Ultrasound-based plant monitoring system

Abstract

45 ABSTRACT: 5 The invention provides a system (1) for monitoring a physical parameter of a tubular structure (15), wherein the system comprises a measurement device (100) and a control system (300), wherein the measurement device (100) comprises fastening means (105), a transmitter (120), a sensor (130), and a bellows (140), wherein the bellows (140) are configured physically coupled to one or more of the transmitter (120) and the sensor (130), and wherein 10 the fastening means (105) is configured to attach the measurement device (100) to the tubular structure such that the bellows (140) are configured to provide a pressure to the tubular structure (15) , wherein the control system (300) is configured to execute an operational mode, wherein in the operational mode: (A) the transmitter (120) is configured to provide acoustic excitation radiation (121) to the tubular structure (15), wherein the acoustic excitation radiation (121) has 15 a frequency selected from the range of 1-500 kHz; (B) the sensor (130) is configured to detect acoustic emission radiation (131) from the tubular structure (15), and to provide a related sensor signal to the control system (300); and (C) the control system (300) is configured to determine the physical parameter based on the sensor signal. 20

Description

FIELD OF THEINVENTION The invention relates to a system for monitoring a physical parameter of a tubular structure. The invention further relates to amethod for monitoring a physical parameter of a tubular structure. BACKGROUND OF THEINVENTION Plant monitoring systems are known in the art. For instance, W02020039434Al describes a system for monitoring plants, the system comprising: one or more sound collectors congured to receive and generate signals based on sounds that plants make; and a computer system congured to receive and process the signals to provide a prole of a plant producing the sounds. SUMMARYOF THEINVENTION Water and nutrient transport in plants has attracted much attention in the last decades. In vascular plants, water and nutrient transport is handled by the vascular tissue. In particular, water transportmay primarily be handled by xylem vessels, and nutrients produced from photosynthesis may primarily be transported by phloem vessels. Obtaining a better understanding of plant physiology as a function of age, genetic and environmental parameters is useful for growing and breeding crops, fruits, owers and trees. In particular, xylem vessels are considered the life-supporting conduits for water and ionic nutrients in plants, and xylem dimensions may be indicative ofwater carrying capacity and stress resilience. Ifgrowers can measure in-plant parameters such as the xylem dimensions, plant transpiration, water ow and water content, this can be used to optimize growth conditions inside a greenhouse and / or to select suitable plants for further cultivation, both of which may allow a grower to improve yield. However, prior art techniques for determining a plant's vascular anatomy, such as optical microscopy and electron microscopy, may generally be destructive and time consuming. For example, current techniques may obtain plant parameters using (i) optical microscopy, (ii) latex paint-infusion coupled to optical microscopy, (iii) scanning electron microscopy, and (iv) uniaxial tensile loading. For all these techniques, the plant may generally need to be cut into pieces to obtain data. Prior art methods may, among others, be wasteful as the plants may (at least partially) be damaged or even destroyed, such that their vascular tissue cannot be studied as a function oftime. The prior art may further describe methods involving detecting ultrasound signals generated within a plant. However, the generation of such radiation may be dependent on substantial drought stress, which may limit the applicability to the monitoring and analyzing ofplants under desirable cultivation conditions. The prior art may further include methods involving providing sound waves, such as ultrasound waves, to a plant. These methods may be non-invasive and thus avoid plant damage, but may yet suffer from challenges in terms of repeatability of the measurements, signal-to-noise ratios, and detection of signals specically coming from the plant, instead of, for instance, detecting ultrasound radiation that traveled around the plant. In particular, the prior artmay be destructive, may be hampered by noise, and / or may have reproducibility issues. Hence, it is desired to provide a more robust system for measuring above described characteristics in plants, achieving higher repeatability of measurement, and therewith improving the measurement reliability. Hence, it is an aspect of the invention to provide an alternative monitoring system, which preferably further at least partly obviates one or more of above-described drawbacks. The present invention may have as object to overcome or ameliorate at least one of the disadvantages ofthe prior art, or to provide a useful alternative. According to a first aspect, the invention may provide a system for monitoring a physical parameter of a tubular structure, such as of a plant stem. The system may comprise a measurement device and a control system. In embodiments, the measurement device may comprise fastening means, a transmitter, a sensor, and a bellows. The bellows may, in embodiments, be congured physically coupled to one or more of the transmitter and the sensor. Further, in embodiments, the fastening means may be congured to attach the measurement device to the tubular structure. The fastening means may especially do so such that the bellows is congured to provide a pressure to (or receive a compression pressure from) the tubular structure. Furthermore, in embodiments, the control system may be congured to execute an operational mode. In embodiments, in the operational mode the transmitter may be congured to provide acoustic excitation radiation to the tubular structure. The acoustic excitation radiation may especially have a frequency selected from the range of 1-500 kHz. Moreover, in embodiments, in the operational mode the sensor may be congured to detect acoustic emission radiation from the tubular structure. Additionally, in such embodiments, the sensor may be congured to provide a related sensor signal to the control system. Yet further, in embodiments, in the operational mode the control system may be congured to determine the physical parameter based on the sensor signal. Hence, in specic embodiments, the invention may provide a system for monitoring a physical parameter of a tubular structure, wherein the system comprises a measurement device and a control system, wherein the measurement device comprises fastening means, a transmitter, a sensor, and a bellows, wherein the bellows are congured physically coupled to one or more of the transmitter and the sensor, and Wherein the fastening means is congured to attach the measurement device to the tubular structure such that the bellows are congured to provide a pressure to the tubular structure, Wherein the control system is congured to execute an operational mode, Wherein in the operational mode: (A) the transmitter is congured to provide acoustic excitation radiation to the tubular structure, Wherein the acoustic excitation radiation has a frequency selected from the range of 1-500 kHz, (B) the sensor is congured to detect acoustic emission radiation from the tubular structure, and to provide a related sensor signal to the control system, and (C) the control system is congured to determine the physical parameter based on the sensor signal. With such a system a physical vessel parameter, e.g. of a vascular tissue, may be obtained quickly, accurately, and non-invasively. Especially, the system may successfully measure changes in plant transpiration, water ow and water content in a repeatable manner, without being invasive to the plant. Hence, the physical vessel parameter of a plant stem may be obtained withoutdamaging the plant. Additionally, the systemmay preventmovement along the stem during operation, therewith reducing the occurrence of, or even preventing the occurrence ofjumps in the data. Furthermore, the system may be conveniently assembled from readily available components. Yet further, the herein described system may facilitate obtaining measurements with a high signal-to-noise ratio and with consistent measurement results, i.e., with reproducible measurements. The invention may thus provide a system for monitoring a physical parameter ofa tubular structure. The term tubular structure may refer to essentially any structure having a tubular, cylindrical and / or elongated shape. Especially, in embodiments, the tubular structure may have a length (L) and an (tubular structure) equivalent circular diameter (Ds) (dened in a cross-sectional plane perpendicular to the length (L)), wherein LEDs, such as LZ2*Ds, like L23 >Ds, especially L25>Ds. The equivalent circular diameter (or ECD) (or circular equivalent diameter) of an (irregularly shaped) two-dimensional shape is the diameter of a circle of equivalent area. For instance, the equivalent circular diameterofa squarewith side a is 2*a*SQRT(1 / 7t). For a circle, the diameter is the same as the equivalent circular diameter. Would a circle in an xy-plane with a diameterD be distorted to any other shape (in the xy-plane), without changing the area size, then the equivalent circular diameter ofthat shape would be D. Furthermore, the tubular structuremay have an axis ofelongation (As). Theterm axis of elongation may especially be dened as an imaginary line that denes the direction along which the tubular structure elongates or extends through the system. Yet further, the tubular structure may have a cross-sectional shape dened in a cross-sectional plane perpendicular to the length (L). In embodiments, the cross-sectional shape of the tubular structure may approximate a shape selected from the group comprising: a circle, an oval, a triangle, a rectangle (such as a square), and a polygon. The term approximate and its conjugations herein, such as in to approximate a shape, may refer to being nearly identical to, especially identical to, the following term, for example nearly identical to a circular or an oval shape. For example, a tubular structure may dene a cylindrical sector but for a defect. In particular, an object approximating a first shape may herein refer to: a first shape realization encompassing the object, wherein the first shape realization is dened as the smallest encompassing shape of the (2D or 3D, respectively) object wherein the first shape realization has the shape ofthe rst shape, Wherein a ratio ofthe area (volume) ofthe rst shape realization to the area (volume) of the object may be < 1.2, especially < 1.1, such as <1.05, especially <1.02. For instance, a cross-sectional shape ofthe tubular structure may approximate a circular shape, wherein the first shape realization may be dened as the smallest encompassing circular shape of the cross-sectional shape, wherein a ratio of the area of the rst shape realization to the area of the cross-sectional shape is < 1.2, especially, especially < 1.1, such as <1.05, especially <1.02, including 1. Further, ifthe dimensions ofthe rst shape are dened, the term approximate may refer to the object and the rst shape being superimposable (in 2D or 3D, respectively) such that an intersection between the object and the rst shape covers at leastn% of the object and at least n% of the shape, wherein n is at least 90%, such as at least 95%, especially at least 98%, such as at least 99%, including 100%. For example, in embodiments, the tubular structure may comprise one of a plant (stem), a tube, a pipe, a cable, a ligament of a human or animal, etc.. In specic embodiments, the tubular structure may comprise a plant stem. In such embodiments, the physical parametermay comprise a physical plant parameter, especially a physical vessel parameter. Hence, in particular, the inventionmay provide a non-destructive system for monitoring a physical parameter of a plant stem. Therefore, the invention will herein, for explanatory purposes, primarily be described in the context ofembodiments related to the monitoring ofplant (stem) parameters. It will be clear to the person skilled in the art that the invention is not limited to such embodiments, and that the invention may further apply to the determination ofparameters ofother types oftubular structures. In embodiments, the system may e.g. be congured for monitoring (in a plant) one or more of: a (stem) density, a (stem) water content, a (stem) water ow, a (plant) perspiration, a (stem) Youngs modulus, a (stem) diameter, a (xylem or phloem) vessel radius, a (xylem or phloem) vessel length, a (xylem or phloem) vessel elasticity, and a (xylem or phloem) wall thickness, i.e., in embodiments the physical parametermay comprise one or more of a (stem) density, a (stem) water content, a (stem) water ow, a (plant) perspiration, a (stem) Youngs modulus, a (stem) diameter, a (xylem or phloem) vessel radius, a (xylem or phloem) vessel length, a (xylem or phloem) vessel elasticity, and a (xylem or phloem) wall thickness. In embodiments, the physical parametermay thus comprise a stem parameter, such as e.g. one or more of a density, a water content, a water ow, a Youngs modulus, and a diameter. Additionally or alternatively, in embodiments, the physical parameter may comprise a plant parameter, such as e.g. one or more of a water content, a water ow, and a perspiration. Yet additionally or altematively, in embodiments, the physical parameter may comprise a xylem parameter, such as e.g. one or more ofa vessel radius, a vessel length, a vessel elasticity, and a wall thickness. Yet additionally or alternatively, in embodiments, the physical parametermay comprise a phloem parameter, a (xylem or phloem) vessel radius, a (xylem or phloem) vessel length, a (xylem or phloem) vessel elasticity, and a (xylem or phloem) wall thickness. Theterm physical parameter may herein especially referto aparameter related to a length, an area, a volume, a thickness, a viscosity and an elasticity. The term physical parameter may also refer to a plurality of(different) physical parameters. In embodiments, the physical parameter may be a geometrical parameter. In embodiments, the plant may especially comprise a vascular plant. The term vascular plant may herein refer to any plant that has vascular tissue. Further, the term vascular plant may herein refer to any plant from the Clade Tracheophytes. Vascular tissue may be a (specialized) tissue for distributing resources through the vascular plant. Vascular tissue may generally be subdivided into the xylem and phloem, which may be closely associated and may often be arranged directly adjacent to one another in a vascular plant, especially in a vascular bundle. In embodiments, the vascular tissue may especially be the xylem. In further embodiments, the vascular tissue may especially be the phloem. Hence, in embodiments, the invention may provide a system for monitoring a physical parameter of a tubular structure, such as of a plant (stem). The system may therefore comprise a measurement device and a control system. Here below, embodiments of the different elements ofthe system will be described in further detail. In embodiments, the measurement device may be congured to provide and receive acoustic radiation (see also further below) to and from the tubular