Electromagnetic noise suppression method

Abstract

The invention discloses an electromagnetic noise suppression method, which comprises the following steps: S1, designing an asymmetric magnetic pole winding: the pole-arc coefficient is the ratio of the magnetic pole arc length to the pole distance, the pole-arc coefficient of odd teeth is 1.2, the pole-arc coefficient of even teeth is 1.0, the symmetry of a magnetic field is broken through asymmetric magnetic field distribution, and low-order harmonics in cogging torque pulsation are suppressed; s2, winding optimization of the winding: adopting a distributed winding technology, adopting a precise winding process with the error of the number of conductors in each groove being less than or equal to + / -2%, and reducing the content of higher harmonics by adjusting the pitch and the distribution mode of the winding (adopting a short-pitch winding or a fractional-slot winding); and S3, designing a nanocrystalline alloy shielding layer: additionally arranging the nanocrystalline alloy shielding layer with the thickness of 0.3 mm between the back side of the stator yoke part and the rotor magnetic steel. According to the invention, the design is reasonable, through the multi-physical field collaborative design of the asymmetric magnetic poles and the nanocrystalline shielding layer, the motor noise is systematically suppressed from both an electromagnetic force harmonic source and a high-frequency magnetic leakage path, and both efficiency and reliability are considered.

Description

Technical Field

[0001] The present invention relates to the technical field of motor manufacturing, and in particular to a method for suppressing electromagnetic noise. Background Art

[0002] A motor is an electromagnetic device that converts or transmits electrical energy based on the law of electromagnetic induction, or converts one form of electrical energy into another. An electric motor converts electrical energy into mechanical energy (commonly known as a motor), while a generator converts mechanical energy into electrical energy. In circuits, an electric motor is represented by the letter "M" (older standards used "D"). Its primary function is to generate driving torque, serving as a power source for electrical appliances and various machines.

[0003] Electromagnetic noise in motors is an inevitable byproduct of motor operation. It is primarily caused by mechanical vibrations caused by electromagnetic harmonics, which are transmitted through the structure to the external environment. Conventional motor stator slots utilize a uniformly distributed, symmetrical magnetic pole design (with identical pole arc coefficients). This results in periodic variations in magnetic reluctance during rotor rotation, generating significant slot torque pulsation. Furthermore, the symmetrical magnetic poles exhibit a highly regular magnetic field distribution, which easily excites low-order electromagnetic harmonics (such as the 6th and 12th harmonics), becoming the primary source of medium- and low-frequency noise (<10kHz). Furthermore, when the motor operates at high speeds, high-frequency leakage flux (>10kHz) between the rotor magnets and the stator yoke penetrates the core, easily inducing eddy current losses and localized temperature rise, while also stimulating high-frequency vibration noise in the stator yoke. Conventional solutions rely primarily on increasing the thickness of the silicon steel sheets or adding copper shielding rings. However, the former increases volume and weight, while the latter, due to its high conductivity, exacerbates eddy current losses. To address these issues, we have designed an electromagnetic noise suppression method. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems existing in the prior art and propose a method for suppressing electromagnetic noise. Through the multi-physics field collaborative design of asymmetric magnetic poles and nanocrystalline shielding layers, it starts from both the source of electromagnetic harmonics and the high-frequency leakage magnetic path, systematically suppresses motor noise, and takes into account both efficiency and reliability.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for suppressing electromagnetic noise comprises the following steps:

[0007] S1. Asymmetric pole winding design: The pole arc coefficient is the ratio of the pole arc length to the pole pitch. The pole arc coefficient for odd-numbered teeth is 1.2, and the pole arc coefficient for even-numbered teeth is 1.0. The asymmetric magnetic field distribution breaks the magnetic field symmetry and suppresses low-order harmonics in the cogging torque ripple.

[0008] S2. Winding optimization: Adopt distributed winding technology and precision winding process with the error of conductor number per slot ≤±2%. Reduce high-order harmonic content by adjusting winding pitch and distribution mode (using short-pitch winding or fractional slot winding).

