love shock and he/she is not in love with you too. And no, you didn’t touch any live wire either. How do you get this electrical shock in the first place then? We call this phenomenon the Electrostatic Discharge (ESD). ESD happens when there is a separation of charges due to physical rubbing against two or more materials. The separated charges are very unstable and ‘looking forward’ to recombine as they build a huge potential difference (in kilo Volt) between the materials. The potential difference can be from 2kV up to 20kV at certain favorable conditions, enough to start a fire to flammable material. While ESD does not manage to start a fire in many occasions (except in a petrol filling station), it can cause irreversible damage to electronics, such as your smartphone, digital television, computers, and other digital circuits just to name a few. You now thought that how have you not damage anything yet? Well, most products are CE certified and among the tests that must be conducted is the ESD immunity test. In EMC testing, products are safeguarded against ESD damage by undergoing the IEC61000-4-2 ESD immunity test.
At this point, you must be confused, who has been secretly rubbing against you. That is certainly a security and privacy breach! Fortunately, that is not the case and no one is rubbing or has been against you. The culprit is the shopping cart but under certain circumstances. What could be possibly rubbing against the cart? When the cart is traveling, the rotating wheels are rubbing against the debris that they collected overtimes. The debris which is in contact with the wheels and the body of the cart begins separating the charges, one goes to the wheel (and probably return to the ground), another one goes to the metal body of the cart, and of course on to your hands and body as you touched it.
So the next time you go for your shopping, if you notice clogged and dirty wheels on the cart, you shall know that ‘love’ shocks await.
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