# US 2018/0023987 A1 · Microfluidic flow sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0023987 A1 - Document ID: US20180023987A1 - Status: Published application - Kind: A1 - Application number: 15/546,327 - Filed: 2015-04-30 - Published: 2018-01-25 - Earliest claimed: 2015-04-30 - Assignees: Hewlett-Packard Development Company, L.P. - Applicants: Hewlett-Packard Development Company, L.P. - Inventors: Alexander Govyadinov; Erik D Torniainen; Pavel Kornilovich - Web page: https://patentgrep.com/patent/US20180023987A1 ## CPC - G01F 1/6845: {Micromachined devices} - B01L 3/502746: {characterised by the means for controlling flow resistance, e.g. flow controllers, baffles or throttle valves} - B41J 2/125: Sensors, e.g. deflection sensors {(nozzle clogging detection for cleaning reasons B41J2/16579; detection for compensation for failed nozzles B41J2/2139)} - B41J 2/175: Ink supply systems {; Circuit parts therefor} - G01F 1/69: of resistive type - G01F 1/6986: {with pulsed heating, e.g. dynamic methods} - B01L 2300/0627: Sensor or part of a sensor is integrated - B01L 2300/0887: Laminated structure - B01L 2400/082: Active control of flow resistance, e.g. flow controllers - G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME - B01L: CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE - B41J: TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS ## Abstract An apparatus includes a microfluidic channel and a flow sensor along the microfluidic channel. The flow sensor includes a heat emitting resistor for connection to an electric current source, analytical parameter sensor and electronics. The heat emitting resistor has a resistance that varies in response to temperature. The electrical parameter sensor is to sense an electrical parameter of the heat emitting resistor that is based on the resistance of the heat emitting resistor. The electronics determine a flow based on the sensed electrical parameter. ## Claims ### Claim 1 An apparatus comprising: a microfluidic channel; and a flow sensor along the microfluidic channel, the flow sensor comprising: a heat emitting resistor for connection to an electric current source, the heat emitting resistor having a resistance that varies in response to temperature; an electrical parameter sensor to sense an electrical parameter of the heat emitting resistor that is based on the resistance of the heat emitting resistor; and electronics that determine a flow based on the sensed electrical parameter. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the flow sensor further comprises: a second heat emitting resistor having a resistance that varies in response to temperature; and a second sensor to sense an electrical parameter of the second heat emitting resistor that is based on the resistance of the second heat emitting resistor. ### Claim 3 (depends on 1) The apparatus of claim 1 further comprising: a substrate supporting the microfluidic channel and the flow sensor; and a fluid interaction component supported by the substrate to interact with fluid directed by the microfluidic channel. ### Claim 4 (depends on 3) The apparatus of claim 3, when the fluid interaction component is selected from a group of fluid interaction components consisting of: a microfluidic branch channel stemming from the microfluidic channel; a microfluidic pump; a microfluidic valve; a microfluidic multi-mixer; a drop ejector; a thermal inkjet resistor; and a nozzle. ### Claim 5 (depends on 1) The apparatus of claim 1, wherein the heat emitting resistor extends across the microfluidic channel in a path selected from a group of paths consisting of: diagonal, serpentine, wavy, zigzag, and square wave. ### Claim 6 (depends on 1) The apparatus of claim 1 further comprising: a substrate underlying the heat emitting resistor; and a thermal insulative layer between the substrate in the heat emitting resistor, the thermal insulative layer having a thermal conductivity of less than or equal to 1-2.5 W/m*° C. ### Claim 7 (depends on 6) The apparatus of claim 6 further comprising a second thermal insulative layer on opposite sides of the heat emitting resistor, wherein a top of the heat emitting resistor is exposed to fluid within the microfluidic channel, the second thermal incident layer having a thermal conductivity of less than or equal to 0.3 W/m*° C. ### Claim 8 (depends on 1) The apparatus of claim 1 further comprising: a substrate underlying the heat emitting resistor; and a thermal insulative layer on opposite sides of the heat emitting resistor, wherein a top of the heat emitting resistor is exposed to fluid within the microfluidic channel, the thermal insulative layer having a thermal diffusivity less than a thermal diffusivity of the substrate. ### Claim 9 (depends on 1) The apparatus of claim 1, wherein the heat emitting resistor comprises at least one material selected from a group of materials consisting of: aluminum, platinum, rhodium, copper, nickel, tantalum, tungsten, ruthenium, nickel chromium, copper nitride, silicon, polysilicon, germanium, carbon, graphing, tin oxide, zinc tin oxide, tantalum nitride, titanium nitride, magnesium oxide, rubidium oxide, vanadium oxide, and tungsten-silicon-nitride (WSixNy). ### Claim 10 (depends on 1) The apparatus of claim 1 further comprising electronic circuitry to transmit time-spaced electrical pulses across the heat emitting resistor. ### Claim 11 (depends on 10) The apparatus of claim 10 further comprising a pump, wherein the time-spaced electrical pulses are asynchronous with pumping by the pump. ### Claim 12 (depends on 1) The apparatus of claim 1 comprising: an array of spaced heat emitting resistors across a microfluidic channel, the array including the heat emitting resistor; and sensors, each of the sensors to sense an electrical parameter of one of the heat emitting resistors that is based on the resistance of the heat emitting resistor. ### Claim 13 (depends on 1) The apparatus of claim 1, wherein the heat emitting resistor has a length-to-width ratio of at least 5 to 1. ### Claim 14 A method comprising: moving fluid through a microfluidic channel; transmitting electrical current through a heat emitting resistor extending within the microfluidic channel; sensing changes in flow of the electrical current through the heat emitting resistor, wherein the changes correspond to the rate at which heat is drawn from the heat emitting resistor by flow of the fluid across the heat emitting resistor; and determining a rate of flow of fluid across the heat emitting resistor based upon the sensed changes in the flow of the electrical current through the heat emitting resistor. ### Claim 15 An apparatus comprising a non-transitory computer-readable medium containing instructions to direct a processor to: transmit electrical current through a heat emitting resistor extending within a microfluidic channel; receive signals indicating flow of the electrical current through the heat emitting resistor, wherein the changes in electrical current flow correspond to the rate at which heat is drawn from the heat emitting resistor by flow of the fluid across the heat emitting resistor; and determine a rate of flow of fluid across the heat emitting resistor based upon the sensed changes in the flow of the electrical current through the heat emitting resistor.