[0009] S3. Nanocrystalline alloy shielding layer design: A 0.3mm thick nanocrystalline alloy shielding layer is added between the back side of the stator yoke and the rotor magnet. Utilizing its high magnetic permeability (μ≥80,000), it guides high-frequency leakage magnetic flux (>10kHz) through the shielding layer and blocks the leakage magnetic path between the iron core and the air gap.

[0010] S4. Synergistic mechanism:

[0011] Asymmetric magnetic poles mainly target low- and medium-frequency noise (<10kHz), weakening cogging torque and low-order electromagnetic force harmonics;

[0012] The nanocrystalline shielding layer targets high-frequency noise (≥10kHz) and blocks core vibration and eddy current loss noise caused by magnetic leakage.

[0013] Preferably, in S3, the stator and rotor slots are matched with non-integer slots to avoid the resonant frequency, and a double-skewed slot structure is adopted to further weaken the harmonic force wave.

[0014] Preferably, in S3, a high temperature resistant epoxy resin is used to adhere the shielding layer to the stator yoke to avoid an increase in the air gap.

[0015] Preferably, the arc length processing error of the magnetic pole is ≤±0.05mm, and the surface roughness of the nanocrystalline shielding layer is Ra≤1.6μm, ensuring the consistency of the magnetic circuit.

[0016] Preferably, in S2, high-precision winding equipment is used to ensure winding uniformity and avoid additional force waves caused by winding asymmetry.

[0017] Preferably, the nanocrystalline alloy shielding layer is protected by an anti-oxidation coating or packaging to prevent the material from being brittle and cracked under high-speed centrifugal force.

[0018] Preferably, the nanocrystalline alloy shielding layer has a low thermal conductivity, and heat dissipation grooves are added to the stator yoke or a liquid cooling system is combined.

[0019] Preferably, verification tests are carried out to analyze the magnetic field distribution, cogging torque and electromagnetic force waves through finite element simulation (such as Maxwell), and optimize parameters in combination with actual measurements (such as vibration sensors and acoustic microphones) to ensure that the noise suppression targets are met.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. This electromagnetic noise suppression method optimizes the air gap magnetic field distribution and weakens tooth harmonic components by adjusting the stator tooth pole arc coefficient (1.2 for odd teeth and 1.0 for even teeth). This difference in pole arc coefficients creates an asymmetric magnetic potential waveform, reducing the amplitude of low-order harmonics. Adjusting the winding pitch and distribution reduces higher-order harmonics. An asymmetric pole winding design, with variable pole arc coefficients, breaks the periodicity of magnetic resistance, dispersing electromagnetic harmonic energy at its source. Combined with high-precision winding technology, this method reduces spatial harmonics.

[0022] This electromagnetic noise suppression method utilizes a nanocrystalline alloy shielding layer. This layer utilizes the high magnetic permeability and high-frequency, low-loss properties of nanocrystalline materials to guide the magnetic flux leakage path, blocking high-frequency stray magnetic flux from penetrating the core while also avoiding additional eddy current losses. Through electromagnetic-structural-acoustic joint simulation, the asymmetry of the magnetic poles, the thickness of the shielding layer, and heat dissipation requirements are balanced to achieve a synergistic effect of noise suppression and efficiency improvement. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0024] A method for suppressing electromagnetic noise comprises the following steps:

[0025] S1. Asymmetric pole winding design: The pole arc coefficient is the ratio of the pole arc length to the pole pitch. The odd-numbered teeth use a pole arc coefficient of 1.2 (wide pole arc), and the even-numbered teeth use a pole arc coefficient of 1.0 (narrow pole arc). The asymmetric magnetic field distribution can break the symmetry of the magnetic field and suppress the low-order harmonics (such as the 6th and 12th) in the tooth slot torque pulsation, thereby reducing the electromagnetic force excitation source from the root.

[0026] Odd-numbered teeth use a wider pole arc, such as increasing the tooth tip width or optimizing the tooth shape, to enhance local magnetic flux concentration and reduce sudden changes in magnetic resistance. Even-numbered teeth are designed to maintain a standard pole arc to balance the overall magnetic circuit symmetry.

[0027] The variable pole arc coefficient magnetic pole (i.e. asymmetric design) reduces the cogging torque pulsation from 15%-20% of traditional motors to ≤10%, reduces rotor "stuck" loss, and equivalently improves motor efficiency by 1.5%-2%.

