A Passive Very Low-Frequency (VLF) Electric Field Imager

It is shown that an array of D-dot sensors can be implemented to not only detect, but for the first time, image very low-frequency electric fields. D-dot sensors sense current proportional to the time derivative of the electric field. The signal of interest is extracted from each D-dot pixel using a lock-in amplifier through an automated multiplexer. We have successfully rendered very low-frequency electric field images from energized wires using the proposed electric field imager. As a proof-of-concept, the arrays were fabricated on both a printed circuit board and a flexible polyethylene naphthalate substrate, the latter of which incorporates a thin-film transistor process. Such a device will have commercial and industrial applications, such as imaging sources of electromagnetic interference as well as security applications for noninvasive monitoring.