Method and apparatus for sensing and characterizing particles

Particle -sensing and -characterizing apparatus comprising:

• (i) a wafer of electrically insulative material having a through-hole therein through which a liquid suspension of particles is adapted to pass, such liquid suspension of particles comprising a particle-suspending medium having an electrical impedance that differs from that of said particles;
• (ii) a pair of electrically conductive collars, each collar having an opening centrally located therein, said collars being attached to opposite sides of said wafer in positions overlying regions surrounding said through-hole, said through-hole and collar openings being of the same size and shape and being arranged to define a hydrodynamically continuous and smooth conduit for the particle suspension;
• (iii) a first circuit for causing a nominal electrical current through said conduit, said current being effective to establish an electric field in the vicinity of said conduit;
• and (iv) a second circuit for monitoring changes in said nominal electrical current as produced by particles passing through a particle-sensitive portion of said electric field, said collars having a thickness by which said particle-sensitive portion is confined within the geometric dimensions of said conduit.

A particle-sensing volumeter assembly adapted for use in an apparatus which characterizes particles by the Coulter principle, said volumeter assembly comprising a solid member having a wall defining a hydrodynamically smooth conduit through which particles to be characterized can be made to pass simultaneously with the passage of an electrical current through said conduit, said electrical current being effective to produce in the vicinity of said conduit an electric field having a particle-sensitive zone through which the passage of said particles is detectable, said wall having an electrical resistivity which varies in an axisymmetric manner along the conduit length to define a delimited central region of high electrical resistivity contiguous on its opposing boundaries to uninsulated distal regions of substantially lesser electrical resistivity, said uninsulated distal regions having a length measured along the longitudinal axis of said conduit which is sufficient to independently (i) shape said electric field so as to substantially confine said particle-sensitive zone within the physical boundaries of the conduit;

• (ii) enable development of quasi-laminar flow through said particle-sensitive zone so as to increase the proportion of particles per second transiting substantially homogeneous areas of said particle-sensitive zone;
• and (iii) prevent particles that have already passed through said conduit and are on recirculating trajectories from re-entering said particle-sensitive zone.

A particle-sensing volumeter assembly adapted for use in an apparatus which characterizes particles by the Coulter principle, said volumeter assembly comprising a solid member having a wall defining a hydrodynamically smooth conduit through which particles to be characterized can be made to pass simultaneously with the passage of an electrical current through said conduit, said electrical current being effective to produce in the vicinity of said conduit an electric field having a particle-sensitive zone through which the passage of said particles is detectable, said wall having an electrical resistivity which varies in an axisymmetric manner along the conduit length to define a delimited first region of high electrical resistivity contiguous on at least one of its opposing boundaries to an uninsulated distal region of substantially lesser electrical resistivity, said uninsulated distal region having a length measured along the longitudinal axis of said conduit which is sufficient to independently (i) shape said electric field so as to substantially confine at least a portion of said particle-sensitive zone within the physical boundaries of the conduit;

• and (ii) either enable development of quasi-laminar flow through said particle-sensitive zone so as to increase the proportion of particles per second transiting substantially homogeneous areas of said particle-sensitive zone, or prevent particles that have already passed through said conduit and are on recirculating trajectories from re-entering said particle-sensitive zone.

A method for sensing and characterizing particles by the Coulter principle, said method comprising:

• (a) passing a liquid suspension of particles to be sensed and characterized through a volumeter conduit formed in a solid material having an electrical resistivity which effectively varies along the conduit length to define a conduit having a delimited central region of high electrical resistivity which is smoothly contiguous on its opposing boundaries to uninsulated distal regions of substantially lesser electrical resistivity;
• (b) producing a nominal electrical excitation current through said volumeter conduit and an electric field in the vicinity of said conduit, said electric field having a particle-sensitive zone in which changes in said nominal electrical excitation current as produced by particles passing through said volumeter conduit simultaneously with said nominal current are measurable, said uninsulated distal regions independently functioning (i) to shape said electric field so as to substantially confine said sensitive zone within the physical boundaries of the conduit;
• and (ii) to enable development of quasi-laminar flow through said sensitive zone so as to increase the proportion of particles per second transiting substantially homogeneous areas of the sensitive zone;
• and
• (c) monitoring the amplitude of the electrical current through said volumeter conduit to sense the presence and characteristics of particles passing through said conduit.