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Fixed And Variable Capacitors Pdf

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Variable capacitor

Year of fee payment : 4. Year of fee payment : 8. A charge storage device having a capacitance that is variable by alteration of the relative permittivity of the dielectric positioned between conductive electrodes within the device. The device consists of two conductive plates sandwiching a conductive grid, typically embedded within a dielectric material. Charging the grid with a negative or positive potential changes the value of the dielectric constant the relative permittivity and thereby changes the capacitance of the device.

Field of the Invention. The present invention relates generally to electronic components suitable for receiving and retaining an electrical charge. The present invention relates more specifically to a charge storage device having a capacitance that is variable by alteration of the relative permittivity of the dielectric positioned between conductive electrodes within the device.

Applicant's novel device consists of two conductive plates sandwiching a conductive grid, typically embedded within a dielectric material. Charging the grid with a negative or positive potential changes the value of the dielectric constant the relative permittivity of the dielectric and thereby changes the capacitance of the device. Capacitors are generally fabricated or constructed in two main forms, fixed and variable.

A fixed capacitor has a preset capacitance that is established during the manufacture of the device through the selection of the dielectric material and the conductive plates that enclose the dielectric material. Variable, or trimmed capacitors, do not have set capacitance values fixed during their manufacture. Instead, variable capacitors are designed to allow a range of capacitance values by adjusting some feature of the capacitor to alter its capacitance value.

Adjustment of a capacitor through its range of capacitance values may, for example, allow the fine tuning of an electronic circuit and various operational features of the circuit.

Variable capacitors are therefore often utilized in electromagnetic wave transmitter and receiver circuitry to vary the frequency response for such transmitters and receivers. Variable capacitors themselves come in a number of different structural and functional configurations. One of the most common methods of varying the capacitance is to interleave several movable plate electrodes among a number of fixed plate electrodes.

Adjusting the position of the variable electrodes, relative to the fixed electrodes, increases or decreases the capacitance as the area between the electrodes changes. One problem with this type of variable capacitor is simply the number of electrodes that are required to implement the method of varying the capacitance. Multiple fixed and variable electrodes are required, and these electrodes themselves require a housing large enough to accommodate both them and their relative motion.

In many instances, the size and geometry of such devices become unsuitable for small scale electronic applications. In addition, if the fixed and variable electrodes are not carefully structured and positioned, the capacitor may be easily damaged such that the geometry of the electrode plates changes in an undesired manner resulting in an inappropriate change in the capacitance. In general, the capacitance value of a capacitor depends upon three factors.

These include the distance between the electrode plates of the capacitor and the area a two dimensional value between the two electrodes or plates. A third factor not normally considered when constructing a variable capacitor is the relative permittivity of the dielectric material utilized. In either case, mechanical motion is required in order to make these adjustments. It would be desirable if the capacitance value of a capacitor could be varied without the need for the mechanical motion of any of the components associated with the construction of the capacitor.

Towards this end, the third factor involved in the capacitance value, the relative permittivity, may be examined as a basis for changing the capacitance value without requiring mechanical motion of the components. The relative permittivity is, as mentioned above, also known as the dielectric constant, and is a relative measured value that depends on the material chosen for the dielectric.

It is expressed as the ratio of a material's absolute permittivity to the absolute permittivity of a vacuum see Equation 1 below. In the field of electronics, capacitors are most often considered discrete electronic components that store electrical energy in the form of a static charge.

A basic capacitor consists of two metal plates that are separated by a dielectric insulator. One of the electrical properties of the dielectric insulator material is the ability to store a static electric charge. Each of the difference types of capacitors has a range of capacitance values that is generally determined by the geometry of the plates and the dielectric. Once again to summarize, the capacitance value of a capacitor is the result of three variables:.

Capacitance values are measured in farads. Most fixed non-variable capacitors have a capacitance value between microfarads and 1 picofarad. There are, as mentioned above, a variety of variable capacitors known in the art. Existing variable capacitors operate on one of two principles, both of which require some form of mechanical movement. First, some variable capacitors change their capacitance value by changing their plate area. Second, some variable capacitors change their capacitance value by changing the distance between their plates.

Varactor or tuning diodes are also sometimes used as capacitors. A varactor or tuning diode is typically a semiconductor device that changes its capacitance by changing the width of its depletion region. Varactor diodes are typically limited to the picofarad range. As mentioned above, capacitors are one of the most frequently used components in electronic circuits. One of the most common uses for variable capacitors is in tuning circuits. For example, the frequency tuner knob on a typical radio receiver is connected to a variable capacitor such that turning the knob changes the capacitance value of the capacitor, which changes the frequency of the radio signal that the radio receives.

