Electric field imaging

Electric field imaging using illumination with a static or quasi-static electric field

Introduction

The human body has an electric activity and an electric field. As this field changes in time, it generates a magnetic field. As a result, the human electric and magnetic field, or more generally the biofield, is characterized by an electric and a magnetic flux, albeit of small intensity. Quantitative determination of the human biofield may be conducted by two main biofield imaging modalities: electric field imaging and magnetic field imaging.

Electric field imaging

Given that the electric field of the human body is of small intensity, it is difficult to detect it passively with an electric field sensor. However, we can conduct active detection by illuminating it using a static electric field. Alternatively, we may use a quasi-static field for illumination. By the term quasi-static, we refer to an electric field that can be considered practically static given that it remains almost unchanged in time; in other words, it stands “still”. Fields which change very slowly or in other words have a very low frequency, such as those that are equal to or less than 60 Hz are considered quasi-static. 

As the human body will distort the illuminating field due to its electric properties (e.g., conductivity, permittivity) including its own electric field emission, a composite electric field can be detected by the sensor. The latter registers voltage and thus measures electric potential. An electric potential image will be created.

A system for electric field imaging of the human body as well as that of objects has been developed by NASA. The system is described on the NASA Technology Transfer website with inclusion of a video presentation of the inventor (Figure 1), which is also available independently on YouTube. A shorter video is also available on YouTube.

Figure 1: NASA Langley's Electric Field Imaging System [1, 2]

In brief, the system consists of the following components:

(a) a low-frequency electric field (2 Hz), termed quasi-static, which is created by a generator and is used to illuminate a human or an object,

(b) an array of electric field sensors (FET transistors).

The human body or an object causes a distortion of the electric field, which is detected by the sensor. This setting is similar to airport detection systems which take pictures using millimeter waves for humans or X-rays for baggage.

The principle of operation of the system is described in Figure 1. In brief, electric field sensors are placed along the red line thus forming an array. The electric field is applied on the blue line. In this case, a quasi-static electric field of 2 Hz created by a generator is applied. A uniform electric field is generated between the two lines. The setting is similar to the plates of a capacitor. The human or the object being illuminated by the electric field disturbs the field. A composite electric field is detected by the sensors, as shown on the right, creating an image of electric potential.

Figure 1: Electric field sensors are placed along the red line thus forming an array. The electric field is applied on the blue line. A uniform electric field is generated between the two lines. The setting is similar to the plates of a capacitor. The human or the object being illuminated by the electric field disturbs the field. A composite electric field is detected by the sensors.

It is noted that the electric field sensor can be used on its own, meaning without illumination, for strong electric field emitting objects such as electric wires. For instance, it can be used to evaluate leakage from poorly shielded wires. Such applications are examples of non-destructive testing. The need for illumination is also dependent on the threshold of detection for the sensor.

NASA reported [*] that an alternative electric field imaging (EFI) system optimized to evaluate electric fields at significant distances (greater than 1 mile) was being developed for weather-related applications.