WO2019223883A1 - Method and device for monitoring polydisperse media - Google Patents

Method and device for monitoring polydisperse media Download PDF

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Publication number
WO2019223883A1
WO2019223883A1 PCT/EP2018/063835 EP2018063835W WO2019223883A1 WO 2019223883 A1 WO2019223883 A1 WO 2019223883A1 EP 2018063835 W EP2018063835 W EP 2018063835W WO 2019223883 A1 WO2019223883 A1 WO 2019223883A1
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WO
WIPO (PCT)
Prior art keywords
signal
stimulating
medium
polydisperse
frequency
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PCT/EP2018/063835
Other languages
French (fr)
Inventor
Emanuele VIVIANI
Daniele SALVALAGGIO
Antonio Boscolo
Cristina Bertoni
Original Assignee
Electrolux Appliances Aktiebolag
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Application filed by Electrolux Appliances Aktiebolag filed Critical Electrolux Appliances Aktiebolag
Priority to EP18728578.8A priority Critical patent/EP3803369A1/en
Priority to PCT/EP2018/063835 priority patent/WO2019223883A1/en
Publication of WO2019223883A1 publication Critical patent/WO2019223883A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/036—Analysing fluids by measuring frequency or resonance of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/06—Investigating concentration of particle suspensions
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/024—Analysing fluids by measuring propagation velocity or propagation time of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/032—Analysing fluids by measuring attenuation of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/222—Constructional or flow details for analysing fluids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/34—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor
    • G01N29/348—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor with frequency characteristics, e.g. single frequency signals, chirp signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/4409—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison
    • G01N29/4436—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison with a reference signal
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/46—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by spectral analysis, e.g. Fourier analysis or wavelet analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/01—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials specially adapted for biological cells, e.g. blood cells
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N2015/0007—Investigating dispersion of gas
    • G01N2015/0011—Investigating dispersion of gas in liquids, e.g. bubbles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N2015/0042—Investigating dispersion of solids
    • G01N2015/0053—Investigating dispersion of solids in liquids, e.g. trouble
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/01—Indexing codes associated with the measuring variable
    • G01N2291/015—Attenuation, scattering
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/024—Mixtures
    • G01N2291/02416—Solids in liquids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/024—Mixtures
    • G01N2291/02466—Biological material, e.g. blood
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/025—Change of phase or condition
    • G01N2291/0258—Structural degradation, e.g. fatigue of composites, ageing of oils
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/10—Number of transducers
    • G01N2291/101—Number of transducers one transducer

Definitions

  • the present invention relates to a method for monitoring polydisperse media within an appliance.
  • the present invention also relates to an appliance comprising a monitoring device for monitoring polydisperse mediums within appliances.
  • a polydisperse medium is a medium comprising more than one phase of which at least one comprises finley divided phase domains, often in the colloidal size range, dispersed throughout a continuous phase.
  • a first example of a polydisperse medium is a washing bath having different phases such as air, organic matter, oil, detergent and others having divided phase domains of different sizes dispersed throughout the water such as bubbles, particles and aggregates, droplets, micelles.
  • a second example are edible oils, such as frying oil. E.g. during operation the frying oil may undertake physiochemical changes due to degradation of the frying oil upon temperature cycling and enrichment of food residue.
  • a third example are pourable food products such as smoothies, which are viscous beverages typically comprising pureed raw fruit or vegetables blended with ice cream, frozen yogurt, water, crushed ice, fruit juice, sweeteners, dairy products nuts, seeds, tea, chocolate, herbal supplements, or nutritional supplements.
  • smoothies are viscous beverages typically comprising pureed raw fruit or vegetables blended with ice cream, frozen yogurt, water, crushed ice, fruit juice, sweeteners, dairy products nuts, seeds, tea, chocolate, herbal supplements, or nutritional supplements.
  • acoustic spectroscopy such as ultrasound spectroscopy.
  • acoustic spectroscopy approaches rely on continuous wave techniques, tone-burst techniques, and broad band pulse techniques.
  • the continuous wave techniques rely on sinusoidal standing waves emitted into the polydisperse medium, which is arranged within a resonant chamber, which advantageously is provided with movable parts for allowing to operate at varying frequencies so as to obtain the frequency response of the system comprising the polydisperse medium.
  • the tone-burst techniques are based on the transmission of a burst of few sine periods and measuring the attenuation and the propagation velocity of the wave. By successive repetitions at different frequencies it is possible to obtain the frequency response of the system.
  • the broad band pulse techniques are based on the emission of a broad band signal and the analysis of the transmitted and the received signal for determining characteristic parameters of the polydisperse medium.
  • the broad band pulse techniques are known to result in a bad signal-to- noise ratio, in particular for these frequencies, different from the resonance frequency.
  • the reliability In order to improve the reliability it is typically needed to perform a series of measurements, which become averaged. This increases the required measurement time.
  • Aim of the present invention is to provide for a method of monitoring polydisperse mediums within an appliance, to overcome, in a straightforward manner, at least one of the aforementioned drawbacks.
  • aim of the present invention is to provide for a method of monitoring polydisperse mediums within an appliance, which enables fast measurement times.
  • a method for monitoring a polydisperse medium within a appliance comprising at least the steps of stimulating an emission probe with an stimulation signal for emitting an emission signal into the polydisperse medium, acquiring a response signal, and analysing the response signal for obtaining and/or determining at least one parameter characteristic of the polydisperse medium.
  • the stimulation signal comprises at least one random multi-sine frequency signal being the sum of a plurality of single harmonic components.
  • the at least one parameter is monitored over time in order to control the polydisperse medium.
  • the method also comprises at least one step of repetition, preferentially a plurality of steps of repetition, and during each step of repetition at least the steps of stimulating, acquiring and analysing are repeated.
  • the response signal is analysed with respect to a reference response signal.
  • the reference response signal become determined prior to the response signal.
  • the method further comprises the step of obtaining and/or determining the reference response signal:
  • the step of stimulating and the step of acquiring are executed using a reference medium;
  • each single harmonic component of the multi-sine frequency signal a respective amplitude is associated; wherein at least a portion of the respective amplitudes is defined in dependence of an attenuation behaviour of the respective single harmonic component.
  • the respective amplitudes of the single harmonic components being subjected to stronger attenuation are increased with respect to the single harmonic components being subjected to lower attenuations.
  • the stimulation signal also comprises a reference signal for synchronizing the stimulating signal with the response signal.
  • the reference signal is a sinusoidal burst.
  • the frequency of the sinusoidal burst is substantially identical to one of the frequencies of the single harmonic components, in particular the frequency of the sinusoidal burst is substantially identical to a fundamental base frequency of the random multi-sine frequency signal.
  • a modified signal resulting from the emission signal progating within the polydisperse medium, is determined and/or measured and the modified signal is transformed so as to obtain the response signal.
  • the modified signal is an echo signal, in particular resulting from the propagation of the emission signal within the polydisperse medium and its reflection at a reflection surface.
  • the polydisperse medium comprises water and at least a detergent and/or macroscopic contaminations, or an edible oil, or a viscous food product, such as a smoothie.
  • a fundamental base frequency of the random multi-sine frequency signal lies within the ultrasound frequency range.
  • the fundamental base frequency ranges between 1 to 100 MHz, in particular between 1 to 50 MHz, even more particular between 1 to 30 MHz.
  • the at least one parameter is an attenuation coefficient of the emission signal and/or a propagation velocity of the emission signal, in particular the attenuation coefficient and the propagation velocity being frequency-dependent.
  • an appliance comprising at least a cavity for containing a polydisperse medium and a monitoring device for monitoring the polydisperse medium; wherein the monitoring device comprises at least an emission probe for emitting an emission signal into the polydisperse medium, a receiving probe for receiving a modified signal, which results, in use, from the emission signal propagation through the polydisperse medium, a signal generator for stimulating the emission probe with a stimulating signal, and an elaboration unit configured to obtain and/or create a response signal from the modified signal and configured to analyse the response signal for obtaining and/or determining at least one parameter characteristic of the polydisperse medium.
