A sensor element includes an element body that contains a measurement-object gas flow section and a heat generation portion. The measurement-object gas flow section includes a main pump chamber, an auxiliary pump chamber, and a measurement chamber. A distance X1 in a left-right direction between a part of a first inner linear portion and a part of a second inner linear portion of the heat generation portion that overlap a main pump chamber projection region is equal to or more than ⅓ of a width Wp of the main pump chamber projection region in the left-right direction. A distance X2 in the left-right direction between a part of the first inner linear portion and a part of the second inner linear portion that overlap an auxiliary pump chamber projection region is equal to or more than 0.4 times the width Wp.

A sensor element includes an element body that contains a measurement-object gas flow section and a heat generation portion. The measurement-object gas flow section includes a main pump chamber, an auxiliary pump chamber, and a measurement chamber. A distance X1 in a left-right direction between a part of a first inner linear portion and a part of a second inner linear portion of the heat generation portion that overlap a main pump chamber projection region is equal to or more than ⅓ of a width Wp of the main pump chamber projection region in the left-right direction. A distance X2 in the left-right direction between a part of the first inner linear portion and a part of the second inner linear portion that overlap an auxiliary pump chamber projection region is equal to or more than 0.4 times the width Wp.

A sensor element for detecting a target gas to be measured in a measurement-object gas includes: an element body including an oxygen-ion-conductive solid electrolyte layer; and a protective layer covering at least a part of a surface of the element body. The protective layer includes a porous material that has a pore inside; and, in the pore in the protective layer, a ratio (Lt/Lf) of a pore length (Lt) in a thickness direction perpendicular to the surface of the element body to a pore length (Lf) in a surface direction perpendicular to the thickness direction is 0.6 to 0.9.

A thermochemical sensor is provided. The thermochemical sensor comprises: a substrate structure comprising a thermoelectric surface having concave portions and convex portions; a base fiber disposed on the thermoelectric surface of the substrate structure; and a catalyst layer that conformally covers the thermoelectric surface of the substrate structure and the base fiber.

A gas sensor element includes a solid electrolyte having oxygen-ion conductivity, a first electrode film located on one side of the solid electrolyte, a second electrode film located on the other side of the solid electrolyte. At least one of the first electrode film and the second electrode film includes noble metal particles, solid electrolyte particles having oxygen-ion conductivity, and pores, and a capacitance in the electrode film is 80 μF or less. A gas sensor includes the gas sensor element.

In one embodiment, a gas sensor includes a sensing layer having a first region containing PdCuSi, and a second region which is provided outside the first region and contains PdCu.

A gas sensor (1) including: a sensor element (21) having a detection section (22) through an element introduction hole (25); a metallic shell (11); and a single-wall tubular protector (51) having a gas introduction hole (56) and a gas discharge hole (53); a gap G is present between the gas introduction hole and a forwardly facing surface (12a) of the metallic shell; when the gas introduction hole is viewed toward the rear end side, an area Sh of a portion of the forwardly facing surface seen through the gas introduction hole, is equal to or greater than ½ of an opening area Sg of the gas introduction hole; the element introduction hole is located on the forward end side in relation to a forwardmost end (12f) of the forwardly facing surface; and a distance L1 of the gap G is smaller than a diameter D of the gas introduction hole.

A gas sensor element includes: a first ceramic structure (100A) having a detection cell (120); a second ceramic structure (100B) having a pump cell (110) disposed apart from the first ceramic structure in a lamination direction; and a third ceramic structure (100C) having a frame-shaped body (200) surrounding a space (150a) formed between the first and second ceramic structures, the frame-shaped body including a gas introduction portion (151) and a peripheral wall portion (141). A gap (150b) connected to the space (150a) is formed between an opposed surface (151b1) and the second ceramic structure. A ceramic buffer layer (300) having a lower shrinkage start temperature than a material for forming the gas introduction portion is formed on the opposed surface so as to overlap a boundary portion X between an edge (150b1) on the external side of the gap and the second ceramic structure when viewed in the lamination direction.

The first electrochemical oxygen sensor includes: a positive/negative electrode; and an electrolyte solution, the electrochemical oxygen sensor further including: a separation membrane for limiting an amount of oxygen supplied to the positive electrode, and a resistance element for connecting the positive electrode and the negative electrode. In one embodiment, a value of current flowing through the resistance element is 7 μA or more in an atmosphere of 50% relative humidity at 25° C. and 1 atm, and a resistance value of the resistance element is set at 1050 Ω or less. In another embodiment, a value of current flowing through the resistance element is 4 μA or more in an atmosphere of 50% relative humidity at 25° C. and 1 atm, and a resistance value of the resistance element is set so that the output voltage between both ends of the resistance element falls within a range from 4 to 9.5 mV.

A gas sensor has a sensing structure that is used for generating, for a variety of gases, multiple corresponding electric signals. It has a plurality of measuring electrodes and a gas-sensitive film coating the measuring electrodes; and a micro-heating structure that is used for providing different heating temperatures for the sensing structure, and a silicon-based substrate and a heating layer disposed on the silicon-based substrate. The heating layer integrates heating electrodes of different sizes or different layouts to form a plurality of heating regions of different temperatures, and the plurality of measuring electrodes are respectively disposed in the corresponding heating regions. By integrating heating electrodes of different sizes or different layouts on a single micro-heating structure to form heating regions of different temperatures, a complex atmosphere detection function of a variety of sensing materials at different temperatures is achieved.