structure. Therefore, in embodiments, the measurement device may comprise a fastening means, a transmitter, a sensor, and a bellows. The fastening means may, in embodiments, be congured to fasten (or attach) the measurement device to a tubular structure. Therefore, in embodiments, the fastening means may comprise one or more of a clamp or clip, a hook, a band or buckle, a string or cord, a magnet, etc... Especially, in embodiments, the fastening means may comprise a clamp or clip congured to clamp the measurement device onto the tubular structure. In such embodiments, the clamp or clip may optionally comprise a magnet congured to further secure the measurement device onto (or around) the tubular structure. The fasteningmeansmay especially be congured to attach the measurement device to the tubular structure such that the bellows (see also further below) are congured to provide a pressure to (or receive a compression pressure from) the tubular structure. Further, in embodiments, the system may comprise a hosting arrangement. The hosting arrangement may for example comprise a housing for at least part of the system. In embodiments, the hosting arrangement may comprise at least part ofthe measurement device. Especially, the hosting arrangement may comprise at least part of the transmitter, the sensor, and the bellows. In embodiments, the fastening means may be comprised by the hosting arrangement. In other words, in embodiments, the hosting arrangement may comprise the fastening means. The hosting arrangement may, in embodiments, be congured to dene a hosting space. In embodiments, the hosting space may be congured for hosting the tubular structure. Hence, in embodiments, the system furthercomprises a hosting arrangement, wherein the hosting arrangement comprises at least part ofthe transmitter, the sensor and the bellows, wherein the hosting arrangement is congured to dene a hosting space for hosting the tubular structure. Such embodiments may be benecial as the hosting arrangement may enable conguration ofthe system in a compact and portable way. As such, the system may be applied for monitoring a physical parameter through the application of a compact and simple device. In embodiments, the hosting space may comprise a cylindrical hosting space. For example, in embodiments, the hosting space may comprise a 3D shape approximating one of a right circular cylinder, an oblique cylinder, a elliptic cylinder, a at topped cone, a at topped pyramid, and a frustum. Especially, the hosting space may have a shape approximating a (tubular section of) the tubular structure. The hosting arrangement may especially be congured to surround the tubular structure over at least 25%, such as at least 40%, like at least 50%, especially at least 60% of a circumference of the tubular structure. Especially, in embodiments, the hosting arrangement may be congured to surround the tubular structure over at least 70%, such as at least 80%, especially at least 90%, more especially at least 95%, including essentially 100% ofthe circumference ofthe tubular structure. Furthermore, in embodiments, the hosting arrangement may comprise a sound- absorbing material congured for physically contacting the tubular structure. As such, in embodiments, the sound-absorbing material may be congured to dene the hosting space for hosting the tubular structure. Furthermore, in embodiments, the sound-absorbing material may be congured to dene an enclosed spacewhen in contact with the tubular structure. Hence, in embodiments where the hosting arrangement is congured in physical contact with the tubular structure, the sound-absorbing material (and the tubular structure) may be congured to (together) provide an enclosed space. In such embodiments, at least part ofthe tubular structure may be arranged in the enclosed space (or may face the enclosed space). Additionally, in embodiments, at least part of the transmitter, the sensor, and the bellows may be arranged in the enclosed space. Especially, in embodiments, the transmitter, the sensor, and the bellows may be essentially fully arranged in the enclosed space (created by the sound-absorbing material of the hosting arrangement and the tubular structure). Hence, in embodiments, the hosting arrangement comprises a sound-absorbing material congured for physically contacting the tubular structure, wherein the sound-absorbing material is congured to dene the hosting space. Such embodiments may be benecial as the sound-absorbing material may reduce the amount of noise from the (external) surroundings entering the enclosed space, therewith improving the signal-to-noise ratio ofmeasurements from the measurement device. As such, the repeatability as well as reliability of the system for monitoring the physical parameter in the tubular structuremay be improved. Furthermore, the sound-absorbing material may aid in aligning the sensor correctly around the tubular structure, which may benet reproducibility and reliability of the measurements. Yet further, the sound-absorbing material may prevent ingress of dirt from entering the sensor. The sound-absorbing material may especially comprise a material congured to absorb sound frequencies selected from the range of0Hz - 500 kHz, such as from the range of 20 Hz - 250 kHz, especially from the range of 100 Hz - 100 kHz. In embodiments, the sound- absorbing material may be congured to dampen ambient sounds by an amount of at least 2 dB, such as at least4 dB, like at least 6 dB, especially at least 12 dB. Moreover, in embodiments, the sound-absorbing material may be congured to dampen ambient sounds by an amount of at most 80 dB, such as at most 60 dB, like at most 40 dB. Especially, in embodiments, the sound absorbing material may be congured to dampen ambient sound by an amount selected from the range of 150 dB, such as from the range of3-40 dB, like from the range of 5-30 dB, especially from the range of 10-25 dB. Such embodiments may be benecial as standard ambient sounds may be absorbed (i.e. dampened) using such a material. Furthermore, in embodiments, the sound-absorbing material may comprise a compressible material, such as a compressible material selected from the group comprising a foam, a polymer, a compressible uid, a rubber, a gel, and a composite material, especially a foam. Such embodiments may be benecial as the compressibility may enable tight compression ofthe measurement device, especially one or more ofthe transmitter, the sensor, and the bellows, onto the tubular structure. Such a tight compression may further help reduce ambient sounds from penetrating towards the part ofthe tubular structure where measurement is to take place. Further, a tight compression may substantially limit, especially prevent, the measurement of excitation radiation that traveled past the tubular structure as such radiation may be dampened by the sound-absorbing material, thereby further improving the signal to noise ratio. In embodiments, the hosting space may have an (relaxed) equivalent circular diameter (DH) (when not engaging the tubular structure). The (relaxed) equivalent circular diameter (DH) may especially be dened in a plane perpendicular to the axis ofelongation (As). In embodiments, the sound-absorbing material may be congured to be compressed by the tubular structure, especially wherein a diameterofthe hosting space is expanded to an expanded equivalent circular diameter (DE) when engaging the tubular structure. Further, in embodiments, themeasurement device may comprise a compressible structure. The compressible structure may be congured physically coupled to one or more of the transmitter and the sensor, such as e.g. physically coupled to both the transmitter and the sensor (see also further below). The compressible structure may herein refer to one ofthe group comprising: a bellows, a spring (or spring-like structure), and a coil. Especially, in embodiments, the measurement device may comprise a bellows. The bellows may be congured physically coupled to one or more of the transmitter and the sensor, such as e.g. physically coupled toboth the transmitter and the sensor (see also furtherbelow). The invention may herein primarily be described in relation to embodiments wherein the compressible structure comprises a bellows. It will be clear to the person skilled in the art that the invention is not limited to such embodiments. In embodiments, the bellows may comprise an essentially hollow structure. Especially, the bellows may comprise a compressible structure at least partially enclosing a bellows space (or cavity). In embodiments, the bellows space may comprise air. Additionally or alternatively, in embodiments, the bellows space may comprise one or more of a gel, a gas, and a rubber. For example, in embodiments, the bellows may be lled with one or more of air, a gel, a gas, and a rubber. Note that it may be clear to the skilled person that other types of llings (or stufngs) may be applied as well and the invention may not be limited to the herein stated examples. The bellows may comprise a relatively exible (or elastic) structure. Especially, in embodiments, the bellows may be congured tobe (slightly) compressible. In embodiments, the term bellows may herein refer to a pleated expansible structure often made ofone or more of a metallic material, a polymeric material (such as e.g. a 3D printed rubber), or a (textile or) cloth ber. The bellows may also be referred to as a exible acoustic horn. In such embodiments, the bellows may have a spring constant selected from the range of5-12000 N / m, especially from the range of 10-10000N / m, such as from the range of20-7500N / m. Especially, the bellows may have a spring constant selected from the range of30-10000 N / m, such as from the range of200-10000 N / m, like from the range of250-5000 N / m, especially from the range of300-2500 N / m. In particular, when the system engages the tubular structure (e.g. the plant), the bellows should be congured to return to its initial conguration thereby pressing (directly or indirectly) on (or compressing) the tubular structure. In embodiments, the system may further comprise a compressible material, such as a foam (see also further above). In such embodiments, (due to surface-dependence) the bellows may have a spring constant selected from the range of 100-10000 kPa / m, especially from the range of 200-10000 kPa / m, such as from the range of500-5000 kPa / m, like from the range of 1000-4500 kPa / m. Moreover, in embodiments, the bellowsmay be congured to provide a pressure to (or receive a compression pressure from) the tubular structure (as a result ofthe fastening of the measurement device to the tubular structure). Similarly, in embodiments, the hosting arrangement, especially the sound-absorbing material, may be congured to provide a pressure to (or receive a compression pressure from) the tubular structure. Thereby, the bellows and / or the hosting arrangement may facilitate positioning the transmitter and the sensor in suitable positions relative to the tubular structure. Further, the bellows may serve as a sound guide between the transmitter and the tubular structure and / or between the tubular structure and the sensor, which may be benecial for the signal to noise ratio (also see below). In particular, the radiation may travel through (a closed space in) the bellows and may thereby be guided along a desired acoustic path. Additionally, the bellows, through its sound guide functionality, may improve impedance matching between the tubular structure and the system. In embodiments, the hosting space equivalent circular diameter (DH) may therefore, when not engaging the tubular structure, be smaller than the tubular structure equivalent circular diameter (Ds). In embodiments, DH / Ds may be selected from the range of 0.10.9, such as from the range of 0.2-0.8, like from the range of 0.3-0.7. In a resting state, the compressible material (comprising the sound-absorbing material) may thus be congured to dene a hosting space having an equivalent circular diameter (DH). Further, in such a resting stage, the compressible material may have an average resting thickness (tr). Conversely, in a compressed state (i.e. when engaged with the tubular structure) the compressible material may have an average compressed thickness (tc). In embodiments, the average compressed thickness (tc) may substantially differ from the average resting thickness (tr). Especially, in embodiments, tcSO.95*tr, such as tc£0.90*tr, like tc£0.80*tr, especially tc£0.70*tr. In further embodiments, tcSO.50*tr, especially tc£03 *tr, such as tCSO.2*tr. In such embodiments, the compressible material may, while engaging the tubular structure, essentially comprise a relatively thin layer ofmaterial being compressed around the tubular structure. Furthermore, in embodiments, the sound-absorbing material may be compressible by the tubular structure to an expanded equivalent circular diameter (DE). In other words, when engaging the tubular structure the sound-absorbing material may be compressible by the tubular structure to an expanded equivalent circular diameter (DE). In embodiments, the expanded equivalent circular diameter (DE)may be smallerthan the tubular structure equivalent circular diameter (Ds). In embodiments, DE / Dsmay be selected from the range of 0. 