Abstract: A system includes a vibration detector to detect a location of vibration and identify a frequency of the vibration. The system also includes a controller to generate audio corresponding to the frequency of vibration detected by the vibration detector and one or more speakers configured to provide the audio as directional sound.

Abstract: Inductive position sensors for sensing relative position (e.g., relative rotary position) between members are provided. In one example implementation, the inductive position sensor includes a transmit aerial having at least one transmit winding. The inductive position sensor can include a receive aerial having one or more receive windings. The inductive position sensor can include a coupling element operable to be disposed on the second member. The inductive position sensor can include processing circuitry configured to provide one or more signals indicative of the position of the first member relative to the second member based on current induced in the one or more receive windings resulting from an oscillating signal provided to the transmit winding. The inductive position sensor includes at least one electrostatic shield. The electrostatic shield can include a plurality of conductive traces arranged so that no current loops are formed in the electrostatic shield.

Abstract: A calibration apparatus for calibrating a laser Doppler vibrometer includes: a frequency shifter stage that: receives, from the laser Doppler vibrometer, primary laser light; produces frequency shifted light; communicates the frequency shifted light to a reflector; receives frequency shifted light reflected by the reflector; produces secondary light; and communicates the secondary light to the laser Doppler vibrometer, such that the laser Doppler vibrometer receives the secondary light from the frequency shifter stage and produces a synthetic velocity shift from the secondary light; and the reflector that receives and reflects the frequency shifted light back to the frequency shifter stage.

Abstract: Ultrasonic sensor (1) includes piezoelectric element (7), first acoustic matching layer (2), and second acoustic matching layer (5) which are laminated and bonded together, piezoelectric element (7) having a rectangular bonding surface. First acoustic matching layer (2), which is adjacent to piezoelectric element (7), is bonded to piezoelectric element (7) using thermoplastic resin injected from a thickness direction of first acoustic matching layer (2) in a manner that a flow direction of the thermoplastic resin matches a longitudinal direction of piezoelectric element (7). With this configuration, ultrasonic sensor (1) that exhibits excellent temperature characteristics against such as thermal shock is provided.

Abstract: The present invention a sparse optimization method based on cross-shaped three-dimensional imaging sonar array, comprising the following steps: first, constructing a beam pattern simultaneously applicable to a near field and a far field based on a cross-shaped array; then, constructing an energy function required by sparse optimization according to the beam pattern; then, introducing an array element position disturbance into a simulated annealing algorithm to increase the degree of freedom of the sparse process and increase the sparse rate of the sparse array, and using the simulated annealing algorithm to sparse optimization of the energy function; finally, after optimization, a sparse optimization cross-shaped array is obtained. The present invention ensures that the three-dimensional imaging sonar system has the desired performance at any distance, and greatly reduces the hardware complexity of the system.

Abstract: Embodiments provide a method for transmitting data from a user terminal to another apparatus. The method has a step of generating a signal for driving an electromagnetic actuator of a loudspeaker of the user terminal, and a step of driving the electromagnetic actuator by the generated signal to produce, by the electromagnetic actuator, a magnetic field which carries the data.

Abstract: Aspects of the present disclosure describe DFOS/DAS systems, methods, and structures that employ active microphones to enhance DAS operational capabilities by using an active circuit to amplify acoustic signals including voice(s). The circuit includes a microphone to collect acoustic signal(s) resulting from voice signals in the environment, and a speaker or a vibration device driven by an amplifier. The circuit can be clipped onto the fiber, with direct contact through the speaker or vibration device. A microcontroller may advantageously be employed to control the circuit for reduced power consumption, by detecting activities locally and only enabling the speaker when needed. The microcontroller may also send other information such as battery status to the DFOS interrogator through vibration codes.

Abstract: The present invention relates to a liquid information sensor comprises at least more than one electrode set including a first electrode, and a second electrode which is disposed spaced apart from the first electrode and to which an alternating current signal is applied between the first electrode and the second electrode; and a ferroelectric layer including a first side in contact with the first electrode and the second electrode and a second side facing the first side and defining a receiving area for receiving the target liquid, and generating sound waves by physical vibration when the AC signal is applied.