  • the signal generator is configured to generate a stimulating signal comprising at least one random multi-sine frequency signal being the sum of a plurality of single harmonic components.
  • the monitoring device is configured such that the stimulation signal also comprises a reference signal for synchronizing the stimulating signal with the response signal.
  • the reference signal is a sinusoidal burst.
  • the frequency of the sinusoidal burst is substantially identical to one of the frequencies of the single harmonic components of the random multi-sine frequency signal, in particular the frequency of the sinusoidal burst is substantially identical to a fundamental base frequency of the random multi-sine frequency signal.
  • the multi-sine frequency signal is generated such that to each single harmonic component of the multi- sine frequency signal a respective amplitude is associated and at least a portion of the respective amplitudes is defined in dependence of an attenuation behaviour of the respective harmonic component within the polydisperse medium.
  • the respective amplitudes of the single harmonic components being subjected to stronger attenuation are increased with respect to the single harmonic components being subjected to lower attenuations within the polydisperse medium.
  • the elaboration unit is configured to analyse the response signal with respect to a reference response signal, in particular being, in use, determined prior to the response signal.
  • the random multi- sine frequency signal is described by the following formula:
  • the monitoring device comprises a reflection surface for reflecting the emission signal back to the emission probe.
  • the monitoring device comprises a reflection element distinct from the cavity and the reflection element comprises the reflection surface.
  • the reflection surface is defined by a portion of the appliance, in particular a portion of the cavity.
  • the appliance is a dishwasher or a frying device or a blender or a mixer or a washing machine.
  • a fundamental base frequency of the random multi-sine frequency signal lies within the ultrasound frequency range.
  • the fundamental base frequency ranges between 1 to 100 MHz, in particular between 1 to 50 MHz, even more particular between 1 to 30 MHz.
  • the at least one parameter is an attenuation coefficient of the emission signal and/or a propagation velocity of the emission signal, the propagation velocity and/or the attenuation coefficient being frequency dependent.
  • FIG. 1 is a schematic illustration of an appliance having a monitoring device for monitoring a polydisperse medium, with parts removed for clarity;
  • FIG. 2a illustrates an example stimulation signal with which a detail of the monitoring device is stimulated, with details removed for clarity;
  • FIG. 2b illustrates an example response signal of the polydisperse medium, with details removed for clarity
  • FIG. 3 illustrates an attenuation coefficient of a signal fed into a first kind of polydisperse medium, with details removed for clarity;
  • FIG. 4 illustrates the progagation speed of a signal fed into a second kind of polydisperse medium, with details removed for clarity.
  • number 1 indicates a portion of an appliance.
  • the appliance comprises a cavity 2 being configured to contain a polydisperse medium and a monitoring device 3 being configured to monitor the polydisperse medium, in particular for obtaining at least one parameter being characteristic of the polydisperse medium.
  • a polydisperse medium is a medium, such as a liquid, comprising more than one phase of which at least one comprises divided phase domains dispersed throughout a continuous phase.
  • the appliance is a dishwasher, in particular of the conveyor-type, for washing dishes and the polydisperse medium is a water solution comprising at least water and detergent and/or (macroscopic) contaminations, such as food residues.
  • a water solution presents different sizes of phase domains dispersed throughout the water such as bubbles, particles and aggregates, droplets, micelles.
  • the appliance could also be a frying device having a cavity for receiving an edible oil, in particular frying oil.
  • the appliance could be a blender having a cavity for receiving solid and/or liquid food products for blending the solid and/or liquid food products so as to obtain a (viscous) pourable food product such as a smoothie.
  • a smoothie being a viscous beverage comprising pureed raw fruit or vegetables blended with ice cream, frozen yogurt, water, crushed ice, fruit juice, sweeteners, dairy products nuts, seeds, tea, chocolate, herbal supplements, or nutritional supplements.
  • appliance within the scope of the present description, with the term appliance we intend to consider any appliance present within both the household and the professional sectors.
  • Example appliances are blenders, frying devices, dishwashers, conveyor-type dishwashers and washing machines.
  • appliance we also consider any kind of white goods such as dishwashers, washing machines and others.
  • monitoring device 3 comprises:
  • a probe 4 for at least emitting an emission signal into the polydisperse medium and, according to the non-limiting embodiment also to receive a modified signal, which results from the propagation of the emission signal within the polydisperse medium;
  • a signal generator 5 in particular (electrically) coupled to probe 4, for stimulating probe 4 with a stimulating signal, in particular an ultrasound stimulating signal s(t), even more particular an electric ultrasound stimulating signal s(t), so that probe 4 generates, in use, the emission signal; and
  • an elaboration unit 6 for transferring the modified signal into a response signal r(t) and for analysing the response signal r(t) for obtaining and/or determining at least one parameter characteristic of the polydisperse medium.
  • probe 4 is a transducer, in particular an ultrasound transducer, configured to transform stimulating signal s(t) into the emission signal, in particular an acoustic (an ultrasound) emission signal.
  • probe 4 is of the immersion-type: i.e. probe 4 is, in use, at least partially in contact (immersed) within the polydisperse medium.
  • An example probe is an ultrasound transducer from Olympus-Panametrics, e.g. of the type V358 (50 MHz) or V354 (20 MHz).
  • single probe 4 defines both an emission probe and a receiving probe.
  • monitoring device 3 comprises an emission probe for emitting the emission signal and a receiving probe for receiving the modified signal.
  • monitoring device 3 could comprise a separate emission probe and a distinct receiving probe.
  • the distinct emission probe and the distinct receiving probe face one another.
  • the modified signal would be a transmission signal.
  • the receiving probe in particular probe 4 is configured to receive the modified signal (originating from the emission signal propagating through the polydisperse medium).
  • monitoring device 3, in particular elaboration unit 6, is configured to convert the modified signal into the response signal r(t), which, preferentially is an electrical response signal r(t).
  • monitoring device 3 further comprises a reflection surface 7 arranged so as to receive at least a portion of the emission signal and being configured to reflect the received portion of the emission signal toward probe 4.
  • reflection surface 7 is distanced from probe 4 and, preferably faces probe 4.
  • reflection surface 7 is in a fixed position so as to define a constant distance between probe 4 and reflection surface 7.
  • reflection surface 7 could be moveable so as to vary the distance.
  • response signal r(t) in particular the modified signal, is based on an echo signal, which results from the emission signal travelling from probe 4 to reflection surface 7 and from reflection surface 7 to probe 4.
  • monitoring device 3 comprises a reflection element 8 having reflection surface 7, in particular reflection element 8 being coupled to a portion of cavity 2.
  • reflection element 8 is distinct from cavity 2.
  • a portion of cavity 2 could define reflection surface 7.
  • the reflection surface 7 is a portion of the appliance, in particular of cavity 2.
  • monitoring device 3 comprises a first amplifier for amplifying stimulation signal s(t) prior to stimulating probe 4.
  • monitoring device 3 also comprises a second amplifier for obtaining an amplified response signal r(t).
  • signal generator 5 is configured to generate the stimulating signal s(t) such to comprise at least one random multi-sine frequency signal si(t).
  • signal generator 5 is configured to generate an electric stimulating signal s(t) and probe 4 is configured to transduce the electric stimulating, in particular into an acoustic wave signal, even more particular into an ultrasound wave signal.
  • random multi-sine frequency signal si(t) is the sum of a plurality of single harmonic components.
  • each single harmonic component is described by a respective sinusoid and is dependent on a respective amplitude A k , a respective frequency f and a respective phase cp k .
  • each frequency of the respective single harmonic components is a multiple of a fundamental base frequency fo.
  • the duration of the random multi-sine frequency signal si(t) is chosen such that it is shorter than the propagation time of the single harmonic component of the emission signal which traverses, in use, the polydisperse medium the fastest. In other words, the duration is chosen such that it is shorter than the propagation distance of the emission signal through the polydisperse medium divided by the maximum propagation velocity.
