Abstract: A piezoelectric composite transducer and method for making same are disclosed. A block of piezoelectric material has a common base and a plurality of uniform-length rods extending from the common base in a parallel spaced-apart fashion to define an array. A first surface region is defined at outboard ends of the rods and a side region is defined about the periphery of the array. Electric conductors extend through the side region, are routed parallel to the first surface region, and are then led substantially parallel to the rods to the first surface region. Spaces between the rods are filled up to the first surface region with a viscoelastic material. The common base of the block is then removed such that a second surface region parallel and opposite to the first surface region is defined. Electrodes are deposited at the first surface region to be in contact with the rods and in electrical contact with the electric conductors.

Abstract: A transducer apparatus is disclosed including a spool member having a body portion and first and second elevated regions formed on the body portion. A piezoelectric film such as a PVDF film surrounds the spool member and is spaced apart from the body portion of the spool member by an elevation of the elevated region, thereby forming a predetermined gap between the piezoelectric film and the body portion of the spool member. The predetermined gap is at least 0.1 mm and enables a predetermined resonance frequency in the piezoelectric film to control the resonance frequency of the transducer. Opposite lateral ends of the piezoelectric film are secured together such that secured ends of the piezoelectric film have substantially the same resonance frequency as a remainder of the piezoelectric film.

Abstract: An electroactive device incorporating the invention includes an electroactive ceramic annular substrate having a pair of opposed planar annular surfaces, a hollowed interior region and a thickness aspect. A first cap having a concave shape that extends into the hollowed interior region includes a rim portion, bounding the hollowed interior region, and joined to a first one of the planar surfaces. A second cap having a concave shape that extends into the hollowed interior region includes a rim portion, bounding the hollowed interior region, and joined to a second one of the planar surfaces. A potential measured across the ceramic substrate enables a field change in the ceramic substrate to be sensed, the field change caused by flexure of the ceramic substrate as a result of a pressure applied to the first and second caps.

Abstract: A piezoelectric component in the form an actuator having a monolithic multi-layer stack is disclosed. The stack comprises a large active cross sectional area and simultaneously exhibits high arc-over resistance between neighboring electrodes of different polarity. For manufacture, only the surface of the stack via which an electrical contacting of the electrode layers ensues is ground after the sintering of a stack composed of piezo ceramic layers and electrode layers arranged on top of one another.

Abstract: A piezoelectric or electrostrictive actuator, comprising a plurality of stages of piezoelectric or electrostrictive active blocks distributed so as to form a tubular structure, the polarization of the active blocks alternating from one stage to the next, separation elements separating the unit active blocks of any one stage in pairs, said elements being superposed on one another in the height direction of the structure, being suitable for sliding over one another, and being of stiffness greater than that of the unit active blocks, a separation element extending over the height of two stages of active blocks, the separation elements on either side of a given unit active block extending respectively through both stages on either side of said unit active block, electrode-forming means enabling voltages of alternating sign to be applied to the various stacks of active blocks, and wherein a separation element is constituted by two bonded-together slabs each belonging to a different stage, the slabs of any one stag

Abstract: A system and method for operating a cylindrical acoustic projector is provided which allows efficient operation of the projector over a wide bandwidth. The system and method use multiple power amplifiers each tuned to operate over separate and narrow bandwidths, the number of seperate bandwidths corresponding to the number of amplifiers such that the total bandwidth is covered. Each tuning network assembly includes the power amplifier, a transformer and a tuning inductor, with the tuning inductor selected for proper tuning over the frequency bands the amplifier is to operate at. The narrow bandwidths for each power amplifier result in a substantial reduction in the reactive power dissipated in the amplifiers and also the total power consumption of the acoustic projector.

Abstract: A piezoelectric transducer of a new laminated structure is provided that is easy to fabricate, produces a large amount of motive energy and has high mechanical strength. Electrodes are installed on one of the surfaces of respectively a first and a second piezoelectric element formed in a thin shape, a second piezoelectric element formed without an electrode is laminated onto the top of the surface of the first piezoelectric element having an electrode to form a laminated piece. The laminated piece is wound to form a tube or folded to form a rod. The tube or rod-shaped laminate is then baked and polarized to produce a piezoelectric transducer.

