Acoustics – Sound-modifying means – Mechanical vibration attenuator
Reexamination Certificate
2001-06-29
2003-02-18
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Mechanical vibration attenuator
C248S638000
Reexamination Certificate
active
06520283
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to filtering and reducing the transmission of undesirable vibrations and signals. More specifically, this invention relates to the filtering of undesirable vibrations and signals by a mechanical means to reduce noise in signals produced by electronic components such as audio/visual components.
BACKGROUND OF THE INVENTION
Noisy music is difficult to enjoy. Similarly, it can be difficult to view a blurry picture on a television screen or video monitor. Electronic devices designed to convey information typically have inherent noise. Generally, as used herein “noise” refers to various properties such as physical vibrations, electrical signals and the like, and similarly, to any other vibrations and/or signals which are generally undesirable and interfere with the intended operation of the device.
Numerous commonplace electronic devices are similarly affected by vibration. For instance, record players, radios, CD players, DVD players, microphones, amplifiers, preamplifiers, power transformers, magnetic resonance imaging equipment, high-speed cameras, and high definition televisions are all susceptible to degradation in reproducing sound and/or visual images because of the interference of vibrations. When these devices are subjected to vibration, vibrational noise can become electrical noise interfering with the intended operation of the electronic device. Often manufacturers of these devices include signal processing filters in the devices to attempt to remove these unwanted signals or noise; however, these signal processing filters may not sufficiently reduce the transmission of and interference caused by undesired signals.
In this respect, the effectiveness of the medium carrying the information is generally proportional to its signal-to-noise ratio; typically an amplitude or a frequency ratio, expressed in percentage of noise-to-signal level or peak. For example, analog circuitry and components generate electronic noise when vibrating. Magnetic-core displacement and capacitor-bank separation movement in a common circuit are examples of electro-magnetic field and current generation or modification. Semiconductor components are also subject to mechanical vibration sensitivity. Similarly, diodes and transistors may also be noisy.
However, in general, analog electronics are typically the most susceptible to vibration. This is generally because noise is additive in analog circuitry. The noisier the components of the circuit, the noisier is the circuit itself is. Large-scale circuit integration, common in modern electronics, is the enemy of signal clarity. This raises the need for noise filtering, reduction, or elimination, especially in signal transmission devices.
Equipment use classifies signal transmission as either external or internal. Signals are externally transmitted between equipment via electrical conductors, fiber optics or other means, such as electromagnetic field, which propagates through vacuums, solids, liquids and gases. For example, one external transmission is a typical radio with a broadcasting station and a remote tuner or receiver. Television broadcasts are similar examples.
Undesirable vibrations can arise from both sources within the electronic device and external sources. External vibrational sources abound in our present environment. These vibrations may be transmitted through the ground and building structures from sources such as vehicles passing on nearby roads and construction. Vibrations may also be transmitted through the air in the form of sound from sources such as airplanes, motors, and other sources of sounds. Many other sources of vibrations exist in buildings, such as the air handling systems, pumps, water running in pipes, and appliances. These vibrations combine, overlap and interfere with each other. Regardless of the original source of the external vibrations, these vibrations may be transmitted through the supporting structure to the tool or electronic device that is resting on the support structure.
Vibrations may also originate from within the device itself Many modern-day electronic devices contain fans and other mechanical devices which can generate various amounts of vibrations. Tape players and CDs/DVDs include motors to spin the CD/DVD or turn the tape. Many people have heard the familiar hum associated with the working of electronic equipment such as power transformers or amplifiers.
The internal signal transfer between electronic components or units, which does not leave the equipment, is an internal source of noise. Electronic, optical and RF transmissions, both external and internal, are further classified by waveforms and bandwidth. Narrow band RF transmission is achieved by transmitting a single frequency wave, modulated either by amplitude (AM) or by frequency (FM). Digital transmission may be either AM or FM. Digital data however are more efficiently transmitted in ultra wide band (UWB) as pulse or wavelet train, which is modulated by the pulse separation time, which is analogous to FM, but referenced as PM or pulse modulation..
The modulation frequency to base frequency ratio is noise level limited. For example, one can fit more channels into a given broadcasting bandwidth if the signal-to-noise ratio of the channels are smaller. UWB broadcast is less limited by bandwidth, than by noise level to pulse amplitude ratio itself. AM, FM or PM applied in different fields based on their characteristic power need, propagation path or penetration capability. For example, AM waves can travel around the globe, but are easily distorted and decay fast. The FM transmitting and receiving antennas need to “see” each other, since FM wave travels straight, remains strong and less prone for distortion.
In contrast, PM waves thus need very little energy to penetrate solids, and therefore can penetrate structure such as walls. However, its transmitter and receiver are bulky and cumbersome. PM technology is emerging quickly, because it needs no precious bandwidth sharing. Regardless of its nature and type though, to be efficient, the transmissions are preferably noiseless. One way to achieve that goal is to eliminate, or at least reduce, the noise generated or strongly affected by mechanical vibrations.
Micro vibrations also affect semiconductor tool operations in unique ways. For example, roentgen or deep ultra violet (UV) lithographic tools mask or etch nanometer wide wires onto complementary metal oxide (CMOS), silicon, germanium or other semiconductor wafer surface. The printed integrated circuit (IC) quality is strongly affected by direct vibration of the tool's optics but also by the signal-to-noise ratio of the very fine picture. Scanning electron microscopy (SEM) and probing tools in semiconductor fabs are other examples of common micro- or nano-vibration sensitivity. Similar noise-vibration problems arise in modern biotechnology, where tweezers need to manipulate microorganisms, cells and molecules. In these, last category of complex equipment, sometimes it s hard to separate the effects of mechanical noise from electronic, optical and signal transmission noises. Nonetheless, mechanical noise reduction, however, invariably improves performance.
In an effort to reduce electronic and mechanical vibration within equipment, isolation of electronic devices with rubber feet, air bearings, rigid cone legs and high damping elastomeric or felt or cork pads has been attempted. Some of these vibration or noise mitigation techniques intend to reduce noise propagation pathway by cross section or by length. Some form dead-end wave-guides or echo-aside chambers. Others attempt to absorb, dissipate, convert to heat, or otherwise attenuate vibration. Still others simply provide elastic support to the chassis to limit equipment-housing resonance.
While these earlier attempts to reduce equipment vibrations are somewhat successful, they fall short in efficiency and even more in reducing electronic noise. They mostly damp and attenuate (shift the phase of) mechanical vibration without evading it. Unfortun
Dang Khanh
Snell & Wilmer LLP
Vistek Inc.
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