I've seen that design in a D-dot sensor. The elements were a couple of spheres. The output impedance of such an "antenna" is quite high, it really is an electric field probe, and works at frequencies where the elements are electrically short. These types of devices really sense the time derivative of the filed, hence the name. They are fitted with an integrating amplifier if a representation of the electric field is desired.
> From: Mike Hopkins <[email protected]> > Reply-To: Mike Hopkins <[email protected]> > Date: Wed, 29 Oct 2003 15:27:31 -0500 > To: "'robert Macy'" <[email protected]>, [email protected], > [email protected] > Subject: RE: Effective length of half wave dipole > > > I think the length of a 1/2 wave dipole in feet is basically 468/f(MHz) > where the ratio of the length to diameter is very large (wire antennas in > the HF region, for example). Making the diameter of the elements larger does > two things: it reduces the overall length of the antenna and increases the > bandwidth of the dipole. > > Sounds like a new product: and infinately short dipole useable over an > infinately large range of frequencies! The only drawback is the diameter > needs to be infinately large.... > Oh well, can't have everything.... > > Best Regards, > > Michael Hopkins > Manager, EMC Technologies > Thermo Electron > Control Technology Division > EMC & ESD Simulation Solutions > One Lowell Research Center > Lowell, MA 01852 > Tel: +1 978 275 0800 ext. 334 > Fax: +1 978 275 0850 > [email protected] > www.thermo.com/esd > > One Thermo, committed to integrity, intensity, innovation & involvement > > > -----Original Message----- > From: robert Macy [mailto:[email protected]] > Sent: Wednesday, October 29, 2003 1:54 PM > To: [email protected]; [email protected] > Subject: Re: Effective length of half wave dipole > > > >> From Dave Cuthbert's comments to me regarding a 1/4 > wavelength dipole; he said that the current moves down the > rod as the rod becomes thicker, which implies that the > current distribution absolutely determines the effective > length. Was that "effective length" or "tuned length"? hmm > > However, the whole thing may start with the conductivity of > real life materials... > > Interesting to see the others' comments. > > - Robert - > > Robert A. Macy, PE .. [email protected] > 408 286 3985 . . . .. . . fx 408 297 9121 > AJM International Electronics Consultants > 101 E San Fernando, Suite 402 > San Jose, CA 95112 > > > On Wed, 29 Oct 2003 16:59:20 +0800 > [email protected] wrote: >> >> >> Dear all >> >> I got confused with the effective length of a half wave >> dipole. >> >> 1) It is due to non-constant current distribution, or >> >> 2) It is due to the wave velocity in materials different >> from that in >> vacuum. >> >> >> What do you think which one is correct? >> >> Regards >> KC Chan >> > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
