Abstract: A liquid-resistant module can be formed as a laminated construct having a housing, a cap, and a port membrane to inhibit liquid from passing across the membrane. The housing defines an internal duct extending from an inlet port to an outlet region. The cap defines an acoustic port and extends across the outlet region of the housing. The port membrane is attached to the cap and extends across the acoustic passage. The port membrane inhibits passage of liquid water through the membrane at differential pressures across the membrane less than a threshold pressure differential, and yet is gas permeable. The module can provide a liquid-resistant seal with an enclosure of an electronic device, and an enclosed microphone transducer or an enclosed loudspeaker transducer can be attached to the cap such that a port opening to or from the transducer is aligned with the acoustic port.

Abstract: A housing for a communication device comprises a first housing section with a membrane opening, wherein the first housing section comprises around the circumference of the membrane opening a first membrane support configured to couple to a sound membrane, and a magnet carrying support, which is integrally formed with the first housing section and is configured to support a magnet in the housing and below the membrane opening. Furthermore, the present invention provides a communication device.

Abstract: Methods and systems for acoustically treating material using a continuous process in which material may be caused to flow in a continuous or intermittent fashion into/out of an acoustic treatment chamber where the material is exposed to focused acoustic energy. The methods and systems may be arranged to permit continuous processing for extended periods while an acoustic energy source operates at a relatively high power output. Treatment chambers may include features such as an acoustic window and/or a chamber wall which may comprise an acoustically reflective material or a gas/wall interface that serves to reflect acoustic energy to form one or more secondary focal zones. Treatment system configurations relating to arrangements of a treatment chamber relative to an acoustic source and coupling medium, material flow paths, and others are provided.

Abstract: Devices for sensing gradients are constructed from material whose properties change in response to gradients. One embodiment of the device is a transducer (200) for sensing gradients that includes the material (210) and two or more electrodes (240, 270) coupled to the material. In one embodiment, gradients in a surrounding medium (110) modify the energy gap of the material in the transducer (130) producing a diffusion current density (150). The material is configured to connect to a current or voltage measurement device (520, 530, 540) where a measurement is used to determine the gradient in the medium (160). The devices can be used to measure pressure, temperature, and/or other properties. The transducer can be built on the same substrate as complementary circuitry. A transducer made of Indium. Antimonide is used in marine seismology to measure pressure gradients.

Abstract: A magnetostrictive actuator comprises an assembly of at least two GMM rods (8, 9) spaced apart from each other on the same longitudinal axis, each rod being surrounded by a respective energising electromagnetic coil (10,11) 5 and being mounted between respective biasing permanent magnets (12, 13, 14), the assembly being mounted between mechanical pre-stressing means (20, 21) and a foot (3) adapted to couple the forces produced by the actuator into a surface.

Abstract: Provided is a system and method for enabling pressure or acoustic waves to induce magnetostrictive volume or shape change, providing greater control over magnetopropants. A coating material and the spacing between a magnetopropant and a magnetic particle are selected such that a certain pressure causes change in the relative distance of magnetopropant and magnetic particle, thereby changing the amount of magnetostriction. The coating material, magnetopropant, and magnetic particle are assembled to form a pressure sensitive magnetopropant. Given this structure, changes in pressure will cause a fluctuation of the amount of magnetostriction. In a pore space environment, this causes a change in pore space with resulting change in permeability and, hence, changes in fluid flow.

Abstract: A ferromagnetic material having non-zero magnetoelasticity, and/or nonzero magnetostriction is driven with vibratory mechanical energy at a frequency producing at least one resonant vibratory mode, by coupling a source of vibratory energy to the ferromagnetic structure. The ferromagnetic material threads at least one conductive wire or wire coil, and couples to at least one source of magnetic induction, and provides an electrical power output driven by the magnetic induction. The origin of vibratory energy and the site or sites of magnetic induction are situated at distinct locations, separated by a specific distance not less than ? the fundamental acoustic wavelength. Various combinations of acoustic wavelength, ferromagnetic material type, and source of vibration produce independent transfer coefficients between acoustic and electromagnetic energy which are either positive, zero, or negative.

