Classifications

• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/02—Mechanical acoustic impedances; Impedance matching, e.g. by horns; Acoustic resonators
  • G10K11/025—Mechanical acoustic impedances; Impedance matching, e.g. by horns; Acoustic resonators horns for impedance matching

Definitions

• This invention relates to a device for matching acoustic impedance between an ultrasonic transducer and a medium, in combination a device for matching acoustic impedance between .an ultrasonic transducer and a medium, and a transducer, a process of constructing a device for matching acoustic impedance between an ultr.asonic transducer and a medium, a system and method for transmitting ultrasonic signals between an ultrasonic tr nsducer and a medium, a system and method for detecting ultrasonic signals between an ultrasonic transducer and a medium, and systems and methods for transmitting and detecting ultrasonic signals between an ultrasonic transducer and a medium.
• a difficulty in acoustics is that devices which will produce sound by virtue of their vibration, are nearly always of a different acoustic impedance to the medium in which it is desired to have the sound propagate.
• the amount of acoustic energy transferred from one medium to another is determined by the impedance match. The worse the match, the more energy is reflected from the interface rather than transmitted through the medium.
• a common problem in the use of ultrasonic transducers in air and other gases is the very large impedance mismatch between the transducer and the medium.
• the wave impedance of a piezoelectric material such as barium titanate exceeds that of air by a factor close to 10 ⁇ and, even when the transducer is operated in a resonant mode, the effective acoustic mismatch is still of order lC ⁇ .
• the intrinsic mismatch for a nonresonant stretched-foil transducer is rather less, but, without the assistance of resonance matching, the acoustic mismatch is still very large.
• SUBSTITUTE SHEET be metals, alloys, liquids, ceramics, glasses or one of a huge array of composite materials mixed to have desired acoustic impedances.
• each layer ought to have an acoustic impedance which is the geometric mean of the acoustic impedances to each side of it and the layers need to be sufficiently thick or the signals sufficiently short that reflections within the layers do not have cancelling effects.
• the layers operate by the combination of physical characteristics so that the impedance is tailored to be the geometric mean of the acoustic impedances to be matched and the thickness is such as to make the matching layer operate at 1/4 wave resonance.
• Another object is to provide in combination a device for matching acoustic impedance between an ultrasonic transducer and a medium, and a transducer.
• a device for matching acoustic impedance between an ultrasonic transducer and a medium comprising: a body comprising a material having a high acoustic impedance to an ultrasonic signal, the body containing a plurality of acoustic impedance matching horns extending between two surfaces of the body wherein:
• a device for matching acoustic impedance between an ultrasonic transducer and a medium comprising: a body comprising a material having a high acoustic impedance to an ultrasonic signal, the body containing a plurality of acoustic impedance matching horns extending between two surfaces of the body wherein: (a) the mouths of the horns are disposed in one surface and the throats of the horns are disposed in another surface;
• an ultrasonic transducer having a transmission/receiving surface capable of transmitting/receiving the ultrasonic signal; wherein the transmission/receiving surface is disposed in relation to the surface in which the mouths are disposed whereby acoustic coupling between the ultrasonic signal from/to the transmission/receiving surface and the mouths is not substantially shunted by the acoustic impedance of the medium between the transmission/receiving surface and the mouths.
• a device for matching acoustic impedance between an ultrasonic transducer and a medium comprising: a body comprising a material having a high acoustic impedance to an ultrasonic signal, the body containing a plurality of acoustic impedance matching horns extending between two surfaces of the body wherein:
• the magnitudes of the lengths and flares of the horns are such that the horns are capable of transmitting the ultrasonic signal; and (c) the magnitude of the flare of each horn being such so as to provide a substantially smooth transition in acoustic impedance between the mouth and throat of the horn; and
• an ultrasonic transducer having a transmission/receiving surface capable of transmitting/receiving the ultrasonic signal; wherein the transmission/receiving surface is disposed in relation to the surface in which the throats are disposed whereby acoustic coupling between the ultr-asonic signal from/to the transmission/receiving surface and the throats is not substantially shunted by the acoustic impedance of the medium between the transmission/receiving surface and the throats.
• a process of constructing a device for matching acoustic impedance between an ultrasonic transducer and a medium comprising: forming a plurality of acoustic impedance matching horns in a body formed of a material having a high acoustic impedance to an ultrasonic signal, whereby the acoustic impedance matching horns extend between two surfaces of the body and wherein: (a) the mouths of the horns are disposed in one surface and the throats of the horns are disposed in another surface;
• a system for transmitting ultrasonic signals between an ultrasonic transducer and a medium comprising: the combination of the second or third embodiments; and means to drive the transducer at a frequency corresponding to the acoustic frequency, operatively associated with the transducer.
