US 3771058 A
The scanner element or aperture tube of a Coulter particle apparatus has a wafer in which the aperture is formed, the wafer being made of a material which has electrical insulating properties but high heat conductivity. The tube is of glass and the wafer is set into the side wall of the tube. The result is a scanner element of increased sensitivity. In one form of the invention, the surfaces of the tube, at least in the vicinity of the wafer, are covered by a coating of highly conductive material coming close to but not engaging within the aperture of the wafer. The coating inside and outside of the tube will comprise electrodes in the bodies of liquid respectively disposed on opposite sides of the tube wall.
Description (OCR text may contain errors)
Nov. 6, 1973 SCANNER ELEMENT FOR COULTER PARTICLE APPARATUS  Inventor: Walter R. Hogg, Miami Lakes, Fla.
 Assignee: Coulter Electronics, Inc., Hialeah,
 Filed: Apr. 5, 1971  App]. No.: 131,361
 US. Cl. 324/71 CP  Int. Cl. G01n 27/00  Field of Search 324/71, 71 CP, 30; 23/252; 65/36, 42; 138/103; 204/274, 106
 References Cited UNITED STATES PATENTS 2,861,932 11/1958 Pohl 204/274 3,345,561 10/1967 3,628,140 12/1971 2,985,830 5/1961 3,457,501 7/1969 3,266,526 8/1966 3,238,452 3/1966 Schmitt 324/71 CP OTHER PUBLICATIONS Handbook of Chem. & Physics, 1966, p. 15-4, 47 Ed., CRC.
Primary ExaminerRudolph V. Rolinec Assistant Examiner-Emest F. Karlsen Attorney-Silverman & Cass 57 ABSTRACT The scanner element or aperture tube of a Coulter particle apparatus has a wafer in which the aperture is formed, the wafer being made of a material which has electrical insulating properties but high heat conductivity. The tube is of glass and the wafer is set into the side wall of the tube. The result is a scanner element of increased sensitivity. In one form of the invention, the surfaces of the tube, at least in the vicinity of the wafer, are covered by a coating of highly conductive material coming close to but not engaging within the aperture of the wafer. The coating inside and outside of the tube will comprise electrodes in the bodies of liquid respectively disposed on opposite sides of the tube wall.
17 Claims, 6 Drawing Figures SCANNER ELEMENT FOR COULTER PARTICLE APPARATUS CROSS-REFERENCE TO RELATED APPLICATION One aspect of the invention herein comprises an improvement upon the structures of a copending application owned by the assignee of this application and entitled Electronic Particle Analyzing Apparatus with Improved Aperture Tube," Ser. No. 128,332, filed Mar. 26, 1971.
BACKGROUND OF THE INVENTION ture while at the same time an electric current is flowing through the aperture. Each time that a particle passes through the aperture it changes to effective impedance of the body of liquid which is subjected to the influence of the field in the aperture and thereby produces a signal which can be detected for making studies of population, concentration, size, etc. of the particulate system in suspension.
. The basic Coulter apparatus is disclosed in U.S. Pat. No. 2,656,508. The apparatus includes a body of sample. suspension retained in vessel of insulating material and a so-called aperture tube immersed in the vessel. The aperture tubehas a small wafer set into its wall close to the bottom of the tube, which is usually made of glass, the wafer commonly being made of corundum, and the interior of the aperture tube is filled with liquid also. The usual arrangement includes a closed liquid system of which the interior of the aperture tube comprises a part. Such a system is disclosed in U.S. Pat. No.
2,869,078 and provides for means to cause the flow of the suspension from the outer vessel through the aperture in theaperture tube while an electric current also flows through the aperture. There is an electronic detector which is coupled to the respective bodies of liquid on the interior and exterior of the aperture tube by means of metal electrodes immersed in the respective bodies of liquid. The source of electric current is also connected to these electrodes.
The aperture which is formed in the aperture tube is a minute hole in a corundum wafer thatis set into the wall of the tube. The aperture tube becomes a scanner element since it scans the liquid flowing through its aperture and produces a measurable signal each time that a particle passes through. The construction of the aperture tube and one method of setting the wafer into the side wall of the tube are disclosed in U.S. Pat. Nos. 2,985,830 and 3,l22,43l.
An understanding of the invention herein will be more readily obtained and its advantages fully appreciated from a discussion of the nature of the scanner element with respect to its requirements.
