How is Industrial Design Crucial for Wrist-based Wearable?

BlogIndustrial Design    November 7, 2019
Industrial Design Posted On

Watches or wrist-based wearable that offer heart-rate monitoring, no doubt, have a quite similar look to their mechanical or analog counterparts. Around all of these gadgets have familiar wrist bands, watch faces, and even the internal components like a photoplethysmography (PPG) sensor that makes the heart-rate measurement or other operations possible in these devices. PPG sensor, being one of the most vital and complex elements, often face a lot of challenges in detecting the heart-rate accurately. Although a bit frustrating, these challenges can be taken care of by the appropriate Industrial Design (ID) of the wearable. Here, in this article, we’ll discuss the hurdles the wearable devices usually face. Besides, the content will highlight how the wrist-based wearable being Industrial by Design can contribute to correct heart-rate monitoring.

What Challenges does Wrist-based Wearable Often Face?

One of the main challenges a PPG sensor in wearable devices commonly faces is that during activities like running, it apart from detecting heart-rate also senses the motion-related blood volume changes take place in the wrist as the wrist-based wearable press the skin and deform the blood vessels under it. Due to this, the PPG sensor senses and mix up the ratings of the blood-volume change and the reflected light-intensity change as it stems from cardiac origins as well as motion.

Another thing that creates confusion in heart-rate detection through PPG is LED scattering. What is the case? When there’s a repetitive arm motion at the time of activities such as running, poorly designed wearable allow an air gap between the human skin and the photodiode, which may cause scattering. Repetitive scattering can further degrade a cardiac-related PPG component from the spectrum, thus making it quite difficult to distinguish the needed cardiac signal.

How to Resolve the Issues/challenges Related to PPG Sensor, i.e., Wrist-based Wearable?

The appropriate industrial design of wrist-based wearable is the most essential, or we can say the foremost factor that needs to be emphasized for achieving accurate heart-rate monitoring results by overcoming all challenges. Let’s go through an example encompassing two spectrograms – one from a watch with an optimized ID and another from a poorly designed watch. These spectrograms are the results of PPG and synchronized accelerometer signals collected during slow walking and treadmill running. Now, as the PPG signal depends on both heart-rate induced pattern and motion-related pattern, the spectrogram of a well-designed wrist-worn watch based on the optimal industrial design will show the precise spectral density of the PPG sensor and accelerometer. Heart-rate frequencies are not just clearly visible during all epochs, no matter whether the person is walking or running, but also easily separable from motion frequencies. However, in the second case, the spectrogram of the PPG signal showcases an invisible or faded heart-rate. Moreover, if the user wears the inappropriately designed watches too tightly, these wearable press blood beds under the skin and the blood perfusion gets decreased to a large extent. It ultimately smears the distinction between heart-rate related readings and thus, generates difficulty in separating heart-rate frequencies from motion frequencies.

Now, as per this example, we can conclude that it is essential to design the wearable appropriately. There is a need to optimize the mesa height and area to minimize the motion effect and allow the blood flow to fluctuate. For achieving this goal, one has to optimize the mesa dimensions along with the components’ weight within the watch case. Some characteristics of ID that we should consider to design apt wearable are as follows:

  1. Mesa (uplifted well that keeps the photodiode sensor in contact with the skin)

In industrial design, the curvature and height of mesa, which is a raised well housing the optical photodiode in close contact with the skin, play a vital role in minimizing light entering into the photodiode sensor. Hence, it is significant to go for industrial design that upkeeps good skin contact and lowers down the effects of ambient light sources. Light sources like Sun and others are strong enough to wipe away the PPG signal or add alternative intensity of light resulted from arm motion to the photodiode sensor.

  1. Wristband Considerations

The tactile quality of the wristband, along with the materials used to make it, are crucial factors that Industrial Designers or component designers must consider while designing the wrist-based wearable. Fabric impregnated with elastic components would cause friction amid the wrist and the band, hampering rotation of the watch around the wrist. On the other hand, a snuggly fit elastic band would maintain the consistent distance between the skins and watch mesa decreasing the effect of motion artifacts. Ideally, a wearable watch should stay on the spot where blood perfuses well, and the distance amid it and the optics should be maintained on the precise optical path.


Providing accurate heart-rate monitoring from the wrist-based wearable isn’t an easy feat as the heart-rate signal of interest often gets corrupted either by arm or hand motion. Such motion-related issues are non-linear and arduous to cancel out. Besides, the frequency domain computation is expensive in a power-stingy wearable platform. Therefore, it is imperative to address and remove the challenges at the Industrial Product Design stage in a way to attain accurate heart-rate detection from wrist-based wearable even in the presence of motion. For more visit: 

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