Technical Field

[0001] The present disclosure relates to an X-ray diffraction sample cell device and method. In particular, the present invention relates to an X-ray diffraction device for the measurement of material properties and structures during the application of electric fields.

Background of the Invention

[0002] The measurement of material structures using X-ray diffraction while the material is in an environment having a high electric field can be used to determine information regarding the atomic and microstructural changes and their relationship to the properties of the material. This information may in particular be of interest to researchers considering electronic materials used for electro-mechanical sensors and actuators. Electro-mechanical materials, such as piezoelectrics, generate an electric charge in response to applied mechanical stress, and/or experience a mechanical strain in the presence of an electric field.

[0003] Currently no commercial device exists for the measurement of material structures using x-ray diffraction while the material is under an environment of high electric field. This is of interest to researchers of electronic materials used for electro-mechanical sensors and actuators.

[0004] In order to obtain an understanding of the functional mechanisms of electro mechanical materials, it can be useful to measure diffraction patterns during the application of an electric field.

[0005] Many of the structural changes occurring in ferro-electrics under the application of an electric field can be measured using diffraction. X-ray diffraction and neutron diffraction offer a unique insight into the atomic and microstructural states of ferroelectric ceramics. The technique has been used to characterise both intrinsic lattice strains, measured as distortions to the unit cell, ferroelastic domain switching, measured as intensity changes between certain reflections, and also phase transformations, measured as unique diffraction signatures.

[0006] Typically, researchers measure diffraction patterns using custom made devices and kits, which generally have a sample cell, to support the desired sample. The sample cell generally has two windows for the incident and scattered X-ray beams. There are various constraints and difficulties which apply to sample cell design such as:

The total thickness of the sample cell must be kept small for versatility to mount on different X-ray diffraction instruments;

It is important to minimise shadowing of the detector solid angle; and

It is necessary to isolate the electric current, for user safety and to avoid damage to the equipment.

[0007] Another problem with setting up such diffraction pattern measuring devices is that the sample is normally very small and it is difficult to mount the sample in a manner that permits it to be put in contact with the electric field and also allowing entrance and exit paths for x-ray scattering measurements.

[0008] Existing devices which are able to secure a sample in an electric field suffer from various drawbacks. For example, the geometry of the sample holding device is not suitable to be located within certain X-ray diffraction equipment. Furthermore, the devices generally do not permit the X-rays to be delivered through a wide angular range which may be required or at least desirable for testing.

[0009] Further drawbacks of existing x-ray diffraction measuring devices relate to both the field and temperature range over which they operate and their ability to simultaneously measure material properties.

[0010] A still further drawback concerning existing X-ray diffraction devices which are able to secure a sample in an electric field relates to their ease of use with respect to sample loading and unloading, which can be difficult due to the small size of the sample, and the need for the sample to be in contact with the electric potential, and held completely stationary during testing.

Object of the Invention

[0011] It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages, or to provide a useful alternative.

Summary

[0012] In a first aspect, the present invention provides an X-ray diffraction sample cell including:

a housing body having a sample support,

a housing cover connected to the housing body with a hinge, the housing cover having an electric contact;

an electric circuit extending on or through the sample cell, the electric circuit having an input terminal, a first path extending from the input terminal to the sample support and a second path extending from the input terminal to the electric contact;

an interlock system which disables the power supply to one of the first or second paths of the electric circuit when the housing cover is open relative to the housing body, wherein the electric contact is located adjacent to and separated from the sample support by a clearance when the housing cover is in the closed position.

[0013] Preferably the electric contact is isolated from the housing cover.

[0014] The X-ray diffraction sample cell further preferably comprises a strain measurement sensor in communication with the contact.

[0015] The second path preferably includes a first electric connector and a second electric connector which electrically engage when the housing cover is pivoted toward a closed position relative to the housing body.

[0016] The contact is preferably selectively moveable between two positions to alter a distance between the contact and the sample support.

[0017] The contact is preferably selectively moveable by a translation stage having a rotatable portion.

[0018] The contact is preferably coupled to the translation stage with a resiliently biased member.

[0019] The resiliently biased member preferably incorporates a leaf spring, and the leaf spring is in communication with the strain measurement sensor.

[0020] The sample support is preferably connected to a heating element that is electrically isolated from the electric circuit.