Abstract: Disclosed herein a method of producing an ultrasound that includes defining a set of criteria for an ultrasound emitter comprising a plate. The set of criteria includes a power output criterion, a frequency criterion and number of nodes for a resonance mode of the plate, a focus criterion, and a durability criterion. The method includes determining an outline and a thickness range for the plate, based on the set of criteria. The method includes using topology optimization to determine internodal zone dimensions for the plate, based on the set of criteria, the outline, and the thickness range. The method includes manufacturing the plate according to the internodal zone dimensions.

Abstract: A shield member electromagnetically shielding at least part of an electric circuit has a first end and a second end. The first end is configured to be constantly connected to a ground wire to electromagnetically shield at least part of the electric circuit; and the second end is configured to be selectively connectable to a power source, the shield member being configured to generate heat when energized while the second end is connected to the power source. Accordingly, the shield member electromagnetically shielding at least the part of the electric circuit can serve as a heater for preventing freezing and snow attachment.

Abstract: In circuitry for applying a pulse train to excite a transducer, the circuitry selects a first set having a first number of pulses at a first frequency and a second set of pulses having a second number of pulses at a second frequency differing from the first frequency. At least one pulse from the first set is located in the pulse train between one or more of the pulses at the second frequency.

Abstract: A device may include an inner layer comprising a polyvinylidene fluoride (PVDF) material. The device may also include a first interface layer, disposed on a first side of the inner layer, and a second interface layer, disposed on a second side of the inner layer. The first interface layer and the second interface layer may comprise a mixture of PVDF material and a scavenger component.

Abstract: The ultrasonic image pickup apparatus includes a transmission/reception control unit that transmits an ultrasonic wave by applying a DC bias voltage and an AC driving voltage between electrodes of the electrostatic capacity type micro-machined ultrasonic transducer and picks up an image by transmitting and receiving two or more kinds of ultrasonic waveforms which have different signs, amplitudes, or phases from each other for one scanning line. In addition, as the AC driving voltage, the ultrasonic image pickup apparatus uses a voltage waveform that is obtained by adding a high frequency pulse waveform and a low frequency waveform that has a longer cycle than that of the high frequency pulse waveform and has such a voltage amplitude as makes the total voltage of the low frequency waveform and the DC bias voltage is equal or smaller than a pull-in voltage.

Abstract: An embodiment of a system includes a light source, an optical assembly, and an electronic circuit. The light source (e.g., a laser) is configured to generate a source optical signal. The optical assembly is configured to direct the source optical signal into an end of an optical-fiber assembly that includes an optical fiber having a section wrapped multiple turns around a mandrel and including mandrel zones, and to receive, from the end of the optical-fiber assembly, a return optical signal. The electronic circuit is configured to select at least one mandrel zone in response to a component of the return optical signal from the at least one mandrel zone, and to detect an acoustic signal incident on the mandrel in response to the component of the return optical signal.

Abstract: An MEMS microphone is provided, comprising a first substrate and a vibration diaphragm supported above the first substrate by a spacing portion, the first substrate, the spacing portion, and the vibration diaphragm enclosing a vacuum chamber, and a static deflection distance of the vibration diaphragm under an atmospheric pressure being less than a distance between the vibration diaphragm and the first substrate, wherein: one of the vibration diaphragm and the first substrate is provided with a magnetic film, and the other one of the vibration diaphragm and the first substrate is provided with a magnetoresistive sensor cooperating with the magnetic film, the magnetoresistive sensor being configured to sense a change in a magnetic field of the magnetic film during a vibration of the vibration diaphragm and output a varying electrical signal.

Abstract: A metal strip and a coil coating process for multilayer coating of an endless metal strip are disclosed in which a curable polymer primer is applied to a flat side of the metal strip with the aid of a roller application in order to form an electrically insulating primer layer, a curable polymer varnish is applied to this primer layer with the aid of a roller application and cured in order to form an electrically insulating varnish layer, and at least one electric conductor layer is printed at least in some areas between the primer layer and the varnish layer. In order to enable a stable and inexpensive electrical functionalization of a metal strip, it is proposed that an electrically polarizable layer be applied to at least some regions of the electric conductor layer and that the electric conductor layer and electrically polarizable layer be applied by means of a wet-on-wet process.

Abstract: Disclosed herein is an ultrasonic probe for acquiring an ultrasound image. The ultrasound probe includes a transducer configured to be movable, a cap configured to transmit an ultrasound signal generated by the transducer to outside, and an impact mitigating member disposed along a circumference of the cap to protect the cap from an external impact.