A variety of other uses of variable capacitors may be found in the literature that involve altering the characteristics of an RC circuit a fundamental circuit component by varying the capacitance value at some point in the circuit. The voltage variable capacitor proposed herein is a modified form of existing capacitors. Charging the conductive grid with a negative potential causes the dielectric constant of the capacitor to decrease in value thereby reducing the capacitor's value.

Placing a positive potential on the grid causes the dielectric constant to increase, thereby raising the capacitor's value. As discussed above, existing variable capacitors vary the area A or the distance between the plates d in order to change the capacitance value C. Both require a change in the physical parameters of the capacitor. This is the principle by which the present invention operates.

It can be seen therefore, from Equation 2, that an increase in the relative permittivity results in an increase in the capacitance value while a decrease in the relative permittivity results in a decrease in the capacitance value.

It is known that altering the electromagnetic field within or surrounding a dielectric material will alter the relative permittivity of the dielectric.

It is upon this principle that the present invention is based. As a practical matter, there are no limitations as to the size or geometry of the capacitor of the present invention or the type of dielectric material used. Thus, the present invention provides a first plate capable of storing a charge therein in electrical contact with a first terminal of a source of power distribution.

A second plate is spaced apart from the first plate and is in electrical contact with a second terminal of the source of power distribution. A dielectric material occupies the space between the plates as does the grid.

The grid is attached to a means of charging, including variably charging the grid. The grid of the present invention is typically comprised of a conductive material. The dielectric of the present invention is typically an insulator.

Direct voltage or alternating voltage may be used as a means for charging the grid. The direct current may be variable. An exemplary method of using the capacitor of the present invention would be to vary the charge on the grid to achieve desired and selected electrical characteristics in a circuit. Reference is made first to FIG. The structure of variable capacitor 10 is shown schematically in FIG. It will be understood by those skilled in the art that the geometry and size of the various elements of the capacitor described could change depending upon the specific application.

Initially it can be seen that the fundamental elements of variable capacitor 10 of the present invention are the same as the fundamental elements of all capacitance devices.

The basic capacitor is comprised of first conductive plate 14 positioned parallel to, but spaced apart from, second conductive plate Each of these two plates 14 and 16 define an area A between them that is a factor in determining the capacitance of the device.

First conductive plate 14 is connected to electrical conductor 18 and second conductive plate 16 is likewise connected to electrical conductor 20 for connecting capacitor 10 into a circuit as discussed in more detail below. Again, as may be typical of most capacitors, dielectric material 22 is positioned between plates 14 and The thickness of dielectric material 22 will typically define the distance d between plates 14 and This distance d is also a factor in determining the capacitance value of the assembled capacitor.

When fully assembled for use, plates 14 and 16 would be in direct contact with the top and bottom surfaces respectively of dielectric material In this manner, the relevant distance d between plates 14 and 16 becomes the thickness of dielectric material The selection of the dielectric in the present invention may be made in accord with standard practices for constructing capacitor devices.

The integration of the novel features of the present invention in to standard elements of a capacitor does not dramatically alter the criteria for selecting dielectric materials, or for defining the geometry of the conductive plates. Integrated into dielectric material 22 , is conductive grid Electrical conductor 24 is connected to conductive grid 26 and provides the means for establishing a charge on the grid.

When fully assembled, therefore, conductive plate 14 and conductive plate 16 sandwich dielectric material 22 , with its incorporated conductive grid 26 , into the electronic component package referenced generally as variable capacitor In this manner according to the capacitance Equation 2 discussed above the capacitance value of the variable capacitor will change as the relative permittivity of the dielectric material changes.

Typically the establishment of a charge on grid 26 will involve placing grid 26 at a potential above positive potential or below negative potential ground, relative to charges that may be established on plates 14 and The structure and geometry of grid 26 may vary, although certain factors are important to the efficient operation of the electronic capacitance component.

In order for the change in a charge on the grid to effect a change in the value of the dielectric, the grid must come into contact with as much of the dielectric material as possible. Dielectric materials of greater strength will require grid networks of much smaller proportions as even modest changes in the charge on the grid will effect significant changes in the dielectric constant.

On the other hand, if the grid area is too large, it can effectively act as an additional plate within the capacitive device. This may result in the charge signal being removed through the grid conductor 24 , although in some instances, this may itself be a desirable feature.

