Humidity and Temperature Sensors Widen Potential for Wearable Devices

Wearables, tiny computers that can be worn as accessories or clothes, are gaining more and more attention in the market. What makes them smart are the integrated sensors inside them. With environmental sensing, these devices can also be made aware of their environment.

Sensors are designed to measure relative humidity and temperature (RH/T) to allow devices and their users to know their ambient condition and what is taking place around them. The key advantages of these sensors are that they are highly energy efficient, do not require much computation power, and are becoming smaller and smaller. Therefore, they are suitable for wearables and provide a wide range of potentially beneficial applications.

Personalized Ambient Conditions

The integration of temperature and humidity sensors into wearable devices enables the measurement of the ambient conditions as well as the physiological information of the user, such as sweating rate or skin temperature. This can offer a better understanding and interpretation of accomplished performance (for example, slower running in high humidity, disturbed sleep in hot weather) and is the basis for a range of potential new applications.

This information can also be employed in a connected home (smart home) to automatically control the indoor climate. If sweat rate and skin temperature are shared with a climate system, the room ambience can be enhanced to personal preferences without the necessity for human intervention. This is mainly applicable if a user is sleeping and is unaware of uncomfortable or unhealthy conditions. Besides increased comfort, energy is consumed only when required, resulting in cost savings.

temperature and humidity sensors

Tracking ambient conditions is also beneficial for other applications. Based on the environmental temperature and dryness, a wearable device could provide valuable skincare tips. The human skin is very sensitive and an understanding about exposure could be used in cosmetics to suggest the correct product for the right skin and exposure.

However, it's not only the beauty sector that can improve its products to gratify customers—the healthcare sector would also gain. People with respiratory diseases need a climate attuned to their condition. A bad indoor climate can escalate the risk of illness— mites, asthma, and mold infestation are just some of RH/T-dependent health risk issues.

By monitoring the ambient condition with a wearable device, distinct patterns will emerge and risky or abnormal conditions will activate the alteration of heating, ventilation, air-conditioning, or humidifiers.

In the near future, watches, spectacles, articles of clothing, and other items will possess the ability to sense humidity and temperature, making it possible to combine the measurement of the environment into every aspect of people’s lives.

This will help one to obtain a better understanding of the environment and the ambient condition in the space one lives in. Consequently, processes in everyday lives could be enhanced, energy consumptions reduced, money saved, and comfort and health enriched.

Integration and Sensor Fusion

Incorporating ambient sensors into wearable devices like smartwatches is a non-trivial task. This is particularly true for ambient temperature sensors and all measures reliant on ambient temperature such as humidity. Temperature sensors integrated into a wearable or mobile device face three significant challenges.

First, the electronic parts in the tightly packed device produce heat and impact the sensor reading. This effect becomes even worse as the heat dissipation of the different components is extremely load dependent and thus is changing all the time. Second, the sensor readings are impacted by the heat of the skin. Third, the device has a definite thermal mass which results in a slow thermal response.

Similar to the fact that a hot cup of coffee needs roughly 30 minutes to cool down to room temperature, a smartwatch or phone needs approximately 30 minutes to adapt to temperature variations.

There are many measures to alleviate or even eliminate this problem. One of the most vital parts is the placement of the sensors. It is imperative that they are very well decoupled from the central device-internal heat sources and the human skin. The placement of the sensor is extremely device specific and has to be well-thought out for every product individually.

A perfect sensor placement, however, is not sufficient as a full decoupling is most likely not possible. To compensate for the remaining effects, the influence factors have to be checked and their impact on the temperature reading has to be established. For instance, to compensate for the body heat, an extra sensor can be placed close to the skin.

A heat-propagation model can be subsequently applied to guess how large the temperature gain of the body heat on the sensor is. This information enables compensation. This environmental sensor fusion software known as Sensirion Engine is already actively used in a number of smartphones enabling accurate humidity and ambient temperature sensing.

Moreover, the Sensirion Engine allows acceleration of the response of the humidity and temperature signal to ambient changes far outside the physical limits. This is essential as no user wants to keep waiting for about 30 minutes to obtain accurate readings. Integrating all these approaches allow wearable devices to provide an accurate measurement of humidity and ambient temperature.

Sensor Packaging Innovation

Implementation of such a system is possible only with ground-breaking technology in both software and hardware. The hardware in question is presently one of the tiniest humidity and temperature sensors in the market. It has been created by the Swiss high-tech company Sensirion especially for devices where there is limited space, and is enhanced for the requirements of the consumer electronics sector.

This advanced product integrates minimal size with maximum performance to define the newest generation of temperature and humidity sensors. The SHTW2 is Sensirion's 2nd generation WLCSP (wafer-level chip-scale package) humidity sensor, providing a complete digital temperature and humidity sensor system in a package that is small enough to fit into nearly any application.

The SHTW2 is provided in a flip chip package, which is a proven technology and signifies one of the simplest and smallest possible ways of packaging for a semiconductor chip. The supply voltage of 1.8 volts and the low power consumption of only 2 µW at 1 measurement per second provide an ideal base for use of the sensor in tiny, wearable devices.

Sensirion offers not only the sensor but also the supplementary software, guaranteeing a substantial time reduction in attaining accurate readings after a change in ambient conditions. The miniature SHTW2 sensor widens the range of probable applications; for instance, as a basis for physiological signals, such as sweat rate and skin temperature, where tailor-made algorithms are essential.

Sensirion has developed the space for new concepts— it is up to wearable providers and app developers to take it to the next level.

All images sourced and provided by Sensirion

Sensirion Inc

Medical devices must meet the highest standards in terms of quality and reliability. Doctors, nurses, and patients benefit daily from applications in the field of medical technology that are getting smarter by the day.

The use of proven Sensirion sensor solutions contributes to this and offers the possibility of making applications safer, more reliable and more convenient. Our many years of experience in the field of medical technology make us the preferred experts for leading medical-technology companies.

  • Home Care Devices (Ventilation)
  • Critical Care Devices (Ventilation)
  • Anesthesia
  • Point-of-Care Diagnostic
  • Drug Delivery / Infusion
  • Catheters
  • Smart Inhalers
  • Metabolic measurements
  • E-Health / M-Health

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Last updated: Aug 28, 2018 at 7:46 AM

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