Acoustics – Sound-modifying means – Sound absorbing panels
Reexamination Certificate
2001-10-30
2003-09-30
Nappi, Robert E. (Department: 2837)
Acoustics
Sound-modifying means
Sound absorbing panels
C174S034000, C052S079100, C455S300000
Reexamination Certificate
active
06626264
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to insulated enclosures and more particularly to radio frequency shielded and acoustically insulated enclosures.
The power of magnetic resonance imaging (“MRI”) equipment is continually increasing to meet the demand in the medical community for better and faster developing images. However, as the power of MRI equipment increases, an increased amount of noise is generated due, in part, to the coil assembly of the MRI equipment. MRI acoustic noise is mainly caused by Lorentz forces acting on the gradient coils of the MRI equipment. As the gradient current switches direction, the gradient windings vibrate in their mountings, leading to the emission of sound waves. The frequency range for such sound waves for certain MRI equipment may be 10 Hz-20 kHz. MRI equipment therefore generates substantial noise, possibly at different frequencies, which travels from the MRI equipment toward the walls, floor and ceiling of the enclosure in which the MRI equipment resides. The MRI equipment transmits noise: (i) through the air to the walls, ceiling and floor of the enclosure; and (ii) through the supports of the MRI equipment to the floor, walls and ceiling of the enclosure.
As a result, the level of noise may at times exceed health and safety regulatory and industry standards, which seek to protect the operator of the MRI equipment (and others in the surrounding areas adjacent to such rooms or enclosures) from potentially dangerous noise levels. Such MRI equipment must therefore be properly contained within a radio frequency (“RF”) shielded and sufficiently acoustically insulated room to protect the MRI equipment from stray electromagnetic radiation and to protect the operators (and others) from continuous, excessive and undesired noise levels.
To absorb the airborne noises in an RF room or enclosure, manufacturers have employed multiple layers of an insulating material in the walls, ceiling and floor of the enclosure to absorb noise up to a particular decibel level. Generally, adding additional layers or thickening existing layers of the insulating material in the enclosure increases the noise absorption characteristics of the enclosure. Although the addition of the extra layers or extra thickness of the insulating materials increases noise absorption of the enclosure, this method of increasing noise attenuation eventually diminishes in efficiency. That is, as additional layers of the insulation are added, the level of noise absorption reaches a plateau, whereby adding additional layers of the insulating material to the enclosure will not overcome the plateau.
For example, a known type of sound insulation is chipboard or particleboard core sheet. It is also known that 50 mm of a certain type of particleboard provides 28 decibels (dB's) of attenuation. 60 mm of the same type of particleboard provides 29 decibels (dB's) of attenuation. 80 mm of the same type of particleboard provides 32 decibels (dB's) of attenuation, etc. As illustrated, the change in attenuation lessens as the particleboard thickens.
Adding layers of insulation or thickening layers begins to take up substantial space and adds to the cost and weight of the enclosure. Therefore, simply adding extra layers of the insulating material or thickening the existing layers increases the cost of the enclosure without maximizing the noise absorption capability of the enclosure.
To better absorb airborne noises from MRI equipment, there is a need for an RF shielded and acoustically insulated enclosure which attenuates RF fields and absorbs increased levels of noise in an efficient, cost effective and spatially acceptable manner.
Additionally, the MRI equipment presents a related noise and vibration problem because the MRI equipment transmits vibration and noise through the supporting floor. The floor below the MRI equipment must therefore support the weight of the magnet present in the MRI equipment and the vibration generated by the MRI equipment. Simply providing layers of sound insulation does not effectively prevent the vibration and related noise from traveling from the equipment through such supports, to the I-beams and other support structures that separate one room from another and one floor from another in the building which houses the RF enclosure. Accordingly, there is a need for an RF shielded and acoustically insulated enclosure that absorbs the vibration and related noise generated by the MRI equipment.
SUMMARY OF THE INVENTION
The present invention provides an RF shielded and acoustically insulated enclosure that efficiently employs multiple layers of sound insulation having different noise absorption characteristics to absorb airborne noise and vibrational noise generated by the MRI equipment. The RF enclosure of the present invention provides multiple layers and multiple types of insulating materials positioned in the walls, ceiling and floor of the enclosure to maximize the noise absorption of the RF enclosure and specifically to maximize the noise absorption effect of each such insulating layer while minimizing the number and size of the insulating layers. The efficient use of the multiple insulating layers reduces the cost of and space required by the RF enclosure. In one embodiment of the present invention, the RF enclosure includes a ceiling, a floor and a plurality of walls. The ceiling and walls include multiple layers of different insulating materials having different noise absorption characteristics that either abut each other or are spaced apart to define or form air gaps therebetween. In one embodiment further discussed below, the floor includes a non-magnetic weighted support such as a relatively heavy stainless steel plate on which the MRI equipment rests. The stainless steel plate is supported by at least one and preferably a plurality of elastomeric vibration dampening members which absorb the vibration of the weighted support. The elastomeric members rest on or above the conductive shield. The elastomeric members are thus adapted to absorb the vibration and related noise of the MRI equipment.
In certain buildings where RF enclosures are constructed, the building walls are designed and built to provide minimum levels of soundproofing. In one embodiment of the present invention, at least one of the walls of the enclosure co-acts with at least one of the walls of the building to provide noise absorption. That is, the enclosure is positioned adjacent to one or more walls of the building in which the enclosure resides. One or more layers of sound insulating material of the enclosure co-act with or are alternatively inserted into one or more walls of the building to increase the overall performance of the enclosure.
More specifically, in one embodiment, the enclosure includes a frame. The walls of the frame form cavities. These cavities in one embodiment are filled with sound insulation. To provide RF shielding, the outside of the frame (including the insulation filled cavities) includes a sheet of copper shielding. The insulated and shielded frame is adjacent to one or more insulated building walls. One or more additional layers of sound insulation is placed between the frame and the building walls before the frame is secured to the building.
It should be appreciated that the above described wall of the present invention thus provides different opportunities or positions to install various layers of sound insulation such as: (i) in the frame; (ii) in the building wall; and (iii) between the frame and the building wall. The amount of insulation needed generally depends on two factors: (i) the level of sound absorption necessary or desired; and (ii) the level of sound absorption provided by the walls of the building, without the enclosure. In a preferred embodiment, different types of insulation having different noise absorption characteristics are used. For instance, a finishing layer or barrier, such as a drywall, resides on the inside of the frame and has certain noise insulating characteristics. The insulation inside the ca
Bell Boyd & Lloyd LLC
IGT
Nappi Robert E.
Warren David
LandOfFree
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