Abstract: Provided is a system and method for enabling pressure or acoustic waves to induce magnetostrictive volume or shape change, providing greater control over magnetopropants. A coating material and the spacing between a magnetopropant and a magnetic particle are selected such that a certain pressure causes change in the relative distance of magnetopropant and magnetic particle, thereby changing the amount of magnetostriction. The coating material, magnetopropant, and magnetic particle are assembled to form a pressure sensitive magnetopropant. Given this structure, changes in pressure will cause a fluctuation of the amount of magnetostriction. In a pore space environment, this causes a change in pore space with resulting change in permeability and, hence, changes in fluid flow.

Abstract: A seismic vibrator includes a transducer, a reactive mass, a base plate to couple motion of the reactive mass to subsurface formations and a linkage system configured to couple motion of the transducer to the reactive mass and the base plate. The linkage system cooperates with the reactive mass and the transducer to define a first resonant frequency and a second resonant frequency within a range of 1 to 300 Hz.

Abstract: The electromagnetic acoustic transducer (EMAT) transducer disclosed herein is useful for the non-destructive analysis of objects. The transducer comprises a core having a winding and a coil disposed between the core and the object to be analyzed. One transducer can be used as a transmitter and another transducer as a receiver. Then selectively switching static magnetic field in either transmitter or receiver and processing data with and without static magnetic field allows for eliminating artifacts due to parasitic coupling between the transmitter/receiver pair. The switching of the static magnetic field can be implemented either by using electromagnet or a pair of permanent magnets where magnetization of one permanent magnet is reversed to provide cancellation of the static magnetic field.

Abstract: A combined electromagnetic acoustic transducer (EMAT) is disclosed adapted to generate both SH-type acoustic waves and LAMB-type acoustic waves in a conductive casing, surroundings of which are to be analyzed. The transducer comprises one magnet assembly and two RF coils implemented as multi-layer printed circuit board. Each coil is used to generate or receive acoustic signals of one wave type. Compared to using two single-wave-type transducers the combined EMAT significantly reduces total attraction force to the casing and, correspondingly, simplifies mechanics of the measurement tool. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Abstract: The present invention relates to an apparatus for measuring pressure inside a vessel using a magnetostrictive acoustic transducer. The apparatus includes a magnetostrictive acoustic transducer, including an exciting coil unit wound on a first magnetization yoke disposed on an outer position of a vessel, a receiving coil unit wound on the first magnetization yoke, and a vibration unit disposed on an inner position of the vessel in which the first magnetization yoke is installed; a control unit for supplying a predetermined excitation current signal to the exciting coil unit; and a pressure measuring unit for measuring an internal pressure of the vessel based on an ultrasonic wave signal received by the receiving coil unit and an excitation current signal into the exciting coil unit.

Abstract: This invention refers to a sonic and/or ultrasonic generator for emission in air with a power capacity and certain radiation characteristics which permit the necessary acoustic levels (>170 dB ref. 2·10?4 ?bar) to be obtained in a way that is safe and controlled for the mechanical breakage of high consistency bubbles constituting industrial foams.

Abstract: A marine vibrator that in a particular embodiment includes a substantially elliptically shaped outer shell, a driver having a first and second end, at least one outer spring connected between the first end and the second end of the driver, and at least one inner spring connected between the first end and the second end of the driver. One or more masses are attached to the inner spring. At least one transmission element connects the outer spring and the outer shell. The outer and inner springs and the masses attached to the inner spring are selected to generate a first resonance frequency and a second resonance within the frequency range between 1 Hz and 300 Hz.

Abstract: An array of magnets designed of flexible components and materials can be easily shaped to fit to the contour of various curved surfaces and structures. EMATs that incorporate these magnets, in addition to being flexible, may be smaller in volume than the conventional EMAT magnets and therefore easier to apply to complex structures where access may be restricted. Also, flexible multiple-pole magnet arrays can be easily and economically fabricated in various shapes and configurations, thereby increasing versatility, utility and cost effectiveness in comparison to the rigid, conventional magnet designs.

Abstract: A control system for controlling a variable of a device by an end element is disclosed. The control system has as its input a magnetostrictive position sensing probe for measuring the value of the variable of the device at time intervals and a digital controller reading the value from the magnetostrictive position sensing probe and having an output and means for calculating control output from the updated value of the variable during the time interval. The digital controller is close coupled to the magnetostrictive position sensing probe to permit time intervals that are very short, such as 500 microseconds to 1 millisecond.

