1. Microflown TechnologiesThe Netherlands www.microflown.com info@microflown.comMicroflown: a new category of sensors1

2. Agenda Introduction to Microflown Technologies [3-29] Sound Intensity [30-69] Measurement techniques traditional[70-88]systems Advancedscanning techniques :Scan&Paint[89-126]2 3. Company introduction 3 4. Company Introduction1994: Invention Microflown by Hans-Elias de Bree at University Twente1997: Ph.D. Hans-Elias de Bree1998: Founding Microflown Technologies B.V. (de Bree, Koers)2001: Industrializing product2003: Introduction broad banded sensor element2004: First applications scientifically proven / first arrays sold2005: Rapid growth in (automotive + aerospace) industry2005: De Bree appointed Professor Vehicle Acoustics at the HAN University, Arnhem School of Automotive Engineering2008: Strategic decision to explore the defense & security market2010: 20 FTE company, 1,3 MEURO turnover2011: Microflown AVISA 4 5. Working principleMicroflown SEM picture: two heated wires 5 6. Working principleMicrophone measures sound pressure (result)Microflown measures Particle Velocity (cause)Acoustical electrical energySound pressure voltage potentialParticle velocity amperes kinetic6 7. Working principlePRESSURE WAVE7 8. Working principlePRESSURE WAVE PARTICLE VELOCITY8 9. Working principleT[k] velocity output 0upstreamdownstream distance9 10. Working principleuuu u uupp p ppp Cu usum sum p pA BD10 11. Working principleSurface velocity measurement: No background noise and reflection problems Figure of eightLow surface velocity High surface velocityand high surface and low surface pressurepressure 11 12. Working principleMems based sensorClean room technology isused to create the smallelements on a waverUniversity of Twente 12 13. Working principleWirebonded elements 13 14. Microflown probes14 15. Standard probes Scanning Probes 1D Velocity For small object High temperatures Non contact vibration 15 16. Standard probesPU probes Particle Velocity Sound Pressure 1D Sound Intensity 1D Sound Energy Impedance 16 17. Standard probesPU Probes: Placement of p and u 17 18. Standard probesMetal Mesh Wind shield, DC flowup to 2 m/s Protecion of thewires Calibration includingmesh 18 19. Standard probesUSP probes 3D Particle Velocity Sound Pressure 3D Sound Intensity 3D Sound Energy Impedance Acoustic Vector Sensor19 20. Standard probesHigh dB Scanning Probe Above 135dB acoustics becomes non linear Standard sensor overloads at 130dB Measurement at 170dB is possible with packaged sensor20 21. Microflown applications21 22. Standard probesFrom product development till end of line control22 23. Automotive Scan & PaintScan&ListenAcoustic cameraPNCARInsitu abosorption 23 24. Space and Aerospace3D intensity stream lines In-situ impedance Reverberant roomcharacterization PNCAR 24 25. Environmental noise3D sound sourcelocation Virtual Arrays25 26. Manufacturing industries Scan & Paint In situ impedanceAcoustic CameraPoint by point intensity26 27. End of Line Control Leak testingAcoustic EOL27 28. Room acousticsSound diffusionImpedancemeasurement3D intensityvisualization28 29. Military applicationsAir to groundapplicationsAircrafts location Hostile fire locationSurveillance 29 30. What is intensity? 31. Theoretical approach 32. IntensitySound intensity is useful for measurement of sound power, identification and ranking ofsources, visualization of sound fields, measurement of transmission loss, identification oftransmission pathsSound intensity is defined as the sound power per unit areaIntensity: Time averaged rate per unit area at which work is done by one element of fluidon an adjacent elementIntensity and Particle velocity are vectors, therefor they have a direction related to theirmagnitude.Sound intensity units are W/m232 33. IntensityIn far field pressure and velocity have equal phase so I is a real quantity.However, in the near field pressure and velocity are out of phase,leading to have an active and reactive part of the intensityActive intensity [ I ]Active intensity is the real part of the time Imaginaryaveraged product between pressure andvelocity. This term is commonly calledacoustic intensity because is associated tothe acoustic energy that propagates away Jfrom the sourceReactive intensity [ J ] IReal Active intensity is the imaginary part of the time averaged product between pressure and velocity. This term is associated with the evanescent energy carried by the particle velocity 33 34. Reactivity indexThe reactivity index is the ratio betweenreactive (J) and active intensity (I)When reactivity takes high values lead tolow active intensity. This can be seem aslack of radiation efficiency, i.e. there is avibrating surface which moves the air butis not able to compress it.The size of the near field is related to thewavelength assessed, therefore thereactivity index also depends onfrequency. 