The presence of an electric current passing through the aperture produces a concentrated electric field in a zone which includes the entire aperture and slight bulges at its opposite ends. The current density outside trolyte of the two liquid bodies in which the electrodes are immersed. This zone, which may be called a sensing zone, is the volume of electrolyte whose impedance is changed by the presence of a particle. If the energy in the sensing zone is provided by a low frequency source of electrical current and the effective electrical impedance of the particles is several orders of magnitude removed from that of the electrolyte (which is practically the case most of the time), then the change in impedance of the effective volume of the sensing zone by the introduction of the particle thereinto will produce a signal which can be detected which. is substantially independent of the shape and orientation of the particle. The principle described above signifies that the signal is proportional to the size or volume of the particle. The linearity of response versus: particle size is best under conditions that the particles are small with -respect to the aperture, for example, having effective diameters less than ten percent of the aperture diameter. Above that size, departure from linearity becomes more apparent but not to the extent that corrections cannot be made in results.
The types of particles which have been analyzed by means of the Coulter apparatus cover a very wide gamut and include biological and industrial particles, as well-known in this art. In any given study, one will choose an aperture diameter to provide fairly linear output for the largest particles which are expected to be involved, but this choice is a compromise with the desire to detect the smallest useful particles as well. In the latter case, the aperture cannot be too large because its sensitivity decreases with increase in size. This should be obvious since the current density decreases for larger apertures. The length of the aperture is generally made about to 100 percent of its diameter, primarily to give the central region of the electric field within the aperture an opportunity to become fairly uniform. It has been mentioned above that the field bulges at the ends of the aperture giving effects which decrease the sharpness of the signal and its uniformity. The average length of an aperture is about percent of its diameter.
Longer apertures provide problems which offset their advantages. The advantages are a small increase in field uniformity in the center of the aperture and a decrease in the required bandwidth of-the amplifiers used in the detector of the Coulter apparatus. The disadvantages are the greater likelihood that coincidence of more than one particle in the aperture will occur; an increased likelihood of debris pluggng the aperture with greater difficulty of dislodging the debris; and an increase in the resistance of the longer path. This latter disadvantage is of especially greater importance since it relates to the invention herein.
Increased resistance in the aperture will generatemore socalled Johnson noise than a lower resistance of a shorter path thus cancelling the gain to be achieved due to decreased bandwidth of the ampli'fieroThe increased resistance also is part of the problem of heating of the electrolyte as it passes through the aperture. The current density in the aperture is very high and the electrolyte remains under this influence for a longer time than in the case of shorter apertures. Heating of the electrolyte will cause it to produce noise components of a random nature above "the normal Johnson noise limiting the size of particles which can be detected to those which are large enough to produce signals greater than the noise. Additionally, should the temperature of the electrolyte rise above the boiling 'point, small bubbles will be generated in the aperture and these appear as particles to the detector.
It should be recognized that while the Johnson noise of the contents of the aperture is relatively constant for the rather narrow range of temperatures normally encountered, being proportional to the square root of the temperature on the Kelvin scale, the electrical signal generated by the passage of a particle is proportional to the intensity of the aperture current. If these were the only considerations, it would be possible to detect any particle so long as it exceeded by several orders of magnitude the ionic dimensions of the electrolyte used, and displaced enough ions to cause a discernible change over and above the random fluctuation in the number of ions in'thesensing zone. The heating of the electrolyte, however, eventually limits the usefulness of increased aperture current as will be seen hereinafter.
It has been found that the type of aperture which is best used in Coulter apparatus is one which has a sharpedged inlet. Obviously, in the manufacture of the wafers which are set into the glass tubes, one makes both ends of the wafers sharp-edged because of the practical problems of identifying which is the sharp-edged entrance in the case only one end were sharp-edged. These types of apertures are easy to clear in the event that debris becomes lodged in them, which is just the opposite of wafers that have funnel-shaped entrances. The sharp-edged wafers are easier to manufacture and inspect.