Abstract: Various approaches for calibrating the geometry of an ultrasound transducer having multiple transducer elements include providing an acoustic reflector spanning an area traversing by multiple beam paths of ultrasound waves transmitted from all (or at least some) transducer elements to a focal zone; causing the transducer elements to transmit the ultrasound waves to the focal zone; measuring reflections of the ultrasound waves off the acoustic reflector; and based at least in part on the measured reflections, determining optimal geometric parameters associated with the transducer elements.

Abstract: The invention provides an integrated output line and an antenna system using the same. The integrated output line includes a jacket, a power supply line, and a signal output line. The power supply line and the signal output line are disposed through the jacket. The power supply line and the signal output line are combined and output through the jacket. Thus, the generation of gaps between the two lines caused by the two lines in separate wiring is avoided, thereby the water resistance is improved and the installation of the lines after combination becomes easier, which is time-saving and labor-saving. The antenna system using the integrated output line further includes an antenna, an antenna amplifier, and a power source module. The antenna, the antenna amplifier, and the signal output line are connected in sequence. The antenna amplifier, the power source module, and the power supply line are connected in sequence.

Abstract: According to one embodiment, a sensor includes a supporter, a first film portion, a first sensing element, and a first magnetic portion. The first film portion is supported by the supporter, is deformable, and includes a first fixed end extending along a first fixed end direction. A first sensing element is fixed to the first film portion, and includes a first magnetic layer, a first opposing magnetic layer provided between the first magnetic layer and the first film portion, and a first intermediate layer provided between the first magnetic layer and the first opposing magnetic layer. A direction from the first opposing magnetic layer toward the first magnetic layer is aligned with a first element direction. The first magnetic portion includes a first end portion extending along a first end portion direction tilted with respect to the first fixed end direction, and overlaps a portion of the supporter.

Abstract: Systems and methods for simulating an effect of multiple seismic sources concurrently on a geologic formation are provided. Data is read from a seismic source file that describes at least two seismic source types. The concurrent propagation of acoustic energy from the at least two seismic sources types through the geologic formation is modeled. A seismic output file is then generated.

Abstract: An electro-acoustic system for downhole telemetry employs a series of communications nodes spaced along a string of casing within a wellbore. The nodes allow wireless communication between transceivers residing within the nodes and a receiver at the surface. The transceivers provide node-to-node communication up a wellbore at high data transmission rates for data indicative of fluid flow within the wellbore. A method of monitoring the flow of fluid within a wellbore uses a plurality of data transmission nodes situated along the casing string sending signals to a receiver at the surface. The signals are then analyzed.

Abstract: A system includes an ultrasound measurement probe. The ultrasound measurement probe includes a lower portion. The lower portion includes a delay block, an array of ultrasound transducers coupled to the delay block, and a first circuit board. The first circuit board further includes a first plurality of pins coupled to the array of ultrasound transducers. The ultrasound measurement probe also includes an upper portion removably coupled to the lower portion. The upper portion includes a second circuit board. The second circuit board further includes a second plurality of pins configured to couple with the first plurality of pins when the upper portion is removably coupled to the lower portion.

Abstract: A system configured to attach a functional measurement or detection body to a vehicle bodywork part, the system including a support having a means for attaching to the functional body, and an interface configured to fasten the support to the bodywork part, the support and the fastening interface being assembled and fitted to one another using grooves.

Abstract: Coated optical fibers and uses of such fibers as sensors in high temperature and/or high pressure environments. The coated optical fiber has improved sensing properties at elevated pressure and/or temperature, such as enhanced acoustic sensitivity and/or a reduced loss in acoustic sensitivity. The use of the coated optical fibers in various sensing applications that require operation under elevated pressure and/or temperature, such as, acoustic sensors for various geological, security, military, aerospace, marine, and oil and gas applications are also provided.

Abstract: The invention relates to a coupling element for acoustically coupling a sound transducer to a body for transmitting high-frequency structure-borne noise from the sound transducer to the body and/or from the body to the sound transducer, wherein the coupling element includes a deformable contact region for positively contacting the body.

Abstract: Various embodiments include methods, apparatus, and systems to operate a tool downhole in a well, where the tool has sensing system to determine different properties of downhole structures. Such an apparatus can include a received signal that is input to a beam splitter with 5 a local oscillator signal. The beam splitter outputs light signals to first and second photodetectors that convert the respective signals to electrical signals. The electrical signals are input to differential amplifier that generates an amplitude representative of the phase difference between the two input signals. A feedback path converts that 10 amplitude to a phase adjustment signal that is couple to the local oscillator.

