Introduction
So far, we've covered some basic electrostatics principles and the importance of considering charge along with voltage for ESD control. Today, we will discuss the missing piece of the puzzle: electric fields. We will cover the sensors that measure these fields and explain how the StatIQ Band measures the charge on your body to prevent damage to your electronics.
E-fields and Charge
This image shows the electric field lines in the space between charged objects. While they are invisible much like charge and voltage, these fields exist all around you, wherever there is charge nearby. You can see the induced charge effects we discussed in the last post, as negative charge on the objects is attracted towards the external positive charge in the middle of the frame.
What is also noticeable from the figure is that the density of the electric field lines is proportional to the density of charge on the surface of the shapes. In fact, it is simple to prove using Gauss’ law that they are exactly proportional on the surface of any conductor.
This got us thinking here at IONA – is there a way to measure the field on the surface of objects in order to determine the underlying charge? It turns out that field meters are quite common in existing electrostatics instrumentation.
Electric Field Measurements
Electric field meters come in many different forms, and are used in several different applications in the ESD mitigation industry. In the case of a static charge meter, the internal field mill is held near an object to determine if it holds any charge. To get accurate readings, the field meter must be grounded, and it is the induced charge effect discussed in the last post that causes the measurable field.
In both the charge plate monitor and the walking body voltage apparatus, the field meter is used to remotely determine the voltage on an object without affecting it (electrostatic charge quickly drains away through the impedance of traditional voltage measurements). But what if we turn a field mill around and place it on the body we wish to measure? New advances in technology have enabled IONA Tech to build an electric field mill small enough to place in a wearable device, and a modern wireless architecture allows us to easily transfer and process the data.
IONA Tech's StatIQ Band
The StatIQ Band contains the smallest and most accurate field meter ever created, enabling a wearable device that straps to the user’s arm. Instead of using the meter for non-contact measurements of other objects, we turned it around to measure the charge on the body itself!
We are often asked, what is the ground reference for the field mill in the StatIQ Band? Well, a ground reference is only necessary for accurate measurements in the traditional non-contact application. The back plate of the Band makes electrical contact with the dissipative smock of the user, so really the body is the reference for measuring the local charge. Embracing this perspective shift requires a slight change in mindset, but the approach is derived from first principles physics and supported by many years of electrostatics research.
Conclusion
By focusing on measuring charge on the body, our technology achieves a more precise picture of ESD risks, enabling proactive measures to prevent damage. But if I told you that you have 3 nC/m^2 of charge on your arm, would it mean anything? Of course not, but it turns out that your body voltage is exactly 100V, barring external charge influences. In the next post, we’ll discuss this ‘Body Voltage Equivalent’ output from the StatIQ Band and when it is and isn’t equal to body voltage.
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