Ferrite Rods, Bars, Plates and Tubes

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FERRITE RODS, BARS, SLUGS, PLATES AND TUBES

Ferrite rods, bars, slugs, plates and tubes are primarily used as magnetic cores in radio antennas, chokes, inductors and filters. In radio antennas, ferrite rods are useful from VLF spectrum to VHF spectrum. The advantages are small size, high Q and compactness.

Ferrite rods and bars are available in standard lengths up to 12" long. These rods are available from 0.25" to 1" in diameter. They are available in materials from permeability of 7.5u_i to 10, 000u_i in both Nickel Zinc (NiZn) and Manganese Zinc (MnZn) compositions.

The table below shows the material characteristics of the various types and of NiZn and MnZn ferrite rods, slugs, tubes, strips, plates and bars.

material characteristics:
material	initial perm- eability	satur- ation flux density	loss factor [@frequency]	curie temp.	volume resistivity	recom- mended freq.	application areas	common shapes
unit		gauss	10^-6	°C	Ω^-cm	MHz
symbol	μ_i	B_sat	tanδ/μ_i	Tc	ρ	f

70	450	1600	<100[2.5MHz]	90	10⁸	10-500	filter, transformer	rod
71	600	2800	<25[0.2MHz]	150	10²	0.05-3	antenna, filter, transformer	rod, tube, strip
77	2000	4900	<15[0.1MHz]	190	10²	.05-0.2	antenna, filter, transformer	slug, rod
77	2000	4900	<15[0.1MHz]	190	10²	0.05-30	emi supression	bead
74	2500	4700	<5[0.1MHz]	210	10³	0.1-0.5	welding (impeder), antenna	rod, tube, strip
55	7.5	1750	<3500[100MHz]	320	10⁷	0.1-400	filter, transformer	toroid, rod, balun
54	12	1800	<850[10MHz]	500	10⁹	0.1-400	filter, transformer	toroid, rod, balun
53	20	2500	<500[100MHz]	500	10⁷	0.1-400	antenna, filter, transformer	toroid, rod, balun
52	40	2300	<150[50MHz]	450	10⁷	0.1-50	antenna, filter, transformer	toroid, rod, balun
61	125	2400	<40[2.5MHz]	350	10⁷	0.1-25	antenna, filter, transformer	plate,strip
61	125	2400	<40[2.5MHz]	350	10⁷	>200	emi supression	bead, rod
62	250	3000	<100[2.5MHz]	250	10⁸	0.1-4	filter, transformer	bead, toroid, rod
93	300	3750	<100[2.5 MHz]	250	10⁸	0.1-10	filter, transformer	toroid, rod, balun
92	370	3200	<65[0.1MHz]	200	10⁶	0.1-5	filter, transformer	toroid, rod, balun
94	400	4600	<35[0.1MHz]	230	10⁸	0.1-10	antenna, particle accelerator	block, custom, rod
90	500	2500	<100[1MHz]	200	10³	0.1-1	antenna, filter, transformer	plate
81	700	3200	<15[0.05MHz] < 80[1MHz]	190	10⁷	0.05-1	antenna, filter, transformer	rod
82	850	3200	<250[1MHz]	155	10⁷	0.05-10	antenna, filter, transformer	toroid
23	2300	1200	<350[1MHz]	95	10⁸	30-1,500	emi supression	plate

Rods with material 61 (u_i = 125), 33 (u_i= 800) and 77 (u_i= 2000) are standard stocking items and can be purchased online from www.cwsbytemark.com. The direct link to the shopping cart is:

http://www.cwsbytemark.com/index.php?main_page=index&cPath=206_216

All other materials are custom manufactured and are readily available with lead time for delivery.

A partial list of Standard Stocking Rods available for immediate delivery that can be purchased through the online shopping carts is also shown below for reference. Please go to the shopping cart directly for a more comprehensive list.

Part Number	Material	Permeability	Diameter (in)	Length (in)	A_L value mh/1000t	Ampere turns
R-025400-61	61	125	.25	4.0	26	110
R-037300-61	61	125	.37	3.0	32	185
R-050400-61	61	125	.50	4.0	43	575
R-050750-61	61	125	.50	7.5	49	260
R-037400-33	33	800	.37	4.0	62	290
R-050200-33	33	800	.50	2.0	51	465
R-050400-33	33	800	.50	4.0	59	300
R-050750-33	33	800	.50	7.5	70	200

Other dimensions and materials are available. Please call or email us at sales@coilws.com for your other requirements.

Custom blocks of ferrites are frequently used in Antenna as well. Please visit www.bytemark.com/customblocks/html <<<link>>>for more information on custom blocks of ferrites and material availability.

