New type RFID Antenna Coil for AM Radios

plastic tray and carton box

Specifications

  Work Principle 

1.Induction coil working principle: 1. An induction coil consists of two coils of insulated copper wire wound around a common iron core. One coil, called the primary winding, is made from relatively few (tens or hundreds) turns of coarse wire. The other coil, the secondary winding, typically consists of many (thousands) turns of fine wire.

2. An electric current is passed through the primary, creating a magnetic field. Because of the common core, most of the primary's magnetic field couples with the secondary winding. The primary behaves as an inductor, storing energy in the associated magnetic field. When the primary current is suddenly interrupted, the magnetic field rapidly collapses. This causes a high voltage pulse to be developed across the secondary terminals through electromagnetic induction. Because of the large number of turns in the secondary coil, the secondary voltage pulse is typically many thousands of volts. This voltage is often sufficient to cause an electric spark, to jump across an air gap separating the secondary's output terminals. For this reason, induction coils were called spark coils.

3. The size of induction coils was usually specified by the length of spark it could produce; a '4 inch' (10 cm) induction coil was one that could produce a 4 inch arc.

4. To operate the coil continuously, the DC supply current must be broken repeatedly to create the magnetic field changes needed for induction. Induction coils use a magnetically activated vibrating arm called an interrupter or break to rapidly connect and break the current flowing into the primary coil. The interrupter is mounted on the end of the coil next to the iron core. When the power is turned on, the magnetic field of the core created by the current flowing in the primary attracts the interrupter's iron armature attached to the springy arm, opening a pair of contacts in the primary circuit. When the magnetic field then collapses, the arm springs away, closing the contacts again and turning on the current again. This cycle is repeated many times per second.

5. Opposite potentials are induced in the secondary when the interrupter 'breaks' the circuit and 'closes' the circuit. However, the current change in the primary is much more abrupt when the interrupter 'breaks'. When the contacts close, the current builds up slowly in the primary because the supply voltage has a limited ability to force current through the coil's inductance. In contrast, when the interrupter contacts open, the current falls to zero suddenly. So the pulse of voltage induced in the secondary at 'break' is much larger than the pulse induced at 'close', it is the 'break' that generates the coil's high voltage output. A "snubber" capacitor of 0.5 to 15 μF is used across the contacts to quench the arc on the 'break', which causes much faster switching and higher voltages. So the open circuit output waveform of an induction coil is a series of alternating positive and negative pulses, but with one polarity much larger than the other.

6. To prevent the high voltages generated in the coil from breaking down the thin insulation and arcing between the secondary wires, the secondary coil uses special construction so as to avoid having wires carrying large voltage differences lying next to each other. In one widely used technique, the secondary coil is wound in many thin flat pancake-shaped sections (called "pies"), connected in series. The primary coil is first wound on the iron core, and insulated from the secondary with a thick paper or rubber coating. Then each secondary subcoil is connected to the coil next to it, and slid onto the iron core, insulated from adjoining coils with waxed cardboard disks. The voltage developed in each subcoil isn't large enough to jump between the wires in the subcoil. Large voltages are only developed across many subcoils in series, which are too widely separated to arc over. To give the entire coil a final insulating coating, it is immersed in melted paraffin wax or rosin, and the air evacuated to ensure there are no air bubbles left inside, and the paraffin allowed to solidify, so the entire coil is encased in wax.

7. To prevent eddy currents, which cause energy losses, the iron core is made of a bundle of parallel iron wires, individually coated with shellac to insulate them electrically. The eddy currents, which flow in loops in the core perpendicular to the magnetic axis, are blocked by the layers of insulation. The ends of the insulated primary coil often protruded several inches from either end of the secondary coil, to prevent arcs from the secondary to the primary or the core.

  Production Process 

Packaging & Shipping

 

1.1000pcs inductor coil per plastic tray / carton box

2. Express,air transport,bus transport,sea transport