- Electromagnetic shielding
Electromagnetic shielding is the process of limiting the penetration of electromagnetic fields into a space, by blocking them with a barrier made of conductive material. Typically it is applied to enclosures, separating electrical devices from the 'outside world', and to cables, separating wires from the environment the cable runs through. Electromagnetic shielding used to block radio frequency electromagnetic radiation is also known as RF shielding.
The shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields, though not static or low-frequency magnetic fields. (A conductive enclosure used to block electrostatic fields is also known as a Faraday cage.) The amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic field.
A Faraday cage or Faraday shield is an enclosure formed by conducting material, or by a mesh of such material. Such an enclosure blocks out external static electrical fields. Faraday cages are named after the English scientist Michael Faraday, who invented them in 1836.
A Faraday cage's operation depends on the fact that an external static electrical field will cause the electrical charges within the cage's conducting material to redistribute themselves so as to cancel the field's effects in the cage's interior. This phenomenon is used, for example, to protect electronic equipment from lightning strikes and other electrostatic discharges.
To a large degree, Faraday cages also shield the interior from external electromagnetic radiation if the conductor is thick enough and any holes are significantly smaller than the radiation's wavelength. For example, certain computer forensic test procedures of electronic components or systems that require an environment devoid of electromagnetic interference may be conducted within a so-called screen room. These screen rooms are essentially work areas that are completely enclosed by one or more layers of fine metal mesh or perforated sheet metal. The metal layers are grounded to dissipate any electric currents generated from the external electromagnetic fields, and thus block a large amount of the electromagnetic interference. See also electromagnetic shielding. Note that the reception of external radio signals, a form of electromagnetic radiation, through an antenna within a cage can be severely reduced or even totally blocked by the cage itself.
The Journal of Experimental Biology 202, 1455–1458 (1999)
Printed in Great Britain © The Company of Biologists Limited 1999
- Animal's ability to sense electromagnetic patterns
EMF frequencies or microwave frequencies are overriding normal control mechanisms in the body and shutting off energy production.Omega-News 2 MRZ 2007
Excerpt from Article:
So not only do animals have the ability to sense electromagnetic patterns but they also may see them in great detail. I will use an analogue. Imagine if someone told you the eye senses light. Well that is a very interesting observation. However you know from your own personal observation that you are accustomed to seeing whole patterns and the patterns themselves have personal meaning for you. The brain does translate these simple appearing signals and if you will extracts the information contained in them.
EVOLUTION & DEVELOPMENT 8:1, 74–80 (2006)
- ELF - EM fields disrupt magnetic alignment of ruminants
Possible Alignment Mechanisms.
We can only speculate about the physiological mechanisms of the magnetic alignment of ruminants. Of the numerous mechanisms proposed for the direct interaction of electromagnetic fields with the human or animal body, 3 stand out as operating potentially (also) at lower field levels: magnetically sensitive radical pair reactions (19), electric field ion cyclotron resonance interactions (20), and mechanisms based on biogenic magnetite (21–24).Magnetic alignment in grazing cattle and deer
- Scientists detail neural circuit that lets eye detect directional motion
Excerpt from nächste Meldung 28.11.2002
Now, in a paper in this week’s issue of the journal Nature, biologists at the University of California, Berkeley, have finally detailed the cellular circuit responsible for motion detection in the eye’s retina.
This circuit, which enables us to track moving objects, serves as an example of other brain circuits, some of which perform thousands of computations every second. The findings could aid the design of bionic eyes that track motion and process visual information like our own eyes.
"This work reveals a very sophisticated neural computation, the first non-linear computation performed by the nervous system for which a circuit is close to being solved," said Frank Werblin, professor of molecular and cell biology at UC Berkeley. "It is a preliminary step in understanding how more sophisticated computations are performed by the brain."
- Temporal detection in human vision: dependence on stimulus energy
R. E. Fredericksen and R. F. Hess
JOSA A, Vol. 14, Issue 10, pp. 2557-2569
We have previously proposed and evaluated an economical model of human performance in tasks requiring spatiotemporal signal detection in spatiotemporal noise [Vision Research (to be published)]. The model was successful in describing human psychophysical performance and provides a means for comparing temporal filters (mechanisms) employed under different stimulus conditions. We present investigations into how estimates of temporal mechanisms depend on the contrast energy of the stimulus. Temporal-sensitivity changes result in co-variation of the cutoff and peak frequencies of the low-pass and band pass mechanisms, respectively, with stimulus energy. The results indicate that sensitivity to high temporal frequencies increases as stimulus energy increases, commensurate with extant physiological evidence in cat and primate.