  • a window function such as a Tucky window or a rectangular window, is applied to the random multi-sine frequency signal si(t) for limiting the duration of the random multi-sine frequency signal si(t).
  • signal generator 5 is configured to synthesize the random multi-sine frequency signal si(t) starting from a defined duration, the fundamental base frequency fo, the number of single harmonic components N of the random multi- sine frequency signal si(t) and a sampling rate of signal generator 5 itself.
  • the amplitudes A k are defined, the phases cp k are randomly chosen, in particular evenly distributed within a phase interval of [0, 2p].
  • the amplitudes A k and the phases cp k are used to define a base multi-sine signal according to the above cited formula. This base multi-sine signal is transformed by means of a reverse Fourier transformation so as to obtain the base multi- sine signal in the time domain.
  • a clipping is applied to this base multi- sine signal in the time domain, in particular the highest peaks are clipped to about 95 % of the maximum value.
  • a window function is applied and the Fourier transformation of the thus obtained signal is performed.
  • This Fourier transformed signal is used to deduce the phases cp k , which are used to generate a new base multi-sine signal in the time domain.
  • the above-mentioned procedure as described after the determination of the amplitudes A k and the phases cp k , is repeated. This is repeated until the respective crest factors (i.e. the ratio of peak values to the effective value; in other words, the crest factor indicates the distribution of the peaks in the signal) do not improve furthermore or in other words no further significant improvement of the crest factor is achieved between successive repetitions.
  • signal generator 5 is configured such to arbitrarily determine the respective amplitudes A k of the single harmonic components.
  • signal generator 5 is configured to determine and/or to define the respective amplitudes A k as a function of the attenuation to which the respective single harmonic component (having the respective frequency kfo) is subjected.
  • each single harmonic component of the random multi sine frequency signal si(t) is subjected to attenuations depending on at least the emission probe (probe 4) and the polydisperse medium. Even more particular, during operation, the stronger the attenuation, the worse becomes the signal-to-noise ratio.
  • the respective amplitudes A k of the single harmonic components being subjected to stronger attenuation are increased with respect to the respective amplitudes A k of the single harmonic components being subjected to lower attenuations within the polydisperse medium.
  • a so-called pre-emphasis is applied to the multi-sine frequency signal.
  • the use of the pre emphasis allows to improve the signal-to-noise ratio over a broader frequency spectrum.
  • the respective amplitudes A k of the single harmonic components are determined with respect to a reference medium, such as e.g. (demineralized) water, or the polydisperse medium itself.
  • a reference medium such as e.g. (demineralized) water, or the polydisperse medium itself.
  • the respective amplitudes A k can be determined and/or defined in dependence of the attenuation of the respective single harmonic component contributable to only probe 4 or only the polydisperse medium, but also considering at least the attenuation due to both probe 4 and the polydisperse medium.
  • signal generator 5 is also configured to generate stimulating signal s(t) to also comprise a reference signal s 2 (t), in particular for synchronizing at least stimulation signal s(t) with the response signal r(t), preferentially also with the emission signal.
  • the multi-sine frequency signal si(t) follows the reference signal s 2 (t) as illustrated in Figure 2a.
  • response signal r(t) comprises a first signal portion n(t) and a second signal portion r 2 (t) being correlated to respectively random multi-sine frequency signal si(t) and reference signal s 2 (t).
  • signal generator 5 is configured such that the reference signal s 2 (t) is a sinusoidal burst, preferentially having a frequency being substantially identical to a multiple of the fundamental base frequency fo, in particular being substantially identical to the fundamental base frequency fo.
  • signal generator 5 is configured to generate stimulating signal s(t) with a fundamental base frequency fo being in the ultrasound regime.
  • fundamental base frequency fo is below 100 MHz, in particular below 50 Hz, even more particular below 30 Hz.
  • the fundamental base frequency fo ranges between 1 to 100 MHz, in particular between 1 to 50 Hz, even more particular between 1 to 30 Hz.
  • elaboration unit 6 is configured to determine, in a manner as will be explained in further detail below, at least the propagation velocity c m (f) of the emission signal within the polydisperse medium and/or at least an attenuation coefficient a m (f) of the emission signal.
  • the attenuation coefficient a m (f) is dependent on the specific physiochemical properties of the polydisperse medium.
  • Figure 3 illustrates the dependency of the frequency- dependent behaviour of the attenuation coefficient a m (f) obtained on different polydisperse mediums being within cavity 2 and comprising water with varying concentrations of standard soil and Ecolab detergent.
  • the polydisperse media used to obtain the behaviour shown in Figure 3 comprise the soil from 0,4 % up to 2,44% in weight and the detergent at a fixed concentration of 0.2% in weight. It is seen that the concentration of the soil within the polydisperse medium has a strong influence on the attenuation coefficient a m (f) illustrating the suitability of the a m (f) for the characterization of the polydisperse medium. In the specific example shown, the increase in the concentration of the soil leads to an increase of the attenuation coefficient a m (f) over a broad frequency range.
  • the propagation velocity c m (f) is dependent on the specific physiochemical properties of the polydisperse medium.
  • the polydisperse medium was frying oil.
  • the appliance was a frying device with its respective cavity 2 being filled with frying oil.
  • the frying oil is subjected to physiochemical changes, which result into changes of the frequency-dependent propagation velocity c m (f).
  • c m (f) the propagation velocity
  • elaboration unit 6 is configured to analyse response signal r(t) with respect to a reference signal r’(t).
  • the method of monitoring the polydisperse medium comprises at least the following steps:
  • one measurement cycle comprises at least the steps of stimulating, acquiring and analysing.
  • the method also comprises at least one step of repetition, preferentially a plurality of steps of repetition.
  • each step of repetition at least the steps of stimulating, acquiring and analysing are repeated.
  • preferentially at least two measurement cycles are executed.
  • substantially one measurement cycle per second is executed.
  • the at least one parameter in particular the propagation velocity c m and/or the attenuation coefficient a m , is/are monitored over time in order to control the polydisperse medium.
  • the polydisperse medium comprises water and detergent and/or macroscopic contaminations it is possible to determine the overall contamination of the polydisperse medium for evaluating whether the polydisperse medium needs to be exchanged.
  • the polydispsere liquid is an edible oil
  • it is possible to control the degradation and/or contamination of the edible oil e.g. allowing to indicate a needed replacement of the edible oil with a fresh edible oil.
  • the stimulation signal s(t) comprises at least the random multi-sine frequency signal si(t).
  • a pre-emphasis is applied to the random multi-sine frequency signal s i (t) .
  • at least a portion of the respective amplitudes A k is defined in dependence of the attenuation behaviour of the respective single harmonic component.
  • the respective amplitudes A k of the single harmonic components which are subjected to stronger attenuations are increased with respect to the single harmonic components which are subjected to lower attenuations.
  • the stimulation signal s(t) also comprises the reference signal s 2 (t), in particular for synchronizing the stimulating signal s(t) with the response signal r(t).
  • the reference signal s 2 (t) is a sinusoidal burst, in particular having a frequency being substantially a multiple of the fundamental base frequency fo, even more particular having a frequency being substantially equal to the fundamental base frequency fo.
  • the fundamental base frequency fo is chosen to be in the ultrasound range, preferably below 100 MHz, even more preferably below 50 MHz, most preferably below 30 MHz.
  • the modified signal is acquired by a receiving probe, in particular probe 4 acting as the receiving probe.
  • the emission signal is acquired.
  • elaboration unit 6 elaborates on the response signal r(t) for obtaining and/or determining the at least one parameter, in particular at least the propagation velocity c m and/or the attenuation coefficient a m of the emission signal propagating within the polydisperse medium.
  • the response signal r(t) is analysed with respect to a reference response signal r’(t), in particular the reference response signal r’(t) being determined prior to the response signal r(t).
  • the complete system comprising monitoring device 3 and the polydisperse medium can be described by a transfer function F(f), with f being the frequency.
  • the transfer function F(f) describes the relationship between the stimulating signal s(t) and the response signal r(t).