[0021] The housing body and the housing cover preferably define a chamber around the sample support when the housing cover is in the closed position.

[0022] The chamber preferably has first and second windows located on opposing lateral sides of the clearance.

[0023] The X-ray diffraction sample cell further preferably comprises a strain measurement sensor in communication with the sample support. [0024] The sample support is preferably mounted to the housing body with a resiliently biased member configured to permit the clearance to be adjusted.

[0025] Preferably the resiliently biased member is a spring and the spring is in

communication with the strain measurement sensor.

[0026] The contact is preferably defined by one of a pair of diametrically opposed arms, separated by a space.

[0027] The arms are preferably configured to abut against an upper surface of a sample located on the sample support, and the sample support is displaceable if a thickness of the sample is larger than the clearance.

[0028] The sample support is preferably connected to a heating element that is electrically isolated from the electric circuit.

[0029] The housing cover further preferably comprises at least one dome shaped shield located over the sample support.

[0030] At least a portion of the shield preferably extends downwardly at least to an underside of each of the first and second diametrically opposed arms.

[0031] In a second aspect, the present invention provides an X-ray diffraction sample cell including:

a housing body having a sample support,

an isolated electric circuit extending on or through the housing body, the electric circuit having an input terminal, a first path extending from the input terminal to the sample support and a second path extending from the input terminal to a first electric connector; a housing cover hingedly connected to the housing body, the housing cover having a third path extending between a second electric connector and a contact,

wherein the first electric connector electrically engages the second electric connector when the housing cover is pivoted toward a closed position relative to the housing body;

further wherein the contact is located adjacent to and separated from the sample support by a clearance when the housing cover is in the closed position.

[0032] In a third aspect, the present invention provides an X-ray diffraction sample cell including:

a housing body having a sample support,

a housing cover hingedly connected to the housing body, the housing cover having an electric contact, configured to abut against an upper surface of a sample located on the sample support;

an electric circuit extending on or through the sample cell, the electric circuit configured to apply an electric field to the sample through the contact and sample support; and

a strain measurement sensor configured to measure strain in the sample during an X-ray diffraction process.

[0033] The strain measurement sensor is preferably coupled to the electric contact.

[0034] The strain measurement sensor is preferably coupled to the sample support.

Brief Description of the Drawings

[0035] A preferred embodiment of the invention will now be described by way of specific example with reference to the accompanying drawings, in which:

[0036] Fig. 1 is a cross-sectional view of an X-ray diffraction sample cell according to a first embodiment;

[0037] Fig. 2 is a front view of the sample cell of Fig. 1 in a closed configuration;

[0038] Fig. 3 is a cross-sectional view of the sample cell of Fig. 1 in an open configuration;

[0039] Fig. 4 is a perspective view of the sample cell of Fig. 1 in an open configuration;

[0040] Fig. 5 is a schematic view depicting the sample cell of Fig. 1 being used for transmission geometry X-ray diffraction;

[0041] Fig. 6 is cross-sectional side view of a X-ray diffraction sample cell according to a second embodiment in a closed configuration;

[0042] Fig. 7 is a cross-sectional side view of the reflection geometry X-ray diffraction sample cell of Fig. 6 in an open configuration;

[0043] Fig. 8 is a perspective view of the X-ray diffraction sample cell of Fig. 6 in an open configuration;

[0044] Fig. 9 is a perspective view depicting the X-ray diffraction sample cell of Fig. 6 in a closed configuration; and

[0045] Fig. 10 is a schematic view depicting the sample cell of Fig. 6 being used for reflection geometry X-ray diffraction. Detailed Description of the Preferred Embodiments

[0046] A first embodiment of a transmission type X-ray diffraction sample cell device 100 is disclosed in Figures 1 to 5. The sample cell 100 is a "transmission" device, meaning that the X-ray beam is used for performing transmission geometry x-ray diffraction experiments on samples, whereby the X ray beam is directed into a front face of the sample, and the diffracted beam subsequently exits through the opposing rear face of the sample.

[0047] The transmission sample cell device 100 is intended for performing transmission geometry x-ray diffraction experiments, up to electrical potentials of +/- 10 kV. These are typically done at large scale x-ray facilities like a synchrotron, where access to high- energy/high-intensity x-rays is possible. However, the device 100 is also configured to fit within laboratory based instruments with higher energy X-ray sources.

