A capacitive humidity sensor using cross-linked cellulose acetate butyrate

This paper reports on the fabrication of a new capacitive humidity sensor having good characteristics and being robust enough to be considered as a component in industrial processes.This sensor is manufactured using a mixture of three cellulose acetate butyrates cross-linked by a melamine formaldehyde resin as sensing material. Details of the fabrication process and sensor characteristics such as linearity, sensitivity, hysteresis, response time, maximum operating temperature or physical and chemical stresses influence are included

Titanium Dioxide Nanoparticle Humidity Microsensors Integrated with Circuitry on-a-Chip

A humidity microsensor integrated with a readout circuit on-a-chip fabricated using the commercial 0.18 μm CMOS (complementary metal oxide semiconductor) process was presented. The integrated sensor chip consists of a humidity sensor and a readout circuit. The humidity sensor is composed of a sensitive film and interdigitated electrodes. The sensitive film is titanium dioxide prepared by the sol-gel method. The titanium dioxide is coated on the interdigitated electrodes. The humidity sensor requires a post-process to remove the sacrificial layer and to coat the titanium dioxide. The resistance of the sensor changes as the sensitive film absorbs or desorbs vapor. The readout circuit is employed to convert the resistance variation of the sensor into the output voltage. The experimental results show that the integrated humidity sensor has a sensitivity of 4.5 mV/RH% (relative humidity) at room temperature

Printed humidity sensor for packaging

Printed electronics is the process of developing electrical devices on different substrates by printing inks by various methods. Flexograhpic printing a Humidity sensor was investigated. Flexographic printing can be cost effective for volume production on label presses. In this research, conductive silver nano-particle ink with a Silver content of 50 (+/-2) Wt.% was used to develop an Interdigitated Electrode (IDE). The printed base Silver interdigitated electrodes had an average resistance of 11.96Ω with a standard deviation of 1.21 indicating that the Silver printed sensors were consistent in the print quality.Nafion (a sulfonated tetrafluoroethylene-based copolymer) resin solution with a 20 wt.% in lower aliphatic alcohols and water, was printed on top of the silver Interdigitated electrode as the active layer for the detection of the change in humidity. Substrate used for the experiment was white Polyethylene terephthalate (PET White) of 0.175mm thickness. The sensors were tested in a Humidity chamber over a range of 40-80% relative humidity at of 25◦C to ascertain the effective working of the design by measuring their resistivity and repeatability. When the resistance of the sensors was checked with Direct Current (DC), there was a change in the resistance. The formation of dendrites due to electro-chemical reactivity on the surface of the sensor was observed, which caused the sensors to short circuit and fail. When the sensors were tested with Alternating Current (AC), it limited the growth of dendrites and the sensors were self-consistent with a repeatability of resistance pattern, but there was variation in the range of resistance between the sensors, where few showed sensing activity that started at around 500 KΩ and others around 2000 KΩ at 40%RH (Relative Humidity). This proved that the materials used worked and showed potential in developing a humidity sensor via Flexographic printing, further worked is required to eliminate the Dendrites formation and to stabilize the range of resistance

Dual-polarized chipless humidity sensor tag

In this letter, a miniaturized, flexible and high data dense dual-polarized chipless radio frequency identification (RFID) tag is presented. The tag is designed within a minuscule footprint of 29 × 29 mm2 and has the ability to encode 38-bit data. The tag is analyzed for flexible substrates including Kapton® HN DuPont™ and HP photopaper. The humidity sensing phenomenon is demonstrated by mapping the tag design, using silver nano-particle based conductive ink on HP photopaper substrate. It is observed that with the increasing moisture, the humidity sensing behavior is exhibited in RF range of 4.1–17.76 GHz. The low-cost, bendable and directly printable humidity sensor tag can be deployed in a number of intelligent tracking applications

Dual-polarized chipless humidity sensor tag

In this letter, a miniaturized, flexible and high data dense dual-polarized chipless radio frequency identification (RFID) tag is presented. The tag is designed within a minuscule footprint of 29 × 29 mm2 and has the ability to encode 38-bit data. The tag is analyzed for flexible substrates including Kapton® HN DuPont™ and HP photopaper. The humidity sensing phenomenon is demonstrated by mapping the tag design, using silver nano-particle based conductive ink on HP photopaper substrate. It is observed that with the increasing moisture, the humidity sensing behavior is exhibited in RF range of 4.1–17.76 GHz. The low-cost, bendable and directly printable humidity sensor tag can be deployed in a number of intelligent tracking applications

Chemically Deposited Optical Fiber Humidity Sensor

Humidity measurement in industries is a critical factor, since it may affect the business cost of the product, end product quality, optimal functioning of equipment, and the health and safety of the personnel. Hence, humidity sensing is becoming very important, especially in the control systems for industrial processes. Since humidity is expressed in different ways, it is very difficult to come up with a reliable, consistent, and repeatable humidity measurement approach. In contrast to other sensors employed for measuring other parameters like temperature and pressure, a humidity sensor has to be in contact with the process environment and hence is difficult to implement. This research was initiated at the Diagnostic Instrumentation and Analysis Laboratory (DIAL) for the requirement from the DOE to monitor the moisture in the soil at the nuclear waste storage facility. The idea was to monitor the leakage, if any, in the storage cylinders to avoid any hazard that may come up. The humidity sensor in this case had to be able to transmit the measurement over a distance far away from the actual measurement site. Keeping all these factors in mind, a chemically deposited optical fiber humidity sensor was developed. It was based on the evanescent tail absorption of light passing through an optical fiber due to hygroscopic material deposited on it. The hygroscopic material used was an aqueous solution of Poly-vinyl-acetate (PVA) and Cobalt Chloride (COCl2). The sensor yielded a consistent humidity measurement from 75% to 95%. Based on the above research, research is currently in progress to bring up a commercial prototype of the sensor