JP2024078465A - Measuring equipment and antenna set - Google Patents

Abstract

[Problem] To provide a measuring device and an antenna set capable of suppressing reception of electromagnetic waves other than those transmitted through the heart. [Solution] A cardiac output measuring sensor 100 includes an antenna set having a transmitting antenna 12 and a receiving antenna 21, and a calculation unit 32. The transmitting antenna 12 is placed on one of the chest side and the back side of a subject 90 facing the heart 91. The receiving antenna 21 is placed on the other of the chest side and the back side of the patient facing the heart, and receives a transmitted wave of the electromagnetic wave radiated from the transmitting antenna transmitted through the subject's living body. The calculation unit calculates the blood volume based on the transmitted wave. The transmitting antenna and the receiving antenna each have a substrate on which an antenna surface including an antenna element is disposed, and a ground surface on the substrate opposite to the antenna surface, and the area of the ground surface of the back antenna placed on the back side of the antenna set is larger than the area of the ground surface of the chest antenna placed on the chest side of the patient. [Selected Figure] Figure 2

Description

The present invention relates to a measurement device and an antenna set.

Cardiac output, which is the amount of blood pumped out by a subject's heart, is an important biological parameter for doctors to treat the subject. In recent years, measurement techniques using electromagnetic waves such as microwaves have been developed as a method for non-invasively measuring cardiac output (for example, see Patent Document 1 below). Patent Document 1 discloses a device equipped with a transmitting antenna, a receiving antenna, and an estimating unit. In this device, the transmitting antenna transmits electromagnetic waves such as microwaves to the patient's chest, the receiving antenna receives the electromagnetic waves transmitted from the transmitting antenna, and the estimating unit detects the cardiac output of the subject based on the phase or amplitude intensity of the electromagnetic waves received by the receiving antenna.

International Publication No. 2018/194093

However, electromagnetic waves other than those that have passed through the subject's heart or its vicinity may also arrive at the receiving antenna. For example, if the receiving antenna receives electromagnetic waves that have passed through organs other than the heart, diffracted waves that do not pass through the body but are diffracted near the body surface, or reflected waves that are reflected off the body surface and then re-reflected by surrounding objects, an error in measuring cardiac output may occur in the estimation unit.

The present invention was made in consideration of the above circumstances, and aims to provide a measurement device and antenna set that can suppress the reception of electromagnetic waves other than those that have passed through the heart.

The above object of the present invention is achieved by the following means:

To achieve the above object, the measuring device of the present invention non-invasively measures the amount of blood pumped by the heart of a subject. The measuring device includes an antenna set having a transmitting antenna installed on one of the chest side and the back side of the subject facing the heart, and a receiving antenna installed on the other of the chest side and the back side of the subject facing the heart and receiving a transmitted wave of an electromagnetic wave radiated from the transmitting antenna that has passed through the living body of the subject, and a calculation unit that calculates the amount of blood based on the transmitted wave, and the transmitting antenna and the receiving antenna each have a substrate on which an antenna surface including an antenna element is arranged, and a ground surface on the substrate opposite to the antenna surface, and the area of the ground surface of the back side antenna installed on the back side of the subject of the antenna set is larger than the area of the ground surface of the chest antenna installed on the chest side of the subject.

In order to achieve the above object, the antenna set of the present invention has a transmitting antenna installed on one of the chest side and back side of the subject facing the heart, and a receiving antenna installed on the other of the chest side and back side of the subject facing the heart, and receives transmitted waves of electromagnetic waves radiated from the transmitting antenna that have passed through the subject's living body, and each of the transmitting antenna and receiving antenna has a substrate on which an antenna surface including an antenna element is arranged, and a ground surface on the substrate opposite the antenna surface, and the area of the ground surface of the receiving antenna is larger than the area of the ground surface of the transmitting antenna.

