Sleep monitor and sleep tracking are rapidly converging with the trading of making smart products. Manufacturers are increasingly investing in new lines of products that connect household items to the internet, adding to the product’s value for the end-user. Mattress manufacturers are quickly catching up to the trend of sleep tracking technologies and are integrating sensors into their mattresses to create smart mattresses and other smart sleep products that can provide useful information about a night’s sleep and the sleeping environment. Why the obsession with sleep? Which sleep monitor devices are cheap to make, and which should be avoided? Read on.

Why is sleep so important?

As we sleep, we pass through various sleep state cycles. The first stage in the sleep cycle is light sleep, which is followed by deep sleep and then the dream state, commonly referred to as rapid eye movement (REM) sleep. A full sleep cycle lasts about 90 minutes and is typically repeated several times each night. Every stage of the sleep cycle fulfills a distinct physiological and neurological function, each of which appears to be necessary for the health of the body and mind. If a person’s sleep is interrupted or if certain stages are missing for any reason, its physiological functions might not be fully executed and the person can feel tired or groggy. According to the National Institute of Neurological Disorders and Stroke (NIH), over 60 million Americans have chronic or intermittent sleep disorders that adversely affect their health.

The trend towards sleep tracking

In recent years, awareness has grown about the damages caused by sleep deprivation and low quality sleep, which has led to an increasing growth in the market of sleep tracking devices. A smart mattress, for example, can monitor a user’s sleep patterns completely unobtrusively and store the valuable information for analysis.

Sleep monitoring refers to the process of monitoring a person’s sleep throughout the night to obtain qualitative sleep measurements. These metrics are used to determine an objective view of the quality of one’s sleep and to help discover sleeping trends over time. The most relevant metrics for sleep monitoring are movement and respiration measured during the sleeping session. Movement metrics are used to distinguish between deep sleep, light sleep and the waking stages of sleep. The respiration per minute (RPM) rate and variability are used to identify REM sleep. With this information one can analyze length of a sleep period, number of awakenings, length of restless sleep periods and the time needed to fall asleep. Adding environmental sensors such as temperature, humidity, air quality and light to the monitoring system can provide additional information used for sleep analysis. All these metrics can result in a comprehensive picture of the user’s sleep quality and suggest ways to improve on it.

hypnogram
Sleep stages and cycles in adult sleep Image credit: howsleepworks

 

Sleep monitoring devices

There are numerous devices that monitor sleep quality using various combinations of sensors and sensor technology that analyze the user’s sleep patterns. The following are various devices used to monitor and track sleep highlighting their advantages and disadvantages.

Smartphones

Smartphones can be used as sleep tracking devices, that uses its embedded accelerometer to track movement. A dedicated app records the sleeper’s movement activity during the night, analyzing how many times the sleeper turns over during the night, gets out of bed or moves the covers. As smartphones only have accelerometers, they don’t provide as detailed an analysis as other devices.

Fitness Trackers and Smartwatches

Fitness trackers and smartwatches, designed to be worn on the wrist, can be used to monitor various metrics, including current elevation, calories burned and heart rate. The advantage of using these devices to measure heart rates for sleep tracking purposes is that one can infer information about the various sleep stages, (i.e., deep sleep, light sleep and REM). Although the stages of sleep can only be reliably measured using an electroencephalogram (EEG), heart rate can also provide useful results, as each stage of sleep has a signature heart rate. Additionally, smartwatches are useful fitness and heart rate trackers, but they often don’t have a long battery life, which can be problematic when using the smartwatch for the entire night.

sleep tracking via fitness trackers and smart watches.
Fitness trackers and smartwatches Image credit: Sporttechie

 

Sleep monitoring has become so popular that it has advanced to the point where there are a number of various devices on the market solely dedicated to monitor and track sleep. All these technologies are used in the smart mattress industry, and their functioning is important to understand in order to determine their usefulness in this fast-growing field. These devices are designed for users looking to examine their personal sleep data such as heart rate, respiration rate, body temperature and galvanic skin response. This data helps to distinguish between REM, light and deep sleep in greater detail, providing the tools to monitor and track nightly sleep cycles. These devices are also useful for monitoring various aspects of the sleeping environment such as ambient light/noise, temperature, relative humidity, and even air quality.