Abstract: An acoustic wave transmission system comprises an acoustic wave generating metal tubular member for converting information about the bottom of a borehole, which is obtained by a bottom hole sensor, into an acoustic wave. The acoustic wave generating metal tubular member includes a acoustic wave generating mechanism having at least a magnetostrictive oscillator which is mounted in a recess formed in an outer wall of the acoustic wave generating metal tubular member, and on which a compressive load is imposed by means of a pre-load mechanism using a vise. The magnetostrictive oscillator is constructed of a stack of thin plates each made of a metal magnetostrictive material having a property of increasing its dimensions when magnetized, the thin plates being bonded together by a heat-resistant adhesive. The magnetostrictive oscillator can thus have a buckling strength large enough to resist the compressive load imposed thereon by the pre-load mechanism and a stress due to a strain caused in itself.

Abstract: A device for regenerating powerful acoustic pressure comprises at least an arrangement for generating sound while utilizing the flextensional technique, i.e. having at least one surface element (2), the opposite ends (4, 5) of which are arranged to be influenced to oscillate away from and towards each other, and the surface element oscillating transversely thereto and generating sound.

Abstract: There is provided an acoustic source especially for use in seismic studies at sea. The acoustic source has a longitudinal axis and sound emitting surfaces adapted to be put into sound emitting movements towards and away from each other by use of a drive unit. The sound emitting surfaces comprise two curved plate members having upper and lower ends essentially symmetrically positioned in relation to the longitudinal axis of the acoustic source, and forming a convex cross section with their respective upper and lower edges converging towards each other. The upper and lower edges of the sound emitting surfaces, respectively, are connected to each other with two corresponding side elements, the side elements each being connected to at least one hinge stretching along at least a part of the length of the source.

Abstract: A microphone for use in underwater applications. The microphone includes a dynamic magnet and coil assembly in a housing which incorporates a hydrophobic membrane. The membrane is sufficiently porous to permit air to pass therethrough. However, water cannot pass through the membrane. The housing permits water to drain away whereby a superior underwater microphone is obtained. This invention provides the diver with a military-style noise canceling microphone that retains exceptional sound reproduction quality because it is not encapsulated. However, the new microphone can be repeatedly exposed to the marine environment without failure.

Abstract: A autonomous borehole data transmission apparatus for transmitting measurement data from measuring instruments at the downhole end of a drill string by generating pressure pulses utilizing a transducer longitudinally responsive to magnetic field pulses caused by electrical pulses corresponding to the measured downhole parameters.

Abstract: A magnetostrictive element generates an ultrasonic wave and the generated ultrasonic wave is propagated through a propagation medium. An acoustic wave receiver receives the propagated ultrasonic wave at the other end of the propagation medium and converts it into an electric signal. A signal transmission is carried out in this way.

Abstract: A method and apparatus is disclosed for making a sliced phased array transducer formed from a single piezoelectric disk which has been bonded to a metal coated support surface. After bonding, the disk and attached metallic coating are cut into a plurality of conductively isolated staves which are then wired into a sequence which allows the array to emit two beams in opposite directions at a depression angle of about 60 degrees. In use, two of the arrays are used adjacent to each other with one emitting beams along the port and starboard sides of the vessel and the other being rotated 90 degrees to emit beams to the force and aft of the vessel, the four beams thereby forming a Janus configuration. Alternatively, the beams could be rotated 45 so that two beams are directed to both the port and starboard sides.

Abstract: The invention relates to an elastic clamping device for at least one body with magnetostrictive properties, wherein a pressure force presses the clamping device against the inner magnetostrictive body with a predetermined force. The pressure force extends in the direction of contraction and perpendicular to the direction of expansion both caused by the influence of a magnetic field on the magnetostrictive body and results in a prestress acting in the direction of contraction in the magnetostrictive body. The predetermined pressure from the pressure force exerted on the clamping device and thus on the magnetostrictive body is adjustable by means of a resilient force or mechanical setting device.

Abstract: A magnetostrictive element includes a magnetostrictive member, an outer magnet disposed coaxially about, spaced apart from, and surrounding the magnetostrictive member, and a soft magnetic yoke for magnetically coupling the magnetostrictive member and the outer magnet to form a closed magnetic circuit. The magnetostrictive member may be either solid or hollow. In the latter case, an inner magnet is disposed coaxially within the magnetostrictive member for producing a biased DC magnetic field. An axial length of the outer magnet is made shorter than an axial length of the magnetostrictive member. In either case, the outer magnet is spaced apart from the magnetostrictive member so that a more uniform magnetization distribution is produced in the magnetostrictive member.