• a system for detecting ultrasonic signals between an ultrasonic transducer and a medium comprising: the combination of the second or third embodiments; and means to detect a signal from the transducer at a frequency corresponding to the acoustic frequency, operatively associated with the transducer.
• a system for transmitting and detecting ultrasonic signals between an ultrasonic transducer and a medium comprising: the combination of the second or third embodiments; means to drive the transducer at a frequency corresponding to the acoustic frequency, operatively associated with the transducer; and means to detect a signal from the transducer at a frequency corresponding to the acoustic frequency, operatively associated with the transducer.
• a system for transmitting and detecting ultrasonic signals between an ultrasonic transducer and a medium comprising: (a) a first combination comprising the combination of the second or third embodiments; means to drive the transducer of the first combination at a frequency corresponding to the acoustic frequency, operatively associated with the transducer of the first combination; and me-ans to detect a signal from the transducer of the first combination at a frequency corresponding to the acoustic frequency, operatively associated with the transducer of the first combination; and (b) a second combination comprising the combination of the second or third embodiments; means to drive the transducer of the second combination at a frequency corresponding to the acoustic frequency, operatively associated with the transducer of the second combination; and means to detect a signal from the transducer of the second combination at a frequency corresponding to the acoustic frequency, operatively associated with the transducer of the second combination.
• an ninth embodiment of this invention there is provided a method for transmitting ultrasonic signals between an ultrasonic transducer and a medium, the method comprising: driving the transducer of the system of the fifth embodiment whereby it transmits ultrasonic signals of frequency above the lower cutoff frequency of the horns.
• a method for detecting ultrasonic signals between an ultrasonic transducer and a medium comprising: detecting ultrasonic signals of frequency above the lower cutoff frequency of the horns with the system of the sixth embodiment.
• a method for transmitting and detecting ultrasonic signals between an ultrasonic transducer and a medium comprising: driving the transducer of the system of the seventh embodiment whereby it transmits ultrasonic signals of frequency above the lower cutoff frequency of the horns; and detecting ultrasonic signals of frequency above the lower cutoff frequency of the horns with the system of the seventh embodiment.
• a method for transmitting and detecting ultrasonic signals between an ultrasonic transducer and a medium comprising: driving the transducer of the first or "second combinations of the eighth embodiment whereby it transmits ultrasonic signals of frequency above the lower cutoff frequency of the horns; and detecting the ultrasonic signals generated by the transducer of the first or second combinations of the eighth embodiment with the transducer of the second or first combinations of the eighth embodiment.
• the body is a plate, the mouths of the horns are disposed on one side of the plate and the throats of the horns are disposed on the other side of the plate.
• the body may comprise a curved or spherical surface in which the mouths of the horns are disposed and/or may comprise a curved or spherical surface in which the throats of the horns are disposed.
• the surface of the body having the throats is adjacent the transmission/receiving surface of the ultrasonic transducer and this surface of the body may have a shape to match the shape of the transmission/receiving surface of the ultrasonic transducer.
• the body may comprise a curved or spherical surface in which the mouths of the horns are disposed and the axes of the horns pass through a common point proximate the throats of the horns so as to form a multi cellular arrangement of the horns.
• the transmission/receiving surface of the ultrasonic transducer is substantially planar.
• the preferred horn shape is catenoidal but other shapes including exponential, parabolic and conical shapes are also suitable.
• the mouths of the horns are to be taken throughout the specification and claims to be of having an equal to or greater diameters than the diameters of the throats of the horns.
• the mouths of the horns are generally closely packed. Preferably the packing is such that it is radially symmetrical so that the area of the mouths of the horns is maximised and energy losses caused by facots such as cancellations (destructive interferences) of ultrasonic waves entering or leaving the horns is minimised.
• the mouths of the horns are arranged in an hexagonal close packed array.
• adjacent centres of the mouths are optimally spaced by less than ⁇ 12 where ⁇ is the wavelength of the ultrasonic signal to be coupled to the surrounding bulk medium.
• ⁇ is the wavelength of the ultrasonic signal to be coupled to the surrounding bulk medium.
• the plate thickness is about ⁇ 12 where ⁇ is the wavelength of the ultrasonic signal to be coupled to the surrounding bulk medium. It is preferred that the plate thickness is less than ⁇ because this results in any resonance effects being kept very small.