According to the measuring device and antenna set of the present invention, the area of the ground surface of the back antenna installed on the back side of the subject of the antenna set is larger than the area of the ground surface of the chest antenna installed on the chest side of the subject, so that it is possible to suppress the reception of electromagnetic waves other than those that have passed through the subject's heart or its vicinity, and to increase the transmission of electromagnetic waves that have passed through the heart or its vicinity, and/or the reception of electromagnetic waves that have passed through the heart or its vicinity. As a result, the measuring device can prevent or suppress a decrease in the measurement accuracy of cardiac output.

1 is a schematic diagram showing an entire cardiac output measuring sensor according to a first embodiment of the present invention; FIG. 2 is a schematic block diagram showing the entire cardiac output measuring sensor shown in FIG. 1 . 3 is a schematic diagram illustrating the transmitting antenna shown in FIG. 2; FIG. 3B is a schematic diagram of the transmitting antenna shown in FIG. 3A as viewed from the −X direction. FIG. 3B is a partially enlarged schematic diagram of an antenna element of the transmitting antenna of FIG. 3A. 1A and 1B are schematic diagrams illustrating the arrangement of dummy antenna elements; 10 is a diagram illustrating a portion of measurement results of VSWR characteristics in the X and Y directions of a transmitting antenna. 11 is a diagram illustrating a portion of the measurement results of the VSWR characteristics in the Z direction of the transmitting antenna. 1 is a diagram illustrating radiation characteristics of a transmitting antenna; 3 is a schematic diagram illustrating the receiving antenna shown in FIG. 2; 7B is a schematic diagram of the receiving antenna shown in FIG. 7A as viewed from the X direction. 7B is a diagram illustrating a portion of the measurement results of the VSWR characteristics in the X direction and the Y direction of the receiving antenna shown in FIG. 7A. 7B is a diagram illustrating a portion of the measurement results of the VSWR characteristics in the Z direction of the receiving antenna shown in FIG. 7A. 1 is a diagram illustrating radiation characteristics of a receiving antenna; 1A and 1B are schematic diagrams illustrating the installation of an electromagnetic wave shield. 7B is a schematic diagram for explaining the relationship between the size of the ground plane of the receiving antenna shown in FIG. 7A and the size of the transmitted microwave. FIG. FIG. 13 is a schematic diagram illustrating, as a comparative example, a case in which the ground surface of the receiving antenna is made smaller. FIG. 11 is a schematic block diagram showing the entire cardiac output measuring sensor according to the second embodiment. 14 is a schematic diagram illustrating the transmitting antenna shown in FIG. 13 . FIG. 14B is a schematic diagram of the transmitting antenna shown in FIG. 14A viewed along the −X direction. 14B is a diagram illustrating a simulation result of the radiation intensity of the transmitting antenna shown in FIG. 14A. FIG. 11 is a diagram illustrating, as a comparative example, a simulation result of the radiation intensity of a transmitting antenna having a wide antenna element. 14 is a schematic diagram illustrating the receiving antenna shown in FIG. 13 . 16B is a schematic diagram of the receiving antenna shown in FIG. 16A as viewed along the X direction. FIG. 13 is a schematic diagram illustrating a transmitting antenna according to a third embodiment. 17B is a schematic diagram of the transmitting antenna shown in FIG. 17A viewed along the −X direction.

Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. Note that in the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted. Also, the dimensional ratios in the drawings have been exaggerated for the convenience of explanation, and may differ from the actual ratios.

First Embodiment
FIG. 1 is a schematic diagram showing an entire cardiac output measuring sensor 100 according to a first embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of the cardiac output measuring sensor 100 shown in FIG.

Figure 1 shows a subject 90 (also called a patient) lying (supine position) on a bed 95 placed horizontally with respect to the X-Y plane. The cardiac output measurement sensor 100 functions as a measurement device and measures (estimates) the amount of blood pumped from the heart, such as the cardiac output, of the subject 90. For example, the cardiac output measurement sensor 100 is used in testing for heart failure, monitoring the progress after cardiac surgery, verifying the effectiveness and side effects of medication for heart disease, etc.