[0048] The transmission sample cell device 100 includes a housing body 110 and a housing cover 120. The housing body 110 includes one or more threaded holes 130, or another suitable mounting formation, which permits the housing body 110 to be mounted on legs 140 or another suitable support structure, plate or stand.

[0049] Each of the housing body 110 and housing cover 120 has an outer aluminium casing and an internal, thermally and electrically insulated housing made for example from a ceramic material, such as MACOR, within which the electrical contact passes (discussed below).

[0050] Referring to Fig. 3, the housing body 110 includes a central pedestal or raised platform 150 which includes a sample support 160. The sample 162 is typically a small pillar of material which has been machined by way of cutting and polishing to a sample

thicknesses from a few micron up to about 4mm.

[0051] The sample is typically located in a receptacle 165 fabricated from a polyimide film such as Kapton™ and containing an electrically inert liquid such as silicone oil. The sample holder 161 is defined by the combination of the sample support 160 and the receptacle 165. The liquid bath filled with inert fluid assists to avoid dielectric breakdown of air at high voltage.

[0052] Referring to Fig. 3, electric current in the form of a high voltage power supply is connected to the housing body 110 at terminal block 170. Beyond the terminal block 170, the power supply is divided into two paths defined by a first path 185 which terminates beneath the sample support 160 and in electric communication with the sample support 160. A second path 175 is in electric communication with a first electric connector in the form of a female port 180. The housing body 110 includes a heating element 190 which can be used to selectively elevate the temperature of the raised platform 150 and the sample support 160, so that the sample temperature can be elevated if desired. The heating element 190 is electrically isolated from the electric circuit. The operating temperature may range from room temperature to about 300°C. The section 164 in Fig. 3, above the heating element 190 and below the sample support 160 is the thermal contact/electrical isolation, which in a preferred embodiment is fabricated from Aluminium Nitride ceramic. This feature, reduces the likelihood of the heater circuit being damaged by overvoltage events on the sample support 160.

[0053] The aluminium nitride section 164 provides high thermal conductivity and low electrical conductivity in order to provide electrical isolation from potential overvoltage events, but still allow efficient heat transfer.

[0054] The housing cover 120 is connected with a hinge to the housing body 110, and preferably with a hinge or pin joint 200. The pin joint 200 defines an axis about which the housing cover 120 rotates relative to the housing body 110.

[0055] The housing cover 120 includes a second electric connector in the form of a male plug 210 which is configured to engage with the female port 180 when the housing cover 120 pivots from the open configuration of Fig. 3 to the closed configuration of Fig. 1. The first electrical connector 180 and the second electrical connector 210 are fully isolated from the housing body 110 and housing cover 120. In contrast, if those paths were not fully isolated from the housing body 110 and the housing cover 120, electrical property measurements could not be taken. In practice, the ability to take such measurements is highly desirable. Referring to Fig. 3, the electric supply line defines a third path 195, extending from the male plug 210 to a contact 130 which is mounted to the housing cover 120, directly above the sample holder 161.

[0056] In each embodiment of the invention, the contact 130 runs through the housing cover 120, but is electrically isolated from it. This is advantageous, as it enables electrical property measurements to be taken which are not possible in prior art devices, and such electrical property measurements can be of considerable value.

[0057] The contact 130 is moveable between two positions, separated by about 5mm. A first position (depicted in Fig. 3) and a second position (depicted in Fig. 1). [0058] When the housing cover 120 is moved to the closed position, if there is a sample 162 on the sample platform 160, the physical contact between the upper surface of the sample 162 and the contact 130 closes the circuit, and allows the electric potential to be applied to the sample 162, thereby applying the electric field, such that the first, second and third electric paths 185, 175, 195 are connected via the sample.

[0059] Referring to Fig. 4, the X-ray diffraction sample cell device 100 includes an interlock system 252. The interlock system 252 includes a button 265 formed on the housing body 110 and a corresponding switch 255 located in the housing cover 120. The switch 255 is in communication with the power supply line defined by the wire 253 depicted in Fig. 3

[0060] It will be appreciated that the placement could alternatively be inverted, or placed in other locations between the housing body 110 and cover 120. The interlock system 252 is electrically connected to the power circuit, such that the electrical supply is disabled whilst the housing cover 120 is open. As the housing cover 120 moves to the closed position relative to the housing body 110, the button 265 and switch 255 engage, and the electric supply is enabled.