[0028] S2. Winding optimization: adopt distributed winding technology and precision winding process with the error of conductor number per slot ≤±2%. By adjusting the winding pitch and distribution mode, such as adopting short-pitch winding or fractional slot winding, the magnetomotive force harmonics are dispersed to make the winding magnetomotive force (MMF) distribution more uniform, weaken the amplitude of higher harmonics (such as 5th and 7th), reduce the spatial harmonic order of radial electromagnetic force wave, and reduce the higher harmonic content. For example, selecting a pitch of 5 / 6 of the full pitch can effectively suppress the 5th harmonic.

[0029] Distributed winding (conductor number error ≤ ±2%) can reduce winding copper loss, and combined with multi-strand twisted wire to reduce skin effect, copper loss is reduced by 8%-10% compared with traditional concentrated winding.

[0030] This is achieved through the following measures:

[0031] Use automated winding equipment: Using high-precision winding equipment, such as an automatic wire-inserting machine, combined with a real-time conductor counting feedback system, can ensure winding uniformity, thereby controlling errors and avoiding additional force waves caused by winding asymmetry;

[0032] Process control: During the processing, the winding tension and guide wheel are positioned and calibrated to avoid deviation in the number of turns;

[0033] Quality inspection: After processing, use an inductance tester or X-ray to detect the uniformity of conductor distribution to ensure quality.

[0034] The stator and rotor slots are matched with non-integer slots to avoid the resonant frequency, and a double-skewed slot structure is adopted to further weaken the harmonic force waves.

[0035] S3. Nanocrystalline alloy shielding layer design: A 0.3mm thick nanocrystalline alloy shielding layer is added between the back side of the stator yoke and the rotor magnet. By utilizing its high magnetic permeability (μ≥80000), it guides high-frequency leakage magnetic flux (>10kHz) through the shielding layer to block the leakage magnetic path between the iron core and the air gap.

[0036] Specifically, nanocrystalline alloys (such as FeSiBC) offer high saturation magnetic flux density (1.7T), low coercivity (<10A / m), and excellent high-frequency loss characteristics, over 80% lower than those of traditional silicon steel. This effectively suppresses high-frequency electromagnetic noise above 10kHz. The nanocrystalline alloy shielding layer blocks high-frequency magnetic flux leakage paths, reducing core loss (iron loss) by 12% (traditional silicon steel sheet iron loss is approximately 2.5W / kg at 10kHz, while nanocrystalline material has ≤2.2W / kg). This is particularly effective in high-speed and high-frequency operating conditions (>10,000 rpm).

[0037] Specifically, the noise reduction mechanism is as follows:

[0038] Leakage magnetic flux blocking: The shielding layer forms a low-resistance magnetic circuit, guiding the high-frequency leakage magnetic flux to flow along the shielding path, reducing the high-frequency magnetic saturation of the stator core.

[0039] Vibration suppression: The low magnetostrictive properties of nanocrystalline materials (3-5 times lower than silicon steel) can reduce the vibration amplitude of the core, thereby reducing noise radiation.

[0040] The nanocrystalline alloy shielding layer is protected with an anti-oxidation coating or encapsulation to prevent brittle cracking under high-speed centrifugal forces. Due to the low thermal conductivity of the nanocrystalline alloy shielding layer, heat dissipation grooves are added to the stator yoke or a liquid cooling system is incorporated. The shielding layer is secured to the stator yoke with an insulating adhesive to ensure mechanical strength and magnetic continuity. Specifically, a high-temperature resistant epoxy resin is used to bond the shielding layer to the stator yoke to prevent air gap expansion. The shielding layer is formed by hot pressing, using annealed nanocrystalline strips and then stamped into an arc shape to match the stator inner diameter.

[0041] The arc length processing error of the magnetic pole is ≤±0.05mm, and the surface roughness of the nanocrystalline shielding layer is Ra≤1.6μm, ensuring the consistency of the magnetic circuit.

[0042] S4. Synergistic mechanism:

[0043] Asymmetric magnetic poles: mainly attack low- and medium-frequency noise (<10kHz), weakening cogging torque and low-order electromagnetic harmonics;

[0044] Nanocrystalline shielding layer: Targets high-frequency noise (≥10kHz), blocking core vibration and eddy current loss noise caused by magnetic leakage.