• the plate is placed in front of the radiating" surface of an ultrasonic transducer at a distance which varies according to the application. This requires the distance to be such that the impedance of the medium in the gap between the plate and transducer does not significantly shunt the throat impedance of the holes.
• the ultrasonic impedance matching device of this invention relies on a fundamentally different principle to the 1/4 wave plates described in relation to the background art.
• An acoustic horn is a length of material, which may be air contained in a pipe or it may be a solid horn of, for example, ceramic material usually but not necessarily of monotonically varying cross section.
• the ultrasonic impedance matching horn parameters which affect its usefulness are its input impedance, its output impedance, its flare, its shape, its gain and its length.
• the input impedance generally closely matches the source impedance for maximum energy transfer.
• the output impedance should closely match the load impedance for maximum energy transfer.
• the flare of a ultrasonic impedance matching horn must not change too quickly with the result that the cross sectional area of the conduit does not change too quickly.
• This criterion is usually expressed in terms of a flare parameter which determines the maximum rate of flare for any given horn geometry and frequency in terms of wavelength.
• a flare parameter which determines the maximum rate of flare for any given horn geometry and frequency in terms of wavelength.
• the ultrasonic pressure gain of a horn is the ratio of the output radius to the input radius, ⁇ 0 / ⁇
• the intensity gain is the corresponding ratio of the areas, S 0 /Sj.
• the form of the horn gain versus frequency for a given horn is different for different geometries when the frequency is near lower cut off but at frequencies more than twice lower cut off all gains tend to the same value.
• Common horn shape choices are conical, parabolic, exponential and catenoidal. These ones happen to be readily calculable.
• the optimum horn shape is immaterial if the horn is operated well above cut-off.
• a conical horn approaches the optimum gain slowly with length whilst exponential and catenoidal horns operate with full gain when frequency is not too far above lower cut-off.
• the catenoidal horn has a more extreme curve to its
• the combination is capable of transmitting and/or receiving ultrasonic vibrations having a vibrational pe-ak in the frequency range 20kHz - 200kHz.
• the range is 22kHz-160kHz, 80kHz-120kHz, 95kHz-105kHz, 15kHz- 60kHz, or 15kHz-30kHz or 30kHz-110kHz.
• the device is generally formed of very rigid material to minimise energy absorption loss by the device.
• horn materials include epoxy resin(s), metals including steel covered with a damping material, lead and aluminium, metal alloys, teflon, particle boards, carbon fibre and wood,
• transducer materials include lead zirconate-titanate, quartz, barium • titanate, fluorspar, sodium potassium tartrate tetrahydrate, tourmaline and lithium niobate.
• a transducer material is a piezoelectric foil which typically comprises a polyvinylidene fluoride (“PVDF”) foil or a foil comprising a copolymer of PVDF.
• PVDF polyvinylidene fluoride
• PVDF piezoelectric transducer of the type described in New Zealand Patent
• the transducer material or foil has at least two electrodes located thereon, typically one electrode on each side of the foil.
• the electrodes may be the same or different material, typically the same material.
• Examples of electrode materials are metals such as Au, Pd, Pt, Ti, Zn, Al, Ag, Cu, Sn, Ga, In, Ni, conducting polymers which require doping with doping agents such as iodine, fluorine, alkali metals and their salts, metal carbonates and arsenic halides, include polyacetylene, polyacetylene • copolymers, polypyrroles, polyacrylonitriles, polyaromatics, polyanilines, polythiophenes, polycarbazoles, polybetadiketone and polydipropargylamine, polyacenaphthene/N- vinyl heterocyclics with Lewis acids, poly(heteroaromatic vinylenes), polyphthalocyanines, polymer reacted with 1 ,9-disub
• the medium is a fluid such as a gas, including air or other gases including gas for domestic, commercial or industrial use or fluids including water and sea water.
• the device of the invention is typically arranged in relation the transducer so that the throats of the horns are adjacent and opposite the transmission/receiving surface of the ultrasonic transducer so as to present a high impedance to the transducer and the mouths of the horns present a low impedance to the surrounding air thereby substantially providing in use an impedance match between ultrasonic signals emerging from the mouths of the horns.
• the conduits which form the horns and interconnect the mouths and the throats of the horns provide a smooth uniform impedance change from the high impedance at the throats to the low impedance at the mouths.