[0061] The electric circuit is arranged such that the high voltage line is applied to one of the housing body 110 or the housing cover 120, and the ground return is applied to the other.

[0062] As discussed above, in the open position, the power supply circuit is interrupted by both the interlock system 252, and also the male plug 210 and corresponding female port 180, which provides increased safety. Flowever, in another embodiment, it is envisaged that the male plug 210 and female port 180 may be omitted, and replaced by a flexible cable or other such wiring arrangement, such that the only interruption to the circuit is provided by the interlock system 252.

[0063] The X-ray diffraction sample cell device 100 includes a translation stage 450 which can be used to selectively move the contact 130 vertically (when the housing cover 120 is in the closed position). By manually winding/rotating the user grip portion 455, the user can vertically shift the contact 130 by about 5mm vertically, to accommodate different sized samples 162, and vary the load applied to the upper surface of the samplel62. A contact load sensor indicates when the contact 130 and sample 162 are in contact with each other.

[0064] The translation stage 450 is coupled to the contact 130 with an arm 135 and an intermediate leaf spring 145. This arm 135 is made from an electrically insulating material, to isolate the strain measurement system from the high voltage. Zirconia provides combined electrical insulation and mechanical durability, but other materials could alternatively be used.

[0065] In a further version the translation stage 450 may be motorised with an electric motor (not shown), such that adjustment of the contact 130 height is controlled without direct user input, but rather is controlled by a computer system.

[0066] The leaf spring 145 provides a means to measure strain and displacement of the upper surface of the sample 162 and the leaf spring 145 is in communication with a strain measurement sensor. However, it will be appreciated that optical sensors or other such strain or displacement measuring devices may alternatively be employed.

[0067] When a user manually winds the grip portion 455 of the translation stage 450, the leaf spring 145 and the arm 135 and the contact 130 all move vertically relative to the sample 162. The contact is selectively moved to a location in which it contacts the upper surface of the sample 162. The contact load sensor is used to indicate when the contact 130 and sample 162 are in contact with each other.

[0068] The X-ray diffraction sample cell device 100 includes a lock in the form of a screw clamp 220. The screw clamp 220 can be used to manually secure the housing cover 120 to the housing body 110 in the closed position. The screw clamp 220 has a threaded stem 230 which engages a threaded hole 240 formed in the base of the housing body 110, and clamps against a flange 250 formed on the housing cover 120. It will be appreciated that alternative locking mechanisms may be deployed to secure the housing cover 120 to the housing body 110.

[0069] Referring to the perspective view of Fig. 4, the housing cover 120 has two side walls 300, 310 which define a central receptacle 320, in which the sample holder 161 is positioned in use. Each of the side walls 300, 310 includes windows 325, 330 fabricated from an X-ray transmissive material, which is stable across a wide temperature range, such as polyimide films. The windows 325, 330 provide an enclosed environment around the sample holder 161 to provide a stable temperature, which is especially important when the sample is tested at elevated temperatures. Furthermore, the windows 320, 330 shield the technicians from the electric voltage, thereby reducing electrocution risks. [0070] A printed circuit board (PCB) 112 for controlling the sample cell device 100 is located within the housing body 110, as depicted in Fig. 3. Other internal locations may also be possible.

[0071] The operation of the transmission type X-ray diffraction sample cell device 100 will now be described. Referring to Fig. 5, an X-ray beam 350 is generated by a laboratory based X-ray instrument, or a synchrotron source and is directed to the first window 320. The incident X-ray beam 350 passes through the first window, and into the sample 162 mounted in the sample holder 161. The diffracted beam subsequently passes through the sample 162, and exits the sample cell device 100 through the second window 330.

[0072] The transmitted X-ray beam is scattered and recorded against a detector 470 which records the beam diffraction pattern for a given electric field. Scattering angles of up to 45 degrees in the scattering cone 460 may be achieved as depicted in Fig. 5. There are several different types of detector which may be used, and detector 470 is one example.

[0073] The electric field may be changed during the X-ray diffraction measurement to observe differing diffraction patterns. In practice, this may be achieved by varying the voltage waveform. The power source is variable and may be applied as an alternating current or a direct current.