Abstract: A piezo-mechanical scanner that provides independent and linear displacements in three orthogonal directions with high sensitivity in the normal z direction and high range in the lateral x and y directions. The independence of the directional displacements is ensured by physically dividing into four distinct sectors the piezoelectric tube chiefly responsible for the generation of the movements. Linearity of the movement is maintained by providing mechanical enhancement of the movements in the x-y plane.

Abstract: A bonding tool for applying pressure and ultrasonic energy simultaneously to join miniature components together includes an ultrasonic driver having four composite wafers separated by electrodes. Such bonding tools are known that use wafers made of wholly of ceramic material. By using wafers having four sector parts of ceramic material separated by layers of polymer as shown, bonding tools are provided with broader bandwidth operation and reduced spurious resonance modes.

Abstract: A linear actuator using a piezoelectric element having high mechanical strength, high driving efficiency and high reliability in which left and right end portions of the piezoelectric element in a tubular shape whose major component is PZT are fixedly supported by supporting members and a slider is frictionally coupled to the piezoelectric element, the slider frictionally coupled to the piezoelectric element is moved by causing elongation displacement and contraction displacement respectively to electrodes at the left and right end portions of the piezoelectric element when drive pulses each in a saw tooth wave having gradual rise portion and steep fall portion are applied to the electrodes at the left and right end portions of the piezoelectric element in a tubular shape and the slider can continuously be moved by continuously applying the drive pulses.

Abstract: An actuator composed of a plurality of telescoping piezoelectric members ch produces a displacement that is the sum of the length of the members.

Abstract: An energy trap type piezoelectric resonator includes a plate-like piezoelectric resonator element constructed to vibrate in a third harmonic of a longitudinal vibration mode in a thickness direction thereof and such that both main surfaces of the resonator element are laminated with sealing substrates. Sealed spaces are provided so as to allow a vibrating portion of oppositely disposed vibrating electrodes to vibrate. Sealing portions, in which the piezoelectric resonator element and the sealing substrates are joined and connected around the sealed spaces, are constructed so that when the thickness of a piezoelectric substrate is represented by t and the shortest distance to the sealing portion from the vibrating electrodes is d, the sealed spaces satisfy the relationship 0<d/t<5.

Abstract: An ultrasonic transducer with a piezoceramic disk in radial resonance operation is created to produce a narrow main cone angle with suppresion of secondary cones. This is accomplished with the help of a ring surrounding the piezoceramic disk on its lateral face with a form fit and frictional engagement, this ring being made of a material whose longitudinal wave velocity is higher than that of aluminum.

Abstract: In a piezoelectric vibrator which has excitation electrodes respectively disposed on the top surface and undersurface of a piezoelectric substrate, at least one of the excitation electrodes being an inverted-mesa electrode that has a recess formed in the opposite side of the electrode from the side which contacts the piezoelectric substrate. Thus, an AT-cut quartz resonator in which the capacitance ratio .gamma. is reduced to a value below the limit value can be provided as a result of use of the inverted-mesa electrodes as excitation electrodes.

Abstract: An actuator includes a ceramic body having a base and an array of tube-shaped or blade-pair-shaped piezoelectric or electrostrictive ceramic elements defining an enclosure and integral with the base. A first electrode contacts the inner surfaces of walls of the elements, while a second electrode contacts the wall outer surfaces. The actuator is driven for d.sub.31 mode or d.sub.15 mode vibration of the walls. The wall vibration is transmitted to a desired medium via a vibration transmission means, e.g., a compliant polymer filler material of Shore A30 to Shore D75 filling the enclosure and bonded to the walls. Alternatively, a stiff cover plate may be used to transmit the tube wall vibration to a desired medium. An acoustic sensor device is also described.

Abstract: A rotary actuator for applying torque to a crank with respect to a member. The rotary actuator has a substantially planar sheet of anisotropic conducting polymer, portions of which are activated in temporal sequence to produce rotation of the crank with respect to the axis of the crank. Actuation is achieved by contraction of successive portions of the sheet as electrical current causes differential strain in the sheet.

Abstract: A variably sound-absorbing device comprises a piezoelectric material 32 the peripheral portion of which is fixed to a frame 31 or the like, at least one pair of electrodes 34 formed on opposite surfaces of the piezoelectric material, and at least one circuit element 36 through which the electrodes are connected to each other. The piezoelectric material 32 is boardlike and curved, and an electrical characteristic of the circuit element 36 (a circuit showing a negative capacitance for example) is variable. The modulus of elasticity (the real number part of the modulus of elasticity) and the loss factor (the imaginary number part of the modulus of elasticity) of the piezoelectric material are thereby varied and the sound-absorbing characteristic is electrically varied to a considerable extent.