In general, the grid should be of minimal conductor dimensions, i. Referring again to FIG. It is also possible to utilize a doped semiconductor as the dielectric, in which case the semiconductor material may be charged without the use of a grid placed within it.

Semiconductor material 23 is positioned between plates 14 and 16 in a manner similar to the structure described above with regard to FIG. Electrical conductors 18 and 20 are also positioned similarly on plates 14 and Instead of a grid, however, a charge may be established within dielectric semiconductor material 23 by means of a contact electrode 25 positioned along one edge of the material. Electrical conductor 24 provides the means for providing a potential to the contact electrode

Variable Capacitor Construction, Working Types and Uses

Skip to main content. This service is more advanced with JavaScript available. Advertisement Hide. Reference work entry First Online: 02 February Capacitors We use capacitors to storecharge, or to conduct current linearly with the rate-of-change of voltage across them. In the time domain: Open image in new window. This process is experimental and the keywords may be updated as the learning algorithm improves.


an electric field is called the dielectric constant. Capacitance is directly proportional FIGURE Schematic symbol for a variable capacitor. Thomas L. Floyd.


Factors Affecting Capacitance

Capacitors an electrical or electronic component that stores electric charges. Basically, a capacitor consists of 2 parallel plates made up of conducting materials , and a dielectric material air, mica, paper, plastic etc. The value of the capacitor is measured in terms of its capacitance value and is expressed in farads, microfarads and nanofarads. The temperature co-efficient represents the stability in capacitance value with the change in temperature.

Capacitor Types: Types of Capacitor

Capacitors are manufactured in their millions each day, but there are several different capacitor types that are available.

Capacitors: Types, Definition, Specifications and Application of Capacitor

There are three basic factors of capacitor construction determining the amount of capacitance created. These factors all dictate capacitance by affecting how much electric field flux relative difference of electrons between plates will develop for a given amount of electric field force voltage between the two plates :. Explanation: Larger plate area results in more field flux charge collected on the plates for a given field force voltage across the plates. Explanation: Closer spacing results in a greater field force voltage across the capacitor divided by the distance between the plates , which results in a greater field flux charge collected on the plates for any given voltage applied across the plates. Explanation: Although it's complicated to explain, some materials offer less opposition to field flux for a given amount of field force. Materials with a greater permittivity allow for more field flux offer less opposition , and thus a greater collected charge, for any given amount of field force applied voltage.

They comprise fixed and flexible electrodes. Deformation, or actuation, of the flexible electrode changes the capacitance of the capacitor. This way, electrical properties of high frequency circuits can be modified. Traditionally, variable capacitors are based on a planar layout architecture, while a newer, vertical-wall, quasi three-dimensional approach theoretically enables increased device performance. Such devices depend on high aspect ratios, i. A few vertical-wall variable capacitors made of nickel or gold have been fabricated to date, using deep X-ray lithography and subsequent electroplating Achenbach et al.

Variable Capacitor Construction, Working Types and Uses

Types of Capacitors

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At Wurth Electronics Midcom, we carry a variety of capacitors to suit your design needs. Read on to learn all about capacitors, including the different types of capacitors, popular capacitor products from Wurth Electronics Midcom, our special ABC of Capacitors design guide, and upcoming webinars on capacitors.

A variable capacitor is a capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically. In mechanically controlled variable capacitors, the distance between the plates, or the amount of plate surface area which overlaps, can be changed. The most common form arranges a group of semicircular metal plates on a rotary axis " rotor " that are positioned in the gaps between a set of stationary plates " stator " so that the area of overlap can be changed by rotating the axis. Air or plastic foils can be used as dielectric material.

Capacitor is an electronic device that stores electric charge. When voltage is applied to the capacitor, it stores electric charge. This charge storage may be fixed or variable depends upon the type of capacitor. Capacitors are mainly classified into two types:.

Capacitors are manufactured in many forms, styles, lengths, girths, and from many materials. They all contain at least two electrical conductors called "plates" separated by an insulating layer called the dielectric. Capacitors are widely used as parts of electrical circuits in many common electrical devices.

A trimmer capacitor is a type of variable capacitor a capacitor that can have its capacitance manually adjusted by changing the positioning of the two conductive plates. It is meant to fine-tune the capacitance set by the larger capacitors in the circuit. Trimmer capacitors have two main applications. When all fixed components are placed in a circuit, the resulting capacitance is often not precisely what was expected. If accuracy is vital, then the trimmer capacitors can be used to tweak the final capacitance value to the desired value.

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