reactive power....
in [DSP]
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From: fisico32 on 13 Jul 2010 16:06 Hello Forum, near any radiating source like an antenna there is a region called the reactive field: the E and H field are 90 degrees out of phase. The reactive field is region where there is no radiated power...... It acts as a storage power. During one cycle power is given and taken back... I am having a hard time understanding what that means. What does it means that energy is given and taken back? To what is it given? And why does it give it back? It is said that if we are in the reactive field we can absorb energy and also affect the behavior of the source. In the radiation field we can only absorb energy. what if the angle between E and H is not zero but either 90? What does that mean? Further away from an antenna the power becomes radiated and E and H are not in phase... thanks fisico32
From: Jerry Avins on 13 Jul 2010 16:21 On 7/13/2010 4:06 PM, fisico32 wrote: > Hello Forum, > > near any radiating source like an antenna there is a region called the > reactive field: the E and H field are 90 degrees out of phase. The reactive > field is region where there is no radiated power...... > > It acts as a storage power. During one cycle power is given and taken > back... > I am having a hard time understanding what that means. > What does it means that energy is given and taken back? To what is it > given? > And why does it give it back? > > It is said that if we are in the reactive field we can absorb energy and > also affect the behavior of the source. In the radiation field we can only > absorb energy. > > what if the angle between E and H is not zero but either 90? What does that > mean? > > Further away from an antenna the power becomes radiated and E and H are not > in phase... How solid is your grasp of AC circuits? Do you know what aero power factor means? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: Jerry Avins on 13 Jul 2010 16:48 On 7/13/2010 4:26 PM, Tim Wescott wrote: ... > This whole thing sounds like an interesting way of looking at antenna > fields, but it also sounds like it could confuse a student (e.g. you), > and I'm just not sure that it isn't either all BS or a way to add > useless complication. ... When a wave undergoes total internal reflection in a dielectric, there is what is called an evanescent wave just outside the dielectric. The evanescent wave decays exponentially with distance from the dielectric surface and normally bleeds no power from the wave being reflected. However, if a receiving element is placed close enough, some of the power will enter it, diminishing the power being reflected. The geometry of antennas makes the fields more difficult to visualize than the corresponding case with prisms that I just described, but the math is not much different. (The prism case is further simplified by total internal reflection suppressing the radiated wave completely. There is also -- in theory -- an evanescent wave with ordinary refraction, but I know no practical way to demonstrate its presence.) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: gpezzella on 14 Jul 2010 07:00 Hi the same problem happen when there is an inductive load. In this case percentage of energy come back. For resolve this issue, you must apply a Condenser that compensate the shift between I and V. So for understand this phenomenon start to study Power Factor. Search on Google "Power Factor.pdf" Giuseppe >Hello Forum, > >near any radiating source like an antenna there is a region called the >reactive field: the E and H field are 90 degrees out of phase. The reactive >field is region where there is no radiated power...... > >It acts as a storage power. During one cycle power is given and taken >back... >I am having a hard time understanding what that means. >What does it means that energy is given and taken back? To what is it >given? >And why does it give it back? > >It is said that if we are in the reactive field we can absorb energy and >also affect the behavior of the source. In the radiation field we can only >absorb energy. > >what if the angle between E and H is not zero but either 90? What does that >mean? > >Further away from an antenna the power becomes radiated and E and H are not >in phase... > >thanks >fisico32 >
From: Clay on 14 Jul 2010 10:19
On Jul 13, 4:06 pm, "fisico32" <marcoscipioni1(a)n_o_s_p_a_m.gmail.com> wrote: > Hello Forum, > > near any radiating source like an antenna there is a region called the > reactive field: the E and H field are 90 degrees out of phase. The reactive > field is region where there is no radiated power...... > > It acts as a storage power. During one cycle power is given and taken > back... > I am having a hard time understanding what that means. > What does it means that energy is given and taken back? To what is it > given? > And why does it give it back? > > It is said that if we are in the reactive field we can absorb energy and > also affect the behavior of the source. In the radiation field we can only > absorb energy. > > what if the angle between E and H is not zero but either 90? What does that > mean? > > Further away from an antenna the power becomes radiated and E and H are not > in phase... > > thanks > fisico32 Find the book "Antennas" by John D Kraus - he covers all of this in great detail. Clay |