{"id":1364,"date":"2016-09-12T13:57:49","date_gmt":"2016-09-12T18:57:49","guid":{"rendered":"http:\/\/android-originals.com\/tulsasound\/?page_id=1364"},"modified":"2016-09-12T14:12:10","modified_gmt":"2016-09-12T19:12:10","slug":"some-single-pole-pickup-magnetic-fields-illustrated","status":"publish","type":"page","link":"http:\/\/android-originals.com\/tulsasound\/tutorials\/some-single-pole-pickup-magnetic-fields-illustrated\/","title":{"rendered":"Some single pole pickup magnetic fields illustrated"},"content":{"rendered":"

Using a 2005 Student Version of Maxwell ™ 2-D electromagnetic field software, I generated field plots for single magnetic pickup poles in cylindrical coordinates (r, z).\u00a0 The left side of the plot is r = 0, the center of the pole.\u00a0 So a rectangle to the right represents 1\/2 of a rod or disk.\u00a0 The major grid marks are 0.5 inch, and the minor grid marks are 0.1 inch.\u00a0 Be aware that this does not take into account the influence of adjacent poles in a 6-pole pickup.\u00a0 But as I recall, where one field overlaps another, field strengths add linearly in air or vacuum.<\/p>\n

Flux lines<\/h2>\n

The plots on the left are flux line, 40 per graph, in linear mode.\u00a0 They do not show the absolute strength of the field so much as its relative distribution.\u00a0 Where lines are closer together, the field is stronger.<\/p>\n

Magnetic B Field<\/h2>\n

The plots on the right show the magnetic B field.\u00a0 I am not prepared to explain that; it’s been a very long time since I took those courses, and the textbooks are lost in storage.\u00a0 Suffice it to say that this shows a measure of absolute strength.\u00a0 The lines are strength in 40 logarithmic steps from 0.001 to 2 (units of Tesla, I think).\u00a0 The equation for the multiplier from one line to the next should be somethink like:<\/p>\n

0.001 x r^(40) = 2,\u00a0\u00a0 or ln(r) = ln(2000)\/40,\u00a0\u00a0 or r = 1.20928<\/p>\n

So if the farthest line out from the pole is of strength 0.001, the next line in is 0.00121, followed by 0.00146, 0.001768, 0.002138, etc.\u00a0 If a plot has 5 lines that extend farther out than a second plot, then the relative increase in magnetic field of the first plot over the second at the outermost line of the second should be about r^5 = 2.586 times<\/p>\n

Steel pole with Ceramic 8D magnet in the base<\/h2>\n

\"2016-07-12-1polecer8d-rz-a0-600\"<\/a>The pole is 1008 steel, 0.188″ dia x 0.683″ tall.\u00a0 The magnet is 0.4″ dia x 0.198″ tall.\u00a0 Note the large concentration of flux lines and field strength about the magnet at the bottom.<\/p>\n

ALNICO 5 pole<\/h2>\n

\"2016-07-12-1polealnico5-rz-a0-600\"<\/a><\/p>\n

The Alnico 5 magnetic pole is the same size as the steel pole in the previous plot.\u00a0 Note that the flux lines are concentrated at the ends of the Alnico pole, and closer to the pole in the middle than for the steel pole with the ceramic magnet.\u00a0 The field extends farther up, about 3 lines in the right-hand plot, for an increase in strength of about 1.77 times.\u00a0 One might expect this pole to produce a more sensitive pickup.<\/p>\n

ALNICO 5 pole with steel base plate<\/h2>\n

\"2016-09-04-alnico5-botplate-rz-a0-600\"<\/a>In this example, a 1008 steel base plate of 1.0″ dia x about 1\/16″ thick has been added to the bottom of the Alnico 5 pole.\u00a0 It moves the concentration of flux lines away from the bottom of the Alnico pole.\u00a0 Note that in effect, the plate pushes the field up slightly, so that it is about 1.209 times stronger where the pole without the plate has a field strength of about 0.001.<\/p>\n

Winding coils?<\/h2>\n

This raises a question: should the pickup coil be wound with the most turns where the field is strongest (the flux lines thickest)?\u00a0 Without much more expensive simulation software, it can only be answered by experiment.\u00a0 Even with software that takes account of dynamic fields and currents, it would still have to be verified by experiment.<\/p>\n","protected":false},"excerpt":{"rendered":"

Using a 2005 Student Version of Maxwell ™ 2-D electromagnetic field software, I generated field plots for single magnetic pickup poles in cylindrical coordinates (r, z).\u00a0 The left side of the plot is r = 0, the center of the … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":947,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"_links":{"self":[{"href":"http:\/\/android-originals.com\/tulsasound\/wp-json\/wp\/v2\/pages\/1364"}],"collection":[{"href":"http:\/\/android-originals.com\/tulsasound\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"http:\/\/android-originals.com\/tulsasound\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"http:\/\/android-originals.com\/tulsasound\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/android-originals.com\/tulsasound\/wp-json\/wp\/v2\/comments?post=1364"}],"version-history":[{"count":4,"href":"http:\/\/android-originals.com\/tulsasound\/wp-json\/wp\/v2\/pages\/1364\/revisions"}],"predecessor-version":[{"id":1371,"href":"http:\/\/android-originals.com\/tulsasound\/wp-json\/wp\/v2\/pages\/1364\/revisions\/1371"}],"up":[{"embeddable":true,"href":"http:\/\/android-originals.com\/tulsasound\/wp-json\/wp\/v2\/pages\/947"}],"wp:attachment":[{"href":"http:\/\/android-originals.com\/tulsasound\/wp-json\/wp\/v2\/media?parent=1364"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}