Band Elimination Filter Layout for Wideband Noise Attenuation
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Solution Overview
Problem
Existing band elimination filters are ineffective in attenuating electromagnetic noise across a wide range of frequencies due to the increasing impedance of capacitors with frequency, leading to reduced noise suppression effectiveness at higher frequencies.
Innovation Solution
A band elimination filter comprising multiple capacitors connected in parallel with an electromagnetic noise source, where the total series inductance of the capacitor-side path is made less than the motor-side path, and resistors are added in series with capacitors to dampen parallel resonance, ensuring effective noise attenuation across a wider frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a capacitor is connected in parallel with the power supply terminals of the starter motor to attenuate electromagnetic noise, then noise suppression effectiveness is improved at lower frequencies, but the effectiveness becomes reduced at bands with higher frequencies due to increasing capacitor impedance
Solution Approach 1:
The patent divides the single capacitor into multiple capacitors with different capacitance values connected in parallel. Each capacitor targets a specific frequency range, with smaller capacitors handling higher frequencies and larger capacitors handling lower frequencies. This segmentation allows the filter to maintain effective noise suppression across a wide frequency spectrum without being limited by the impedance increase of a single capacitor at high frequencies.
Solution Approach 2:
The patent changes the parameter of capacitance by using multiple capacitors with different capacitance values instead of a single capacitor. By selecting capacitors with progressively smaller capacitance values, the system optimizes the impedance characteristics across different frequency ranges, ensuring that at least one capacitor maintains low impedance at any given frequency, thereby maintaining effective noise suppression.
2Object-affected harmful factors
If multiple capacitors with different capacitance values are connected in parallel, then the frequency range for effective noise attenuation is widened, but the device complexity increases
Solution Approach 1:
The patent combines multiple capacitors with different capacitance values into a single parallel circuit configuration connected across the power supply terminals. This merging approach allows the system to achieve wide frequency range noise attenuation while maintaining a relatively simple overall structure. The capacitors share common connection points, and their combined effect provides broad-spectrum noise suppression without requiring complex multi-stage filtering circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides high attenuation of electromagnetic noise over a predetermined wide range of frequencies, effectively suppressing noise interference in power supply networks, such as those affected by starter motors in vehicles.
Implementation Method 1
the electromagnetic noise becomes attenuated by voltage-division of the noise voltage at each capacitor stage, with the above-described increase of capacitor impedance with increase of frequency (described hereinabove referring to FIG. 13) being eliminated
Implementation Method 2
the impedance should ideally decrease linearly with increasing frequency values. However in practice, the capacitor has a small inductance component (equivalent series inductance). As a result, in a range of frequencies above a specific value, the effects of the inductance component begin to become strong, and the impedance of the capacitor thereafter increases
Implementation Method 3
at least one parallel resonance circuit is formed by a closed circuit containing an adjacent pair of parallel capacitors, due to inductance components of the closed circuit
Implementation Method 4
a resistor is connected in series with at least one capacitor in each of adjacent parallel pairs of capacitors. Such a circuit has a parallel resonance frequency which is determined mainly by the capacitance values of the pair of capacitors and the equivalent series inductance values of these capacitors. With the present invention, a resistor is connected in series with at least one of the capacitors of such an adjacent pair, for damping the parallel resonance
Data Source
AI summary
In a band elimination filter, a plurality of capacitors are connected in parallel between first and second terminals of an electromagnetic noise source which generates voltage fluctuations in a connecting lead connected to the first terminal, with the capacitors being connected to the connecting lead at respectively corresponding branch points. For each capacitor, the total series inductance of a first circuit path is made less than that of a second circuit path, where the first circuit path extends from the corresponding branch point to the second terminal via the capacitor, and the second circuit path extends from that branch point to the first terminal of the electromagnetic noise source. A resistor is connected in series with at least one of the capacitors, for damping parallel resonance caused by inductance components of an adjacent pair of capacitors.