Feature Article 1
Visualize Health Conditions Easily as a Daily Routine:
Development of Compact Blood Flow Sensor Using Optical Doppler Effect

photo:Development of Compact Blood Flow Sensor Using Optical Doppler Effect

In recent years there are increasing social demands for visualization of health conditions — such as stress — for effective use in preventive medicine. Kyocera developed a technique for measuring blood flow using laser light without placing any burden on the patient’s body, namely blood sampling. The principle of the optical Doppler effect was used in this development. In the future, this technique is expected to be used in mobile health applications, such as an ear phone that can check stress or relaxation conditions, or wearable devices designed to prevent dehydration, heat stroke or altitude sickness.

Optical Doppler Effect

The Doppler effect is a phenomenon of change in frequency of waves such as sonic waves or electric waves depending on the relative speed of the waves with the source or observer. For example, when you hear an ambulance siren, the sound is heard at a higher pitch as the ambulance moves closer to you but at a lower pitch as it moves farther from you. This phenomenon also occurs in light. You see bluer light as you move closer to the light but a redder light as you move farther from the light. This is called the optical Doppler effect.

Principle of Blood Flow Sensor

Kyocera applied the optical Doppler effect to development of a blood-flow sensor capable of easily checking the changes of blood flow as a daily routine. Devices equipped with this sensor measure the blood flow under the hypodermal tissue when it is in contact with an ear, a finger, or the forehead. When light from a light emitting element (laser) reflects off red cells in the blood vessel, the frequency shift (Doppler shift), in which the frequency of the reflected light changes, occurs depending on the speed of the light. The blood-flow sensor detects the frequency shift (the greater the shift, the faster the blood flow) and the intensity of the reflected light (the more intense, the more red cells the light hits) with its light receiving element. The light receiving element also detects light reflected from the skin but extracts the frequency components that caused the Doppler shift and calculates the blood flow.

photo:Principle of Blood Flow Sensor

Principle of Blood Flow Sensor

Application in Wearable Devices and Smartphones

Wearable devices, which have recently drawn a lot of attention, have so far mainly been applied in fitness applications, but have recently been used in the health care field such as for chronic diseases, nursing care of the aged, or health promotion programs. We realized high S/N ratio*, downsizing, a thin profile, and high power-saving (0.5mW in output) for this blood-flow sensor by incorporating a laser diode (light-irradiating semiconductor) and photo diode (semiconductor serving as a light detector) into a single ceramic package using our technology accumulated over many years in Kyocera’s components business. Currently, we are working on development of an algorithm to detect signs of dehydration, heat stroke or altitude sickness so that the sensor can be incorporated in wearable devices or smartphones.

* Ratio of signal to noise. The higher the ratio, the higher optical sensitivity.

photo:Blood flow sensing earphone Blood-flow sensor

Blood flow sensing earphone

Blood-flow sensor
Size: 3.2 x 1.6 x 0.9mm

Comment from Measuring Technique Development Staff

We were involved in development of a blood flow measuring technique as a theme in the medical and health care field for the first time. Although we faced a lot of challenges, we successfully established a high precision measuring technique through coordination and cooperation with other departments. At present, we are developing a new algorithm, equipment, and systems based on the measuring technique. We are determined to continuously solve problems in the medical and health care field and develop techniques and products that satisfy consumers.

Comment from Sensor Development Staff

Ceramic packages are used in a wide variety of products, including smartphones, camera modules, and LED lighting. We were looking for a new application beyond those existing businesses. Then, a different development department came to us and suggested development of a blood-flow sensor. This is how we got started. Since it was an uncharted field for us, we worried and wracked out brains quite a lot about how we should develop the sensor and what sensor would satisfy users. The conventional blood-flow sensors were big and expensive and not something that ordinary people could easily use for measurement. Against such a reality, our goal was not only to achieve higher optical sensitivity but also realize features that help the user easily measure health conditions as a daily routine, namely downsizing and low power consumption. We aim to contribute to the development of the health care field by providing devices equipped with Kyocera’s blood-flow sensor to the market.

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