Abstract: A marine seismic source for generating acoustic source energy from electrical power. A slotted housing has an exterior surface engaged with an electrically activated transducer such as a piezoelectric transducer. One or more piezoelectric components can be adhered or otherwise attached to the exterior surface of the housing. A case can cover all or part of the piezoelectric components, and the case can be waterproof to prevent contact between the transducer and the water. The case can be integrated with the slotted housing to form a composite structure, or a cavity, for containing a transducer such as piezoelectric components.

Abstract: This invention relates to a new class of piezoelectric composites with a radial design. More particularly, the radial design of these new ceramic/polymer composites show a higher sensitivity in the radial direction than conventional tube structured devices. Devices made utilizing this novel design will therefore show significantly enhanced performance in many applications.

Abstract: Ultrasonic transducer with a selectable beamwidth comprising a body of piezoelectric material in the form of an annulus having an outer diameter D and a thickness T. The body has proximal and distal generally planar parallel surfaces and a centrally disposed hole extending therethrough. The body has a cylindrical wall with a width W extending from the hole to the outer diameter. The transducer is capable of operating at low and high resonance frequencies with the low frequency resonance being determined by the diameter D and an aspect ratio of D/T and the high frequency resonance being determined by the thickness T and an aspect ratio of W/T.

Abstract: A piezoelectric actuator has at least one monolithic piezoelement of a piezoelectric material, having a tubular form and a penetrating bore extending along a longitudinal direction surrounded by a tubular wall. An inner electrode is provided on the inside of the tubular wall of each piezoelement. Correspondingly, an outer electrode is provided on the outside of the tubular wall of each piezoelement. When an electric voltage is applied between the inner electrode and the outer electrode, an electrical field is formed that is essentially aligned perpendicularly to the longitudinal direction of the tubular piezoelement, the electrical field effecting a deformation of the piezoelement in its longitudinal direction in order to exert an actuation force in the longitudinal direction of the piezoelement.

Abstract: A torsional actuator includes a plurality of segments, each segment having a substantially rectangular shape. Each segment is comprised of an electroactive material that is poled along an elongated dimension of the rectangular shape. The segments are arranged side-by-side, with adjacent segments poled in opposing directions along their long dimensions. Conductors are positioned between adjacent sides of the side-by-side segments, with all of the juxtaposed segments being bound together in an integral structure. A power supply is connected to the conductors and applies oppositely poled electric fields across adjacent segments to cause like shear deformations of each of the segments and a resultant angular rotation of a non-fixed end thereof.

Abstract: A resonator having piezoelectric properties is tuned to respond at a specific overtone of its parallel plate resonant frequency. A channel is etched in a blank to confine the oscillations to a predefined area thereby maximizing a predetermined overtone. The position and dimension of the channel are selected to confine the oscillation to a radius that maximizes the response at a desired frequency. The desired frequency is a predetermined overtone of the fundamental frequency. The channel limits the area of oscillation of the blank. The channel may be formed using grooves or slots. The slots are arranged to form a ring. The channel may be positioned inside or outside an electrode.

Abstract: An apparatus for establishing and/or monitoring a pre-determined filling level in a container is provided, in which the reception signal (E) corresponds to the desired measurement signal and in which a fixed phase difference (.DELTA..phi..sub.R), which is independent of the oscillation quality of the apparatus, exists between the transmission signal and the reception signal (E) at the resonant frequency (f.sub.r) of the mechanical oscillatory structure (1).

Abstract: In a piezoelectric transformer having a piezoelectric body in polarized condition, input electrodes provided on the surface of the piezoelectric body and applied an alternating voltage of a frequency depending upon the resonance frequency of the piezoelectric body and a leading electrode provided on the surface of the piezoelectric body and taking out a voltage depending upon vibration of the piezoelectric body, and a grounding electrode is further provided on the surface of the piezoelectric body and electrically isolated from the input electrode and taking out output voltage in cooperation with the leading electrode by forming a pair, depending on the vibration of the piezoelectric body. Thus, even when an alternating voltage having a frequency equal to the resonance frequency of the piezoelectric body, respective junctions have sufficient strength against vibration.