10.9, such as from the range of 0.2-0.8, like from the range of0.3-0.7. Moreover, in embodiments, DESDH. In specic embodiments, the invention may provide a system for monitoring a physical parameter of a tubular structure, wherein the system comprises a hosting arrangement, a transmitter, a sensor, a bellows and a control system, wherein: (A) the hosting arrangement comprises at least part of the transmitter, the sensor and the bellows, (B) the hosting arrangement comprises a sound-absorbing material congured for physically contacting the tubular structure, wherein the sound-absorbing material is congured to dene a (cylindrical) hosting space for hosting the tubular structure, (C) the bellows are congured physically coupled to one ormore ofthe transmitter andthe sensor, andwherein thebellows are congured to provide a pressure to (or receive a compression pressure from) the tubular structure (when the tubular structure is hosted in the hosting space), (D) the transmitter is congured to provide acoustic excitation radiation to (the tubular structure in) the hosting space, wherein the acoustic excitation radiation has a frequency selected from the range of 48-500 kHz, (E) the sensor is congured to detect acoustic emission radiation from (the tubular structure in) the hosting space, and to provide a related sensor signal to the control system, (F) the control system is congured to determine the physical parameter based on the sensor signal. In embodiments, the hosting arrangement may be congured switchable between an open conguration and a closed conguration. Especially, the hosting arrangement may be congured for being placed around the tubular structure in the open conguration. Additionally, in embodiments, the hosting arrangement may be congured for switching from the open conguration to the closed arrangement while placed around the tubular structure, especially such that the sound-absorbing material is congured for physically contacting the tubular structure in the closed arrangement, and / or especially such that the bellows are congured for physically contacting the tubular structure in the closed arrangement, or especially such that the transmitter and / or the sensor are congured for physically contacting the tubular structure in the closed arrangement (see below). The hosting arrangement may further, in embodiments, comprise a hinge. The hinge may, in embodiments, be congured to facilitate switching between the open conguration and the closed conguration. In embodiments, the hinge may be comprised by the hosting arrangement. Especially, the hinge may be comprised by the fastening means (such as e.g. a clamp). In embodiments, the fastening means may essentially be the hinge. In embodiments, in an operational mode ofthe system, the measurement device may thus be congured physically coupled (such as attached) to the tubular structure through the function ofthe fastening means (optionally comprised by the hosting arrangement). The system, especially the measurement device, may further comprise a transmitter, a sensor, and a bellows. In embodiments, the bellowsmay be congured physically coupled to one or more ofthe transmitter and the sensor. As described above, the systemmay be congured to provide acoustic excitation radiation to the tubular structure. Therefore, in embodiments, the system may comprise the transmitter. Instead ofthe term transmitter also the terms speaker or communicator may herein be applied. The transmittermay be congured to provide acoustic excitation radiation to the tubular structure. In particular, the transmitter may be congured to expose the tubular structure, such as a vascular plant, to the acoustic excitation radiation. The term acoustic excitation radiation may herein refer to acoustic radiation having a frequency suitable to excite (part of) the tubular structure, such as (part of) the vascular plant. In particular, the acoustic excitation radiation may comprise a frequency suitable to excite an (internal) resonance ofthe tubular structure, such as of the vascular plant. It will be clear to the person skilled in the art that the frequency suitable to excite an (internal) resonance ofthe tubular structuremay depend on the type and / or size of the tubular structure, as well as on the physical parameter to be monitored. For example, relatively low frequencies may be selected for the acoustic excitation radiation when employing the system in relation to a relatively large vascular plant, such as a tree, whereas relatively large frequencies may be selected when employing the system in relation to a (blood vessels in a) ligament or a relatively small vascular plant. In particular, in embodiments, the acoustic excitation radiation may especially comprise radiation having a frequency selected from the range of 1-500 kHz, like from the range of5250 kHz, especially from the range of48-500 kHz. In embodiments, the acoustic excitation radiation may comprise radiation having a frequency of at least 1 kHz, such as at least 5 kHz, especially at least 10 kHz, such as at least 20 kHz, especially at least 30 kHz. In further embodiments, the acoustic excitation radiation may comprise radiation having an (acoustic excitation radiation) frequency of at most 500 kHz, especially at most 250 kHz, such as at most 200 kHz, especially at most 170 kHz, such as at most 150 kHz, especially at most 130 kHz. In further embodiments, the acoustic excitation radiation frequency and / or acoustic excitation radiation amplitude may be varied in time, especially while the emitted radiation spectra and variations therein are determined to infer properties of the tubular structure, especially of the vascular plant, or to determine acoustic excitation radiation frequencies at which acoustic emission radiation emission is stimulated most by the acoustic excitation radiation. In further embodiments, excitation pulses (e.g. block pulses) of different duration and amplitudes may be applied, especially where the frequency content depends on the pulse width. In embodiments, the acoustic excitation radiation may especially be provided via a pulse (or a frequency sweep), especially wherein the pulse has a pulse duration that is larger than a characteristic settling time due to damping in the tubular structure (e.g. vascular tissue). In particular, the pulse duration may be larger than 1 ms. In further embodiments, the pulse duration may be selected from the range of 0.5 - 10 ms, such as from the range of 1-10 ms. In further embodiments, the pulse duration may be at least 0.5 ms, such as at least 1 ms, especially at least 1.1 ms, such as at least 1.2 ms, especially at least 1.5 ms, such as at least 2 ms. In further embodiments, the pulse duration may be at most 20 ms, such as at most 15 ms, especially at least 10 ms, such as at most 5 ms, especially at most 3 ms, such as at most 2 ms. In further embodiments, the acoustic excitation radiation may especially be provided via a step excitation or a narrow rectangular pulse. The settling time may especially be determined by tting an amplitude-envelope to a time-domain signal with a single exponential function. Radiation above 20 kHz may generally be referred to as ultrasound radiation, i.e., radiation with frequencies higher than the upper audible limit ofhuman hearing. In further embodiments, the excitation radiation may be ultrasound excitation radiation, i.e., the excitation radiation may comprise radiation having a frequency in the ultrasound range. In embodiments, the acoustic excitation radiation may comprise one of a square wave, a sine wave, an impulse, a burst, a (frequency) sweep, or any other type ofgeneral xed waveform. Especially, in embodiments, the acoustic excitation radiationmay comprise a square wave or a sinewave.A frequency sweep (orfrequency response analysis)may herein especially refer to a technique in electronics used to evaluate and characterize a circuit's response across a spectrum of different frequencies. Such a frequency sweep may especially be applied to determine the time-dependent behavior of a sample in the non-destructive deformation range. Furthermore, as described above, the system may be congured to receive acoustic excitation radiation from the tubular structure. Therefore, in embodiments, the system may comprise the sensor. Instead of the term sensor also the terms microphone or receptor may herein be applied. The sensor may be congured to sense (or detect) acoustic emission radiation from the tubular structure. Additionally, the sensormay be congured to provide an emission- related signal. Especially, the sensor may be congured to detect resonance acoustic emission radiation from the tubular structure, especially from the vascular plant, and provide an emission-related signal. It will be clear to the person skilled in the art that, strictly speaking, the measured (or observed) frequency acoustic emission radiation may be slightly lower than the true resonant frequency due to non-zero damping. The term acoustic emission radiation may herein refer to acoustic radiation emitted from the tubular structure, especially from the vascular plant. In particular, the tubular structure, especially the vascular plant, may have been excited by acoustic excitation radiation by the transmitter andmay subsequently emit acoustic emission radiation. However, the tubular structure, especially the vascular plant, may also emit acoustic emission radiation without specically being excited by acoustic excitation radiation. For instance, if a plant experiences drought stress, gas bubbles can nucleate in these vessels, which may result in emission radiation, especially ultrasound emission radiation, being emitted from the plant. The term resonance acoustic emission radiation may herein especially refer to radiation emitted from the tubular structure, especially from the vascular plant. The resonance acoustic emission radiation may especially match an (internal) resonance frequency of the tubular structure. In particular, the acoustic excitation radiation may comprise radiation having a resonance frequency of the tubular structure, i.e., radiation having a frequency matching a natural frequency ofvibration of the tubular structure, which may cause the tubular structure to vibrate and emit resonance acoustic emission radiation at the resonance frequency. The acoustic emission radiation may comprise radiation having the same frequency as the acoustic excitation radiation. The term frequency may also refer to a plurality of different frequencies. In particular, in embodiments, the acoustic emission radiation may comprise radiation selected from the same range as the acoustic excitation radiation. Especially, the acoustic excitation radiation and the acoustic emission radiation may overlap in one or more frequencies. In general, in embodiments, the acoustic emission radiation may be selected from the range of 1-500 kHz, like from the range of 5250 kHz, or especially from the range of48-500 kHz. In embodiments, the acoustic emission radiation may comprise radiation having a frequency of at least 1 kHz, such as at least 5 kHz, especially at least 10 kHz, such as at least 20 kHz, such as at least 30 kHz. In further embodiments, the acoustic emission radiation may comprise radiation having a frequency of at most 500 kHz, especially at most 250 kHz, such as at most 200 kHz, especially at most 170 kHz, such as at most 150 kHz, especially at most 130 kHz. In further embodiments, the emission radiation may be ultrasound emission radiation, i.e., the emission radiation may comprise radiation in the ultrasound range. The term emission-related signal may herein refer to a signal that is related to the detected acoustic emission radiation. In particular, the emission-related signal may comprise raw and / or processed data related to the (detected) acoustic emission radiation. Hence, in embodiments, the sensor may be congured to detect acoustic emission radiation from the tubular structure, and to provide a related sensor signal to the control system. Hence, in embodiments, the control system may be congured to receive the sensor signal from the sensor. The control system may be congured to control the measurement device. Especially, the control system may be congured to determine the physical parameter (of the tubular structure) based on the sensor signal. The control system may especially be congured to determine the physical parameter based on the emission-related signal. In particular, the detected acoustic emission radiation may represent one or more resonant modes ofvibration of the dimensions and elasticity of the tubular structure, such as of a vascular plant tissue. The resonant modes ofvibration may relate to the dimensions and elasticity ofthe tubular structure. Hence, the detected acoustic emission radiation may be a signature of the tubular structure dimensions and elasticity. In embodiments, the control system may be congured to t at least part of the emission-related signal to a model of exural modes of a cylindrical beam, and determine the physical parameter based on the model. In embodiments, the control system may be congured to determine the physical parameter, especially the physical vessel parameter, from the sensor signal as described inWO2022055353A1, which is hereby herein incorporated by reference. In further embodiments, the control system may be congured to t an exponential decay curve to at least part ofthe emission-related signal and to determine a decay parameter, Wherein the physical parameter is determined based on the decay parameter, especially Wherein the physical parameter comprises one or more of a xylem vessel radius, a sap viscosity, and axylem viscoelasticity. In further embodiments, the control system may be congured to determine one or more peaks in at least part ofthe emission-related signal in the frequency domain, wherein the physical parameter may be determined based on the one or more peaks, and especially wherein the physical parameter comprises one or more of a xylem vessel element length, and a Youngs modulus. Furthermore, in embodiments, the control system may be congured to execute an operational mode ofthe system, such as the operational mode described above. Especially, in embodiments, the control system may be congured to execute an operational mode comprising controlling a plant cultivation condition (of the vascular plant) based on the physical parameter, wherein the plant cultivation condition may be selected from the group comprising a watering regime, a lighting regime, and a nutrient regime. Hence, in embodiments, the system may comprise or be functionally coupled to a plant cultivation system, especially wherein the plant cultivation system is congured to control one or more of (a) water, (b) lighting, and (c) nutrients provided to the vascular plant. The term controlling and similar terms especially refer at least to determining the behavior or supervising the running ofan element. Hence, herein controlling and similar terms may e.g. refer to imposing behavior to the element (determining the behavior or supervising the running of an element), etc., such as e.g. measuring, displaying, actuating, opening, shifting, changing temperature, etc.. Beyond that, the term controlling and similar terms may additionally include monitoring. Hence, the term controlling and similar terms may include imposing behavior on an element and also imposing behavior on an element and monitoring the element. The controlling of the element can be done with a control system, which may also be indicated as controller. The control system and the element may thus at least temporarily, or permanently, functionally be coupled. The element may comprise the control system. In embodiments, the control system and elementmay notbe physically coupled. Control can be done via wired and / or wireless control. The term control system may also refer to a plurality of different control systems, which especially are functionally coupled, and ofwhich e.g. one control system may be a master control system and one or more others may be slave control systems. A control system may comprise ormay be functionally coupled to a user interface. The control system may in embodiments be congured to receive and execute instructions from a remote control. In embodiments, the control system may be controlled via an App on a device, such as a portable device, like a Smartphone or I-phone, a tablet, etc.. The device is thus not necessarily coupled to the system, but may be (temporarily) functionally coupled to the system. The system, or apparatus, or device may execute an action in a mode or operation mode ormode ofoperation or operational mode. The term operational mode may also be indicated as controlling mode. Likewise, in a method an action or stage, or step may be executed in a mode or operation mode or mode of operation or operational mode. This does not exclude that the system, or apparatus, or device may also be adapted for providing another controlling mode, or a plurality of other controlling modes. Likewise, this may not exclude that before executing the mode and / or after executing the mode one or more other modes may be executed. Would other modes be available, the choice of such modes may especially be executed via a user interface, though other options, like executing a mode in dependence ofa sensor signal or a (time) scheme, may also be possible. The operation mode may in embodiments also refer to a system, or apparatus, or device, that can only operate in a single operation mode (i.e. on, without further tunability). Referring back to the bellows, in embodiments, the bellows may have a rst end and a second end. The rst end may