  • the transfer function F(f) depends at least on a transfer function X(f) describing the propagation phenomena of the emission signal within the polydisperse medium.
  • the transfer function X(f) is a function of the, in particular frequency-dependent, propagation velocity c m and the, in particular frequency-dependent, attenuation coefficient a m .
  • the transfer function F(f) also depends on the respective transfer functions of the signal generator 5, the elaboration unit 6 and the emitting probe and the receiving probe (i.e. probe 4 acting as an emitting probe and probe 4 acting as a receiving probe).
  • the transfer function X(f) describing the propagation phenomena of the emission signal within the polydisperse medium, in particular for determining and/or obtaining the at least one parameter characteristic for the polydisperse medium.
  • the propagation phenomena, in particular being frequency-dependent, of the emission signal within the polydisperse medium lead to the modified signal.
  • the transfer function X(f) is obtained from the reference response signal r ’ (t) acquired during a first measurement cycle and from the response signal r(t) acquired during a further measurement cycle.
  • the method also comprises a step of obtaining and/or determining the reference response signal r’(t) during which the step of stimulating and the step of acquiring are executed using a reference medium.
  • a reference medium is (demineralized) water.
  • an example reference medium is the edible oil prior to its use, e.g. prior to its heating.
  • the reference response signal r’(t) was obtained previously and is stored within elaboration unit 6.
  • the method also comprises the step of obtaining and/or determining a reference response signal r’(t), during which the step of stimulating and the step of acquiring is executed and during which the propagation distance of the emission signal within the polydisperse medium differs with respect to when executing the step of stimulating and the step of acquiring for obtaining the response signal (r(t)).
  • the distance between reflection surface 7 and probe 4 is varied.
  • the response signal r(t) is obtained and/or determined after obtaining and/or determining the reference response signal r’(t).
  • the stimulation signal s(t) also comprises the reference signal s 2 (t), in particular a sinusoidal burst, even more particular a sinusoidal burst having a frequency being substantially identical to a multiple of the fundamental base frequency f 0 , most preferably having a frequency being substantially identical to the fundamental base frequency fo.
  • the reference signal s 2 (t) it is possible to improve the determination of the propagation time of the emission signal within the polydisperse medium. This allows to synchronize the respective first signal portions ri(t) of the response signal r(t) and the reference response signal r’(t) with one another.
  • the respective second signal portions r 2 (t) of both the response signal r(t) and the reference response signal r’ (t) are determined. This can e.g. be done by applying a threshold algorithm.
  • the obtained cross-correlation result is a function of the group delay.
  • the propagation velocity is a function of the group delay it is possible by determining the group delay by means of the second signal portions s 2 (t), which have a limited band width, to improve the determination of the propagation velocity c m .
  • a stimulating signal s(t) comprising the random multi-sine frequency signal si(t) allows to perform measurements for the control of the polydisperse medium on a fast time scale.
  • the fast measurement time scale allows to neglect any variations in temperature of the polydisperse medium. This also means that it is possible to avoid the need to precisely control the temperature of the polydisperse medium.
  • Another advantage resides in using the pre-emphasis on the random multi- sine frequency signal si(t) allowing to obtain a good signal-to-noise ratio over a broad frequency band.
  • the stimulating signal s(t) comprising a reference signal s 2 (t) allowing to simplify and to improve the determination of the propagation time of the emission signal within the polydisperse medium. This again allows to improve the determination of the propagation velocity c m (f).

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Abstract

There is described a method for monitoring a polydisperse medium within an appliance (1) comprising at least the steps of stimulating an emission probe (4) with a stimulation signal (s(t)) for emitting an emission signal into the polydisperse medium, acquiring a response signal (r(t)), and analysing the response signal (r(t)) for obtaining and/or determining at least one parameter characteristic of the polydisperse medium. The stimulation signal (s(t)) comprises at least one random multi-sine frequency signal (si(t)) being the sum of a plurality of single harmonic components.

Description

METHOD AND DEVICE FOR MONITORING POLYDISPERSE MEDIA
The present invention relates to a method for monitoring polydisperse media within an appliance.
Advantageously, the present invention also relates to an appliance comprising a monitoring device for monitoring polydisperse mediums within appliances.
It is known that a series of varying appliances such as mixers, frying devices, dishwashers, washing machines and other have to treat varying kinds of liquid media, which fall under the definition of polydisperse media. A polydisperse medium is a medium comprising more than one phase of which at least one comprises finley divided phase domains, often in the colloidal size range, dispersed throughout a continuous phase.
A first example of a polydisperse medium is a washing bath having different phases such as air, organic matter, oil, detergent and others having divided phase domains of different sizes dispersed throughout the water such as bubbles, particles and aggregates, droplets, micelles.
A second example are edible oils, such as frying oil. E.g. during operation the frying oil may undertake physiochemical changes due to degradation of the frying oil upon temperature cycling and enrichment of food residue.
A third example are pourable food products such as smoothies, which are viscous beverages typically comprising pureed raw fruit or vegetables blended with ice cream, frozen yogurt, water, crushed ice, fruit juice, sweeteners, dairy products nuts, seeds, tea, chocolate, herbal supplements, or nutritional supplements.
It is a vital interest in the sector to monitor the polydisperse media as used or obtained in appliances in order to determine e.g. the quality of the polydisperse medium.
In general, it is known to investigate on parameters characteristic of a polydisperse medium by means of e.g. acoustic spectroscopy such as ultrasound spectroscopy. Commonly used acoustic spectroscopy approaches rely on continuous wave techniques, tone-burst techniques, and broad band pulse techniques. The continuous wave techniques rely on sinusoidal standing waves emitted into the polydisperse medium, which is arranged within a resonant chamber, which advantageously is provided with movable parts for allowing to operate at varying frequencies so as to obtain the frequency response of the system comprising the polydisperse medium.
The tone-burst techniques are based on the transmission of a burst of few sine periods and measuring the attenuation and the propagation velocity of the wave. By successive repetitions at different frequencies it is possible to obtain the frequency response of the system.
The broad band pulse techniques are based on the emission of a broad band signal and the analysis of the transmitted and the received signal for determining characteristic parameters of the polydisperse medium.
A drawback of all these approaches resides in being time consuming, which typically requires a precise control of the temperature of the polydisperse medium.
E.g. the broad band pulse techniques are known to result in a bad signal-to- noise ratio, in particular for these frequencies, different from the resonance frequency. In order to improve the reliability it is typically needed to perform a series of measurements, which become averaged. This increases the required measurement time.
Aim of the present invention is to provide for a method of monitoring polydisperse mediums within an appliance, to overcome, in a straightforward manner, at least one of the aforementioned drawbacks.
In particular, aim of the present invention is to provide for a method of monitoring polydisperse mediums within an appliance, which enables fast measurement times.
It is a further aim of the present invention to provide for an appliance having a monitoring device, to overcome, in a straightforward manner, at least one of the aforementioned drawbacks.
According to the present invention, there is provided a method and an appliance the independent claims.
Preferred embodiments are claimed in the dependent claims.
In addition, according to the present invention, there is provided a method for monitoring a polydisperse medium within a appliance comprising at least the steps of stimulating an emission probe with an stimulation signal for emitting an emission signal into the polydisperse medium, acquiring a response signal, and analysing the response signal for obtaining and/or determining at least one parameter characteristic of the polydisperse medium. According to the invention the stimulation signal comprises at least one random multi-sine frequency signal being the sum of a plurality of single harmonic components.
According to a preferred non-limiting embodiment, the at least one parameter is monitored over time in order to control the polydisperse medium.
According to a preferred non-limiting embodiment, the method also comprises at least one step of repetition, preferentially a plurality of steps of repetition, and during each step of repetition at least the steps of stimulating, acquiring and analysing are repeated.
According to a preferred non-limiting embodiment, during the step of analysing, the response signal is analysed with respect to a reference response signal.
Preferably but not necessarily, the reference response signal become determined prior to the response signal.