During measurement, the user, such as a nurse or doctor, places both antenna units (hereinafter, simply referred to as "transmitting and receiving antennas") facing each other across the heart 91 so that the line connecting the centers of the transmitting antenna 12 and the receiving antenna 21 corresponds to the heart 91. In order to reduce the influence of external electromagnetic waves, the chest of the subject 90 and the entire transmitting and receiving antennas may be covered with something capable of reflecting electromagnetic waves, such as a cloth electromagnetic shield (described later), or something capable of absorbing electromagnetic waves, such as a radio wave absorber, during measurement. For example, the receiving antenna 21 is placed under the subject 90, and the transmitting antenna 12 is placed above the subject 90. Specifically, the receiving antenna 21 is placed on a bed 95, and the subject 90 lies on his back on the receiving antenna 21. The upper transmitting antenna 12 is attached to a movable fixed base (not shown) that is U-shaped in side view. This fixed base can be manually adjusted in the horizontal direction (X direction and Y direction) and height (Z direction) of the transmitting antenna 12. The transmitting antenna 12 is placed above the subject 90, slightly separated from the subject 90 by a fixed base. The reason for the separation is to not interfere with the breathing of the subject 90 and to prevent unintended movement of the transmitting antenna 12 due to contact with the subject 90. The arrangement of the transmitting and receiving antennas is not limited to that shown in FIG. 1, etc. For example, the transmitting antenna 12 may be placed upside down, below the subject 90 (on the back side), and the receiving antenna 21 may be placed above the subject 90 (on the chest side). The transmitting antenna 12 and the receiving antenna 21 constitute an antenna set.

As shown in FIG. 2, the cardiac output measurement sensor 100 has a transmitting unit 10, a receiving unit 20, and a device main body 30. The device main body 30 is placed on a mobile stand (not shown) and placed beside the bed 95. The device main body 30 operates using power supplied from an internal battery or a commercial power source. The transmitting unit 10 and the receiving unit 20 are also connected to the device main body 30 via a signal cable 13, and data signals are transmitted and received and power is supplied via this signal cable 13. Details of the transmitting unit 10 and the receiving unit 20 will be described later.

(Device body 30)
The device main body 30 includes a transmission/reception controller 31 , a control unit 32 , a storage unit 33 , an input/output I/F (interface) 34 , and a communication I/F 35 .

(Transmission/reception controller 31)
The transmission/reception controller 31 is electrically connected to the transmission unit 10 and the reception unit 20 via the signal cable 13. Under the control of the control unit 32, the transmission/reception controller 31 controls the timing of transmission and reception of the transmission unit 10 and the reception unit 20, and acquires measurement values (reception signals) from the reception unit 20.

(Control unit 32)
The control unit 32 includes a CPU, a RAM, a ROM, etc., and controls each unit in the device main body 30 according to a program stored in the ROM or the storage unit 33. By executing the program, the control unit 32 receives a reception signal corresponding to the microwave received by the receiving unit 20 from the transmission/reception controller 31, analyzes the amplitude and phase of the reception signal, and estimates (calculates) the cardiac output of the subject 90, that is, the amount of blood pumped out from the heart 91. The control unit 32 functions as a calculation unit. The calculation unit may be configured to further calculate a cardiac index from the cardiac output. The cardiac index is an index obtained by converting the cardiac output per body surface area of the subject 90. The calculation unit may be configured to further calculate a stroke volume from the cardiac output. The stroke volume is an index obtained by converting the cardiac output per heart rate of the subject 90. The calculation unit may also be configured to first calculate the stroke volume, and then convert it to the cardiac output using the heart rate. As used herein, cardiac output is defined as parameters that describe the amount of blood pumped from the heart 91, including cardiac index and stroke volume.

(Memory unit 33)
The storage unit 33 is composed of a semiconductor memory that stores various programs and various data in advance, a magnetic memory such as a hard disk, etc. The storage unit 33 also stores point data, waveform data, etc.