especially be arranged to abut (especially at least partially surround) the transmitter and / or the sensor. In embodiments, the rst end of the bellows may be arranged to abut, especially to at least partially surround, the transmitter. Additionally or alternatively, in embodiments, the rst end ofthe bellows may be arranged to abut, especially to at least partially surround, the sensor. Conversely, in embodiments, the second end of the bellows may be congured to contact the tubular structure. In specic embodiments, the bellows may comprise a rst bellows and a second bellows. In such embodiments, the rst end of the rst bellows may be arranged to abut (especially at least partially surround) the transmitter. Further, in such embodiments, the rst end ofthe second bellows may be arranged to abut (especially at least partially surround) the sensor. Yet, in such embodiments, both the second end ofthe rst bellows and the second end ofthe second bellows may be arranged to contact the tubular structure. The bellows may, in embodiments, comprise a suction cup congured on one or both of the rst end and the second end. The suction cup may especially be congured to suction the bellows onto the tubular structure, the transmitter, or the sensor. Such embodiments may be benecial as the suction cup may improve the contact between the bellow and the tubular structure, and may facilitate maintaining suitable relative positions between the transmitter, the sensor and the tubular structure. Through the improved contact between the bellow and the tubular structure, the suction cup (as does the bellow) may function as a waveguide and may block sound from going around the tubular structure rather than through it. The suction cup may thus provide a tight seal therewith effectively blocking other sound paths than the desired path through the tubular structure. Hence, in embodiments, at least the second end ofthe bellows may comprise a suction cup. Further, in some embodiments, the rst end of the bellows may comprise a suction cup congured to suction the bellows to the transmitter and / or sensor. Alternatively, in embodiments, the rst end ofthe bellows may comprise a exible sack congured to envelop around the circumference ofthe transmitter and / or sensor. Hence, in specic embodiments, the bellows comprise a rst bellows and a second bellows, wherein the rst end ofthe rst bellows is arranged to abut (especially at least partially surround) the transmitter, and wherein the rst end ofthe second bellows is arranged to abut (especially at least partially surround) the sensor. In such embodiments, the bellows are especially congured between (i) the tubular structure and the transmitter, and (ii) the tubular structure and the sensor. With such congurations, itmay be especially useful forthe bellows to comprise an acoustic horn (as described above). In such embodiments, the bellows may provide the functions of: (i) facilitating positioning of the transmitter and the sensor in suitable positions relative to the tubular structure (by providing or receiving compression pressure), (ii) providing acoustic wave-guiding, and (iii) reducing ambient sounds. Especially, the bellows may provide exibility, such that the tubular structure (such as a plant stem or a human or animal ligament) may expand or contract (slightly) without loss ofcontact between the measurement device and the tubular structure. In embodiments, the system may also comprise a transceiver. In such embodiments, the transceivermay comprise (both) the transmitter and the sensor. Furthermore, in such embodiments, the rst end (of the bellows) may at least partially surround the transceiver. Hence, in such embodiments, the bellows are especially congured between the tubular structure and the transceiver (comprising both the transmitter and the sensor). The combination ofthe transceiver with the bellows, ofwhich the rst end is congured to at least partially surround the transceiver, may herein also be referred to as a sensing arrangement. In embodiments, the system may thus comprise a sensing arrangement congured to provide acoustic excitation radiation to and receive acoustic emission radiation from the tubular structure. Furthermore, in embodiments, the system may comprise more than one sensing arrangement. Especially, the system may comprise a plurality of sensing arrangements, wherein each sensing arrangement may comprise a transceiver (comprising a transmitter and a sensor) and a bellows (congured to at one end at least partially surround the transceiver and to at the other end contact the tubular structure). When the system comprises a plurality of sensing arrangements, in embodiments, the sensing arrangements may function separately, i.e., the different sensing arrangements may be operated temporally separated and essentially independently of each other. Additionally or alternatively, in embodiments, one or more of the plurality of sensing arrangements may be operated together. For example, in such embodiments one or more ofthe sensing arrangements may function as the transmitter, whereas (at least a part of) the other sensing arrangements may function as the sensor. Moreover, in such embodiments, the functions of the different sensing arrangements may alternate over time. For example, a rst sensing arrangement may be operated as a transmitter at a rst point in time, while a second and third (or even more) sensing arrangementmay be operated as sensors. In such an example, at a second point in time the functionality may be switched, e.g., the rst and third (or even more) sensing arrangement may be operated as sensors, whereas the second sensing arrangement may be operated as a transmitter. It will be clear to the skilled person that many variations of such embodiments may be possible. Hence, in embodiments, the transmitter may be congured to provide acoustic excitation radiation to the tubular structure via the bellows. Moreover, in embodiments, the sensor may be congured to receive acoustic emission radiation from the tubular structure via the bellows. Alternatively, in embodiments, the transmitter may be congured between the bellows and the tubular structure, and the sensor may be congured between the bellows and the tubular structure. As such, the bellows may, in embodiments, not be congured in direct physical contactwith the tubular structure. Such embodiments are further described here below. The transmitter may thus, in embodiments, be arranged between the (rst) bellows and the hosting space. In embodiments, the transmitter may comprise a transmitter transducer. The transmitter transducer may be congured for contacting the tubular structure. Moreover, in embodiments, the (suction cup ofthe) bellows may be congured to contact the transmitter. As such, the bellows may be congured to provide a compression pressure to the tubular structure indirectly, especially via the transmitter. Additionally or alternatively, in embodiments, the sensormay thus be arranged between the (second) bellows and the hosting space. In embodiments, the sensormay comprise a sensor transducer. The sensor transducer may be congured for contacting the tubular structure. Moreover, in embodiments, the (suction cup of the) bellows may be congured to contact the sensor. As such, the bellows may be congured to provide a compression pressure to the tubular structure indirectly, especially via the sensor. In such congurations, the primary function of the compressible structure, especially the bellows, may be to provide the (compression) pressure to the tubular structure, e.g., to position the transmitter and / or the sensor against the tubular structure, especially against a section of the tubular structure. In such embodiments, instead of the bellows optionally a spring or a coil (as described above) congured for providing or receiving the compression pressure may be used. In embodiments, the measurement device may be congured to at least partially surround (only) a part of the tubular structure. Especially, in embodiments, the measurement device may be congured to at least partially surround a tubular structure section where measurement or monitoring ofthe tubular structuremay be desired. Hence, the above described surrounding of the tubular structure by the hosting arrangement over at least 25% of the circumference of the tubular structure may refer to the circumference of the tubular structure at the tubular structure section. The tubular structure, especially the tubular structure section, may further have an (average) acoustic impedance (Za). Herein the term acoustic impedance may refer to a measure of opposition that an element (i.e. the tubular structure) may present to an acoustic ow (i.e. the acoustic radiation wave) resulting from an acoustic pressure applied to said element. In other words, the acoustic impedance may describe the amount ofresistance that an ultrasound beam may encounter when passing through the element, i.e., the tubular structure. In embodiments, the (average) acoustic impedance Za may be selected from the range of 1.4- 34 kg / (m2*s), such as from the range of 1 .5-30 kg / (m2*s), like from the range of3-10 kg / (m2*s). It may be desirable to match an impedance of the system to the impedance of the tubular structure. Hence , in embodiments, the transmittertransducermay have a transmitter acoustic impedance (Z). In embodiments, Zt / Za may be selected from the range of at least 0.1, such as at least 0.2. Especially, in embodiments, Zt / Za may be selected from the range of at least 0.3, such as at least 0.4, like at least 0.5. Moreover, in embodiments, Zt / Zamay be selected from the range of at most 30, such as at most 20, like at most 10. In embodiments, Zt / Za may be selected from the range of at most 3, such as at most 2.5, like at most 2.2. Especially, Zt / Za may be selected from the range of05-30, such as from the range of05-25, like from the range of08-15, especially from the range of 1.1-5. More especially, Zs / Za may be selected from the range of 0.52, such as from the range of 0.6-1.8, like from the range of 0.7-1.5. Furthermore, in embodiments, the sensor transducermay have a sensor acoustic impedance (ZS). In embodiments, ZS / Za may be selected from the range of at least 0.1, such as at least 0.2. Especially, in embodiments, ZS / Za may be selected from the range of at least 0.3, such as at least 0.4, like at least 0.5. Moreover, in embodiments, Zs / Za may be selected from the range of at most 30, such as at most 20, like at most 10. In embodiments, Zs / Za may be selected from the range of at most 3, such as atmost 2.5, like at most 2.2. Especially, ZS / Zamay be selected from the range of 05-30, such as from the range of05-25, like from the range of 08-15, especially from the range of 1.1-5. More especially, Zs / Za may be selected from the range of0.52, such as from the range of0.6-1 .8, like from the range of 0.7-1.5. The transmitter acoustic impedance and / or the sensor acoustic impedance may especially be selected to provide a transmission between respectively, the transmitter transducer and / or the sensor transducer, and the tubular structure of at least 60%, such as at least 70%, like at least 80%, especially at least 90%, more especially at least 95%, including essentially 100%. Hence, in specic embodiments, the tubular structure(, especially the tubular structure section,) may have an (average) acoustic impedance Za, and Wherein one or more may apply of: (A) the transmitter comprises a transmitter transducer for contacting the tubular structure, Wherein the transmitter is arranged between the bellows and the hosting space, Wherein the transmitter transducer ,has a transmitter acoustic impedance (Zt), wherein Zt / Za is selected from the range of 0.5 30, and (B) the sensor comprises a sensor transducer for contacting the tubular structure, wherein the sensor is arranged between the bellows and the tubular space (15), wherein the sensor transducer has a transmitter acoustic impedance (ZS), wherein Zs / Za is selected from the range of 0.5 30. Matching the impedance ofthe system (especially the sensor and / or transmitter) to the impedance ofthe tubular structuremay minimize signal reection and / or maximize power transfer between the system and the tubular structure. Such impedance matching may further be aided through the application of the bellows, which may help center the sound waves like an acoustic horn. Moreover, in embodiments, the system may also comprise a transceiver. The transceivermay especially comprise (both) the transmitter and the sensor. Furthermore, in such embodiments, the transceivermay comprises a transceiver contact structure for contacting the tubular structure. Especially, the transceiver may be arranged between the bellows and the tubular space. In such embodiments, the rst end (ofthe bellows) may be arranged to contact the transceiver. As described above, the tubular structure may have an axis of elongation (As). In embodiments, in the operational mode of the system the bellows, a part of the fastening means, and one or both ofthe transmitter and the sensor (such as e.g. the transceiver comprising both the transmitter and the sensor) may be arranged in an orthogonal projection from the axis ofelongation (As). As such, the part ofthe fastening means may be arranged downstream from the bellows and the one or more of the transmitter and the sensor. The terms upstream and downstream relate to an arrangement of items or features relative to the propagation of the acoustic emission radiation from an acoustic emission radiation generating means (here especially the tubular structure), wherein relative to a rst position within a wave of radiation from the acoustic emission radiation generating means, a second position in the wave of radiation closer to the acoustic emission radiation generating means is upstream, and a third position within the wave of radiation further away from the acoustic emission radiation generating means is downstream. Although the bellows and / or the sound-absorbing material may shield the tubular structure and the sensor from ambient noise, other ambient factors may yet inuence the measurements. For instance, as will be clear to the person skilled in the art, a change in temperature may affect the speed of ultrasound waves, which may in turn affect resonant frequencies. Similarly, other ambient factors may (also) inuence the measurements of the tubular structure. To compensate for ambient factors the system may, in embodiments, comprise an ambient sensor. The ambient sensor may, in embodiments, be congured external to the hosting arrangement. In some embodiments, the ambient sensormay be congured in physical contact with the hosting arrangement. In other embodiments, the ambient sensor may be congured at a distance from the hosting arrangement. In such embodiments, the ambient sensor may be congured communicatively coupled (such as e.g. electrically coupled or coupled through wireless transmission) to the control system. The ambient sensor may especially be congured to detect one or more of a(n ambient) temperature, a(n ambient) humidity, and an (ambient) acoustic radiation. In further embodiments, the ambient sensormay be congured to provide an ambient sensor signal based on said detection of one or more of a(n ambient) temperature, a(n ambient) humidity, and an (ambient) acoustic radiation. Especially, the ambient sensor may be congured to provide an ambient sensor signal to the control system. In such embodiments, the