Preferably but not necessarily, the method further comprises the step of obtaining and/or determining the reference response signal:
wherein during the step of obtaining and/or determining, the step of stimulating and the step of acquiring are executed using a reference medium; or
wherein during the step of obtaining and/or determining the step of stimulating and the step of acquiring is executed and during which a propagation distance of the emission signal within the polydisperse medium differs with respect to when executing the step of stimulating and the step of acquiring for obtaining the response signal.
According to a preferred non-limiting embodiment, the random multi- sine frequency signal is described by the following formula: ¾( t) = åfc=1 Ak cos(2 nkf0t + <pfe), wherein si(t) is the random multi-sine frequency signal, fo describes a fundamental base frequency, t represents the time, N indicates the number of harmonic components of the multi-sine frequency signal si(t) and Ak and (pk are respectively the amplitude and the phase of the single harmonic components.
According to a preferred non-limiting embodiment, wherein to each single harmonic component of the multi-sine frequency signal a respective amplitude is associated; wherein at least a portion of the respective amplitudes is defined in dependence of an attenuation behaviour of the respective single harmonic component. Preferably but not necessarily the respective amplitudes of the single harmonic components being subjected to stronger attenuation are increased with respect to the single harmonic components being subjected to lower attenuations.
According to a preferred non-limiting embodiment, the stimulation signal also comprises a reference signal for synchronizing the stimulating signal with the response signal. Preferably but not necessarily, the reference signal is a sinusoidal burst. Even more preferably but not necessarily, the frequency of the sinusoidal burst is substantially identical to one of the frequencies of the single harmonic components, in particular the frequency of the sinusoidal burst is substantially identical to a fundamental base frequency of the random multi-sine frequency signal.
According to a preferred non-limiting embodiment, during the step of acquiring, a modified signal, resulting from the emission signal progating within the polydisperse medium, is determined and/or measured and the modified signal is transformed so as to obtain the response signal. Preferably but not necessarily, the modified signal is an echo signal, in particular resulting from the propagation of the emission signal within the polydisperse medium and its reflection at a reflection surface.
According to a preferred non-limiting embodiment, the polydisperse medium comprises water and at least a detergent and/or macroscopic contaminations, or an edible oil, or a viscous food product, such as a smoothie.
According to a preferred non-limiting embodiment, a fundamental base frequency of the random multi-sine frequency signal lies within the ultrasound frequency range. Preferably but not necessarily, the fundamental base frequency ranges between 1 to 100 MHz, in particular between 1 to 50 MHz, even more particular between 1 to 30 MHz.
According to a preferred non-limiting embodiment, the at least one parameter is an attenuation coefficient of the emission signal and/or a propagation velocity of the emission signal, in particular the attenuation coefficient and the propagation velocity being frequency-dependent.
In addition, according to the present invention, there is provided an appliance comprising at least a cavity for containing a polydisperse medium and a monitoring device for monitoring the polydisperse medium; wherein the monitoring device comprises at least an emission probe for emitting an emission signal into the polydisperse medium, a receiving probe for receiving a modified signal, which results, in use, from the emission signal propagation through the polydisperse medium, a signal generator for stimulating the emission probe with a stimulating signal, and an elaboration unit configured to obtain and/or create a response signal from the modified signal and configured to analyse the response signal for obtaining and/or determining at least one parameter characteristic of the polydisperse medium. According to the invention the signal generator is configured to generate a stimulating signal comprising at least one random multi-sine frequency signal being the sum of a plurality of single harmonic components.
According to a preferred non-limiting embodiment, the monitoring device is configured such that the stimulation signal also comprises a reference signal for synchronizing the stimulating signal with the response signal. Preferably but not necessarily, the reference signal is a sinusoidal burst. Even more preferably but not necessarily, the frequency of the sinusoidal burst is substantially identical to one of the frequencies of the single harmonic components of the random multi-sine frequency signal, in particular the frequency of the sinusoidal burst is substantially identical to a fundamental base frequency of the random multi-sine frequency signal.
According to a preferred non-limiting embodiment, the multi-sine frequency signal is generated such that to each single harmonic component of the multi- sine frequency signal a respective amplitude is associated and at least a portion of the respective amplitudes is defined in dependence of an attenuation behaviour of the respective harmonic component within the polydisperse medium. Preferably but not necessarily, the respective amplitudes of the single harmonic components being subjected to stronger attenuation are increased with respect to the single harmonic components being subjected to lower attenuations within the polydisperse medium.
According to a preferred non-limiting embodiment, the elaboration unit is configured to analyse the response signal with respect to a reference response signal, in particular being, in use, determined prior to the response signal.
According to a preferred non-limiting embodiment, the random multi- sine frequency signal is described by the following formula:
Si (t) = åfc=1 Ak cos(2nkf0t + <pfe), wherein si(t) is the random multi-sine frequency signal, fo describes a fundamental base frequency, t represents the time, N indicates the number of harmonic components of the multi-sine frequency signal si(t) and Ak and (pk are respectively the amplitude and the phase of the single harmonic components.
According to a preferred non-limiting embodiment, the monitoring device comprises a reflection surface for reflecting the emission signal back to the emission probe.
According to a preferred non-limiting embodiment, the monitoring device comprises a reflection element distinct from the cavity and the reflection element comprises the reflection surface.
According to a preferred alternative non-limiting embodiment, the reflection surface is defined by a portion of the appliance, in particular a portion of the cavity.
According to a preferred non-limiting embodiment, the appliance is a dishwasher or a frying device or a blender or a mixer or a washing machine.
According to a preferred non-limiting embodiment, a fundamental base frequency of the random multi-sine frequency signal lies within the ultrasound frequency range. Preferably but not necessarily, the fundamental base frequency ranges between 1 to 100 MHz, in particular between 1 to 50 MHz, even more particular between 1 to 30 MHz.
According to a preferred non-limiting embodiment, the at least one parameter is an attenuation coefficient of the emission signal and/or a propagation velocity of the emission signal, the propagation velocity and/or the attenuation coefficient being frequency dependent.
A non-limiting embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
- Figure 1 is a schematic illustration of an appliance having a monitoring device for monitoring a polydisperse medium, with parts removed for clarity;
- Figure 2a illustrates an example stimulation signal with which a detail of the monitoring device is stimulated, with details removed for clarity;
- Figure 2b illustrates an example response signal of the polydisperse medium, with details removed for clarity;
- Figure 3 illustrates an attenuation coefficient of a signal fed into a first kind of polydisperse medium, with details removed for clarity; and
- Figure 4 illustrates the progagation speed of a signal fed into a second kind of polydisperse medium, with details removed for clarity.
With reference to Figure 1, number 1 indicates a portion of an appliance. In particular, the appliance comprises a cavity 2 being configured to contain a polydisperse medium and a monitoring device 3 being configured to monitor the polydisperse medium, in particular for obtaining at least one parameter being characteristic of the polydisperse medium.
A polydisperse medium is a medium, such as a liquid, comprising more than one phase of which at least one comprises divided phase domains dispersed throughout a continuous phase.
In the specific non- limiting example embodiment of Figure 1 , the appliance is a dishwasher, in particular of the conveyor-type, for washing dishes and the polydisperse medium is a water solution comprising at least water and detergent and/or (macroscopic) contaminations, such as food residues. Such a water solution presents different sizes of phase domains dispersed throughout the water such as bubbles, particles and aggregates, droplets, micelles.
In an alternative non-limiting embodiment, the appliance could also be a frying device having a cavity for receiving an edible oil, in particular frying oil.
In an even other alternative non-limiting embodiment, the appliance could be a blender having a cavity for receiving solid and/or liquid food products for blending the solid and/or liquid food products so as to obtain a (viscous) pourable food product such as a smoothie. A smoothie being a viscous beverage comprising pureed raw fruit or vegetables blended with ice cream, frozen yogurt, water, crushed ice, fruit juice, sweeteners, dairy products nuts, seeds, tea, chocolate, herbal supplements, or nutritional supplements.
Within the scope of the present description, with the term appliance we intend to consider any appliance present within both the household and the professional sectors. Example appliances are blenders, frying devices, dishwashers, conveyor-type dishwashers and washing machines.