Abstract: The disclosure is directed to a device that includes a multi-layered porous display that permits the passage of sound through the display, while avoiding dead-spots that produce no light. Embodiments of the invention include a display that has first porous layer overlaying a second porous layer. The pores of each layer do not align so that light cannot pass directly through pores of each layer. In this way, a user may not view the pores of the second layer through the pores of the first layer. Further, because the first layer is backed by a second layer, the image displayed will be viewable through the pores of the first layer and, thus, a user will not perceive the pores of the first layer.

Abstract: A system for downhole telemetry is provided herein. The system employs a series of communications nodes spaced along a tubular body either above or below ground, such as in a wellbore. The nodes allow for wireless communication between one or more sensors residing at the level of a subsurface formation or along a pipeline, and a receiver at the surface. The communications nodes employ electro-acoustic transducers that provide for node-to-node communication along the tubular body at high data transmission rates. A method of transmitting data in a wellbore is also provided herein. The method uses a plurality of data transmission nodes situated along a tubular body and a specially configured network to accomplish a wireless transmission of data along the wellbore using acoustic energy.

Abstract: A fiber optic sensor for detecting an excitation in proximity to a fiber optic assembly, the excitation inducing a modulation of the phase of an optical signal propagating in the fiber optic assembly, the sensor comprises: a laser assembly emitting at least one laser beam; a fiber optic assembly; an optical system configured to: inject at least one portion of the laser beam; generate at least one laser signal beam issued from the laser beam injected into and propagated in the fiber assembly; generate at least one reference beam from the laser beam or the signal beam; produce at least one interference zone corresponding to the interference between a portion of the reference beam and a portion of the interference signal beam corresponding to the interference between a portion of the reference beam and a portion of the signal beam; a digital holography assembly comprising: a liquid-crystal spatial light modulator; a video camera configured to receive the interference zone and to transcribe it electrically to the

Abstract: A fiber optic sensor system for measuring electric currents, such as the associated with geomagnetic disturbances and electromagnetic pulses. A fiber optic sensor system is disclosed including at least one light source, one or more first optical fibers having a first end arranged to receive light from the light source(s) and transmit the light to at least one of the sensor, and one or more second optical fibers arranged to receive reflected light from the fiber optic sensors and transmit the reflected light to a light sensing element. Using the sensors and the system, it is possible to measure currents within a structure of interest, such as upon the grounded neutral of an electric power transformer, take multiple measurements of current at the same piece of equipment or at multiple locations, or measure current and other physical phenomena on separate materials or structures.

Abstract: Systems and methods for manufacturing laser-perforated nanoreinforced materials are disclosed. A honeycomb core may utilize a perforated top sheet and a microperforated overlay film coupled to the perforated top sheet. The perforated top sheet and/or the microperforated film may include thermally conductive nanomaterials. The perforations in the top sheet and the microperforations in the film may be laser drilled. The nanomaterials may dissipate heat generated by the laser drilling, allowing for increased perforation speeds.

Abstract: Micromachined ultrasonic transducers integrated with complementary metal oxide semiconductor (CMOS) substrates are described, as well as methods of fabricating such devices. Fabrication may involve two separate wafer bonding steps. Wafer bonding may be used to fabricate sealed cavities in a substrate. Wafer bonding may also be used to bond the substrate to another substrate, such as a CMOS wafer. At least the second wafer bonding may be performed at a low temperature.

Abstract: A system for downhole telemetry is provided herein. The system employs a series of communications nodes spaced along a tubular body either above or below ground, such as in a wellbore. The nodes allow for wireless communication between one or more sensors residing at the level of a subsurface formation or along a pipeline, and a receiver at the surface. The communications nodes employ electro-acoustic transducers that provide for node-to-node communication along the tubular body at high data transmission rates. A method of transmitting data in a wellbore is also provided herein. The method uses a plurality of data transmission nodes situated along a tubular body to accomplish a wireless transmission of data along the wellbore using acoustic energy.