The effect of such sharp-edged inlets upon the flow of liquid through the aperture is to produce a pattern of flow that is known as vena contracta. The flow pattern commences to constrict at the entrance and grows progressively smaller downstream of the entrance, leaving a space between the vena contracta and the wall of the aperture in which the electrolyte has no definite velocity, certainly not the average velocity of the stream passing through the axis of the aperture. The electrolyte in this region has eddy currents in it, tha part being swept out by reason of proximity to the vena contracta being replaced by electrolyte which enters the region from the downstream end of the aperture next to its walls. This effectively stagnant region has no organized flow pattern and has substantially less motion than the main flow of liquid.
It will be recalled that simultaneously with fluid flow, there is an electric current flowing in the aperture, generating heat in the electrolyte. The temperature of any volume increment of electrolyte rises in accordance with its stay in the region of high current density. It follows that the central laminar flow of the vena contracta will produce thecoolest electrolyte but that the electrolyte in the quasi-stagnant region described above will have increments of electrolyte of higher temperatures and of differing temperatures depending upon how long they remain in the aperture.
The electrical conductivity of an electrolyte varies with its temperature quite rapidly. For instance, a 0.1 normal solution of potassium chloride at 3 lC has double the conductivity that it has at C. Thus, an appreciable proportion ofthe contents of the aperture has an unpredictable conductivity when high aperture currents are used, a fact which causes random modulation of the aperture resistance which-is in turn interpreted by theapparatus as noise. In additionto the-simple.
modulation of the aperture resistance due to changes in conductivity, the temperature rises in various locations within theaperture may permit the release of occluded gases in the form of microscopic bubbles, which displace electrolyte and hence are interpreted by the apparatus as particles. Volatile electrolyte may boil, as mentioned above, and these bubbles also produce signals which look like particle pulses. Accordingly, there is an optimum value of aperture current beyond which the phenomena described are intolerable.
From the above discussion, it will follow that the signal-to-noise ratio of the Coulter apparatus improves linearly with aperture current for small aperture currents since the noise is constant whereas the signal developed is proportional to aperture current. Sensitivity also increases. The point is reached, however, at which in addition to the Johnson noise, noise due to the heating effects described above, increase at the same rate as the signal, beyond which point no further improvement is gained in the signal-to-noise ratio. As a matter of fact, noise increases more rapidly than the signal after this latter mentioned point is reached so that the signal-to-noise ratio is instead worsened.
The invention herein provides a structure for a scanner element which results in cooling the electrolyte located in the region on quasi-stagnation, thereby lessening the degree of modulation of resistance for a given aperture current. Absent the heating noise, sensitivity and signal-tonoise ratio are substantially improved with the result that a given aperture is capable of distinguishing between very much smaller particles than have heretofore been detected by the normal Coulter apparatus. It can be seen that an entire new field of particle technology can be opened by theinvention.
Just, for example, up to the present time by careful control of aperture current and the use of relatively small apertures, it has been feasible to study particles of the order of one micron in size. Below this approximate range, noise prevented distinguishing between small particles. The invention enables studies to be made of particles which are appreciably smaller than was heretofore possible.
SUMMARY OF THE INVENTION The scanner element of the invention is characterized by the provision of an aperture wafer that is formed of a hard material that is insulative with respect to the electrical current flowing in the aperture but which has high thermal conductivity. Accordingly, the wall of the aperture conducts heat away from the aperture thereby cooling the electrolyte in the quasistagnant region that is in closest contact with the wall. For very small apertures, the wafer itself and the electrolyte in contact with it may function as a heat sink. In the case of larger apertures, metallic means may be used in contact with the wafer to serve as a heat conduit. The material of the wafer, in addition to the above qualities, must be capable of securement to the wall of anaperture tube by some suitable means. The example described herein is beryllium oxide.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view illustrating lines of flow of a liquidthrough an aperture of any type;
FIG. 2 is a fragmentary sectional view through a "scanner-element of the invention illustrating one ing-"the aperture wafer to the side wall;
FIG. 3 is a fragmentary front elevational view of the FIG. 4 is a fragmentary sectional view through a scanner element showing another method of securing the aperture wafer to the side wall thereof;
FIG. 5 is a fragmentary sectional view through a modified form of scanner element; and
FIG. 6 is a diagrammatic view showing a conventional Coulter apparatus setup using a scanner element of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT conventional wafer of the Coulter apparatus such as, for example, the wafer 10 has at least its entrance edge 12 opening to the aperture 14 sharp. It is presumed, in this case, that there is liquid on opposite sides of the wafer but this is not diagrammed in order to render the illustration clear. This is also true of the other illustrations herein.