Abstract: Piezoelectric resonator structures and circuits therefor are provided to p the energy available for vibrational deformation in a resonator, between the driving electrodes of the resonator structure. Field trapping electrodes are disposed to enclosed the driving electrodes in the resonator structures which are arranged in circuits to derive electric fields between the field trapping electrodes in an opposite direction to that of an electric field between the driving electrodes.

Abstract: A motor itself has multi-functions to be able to drive a plurality of objects to be controlled, so that the whole apparatus is compact and provided at low cost. The rotation planes of first and second rotating units B1 and B2 are faced with each other to make these planes in a mutually pressed state. A current is supplied to a piezoelectric element provided on the rotation plane of any one or both of the first and second rotating units, and the rotation of any one of the first and second rotating units is selectively stopped by pressing members, so that any one of the rotating units can be selectively rotated.

Abstract: An ultrasonic transducer is disclosed for emitting an ultrasonic wave radially inward. The transducer is constructed with a strip of piezoelectric material laminated with a pair of electrically conductive metal layers that are conductively isolated from one another. In a preferred embodiment, the strip of piezoelectric material is formed in a cylindrical shape and with continuous sinusoidal ripples along the circumference. The sinusoidal ripples are designed to emit a specific wave length of a desired frequency. The radius of the sinusoidal wave is based on material characteristics and the desired resonance frequency. The invention discloses various methods and apparatus for constructing and maintaining the transducer sinusoidal shape. One method includes attachment of a pair of rigid end caps on the laminated piezoelectric material, and another discloses weaving the laminated piezoelectric material through a nonconductive mesh cage, and yet another includes adhesively attaching the transducer to a housing.

Abstract: There is provided a piezoelectric transformer including (a) a cylindrical body made of piezoelectric material and longitudinally defining a driven section and a voltage generating section, the voltage generating section being polarized in one of directions in a direction of a longitudinal axis of the cylindrical body, (b) a pair of first electrodes formed at a curved surface of the cylindrical body in the driven section and defining a plurality of regions in the driven section in a direction of a longitudinal axis of the cylindrical body, the first electrodes being electrically isolated with each other, the regions being polarized so that every other regions are polarized in opposite directions in a direction of a longitudinal axis of the cylindrical body, the pair of first electrodes comprising a plurality of strip-shaped electrodes wound around the cylindrical body and disposed in parallel with one another in a direction of a longitudinal axis of the cylindrical body, every other strip-shaped electrodes bei

Abstract: A transducer including a ceramic body having a base and an array of tube-shaped piezoelectric or electrostrictive ceramic elements integral with the base. A first electrode contacts the tube wall inner surface, while a second electrode contacts the tube wall outer surface and is electrically isolated from the first electrode and from the lower surface of the transducer. The first electrode extends onto the transducer lower surface for electrical connection to a power source for driving the transducer across the tube walls for d.sub.31 mode vibration of the tube walls. A stiff cover plate may be used to transmit the tube wall vibration to a desired medium. The ceramic base may be removed if an electrically insulating layer is provided between the elements at the lower surface of the transducer. The insulating layer and tube wall upper edges then electrically isolate the second electrode from the first electrode and the transducer lower surface.

Abstract: Traveling-wave piezoelectric motor comprising at least one stator (1, 2) consisting of an annular body with which are associated two groups of piezoelectric elements (3, 4) in the form of rods in permanent contact with the stator and with a connector (7) for their excitation, and a rotor (12, 13). The rods (3, 4) are housed in a drum (5, 6) made of an insulating material whose holes have a constriction (24) for holding the rods.

Abstract: The invention relates to a device for rapping electrodes, preferably collecting electrodes, in a high voltage supplied electrostatic precipitator. The device has at least one piezo electric element adapted to supply a rapping impact to at least one electrode at a predetermined level and frequency.

Abstract: A vibrating gyroscope 10 comprises a tubular member 12 made of a piezoelectric material. The tubular member 12 is polarized in its thickness direction. A common electrode 14 is formed on the inner surface of the tubular member 12, and outer electrodes 16a, 16b, 16c are formed on the outer surface of the tubular member 12. The outer electrodes 16a, 16b, 16c are spaced in the circumferential direction of the tubular member 12. A vibrating member 18 passes through the inside of the tubular member 12.