Abstract: A transducer subassembly with combined imaging and therapeutic capabilities is disclosed. The subassembly includes heat sinks that are configured to maintain the transducer at a low operating temperature so that the transducer operates at high efficiency and also can handle a wider range of frequencies. The subassembly is also configured to allow cooling fluid to flow past the transducer element. One heat sink in the subassembly also acts as an acoustic matching layer and another heat sink acts as a backing Alternatively, the second heat sink which acts as a backing is optional. The transducer is configured to transmit at one power level for imaging, and at a second power level for ablating. The transducer may comprise sub-elements transmitting at different power levels. The subassembly may be operated at one power level for imaging and a second power level for ablating.

Abstract: Piezoelectric micromachined ultrasonic transducer (pMUT) arrays and techniques for frequency shaping in pMUT arrays are described, for example to achieve both high frequency and low frequency operation in a same device. The ability to operate at both high and low frequencies may be tuned during use of the device to adaptively adjust for optimal resolution at a particular penetration depth of interest. In embodiments, various sizes of piezoelectric membranes are fabricated for tuning resonance frequency across the membranes. The variously sized piezoelectric membranes are lumped together by two or more separate electrode rails, enabling independent addressing between the two or more subgroups of sized transducer elements. Signal processing of the drive and/or response signals generated and/or received from each of the two or more electrode rails may achieve a variety of operative modes for the device, such as a near field mode, a far field mode, and an ultra wide bandwidth mode.

Abstract: Even when electroacoustic conversion elements with high nonlinearity are employed, a nonlinear imaging is carried out with extracting more nonlinear components. An ultrasonic wave beam is transmitted twice from the transmitter to an identical position on the imaging target, and the signal processor performs computation on the reception signals obtained in every transmission performed twice, thereby extracting a nonlinear component included in the reception signals. In one transmission out of the transmission performed twice, the transmitter delivers the transmission signal to all of multiple electroacoustic conversion elements for driving the electroacoustic conversion elements, and in the other transmission, the transmission signal is delivered selectively only to a part of the multiple electroacoustic conversion elements for driving the electroacoustic conversion elements.

Abstract: A waveguide includes: a dielectric including two surfaces, an electric field intersecting with the two surfaces; metal-plating layers coating the two surfaces of the dielectric, the electric field intersecting with the two surfaces; and a protective layer coating a periphery of the dielectric including the two surfaces coated with the metal-plating layers. A wireless transmission system includes: a sender configured to send a high-frequency signal; and a receiver configured to receive the high-frequency signal. The waveguide is used as a waveguide configured to transmit the high-frequency signal between the sender and the receiver in the wireless transmission system.

Abstract: Embodiments disclosed herein include a device with an integrated acoustics function that includes a patterned touch screen cover, an acoustic thin film, a plurality of electrodes, and a substrate. In some embodiments, the substrate is coupled to the acoustic thin film and reduces heat loss from the acoustic thin film through the substrate. The acoustic thin film may be coupled to the patterned touch screen cover and conducts an oscillating electrical current provided by the plurality of electrodes, thereby acting as a nano-scale acoustic generator. In still some embodiments, the patterned touch screen cover provides an array of microspeakers and a viewing area, where the array of microspeakers is disposed around a perimeter of the patterned touch screen cover.

Abstract: A method of manufacturing a cosmetic product for regenerating a skin cell including generating a water into a magnetized hexagonal water through a magnetized hexagonal water generator, separating a body fat stem cell from a body skin through a first extractor to extract a natural protein from a culture medium of a stem cell including the adipose-derived stem cell, extracting at least one skin beneficial ingredient from the culture medium of the stem cell through a second extractor, extracting a plant extract from at least one plant of a pomegranate, red ginseng, liquorice, ginseng seed, milk vetch, poria cocos, scutellaria, portulaca oleracea, pleuropterus multiflorus, angelica, angelica tenuissima, coix, codonopsis, morus alba and cucumber, and mixing the magnetized hexagonal water, natural protein, the at least one skin beneficial ingredient and the at least one plant extract through a mixer to manufacture a cosmetic product for regenerating a skin cell.

Abstract: The present invention generally relates to high frequency piezoelectric crystal composites, devices, and method for manufacturing the same. In adaptive embodiments an improved imaging device, particularly a medical imaging device or a distance imaging device, for high frequency (>20 MHz) applications involving an imaging transducer assembly is coupled to a signal imagery processor. Additionally, the proposed invention presents a system for photolithography based micro-machined piezoelectric crystal composites and their uses resulting in improved performance parameters.