ANTENNA APPLICATION:

For antenna application, the design objective is to get high Q at the center of the design frequency of operations. Ferrite Rods are widely used as loop antennas such as broadcast-band receivers, low and medium frequency direction-finder receivers, airborne navigation receivers, AM, FM and VHF receivers.

The material 61 (u_i = 125) rods are mainly used in the 550 Khz to 1660 Khz commercial AM radio antennas.

Material 61 (u_i = 125) rods are also used by radio amateurs in the 2 MHz to 30 MHz range.

The material 33 (u_i= 800) rods are more suitable for lower frequencies in the 100 Khz to 1 Mhz or the low frequency (LF) ranges. The table above shows the recommended frequency ranges for different materials. As a general rule, the higher the operating frequency, the lower permeability of the rod cores are needed.

The material 77 (u_i = 2000) rods are most suitable for very low frequency (VLF) receiver application. Material 77 is typically used in receiver application below 10 Khz.

Toroids cannot be used as receivers as they have closed loops. Rods, bars and plates have open loops and are thus suitable as radio receivers. However, the efficiency of the rod as antennas degrades as the rod overall length versus the diameter ( l/d) increases. When the l/d goes over 35, the rod behaves more like an toroidal cores, and the close loop effects kicks in making these rods ineffective as an antenna. On the other hand, for very short rods where the l/d is less than 5, the effectiveness of the antenna is also diminished. Therefore, optimum l/d ratio is from 10 to 25 for a rod antenna.

Loop antennas have a height factor called effective height, h_e (in m), which when multiplied with field strength, F (in uV/m), provides the loop-induced voltage (in uV).

Where:
N = number of turns
A = area in square meters (m2)
^ = wavelength in meters
u_e= effective permeability of rod, and
d/^ < 1, d = diameter of rod.

It can be seen from the equation that the highest induced voltage occurs when the windings occupied the entire rod (when N is largest).

CHOKE AND FILTER APPLICATION

In a choke and filter application, the design objective is to get the highest impedance over the frequencies to be suppressed. Chokes and filters application is in a way, similar to the antenna application. As a general rule, the highest permeability rods are used to suppress the lowest frequency range.

The material 77 has a wide suppression frequency range. It is suitable for 1 Mhz to 30 Mhz in the amateur radio band.

The material 33 has a somewhat narrower band, and is suitable for the 3.75 - 7.5 MHz (40-80 meters band). Both material 77 and material 33 rods are also often used in speaker cross-over networks.

The material 61 is most suitable for the 7.5-30 MHz (10-40 meters band) range.

Due to the open magnetic structure of the rod configuration, considerable current can be tolerated before these rod cores will saturate.

There are several factors that have a direct bearing on the effective permeability of a ferrite rod, which in turn will effect inductance and 'Q', as well as the A_L value of the rod and its ampere-turns rating. These are: (1) Length to diameter ratio of the rod, (2) Placement of the coil on the rod, (3) Spacing between turns and, (4) Air space between the coil and the rod. In some cases, the effective permeability of the rod will be influenced more by a change in the length to diameter ration than by a change in the initial permeability of the rod. At other times, just the reverse will be true.

Greatest inductance and A_L value will be obtained when the winding is centered on the rod rather than placed at either end. The best 'Q' will be obtained with the winding covers the entire length of the rod.

Because of all of the above various conditions it is very difficult to provide workable A_L values. The set of A_L and NI values for various types of rods in the above table should be used as a guide only. These figures are based on a closely wound coil of #22 wire, placed in the center of the rod and covering nearly the entire length. Please note that there are many variables and that the inductance will vary according to winding technique.

EFFECTIVE PERMEABILITY
Coil placements and the length of windings on the rods, bars, plates and tubes affect the effective permeability of these devices. The corrected permeability for variation in coil length versus rod length is:

Where u' = corrected u
u_e = effective permeability from the chart
l_r = rod length in cm or inches
l_c = length of coil windings in cm or inches

EFFECTS ON 'Q'
The spacing between the turns has a significant effect on the 'Q', and the inductance of the rods. The best values of 'Q' are obtained when the coil turns are spaced one wire diameter apart, with the windings located at the center of the rod. Litz wire provides the highest level of 'Q'.

Rods, tubes and strips can be custom manufactured in lengths up to a maximum of 18 inches. However, in most application requiring very long rods, multiple shorter rods are bonded together in a tubing to acheive length of over several feet long.

The dimensional tolerances for rods, tubes, and strips are approximately +/- 6%, and for plates are +/- 2%. All length tolerances are +/- 2%. The camber tolerance is 0.11 per inch.

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