[0045] The pole-changing arc design reduces the harmonic order of the air gap magnetic field, while the shielding layer blocks residual high-frequency leakage flux. These two elements work together to reduce the amplitude and frequency content of electromagnetic force waves, ultimately lowering the motor's noise level under all operating conditions. Overall energy efficiency is also improved. At 30,000 rpm, the motor's efficiency increases from 94% compared to conventional designs to 96%-97% (for a 100kW motor, this saves 2-3 kilowatt-hours of electricity per hour).

[0046] After the design is completed, verification testing is carried out. Finite element simulation (such as Maxwell) is used to analyze the magnetic field distribution, cogging torque, and electromagnetic force waves. Parameters are optimized in combination with actual measurements (such as vibration sensors and acoustic microphones) to ensure that the noise suppression target is met. Specifically, performance testing and noise testing are included:

[0047] Performance testing:

[0048] Use a cogging torque tester to measure the torque ripple reduction;

[0049] Use a harmonic analyzer to detect the electromagnetic force harmonic spectrum (focus on verifying that the 100th harmonic is ≤ 5% of the fundamental wave);

[0050] Use an iron loss tester to compare the loss values before and after adding the shielding layer.

[0051] Noise test:

[0052] The sound pressure level in the frequency band above 10kHz was measured in a semi-anechoic chamber to verify the noise suppression effect.

[0053] The electromagnetic noise suppression method is further described below through specific embodiments:

[0054] 1. Target motor specifications and noise suppression requirements

[0055] 1. Target motor parameters:

[0056] Type: Permanent Magnet Synchronous Motor (PMSM);

[0057] Power: 5kW;

[0058] Speed: 3000rpm;

[0059] Pole-slot configuration: 8 poles and 48 slots (8P48S);

[0060] Stator outer diameter / inner diameter: 150mm / 90mm;

[0061] Air gap length: 0.8mm.

[0062] 2. Noise suppression objectives:

[0063] Cogging torque: reduced by ≥30% (original value 1.2 N·m → target ≤0.84 N·m);

[0064] Electromagnetic harmonics: 100th harmonic amplitude ≤ 5% of fundamental wave;

[0065] High-frequency noise: sound pressure level reduction in the frequency band above 10kHz ≥ 10dB(A);

[0066] Core loss: Reduction ≥12% (original value 120W → target ≤105.6W).

[0067] 2. Design and implementation of asymmetric pole winding

[0068] 1. Stator tooth structure optimization:

[0069] Magnetic pole grouping: 48 slots correspond to 8 poles, 6 slots per pole, odd-numbered teeth and even-numbered teeth are arranged alternately.

[0070] Pole arc coefficient allocation:

[0071] Odd-number teeth: pole arc coefficient 1.2, tooth top width increased from standard 3.2mm to 3.8mm, optimizing magnetic flux concentration;

[0072] Even-numbered teeth: pole arc coefficient 1.0, tooth top width maintained at 3.2mm, balanced magnetic circuit symmetry;

[0073] Tooth design:

[0074] The odd-numbered teeth adopt trapezoidal tooth tops with a top width of 3.8mm and a root width of 4.5mm to avoid local magnetic flux saturation;

[0075] The even-numbered teeth maintain a rectangular top and the tooth roots are rounded (R0.5mm) to reduce stress concentration.

[0076] 2. High-precision distributed winding manufacturing

[0077] Winding parameters:

[0078] Number of slots per pole per phase (q) = 2 (48 slots / 8 poles / 3 phases);

[0079] Coil pitch: 5 slots (short pitch design, pitch coefficient 0.833).

[0080] Conductor number control:

[0081] Number of conductors per slot: 42 turns, with an allowable error of ±2% (i.e. 41-43 turns).

[0082] Process realization:

[0083] A fully automatic winding machine (accuracy ±0.5 turns) is used, equipped with a laser rangefinder to monitor the winding layer thickness in real time;

[0084] Use polyimide enameled copper wire (temperature resistance level 220℃), wire diameter 0.8mm, and winding tension control at 3.5±0.2N.