• Figure 1 is a perspective view of an impedance matching device according to this invention fitted to a transducer
• Figure 2 is a plan view of an ultrasonic impedance matching device according to this invention.
• Figure 3 is an enlarged elevation of part of the device shown in Figure 2; and Figure 4 is a schematic sectional elevation of an impedance matching device according to this invention fitted to a transducer;
• Figure 5 is a schematic sectional side elevation of system for transmitting or receiving an ultrasonic signal according to this invention.
• Figure 6 illustrates three horn shapes and the respective transmissivities as functions of frequency
• Figure 7 is a graph of measured sound gain as a function of frequency for horn " mouth radius 1.0 mm, horn throat radius 0.28 mm and cut-off frequency 22kHz;
• Figure 8 is a graph of measured sound gain as a function of frequency for horn mouth radius 1.2 mm, horn throat radius 0.30 mm and cut-off frequency 22kHz;
• Figure 9 is a graph of measured sound pressure gain as a function of gap spacing for the design shown in Table II but the horn throat radii of (a) 0.18 mm and (b) 0.30 mm.
• System 500 for transmitting and detecting ultrasonic signals between ultrasonic transducer 501 and a gaseous medium 502.
• System 500 includes device 503 for matching acoustic impedance between ultrasonic transducer 501 and medium 502.
• Device 503 has body 504 comprising a material having a high acoustic impedance to the ultrasonic signal transmitted and/or received by transducer 501.
• Body 504 contains a plurality of acoustic impedance matching horns 505 extending between two surfaces 506 and 507 of body 504. Mouths 508 of horns 505 are disposed in surface 506 and throats 509 of horns 505 are disposed in surface 507.
• the magnitudes of the lengths and flares of horns 505 are such that horns 505 are capable of transmitting the ultrasonic signal. Further, the magnitude of the flare of each horn 505 is such so as to provide a substantially smooth transition in acoustic impedance to the ultrasonic signal between the mouth 508 and throat 509 of the horn 505.
• Ultrasonic transducer 501 has a transmission/receiving surface 510 capable of transmitting/receiving the ultrasonic signal.
• Transmission/receiving surface 510 is separated from surface 507 in which throats 509 are disposed, by gap 511 by utilising spacers 512 and 513.
• Transducer 501 and device 503 are supported by supports 514 and 515 as are spacers 512 and 513.
• Supports 514 and 515 generally form a gas tight seal between device 503 and transducer 501.
• the size of gap 511 is selected so that ultrasonic coupling between the ultrasonic signal from/to the transmission/receiving surface and throats 509 is not substantially shunted by the acoustic impedance of the medium in gap 511.
• Surfaces 510 and 516 of transducer 501 have electrically conductive films thereon. Surfaces 510 and 516 are electrically coupled to switch 519 by lines 517 and 518 respectively.
• Switch 519 is in turn electrically coupled to switch 520 via lines 521 and 522 and amplifier 523 via lines 524 and 525.
• Amplifier 523 is electrically coupled to oscilloscope 526 via filter 527 via lines 528, 529, 530 and 531.
• Switch 520 enables switching between pulse generator 532 via lines 533 and 534 and square/ sine wave generator 535 via lines 536 and 537.
• Switch 519 enables switching between switch 520 and amplifier 523.
• system 500 is located in gaseous medium 502 in which ultrasonic signals are required to be transmitted/detected.
• Transducer 501 is driven by ultrasonic electrical signals from pulse generator 532 or square/sine wave generator 535 via switches 519 and 520.
• Ultrasonic signals are transmitted from surface 510 and pass through horns 505 to medium 502 though which they pass to reflecting surface 538.
• Ultrasonic vibrations reflected from reflecting surface 538 pass through horns 505 via gaseous medium 502 and cause transducer 501 to vibrate ultrasonically and are converted to ultrasonic electrical signals by transducer 501.
• the electrical signals from transducer 501 pass to amplifier 523 via switch 519 where they are amplified and then filtered by filter 527 and displayed subsequently on cathode ray oscilloscope 526.
• the impedance of transducer 21 is 3 x 10 ⁇ mks Rayls and the impedance of air is 400 mks Rayls.
• a horn 23 works by presenting the transducer face with a larger impedance, the throat impedance of the horn, than it would see operating straight into air.
• the horn transforms the throat impedance to the mouth impedance at horn mouths 40 (Fig.3) which more closely matches the air impedance.
• transducer 21 sees the impedances of the horn throats 41 (Fig.3) shunted by the impedance of the air cavity in spacing gap 22 between transducer 21 and the throats 41 of horns 23 in horn plate 20.
