Analytical device
A sensor for chemical species or biological species or radiation presenting to test fluid a polymer composition comprises polymer and conductive filler metal, alloy or reduced metal oxide and having a first level of electrical conductance when quiescent and being convertible to a second level of conductance by change of stress applied by stretching or compression or electric field, in which the polymer composition is characterized by at least one of the features in the form of particles at least 90% w/w held on a 100 mesh sieve; and/or comprising a permeable body extending across a channel of fluid flow; and/or affording in-and-out diffusion of test fluid and/or mechanically coupled to a workpiece of polymer swellable by a constituent of test fluid.
1. A sensor comprising
i) a conduit for through-flow of a test fluid;
ii) a porous body of granules of a polymer composition having particles of conductive filler metal, alloy or reduced metal oxide dispersed therein, said body having a first level of electrical conductance when quiescent and being convertible to a second level of conductance by change of stress applied to the body by stretching or compression or electric field, said body being permeable to the test-fluid and disposed across the conduit whereby, in use, said test fluid flows through said body; and
iii) electrodes connected to said body for connection to an electrical circuit responsive to a change in conductance of said body.
2. A sensor according to claim 1 wherein a bed of granules is supported in the conduit between a pair of perforate grids forming the electrodes.
3. A sensor according to claim 2 wherein at least one of the grids is moveable towards the other whereby the bed can be compressed.
4. A sensor according to claim 3 wherein the porous body is held between clamps forming the electrodes disposed on either side of the conduit.
5. A sensor according to claim 3 wherein the bed of granules comprises a foam or textile having granules of the polymer composition dispersed therein.
6. A sensor according to claim 1 wherein the porous body comprises a sheet and wherein means are provided to stretch the sheet.
7. A sensor according to claim 6 wherein the means to stretch the sheet comprises a hollow member bearing against one surface of the sheet and moveable in a direction perpendicular to the plane of the sheet.