The flow of. liquid through such an aperture 14 is characterized by a flow field illustrated, the flow of FIG. I being assumed to be in the direction of the arrows. Jet contraction and flow curvatures are produced by the radial approach of fluid to the aperture 14, this being illustrated in region 16 after which the streamlines become essentially straight and parallel at a section termed the vena contracta a short distance downstream from the entrance 12. In the illustration of FIG. 1, the vena contracta is shown at approximately the region 18 but it may well occur within the bore of the aperture 14 shortly after the liquid has passed the entrance 12. a
. In any event, it will be seen that the principal flow of liquid through the aperture 14 is radially inward of the aperture wall 20 thereby producing a region of turbulence or quasi-stagnation at 22. Liquid is detached from the downstream end of the main flow to replace electrolyte drawn into the flow as indicated by the small arrows 24. It is in this region 22 that heating noise is produced as the aperture current is increased due to thefact that the time that increments of electrolyte remain in the aperture 14 in these regions 22 is much greater and more variable than the time that an increment in the principal flow remains in the aperture.
FIGS. 2 and 3 illustrate a scanner element 26 which is constructed in accordance with the invention. As in the case of the usual scanner element or aperture tube of a Coulter apparatus, there is a tube 28 made of a principally transparent material such as glass. The glass wall of the tube is designated 30 and any of the known techniques may be used to prepare the wall 30 for receiving the aperture wafer. The wafer 32 in FIGS. 2 and 3 has been fused into the outer surface of the wall 30 immediately over a large orifice 34 that is formed in the wall 30. The wafer 32 has a central aperture 36 not much different in configuration than the aperture 14 of FIG. 1 and probably formed in the wafer 32 by similar technique. The wafer 32 is made of a meterial which is electrically insulative and yet heat-conductive such as, for example, beryllium oxide or diamond. Of these, beryllium oxide is preferred, since it is relatively inexpensive, about the same hardness as corundum, its thermal conductivity is greater than that of many metals and it is easy to handle and fuse to glasses having the same or slightly greater coefficients of thermal expansion, such as some soda-lime glasses. It is desirable for the glass to have slightly higher rates of expansion so that the beryllium oxide is in compression when the assembly cools. In case of apertures substantially. less than microns in diameter, the wafer 32 will serve as a heat sink together with the electrolyte which contacts the same and draws heat from the region of quasi-stagnancy such as 22 illustrated in FIG. 1. This cooling effect decreases heat noise and enables higher aperture currents to be used with resulting increased sensitivity to smaller particles.
FIG. 4 illustrates a similar wafer 32 but in this case the wafer is secured to the outer surface of the wall 30 by means of an adhesive 38 such as, for example, an epoxy type. Some epoxy type adhesives have very high thermal conductivity and good electrically insulative properties.
FIG. 5 illustrates a scanner element 40 having an orifree 42 in its wall 44 and having an aperture wafer 46 fused into the wall over the orifice. The aperture wafer 46 has a central aperture 48 and the material from which the wafer 46 is made has good electrically insulative properties and high thermal conductivity.
In this case, it is assumed that the aperture 48 is of the order of 100 microns or greater. A metallic coating is shown at 50 on the exterior and 52 on the interior of the wall 44 with portions 54 and 56 overlying the surface of the wafer 46 and being in intimate contact therewith. Such coatings could also be in the form of wires, strips or bars. In this case, the heat generated in the aperture 48 is conducted by the wafer 46 and the metallic members 54 and 56 to the electrolyte which is disposed on both sides of the wall 44. These metallic heat-conducting members 50 and 52 need not be connected to the electrodes leading; to the detector of Coulter particle device. Under such circumstances, the metallic coatings or connections serve as conduits of heat, drawing same from the wafer to the electrolyte bodies. They may also serve as such electrodes and be connected as shown by leads 58 to the Coulterparticle device. The full coating is especially useful in case of high frequency aperture current as disclosed in said copending application.
In addition to the structures illustrated herein, the copending application illustrates a form of scanner element or aperture tube in which the walls are made of synthetic resin enclosed within metallic tubes that serve as the inner and outer electrodes. In such case, the wafer used is required to be set into the wall of the aperturetube in a suitable cavity provided such as, for example, at the bottom end. This may also be done with an aperture wafer of the material disclosed herein.
