**1. Introduction**

478 Remote Sensing – Applications

Van Caillie X.D. (1997). La carte des pentes (1/20 000) de la région des collines à Kinshasa.

Yebe Musieme B. (2004). L'impact des érosions sur l'habitat à Kisenso et les travaux de lutte

méditerranéennes, pp. 198-204.

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anti-érosive par la population locale. Travail de fin de cycle, Unikin, Faculté des Sciences, Département des Sciences de la terre, Géographie, 63p, unpublished. Yuan F., Sawaya K.E., Loeffelholz B.C. & Bauer M.E. (2005). Land cover classification and

change analysis of the Twin Cities (Minnesota) Metropolitan Area by multitemporal Landsat remote sensing, *Remote Sensing of Environnement,* Vol.98,

> Radar-based remote sensing techniques are typically employed to determine the velocities and positions of targets such as aircraft, ships, and land vehicles. In particular, X- and Kband microwave devices, including oscillators and antennas, have been used to measure the velocity of automobiles and other moving objects in recent years. Microwave devices that are compact, accurate, reliable, and inexpensive are currently commercially available. Over the past few years, there have been increasing attempts to apply such techniques to biomedical measurements. Although some studies have applied these devices to medicine and health care, such research is still in its infancy. This chapter focuses on the mechanisms of and the recent research trends in microwave remote sensing techniques that are used to detect minute vibrations on the body surface induced by heartbeat and respiration.

### **1.1 Background**

The increasing proportion of elderly in the population represents an appreciable problem in developed countries due to social concerns such as increased medical and social welfare costs and a shortage of manpower. Such concerns are expected to worsen in the future. It is thus necessary to focus on preventing illnesses and to promote healthy lifestyles. Consequently, simple equipment that can be used to self-monitor medical conditions and to acquire related data is required for homes as well as medical facilities.

Vital signs are parameters of physiological functions that are used to express the physical condition. They are used by medical professionals for making initial diagnoses. There are four primary vital signs: heart rate, respiratory rate, body temperature, and blood pressure. Thermometers for home use are commercially available and are generally approved by medical bodies. In addition, heart rate and respiratory rate can be easily confirmed by visual and palpation methods. However, there is currently still not spread to home device capable of accurately measuring and recording vital sign data that can be used to make detailed diagnoses. Monitoring cardiac function can be used for diagnosing arrhythmia and mental stress (Akselrod et al., 1981, Singh et al., 1996, Carney et al., 2001). Recently, monitoring mental condition has attracted more attention than monitoring physiological parameters. And also obesity and aging are thought to contribute to the risk of developing sleep apnea

Remote Sensing for Medical and Health Care Applications 481

Such sensing techniques have the advantages of being inexpensive because of their simple structure and of enabling stable relatively stable data acquisition because they employ direct contact with the body. Some of these sensors are already commercially available. However, they suffer from one drawback: measurement is not possible when the sensor is separated from the body by moving their bodies. This raises the question: "Is a remote sensing method

Radio-frequency sensing techniques were originally developed for military applications and they were used to determine the location and velocity of aircraft and ships. The same technology was then applied to search and rescue; for example, they have been used to locate survivors buried under earthquake rubble (Chen et al., 1986, 2000, Lin et al., 1992). Radar can remotely acquire information on the motion of targets. Additionally, depending on the frequency of the electromagnetic wave used, radar can penetrate barriers. These characteristics of radar have been employed to detect body motion of survivors under earthquake rubble. Such devices initially had very limited effectiveness because of their poor resolution by using low-frequency waves to penetrate rubble; they could only detect relatively large body motion (at best, the abdominal motion due to breathing). However, the permeability is not a problem for everyday applications since microwaves can readily

A cheap, small unit that is stable and can oscillate at high frequencies has recently been developed and ongoing development is being conducted to produce safer, more flexible devices. As a consequence, higher frequency electromagnetic waves were contributed to enhance the resolution of measurement. At the same time, the output power was reduced to reduce its effect on humans, allowing microwaves to be used in everyday applications.