Abstract: A movement actuator includes an elongate filament made of a flexible material, and a strip of shape memory alloy disposed on the surface of one side of the filament. The shape memory alloy is responsive to actuation signals, heat or electrical signals, for changing its shape and when its shape changes, it causes the filament to move, i.e., bend, to accommodate the change in shape of the alloy. Also included is a signal supply device for selectively applying heat signals or electrical current to the strip of shape memory alloy to causes the alloy to change its shape and cause the filament to bend. Other patterns for the shape memory alloy could be disposed on the filament to cause other kinds of movements. For example, a helical pattern of the shape memory alloy about the filament would cause the filament to twist when the helical pattern were caused to shorten or lengthen.

Abstract: Ultrasonic transducer with a selectable beamwidth comprising a body of piezoelectric material in the form of an annulus having an outer diameter D and a thickness T. The body has proximal and distal generally planar parallel surfaces and a centrally disposed hole extending therethrough. The body has a cylindrical wall with a width W extending from the hole to the outer diameter. The transducer is capable-of operating at low and high resonance frequencies with the low frequency resonance being determined by the diameter D and an aspect ratio of D/T and the high frequency resonance being determined by the thickness T and an aspect ratio of W/T.

Abstract: A metal-ceramic device includes an electroactive ceramic substrate having a pair of opposed planar surfaces and a thickness aspect. Conductive electrodes sandwich the ceramic substrate and a first sheet metal cap having a concave shape, a substantially unchanging thickness and a rim is joined to a first planar surface of the ceramic substrate. A second sheet metal cap having a concave shape, a substantially unchanging thickness and a rim is bonded to a second planar surface of the ceramic substrate, the second planar surface opposed to the first planar surface. In an actuator embodiment, a potential is applied across the conductive electrodes to cause an expansion of the ceramic substrate in the thickness dimension and a concomitant contraction in its planar dimensions. The contraction causes a flexure of the sheet metal caps, which flexures are used for actuation purposes.

Abstract: A device for use in vehicular rear view mirrors which comprises a mirror and a vibrator so arranged to propagate pressure waves or vibrations in the mirror primarily perpendicular to the plane of the mirror. The vibrations are of sufficient magnitude as to cause water droplets to leave the surface of the mirror by atomization of the fine droplets or by the running together of droplets and subsequent dripping off by gravity. The bonds between the mirror face and other solid deposits including ice are quickly broken allowing the debris to fall clear, thus enhancing the clarity of vision of the mirror. The vibrators are ceramic piezoelectric transducers mounted in a Bi-Morph configuration directly on the back of the mirror.

Abstract: A three-dimensional scanner incorporates a flat stage for receiving samples. The stage is supported in a scanning frame by four identical quadrant tube piezo-electric scanner elements. Each element is fixed at one end to a fixed chassis and is fastened at its opposite end through a connector to the scanner frame. The scanner elements are operated in pairs to move the stage in an X-Y plane, and are operated together to move the stage in a Z direction perpendicular to the X-Y plane.

Abstract: A chemical sensor for measuring a change in the sensor mass relating to the interaction of a surface of the sensor with a solution comprises a crystal detector oscillator capable of providing a measurement signal based upon the resonant frequency of the crystal detector oscillator. The crystal detector oscillator has a first crystal side for directly contacting the solution, and a second crystal side isolated from contacting the solution. A first electrode is integral to the first crystal side, with the first electrode having an inner and outer perimeter defining an outer portion of the first crystal side which is exterior to the outer perimeter of the first electrode and an inner portion of the first crystal side which is interior to the inner perimeter of the first electrode. A second electrode is integral to the second crystal side.

Abstract: For industrial applications, there is a need for compact ultrasonic transducers which at the same time have a radiation characteristic with small side lobes. This requirement is met by an ultrasonic transducer of conventional design and having a piezoelectric transducer element (1) which is bonded over its main surface (7) to a disk-shaped .lambda./4 matching element (2), it being the case according to the invention that the circumferential surface (3) of the .lambda./4 matching element is profiled with a notch (4) of suitable depth (5).