Abstract: An underwater low-frequency sound producer comprises vibrator units each including a magnetostrictive rod formed of a rare-earth alloy, a permanent magnet for providing a magnetic bias to the rod, prestress bolts for prestressing the rod, a coil wound on the rod for causing magnetostriction of the rod corresponding to an input AC signal applied to the coil, and first and second masses on opposite ends of the rod. The vibrator units are arranged seriatim end-to-end to define a polygon or ring centered on an axis. Connection blocks respectively connect the first and second masses of the vibrator units adjacent to each other. Vibration plates are respectively attached to the connection members. Outer and inner cylindrical boots and upper and lower plates define an annular space in which the vibrator units are disposed. The annular space is filled with oil having an acoustic impedance similar to that of the water in which the sound producer is placed for use.

Abstract: A drive package for acoustic transmitters includes a frame (6) of magnetic material with windows for accommodating driving members (20) and prestress devices (22) . Two windows with driving members and an intermediate window with a prestress device form a column which, by way of pressure studs (24) in the driving members and holes (14) in the frame, clamp pressure rods (4) located inside the transmitter against the shell (1) of the transmitter. The drive package may include several columns.

Abstract: This invention concerns a low frequency, high energy output electroacoustic transducer. It utilizes a vibratory unit formed of a stack of hollow ceramic cylinders about which is fitted a resilient metal sleeve. The metal sleeve is tensioned outwardly during assembly of the unit so that, upon relaxation, it will fit about the stack as tightly as possible. To further make the stack and sleeve integral, a bonding material is placed between the two. A gap in the sleeve serves as a cutting guide for gapping the stack. Air backing is used to further increase the energy output of the transducer.

Abstract: The invention concerns an omnidirectional loudspeaker. This loudspeaker comprises a spherical membrane which includes spires formed of a strip (2) made of a magnetostrictive material, the spires being spiral wound according to a sphere; these spires are kept in place by an elastic support (1) so that, along with the support, they form a spherical membrane. The strip has two opposing faces (11, 12), one of which is directed towards the inside (I) of the sphere, the other being directed towards the outside (E) of the sphere, and two extremities (3, 4) situated in two diametrically opposing zones of the sphere so as to be connected to an electric control device (5) providing a signal corresponding to sound waves to be reproduced, and a device (7) for the continuous polarization of the membrane. According to the invention, one of the faces (11) of the strip (2) is at least partly coated with a thin coating (13) made of a rigid material.

Abstract: A driving member for a diaphragm in acoustic devices includes a body with opposite recesses into which driving rods are inserted. One end of the driving rods is attached to pressure rods which directly influence the diaphragm and the other end of the driving rods makes contact with the bottom of the recesses.

Abstract: An electroacoustic transducer according to the invention comprises a stacking of annular plates (13) made of piezoelectric ceramics alternating with annular electrodes (14) and pressed by an axial prestressing stem (15). The contact faces between each plate and the adjacent ones are made of two flat parts (16a, 16b) whose surface is smaller than the maximum cross section, due to the chamfers (19a, 19b, 20a, 20b) which truncate the edges of each plate. One application is the construction of low frequency sonar transmitters. Referenced elements refer to FIG. 3.

Abstract: An acoustic wellbore logging tool transducer formed of a composite plate member having at least one plate of a magnetostrictive material which responds to a magnetic field to elongate or contract to effect displacement of said plate member within a cavity formed in a housing section of the logging tool. The logging tool cavity may be exposed to wellbore fluid in direct contact with the plate member whereby acoustic pressure pulses may be delivered directly to the wellbore fluid by the transducer element. Spaced apart electromagnets are disposed in the housing section on opposite sides of the cavity for effecting controlled displacement of the plate member to generate acoustic waves in a liquid-filled wellbore.

Abstract: A magnetostrictive flexible line hydrophone having a magnetostrictive elet which is an annealed nickel strip within a toroidal winding. Electrical wires are disposed inside the cylinder formed by the nickel strip and abut a pressure release material about which the strip has been wound. These wires form a toroidal winding by coupling to a second group of insulated wires disposed against the outer surface of the nickel strip.