Sleep analysis technologies: Pros & cons

Piezo crystal technology

Piezo crystals are electromechanical devices that convert mechanical movements into electrical signals, which increase according to the strength of mechanical movements. They can be used to create respiration effort sensors. Here respiration movements of the chest or abdomen exert stress on the crystals and generate a small voltage that is proportional to the movement or tension of an elastic belt worn around the body. Although any piezo sensor will produce an acceptable signal in bench tests, designing a truly effective device is a significant technical challenge. Piezo crystals are extremely sensitive, therefore a high degree of isolation from the environment is required, since even minor temperature changes, acoustic signals or moisture can generate a significant influence. Respiration movements are transmitted to the crystals using a specialized belt that has considerable stiffness in the axial direction, but which is relatively flexible for bending. This maximizes the transmission of respiration movements, while damping other, unrelated movements.

Piezo film

Plastic films with piezoelectric properties were first produced over fifteen years ago, and are used to create many types of sensors. The same guidelines that are applicable to Piezo Crystal sensors generally also apply to Piezo Film. It is also essential that the film is insulated from the environment as much as possible. The requirement for flexibility dictates that the film cannot be enclosed in a rigid box (which would be the best option). Thick elastic material should be used both under and over the Piezo Film element, and the elastic should be sealed as much as possible to prevent any exposure of the film. Piezo Films are significantly less sensitive than crystals. It is important that the Piezo Film is anchored in such a way as to produce a linear signal, starting with a very weak tension all the way to a very tight tension.

Radar: Electromagnetic waves (6.0 – 10.2 GHz)

A radar-based respiration sensor uses radio waves to determine the range, angle, or velocity of objects. The sensor transmits a high-frequency radio waves pulse and measures the time it takes for the waves to reflect back to it. The distance from the user is calculated by using the speed of the radio waves. The sensor detects small changes in the distance from the user’s chest when he is breathing and counts them using digital signal processing (DSP). The sensor can detect very small changes due to the high frequency of the radar waves,
6 – 10.2 GHz.

Capacitance sensor

The capacitance sensor provides movement pattern data. The sensor is designed as a mat and is based on a compressible foam sandwiched between two orthogonal arrays of cPaper capacitance sensors. A low-cost variation of conductive paper is used as the capacitance sensor electrode. When the user lies on the mat they will come into contact with some of the array junctions and like any other capacitive touch sensor, a signal will then be sent to the system processor. When the users moves or breathes different junctions will come into contact with them. A typical mat design uses a 3mm thick foam with a 5mm row/column grid array that has a measurement resolution of 0.1 PSI pressure. The resolution of the system can be controlled by modifying properties of both the conductive paper and the foam. While they don’t require direct contact, capacitive solutions generally need to operate in close proximity to the subject and their reliability can be affected by variations in temperature and humidity.

Fiber optics sensor

This technology uses a fiber-optic micro-bending filament and light sensor that picks up the user’s breathing movements transmitted via the mattress. The sensor picks up light that is propagated through the mattress fiber via the filaments, reaching the sensor on the other side of the fiber. When the user breathes, they apply pressure on the mattress which bends the fiber-optic filament and reduces the amount of light from reaching the sensor. The light sensor interprets the reduced amount of light as an indication of breathing movement.

As the effects of lack of sleep can significantly affect our health, smart sleep monitoring technology and smart mattresses are quickly becoming more popular and widely used — and the technologies used for sleep tracking and monitoring are increasingly relied upon to ensure a good night’s rest.





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Yarden Hod
Yarden has exceptional experience in all stages of the product development life cycle and has a strong interest in consumer behavior and cognitive skills development. In her free time, Yarden enjoys modern dance and mastering the latest addictive game!