[0085] Quality inspection:

[0086] Inductance consistency test: Randomly select 10% of the slots, inductance value deviation ≤ ±1.5% (LCR meter measurement, 1kHz);

[0087] X-ray imaging: Check the uniformity of conductor distribution to avoid cross-layer or overlap.

[0088] 3. Pole-winding collaborative simulation verification

[0089] FEA simulation parameters:

[0090] Software: ANSYS Maxwell 2D transient field analysis;

[0091] Mesh division: The stator teeth are locally encrypted to 0.2mm, and the air gap area is 0.1mm.

[0092] Results comparison:

[0093] parameter Traditional symmetrical magnetic poles Asymmetric magnetic poles Cogging torque peak 1.2N·m 0.78N·m (↓35%) 100th harmonic ratio 8.5％ 4.2％ Air gap magnetic flux density THD 12％ 7.3％

[0094] 3. Nanocrystalline shielding layer integration process

[0095] 1. Shielding layer design and installation

[0096] Material selection:

[0097] Nanocrystalline alloy material: FT-3K, thickness 0.3mm, width 10mm, covering the axial length of the stator yoke;

[0098] Key performance: initial magnetic permeability μ_i=1.8×10 4 , saturation magnetic induction B_s = 1.25T, 10kHz loss P = 45W / kg.

[0099] Installation Location:

[0100] The back side of the stator yoke (5mm away from the air gap surface) is continuously covered in the circumferential direction, with a spacing of 0.5mm from the rotor magnet (to avoid contact).

[0101] Fixed process:

[0102] 1. Surface treatment: The nanocrystalline ribbon is hydrogen annealed (450°C x 1h) and then chemically passivated (to improve corrosion resistance).

[0103] 2. Bonding process:

[0104] High-temperature resistant epoxy adhesive (LOCTITE ABLESTIK 8360) was used, with curing conditions of 120°C for 30 min and a pressure of 0.3 MPa.

[0105] The thickness of the glue layer is controlled at 50±5μm to avoid increasing the air gap in the magnetic circuit.

[0106] 2. Magnetic circuit and heat dissipation adaptation

[0107] Magnetic circuit compensation design:

[0108] Because the shielding layer introduces additional magnetic resistance, the rotor magnet thickness is increased by 0.2mm (from 4.0mm to 4.2mm) to compensate for the magnetic flux loss.

[0109] Thermal Optimization:

[0110] The stator yoke is provided with axial heat dissipation slots (2mm wide, 3mm deep, 15mm apart) to enhance air convection;

[0111] The shielding layer is sprayed with Al2O3 ceramic coating (thickness 0.1mm, thermal conductivity 30W / m·K) to improve heat dissipation.

[0112] 4. Prototype Manufacturing and Test Verification

[0113] 1. Key steps in the prototype assembly process

[0114] 1. Stator core lamination: DW470-50 silicon steel sheet, lamination coefficient 0.97, V-groove buckle point fixation;

[0115] 2. Winding embedding: Automatic embedding by robot, slot insulation adopts Nomex 410 (thickness 0.25mm);

[0116] 3. Shielding layer installation: After heating the stator to 80℃, attach the nano-wafer and solidify under vacuum pressure;

[0117] 4. Rotor assembly: NdFeB magnet (N38SH), surface mount installation, carbon fiber protective cover with an interference fit of 0.1mm.

[0118] 2. Performance test data

[0119] Cogging torque test:

[0120] Method: Low-speed drag method (0.5 rpm), torque sensor (HBM T40B) acquisition;

[0121] Results: Peak torque 0.75 N·m (↓37.5%), periodic fluctuation amplitude ΔT = 0.15 N·m.

[0122] Electromagnetic harmonic analysis:

[0123] Equipment: multi-channel strain gauge (attached to the stator tooth root) + FFT analyzer;

[0124] Spectrum results: The 100th harmonic amplitude accounts for 4.8% (meeting the ≤5% target);

[0125] Core loss test:

[0126] Method: Input-output method (minus copper loss and mechanical loss).

[0127] Results: Iron loss 103W (↓14.2%), of which eddy current loss decreased from 65% to 52%.