34 35. Pressure-Intensity index 35 36. Sound Intensity-PP probes 37. PP intensityTraditionally the measurement of sound intensity is performed by P-P probes.The measurement procedure makes use of two microphones. The sound pressureis the average of the two corresponding pressure signals. The intensity is calculatedat the center of the space separating the two microphones.The P-P intensity is then obtained by the following relation:p1 t p2 tt p1p2I pp pu td2 rtWhere the first term is the promediated pressure value and the second term is theestimated particle velocity.37 38. PP intensityAverage pressurebetween the two closelyspaced microphonesEstimation of the particlevelocity from the pressuregradient valid for free fieldplane waves38 39. PP intensity - ERRORSPhase mistmatch errorbetween pressuremicrophonesPressure-intensity index is directlyrelated with the measurement error39 40. PP intensity - ERRORSPhase mismatch error :22peprms prms / cpeI pp I pp I 1k r c k r IA small error in the microphones phase matching can lead to an uncorrect intensityestimation.This is the reason why the manufacturers need to pair the microphones, to try tofind in the production, the more similar sensors to form the probe. 40 41. PP intensity - ERRORS Finite difference error (depends on the microphone separation): sin k r I pp / Ik r The estimation of the velocity term is the pressure gradient between the twopressure signals, this can lead to the following casesToo low frequency: the pressure gradient istoo small to determine the velocityToo high frequency: the wavelength istoo small compared to the microphonespacing41 42. PP intensity - LimitationsReverberant sound fields:The usable frequency region of thesesensors is drastically reduced when thepressure-intensity index is HIGH,because of the small ratio betweenphase measurements at microphonepositions. This effect appears inreverberant conditions where: high pressure level Intensity level tending to 0Free field conditions:The spacer needs to be changed foreach frequency range, in order toadapt it to the interest wave legth.42 43. PP intensity - LimitationsNear field measurements:The probe can be used but the usablefrequency range is reduced drasticallybecause of the appearance ofevanescent waves.The gradient of pressure to estimatethe particle velocity is on longer usableNOTE: Evanescent waves:Anevancescent wave is a near fieldstanding wave with an exponentialamplitude decay from the boundary atwhich the wave was formed43 44. Properties of PP probesAdvantages Not sensitive to DC flow Flat frequency responseDisadvantages Only for plane waves Distributed sensor Exact microphone pairing needed Microphone spacing depends on frequency Accuracy is strongly dependent into thepressure-intensity index44 45. Sound intensity P-U probes 46. PU intensity The working principle is based upon measuring the temperaturedifference in the cross sections of two extremely sensitive heatedplatinum wires that are placed in parallel. The incident sound flownproduces a difference in temperature, leading into a voltagedifference proportional to the flow. P-U intensity :Pressure and particle velocity are directly measured so no assumptionsabout the sound field are requiredIntensity is then described by the real part of the product of pressure andparticle velocity, both measured quantities.46 47. PU probes - ERRORSReactivity index:The reactivity is the ratio between active (Re) andreactive ( Im) intensity of the sound field.Reactive intensity :J pu 1 / 2 Im puIf the reactivity takes a HIGH value there is notintensity produced, the sound source is only pushingair back and forward. In this case a small phasemismatch between P and U sensor can produce anerror: J I pu I 1 e I1 e tan fieldIThis is due to happen fat the vicinity of the soundsource at low frequencies.This effect can be solved by the usage of the particlevelocity itself for sound localization purposes. 47 48. Calibration errors of P-U probesMeasurements show that a phasematching of 1 degree is possible withacalibration based on a shortstanding wave tube method or thepiston on a sphere method. Theenhanced calibration based on thesound power ratio technique a phasematching error of 0.15 degrees canbe obtainedOne can state that if the measured phase of the sound field is less than 80 degrees(less than 7dB of reactivity index), a calibrated P-U probe has a measurement errorless than 0.5dB48 49. Properties of P-U probes Advantages Small size. Point measurement Usable for near field measurement Broadband solution Usable in reverberant conditions Pressure and Velocity measuredalmost in same point ( nondistributed sensor). Disadvantages Response decreases with frequency Sensitive to DC flow Accuracy is dependent into thereactivity index 49 50. PU and PP performance comparisson 51. Experimental resultsSound intensity measurements of a broadband noise source using a P-Uprobe (red) and a P-P probe (blue) 51 52. PP and PU intensity measurements 52 53. PP and PU intensity measurements 53 54. PP and PU intensity measurementsDifferencebecause ofareaassigned ineach method54 55. Sound power measured at two surfacesExpected 10,6 dB difference because ofDipole sound sourcedimensions 1 dB deviation because of bad location of PP probe while measuring 55 56. Sound power measured at two surfaces Very reactive worst scenario for PU probe After