Abstract: A low frequency sound producer including a plurality of magnetostrictive vibrators arranged seriatim end to end to define a ring. Each vibrator unit includes a plurality of laterally related magnetostrictive rods which, in the illustrated embodiment, are formed of rare earth magnetostrictive material. Structure is provided for compressively prestressing the rods. The prestressing structure includes permanent magnets for providing a permanent magnetic bias in the rods. Coils are magnetically coupled to the rods for causing the desired magnetostriction thereof corresponding to an input AC signal applied to the coils. Opposite ends of the individual vibrator units define facial abutments in defining the continuous ring configuration. In the illustrated embodiment, the ring configuration is polygonal and the facial abutment surfaces at the ends of the units define a 60.degree. included angle.

Abstract: A flextensional transducer driven by magnetically biased rare earth rods 31. The rods 31 are arranged in stacks with rare earth magnets 34 mounted on each end of each stack for providing the bias field. The rods 31 are slotted to reduce eddy currents and surrounded by a slotted drive coil 32 with a slot 32a in the coil bobbin. The ends of the flextensional shell associated with the shell major axis have a full radius curvature which stiffens the shell ends so that the axial bias and drive forces will not break the rare earth magnets 34 in flexure.

Abstract: The present invention is directed to an ultrasonic device comprising a plurality of transducer elements arranged in rows and columns and acoustic insulation material maintained between each two adjacent rows of transducer elements. The ultrasonic device comprises (i) a plurality of rows of the transducer elements, each row being disposed on an imaginary circle, (ii) a plurality of circular plates each supporting one of said rows and (iii) spacers for spacing adjacent plates of the plurality of plates at a predetermined space interval, thereby forming a cylindrical array.

Abstract: An acoustic transducer for providing large displacements particularly at low acoustic frequencies is formed from a minimum of three curved shells which are attached to each other at their ends. The shells are driven by a ring or corresponding number of attached piezoelectric or magnetostrictive type rod or bar drivers. The curved shells are attached to the ends of the driver and vibrate with a magnified motion as the rods execute extensional motion. As the polygon expands the curved shells deform and produce additional motion in the same radial direction resulting in a large total displacement and corresponding large acoustic output.

Abstract: Wide pass band elastic wave omnidirectional transducer.It comprises a magnetostrictive material membrane (34, 36) provided with two electrical connections at two diametrically opposite points. The potential difference between these connections is proportional to the elastic wave transmitted or received by said membrane. A continuous polarization means of the magnetostrictive membrane is also provided. It comprises a high magnetic permeability part (40, 42), whose shape substantially corresponds to that of the membrane and which is placed in the vicinity of the latter, and a permanent magnet (38) in contact with said part.Application to the transmission of high frequency elastic waves in water (hydrophone) and to high fidelity sound reproduction in air.

Abstract: An electro-mechanical spring which provides amplified motion as well as a compliant structure for attachment, at the locations of maximum motion, to other mechanical or acoustical loads or elements. The spring produces motion in a directional orthogonal to the direction of a piezoelectric or magnetostrictive drive member connected along the major axis of a complete shell. The electro-mechanical spring provides a means for obtaining a low frequency large displacement piston type transducer.

Abstract: Omnidirectional, wide pass band, elastic wave transducer comprising a rigid magnetostrictive diaphragm, each surface element of the diaphragm constituting a unidirectional elastic wave transducer in its normal direction, and an electric control means provided with two electric terminals for producing in the vicinity of the diaphragm a homogeneous magnetic field in keeping with an electric signal applied to the terminals of the control means or for supplying an electric signal in keeping with the variation of the magnetic field in the diaphragm as a function of an elastic wave received. The diaphragm is preferably a closed surface of revolution.Application in submarine transmission (hydrophone) and in high fidelity sound reproduction (loudspeaker, microphone) with a very wide pass band.

Abstract: A directional flextensional transducer including a transducer shell capable of operation in odd and even drive modes and a transduction drive bar or the like. The transduction drive bar is excited in an even mode to impart extensional motion thereto and is simultaneously excited in an odd mode to impart inextensional motion thereto. The combined excitation causes the flextensional transducer shell to move unidirectionally.

Abstract: An acoustic transducer for providing large displacements particularly at low acoustic frequencies is formed from a minimum of three curved shells which are attached to each other at their ends. The shells are driven by a ring or corresponding number of attached piezoelectric or magnetostrictive type rod or bar drivers which take the form of a regular polygon. The curved shells are attached to the ends of the driver and vibrate with magnified motion as the rods execute extensional motion. As the polygon expands the curved shells deform and produce additional motional in the same radial direction resulting in a large total displacement and corresponding large acoustic output.