Here, we describe a system that employs microwaves to remotely measure vital signs by detecting vibrations on the body surface induced by cardiac and respiratory activity. Vibrations induced by heartbeat are particularly small with amplitudes of about 0.1–0.2 mm on average. This section discusses approaches using continuous-wave (CW) Doppler radar and ultra-wideband (UWB) pulse radar, which are generally used for measuring vital signs,

While frequency-modulated continuous wave (FMCW) radar is used to identify the exact location of a subject in some reports, UWB or CW Doppler radar are generally used for

In a UWB pulse radar, the transmitter sends very short electromagnetic pulses toward the target. A pulse duration of about 200–300 ps and a pulse repetition frequency in the range of 1–10 MHz are typically used for vital sign detection. When the transmitted pulse reaches the chest wall, some of the energy is reflected and captured by the receiver. The nominal round-

monitoring vital signs. (Saunders, 1990, Immoreev & Tao, 2008, Li & Lin, 2010)

Gradual progress, therfore, has made it possible to detect even human heartbeat.

available?"

**2. Theory and methods** 

and their mechanisms.

**2.1 Mechanisms of measurement** 

**1.3 Biomedical measurement using microwaves** 

penetrate materials such as clothing, bedding, and mattresses.

syndrome (SAS). Airway obstruction due to fat deposition in the neck is one cause of SAS and it is related to reduced alertness during the daytime (Morriset al., 2008). A simple device that can monitor respiratory activity throughout the night is thus required. These examples show the necessity for monitoring of the vital signs in daily life. Moreover, these sensing technique are presently being studied in the research area on human–machine interfaces that can be applied anywhere (for example, in a car or at the workplace) (Sirevaag et al., 1993, Gould et al., 2009).

In addition, patients who have been exposed to toxic chemicals or infectious diseases are often treated in isolation chambers to prevent secondary exposure to health-care workers. In such cases, a doctor must often make a diagnosis without touching the patient, which is difficult as the vital signs are of primary importance for emergency medical treatment. With the exception of body temperature (which can be measured by infrared radiation), it is difficult to measure vital sign parameters without contact. Consequently, remote sensing of vital signs has attracted much attention.

In this way, several fields require remote sensing of vital signs and various remote sensing methods have been proposed. However, such methods should perform biomedical measurements described as non-invasive, non-restrictive, or non-contact means that can be used without the user being conscious of them. The use of physically attaching sensors should be minimized to reduce the burden on users.

#### **1.2 Purpose and requirements of remote sensing in medicine and health care**

Monitoring cardiac and respiratory parameters is useful for health-care management as users go about their everyday lives. However, such daily monitoring needs to overcome many problems. For example, users must have sufficient technical and medical competence to set electrodes to themselves and they must not feel physically restricted by the electrodes and leads. To overcome such problems, research is increasingly being conducted on developing non-invasive and non-restrictive sensing techniques for acquiring vital signs (Jacobs et al., 2004, Wang et al., 2006, Ciaccio et al., 2007). This kind of sensing technique aims to detect and measure vibrations on the body surface induced by cardiac and respiratory activity. In the case of respiratory activity, a person's abdomen expands and contracts during the breathing cycle and this movement can be detected by sensing techniques. Similarly, for cardiac activity, the body surface moves in response to the heartbeat in minute scales. Although the vibration is slight and its amplitude depends on the individual and the part of the body, it has been observed from all parts of the body with an average amplitude of about 0.1–0.2 mm by a high-resolution laser distance meter (Suzuki et al., 2011).

Some studies have measured heart rate by placing a pressure sensor (Jacobs et al., 2004) or polyvinylidene fluoride piezoelectric sensors (Wang et al., 2006) between the user and the mattress on which they sleep. This kind of measurement method measures responses to pressure changes. Other trials have used strain gauges to measure the heart rate (Ciaccio et al., 2007). The size of minute changes due to pressure changes on the body surface induced by the heartbeat and information relating to heartbeat and respiration were obtained. A similar procedure was employed in studies using air mattresses (Watanabe et al., 2005).