© 1997 Optical Society of America
[Optical Society of America]
- Motion detection in human vision: a unifying approach on energy & features
A. T. Smith* and T. Ledgeway
Department of Psychology, Royal Holloway, University of London, EghamTW20 0EX, UK
Most studies of human motion perception have been based on the implicit assumption that the brain has only one motion-detection system; or at least that only one is operational in any given instance. We show, in the context of direction perception in spatially altered two-frame random-dot kinematograms, that two quite different mechanisms operate simultaneously in the detection of such patterns. One mechanism causes reversal of the perceived direction (reversed-phi motion) when the image contrast is reversed between frames, and is highly dependent on the spatial-frequency content of the image. These characteristics are both signatures of detection based on motion energy. The other mechanism does not produce reversed-phi motion and is unaffected by spatial altering. This appears to involve the tracking of unsigned complex spatial features. The perceived direction of an altered dot pattern typically reflects a mixture of the two types of behavior in any given instance. Although both types of mechanism have previously been invoked to explain the perception of motion of different types of image, the simultaneous involvement of two mechanisms in the detection of the same simple rigid motion of a pattern suggests that motion perception in general results from a combination of mechanisms working simultaneously on different principles in the same circumstances.
- Electroreception in elasmobranches
As a bioengineer I learn to apply mathematical, chemical, and physical concepts to the analysis of biological systems. In the Writing 405 course that I took with Roberta Kirby-Werner, I was given an opportunity to address research issues in my discipline in a formal project. I chose to analyze electroreception, a sensory modality that enables sharks and other animals to perceive electric fields, and wrote a professional-technical paper in which I reported my findings. I studied electroreception because of the insight it gives into the life of animals that perceive the world in a way that we cannot. It also teaches us about identifying and classifying receptors. My objective for this particular paper was to make some of the technical concepts in my discipline accessible to a more general audience which possesses an interest in science.
The Physical Stimulus for Electroreception
In oceans, electric fields are induced by both biological and geological causes. In the latter case electric fields are induced by water flowing or fish swimming through the earth's magnetic field by geomagnetic variations4 and by geophysical events5. The animals use these electric fields for navigation and identification of their environment.
Electric fields in the oceans can also be produced by marine animals. The internal and external electrochemical environments of marine animals differ. The difference creates a voltage gradient across the water skin boundary. The potential difference produces current loops which yield a bioelectric field in the surrounding waters. An animal's behavior can produce additional electric fields. For example, when a fish swims, muscles contract. Muscle contraction takes place when chemically-dependent channels, impermeable to sodium and potassium, open. The movement of such ions across the membrane produces an electric field that travels away from the animal in the conducting medium (salt water).
The number of muscle contractions affects the magnitude of the electric fields. If more muscles contract, the magnitude of the field is greater and vice versa. Furthermore, the intensity of the electric fields changes in the case of a wounded animal. For example, crustaceans can generate a voltage of 50.0 mV measured with a sensing electrode 1 mm away from the surface of the animal. The same crustacean, if wounded, generates a much higher voltage of 1250.0 mV (Kalmijn, 1974). H. S. Burr in 1947 established the presence of these bioelectric fields in the vicinity of marine animals (Kalmijn, 1974). These gradients can be easily detected by certain members of elasmobranches.
- The future of research on electroreception and electrocommunication
Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093-0201, USA
Excerpt from text:
These revelations are sure to change the big picture drastically – not only the picture of how electric fish work and what teleosts with advanced brains can do, but the understanding of mammalian achievement and of the evolutionary biology of complexity. The evolution of complexity has hitherto been discussed with almost no appreciation of the uniqueness of the brain with respect to specific traits that measure complexity.
Bioelectromagnetics 28:379^385 (2007) Source:
- Developmental origin of shark electro sensory organs
Excerpt from above journal:
Vertebrates have evolved electro-sensory receptors that detect electrical stimuli on the surface of the skin and transmit them somatotopically to the brain. In chondrichthyans, the electro sensory system is composed of a cephalic network of ampullary organs, known as the ampullae of Lorenzini, that can detect extremely weak electric fields during hunting and navigation. Each ampullary organ consists of a gel-filled epidermal pit containing sensory hair cells, and synaptic connections with primary afferent neurons at the base of the pit that facilitate detection of voltage gradients over large regions of the body. The developmental origin of electroreceptor’s and the mechanisms that determine their spatial arrangement in the vertebrate head are not well understood.
- Glyco-proteins bound to ion channels mediate detection of electric fields
A proposed mechanism and supporting evidence
According to our model (Fig. 2), the minimal mass of glycoproteins needed to detect a field of 2 mV/m is M&1.4_10_18/2_10_6&0.7_10_12 kg, which corresponds to a sphere of about 11 mm in diameter. Electroreceptor cells have diameters of 10–20 mm. If we assume that the glycoproteins form prolate ellipsoids, it is easy to see that they could control the opening of 10–20 ion channels per cell, which could be sufficient to initiate transduction by the same mechanism as that occurring in stretch receptors. A 2-MDa hyaluronan molecule has a length of about 5 mm, and individual hyaluronan molecules can be linked together to form cables >200 mm [Day and de la Motte, 2005]. Thus, the force applied to the glycoproteins by the field could cause a simultaneous response in many cells.