control system may further be congured to determine the physical parameter based on (a combination of) the sensor signal and the ambient sensor signal. Hence, in embodiments, the system comprises an ambient sensor, wherein the ambient sensor is congured external to the hosting arrangement, wherein the ambient sensor is congured to detect one or more of a temperature, a humidity, and an acoustic radiation, wherein the ambient sensor is congured to provide an ambient sensor signal to the control system, and wherein the control system is congured to determine the physical parameter based on the sensor signal and the ambient sensor signal. Such embodiments provide the benet ofadaptability to ambient factors as the ambient sensor signal may be used to adjust measurement through the control system. For example, the ambient sensor may be congured to detect an ambient temperature and provide an ambient sensor signal to the control system. The control system may be congured to compensate for temperature-dependent (speed) differences based on the ambient sensor signal. As such, the reliability and repeatability ofthe measurements may further be improved. In further embodiments, the hosting arrangement may comprise an alignment mechanism. The alignment mechanism may be congured to contact the tubular structure to centralize the tubular structure in the hosting space. Especially, the alignment mechanism may be congured to contact the tubular structure, such that the tubular structure may be arranged between the transmitter and the sensor. The alignment mechanism may thus, in embodiments, be congured to centralize or align the tubular structure between the transmitter and the sensor. Such embodiments may provide the benet that proper paths of the acoustic (excitation / emission) radiation from the transmitter to the tubular structure and from the tubular structure to the sensor may be ensured. In embodiments, the alignment mechanism may be congured compliant with the tubular structure. Therefore, instead of the term alignment mechanism also the term compliant mechanism may be applied. In yet further embodiments, the system may comprise a stent arrangement. The stent arrangement may, in embodiments, comprise the bellows and the alignment mechanism. Hence, in embodiments, the stent arrangementmay comprise an integrated arrangement ofthe bellows with the alignment mechanism. In embodiments, the stent arrangement may for example comprise a material selected from the group comprising a polymeric material and a metallic material. The stent arrangementmay especially comprise a material having a relatively high stiffness. Such embodiments comprising the stent arrangement may be benecial as the stent arrangementmay prevent the bellows from bending sideways or upwards, thus preventing the bellows from deformation which may lead to reduced wave-guiding efciency. In a further aspect, the invention may provide a method for monitoring a physical parameter of a tubular structure. In embodiments, the method may comprise arranging a transmitter to provide acoustic excitation radiation to a tubular structure section ofthe tubular structure. Additionally, in embodiments, the method may comprise arranging a sensor to detect acoustic emission radiation from the tubular structure section of the tubular structure. Yet additionally, in embodiments, the method may comprise arranging a bellows to provide a pressure to (or receive a compression pressure from) the tubular structure. The method may further comprise providing acoustic excitation radiation to the tubular structure section, especially via the bellows, using the transmitter. In embodiments, the acoustic excitation radiation may have a frequency selected from the range of 1-500 kHz, especially from the range of5250 kHz, or especially from the range of48-500 kHz. Further, in embodiments, the acoustic excitation radiation may comprise a pulse comprising a plurality of square waves and / or sine waves. Especially, the acoustic excitation radiation may comprise a pulse comprising a plurality of square waves. Additionally or alternatively, the acoustic excitation radiation may comprise a pulse comprising a plurality of sine waves. However, in embodiments, other types ofwaves as described further above may also apply. Yet further, in embodiments, the method may comprise detecting acoustic emission radiation (traveling) from the tubular structure section, and especially via the bellows, using the sensor and providing a related sensor signal. Especially, the method may comprise determining the physical parameter ofthe tubular structure based on the sensor signal. In short, the method may comprise providing a wave of acoustic excitation radiation through the measurement device from the transmitter to the tubular structure. As such, the acoustic excitation radiation may penetrate the tubular structure, whereupon it may cause a related acoustic emission radiation to be provided from the tubular structure through the measurement device to the sensor. Through the application ofthe bellows and the sound-absorbing material, the acoustic excitation / emission radiation may efciently propagate through the system, whereas ambient sounds and radiation may be dampened. The acoustic emission radiation received by the sensor may then be used to provide a sensor signal, from which physical parameter information relating to the tubular structure may be obtained. Hence, in specic embodiments, the invention may provide a method for monitoring a physical parameter of a tubular structure, wherein the method comprises: (A) arranging (a) a transmitter to provide acoustic excitation radiation to a tubular structure section ofthe tubular structure, (b) a sensor to detect acoustic emission radiation from the tubular structure section ofthe tubular structure, and (c) abellows to provide a pressure to the tubular structure, wherein the bellows are arranged in physical contact with one or more ofthe transmitter and the sensor, (B) providing acoustic excitation radiation to the tubular structure section using the transmitter, wherein the acoustic excitation radiation has a frequency selected from the range of 1-500 kHz, (C) detecting acoustic emission radiation from the tubular structure section using the sensor and providing a related sensor signal, and (D) determining the physical parameter ofthe tubular structure based on the sensor signal. Yet additionally, the method may comprise arranging a sound-absorbing material to contact the tubular structure to provide an enclosed space. In embodiments, the enclosed space may comprise the transmitter, the sensor, the bellows and at least part of the tubular structure section. Further, in embodiments, the sound-absorbing material may be arranged in contact with the tubular structure. Furthermore, in embodiments, the bellows may be arranged in physical contact with one or more of the transmitter and the sensor. Hence, in specic embodiments, the invention may provide a method for monitoring a physical parameter of a tubular structure, wherein the method comprises: (A) arranging (a) a transmitter to provide acoustic excitation radiation to a tubular structure section ofthe tubular structure, (b) a sensor to detect acoustic emission radiation from the tubular structure section ofthe tubular structure, and (c) a bellows to provide a pressure to (or receive a compression pressure from) the tubular structure, and (d) a sound absorbing material to contact the tubular structure to provide an enclosed space, wherein the enclosed space comprises the transmitter, the sensor, the bellows and at least part ofthe tubular structure section, wherein the sound absorbing material is arranged in contact with the tubular structure, and wherein the bellows are arranged in physical contact with one or more of the transmitter and the sensor, (B) providing acoustic excitation radiation to the tubular structure section using the transmitter, wherein the acoustic excitation radiation has a frequency selected from the range of 1-500 kHz, (C) detecting acoustic emission radiation from the tubular structure section using the sensor and providing a related sensor signal, and (D) determining the physical parameter ofthe tubular structure based on the sensor signal. The method ofthe invention may provide the benet that a physical parameter of a tubular structure (such as a plant vascular tissue) may be obtained both quickly and non- invasively. Hence, when applying the method to a plant (as the tubular structure), the physical parametermay be obtained without damaging the plant. In particular, by recording spontaneous or induced acoustic emission radiation, especially ultrasound emission radiation, of the plant, especially from the vascular tissue, data related to the vessel dimensions and / or vessel elasticities may be obtained in a non-destructive way. The invention may facilitate rapid in- vivo plant phenotyping. The invention may particularly relate to sending an external radiation pulse, especially an ultrasound pulse, through the (tubular structure, e.g.) plant stem and recording induced acoustic emission radiation. In embodiments, the acoustic excitation radiation may comprise a plurality of acoustic radiation signals. Further, the acoustic emission radiation may have a settling time (ts). The setting time (ts) may herein be dened as the duration it takes for an emission signal strength to decrease to 5% or less ofan excitation radiation signal strength. In embodiments, successive acoustic radiation signals may be (temporally) separated by independently selected wait times (tw). In embodiments, the wait times (tw) may be longer than the settling time (ts). Especially, in embodiments, tw-tle min, such as tw-tsz2 min, like tW-tSZS min, especially tW-tleO min. Further, in embodiments, tw-tSS60 min, such as tw-tsS45 min, like, tw-tSS30 min. Especially, in embodiments, tw-ts may be selected from the range of 030 min, such as from the range of 0-20 min, like from the range of 1-15 min, especially from the range of 5-12 min. In embodiments, the waiting time (tw) may especially be selected at least for as long it takes such that the acoustic radiation signals may be reduced to at most 25%, such as at most 15%, especially at most 5% of the highest signal (of the respective pulse). Moreover, in embodiments, the acoustic emission radiation may comprise a plurality ofacoustic emission signals. In embodiments, the method may comprise providing a plurality ofrelated sensor signals. The method may further comprise averaging the plurality of sensor signals to provide an averaged sensor signal. For example, the method may comprise Welch averaging the plurality of sensor signals to provide an averaged sensor signal. However, in embodiments, other suitable methods ofaveraging may be known to the skilled person and may thus also be applied. Furthermore, in embodiments, the methodmay comprise determining the physical parameter ofthe tubular structure based on the averaged sensor signal. Further, in embodiments, the method may comprise determining a mean (Xa) and a standard deviation (ca) of the averaged sensor signal. Especially, the method may comprise determining a deviation (A) from the mean (Xa) for each of the plurality of sensor signals. Further, in embodiments, the method may comprise determining a representative sensor signal based on a subset of sensor signals for which A 5 Ga may apply. Yet further, in embodiments, the method may comprise determining the physical parameter of the tubular structure based on the representative sensor signal. Determination of such mean and standard deviation may be advantageous in dening outliers (,i.e. outlier signals in the time domain,) in the dataset. The method may especially be performed using the system of the invention. Hence, the embodiments ofthe tubular structure, the transmitter, the sensor, and the bellows as described above for the system may similarly be applicable for the method of the invention. However, itmay be clear to the skilled person that other embodiments ofsystem components for use in the method as described here are herein not excluded. In embodiments, the method may thus be performed using the system of the invention. The system may comprise a control system. In particular, in such embodiments, the control system may be congured to execute the method ofthe invention. Hence, the embodiments described herein are not limited to a single aspect of the invention. For example, an embodiment describing the method may, for example, further relate to the system, especially to an operational mode ofthe system, or especially to the control system. Similarly, an embodiment of the system describing an operation of the system may further relate to embodiments of the method. In particular, an embodiment of the method describing an operation (ofthe system) may indicate that the system may, in embodiments, be congured for and / or be suitable for the operation. Similarly, an embodiment of the system describing actions of (a stage in) an operational mode may indicate that the method may, in embodiments, comprise those actions. BRIEF DESCRIPTION OF THEDRAWINGS Embodiments ofthe invention will now be described, by way ofexample only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: Figs. 1-4 schematically depict embodiments of the system of the invention. The schematic drawings are not necessarily on scale. DETAILED DESCRIPTION OF THEEMBODHVIENTS Fig. 1A schematically depicts an embodiment ofthe system 1 for monitoring a physical parameter of a tubular structure 15 of the invention. In the depicted embodiment the system comprises a measurement device 100 and a control system 300. The measurement device 100 comprises fastening means 105, a transmitter 120, a sensor 130, and a bellows 140. In embodiments, the bellows 140 may be congured physically coupled to one or more ofthe transmitter 120 and the sensor 130. As depicted here, the bellows 140 may have a rst end 141 and a second end 142. In embodiments, the rst end 141 may be arranged to abut (especially at least partially surround) the transmitter 120 and / orthe sensor 130. Moreover, the second end 142 may be congured to contact the tubular structure 15. Therefore, the second end may for example comprise a suction cup, as depicted schematically in Fig. 1A. The system 1 may further comprise a hosting arrangement 110. In embodiments, the hosting arrangement 110 may comprise at least part ofthe transmitter 120, the sensor 130 and the bellows 140. In further embodiments, the hosting arrangement 110 may be congured to dene a hosting space 115 for hosting the tubular structure 15. The hosting arrangement 110 may comprise a sound-absorbing material 111 congured for physically contacting the tubular structure 15. Especially, the sound-absorbing material 111 may be congured to dene the hosting space 115. Hence, in embodiments, the hosting arrangement 110, especially the sound-absorbing material 111, may be congured to dene an enclosed space when in contact with the tubular structure 15. Especially, the transmitter 120, the sensor 130, and the bellows 140 may be arranged in the enclosed space. In embodiments, the sound-absorbing material 111 may comprise a compressible material selected from the group comprising a foam, a polymer, a compressible uid, a rubber, a gel, and a composite material. Especially, in embodiments, the sound absorbing material 111 may be congured to dampen ambient sound by an amount selected from the range