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SHIELDED COIL WITH REDUCED MICROPHONIC SUSCEPTIBILITY

IP.com Disclosure Number: IPCOM000006888D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2002-Feb-08
Document File: 1 page(s) / 55K

Publishing Venue

Motorola

Related People

John W. Chapman: AUTHOR

Abstract

In the design of VHF and UHF oscillators the com- ponent of choice for creating an inductive element is often a shielded, tunable coil. While this component offers a number of advantages to the designer it also has some disadvantages, one of which is a propensity to change reactance in the presence of physical perturbations. This effect is usually referred to as microphonism and has typically been associated with movements of the entire shielded coil or movement of the coil within the shield.

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MO-LA INC. Technical Developments Volume 19 June 1993

SHIELDED COlL WITH REDUCED MICROPHONIC SUSCEPTIBILITY

by John W. Chapman

   In the design of VHF and UHF oscillators the com- ponent of choice for creating an inductive element is often a shielded, tunable coil. While this component offers a number of advantages to the designer it also has some disadvantages, one of which is a propensity to change reactance in the presence of physical perturbations. This effect is usually referred to as microphonism and has typically been associated with movements of the entire shielded coil or movement of the coil within the shield.

  It was found that under certain physical excitations movement of the entire component or the coil within the shield were not responsible for observed electrical degradation; the walls of the shield were vibrating much lie the skin of a drum. Figure 1 shows a cross section of the coil structure and illustrates how the sidewalls of

the shield are free to vibrate. Electrical degradation due to the specific source which led to this discovery was eliminated by tilliig the void between shield and plastic form, increasing the thickness of the shield wall, or by modifying the shield walls to reduce their ability to sup- port physical resonances.

  The tirst two methods create significant manufac- turing problems which make them unattractive. The third method is easily implemented by embossing the shield walls with a pattern that leaves no large flat areas (see...