A fully printed flexible multidirectional thermal flow sensor

Abstract

This work presents the development and evaluation of a fully printed multi-directional thermal flow sensor on PET substrate. The device consists of conductive Ag tracks and printed thermistors based on BaTiO 3 , activated carbon and a solvent based thermoset polymeric system. Each element presents similar temperature-electrical resistance behavior (in terms of normalized values), thus enabling utilization as sensing and active elements for thermal two-dimensional flow sensing. A custom experimental setup was used for evaluating the device under two modes of operation, namely constant current and constant resistance. It was observed that in the range of 0 to 25 standard liters per second (SLPM) of air flow, constant resistance provided better input dynamic range than constant current (2.75 and 0.12 mW respectively), while constant resistance mode exhibited a sensitivity of approximately two orders of magnitude greater than that of constant current mode. For constant resistance mode, sensitivities of 0.46 mW/SLPM for zero flow and 0.08 mW/SLPM for flow greater than 6 SLPM were extracted, while for constant current mode the corresponding sensitivity values were 0.018 mW/SLPM for zero flow and 0.0036 mW/SLPM for flow greater than 6 SLPM. The device was capable of successfully detecting the flow direction throughout the target flow range. The influence of the flow magnitude on detecting flow angle was found to be negligible. The proposed device can be mounted to various non-planar surfaces, after the necessary re-calibration. It can be mass produced with various printing technologies for applications as a flexible two-dimensional flow sensor with low fabrication cost.

Study of Single and Multipass f–rGO Inkjet-Printed Structures with Various Concentrations: Electrical and Thermal Evaluation

“…Heating small areas with microheaters is an important task for several applications, from flow-sensing [ 37 , 38 ], degassing, driving and assisting electrochemical sensors [ 39 , 40 , 41 , 42 , 43 , 44 ], to microfluidic system temperature control and sensing [ 45 , 46 , 47 ]. Carbon and graphene-based printed devices have recently demonstrated unprecedented performance in temperature sensing and microheater fabrication [ 16 , 48 , 49 , 50 , 51 ]; due to their unique properties, such as high mechanical durability, resistance to environmental corrosion and contamination, and an ability to reach high temperatures without changing their properties, these materials are excellent candidates for these applications.…”

A fully printed sensor with optical readout for real-time flow monitoring

“…Flow sensors can be divided, based on their principle of operation, mainly into thermal, differential pressure, ultrasonic, piezoresistive and piezoelectric devices [16]. Thermal flow sensors work by exploiting heat transfer caused by a working flow [17]. They can operate in 'hot-wire' and 'hot-film' mode, where the flow magnitude is extracted by the power required to keep a heating element at constant temperature, or by the temperature difference caused by convection cooling when the heater is supplied with constant power.…”

Flexible Inkjet-Printed Heaters Utilizing Graphene-Based Inks

“…Selective controllable heating of predefined areas in electronic devices is a key feature for various sensors operation. For example, 2D thermal flow sensors utilize a heating element and exploit variations in the thermal field distribution, which are detected by a set of peripheral sensors to accurately extract the flow vector [ 1 , 2 ]. In chemical sensors, microheaters are usually utilized for either enhancing detection performance or assistance in degassing [ 3 , 4 ]; more specifically, in metal–oxide gas [ 5 ], ammonia [ 6 ], fully printed SnO 2 gas [ 7 ], HCHO [ 8 ], and humidity [ 9 , 10 ] sensors.…”