Abstract: A piezoelectric device includes a ceramic substrate having at least one cavity defined by a thin-walled region of the substrate. The thin-walled region has an outer surface provided with at least one piezoelectric transducer and also with a non-operative portion situated adjacent to the piezoelectric transducer such that each piezoelectric transducer surrounds the non-operative portion, or two piezoelectric transducers are arranged on both sides of the non-operative portion.

Abstract: The sonic or ultrasonic transducer includes a circular piezo-ceramic disk capable of generating radial oscillations, and a metal ring, which embraces in tight close fitting relationship the circumferential surface area of the disk to form a radial oscillator in conjunction with the disk. The sonic or ultrasonic transducer formed in this manner has an emission surface corresponding to the entire surface area of the piezo-ceramic disk and metal ring, and displays a radial resonant frequency which is lower than that of the piezo-ceramic disk.

Abstract: Ultrasonic transducer with a selectable beamwidth comprising a body of piezoelectric material in the form of an annulus having an outer diameter D and a thickness T. The body has proximal and distal generally planar parallel surfaces and a centrally disposed hole extending therethrough. The body has a cylindrical wall with a width W extending from the hole to the outer diameter. The transducer is capable of operating at low and high resonance frequencies with the low frequency resonance being determined by the diameter D and an aspect ratio of D/T and the high frequency resonance being determined by the thickness T and an aspect ratio of W/T.

Abstract: An electromechanical positioning device to be used for positioning, for example, a probe-tip (12) in a scanning tunneling microscope, an electron emitter in a field electron gun, a mirror in an interferometer etc. comprises a low-mass support (10) as a moving drive means. The support, which is mounted to be frictionally movable in an electromechanical movement activating means, can be moved comparatively fast owing to its low mass and very precisely because its response to the movement force is controlled by sawtooth control pulses, preferably via a piezo-mechanical structure.

Abstract: A thermotherapy device for use in treating cancer. The thermotherapy device includes a radio frequency power source for energizing transducers to output ultrasound waves to heat a patient treatment site. The transducers are arranged in a cylindrical shape to treat the patient and a variable number of ultrasound transducers can provide a customized therapy treatment.

Abstract: A piezoelectric vibrator includes a thin quartz plate portion for generating vibrations, and non-contact electrodes for applying an alternating electric field. The electrodes are arranged on opposing sides of the thin quartz plate portion so as to not contact with the thin quartz plate portion. The electrodes may be formed on a supporter which can be bonded directly to the thin quartz plate. The electrodes may also be formed above the thin quartz plate and supported by the plate outside the thin quartz plate portion. The piezoelectric vibrator has a superior Q of resonance at high frequencies.

Abstract: A thermotherapy device for use in treating cancer. The thermotherapy device includes a radio frequency power source for energizing transducers to output ultrasound waves to heat a patient treatment site. The transducers are arranged in a cylindrical shape to treat the patient and a variable number of ultrasound transducers can provide a customized therapy treatment.

Abstract: A piezoelectric transducer (100) may be achieved by mounting a piezoelectric bender (101) within a housing (102). Maximum resonation may be obtained by mounting the piezoelectric bender (101) on a single post (103). The housing (102) is constructed to have essentially the same geometry as the piezoelectric bender (101) and is separated by a predetermined distance (104). This predetermined distance (104) provides an acoustic impedance such that sound may resonate from the transducer.

Abstract: Piezoelectric actuator having at least one piezoelectric element assigned to an electrode for applying a control voltage includes a hollow body having a volume filled with an incompressible liquid, an elastic membrane closing an opening formed in the hollow body, and a device for controlling the piezoelectric element so as to vary the volume of the hollow body during a deformation of the elastic membrane caused by the incompressible liquid.

Abstract: Monolithic, internally asymmetrically stress biased electrically active ceramic devices and a method for making same is disclosed. The first step in the method of the present invention is to fabricate a ceramic element having first and second opposing surfaces. Next, only the first surface is chemically reduced by heat treatment in a reducing atmosphere. This produces a concave shaped, internally asymmetrically stress biased ceramic element and an electrically conducting, chemically reduced layer on the first surface which serves as one of the electrodes of the device. Another electrode can be deposited on the second surface to complete the device. In another embodiment of the present invention two dome shaped ceramic devices can be placed together to form a completed clamshell structure or an accordion type structure. In a further embodiment, the clamshell or accordion type structures can be placed on top of one another.