[0074] In the first embodiment of the X-ray diffraction sample cell device 100, the voltage applied is typically up to magnitudes of +/- 10 kV.

[0075] A second embodiment of a "reflection" type X-ray diffraction device 500 is disclosed in Figs 6 to 10. The reflection type diffraction device 500 operates with an electric field and temperature range which is similar to the diffraction sample cell device 100 described above in the first embodiment. Flowever, they differ in the type of X-ray diffraction geometry they are suited for.

[0076] There are numerous common design features between the first and second embodiments, and the description below focuses on the key areas of difference.

[0077] The reflection X-ray diffraction device 500 is primarily for use in laboratory based X- ray diffractometers where the X-ray beam is required to scatter from a surface of the material into the X-ray detector unit 505. As depicted in Fig. 10, the angle of the X-ray source and detector 505 will be scanned relative to the sample surface normal. A difficulty with this reflection type design is having the ability to bring the X-ray beam parallel to the upper surface of the sample, or at least close to parallel. [0078] In a similar manner to the first embodiment described above, the sample holder 530 has a housing body 510 and a housing cover 520 which are connected with a hinge or pin joint 600.

[0079] The X-ray diffraction device 500 is suitable for sample thicknesses from a few micron (with spacers used) up to 2mm. The sample 565 is seated on a sample holder 530.

[0080] A PCB control system 512 is located within the housing body 510, as depicted in Fig. 7.

[0081] Referring to Figs. 6 and 7, the sample stage 530 is depicted as a disc. The sample 565 is seated on the sample holder 530. The sample 565 is held onto the stage 530 with a pair of arms 570, 580 of the housing cover 520 and best seen in Fig. 8. When the housing cover 520 is closed, the arms 570, 580 contact the sample 565, in the manner depicted in Fig. 6. The arms 570, 580 serve the purpose of holding the sample surface at a fixed position relative to the bottom of the housing body 510, and define an electric contact between the sample stage and the high voltage electric potential. The power supply extends along one of the two arms 570 and is in electric contact with the sample 565. The other arm 580 may include a thermometer to detect the temperature near the sample surface.

[0082] The arms 570, 580 are diametrically opposed, and as shown in Fig. 8, there is a clearance between the two arms 570, 580. The geometry of the arms 570, 580 permits the X-ray beam to be applied in a direction which extends generally perpendicular to a longitudinal axis of the arms 570, 580, in order to achieve low X-ray beam angles, which may be parallel to the upper surface of the sample and sample holder 530.

[0083] The X-ray diffraction device 500 includes a dome shaped cover or shield 620, which has a generally spherical outer surface, and a centre of the sphere being located at or near the sample holder 530, where the sample 565 is located in use. The shield 620 is

manufactured from a polyimide film such as Kapton™ which is stable at high temperatures.

[0084] The shield 620 is defined by two covers 625, 635. The inner cover 625 is intended to provide temperature stability of the sample volume area. The outer cover 635 contributes to temperature stability but is primarily provided for electrical safety to isolate any high- voltage from a user.

[0085] The shield 620 provides thermal management to maintain the temperature of the sample 565 within a desired range, which is especially important when the sample is being heated. In addition, the shield 620 provides a safety shield to protect users from the electric field.

[0086] The X-ray diffraction device 500 includes a flexural strain sensor. However, it will be appreciated that measurement of the strain can be done in different ways, including with an optical sensor. Referring to Fig. 6, the stage 530 is mounted to the housing body 510 with a spring 640. The spring 640 permits the entire stage assembly 535 to move vertically, when the arms 570, 580 apply a load to the upper surface of the sample holder 530. The spring 640 enables the stage 530 to be deflected downwardly when the housing cover 520 is closed, clamping the sample between the arms 570, 580 and the stage 530.

[0087] The inner cover 625 of the shield 620 extends downwardly at least to an underside of each of the first and second diametrically opposed arms 570, 580. The outer cover 635 finishes on top of arms 570 and 580 in some regions, but extends below the sample surface perpendicular to them to allow the x-ray beam to pass parallel to the surface.