Abstract: An acoustic transducer is provided that uses a layer of magnetostrictive ferromagnetic material having high magneto-mechanical coupling. The ferromagnetic material is adhered to a part of the outer surface of a resilient rod, so that an incident acoustic signal causes a change in stress in the magnetic material and, in turn, a change in the material's magnetization. An electrical coil surrounds the magnetic material and converts the changing magnetization into an electrical signal. A plurality of transducers may be assembled into an array and towed behind a ship to detect underwater acoustic signals.

Abstract: Non-active columnar members are disposed on both sides of an active columnar member consisting of a piezoelectric ceramic material or a magnetically strainable material. Levers are connected to the active and non-active columnar members via first and second hinges. Convex shells are connected to the levers via third hinges. The displacement of the active columnar member is enlarged via the lever action, thereby enabling a miniaturized ultrasonic wave transmitter having high power capability.

Abstract: A transducer which uses paramagnetic magnetostrictive rods or bars, e.g., compositions of the lanthanide series of elements such as Tb.sub.0.3 Dy.sub.0.7 Fe.sub.2, has the bars biased with a lengthwise flux by a permanent magnet, e.g. samarium-colbalt, of high resistance to demagnetization by the alternating field applied to the bars by alternating current in a coil surrounding the bar. The magnet is outside the coil to reduce the ac field to which it is subjected. Uniformity of flux density along the length of the bars is enhanced by having adjacent ends of the bars subjected to like-polarity poles of the permanent magnets associated with each bar.

Abstract: For use in acoustic logging, an acoustic wave transducer system forming both compression and shear waves is disclosed, the system having the preferred form of a plurality of radially directed magnetostrictive expansion means, being N in number, each having a transducer plate affixed to the outer end thereof and further including means for providing a current to a coil wound thereabout forming flux initiating magnetostrictive expansion and contraction to form compression or shear waves.

Abstract: The transducer of this invention provides a one-to-one input-to-output frequency relationship by the use of different magnetostrictive materials within the same transducer, the materials each having positive and negative strain expansion coefficients. The materials are selectively driven so that the transducer motion is in one direction for one polarity of the sinusoidal drive signal and in the opposite direction for the other polarity of the drive signal. The resultant transducer is capable of greater peak-to-peak excursion of the radiating face for the same length of magnetostrictive material than in the prior art biased-material transducer.

Abstract: A plurality of piezoelectric or magnetostrictive rectangular planar staves are held in side-by-side relation in a laminate assembly including insulative spacers. The widthwise polarity of adjacent pairs of the staves are inverted relative to each other. The acoustic centers of the staves are spaced apart a distance of approximately one-half of a wavelength of the operating frequency. Electrical connections are made to the opposite side edges of each of the staves through leads and bus wires. The array of staves define an active planar acoustic face for simultaneously sending and simultaneously receiving a pair of angularly separated beams of acoustic energy without electronically phasing or time delaying the signals transmitted to and from the individual staves and without mechanically rotating the array.

Abstract: A magnetostrictive generator includes a magnetostrictive transducer having a vanadium permandur core and series connected primary and secondary windings, the secondary winding having more turns that the primary winding. A commutating capacitor is connected in parallel with the primary and secondary windings of the transducer and a switch is connected in series with the primary winding. A storage capacitor, which is connected in parallel with the switch and the primary winding of the inductive transducer, is charged by a remotely located low voltage power supply when the switch is open. When the switch is closed, the storage capacitor discharges through the primary winding of the transducer to charge the commutating capacitor until the transducer reaches saturation, the commutating capacitor discharging thereupon to drive the transducer into hard saturation to produce magnetostrictive action in the core and physically deform the transducer and produce an acoustic signal.

Abstract: An ice detector to detect a lyaer of ice on a thin solid sheet 14, such as the skin of an aircraft wing, even in the presence of water, comprises two ultrasonic transducers attached to the sheet. The first transducer 10 is adapted to cause propagation of ultrasonic waves through the sheet 14 having their predominant component parallel to the surface of the sheet 14. Such waves will dissipate energy into an ice layer adhering to the surface, but not into air or a liquid layer. The second transducer 30 is adapted to detect the waves propagating in the sheet and to give a signal representative of their amplitude. A discriminator 34 responsive to the signal detects the presence of an ice layer on the surface.