Abstract: Provided is a capacitive transducer having broadband frequency characteristics. The capacitive transducer includes an element which has multiple kinds of cells, each cell including: a first electrode; a vibrating film including a second electrode, the second electrode being opposed to the first electrode with a gap; and a support portion that supports the vibrating film so as to form the gap. The multiple kinds of cells have different ratios of an area of one of the first electrode and the second electrode to an area of the gap when viewed from a normal direction of the vibrating film. The first electrodes or the second electrodes in the multiple kinds of cells are electrically connected together.

Abstract: An actuation system for generating a physical effect, the system comprising at least one array of translating elements each constrained to travel alternately back and forth along a respective axis, toward first and second extreme positions respectively, in response to activation of first and second forces respectively; and a controller operative to use the first and second forces to selectably latch at least one subset of said translating elements into the first and second extreme positions respectively.

Abstract: A photoacoustic wave measurement device includes a pulsed-light outputter, an arrangement member and a photoacoustic wave detector. The pulsed-light outputter outputs a pulsed light. The arrangement member is disposed between a pulsed-light output end of the pulsed-light outputter and a measurement object, the arrangement member being adapted to allow the pulsed light to pass therethrough. The photoacoustic wave detector receives a photoacoustic wave generated by the measurement object by the pulsed light and converts the photoacoustic wave into an electric signal. The photoacoustic wave detector is farther from the measurement object than the pulsed-light output end. The arrangement member has such a sufficient thickness that noise to be detected by the photoacoustic wave detector after a start time of detection of the photoacoustic wave starts to be detected after an end time of the detection of the photoacoustic wave.

Abstract: An actuation system for generating a physical effect, the system comprising at least one array of translating elements each constrained to travel alternately back and forth along a respective axis, toward first and second extreme positions respectively, in response to activation of first and second forces respectively; and a controller operative to use the first and second forces to selectably latch at least one subset of said translating elements into the first and second extreme positions respectively.

Abstract: Disclosed is an ultrasound probe which outputs ultrasound on a basis of a drive signal which is to be received. The ultrasound probe including a composite piezoelectric layer in which a piezoelectric material and a polymer material are arranged alternately in a one-dimensional array or in a two-dimensional array, an acoustic reflection layer which has an acoustic impedance higher than an acoustic impedance of the composite piezoelectric layer and an adhesion layer which bonds the composite piezoelectric layer and the acoustic reflection layer wherein in a bonding surface of the composite piezoelectric layer that bonds with the acoustic reflection layer, a polymer material part is concaved in a direction opposite to an acoustic reflection layer side comparing to an piezoelectric material part.

Abstract: A miniature speaker is disclosed. The miniature speaker includes a frame providing a receiving space, a magnetic circuit accommodated in the receiving space, a voice coil, a membrane activated by the voice coil for generating sounds, a number of contacts for electrically connected to the voice coil, and a front cover for fixing the membrane to the frame. The front cover includes an outer ring and a top cover coupled with the outer ring. The top cover includes a step engaging with the outer ring. By virtue of the configuration of the front cover, the assembling precision of the outer ring and the top cover is ensured, and the thicknesses of the outer ring and the top cover are maintained for providing sufficient strength.

Abstract: A method for producing an ultrasonic sensor for a motor vehicle is disclosed. The method involves providing a sensor housing, a membrane for emitting and/or receiving ultrasonic signals, and a decoupling element, which is arranged between the sensor housing and the membrane, the decoupling element being injection-moulded onto an inner surface of the sensor housing and the membrane being subsequently inserted into the sensor housing.

Abstract: A driver assistance device for a motor vehicle includes a control unit that is designed for delivering control signals for carrying out an autonomous parking maneuver to a drive and/or steering system of the motor vehicle. The driver assistance system is configured to abort a parking maneuver in progress when an abort command is received. A detection device for detecting an electrostatic field is connected to the control unit in order to generate the abort command.

Abstract: The invention relates to a method and apparatus for determining the nature of a material in a cavity between one inner metal wall and one outer metal wall provided outside the inner metal wall. First a tool is located on the inside of the inner metal wall, where the tool comprises a pulse generator and a signal recorder. An electromagnetic short duration pulse is generated by means of the pulse generator, the pulse inducing mechanical vibrations in the walls. Data representing the reflections of the mechanical vibrations from said cavity is recorded by means of the signal recorder. The recorded data is analyzed to determine the nature of the material in the cavity.