correction of phase mismatch of PU, intensity graphs coincide56 57. PU probes calibration method 58. Piston on a sphereAs there is not a reference particle velocity sensor the principle is to insert thepressure and velocity sensors into a known sound field in which P and U arerelated by the known acoustic impedance ( Z). Problem: this is not possible for all frequencies, low frequencies: Lower loudspeaker radiation Spherical waves Solution: 3 step method Step1: High frequencies Step2: Low frequenciesStep 3: Combination Applying the 3 steps the calibration is usable for 20-20KHz58 59. Step 1: High frequency calibration A known sound field is generated Known relation between U-P via Z ( Z= P/U) Usable for 100-20.000 Hz. 59 60. Step 2: Low frequencies Loudspeaker cannot radiate as much energy as in high frequencies Backgound noise too much influence Different method: Pref is inserted IN the sphere U is located next to the membrane Known noise field generated From the relation of the difference in pressure inside the sphee andthe movement of the membrane, is obtained the response. Usable until first mode of sphere The phase is obtaine dbut the results magnitud is notdetermined. Need of Step 3 60 61. Step 3: Combination 1 and 2 Not known magnitude of calibration at low frequencies because of lackof: Vo: exact sphere volume Ao: piston area R: exact distance to membraneStep 1 and 2 overlay61 62. ResultResult: non flat response of the sensor. Needs to be equalized via Signalconditioner+62 63. 3D intensity 64. 3D sound intensity probes64 65. 3D sound intensity probes 100HzSound intensity streamlines of loudspeakers vibrating in phase (left) and vibrating in anti-phase (right). 65 66. 3D sound intensity probes 500HzSound intensity streamlines of loudspeakers vibrating in phase (left) and vibrating in anti-phase (right). 66 67. 3D sound intensity probesSound intensity streamlines ofa loudspeaker driven close toa metal plate. 67 68. 3D sound intensity probesNoise mapping 68 69. 3D sound intensity probesEnergy characterization and difussion 69 70. Measurement Techniques 71. Theoretical approach 72. Type of noisesNoise Deterministic Non deterministic PeriodicNon periodic Random TransientComplex Non-SinusoidalStationaryperiodic Stationary Ergodic Non-Ergodic 72 73. Deterministic noise Deterministic: a signal whos values can be predicted from current or pastinformation Numerical: denoted by a number or colletion of numbers Analytic: denoted by an equation which defines the process.73 74. Non deterministic noise Random / Stochastic process: a function usually of time, that takes on a definitewave form each time a chance experiment is performed that cannot bepredicted in advance. DEF 2: a family of time dependent signals for which the value at a specific timemay be regarded as a random variable. Stationarity: invariance of stadistical properties with respect to the time origin. Narrow band process: stationary process in which significant samples are limited to a slim band of frequencies in relation with a central frequency of the band. Color noises: narrow band processes which energetic content and statistical properties are distributed in a certain manner Wide band process: stationary process which significant values appear in a range proportional of the magnitud of the central frequency of the band.74 75. Color noiseWhite noise is a signal/process with a flat spectrum. Thesignal has equal power in any band of a givenbandwith.Grey noise: is random white noise subjected to apsychoacoustic equal loudness curve over a givenrange of frequencies, giving the listener theperception that it is equally loud at all frequenciesPink noise: the frequency spectrum is linear in logarithmicspace, it has equal power in bands that areproportionally wide.Brown noise: stationary random signal whos powerspectrum falls of at a constant rate of 6 dB per octaveViolet noise: Violet noises power density increases 6 dBper octave with increasing frequency(densityproportional to f 2) over a finite frequency rangeBlue noise: Blue noises power density increases 3 dB peroctave with increasing frequency (density proportionalto f ) over a finite frequency range75 76. Transient noiseImpulse: unwanted, almost instantaneous (thus impulse-like) sharp soundsBurst noise : sudden step-like transitions between two or more discrete levelsSweep noise: a signal, commonly of constant amplitude, that locally resembles asine wave but whose instantaneous frequency changes with timeChirp noise: rapid frequency sweep signal76 77. Measurement techniques 78. Conventional measurement techniques 79. Point by point measurementsSuitable for: Stationary noiseMeasurement process: Definition of an imaginary measurementplane. Definition of a grid on the plane In every grid position perform ameasurement for every noise componentto be characterizedResult: Vector per grid point.79 80. Traditional scanning techniqueSuitable for: Stationary noiseMeasurement process: Definition of an imaginary measurement plane. Scanning of the whole interest areaResult: Single intensity value per area promediated value 80 81. Simultaneous