(Input/output I/F 34)
The input/output I/F 34 functions as an input/output unit, and is an interface that has input/output terminals conforming to USB and DVI standards and connects to input devices such as a keyboard, mouse, and microphone, and output devices such as a display, speaker, and printer. In the example shown in Figs. 1 and 2, a touch panel 41 is connected to the input/output I/F 34. The touch panel 41 is composed of a liquid crystal panel and a touch pad superimposed thereon, and receives an instruction from a user to start an antenna element determination process and cardiac output measurement through the touch panel 41. Note that the input/output device such as the touch panel 41 may be included in the configuration of the device main body 30.

(Communication I/F 35)
The communication I/F 24 is an interface for transmitting and receiving data via wired or wireless communication with an external terminal device such as a PC (personal computer) or tablet terminal via a network or peer-to-peer. For wired communication, a network interface based on a standard such as Ethernet (registered trademark), SATA, PCI Express, IEEE 1394, etc. may be used, and for wireless communication, a wireless communication interface such as Bluetooth (registered trademark), IEEE 802.11, 4G, etc. may be used. In the example shown in Figs. 1 and 2, a PC 51 is connected to the communication I/F 35.

(Transmitter 10)
The transmitter 10 includes a transmission circuit 11 and a transmission antenna 12. The transmitter 10 radiates electromagnetic waves to the subject 90. The frequency of the electromagnetic waves is not particularly limited as long as it can pass through the heart 91 of the living body without ionization. For example, microwaves with a frequency of 300 MHz to 30 GHz are preferable, and microwaves with a frequency of 400 MHz to 1.0 GHz are more preferable. Hereinafter, a case where the electromagnetic waves are microwaves will be described as an example. Microwaves are suitable for measuring cardiac output because of their high biological permeability and high sensitivity (rate of change in electric field intensity) due to the change in dielectric constant during contraction/expansion of the heart 91. The power of the generated microwaves is not particularly limited as long as sufficient power can be detected by the receiving antenna 21, and may be, for example, several mW to several tens of mW. The generated microwaves may be continuous waves, pulse waves, or microwaves that have been subjected to phase modulation or frequency modulation.

The transmission circuit 11 generates a high-frequency signal corresponding to microwaves using an oscillator (not shown) and supplies it to the transmission antenna 12. More specifically, in this embodiment, as described below, the transmission antenna 12 has multiple antenna elements, so a switching circuit (not shown) selects one of the multiple antenna elements and supplies the high-frequency signal to the selected antenna element. Note that the unselected antenna elements are terminated and are not involved in microwave transmission.

Figure 3A is a schematic diagram illustrating the transmitting antenna 12 shown in Figure 2, and Figure 3B is a schematic diagram of the transmitting antenna 12 shown in Figure 3A viewed from the -X direction (the direction opposite to the X direction).

The transmitting antenna 12 functions as a chest-side antenna for the subject 90. The transmitting antenna 12 includes a substrate 120, an antenna array 121, and a ground plate 122. The antenna array 121 is formed on the substrate 120, which is an entirely rectangular plate with each side measuring several tens of millimeters to two hundred millimeters.

The antenna array 121 is composed of multiple antenna elements t1 to tx (hereinafter collectively referred to as "antenna element t"), which are arranged in a lattice pattern on the same plane (X-Y plane) on the surface of the planar substrate 120. The antenna array 121 has, for example, a substantially square lattice array structure. The surface of the antenna array 121 is referred to as the antenna surface of the transmitting antenna 12.

In addition, on the side of the substrate 120 opposite the antenna surface, a ground plate 122 is formed on the entire surface or part of the substrate 120. The surface of the ground plate 122 is referred to as the ground surface of the transmitting antenna 12. The ground plate 122 is formed, for example, at a distance equivalent to the thickness of the substrate 120 away from the antenna surface, and the distance between the ground plate 122 and the antenna surface (shown as A2 in FIG. 3B) is preferably about 5 mm. This has the effect of increasing the microwaves that have passed through the heart 91 or its vicinity (hereinafter referred to as "transmitted microwaves (transmitted waves)"), and improving the output of the transmitting antenna 12.