of 3 40 dB. As depicted in Fig. 1B, the tubular structure 15 may have a equivalent circular diameter Ds. Similarly, the hosting space 115 may have an equivalent circular diameter DH (when not engaging the tubular structure 15). In embodiments, the hosting arrangement 110 may be congured to surround the tubular structure 15 over at least 25%, such as at least 80%, of a circumference of the tubular structure 15. Moreover, in embodiments, DH / Ds may be selected from the range of 0.10.9. Yet similarly, the sound-absorbing material 111 may be compressible by the tubular structure to an expanded equivalent circular diameter DE. In embodiments, DE / Ds may be selected from the range of 0.91.0. The tubular structure 15 may further have an axis of elongation As as depicted here. In the operational mode of the system 1 may apply that: the bellows 140, a part of the fastening means 105, and one or both ofthe transmitter 120 and the sensor 130 may be arranged in an orthogonal projection from the axis ofelongation As. Especially, the part ofthe fastening means 105 may be arranged downstream from (i.e. further away from the axis ofelongation As or center ofthe system 1 than) the bellows and the one ormore ofthe transmitter 120 and the sensor 130. The above described tubular structure equivalent circular diameter Ds, the hosting space equivalent circular diameter DH, and the expanded equivalent circular diameter DE may each be dened in a plane perpendicular to the axis ofelongation As. In embodiments, the tubular structure, when engaged with the system, may be congured in acoustic communication with the transmitter and the sensor. Especially, in an operational mode of the system, the transmitter may be congured to provide acoustic excitation radiation 121 to the tubular structure 15. In embodiments, the acoustic excitation radiation 121 may have a frequency selected from the range of 1-500 kHz. Conversely, in the operational mode ofthe system, the sensormay be congured to detect acoustic emission radiation 131 from the tubular structure 15, and to provide a related sensor signal to the control system 300. The control system may especially be congured to determine the physical parameter based on the sensor signal. Furthermore, in embodiments, the control system may be congured to execute the operational mode ofthe system. Fig. 1A schematically depicts a cross-section ofan embodiment ofthe system 1 taken in a plane parallel to (and intersecting with) the axis of elongation As. Fig. 2A schematically depicts a perspective view of an embodiment of the system 1. As depicted here, in embodiments, the hosting arrangement 110 may comprise an alignment mechanism 170. In embodiments, the alignment mechanism 170 may be congured to contact the tubular structure 15 to centralize the tubular structure 15 in the hosting space 115, especially such that the tubular structure 15 is arranged between the transmitter 120 and the sensor 130. Fig. 2B further schematically depicts some aspects of the system 1, especially in a cross-sectional plane parallel to (and intersecting with) the axis ofelongation As. As mentioned above, in embodiments, the system 1, especially the measurement device 100, may further comprise fastening means 105. As depicted here in Fig. 2B, in embodiments, the fastening means 105 may essentially be comprised by the hosting arrangement 110. Altematively, in embodiments, the fastening means 105 may be a separate component. For example, in embodiments, the fastening means 105 may comprise one ormore of a clamp or clip, a hook, a band or buckle, a string or cord, a magnet, etc. .. The fastening means 105 may especially be congured to attach the measurement device 100 to the tubular structure 15 such that the bellows 140 may be congured to provide a pressure to (or receive a compression pressure from) the tubular structure 15. Additionally or alternatively, in embodiments, the system may comprise a transceiver 125. In such embodiments, the transceiver 125 may comprise the transmitter 120 and the sensor 130. Furthermore, the transceiver 125 may comprise a transceiver contact structure for contacting the tubular structure 15. In embodiments, the transceiver 125 may be arranged between the bellows 140 and the tubular space 15. Moreover, in such embodiments, the rst end 141 of the bellows 140 may be congured to abut (especially at least partially surround) the transceiver 125. In embodiments, the combination of the bellows 140 and the transceiver 125 may herein also be referred to as a sensing arrangement 200. Hence, in embodiments, the system 1 may comprise a sensing arrangement 200 comprising the bellows 140 and the transceiver 125. Moreover, in embodiments, the system 1 may comprise a plurality of sensing arrangements 200. In such embodiments, each ofthe sensing arrangements 200 may comprise a transceiver 125 and a bellows 140. Figs. 3A-B further schematically depict cross-sections of embodiments of the system 1 taken in a plane parallel to (and intersecting with) the axis of elongation As. Especially, as depicted in g. 3A, in an embodiment, the bellows 140 may comprise a rst bellows 146 and a second bellows 147. The rst end 141 ofthe rst bellows 146may especially be arranged to abut (especially at least partially surround) the transmitter 120. Additionally, in embodiments, the rst end 141 ofthe second bellows 147 may be arranged to abut (especially at least partially surround) the sensor 130. Hence, in embodiments, as depicted in Fig. 3A, the bellows 140 may be congured (i) between the transmitter 120 and the tubular structure 15, and (ii) between the sensor 130 and the tubular structure 15. Furthermore, in embodiments, the system 1 may comprise an ambient sensor 160. The ambient sensor 160 may be congured external to the hosting arrangement 110. Especially, the ambient sensor 160 may be congured to detect one or more of a(n ambient) temperature, a(n ambient) humidity, and an (ambient) acoustic radiation. Further, in embodiments, the ambient sensor 160 may be congured to provide an ambient sensor signal to the control system 300. In further embodiments, the control system 300 may be congured to determine the physical parameter based on the sensor signal and the ambient sensor signal. Conversely, as depicted in Fig. 3B, in embodiments, the transmitter 120 may comprise a transmitter transducer 122 for contacting the tubular structure 15. Furthermore, in embodiments, the transmitter 120 may be arranged between the (rst) bellows 140 and the hosting space 115. Moreover, in embodiments, the sensor 130 may comprise a sensor transducer 132 for contacting the tubular structure 15. Furthermore, in embodiments, the sensor 130 may be arranged between the (second) bellows 140 and the tubular space 15. Hence, in such embodiments, the bellows 140 may be congured to compress the transmitter 120 and / or the sensor 130 to the tubular structure 15 (rather than be congured between the transmitter 120, sensor 130 and tubular structure 15). Furthermore, in embodiments, the tubular structure 15(, especially a tubular structure section 25 where the measurement is to be performed,) may have an (average) acoustic impedance Za. Similarly, in embodiments, the transmitter transducer 122 may have a transmitter acoustic impedance (Zt). Especially, Zt / Za may be selected from the range of 0.5 30. In further embodiments, the sensor transducer 132 may have a transmitter acoustic impedance (ZS). Especially, in embodiments, Zs / Za may be selected from the range of0.530. Yet further, in embodiments, the hosting arrangement 110 may be congured switchable between an open conguration and a closed conguration. Especially, the hosting arrangement may be congured for being placed around the tubular structure 15 in the open conguration. Furthermore, the hosting arrangementmay be congured for switching from the open conguration to the closed arrangement while placed around the tubular structure 15. In embodiments, the sound-absorbing material 111 (and the bellows 140) may be congured for physically contacting the tubular structure 15 in the closed arrangement. Further, the hosting arrangement 110 may comprise a hinge. The hinge may especially be congured to facilitate switching between the open conguration and the closed conguration. In embodiments, the tubular structure 15 may comprise a plant stem 16, such as depicted in Figs. 3A-B. Moreover, in embodiments, the physical parameter may comprise a physical plant parameter(especially a physical vessel parameter). However, in alternative embodiments, the tubular structure 15 may be selected from the group comprising a pipe, a cable, a (human or animal) ligament, etc... In another aspect, in embodiments, the invention may provide a method for monitoring a physical parameter of a tubular structure 15. In embodiments, the method may be performed using the system 1 ofthe invention. Hence, in such embodiments, the control system 300 may be congured to execute the method ofthe invention. The method may especially comprise arranging a transmitter 120 to provide acoustic excitation radiation 121 to a tubular structure section 25 of the tubular structure 15. For example, the transmitter 120 may be arranged in direct physical contact with the tubular structure 15 such as depicted in e.g. Fig. 3B. Alternatively, the transmitter 120 may be arranged such that the acoustic excitation radiation 121 may be provided via the bellows 140 to the tubular structure 15 as depicted in e.g. Fig. 3A. Additionally, themethodmay comprise arranging a sensor 120 to detect acoustic emission radiation from the tubular structure section 25 of the tubular structure 15. For example, the sensor 130 may be arranged in direct physical contact with the tubular structure 15 such as depicted in e.g. Fig. 3B. Alternatively, the sensor 130 may be arranged such that the acoustic emission radiation 121 may be provided from the tubular structure 15 via the bellows 140 to the sensor 130 as depicted in e.g. Fig. 3A. The method may thus also comprise arranging a bellows 140 to provide a pressure to (or receive a compression pressure from) the tubular structure 15. Such compression pressure may thus occur through (when engaging the tubular structure 15) compression of the bellows 140 between the tubular structure 15 and the transmitter 120 and sensor 130 (see e.g. Fig. 3A). Alternatively, the compression pressuremay occurthrough(when engaging the tubular structure 15) compression ofthe bellows 140 between the transmitter 120 and / or sensor 130 and the fastening means 105. Especially, as depicted in Fig. 3B, the compression pressuremay occurthrough (when engaging the tubular structure 15) compression ofthe bellows 140 between the transmitter 120 and / or sensor 130 and the hosting arrangement 110. Hence, in embodiments, the bellows 140 may be arranged in physical contact with one or more ofthe transmitter 120 and the sensor 130. Yet additionally, the method may comprise arranging a sound absorbing material 111 to contact the tubular structure 15 to provide an enclosed space 116. In embodiments, the enclosed space 116 may comprise the transmitter 120, the sensor 130, the bellows 140 and at least part of the tubular structure section 25. Moreover, in embodiments, the sound absorbing material 111 may be arranged in contact with the tubular structure 15. Moreover, in embodiments, the method may comprise providing acoustic excitation radiation to the tubular structure section 25 (optionally via the bellows 140) using the transmitter 120. Especially, the acoustic excitation radiation 121 may have a frequency selected from the range of 1-500 kHz. Further, in embodiments, the method may comprise detecting acoustic emission radiation 131 from the tubular structure section 25 (optionally via the bellows 140) using the sensor 130 and providing a related sensor signal. In embodiments, the method may comprise determining the physical parameter ofthe tubular structure 15 based on the sensor signal. In specic embodiments, the acoustic excitation radiation may comprise a square wave or a sine wave. Moreover, in embodiments, the acoustic excitation radiation 121 may comprise a pulse comprising a plurality of square waves and / or sine waves. In further embodiments, the acoustic excitation radiation 121 may comprise a plurality of acoustic radiation signals. Furthermore, in embodiments, the acoustic emission radiation may have a settling time (ts). In embodiments, successive acoustic radiation signals may be (temporally) separated by independently selected wait times (tw). Especially, tw-ts may be selected from the range of020 min. The acoustic excitation radiation 121 may especially be provided by the transmitter 120 and may propagate from the transmitter 120 (optionally via the bellows 140) to the tubular structure 15. For example, in embodiments, the tubular structure 15 may comprise a (vascular) plant stem 16. The plant stem may comprise plant vessels 17. Hence, in embodiments, the acoustic excitation radiation 121 may be provided to the plant vessels 17 in the plant stem 16. Physical characteristics of the plant vessels 17 may inuence the acoustic excitation radiation 121, therewith propagating a different type ofradiation further through the system 1. Especially, the plant vessels 17 of the plant stem 16 may provide the acoustic emission radiation 131, which may propagate (optionally via the bellows 140) to the sensor 130. Therefore, in embodiments, the transmitter acoustic impedance and / or the sensor acoustic impedance may be selected to provide a transmission between the transmitter transducer 121 and the sensor transducer 131 and the tubular structure 15 of at least 70%. Moreover, in embodiments, the acoustic emission radiation 131 may comprise a plurality of acoustic emission signals. The method may especially comprise providing a plurality of related sensor signals. Moreover, in embodiments, the method may comprise averaging the plurality of sensor signals to provide an averaged sensor signal. Furthermore, in embodiments, the method may comprise determining the physical parameter of the tubular structure based on the averaged sensor signal. Especially, the method may comprise determining a mean (Xa) and a standard deviation (ca) of the averaged sensor signal. Further, in embodiments, the method may comprise determining a deviation (A) from the mean (Xa) for each of the plurality of sensor signals. In further embodiments, the method may comprise determining a representative sensor signal based on a subset of sensor signals for which A 5 Ga may apply. The method may especially comprise determining the physical parameter ofthe tubular structure 15 based onthe representative sensor signal. Moreover, in embodiments, the system 1 may comprise a stent arrangement 180. As depicted in Fig. 4, in embodiments, the stent arrangement 180 may comprise (both) the bellows 140 and the alignment mechanism 170. The stent arrangement 180 may especially be congured, during the operational mode of the system 1, in physical contact with the tubular structure 15. As such, the stent arrangement 180 may be congured to protect themeasurement device 100 and the tubular structure 15 from deformation. Experiments Experiments were performed based on emitted ultrasound radiation by a tubular structure (especially plants) in response to excitation ultrasound radiation provided to the tubular structure 15 by the system 1. For example, during water-shortage in the roots and / or heavy transpiration, a water