[0128] Noise test:

[0129] Environment: semi-anechoic room, background noise ≤ 20dB(A);

[0130] Working conditions: Rated load 3000rpm, measurement with microphone array (GRAS 46AE).

[0131] result:

[0132]

[0133] This embodiment uses the dual design of asymmetric magnetic poles and nanocrystalline shielding layer to achieve the following on a 5kW permanent magnet synchronous motor:

[0134] The cogging torque is reduced by 37.5%, and the amplitude of the 100th electromagnetic force harmonic is reduced to 4.8% of the fundamental wave;

[0135] High-frequency noise (10-15kHz) is reduced by 12dB(A) and core loss is reduced by 14.2%;

[0136] The total noise value of the entire frequency band is reduced from 78dB(A) to 70dB(A), meeting the noise standard for precision machine tool spindle motors (ISO3744Class 2).

[0137] Therefore, in this application, through the multi-physics field collaborative design of asymmetric magnetic poles and nanocrystalline shielding layers, it is possible to systematically suppress motor noise from both the source of electromagnetic harmonics and the high-frequency leakage magnetic path, while taking into account both efficiency and reliability.

[0138] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for suppressing electromagnetic noise, characterized in that: The following steps are involved: S1. Asymmetric pole winding design: The pole arc coefficient is the ratio of the pole arc length to the pole pitch. The pole arc coefficient for odd-numbered teeth is 1.2, and the pole arc coefficient for even-numbered teeth is 1.

0. The asymmetric magnetic field distribution breaks the magnetic field symmetry and suppresses low-order harmonics in the cogging torque ripple. S2. Winding optimization: adopt distributed winding technology and precision winding process with the error of conductor number per slot ≤±2%. Reduce high-order harmonic content by adjusting winding pitch and distribution mode. S3. Nanocrystalline alloy shielding layer design: A 0.3mm thick nanocrystalline alloy shielding layer is added between the back side of the stator yoke and the rotor magnet. Utilizing its high magnetic permeability (μ≥80,000), it guides high-frequency leakage magnetic flux (>10kHz) through the shielding layer and blocks the leakage magnetic path between the iron core and the air gap. S4. Synergistic mechanism: Asymmetric magnetic poles mainly target low- and medium-frequency noise (<10kHz), weakening cogging torque and low-order electromagnetic force harmonics; The nanocrystalline shielding layer targets high-frequency noise (≥10kHz) and blocks core vibration and eddy current loss noise caused by magnetic leakage.

2. The electromagnetic noise suppression method according to claim 1, characterized in that: In the above-mentioned S3, the stator and rotor slots are matched with non-integer slots to avoid the resonant frequency, and a double-skewed slot structure is adopted to further weaken the harmonic force wave.

3. The electromagnetic noise suppression method according to claim 1, characterized in that: In the above-mentioned S3, the shielding layer is bonded to the stator yoke using a high-temperature resistant epoxy resin to avoid an increase in the air gap.

4. The electromagnetic noise suppression method according to claim 1, characterized in that: The arc length processing error of the magnetic pole is ≤±0.05mm, and the surface roughness of the nanocrystalline shielding layer is Ra≤1.6μm, ensuring the consistency of the magnetic circuit.

5. The electromagnetic noise suppression method according to claim 1, characterized in that: In S2, high-precision winding equipment is used to ensure winding uniformity and avoid additional force waves caused by winding asymmetry.

6. The electromagnetic noise suppression method according to claim 1, characterized in that: The nanocrystalline alloy shielding layer is protected by an anti-oxidation coating or packaging to prevent the material from being brittle and cracked under high-speed centrifugal force.

7. The electromagnetic noise suppression method according to claim 1, characterized in that: The nanocrystalline alloy shielding layer has a low thermal conductivity, and a heat dissipation groove is added to the stator yoke or a liquid cooling system is combined.

8. The electromagnetic noise suppression method according to claim 1, characterized in that: Verification tests are conducted to analyze the magnetic field distribution, cogging torque, and electromagnetic force waves through finite element simulation (such as Maxwell), combined with actual measurements such as vibration sensors and acoustic microphones to optimize parameters to ensure that noise suppression targets are met.

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