Furthermore, with the term appliance we also consider any kind of white goods such as dishwashers, washing machines and others.
In more detail, monitoring device 3 comprises:
- a probe 4 for at least emitting an emission signal into the polydisperse medium and, according to the non-limiting embodiment also to receive a modified signal, which results from the propagation of the emission signal within the polydisperse medium;
- a signal generator 5, in particular (electrically) coupled to probe 4, for stimulating probe 4 with a stimulating signal, in particular an ultrasound stimulating signal s(t), even more particular an electric ultrasound stimulating signal s(t), so that probe 4 generates, in use, the emission signal; and
- an elaboration unit 6 for transferring the modified signal into a response signal r(t) and for analysing the response signal r(t) for obtaining and/or determining at least one parameter characteristic of the polydisperse medium.
In a non-limiting embodiment, probe 4 is a transducer, in particular an ultrasound transducer, configured to transform stimulating signal s(t) into the emission signal, in particular an acoustic (an ultrasound) emission signal.
In a preferred non-limiting embodiment, probe 4 is of the immersion-type: i.e. probe 4 is, in use, at least partially in contact (immersed) within the polydisperse medium. An example probe is an ultrasound transducer from Olympus-Panametrics, e.g. of the type V358 (50 MHz) or V354 (20 MHz).
In the non-limiting embodiment shown in Figure 1 , single probe 4 defines both an emission probe and a receiving probe. In other words, monitoring device 3 comprises an emission probe for emitting the emission signal and a receiving probe for receiving the modified signal.
In an alternative embodiment not shown, monitoring device 3 could comprise a separate emission probe and a distinct receiving probe.
Preferably but not necessarily, the distinct emission probe and the distinct receiving probe face one another. In particular, in such a configuration the modified signal would be a transmission signal.
Preferentially, the receiving probe, in particular probe 4 is configured to receive the modified signal (originating from the emission signal propagating through the polydisperse medium). Preferably, monitoring device 3, in particular elaboration unit 6, is configured to convert the modified signal into the response signal r(t), which, preferentially is an electrical response signal r(t).
In a non-limiting embodiment, monitoring device 3 further comprises a reflection surface 7 arranged so as to receive at least a portion of the emission signal and being configured to reflect the received portion of the emission signal toward probe 4. Preferentially but not necessarily, reflection surface 7 is distanced from probe 4 and, preferably faces probe 4. In the non-limiting example embodiment shown in Figure 1 , reflection surface 7 is in a fixed position so as to define a constant distance between probe 4 and reflection surface 7. In an alternative non-limiting embodiment, reflection surface 7 could be moveable so as to vary the distance.
More specifically, response signal r(t), in particular the modified signal, is based on an echo signal, which results from the emission signal travelling from probe 4 to reflection surface 7 and from reflection surface 7 to probe 4.
In a preferred non-limiting embodiment, monitoring device 3 comprises a reflection element 8 having reflection surface 7, in particular reflection element 8 being coupled to a portion of cavity 2. In other words, reflection element 8 is distinct from cavity 2.
In an alternative preferred non-limiting embodiment, a portion of cavity 2 could define reflection surface 7. Or in other words, the reflection surface 7 is a portion of the appliance, in particular of cavity 2.
In a non- limiting embodiment, monitoring device 3 comprises a first amplifier for amplifying stimulation signal s(t) prior to stimulating probe 4.
In a preferred non-limiting embodiment, monitoring device 3 also comprises a second amplifier for obtaining an amplified response signal r(t).
Advantageously, signal generator 5 is configured to generate the stimulating signal s(t) such to comprise at least one random multi-sine frequency signal si(t).
In more detail, signal generator 5 is configured to generate an electric stimulating signal s(t) and probe 4 is configured to transduce the electric stimulating, in particular into an acoustic wave signal, even more particular into an ultrasound wave signal.
In particular, random multi-sine frequency signal si(t) is the sum of a plurality of single harmonic components.
Even more particular, each single harmonic component is described by a respective sinusoid and is dependent on a respective amplitude Ak, a respective frequency f and a respective phase cpk. Preferentially, each frequency of the respective single harmonic components is a multiple of a fundamental base frequency fo.
Overall, the random multi-sine frequency signal is described by the following formula:
Figure imgf000011_0001
with t representing the time and N indicating the total number of single harmonic components of the multi-sine frequency signal si(t).
In a preferred non-limiting embodiment, the duration of the random multi-sine frequency signal si(t) is chosen such that it is shorter than the propagation time of the single harmonic component of the emission signal which traverses, in use, the polydisperse medium the fastest. In other words, the duration is chosen such that it is shorter than the propagation distance of the emission signal through the polydisperse medium divided by the maximum propagation velocity.
In a preferred non-limiting embodiment, a window function such as a Tucky window or a rectangular window, is applied to the random multi-sine frequency signal si(t) for limiting the duration of the random multi-sine frequency signal si(t).
In a preferred non-limiting embodiment, signal generator 5 is configured to synthesize the random multi-sine frequency signal si(t) starting from a defined duration, the fundamental base frequency fo, the number of single harmonic components N of the random multi- sine frequency signal si(t) and a sampling rate of signal generator 5 itself. Once, the amplitudes Ak are defined, the phases cpk are randomly chosen, in particular evenly distributed within a phase interval of [0, 2p]. The amplitudes Ak and the phases cpk are used to define a base multi-sine signal according to the above cited formula. This base multi-sine signal is transformed by means of a reverse Fourier transformation so as to obtain the base multi- sine signal in the time domain. A clipping is applied to this base multi- sine signal in the time domain, in particular the highest peaks are clipped to about 95 % of the maximum value. Afterwards, a window function is applied and the Fourier transformation of the thus obtained signal is performed. This Fourier transformed signal is used to deduce the phases cpk, which are used to generate a new base multi-sine signal in the time domain. Then again the above-mentioned procedure, as described after the determination of the amplitudes Ak and the phases cpk, is repeated. This is repeated until the respective crest factors (i.e. the ratio of peak values to the effective value; in other words, the crest factor indicates the distribution of the peaks in the signal) do not improve furthermore or in other words no further significant improvement of the crest factor is achieved between successive repetitions.
In a non-limiting embodiment, signal generator 5 is configured such to arbitrarily determine the respective amplitudes Ak of the single harmonic components. In a preferred non-limiting embodiment, signal generator 5 is configured to determine and/or to define the respective amplitudes Ak as a function of the attenuation to which the respective single harmonic component (having the respective frequency kfo) is subjected. In particular, each single harmonic component of the random multi sine frequency signal si(t) is subjected to attenuations depending on at least the emission probe (probe 4) and the polydisperse medium. Even more particular, during operation, the stronger the attenuation, the worse becomes the signal-to-noise ratio.
In particular, the applicant has observed that these harmonic frequencies being farther distant from the fundamental base frequency fo are subjected to stronger attenuations than the ones being closer to the fundamental base frequency fo. This influences the effective frequency range, which is useable during the measurements.
Preferentially though not necessarily, the respective amplitudes Akof the single harmonic components being subjected to stronger attenuation are increased with respect to the respective amplitudes Ak of the single harmonic components being subjected to lower attenuations within the polydisperse medium. In other words, a so- called pre-emphasis is applied to the multi-sine frequency signal. The use of the pre emphasis allows to improve the signal-to-noise ratio over a broader frequency spectrum.
In a preferred non- limiting embodiment, the respective amplitudes Ak of the single harmonic components are determined with respect to a reference medium, such as e.g. (demineralized) water, or the polydisperse medium itself.
It should be mentioned that the respective amplitudes Ak can be determined and/or defined in dependence of the attenuation of the respective single harmonic component contributable to only probe 4 or only the polydisperse medium, but also considering at least the attenuation due to both probe 4 and the polydisperse medium.
In a preferred non-limiting embodiment, signal generator 5 is also configured to generate stimulating signal s(t) to also comprise a reference signal s2(t), in particular for synchronizing at least stimulation signal s(t) with the response signal r(t), preferentially also with the emission signal.