column in the xylem ofplantsmay be subjected to a large tensile stress. Beyond a critical tension, water may exist in a metastable state for a short time, which may lead to local cavitation. The stress may be released via gas-bubble nucleation. Apart from cavitation, bubble formation inside the xylem can occur through air-seeding, due to a pressure difference across the air-watermeniscus at pores onxylem cell walls. The process ofbubble formationmay result in a release ofthe elastic energy stored in the water column, a part ofwhich may be converted to acoustic emission radiation. In particular, peak frequencies may be observed across a multitude of (ultra-)sound pulses in the range 1-250 kHz, especially in the range of 10-150 kHz, which may be much lower than the theoretical resonant bubble frequencies. When the sound (i.e. the excitation ultrasound radiation provided to the tubular structure 15 by the system 1) travels through the (tubular structure 15, e.g. the) plant 16 certain frequencies may be strongly attenuated while others are not. For example, low frequency sound that attenuates through the bulk vascular tissue of a plant may be used to estimate the water content state of the plant. Similarly, higher frequencies may be related to the xylem vessels and / or other tissue. Experiment 1: Signal-to-noise experiment A solid polyvinylchloride (PVC) tube (i.e. the tubular structure 15) having a diameter of 16 mm and a height of 70 mm was placed inside the (hosting space 115 of the) system 1. For the system 1 a Murata MA40S4S ultrasound speaker (with an input voltage of 10 Vpp (i.e. volt peak-to-peak)) was used as the transmitter 120 and an Inneon IM73A or HVI69AMEMS ultrasound microphone (sampled at 500 kHz and amplied 100 times)) was used as the sensor 130. Acoustic emission radiation was recorded by sweeping (using the transmitter 120) between 20 to 100 kHz using a sine or block wave. Upon, for example, ten repetitions of the same sine sweep, the average signal was calculated. The frequency spectra ofthe measured signals were obtained via a 12500-point Discrete Fourier Transform. In one measurement, acoustic excitation radiation was provided to the tubular structure 15 using the system 1 comprising the bellows 140. In another measurement, acoustic excitation radiation was provided to the tubular structure 15 using the system 1 but without the bellows 140. Comparison ofsuch measurements showed that the inclusion ofthe bellows 140 led to a 2x higher signal to noise ratio compared to the measurement without the bellows 140. Furthermore, in the measurement including the bellows 140, the frequency peaks appeared to provide a much clearer signal, i.e. less noise was observed overall on the frequency peaks, which may be indicative of the peaks being the result of sound travelling through air alone, rather than the tubular structure 15. Hence, in measurements with a bellows 140, a larger proportion ofthe sound may pass through the tubular structure 15, thereby resulting in a higher signal to noise ratio. Experiment 2: Desiccation experiment Tomato plants were grown in three large pots with two plants (each with two stems) per pot. The plants were grown, under typical summer weather conditions (i.e. around 18-26 0C), up to three meters to simulate greenhouse conditions. Measurement of spectral power by the plants was performed using the system 1, especially, a device 100 was placed such that each of the stems of the plants engaged a respective hosting space 115 (i.e. 12 devices 100 were placed around the 12 stems). On day zero ofthe measurements all sample plants were treated equally. On day 1.5 one sample plant (referred to as D1) was dehydrated by drying out the soil. The same dehydration was applied to another sample plant (referred to as D2) on day 4.5. Sample plantDc was treated the same over time from day zero to day 8 and was used as a control. Fig. 5 schematically depicts the data retrieved from the measurements. The graph depicts the moving average ofthe (normalized) sum spectral power (PSUM in a.u., which was summed over the frequency domain of50 kHz to 140 kHz) ofthe sample plants over time (in days). As can be seen from the lines for D1 and D2 in the graph, the plant sum spectral power started to decrease around 2 days after start ofdehydration, therewith showing a signal- response indicating drought stress in the stem ofthe sample plants. Hence, experimentswere performed to determinewhether this acoustic emission radiation is indicative ofphysical parameters, especially a physical vessel parameter of a plant tissue. Simultaneously, in the early phases, other sensor data was collected. For example, a weighing scale was used to estimate how much water is in the plant. Using this reference data itmay be determined which frequencies correspond to which part ofthe plant. Hence, a (vascular) plant 16 may (spontaneously and / or upon stimulation with acoustic excitation radiation 121) emit acoustic emission radiation 131, especially from the plant vessels 17, which may be indicative of a physical vessel parameter. Analysis methods The physical parameter, especially the physical vessel parameters, may be determined from the sensor signal e.g. using the following procedures. Time of ight - Using the measurement device 100, especially the transmitter 120 and the sensor 130, a time ofight (tof) may be determined for the time that the acoustic radiation may require from being provided by the transmitter 120 to (after passing through the tubular structure 15) being detected by the sensor 130. Herein, the time of ight may be assumed as the time it takes the acoustic radiation (or ultrasound) togo through air (e.g., within the bellows) and the tubular structure by using the following sum: tof % =Ë Wherein duo is a distance between the transmitter 120 and the sensor 130 in m, Ds is the equivalent circular diameter of the tubular structure 15 in m, can is the speed of the radiation in air in m / s, and C15 is the speed ofthe sound in the tubular structure 15, e.g., in the plant, in m / s. When setting a reference temperature (T0) at zero 0C, the temperature dependence of c; may be given by: cal-r = 331.3 + 0.606 - T wherein T is the (measurement) temperature in oC. Similarly the following expression may be given for C15: 615 = % (1+a%-T) Wherein p is the tubular structure density in kg / m3 at 20 °C, K is a tubular structure bulk modulus in N / m2 at 20 °C, a is a thermal expansion coefcient determined for % in °C'1, and T is again the (measurement) temperature in °C. After implementing these formulas for Cair and C15, the formula for the time-ofight then becomes: tof=D5- / Zî-(1+a%-T)+Æä where po and Ko are the density and bulk modulus ofthe tubular structure 15 at 0 °C. Of note, the analysis steps in the above described analysis framework do not account for (i) temperature-dependence of anisotropy, (ii) anisotropy in the transverse direction, (iii) the impact ofow speed on acoustic impedance, and (iv) defects in cylindrical geometry ofthe tubular structure, as the effects thereof are expected to be minor to negligible. Acoustic impedance The acoustic impedance of the tubular structure 15 (i.e. Za) may be determined based on the transmission of acoustic radiation through the system 1 and the amount ofdamping resulting from the presence ofthe tubular structure 15. Firstly, the acoustic impedance (or transmission) Tamis ofthe sound path from air to the tubular structure 15 may be dened by: ZZa Tair,15 =m where Za is the (average) acoustic impedance of the tubular structure in kg / (m2*s) and Zair is the (average) acoustic impedance ofthe air in kg / (m2*s). Conversely, the acoustic impedance (or transmission) T15,a11 of the sound path from the tubular structure 15 to airmay be dened by: ZZair T15air =Z-lT a cur where Za is the (average) acoustic impedance of the tubular structure in kg / (m2*s) and Zair is the (average) acoustic impedance ofthe air in kg / (m2*s). The full path ofthe sound may thus be represented by: Tsound = Tair,15 ' T15air Implementing the above formulas into the formula for Tsound results in: 4 ' Za ' Zair Tsound =2 (Za + Zair) An input sound pressuremay be dened using: A130 Tsound =Æ where A130 refers to a relative sound pressure provided by the sensor 130 and A120 refers to a relative sound pressure provided by the transmitter 120. To determine the input sound pressure a reference measurement may be performed where (i) no tubular structure 15 is provided in the system 1 and (ii) the impedance is known (or optionally a reference object with a known impedance is provided in the system 1). Using such a reference measurement one can determine the input sound pressure as follows: Tref =î130mef : 4 ' Zref ' Zair2 120,ref (Zref + Zair) where A130 refers to a relative sound pressure provided by the sensor 130 in the reference measurement and A120 refers to a relative sound pressure provided by the transmitter 120 in the reference measurement. The above formula may be rewritten to provide the input sound pressure as: A120,ref = A130,ref'M ref air Adding this input sound pressure in the abovementioned formula for Tsound one obtains the following formula from which the (average) acoustic impedance Za of the tubular structure 15 can be extracted: A130 (Zref +Zair)2 _ 4 ' Za ' Zair A ' 41 -Z _ (za +Z)Z Of note, the analysis steps in the above described analysis framework do not account for the impact ofow speed on acoustic impedance, as the effects thereof are expected to be minor to negligible Bulk resonance The system 1 may be applied to determine the tubular structure 15 equivalent circular diameter Ds, based on bulk resonance. Therefore, a bulk mode of the tubular structure equivalent circular diameterDs may be equated to the wavelength ofthe bulk mode as follows: %. = i,. =f where kn is the mode number, ? is the wavelength at the respective mode, C15 is the speed ofthe sound in the tubular structure 15, and fbulk,n is the bulk resonance frequency for the respective mode. It may be clear to the skilled person that a compensation factor may be used in the above formula to compensate for the shape of the tubular structure 15 in case the tubular structure 15 is not (perfectly) cylindrical. Finally, the tubular structure 15 equivalent circular diameter Ds may be extracted, using the above dened formulas for Cair and C15, from the following denition: & _ = C15 tof d D5 Of note, the analysis steps in the above described analysis framework do not account for a frequency shift due to damping, as the effects thereof are expected to be minor to negligible Ä Assuming that the rst mode (i.e. kn = 1) is visualized in the measurements using the system 1, a xylem transverse resonance may be dened by: E = (LZ - (4 - 7T ' f1transverse 'W)? R where E is a Youngs modulus (of the xylem), L is the length of the tubular structure 15, f1transverse is the resonance frequency oftransverse vibrations, pxylem is the density ofthe xylem at 20 °C, andR is the radius ofthe tubular structure 15. The time-domain damping in the (radially recorded) ultrasound may be dominated by the viscosity (Tlsolid) in the solid matter of the tubular structure 15 (e.g. a plant comprising a cell wall, xylem bres, cambium, and other vascular tissues). Such a system may be modeled as a linearMaxwell material and Tlsolid may be obtained from the settling time rs of the pulse amplitude as: Another example of an analysis method may be to measure the total power (or sum spectral power) in all frequencies (e.g. over a frequency domain from 0-250 kHz, such as from 5-100 kHz, especially from 20-100 kHz) ofthe sensor signal, or as described above the sum spectral power over a frequency domain from 50 kHz to 140 kHz. This total power may be used to obtain information about the mass of the tubular structure 15 in between the transmitter 120 and the sensor 130, as more mass attenuates the signal more. The term plurality refers to two or more. Furthermore, the terms a plurality of and a number of may be used interchangeably. The terms substantially or essentially herein, and similar terms, will be understood by the person skilled in the art. The terms substantially or essentially may also include embodiments with entirely, completely, all, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term substantially or the term essentially may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. Moreover, the terms about and approximately may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. For numerical values it is to be understood that the terms substantially, essentially, about, and approximately may also relate to the range of90% - 110%, such as 95%-105%, especially 99%-101% ofthe values(s) it refers to. The term comprise also includes embodiments wherein the term comprises means consists of. The term and / or especially relates to one or more of the items mentioned before and after and / or. For instance, a phrase item 1 and / or item 2 and similar phrases may relate to one or more ofitem 1 and item 2. The term "comprising" may in an embodiment refer to "consisting of' but may in another embodiment also refer to "containing at least the dened species and optionally one or more other species". Furthermore, the terms rst, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable ofoperation in other sequences than described or illustrated herein. The devices, apparatus, or systems may herein amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation, or devices, apparatus, or systems in operation. The term further embodiment and similar terms may refer to an embodiment comprising the features of the previously discussed embodiment, but may also refer to an alternative embodiment. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope ofthe appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the Claim. Use ofthe verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a Claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words comprise, comprising, include, including, contain, containing and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense ofincluding, but not limited to. The article "a" or "an" preceding an element does not exclude the presence ofa plurality ofsuch elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device Claim, or an apparatus Claim, or a system claim, enumerating several means, several ofthese means may be embodiedby one and the same item ofhardware. Themere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination ofthese measures cannot be used to advantage. The invention also provides a control system that may control the device, apparatus, or system, or thatmay execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements ofsuch device, apparatus, or system. The invention further applies to a device, apparatus, or system comprising one or more ofthe characterizing features described in the description and / or shown in the attached drawings. The invention further pertains to a method or process comprising one or more ofthe Characterizing features described in the description and / or shown in the attached drawings. Moreover, ifa method or an embodiment ofthe method is described being executed in a device, apparatus, or system, it will be understood that the device, apparatus, or system is suitable for or congured for (executing) the method or the embodiment ofthe method, respectively. The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some ofthe features can form the basis for one or more divisional applications.