• the minimum horn length can be calculated once the horn shape is decided.
• any material can be used to form the plate 20 so long as it is reasonably rigid and has a high ultrasonic impedance.
• an epoxy resin was used.
• the bundle of pins is lowered tapered ends first into the epoxy and the epoxy is allowed to set.
• the pins may be pulled out one by one after being slightly warmed.
• the resultant disc is brass ring 33 with epoxy plate 32 in the middle, perforated by close packed array of horn shaped holes 31.
• horn plate 20 is finished on both sides using fine wet and dry paper on an optical flat. During this process the throat radii, ⁇ [, can be adjusted.
• Figure 4 shows the impedance matching horn plate 20 fitted to transducer 21.
• gap 22 between plate 20 and transducer 21 is formed by placing conducting spacer ring 50, e.g. cut from metal foil, between transducer 21 and plate 20.
• Transducer 21, plate 20 and spacer ring 50 are supported by supports 51 and 52.
• the electrical contact to the front of the piezoelectric transducer (PZT) is made via supports 51 and 52 which are insulated from back contact 53 of transducer 21 by insulator layers 54 and 55, the brass edge of plate 20 and foil spacer ring 50.
• PZT piezoelectric transducer
• the lower cutoff frequency of a horn is determined by the flare rate of the horn profile, and details of the cut off behaviour by details of the profile. Its upper cutoff frequency is determined by the total curvature of the wavefront at the horn mouth, and thus by the mouth diameter and the semiangle of the cone tangent to the horn surface. Between these two cutoff frequencies, and assuming the throat to be terminated by a relatively high impedance, the pressure gain above the free-field value for a source on the axis is between 1 and 2 times the ratio of the mouth diameter to the throat diameter. The floating factor is 1 if the diameter of the horn mouth is small compared with the wavelength, and 2 if it is large or if the mouth is surrounded by a baffle. Below the lower cutoff frequency the pressure gain tends to unity, while above the upper cutoff frequency the gain is small and strongly frequency dependent.
• the present invention overcomes this difficulty by replacing this single horn by an array of much smaller horns, distributed over a horn plate which covers the surface of a transducer (see Fig. 5, for example).
• the transducer surface itself is separated by a very small distance from the side of the plate through which the throats of the small horns open.
• Each horn can be designed to operate efficiently at the desired high
• the diameter of the horn throat is set by a compromise between the desirability of a small diameter to give a large pressure gain in the horn, and the desirability of a larger diameter to allow optimum matching to the space between the plate and the transducer surface.
• the nominal pressure gain of the horn refers to a situation in which the horn throat is rigidly blocked, and of course this is not so in the present invention.
• the incident pressure excites standing waves in this space, and they are damped both by motion of the transducer and, more importantly, by viscous and thermal losses at the two bounding surfaces.
• the boundary-layer thickness at the ultrasonic frequencies with which we are dealing is less than about 5 microns, so that the gap can be a few tens of microns, which is reasonable to achieve in practice.
• the area of the annular entry to the cell is generally small compared with the area of the horn throat, which dictates a throat diameter that is preferably an order of magnitude greater than the gap height. For a frequency near 100 kHz, this implies a throat diameter of a few tenths of a millimetre.
• the dimensional limits are set by the lower rather than the upper cutoff frequency, and, for the diameter ratio suggested above, the horn needs to be rather more than half a wavelength long. This gives a matching-plate thickness of a few millimeters, which is mechanically convenient.
• multi-horn plate lends itself to fast and cheap manufacture. Since the constituent material is only required to be acoustically inert compared to air, great flexibility is allowed in its choice and the optimum dimensions lend themselves to fabrication by injection moulding. However, in the laboratory, we need to make individual plates with different characteristics without recourse to elaborate production methods.
• the experimental plates were cast using a casting araldite To make the molds, the individual horn shapes were turned from narrow diameter brass rod using a numerically controlled jeweller's lathe. These horn pins had the horn shape at one end and a residual cylindrical section about 10 mm long. According to the desired diameter of the completed plate, bundles of the pins were held tightly in a teflon ring machined to a hexagonal shape, with the horn shaped points all protruding from one side. With this encouragement the pins readily organised themselves into a close packed order.
• the casting resin was mixed and warmed to remove air bubbles and then poured into a brass holding ring set on a flat base.
• the pin bundle, coated with teflon mold release, was lowered, horn end first, into the resin.
• the individual pins were lightly tapped to make sure that their tips were all lined up on the base.