In a preferred non-limiting embodiment, the multi-sine frequency signal si(t) follows the reference signal s2(t) as illustrated in Figure 2a.
With particular reference to Figure 2b, response signal r(t) comprises a first signal portion n(t) and a second signal portion r2(t) being correlated to respectively random multi-sine frequency signal si(t) and reference signal s2(t).
More specifically, signal generator 5 is configured such that the reference signal s2(t) is a sinusoidal burst, preferentially having a frequency being substantially identical to a multiple of the fundamental base frequency fo, in particular being substantially identical to the fundamental base frequency fo.
In particular, by providing for the reference signal s2(t) it is possible to improve, in a manner as will be explained further below, the determination of a propagation velocity cm(f) of the emission signal within the polydisperse medium.
Preferentially, signal generator 5 is configured to generate stimulating signal s(t) with a fundamental base frequency fo being in the ultrasound regime. Preferentially, fundamental base frequency fo is below 100 MHz, in particular below 50 Hz, even more particular below 30 Hz. Even more preferentially, the fundamental base frequency fo ranges between 1 to 100 MHz, in particular between 1 to 50 Hz, even more particular between 1 to 30 Hz.
In a preferred non-limiting embodiment, elaboration unit 6 is configured to determine, in a manner as will be explained in further detail below, at least the propagation velocity cm(f) of the emission signal within the polydisperse medium and/or at least an attenuation coefficient am(f) of the emission signal.
With particular reference to Figure 3, the attenuation coefficient am(f) is dependent on the specific physiochemical properties of the polydisperse medium.
More specifically, Figure 3 illustrates the dependency of the frequency- dependent behaviour of the attenuation coefficient am(f) obtained on different polydisperse mediums being within cavity 2 and comprising water with varying concentrations of standard soil and Ecolab detergent.
More particular, the polydisperse media used to obtain the behaviour shown in Figure 3 comprise the soil from 0,4 % up to 2,44% in weight and the detergent at a fixed concentration of 0.2% in weight. It is seen that the concentration of the soil within the polydisperse medium has a strong influence on the attenuation coefficient am(f) illustrating the suitability of the am(f) for the characterization of the polydisperse medium. In the specific example shown, the increase in the concentration of the soil leads to an increase of the attenuation coefficient am(f) over a broad frequency range.
With respect to Figure 4, the propagation velocity cm(f) is dependent on the specific physiochemical properties of the polydisperse medium.
In the specific case of Figure 4, the polydisperse medium was frying oil. In the specific case, the appliance was a frying device with its respective cavity 2 being filled with frying oil. During the operation of the frying device the frying oil is subjected to physiochemical changes, which result into changes of the frequency-dependent propagation velocity cm(f). In particular, with increasing exposure of the frying oil to high temperatures, there is an overall reduction of the propagation velocity cm(f), which in particular is true over a broad frequency range.
In particular, by monitoring the propagation velocity cm(f) and/or at least the attenuation coefficient am(f) it is possible to monitor the physiochemical properties of the polydisperse medium.
In a preferred non-limiting embodiment, elaboration unit 6 is configured to analyse response signal r(t) with respect to a reference signal r’(t).
In use, the method of monitoring the polydisperse medium comprises at least the following steps:
- stimulating probe 4 with stimulation signal s(t) for emitting the emission signal into the polydisperse medium;
- acquiring the response signal r(t), in particular being executed after the step of stimulating; and
- analysing the response signal r(t) for obtaining and/or determining at least one parameter characteristic, preferentially the propagation velocity cm and/or the attenuation coefficient am of the polydisperse medium, in particular being executed after and/or during the step of acquiring.
In other words, one measurement cycle comprises at least the steps of stimulating, acquiring and analysing. Preferentially, the method also comprises at least one step of repetition, preferentially a plurality of steps of repetition. During each step of repetition at least the steps of stimulating, acquiring and analysing are repeated. In this manner it is possible to obtain information about the time evolution of the at least one parameter, preferentially the propagation velocity cm and/or the attenuation coefficient am. In other words, preferentially at least two measurement cycles are executed.
In a preferred non-limiting embodiment, substantially one measurement cycle per second is executed.
In a preferred non-limiting embodiment, the at least one parameter, in particular the propagation velocity cm and/or the attenuation coefficient am, is/are monitored over time in order to control the polydisperse medium. E.g. in the example embodiment shown in Figure 1 , in which the polydisperse medium comprises water and detergent and/or macroscopic contaminations it is possible to determine the overall contamination of the polydisperse medium for evaluating whether the polydisperse medium needs to be exchanged. In an alternative example of when the polydispsere liquid is an edible oil, it is possible to control the degradation and/or contamination of the edible oil, e.g. allowing to indicate a needed replacement of the edible oil with a fresh edible oil.
In more detail, during the step of stimulating the stimulation signal s(t) comprises at least the random multi-sine frequency signal si(t).
Preferentially, a pre-emphasis is applied to the random multi-sine frequency signal s i (t) . In particular, at least a portion of the respective amplitudes Ak is defined in dependence of the attenuation behaviour of the respective single harmonic component. Even more particular, the respective amplitudes Ak of the single harmonic components which are subjected to stronger attenuations are increased with respect to the single harmonic components which are subjected to lower attenuations.
Preferentially, in alternative or additionally, the stimulation signal s(t) also comprises the reference signal s2(t), in particular for synchronizing the stimulating signal s(t) with the response signal r(t). Preferentially but not necessarily, the reference signal s2(t) is a sinusoidal burst, in particular having a frequency being substantially a multiple of the fundamental base frequency fo, even more particular having a frequency being substantially equal to the fundamental base frequency fo.
In a preferred non-limiting embodiment, the fundamental base frequency fo is chosen to be in the ultrasound range, preferably below 100 MHz, even more preferably below 50 MHz, most preferably below 30 MHz.
In more detail, during the step of acquiring the modified signal is acquired by a receiving probe, in particular probe 4 acting as the receiving probe.
In a preferred non-limiting embodiment during the step of acquiring also the emission signal is acquired.
In more detail, during the step of analysing, elaboration unit 6 elaborates on the response signal r(t) for obtaining and/or determining the at least one parameter, in particular at least the propagation velocity cm and/or the attenuation coefficient am of the emission signal propagating within the polydisperse medium.
In a preferred non-limiting embodiment, the response signal r(t) is analysed with respect to a reference response signal r’(t), in particular the reference response signal r’(t) being determined prior to the response signal r(t).
It should be considered that the complete system comprising monitoring device 3 and the polydisperse medium can be described by a transfer function F(f), with f being the frequency. The transfer function F(f) describes the relationship between the stimulating signal s(t) and the response signal r(t). The transfer function F(f) depends at least on a transfer function X(f) describing the propagation phenomena of the emission signal within the polydisperse medium. In particular, the transfer function X(f) is a function of the, in particular frequency-dependent, propagation velocity cm and the, in particular frequency-dependent, attenuation coefficient am. In particular, the transfer function F(f) also depends on the respective transfer functions of the signal generator 5, the elaboration unit 6 and the emitting probe and the receiving probe (i.e. probe 4 acting as an emitting probe and probe 4 acting as a receiving probe).
In particular, in order to monitor the polydisperse medium, it is desired to determine the transfer function X(f) describing the propagation phenomena of the emission signal within the polydisperse medium, in particular for determining and/or obtaining the at least one parameter characteristic for the polydisperse medium. The propagation phenomena, in particular being frequency-dependent, of the emission signal within the polydisperse medium lead to the modified signal.
In a preferred-non limiting embodiment, the transfer function X(f) is obtained from the reference response signal r’(t) acquired during a first measurement cycle and from the response signal r(t) acquired during a further measurement cycle. In particular, the response signal r(t) and the reference response signal r’(t) are transferred into the frequency domain, in particular by means of a Fourier transformation, in order to determine the transfer function X(f) = r(f) / r’(f), with r(f) and r’(f) being respectively the response signal r(t) and the reference response signal r’ (t) transformed into the frequency domain.