Claims

1. A system (1) for monitoring a physical parameter of a tubular structure (15), where the system (1) is a measuring device (100) and includes a control system (300), where the measuring device (100) fasteners (105), a transmitter (120), a sensor (130) and a bellows (140) includes, where the bellows (140) are physically coupled to one or more of the transmitters (120) and the sensor (130) is configured, and where the fasteners (105) configured to the measuring device (100) on the tubular to secure structure (15) so that the bellows (140) is configured to apply pressure to supply the tubular structure (15), with the control system (300) is configured to execute an operational mode, where in the operating mode: - the transmitter (120) is configured to acoustic excitation radiation (121) to provide the tubular structure (15), whereby the acoustic excitation radiation (121) a frequency selected from the range of 1-500 kHz has, - the sensor (130) is configured to acoustic emission radiation (131) to detect originating from the tubular structure (15) and a related to provide sensor signal to the control system (300), and - the control system (300) is configured to the physical to determine parameter based on the sensor signal.

2. The system (1) according to conclusion 1, whereby the system (1) further includes a housing arrangement (110), where the housing arrangement (110) includes at least part of the transmitter (120), the sensor (130) and the bellows (140), where the housing arrangement (110) is configured to a to define accommodation space (115) for housing the tubular structure (15).

3. System (1) according to conclusion 2, where the accommodation arrangement (110) a sound-absorbing material (111) includes that for physical contact with the tubular structure (15) is configured, where the sound-absorbing material (111) is configured to define the housing space (115).

4. The system (1) according to conclusion 3, where the sound-absorbing material (111) includes a compressible material that is selected from the group comprising a foam, a polymer, a compressible liquid, a rubber, a gel and a composite material, where the tubular structure (15) has an equivalent circular diameter (Ds), where the housing space (115) has an equivalent circular diameter (DH) has, and where DH / Ds is selected from the range of 0.1 - 0.

9.

5. The system (1) according to one of the preceding conclusions 3-4, where the sound-absorbing material (111) is configured to to attenuate ambient noise by an amount within the range of 3 - 40 dB has been selected 6. The system (1) according to one of the preceding conclusions, whereby the bellows (140) has a spring constant in the range of 10 - 10000 N / m has been selected 7. The system (1) according to one of the preceding conclusions, whereby the bellows (140) has a first end (141) and a second end (142), where the first end (141) is configured to connect to the transmitter (120) and / or the sensor (130) to connect, and where the second end (142) is configured to make contact dealing with the tubular structure (15).

8. The system (1) according to conclusion 7, where the bellows (140) a first bellows (146) and a second bellows (147) comprising the first end (141) of the first bellows (146) is designed to connect to the transmitter (120), and where the first end (141) of the second bellows (147) is designed to connect close on the sensor (130).

9. The system (1) according to conclusion 7, where the system a transceiver (125) comprises, where the transceiver (125) the transmitter (120) and the sensor (130) comprises, and where the first end (141) the transceiver (125) surrounds at least partially.

10. The system (1) according to one of the preceding conclusions 1-6, where the tubular structure has an acoustic impedance Za, and where one or more of the following applies: - the transmitter (120) includes a transmitter converter (122) for the contacting the tubular structure (15), where the transmitter (120) between the bellows (140) and the accommodation space (115) have been fitted, whereby the transmitter converter (122) has an acoustic transmitter impedance (Zt), where Zt / Za is selected from the range of 0.5 - 30, - the sensor (130) includes a sensor converter (132) for the contacting the tubular structure (15), placing the sensor (130) between the bellows (140) and the tubular space (15) are fitted, whereby the sensor transducer (132) has an acoustic sensor impedance (ZS), where Zs / Za is selected from the range of 0.5 - 2.

11. The system (1) according to one of the preceding conclusions, whereby the acoustic excitation radiation comprises a square wave or a sine wave.

12. The system (1) according to one of the preceding conclusions, whereby the system (1) includes an ambient sensor (160), where the ambient sensor (160) is externally configured relative to the housing arrangement (110), where the ambient sensor (160) is configured to one or more of a to detect temperature, humidity and acoustic radiation, whereby the ambient sensor (160) configured to send an ambient sensor signal to the to supply control system (300), and where the control system (300) is configured to based on the sensor signal and the to determine the physical parameter ambient sensor signal.

13. The system (1) according to one of the preceding conclusions, whereby the tubular structure (15) encloses a plant stem (16), and where the physical parameter includes a physical plant parameter.

14. The system (1) according to one of the preceding conclusions, whereby the housing arrangement (110) includes an alignment mechanism (170), where the alignment mechanism (170) is configured to make contact with the tubular structure (15) to the tubular structure (15) in the to centralize housing space (110).

15. The system (1) according to claim 14, where the system (1) a stent arrangement (180) includes, where the stent arrangement (180) the bellows (140) and the alignment mechanism (170) includes.

16. A method for monitoring a physical parameter of a tubular structure (15), the method of which involves: - arranging (a) a transmitter (120) to acoustic excitation radiation (121) to a tubular structure section (25) of the tubular structure (15) to provide, (b) a sensor (130) to acoustic emission radiation (131) from the tubular structure section (25) of the tubular structure (15) to detect, and (c) a bellows (140) to apply pressure to the to supply tubular structure (15), and (d) a sound-absorbing material (111) to make contact with the tubular structure (15) to a closed to provide space (116), whereby the enclosed space (116) the transmitter (120), the sensor (130), the bellows (140) and at least part of the tubular structural section (25) includes, where the sound-absorbing material (111) in contact with the tubular structure (15) is arranged, and where the bellows (140) in physical contact with one or more of the transmitter (120) and the sensor (130) is ranked, - providing acoustic excitation radiation (121) to the tubular structure part (25) using the transmitter (120), where the acoustic excitation radiation (121) has a frequency that is in the range of 1- 500 kHz is selected, - detecting acoustic emission radiation (131) from the tubular structure section (25) using the sensor (130) and the providing a related sensor signal, and - determining the physical parameter of the tubular structure based on the sensor signal.

17. The method according to conclusion 16, whereby the acoustic excitation radiation (121) comprises a multitude of acoustic radiation signals, where the acoustic emission radiation has a setting time (ts), and where successive acoustic radiation signals by independently selected wait times (tw) are separated, where tw-ts are in the range of 0 - 20 min has been selected 18. The method according to one of the conclusions 16-17, whereby the acoustic emission radiation (131) a multitude of acoustic emission signals includes, whereby the method involves providing a multitude of related includes sensor signals, where the method further involves averaging the multiple includes sensor signals to provide an average sensor signal, and where the method involves determining, based on the average sensor signal, includes the physical parameter of the tubular structure (15).

19. The method according to claim 18, where the method the determining an average (Xa) and a standard deviation (oa) of the average sensor signal comprises, where the method of determining a deviation (A) from the mean (Xa) for each of the multiples of includes sensor signals, where the method based on a subset of sensor signals for which A5 Ga applies determining a representative sensor signal includes, and where the method based on the representative sensor signal determining the physical parameter of the tubular structure (15) involves.

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