Type Humidity Sensor Research Articles

A piezoresistive humidity sensor

Abstract This paper deals with a new type of humidity sensor. Whereas conventional humidity sensors utilize the change of the specific resistivity or the dielectric properties here the humidity induced volume change of a polyimide layer leads to a deformation of a silicon membrane. The bending stresses will be transformed into an output voltage by a piezoresistive Wheatstone bridge. This principle offers many advantages: (i) a separation of electrical transducing elements (piezoresistors) from measured humidity value, (ii) an advanced electrical long-term stability owing to qualified passivation concepts for the piezoresistors, (iii) the well-known opportunities to miniaturize humidity sensors using semiconductor technologies and micromechanics, (iv) use of only conventional IC processes. The fabrication process of the developed humidity sensor is nearly like that of a common pressure sensor. The first fabricated and tested piezoresistive humidity sensors showed a comparable behaviour to capacitive thin-film humidity sensors, that means fast transient response (T90≈20–25 s) and high accuracy (down to 1% r.h.).

A humidity sensor of a new type

The recently most talked about and used humidity sensors are capacitive sensors with a thin polymer film as the sensitive layer. Despite the many advantages, these sensors have shown some reliability problems caused by special effects of the polymer (e.g. swelling) and the direct moisturising action on the electrical transducing elements. To overcome these disadvantages we have developed a new type of humidity sensor, a piezoresistive transducer, fabricated with integrated circuit technology. In this paper we describe the sensor design, methods of analytical simulation of the sensor behaviour and measured characteristics of fabricated sensors. The tested elements showed a fast transient response to humidity and a very good reproducibility.

ChemInform Abstract: Galvanic Cell Type Humidity Sensor with NASICON‐Based Material Operative at High Temperature.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Galvanic cell type humidity sensor with NASICON-based material operative at high temperature

Galvanic cell type humidity sensor with NASICON-based material operative at high temperature

Water Activity of Some Food Hydrogels Examined by Thermal Conduction Type Humidity Sensor.

In order to investigate the state of water in food hydrogels from the standpoint of water activity (Aw), their desorption isotherm was recorded at 25°C using a hand-made Aw meter equipped with a thermal conduction type humidity sensor. In the free water region of the isoltherm, little difference was observed between the Aw of 5% gelatin or starch gels and that of their 10% gels, but the Aw of the 10% gels decreased before that of the 5% gels by lowering their water content. The isotherm of kon-nyaku jelly was not unduly changed by heating at 80°C for 10min, but the Aw of chicken mince (pectorals) was increased by heating in the multilayer water region. The Aw decreased in this region by grinding the mince with 3% NaCl, but was not increased unduly by heating the mince after grinding. The addition of 4% dried egg white, soy protein, potato starch, or wheat gluten only slightly decreased the Aw of kamaboko from Alaska pollack frozen surimi in the free water region, but decreased it considerably in the multilayer region except in the case of the starch.

Optical-fibre and quartz oscillator type gas sensors: Humidity detection by Nafion® film with crystal violet and related compounds

By using Nafion® film with crystal violet and malachite green, an optical-fibre and quartz oscillator type humidity sensor has been fabricated. The optical intensity, with a minimum at 615 nm in the reflection mode, decreases with relative humidity for a film with malachite green. The rise and recovery times are less than 1 min and the hysteresis is only ± 1%RH at 50%RH. For the film with crystal violet, a similar characteristic is confirmed at 630 nm. Composite films can be used as an optical and quartz oscillator type humidity sensor, since the sorption of water induces colour and oscillating frequency changes.

酢酪酸セルロースを感湿材料とする容量型湿度センサの長期信頼性

酢酪酸セルロースを感湿材料とする容量型湿度センサの長期信頼性

容量型湿度センサの応答性と斜方向蒸着電極

High water vapor permeable metal electrode of condenser type humidity sensors is formed by using oblique deposition method to improve response.Response time of the sensors with the electrode deposited at an incident angle θ= 75° is about 0.2 s even in the thickness of 1800A or more. The process how to build up the electrodes in form and their density are also investigated. It is estimated that quick response comes from the formation of a columnar microstructure with porosity due to shadowing effect in this deposition technique.

Theoretical studies on the impedance-humidity characteristics of ceramic humidity sensors

The impedance-humidity characteristics of ionic type humidity sensors depend on the microstructure of their elements i.e., surface roughness and pore size distribution. A theoretical calculation is proposed to clarify the relationship between the impedance-humidity characteristics and the pore size distribution. A general equation is derived to calculate the impedance of the model sensor at a certain relative humidity using the Kelvin equation. Controlling the pore size distribution, selecting the intrinsic impedance of the element and evaluating the conductivity of condensed water are found to be the most important factors for achieving a high sensitivity to humidity. This calculation method is applied to two sensor elements: MgAl 2O 4 containing a large volume of micropores and MgFe 2O 4 containing a small volume of micropores. Approximate agreement between the theoretical and experimental results is obtained if the dissolved ions from the sensor element are liquated out with distilled water.