In the non-limiting example embodiment shown, the method also comprises a step of obtaining and/or determining the reference response signal r’(t) during which the step of stimulating and the step of acquiring are executed using a reference medium. In the specific case of the polydisperse medium comprising water and detergent and/or macroscopic contaminations an example of a reference medium is (demineralized) water.
In the specific case of the polydisperse medium being an edible oil, an example reference medium is the edible oil prior to its use, e.g. prior to its heating.
In an alternative non-limiting embodiment, the reference response signal r’(t) was obtained previously and is stored within elaboration unit 6.
In an alternative non-limiting embodiment, the method also comprises the step of obtaining and/or determining a reference response signal r’(t), during which the step of stimulating and the step of acquiring is executed and during which the propagation distance of the emission signal within the polydisperse medium differs with respect to when executing the step of stimulating and the step of acquiring for obtaining the response signal (r(t)). In particular, between a first step of stimulating and a first step of acquiring and a second step of stimulating and a second step of acquiring, the distance between reflection surface 7 and probe 4 is varied. In a preferred non-limiting embodiment, the response signal r(t) is obtained and/or determined after obtaining and/or determining the reference response signal r’(t).
In a preferred non-limited embodiment, the stimulation signal s(t) also comprises the reference signal s2(t), in particular a sinusoidal burst, even more particular a sinusoidal burst having a frequency being substantially identical to a multiple of the fundamental base frequency f0, most preferably having a frequency being substantially identical to the fundamental base frequency fo.
In particular, by providing for the reference signal s2(t) it is possible to improve the determination of the propagation time of the emission signal within the polydisperse medium. This allows to synchronize the respective first signal portions ri(t) of the response signal r(t) and the reference response signal r’(t) with one another.
Even more particular, by providing for the reference signal s2(t) it is possible to determine the phase delay of the response signal r(t) and the reference response signal r’(t) with one another.
More specifically, in order to determine a group delay of the response signal r(t) and the reference response signal r’(t), in a first step the respective second signal portions r2(t) of both the response signal r(t) and the reference response signal r’ (t) are determined. This can e.g. be done by applying a threshold algorithm.
Then a cross-correlation between the respective second portions r2(t) is executed. The obtained cross-correlation result is a function of the group delay.
As the propagation velocity is a function of the group delay it is possible by determining the group delay by means of the second signal portions s2(t), which have a limited band width, to improve the determination of the propagation velocity cm.
The advantages of the method and the appliance according to the present invention will be clear from the foregoing description.
In particular, by providing for a stimulating signal s(t) comprising the random multi-sine frequency signal si(t) allows to perform measurements for the control of the polydisperse medium on a fast time scale. The fast measurement time scale allows to neglect any variations in temperature of the polydisperse medium. This also means that it is possible to avoid the need to precisely control the temperature of the polydisperse medium. Another advantage resides in using the pre-emphasis on the random multi- sine frequency signal si(t) allowing to obtain a good signal-to-noise ratio over a broad frequency band.
An even other advantage resides in the stimulating signal s(t) comprising a reference signal s2(t) allowing to simplify and to improve the determination of the propagation time of the emission signal within the polydisperse medium. This again allows to improve the determination of the propagation velocity cm(f).
Clearly, changes may be made to the method and the appliance without, however, departing from the scope of the present invention.

Claims

1.- Method for monitoring a polydisperse medium within an appliance (1) comprising at least the steps of:
- stimulating an emission probe (4) with an stimulation signal (s(t)) for emitting an emission signal into the polydisperse medium;
- acquiring a response signal (r(t)); and
- analysing the response signal (r(t)) for obtaining and/or determining at least one parameter characteristic of the polydisperse medium;
wherein the stimulation signal (s(t)) comprises at least one random multi-sine frequency signal (si(t)) being the sum of a plurality of single harmonic components.
2.- Method according to claim 1, wherein during the step of analysing the response signal (r(t)) is analysed with respect to a reference response signal (r’(t)), in particular being determined prior to the response signal (r(t)).
3.- Method according to claim 2, further comprising the step of obtaining and/or determining the reference response signal (r’(t));
wherein during the step of obtaining and/or determining, the step of stimulating and the step of acquiring are executed using a reference medium; and/or
wherein during the step of obtaining and/or determining the step of stimulating and the step of acquiring is executed and during which a propagation distance of the emission signal within the polydisperse medium differs with respect to when executing the step of stimulating and the step of acquiring for obtaining the response signal (r(t)).
4.- The method according to any one of the preceding claims, wherein the random multi-sine frequency signal (si(t)) is described by the following formula:
Figure imgf000021_0001
wherein si(t) is the random multi-sine frequency signal, fo describes a fundamental base frequency, t represents the time, N indicates the number of harmonic components of the multi-sine frequency signal si(t) and Ak and (pk are respectively the amplitude and the phase of the single harmonic components.
5.- The method according to any one of the preceding claims, wherein to each single harmonic component of the multi-sine frequency signal (si(t)) a respective amplitude (Ak) is associated; wherein at least a portion of the respective amplitudes (Ak) is defined in dependence of an attenuation behaviour of the respective single harmonic component.
6.- The method according to claim 5, wherein the respective amplitudes (Ak) of the single harmonic components being subjected to stronger attenuation are increased with respect to the single harmonic components being subjected to lower attenuations.
7.- The method according to any one of the preceding claims, wherein the stimulation signal (s(t)) also comprises a reference signal (s2(t)) for synchronizing the stimulating signal (s(t)) with the response signal (r(t)).
8.- The method according to claim 7, wherein the reference signal (s2(t)) is a sinusoidal burst.
9.- The method according to claim 8, wherein the frequency of the sinusoidal burst is substantially identical to one of the frequencies of the single harmonic components, in particular the frequency of the sinusoidal burst is substantially identical to a fundamental base frequency (f0) of the random multi-sine frequency signal (si(t)).
10.- The method according to any one of the preceding claims, wherein during the step of acquiring, an echo signal is determined and/or measured and the echo signal becomes transformed so as to obtain the response signal (r(t)).
11.- The method according to any one of the preceding claims, wherein the polydisperse medium comprises:
- water and at least a detergent and/or macroscopic contaminations;
- an edible oil; or
- a viscous food product.
12.- The method according to any one of the preceding claims, wherein a fundamental base frequency (fo) of the random multi-sine frequency signal (si(t)) lies within the ultrasound frequency band.
13.- The method according to any one of the preceding claims, wherein the at least one parameter is an attenuation coefficient (am) of the emission signal and/or a propagation velocity (cm) of the emission signal.
14.- An appliance (1) comprising at least a cavity for containing a poly disperse medium and a monitoring device for monitoring the poly disperse medium;
wherein the monitoring device comprises at least:
- an emission probe (4) for emitting an emission signal into the polydisperse medium;
- a signal generator (5) for stimulating the emission probe (4) with a stimulating signal (s(t));
- a receiving probe (4) for receiving a modified signal resulting from, in use, from the propagation of the emission signal within the polydisperse medium; and
- an elaboration unit (6) configured to obtain and/or create a response signal (r(t)) from the modified signal and being configured to analyse the response signal (r(t)) for obtaining and/or determining at least one parameter characteristic of the polydisperse medium;
wherein the signal generator (5) is configured to generate a stimulating signal
(s(t)) comprising at least one random multi-sine frequency signal (si(t)) being the sum of a plurality of single harmonic components.
15.- Appliance according to claim 14, wherein the monitoring device (3)) is configured such that:
- the stimulating signal (s(t)) also comprises a reference signal (s2(t)) for synchronizing the stimulating signal (s(t)) with the response signal (r(t)); and/or
- the multi-sine frequency signal (si(t)) is generated such that to each single harmonic component of the multi-sine frequency signal (si(t)) a respective amplitude (Ak) is associated and at least a portion of the respective amplitudes (Ak) is defined in dependence of an attenuation behaviour of the respective single harmonic component within the polydisperse medium.
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