Electric heating – Heating devices – Combined with diverse-type art device
Reexamination Certificate
2000-04-07
2001-10-09
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with diverse-type art device
C219S529000, C219S544000, C219S546000, C219S549000
Reexamination Certificate
active
06300597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electrically heated pads, and more particularly to electrical pads having a heating element that eliminates magnetic field being emitted from heating wires.
2. Discussion of the Related Art
It has been discovered that electromagnetic fields affect biological matter and, consequently, cause health problems in human. Such health problems may be linked to cancer and other ailments. The electromagnetic fields are very common in modern society where consumer electric appliances are frequently used at homes and offices. Commonly, electromagnetic fields are generated by power lines and transformers. The electric blankets or pads which we use to keep warm also generate one or more forms of electromagnetic field, which includes magnetic field. In fact, some studies have shown that there may be a direct correlation between electric blankets and certain medical conditions.
As it is well known that the electromagnetic field permeates through practically every kind of substances with the exception of ferromagnetic materials. Thus, attempting to block electromagnetic field in such appliances as electric blanket using ferromagnetic materials may not be practical due to its cost.
For example,
FIG. 1
is a block diagram of a temperature controller and a heating element of a conventional electric blanket. The temperature controller
10
includes a bimetal thermostat switch
12
which can be set to appropriate temperatures to provide current to the heating element
20
. Alternatively, as shown in
FIG. 2
, the temperature controller
10
may include an integrated circuit switch
14
instead of the thermostat switch
12
to provide the same function. The common characteristic of both
FIGS. 1 and 2
is that the output voltage Vout at node
18
comprises a sinusoidal wave alternating current (AC). When using a conventional household line voltage, the Vout will be 60 Hz wave with peak voltage slightly higher than 120V. The output voltage Vout is connected to the heating element
20
. The heating element
20
is made with a resistive wiring
22
which produces heat when electricity is applied. Furthermore, the devices shown in
FIGS. 1 and 2
use a resistive wiring
22
which is arranged to produce magnetic and electromagnetic field which may be harmful to human.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an electrical heating pad that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an improved electrical heating pad substantially eliminating magnetic fields generated from the heating wires.
Another object of the present invention is to substantially eliminate electric fields by providing conductive shielding around the heating element.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an electrical heating pad for use with an ungrounded source voltage comprises a heating element arranged in the heating pad and defining a substantially coplanar plane and a fabric outer cover coplanarly enclosing the heating element. The heating element includes a first core made of an insulating material; a first conductive element wound around the first core using the first core as an axis; a second core made of an insulating material arranged in surrounding relation to the first core and the first conductive element; and a second conductive element wound around the second core using the second core as an axis. The first and second conductive elements are connected to each other at one ends and are connected to the ungrounded source voltage at the other ends to at least partially cancel out magnetic field generated from each conductive element.
According to one aspect of the present invention, the heating element further comprises an insulating cover that covers the second core and the second conductive element. Preferably, there is at least one shield layer located at one side of the coplanar plane defined by the heating element for substantially shielding electric field. Alternatively, there are two shield layers, each shield layer being located at one side of the coplanar plane defined by the heating element for substantially shielding electric field, wherein both shield layers are electrically connected to each other.
According to another aspect of the present invention, the first core is made of glass fibers, and the second core is made with silicone. The conductive wire is preferably made with copper having a non-conductive coating. Moreover, the first and second cores are made of a material with high heat transmitting coefficient.
According to another aspect of the present invention, the second conductive element preferably generates more heat than the first conductive element. In that regard, the second conductive element has a lower total resistance than the first conductive element. In particular, the first conductive element, when measured at both ends, has resistance of about 60-80 Ohms. The second conductive element, when measured at both ends, has resistance of about 20-40 Ohms. The first and second conductive elements has a series resistance of about 80-120 Ohms.
According to another aspect of the present invention, the shield layer is a wire mesh made of conductive wire. Alternatively, the shield layer is a conductive sheet.
These and other aspects, features and advantages of the present invention will be better understood by studying the detailed description in conjunction with the drawings and the accompanying claims.
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Dahbour Fadi H.
Lee & Hong
Walberg Teresa
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