syndrome (SAS). Airway obstruction due to fat deposition in the neck is one cause of SAS and it is related to reduced alertness during the daytime (Morriset al., 2008). A simple device that can monitor respiratory activity throughout the night is thus required. These examples show the necessity for monitoring of the vital signs in daily life. Moreover, these sensing technique are presently being studied in the research area on human–machine interfaces that can be applied anywhere (for example, in a car or at the workplace) (Sirevaag et al.,

In addition, patients who have been exposed to toxic chemicals or infectious diseases are often treated in isolation chambers to prevent secondary exposure to health-care workers. In such cases, a doctor must often make a diagnosis without touching the patient, which is difficult as the vital signs are of primary importance for emergency medical treatment. With the exception of body temperature (which can be measured by infrared radiation), it is difficult to measure vital sign parameters without contact. Consequently, remote sensing of

In this way, several fields require remote sensing of vital signs and various remote sensing methods have been proposed. However, such methods should perform biomedical measurements described as non-invasive, non-restrictive, or non-contact means that can be used without the user being conscious of them. The use of physically attaching sensors

Monitoring cardiac and respiratory parameters is useful for health-care management as users go about their everyday lives. However, such daily monitoring needs to overcome many problems. For example, users must have sufficient technical and medical competence to set electrodes to themselves and they must not feel physically restricted by the electrodes and leads. To overcome such problems, research is increasingly being conducted on developing non-invasive and non-restrictive sensing techniques for acquiring vital signs (Jacobs et al., 2004, Wang et al., 2006, Ciaccio et al., 2007). This kind of sensing technique aims to detect and measure vibrations on the body surface induced by cardiac and respiratory activity. In the case of respiratory activity, a person's abdomen expands and contracts during the breathing cycle and this movement can be detected by sensing techniques. Similarly, for cardiac activity, the body surface moves in response to the heartbeat in minute scales. Although the vibration is slight and its amplitude depends on the individual and the part of the body, it has been observed from all parts of the body with an average amplitude of about 0.1–0.2 mm by a high-resolution laser distance meter (Suzuki

Some studies have measured heart rate by placing a pressure sensor (Jacobs et al., 2004) or polyvinylidene fluoride piezoelectric sensors (Wang et al., 2006) between the user and the mattress on which they sleep. This kind of measurement method measures responses to pressure changes. Other trials have used strain gauges to measure the heart rate (Ciaccio et al., 2007). The size of minute changes due to pressure changes on the body surface induced by the heartbeat and information relating to heartbeat and respiration were obtained. A similar procedure was employed in studies using air mattresses (Watanabe et

**1.2 Purpose and requirements of remote sensing in medicine and health care** 

1993, Gould et al., 2009).

et al., 2011).

al., 2005).

vital signs has attracted much attention.

should be minimized to reduce the burden on users.

Such sensing techniques have the advantages of being inexpensive because of their simple structure and of enabling stable relatively stable data acquisition because they employ direct contact with the body. Some of these sensors are already commercially available. However, they suffer from one drawback: measurement is not possible when the sensor is separated from the body by moving their bodies. This raises the question: "Is a remote sensing method available?"

### **1.3 Biomedical measurement using microwaves**

Radio-frequency sensing techniques were originally developed for military applications and they were used to determine the location and velocity of aircraft and ships. The same technology was then applied to search and rescue; for example, they have been used to locate survivors buried under earthquake rubble (Chen et al., 1986, 2000, Lin et al., 1992). Radar can remotely acquire information on the motion of targets. Additionally, depending on the frequency of the electromagnetic wave used, radar can penetrate barriers. These characteristics of radar have been employed to detect body motion of survivors under earthquake rubble. Such devices initially had very limited effectiveness because of their poor resolution by using low-frequency waves to penetrate rubble; they could only detect relatively large body motion (at best, the abdominal motion due to breathing). However, the permeability is not a problem for everyday applications since microwaves can readily penetrate materials such as clothing, bedding, and mattresses.

A cheap, small unit that is stable and can oscillate at high frequencies has recently been developed and ongoing development is being conducted to produce safer, more flexible devices. As a consequence, higher frequency electromagnetic waves were contributed to enhance the resolution of measurement. At the same time, the output power was reduced to reduce its effect on humans, allowing microwaves to be used in everyday applications. Gradual progress, therfore, has made it possible to detect even human heartbeat.