As will be obvious from the above discussion, the invention may be embodied in scanner elements of many different constructions. In addition to the type of Coulter apparatus in which intermittent flow is achieved by means of such systems as disclosed in US. Pat. No. 2,869,078, the wafers of the invention may be utilized in continuous flow structures and, in fact, practically anywhere that a Coulter scanner element is used.
FIG. 6 shows a conventional arrangement using an aperture tube such as 26 with an aperture wafer 32 in the side wall thereof near the lower end, set into a vessel 60 having a suspension 62 of particles therein. The interior of the aperture tube 26 has a second body of fluid 64 therein and is connected into a system of the type disclosed in US. Pat. No. 2,869,078. Electrodes 66 and 68 connect to the Coulter particle analyzing device 70. The suspension 62 flows through the aperture of the wafer 32 to the body of fluid 64 and passage of particles is detected by the apparatus 70.
It is preferred that the Wall of the aperture tube 26 by transparent so that the image of the aperture 36 may be optically projected onto some surface for viewing during use.
What it is desired to secure by Letters Patent of the United States is:
1. In a particle studying apparatus the improvement comprising a scanner element including a wall of electrically insulative material having an orifice therein and a wafer being of a flat disc configuration and having an aperture therein secured to said wall over said orifice whereby liquid flow from one side of the wall to the other will pass through said aperture, while an electric current also flows through the aperture, a signal being produced each time a particle passes through the aperture, said wafer being of a material of electrically insulative property and thermal conductivity of at least 50 Btu/hr/sq ft/F/ft, such as to reduce excessive noise in the aperture, improve the signal-to-noise ratio, and increase sensitivity of the scanner element.
2. The scanner element as claimed in claim 1 which the wafer is fusedly secured to said wall.
3. The scanner element as claimed in claim 1 which the wafer is adhered to said wall.
4. The scanner element as claimed in claim 1 which the wafer is formed of an oxide of beryllium.
5. The scanner element as claimed in claim 2 which the wafer is formed of an oxide of beryllium.
6. The scanner element as claimed in claim 3 which the wafer is formed of an oxide of beryllium.
7. The scanner element as claimed in claim 4 which the wall is formed of glass.
8. The scanner element as claimed in claim 7 which the glass is of the soda-lime variety.
9. The scanner element as claimed in claim 1 in which the wafer has metallic means engaged therewith to serve as heat conduit means, said metallic means comprising separate members engaged against opposite faces of said wafer.
10. The scanner element as claimed in claim 9 in which said separate members surround said aperture at opposite ends thereof and come in close proximity thereto.
11. The scanner element as claimed in claim 9 in which said separate members comprise electrodes adopted to be connected to a Coulter particle device.
12. in particle studying apparatus which includes a vessel having an aperture therein through which fluids carrying suspensions of particles are adapted to pass, the passage of a particle through the aperture resulting in a change of the impedance of the fluid in the aperture, and in which electrical means are provided to detect the passage of particles in terms of the change in impedance, the improvement comprising, a scanner element which comprises a wall of insulating material having an orifice therein, a substantially inert wafer having a flat disc configuration and being of electrically insulative material and having thermal conductivity of at least 50 Btu/hr/sq ft/F/ft and having an aperture therein secured to said wall in face-to-face engagement and with the aperture and orifice aligned, wherein excessive noise in the aperture is reduced, the signal-tonoise ratio is improved, and the sensitivity of the scanner elmement is increased.
13. The structure as claimed in claim 12 in which the aperture is of right cylindrical configuration and having a sharp entrance edge.
14. The structure as claimed in claim 12 in which the wafer is formed of an oxide of beryllium.
15. The structure as claimed in claim 13 in which the wafer is formed of beryllium oxide.
16. An aperture tube for use with a Coulter particle apparatus comprising an elongate glass tube having an orifice in its wall adjacent the lower end thereof, an electrically insulative wafer being of a flat disc configuration and having thermal conductivity of at least 50 Btu/hr/sq ft/F/ft engaged to said wall and blocking said orifice and there being a through aperture in said wafer aligned with said orifice, wherein excessive noise in the aperture is reduced, the signal-to-noise ratio is improved, and the sensitivity of the aperture tube is increased.
17. The aperture tube as claimed in claim 15 in which the wafer is formed of an oxide of beryllium.