[0088] The underside of the stage assembly 535 includes a projection 545 which abuts against a bar 555. The bar 555 is configured to deflect, and is coupled with a strain sensor. Accordingly, during use, deflection of the bar 555 can be used to measure strain of the sample without the upper surface of the sample displacing relative to the x-ray instrument, which is functionally important, and significantly improves the accuracy of the device.

[0089] The position of the arm or bar 555 is vertically adjustable. Referring to Figures 6 and 8, the adjustment is done in a very similar manner to the transmission cell 100. The arm 555 is translated up until the contact is made and the contact load can then be set. It then measures the strain by deflecting downwards. The vertical position adjustment is made via this adjustment screw 552, accessed from the side of the cell 500, which may be adjusted with a tool, or an electric actuator may alternatively be provided. By adjusting the screw 552, the section 545 vertically translates to adjust the relationship between the contact 545 and the bar 555.

[0090] As depicted in Fig. 6, the X-ray diffraction device 500 enables scattering X-ray beam angles from 2theta = 0 degree to 180 degrees when the scattering plane is perpendicular (+/-30 degrees) to the line of arms 570 and 580. Outside this, the angle is restricted to 2theta =30 degrees minimum. [0091] The X-ray diffraction device 500 enables scattering at azimuthal angles around the surface normal over the full 360 degrees at 2theta angles >30 degrees, that is around the circumference of the shield 620.

[0092] The stage 530 may be heated, from room temperature up to about 300 Degrees C. The heating element is similar to that described earlier with respect to the first embodiment. The stage 530 is mounted on a precision spring 640, as seen in Fig. 7, which allows combined temperature and strain measurements without the sample upper surface position moving relative to the x-ray measurement device.

[0093] In a similar manner to the first embodiment, the second embodiment 500 includes an electric circuit for generating the electric field. The electric circuit is arranged such that the high voltage line is applied to one of the housing body 510 or the housing cover 520, and the ground return is applied to the other.

[0094] The X-ray diffraction device 500 includes an interlock system 525. The interlock system 525 includes a button 535 formed on the housing cover 520 and a corresponding switch 536 located in the housing body 510. It will be appreciated that the placement could alternatively be inverted or positioned in alternative locations. The interlock system 525 is electrically connected to the power circuit, such that the power supply is disabled whilst the housing cover 520 is open. As the housing cover 520 moves to the closed position relative to the housing body 510, the button 535 and switch 536 engage, and the power supply is enabled.

[0095] The circuit is only completed when the housing cover 520 is closed and the underside of the arm 570 makes contact with the sample surface 565.

[0096] The screw 585 shown in Fig. 7 provides a means to secure the housing cover 520 to the housing body 510 when the chamber is closed. In both sample cell devices 100, 500 an electric field is applied through the thickness of the sample with top and bottom contact.

[0097] Advantageously, in each of the first and second embodiments of the diffraction sample cell device 100, 500, the hinged interaction between the housing body 110, 510 and the housing cover 120,520 prevents or at least significantly reduces the risk of electrocution, as the electrical power supply is only enabled when the diffraction sample cell device 100, 500 is closed.

[0098] Advantageously, in each of the first and second embodiments of the diffraction sample cell device 100, 500, the sample holder 161, 565 is easily accessed for insertion/removal due to the hinged connection between the housing body 110, 510 and the housing cover 120, 520.

[0099] In use, each embodiment of the X-ray diffraction devices 100, 500 measures the strain and electrical properties of the sample during testing.

[00100] The electric field may be changed during the test, for example by increasing or decreasing the voltage applied. In addition, the voltage waveform may be changed.

[00101] During the test, the X-ray scattering pattern which may be a transmission beam as depicted in Fig. 5, or a reflected beam as depicted in Fig 10 is measured against a detector 470, 505. It will be appreciated that different detectors may be used.

[00102] Furthermore, in the X-ray diffraction device 500, the beam angle theta and azimuth angle may be varied if desired during testing. In some types of experiments it may be desired to rotate the X-ray beam around the sample position.

In each of the X-ray diffraction devices 100, 500, the data regarding strain information and electrical property information of the sample is communicated with a computer or computer network. A user can monitor the process in real time, and also record the diffraction data regarding the material properties at given electric loads and times within waveforms.

For example, the below figure is displacement data collected in the first embodiment of the transmission type X-ray diffraction sample cell 100. The data is generated from a commercial PZT material PIC151 from PI-ceramic.

[00103] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.