measurement Suitable for: Stationary noise Transient noise Measurement process: Allocation of sensors/ array deployment Audio capture of several channels Direct measurement, nosignalprocessing Result: Color maps of noise distribution in time81 82. Advanced measurement methods 83. New scanning techniques: Scan&PaintSuitable for: Stationary noiseMeasurement process: Definition of an imaginary measurementplane. Scanning of the whole interest area Automatic post process assigning locationof probe- audio measurementResult: Color map of various indexes Spectrogramsof everylocatedmeasurement point Global index to characterize an area83 84. Intensity based sound source localizationSuitable for: Any noiseMeasurement process: Sensors allocation Simple signal processingResult: DOA: direction of arrival of noise Spectrograms of each 3D directions Global and narrow band levelsLimitations: Free field assumptions for simple algorithm Increase number of sensors to detect coherent noise sources84 85. Conventional beamformingSuitable for: Stationary noise Transient noiseMeasurement process: Definition: Signal processing techniqued ised in arrays for directional signaltransmission . This directional information is obtained by combining elements inthe array Allocation of sensors/ array deployment Audio capture of several channels Beam forming signal processingResult: Color maps of noise distributionLimitations Frequency limitations by spacing and array size High cost 85 86. HolographySuitable for: Stationary noiseMeasurement process: Definition: Method to estimate the sound field near a source by measuringacoustic parameters away from the source via an array of pressure and/orparticle velocity transducers. Processing after acquiring information from arrayResult: Color map of the interest areaLimitations: Frequency limitations because of spacing and array dimension Assumes free field Regular grid Heavy calculations High cost86 87. Airborne transfer path measurementsSuitable for: Stationary noiseMeasurement process: Combination of the characterization of a noise sourcewith the propagation path to the listener in order toobtain information about the contribution of a specificnoise in the whole perceive sound pressure levelS Measurements divided in two steps: source andtransfer path characterizationResult: Noise source listener rankingLimitations: High cost Typically measured in reverberant environments Surface noise source detected not structural problems87 88. Virtual arrays beamformingSuitable for: Stationary noiseMeasurement process: Deffinition of an imaginary measurement plane. Scanning of the whole interest area Measurement of two reference positions Automatic post process assigning location of probe-audio measurementResult: Color map of various indexes Spectrograms of every located measurement point Global index to characterize an area and noise sourcelocationLimitations: Size and distance Heavy calculations88 89. Advanced measurement techniques:Scan & Paint 90. Theoretical approach 91. Scan&Paint principleThe PU probe is moved along the virtual plane while the movement is recorded by the video camera.The location of each measured position is extracted from the video and synchronized with the 2 audio channels. 91 92. Scan&Paint principlePressure Velocity92 93. Scan&Paint principle: post-processingTwo methods to cover the fullfrequency range: - Velocity method (for lowfrequencies) - Intensity method (for highfrequencies) 93 94. Low frequenciesIn the near field of the surface the particle velocity is equal to the surfacevelocity. The influence to background noise is low.At higher frequencies the velocity method fails because: The area of consistent velocity is too small. There are many modes in the material which require many measurement points The sensor is not in the near field any moreHigh frequencies At high frequencies the sensor is not in the (very) near field any more and the intensity is used. There are no P-I index problems like with P-P intensity probes At low frequencies the intensity method fails because the sound source is too reactive94 95. Measurement procedure 96. Measurement procedure96 97. Measurement examples 98. Scan & PaintExample 1: Large gas turbine enclosureThere are big stationary engines ( used for Heat & Power )The goal was to measure the performance of the special designed enclosures.Specially regarding acoustic leakages. With Scan & Paint we could perform themeasurement on a large surface in short time period in highly reverberantconditions. 