• the pins slid out readily one by one if they were individually warmed with the tip of a soldering iron.
• the plate was then allowed to harden for a further 24 hours until it was ready for finishing. Achieving an effective finish on the plates involved several steps, starting with initial rough
• the variation in throat diameters over a single plate was typically less than 5% although the smallest throat sizes were proportionally less smooth around the throat opening.
• the plates were used with a PZT-4 transducer 12 mm thick and 30 mm across. It had five useful resonances up to 200 kHz, of which the lowest was a radial mode at 60 kHz.
• the transducer was mounted in a case, making electrical contact to the back, and a fine wire contact was attached to the rim of the front using epoxy, so that it did not get in the way of the plates.
• the transducer was driven from the output of a HP- 4194 gain-phase analyser, and the acoustic signal was detected with a l/8th inch condenser microphone, B&K 4180, positioned about 12 cm in front of the plate.
• the microphone was equipped with a conical screen to eliminate unwanted reflections.
• the transducer and plate were used as the transmitter but, when used as a receiver, a second transducer of the same type acted as the sound source. All the readings were normalised using the output of the transducer with a hexagonally shaped mask the same area as the active area of the horn plate placed in front of it, to give a true reading of the gain. Such a procedure was essential since the high Q of the transducer rendered its acoustic output highly variable with respect to frequency. The results .are all given as the ratio of the detected sound pressure with the horn plate to that of the same quantity with the mask, p/p 0 .
• the transducer was mounted on a table having a microscope traversing mechanism and the multi-horn plate was mounted separately. In this way the transducer-plate spacing could be continuously varied with a resolution of 2 - 3 microns.
• the frequency response of the transducer plus matching plate was measured between 2 kHz .and 200 kHz using the swept frequency of the gain-phase analyser.
• the spacing gap was adjusted to give maximum response at 60 kHz in each case, as will be described below.
• Typical results are shown plotted as points in Figs. 7 and 8. Measurements to determine the optimum spacing gap were all performed at 60 kHz largely for reasons of convenience, since the transducer output at this frequency was high, the radial mode driving the transducer in the thickness direction by virtue of Poisson coupling. Measurements of the output were made at 5 micron intervals, with a 2 - 3 micron resolution, starting with the plate resting against the transducer face.
• Fig. 9 shows the measured results for the horn plate of Table II, modified by surface grinding to give two different values of the horn throat radius.
• the curves show a broad maximum for a spacing of about 30 microns, and the peak gain is a little more than 10 dB.
• a notable feature of the experimental measurements is the relative insensitivity of the gain to the radius of the horn throats, caused by approximate balance between the loss in horn gain and the improvement of coupling to the gap as the throat radius is increased.
• the lack of sensitivity in these two fine dimensions is clearly a great advantage when manufacture is considered.
• the matching plates developed in this example are able to provide gain of about 10 dB over a frequency range from about 30 to 90 kHz. It is straightforward to scale the design to produce plates of higher or lower operating frequency.
• This example and the previous example also show that it is possible to fabricate adequately precise multi-horn plates by hand in the laboratory, and gives confidence that these devices could be produced simply, cheaply and to adequate tolerance in a manufacturing operation.
• the two fine dimensions, the separation gap between the multi-horn plate and the transducer surface, and the radius of the horn throat, are inevitably not critical in magnitude, so that simple assembly and testing techniques should be adequate.
• the ultrasonic impedance matching device of this invention has the following advantages: 1.
• the plate may be formed from any material whose ultrasonic impedance is high so that other engineering imperatives can be catered for e.g. corrosion, price, ease of fabrication, material properties.
• the horns are non resonant in that they do not rely on a resonant principle to operate so that the plate operates identically for both continuous waves and pulses. By the same token the horn length resonance possibilities can be utilised to further enhance continuous wave output. 5.
• the dimensions of the horn are not as critical for good operations as 1/4 wave matching layers. The frequency range of operation for any particular design is relatively wide. Thus it has a wider bandwidth and is easier to make.
• the horn matching plate works best at the lower ultrasonic frequencies, 40 - 100 kHz, which is the frequency range not presently covered by solid matching layer technology.
• a combination of the invention is especially useful in systems for detecting and/or transmitting ultrasonic vibrations in air or other gases including gas for domestic, commercial or industrial use or fluids including water and sea water.

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• 1991
  • 1991-05-14 WO PCT/AU1991/000206 patent/WO1991018486A1/en not_active Application Discontinuation
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