Labs Idea #15: Tobacco Moisture Measurement
Modern tobacco based electronic nicotine delivery systems (ENDS), such as tobacco heating products (THP) and heat-not-burn (HnB) devices reduce the amount of harmful substances in the inhaled aerosol by means of controlled tobacco heating instead of high temperature burning. Users expect a cigarette-like smoking experience at lower exposure to harmful substances. The moisture content of tobacco stick affects the smoke chemistry, resulting in different smoking experiences for moist or dry tobacco sticks. After opening a cigarette pack the tobacco stick moisture will dry out quickly, if the ambient relative humidity is low. Measurement of the tobacco stick moisture content would allow to set heating temperature of THP and HnB devices as a function of tobacco moisture to generate a consistent user smoking experience.
Sensirion's SHTxx relative humidity and temperature sensor is a low power sensor suited for battery operation. SHTxx sensors are polymer-based, capacitive humidity sensors. The capacitor is realized with an interdigitated structure in MEMS technology. It features an on-chip temperature sensor allowing to easily calculate precisely absolute humidity from the relative humidity and temperature value.
Sensirion's SHTxx relative humidity and temperature sensor was used to measure the relative humidity of tobacco sticks (Figure 2) consumed in tobacco heating products (THP) and heat-not-burn (HnB) devices.
The decrease of tobacco stick moisture at low ambient relative humidity was measured by putting the sensor into direct contact with the tobacco (Figure 3) and remeasure moisture content after one and two hours.
In order to measure the tobacco stick moisture content over time, it was characterized right after unpacking and remeasured one and two hours later (Figure 4). The data shows that the tobacco drying out process at low ambient relative humidity happens within a few hours after removing the protective plastic foil of the cigarette pack.
To demonstrate the quick response time of Sensirion's SHTxx relative humidity and temperature sensors, the sensor was brought into contact with the tobacco stick at t=0. The measurement data (Figure 4) shows that the measurement of tobacco stick moisture content takes less than 30 seconds. This response time could even be reduced to a few seconds by special algorithms provided by Sensirion on request.
The measurement results demonstrate that Sensirion's SHTxx relative humidity and temperature sensor is well suited to characterize tobacco moisture content within seconds. Thus, a tobacco stick ready to be used in a tobacco heating product (THP) or heat-not-burn (HnB) device could be charaterized directly before smoking to opimize a consistent user smoking experience independent of initial tobacco moisture content.
Specifically, the SHTxx relative humidity and temperature sensor integrated into e-cigarettes, tobacco heating products (THP) or heat-not-burn (HnB) devices allows to measure:
- tobacco stick moisture content
- ambient relative humidity
- ambient absolute humidity
For first feasibility tests we propose to use the evaluation kit SEK-SHTxx/SGP30 including SHTC and SHTW2 relative humidity and temperature sensors (Figure 7).
Sensirion's download center offers extensive application notes about relative humidity sensing: