The unit is constructed from a number of planar log-periodic spiral antennas etched on printed circuit boards (PCBs) as well as other components, enclosed inside a resonant cavity (the case). The individual antennas are tuned-in precisely to work together seamlessly as a system.
Spiral antennas belong to the class of “frequency independent” antennas, characterized by very wide bandwidths and compact size. They were invented in the mid-1950s by wrapping the arms of a simple dipole antenna around each other to form a spiral.
Further developments have been made in the 1960s leading to the development of several types of spiral antennas including the Archimedean spiral, square spiral, log-periodic, conic and other types.
Spiral antennas – due to their very wide bandwidth and compact size – are widely used today in the defense and communication industry for sensing applications including military aircrafts, landmine detection, GPS receivers, satellite communications networks.
Research is also ongoing in the medical field where the potential use of miniature sized spiral antennas is explored for implantable bio-medical applications.
Our magnetic DPC system uses three-arm spiral antennas, however other types of spiral antennas with one, two, three, four or more arms can also be built and utilized.
For simplicity, we are going to illustrate some of the concepts on one of our smaller units – larger devices are more complex in construction but their working principle is similar.
As shown below, the unit is composed of the following modules:
The Case (Resonant Cavity)
The primary role of the case is not decorative but a functional one, so in its design functional considerations have given precedence over aesthetic aspects. The case is made of high-purity aluminium, which is a paramagnetic material – it is not magnetic; it does not hold onto any magnetism.
The case acts as a Faraday cage, blocking some of the high frequency electromagnetic wavelengths which could interfere with the operation of the device. It is a common misconception that Faraday cages provide full blockage or attenuation; this is not true. They cannot block stable or slowly varying magnetic fields, such as the Earth's magnetic field. A compass, for example, still works inside a Faraday cage, but it shields to a large extent external electromagnetic radiation.
The top circuit is a receiving antenna or an energy intake circuit. The receiving antenna picks up slowly varying low-frequency magnetic components from Earth’s geomagnetic field. The induced currents in the copper arms of the antenna – through a hard-wired connection in the center – are passed on to the central and bottom circuits for further processing.
Central & Bottom Circuits
The central & bottom circuits are elaborate filtering circuits that are tuned on the critical frequencies that have been identified to be responsible for the rise of water inside the capillaries. The bottom circuit deals with the lower frequency band (1 – 25 MHz) while the central circuit with the higher frequency band (25 MHz – 2 GHz).
The filtering circuits are passive bandpass filters formed by a complex LC (inductance-capacitance) network that lets through everything except the critical frequencies onto which they are tuned, which will be dissipated (short-circuited) inside the case.
The filtered signal can easily be visualized on a spectrum analyser, a special instrument used for visualizing high frequency signals. Depending on the instrument and measurement type, filtered-out frequencies show up on the screen either as sharp peaks or valleys. Please see below some actual pictures of the final filtered signal showing up as narrow pin-type signals on the screen.