98 99. Scan & Paint Example 1: Large gas turbine enclosureSelection of measurement points on the backside of the housing 99 100. Scan & PaintExample 1: Large gas turbine enclosureVelocity map at 65Hz 100 101. Scan & PaintExample 1: Large gas turbine enclosureLow frequencyHigh frequency101 102. Scan & PaintExample 2: Building acoustics102 103. Scan & PaintExample 3: Leak detection in buildingsStudying the spectra ofdifferent areas allows toproduce narrow band mapsfocused ondetectingweaknessesThis technique is suitable forlocalizing acoustic leakagewith a very high spatialresolution in a clear and easyway 103 104. Scan & PaintExample 4: Automotive | Comparison test of compo-nents in a windtunnelSee the effect of the noise due to windflowrelated to the interior noise when usingdifferent type of components or makeadjustment to the components used on theoutside of a car like a mirror or window wiper.The test are performed with the car in awindtunnel when using Scan & Paint to mapthe effect to the noise in the interior insidethe car. 104 105. Scan & PaintExample 4: Automotive | Comparison test of compo-nents in a windtunnelLeft the velocity map of the standard wiper and right the velocity map ofthe wiper with adjustments made. 105 106. Scan & PaintExample 4: Automotive | Comparison test of compo-nents in a windtunnelLeft the velocity map of the car without rearview-window and right thevelocity map of the car with the rearview-window. 106 107. Scan & PaintExample 5: Automotive | Optimization material packageTo see where to place absorbingmaterials effectively and measure theeffect after installing the materials. Firstthe door was measured withoutmaterials and secondly with materialsplaced based on the first measurement.A sound source is positioned in theinterior and with pink noise asexcitation.107 108. Scan & PaintExample 5: Automotive | Optimization material packageDoor | no dampingDoor | with damping 108 109. Scan & Paint Example 6: Automotive NVH| Component optimization The opening of the ventilation system of the dashboard show important acoustic leakagesThe shell radiation of an intake systemis measured on the test bench excitingthe plastic filter with white noise froma loudspeaker109 110. Scan & PaintExample 6: Automotive NVH| Component optimizationA volume super-charger show the crankfrequency emission from the aluminumcase.The intake system radiation at lowerfrequency in engine running conditioncan be optimized 110 111. Scan & PaintExample 7: Automotive NVH| Sound source localization Exterior noise of a car. The colormap show the engine radiation through the weak areas.The front part of the engine withoutcover show high velocity emission.111 112. Scan & PaintExample 8: Electronic / white consumer goodsOptimize the noise performance of a washingmachine. Localize the hotspots suggest andadapt changes and compare result.Overall result of this case: 4dB lower SoundPower ( measured by the standard soundpressure method )112 113. Scan & PaintExample 8: Electronic / white consumer goods Dominant source200Hz113 114. Scan & Paint0.5Kg damping72dB PVL68dB PVL114 115. Scan & PaintExample 9: Electronic goods | Commercial printerOptimize the noise performance of a printersdeveloped for offices. Localize the origin of thenoise problem. A mode is created in the backplate. This mode made the printer very noisy but the origin causing the mode was needed to be localized.115 116. Scan & PaintExample 9: Electronic goods | Commercial printer With Scan & Paint the gear wheel that was causing structure borne noise ( the created mode in the backplate). The amount of teeth, the material of the gear wheel or the connection with the backplate could be options to reduce this structure borne noise. 116 117. Scan & PaintExample 9: Electronic goods | Commercial printer 117 118. Scan & Paint Example 10: Electronic goods | Clima and MicrowaveWith Scan & Paint low frequency noisefrom the cooling system (airflow)can beseparated by the noise coming from thebody frame of the clima.The button panel on the rightside show higher sound emissionabove 2000Hz. 118 119. Scan & PaintExample 11: Ground Vehicles | High speed train | In situtransparency measurements In situ transparency measurements using Scan & Paint were performed as alternative to the traditional transmission loss measurements. Mainly to identify positions of leakages.119 120. Scan & PaintExample 11: Ground Vehicles | High speed train | In situtransparency measurements The pressure distribution (and the velocity distribution) is measured both out and inside the train, to correct the non- uniformity of the sound field as the excitation pattern (emitter side). The average velocity over the surface is calculated for both sides, and a simple formula is applied to estimate the transmission loss from the velocity or so called the transparency: 120 121. Scan & Paint Example 11: Ground Vehicles | High speed train | In situ transparency measurementsOutside TGV velocity distribution Inside TGV velocity distribution 121 122. Scan & PaintExample 11: Ground Vehicles | High speed train | In situtransparency measurements122 123. Scan & PaintExample 12: Industrial machinery | Sound source localization Industrial machinery can be tested in non-anechoic conditions. 123 124. Scan & PaintExample 13: Airplane | Leakage detectionAcoustic leakage on a plane section. Thesound is generated out from the plane tosimulate the engine noise level. 124 125. Scan & PaintExample 14: Airplane | In situ absorptionThe Scan&Paintabsorption showthe effect of theflame cover on aplane seat.The colormap ofabsorption canbecalculatedmeasuring withthe impedancegun.125 126. Scan & PaintExample 15: Absorption & Reflection coefficients 126