In this embodiment, a small loop antenna or a dipole-type linear antenna can be applied as each antenna element t. In the example shown in Figures 3A and 3B, each antenna element t is a small loop antenna element that is approximately rectangular with one side a1. The size of the small loop antenna element is small compared to the size of the heart 91 (e.g., 110 mm), and one side a1 is, for example, within 20 mm, preferably within 12 mm. This configuration has the effect of increasing the transmitted microwaves.

The overall size of the antenna array 121 is set to be approximately the same as or larger than the size of the heart 91 when viewed from the rear side of the subject 90. The antenna array 121 may be, for example, rectangular with a side A1 of several tens of mm to several hundred mm.

The total number of antenna elements t is preferably 4 to 150 inclusive. In the example shown in FIG. 3A, the antenna array 121 is composed of 49 antenna elements t1 to t49, 7 in each direction.

For example, as shown in FIG. 3C, in this embodiment, each antenna element t can be a minute loop antenna element with a total length (effective length) L of λg/10. Here, λg is the length of one wavelength λ of a microwave with frequency f in free space, shortened by the substrate 120 as a dielectric, and is expressed by the following formula (1) where ε is the effective dielectric constant of the substrate 120.

Furthermore, adjacent antenna elements t are arranged without being in close contact with each other. The distance between adjacent antenna elements t can be, for example, about 2 mm.

3D, a configuration may be adopted in which a plurality of dummy antenna elements d are arranged in the vicinity of the outer periphery of the antenna array 121. That is, the transmitting antenna 12 has a plurality of dummy antenna elements d arranged so as to surround the antenna array 121 on the substrate 120 adjacent to the antenna surface. This makes it possible to equalize the surrounding environment (conditions) of the antenna elements due to the presence of adjacent antenna elements between the outermost antenna element and the innermost antenna element of the antenna array 121.
Furthermore, a thin resin layer may be provided to cover the entire antenna surface, and the antenna element may be in contact with the subject 90 during measurement, but not directly. With such a configuration, the area that has been in contact with the subject 90 after measurement can be easily wiped clean with alcohol or the like, and damage to the antenna element during measurement can be suppressed. As the resin, a general resin, such as ABS, may be used. The thickness may be, for example, about 1 mm.

In this way, by arranging the antenna elements t in a lattice pattern and configuring it so that the antenna element t suitable for measurement can be selected, the antenna positioning operation can be simplified. For example, the antenna element t that maximizes the amount of microwaves that pass through the heart 91 or its vicinity is selected by the transmitting unit 10. The inventor has found that in order to be able to select the antenna element t most suitable for measurement from the antenna elements t arranged in a lattice pattern as described above, it is effective to arrange the antenna elements t taking into consideration the size of the heart 91.

<Design example of transmitting antenna 12>
For example, when the frequency f is 430 MHz and the effective dielectric constant ε of the substrate 120 is 4.3, the side a1 of the antenna element t can be calculated to be about 10.8 mm from the above formula (1). If the interval between adjacent antenna elements t is 1.7 mm, the overall size of the antenna array 121 can be calculated to be about 100 mm square.

It is also possible to make one side a1 of the antenna element t smaller than 10.8 mm and increase the total number of antenna elements t in the antenna array 121. For example, the antenna array 121 can be configured with one side a1 of the antenna element t being 6.7 mm and with a total of 121 antenna elements t1 to t121, 11 in each direction.

<Antenna characteristics of transmitting antenna 12>
The antenna characteristics include at least one of impedance characteristics and radiation characteristics. Fig. 4 is a diagram illustrating a portion of the measurement results of the VSWR characteristics in the X-direction and Y-direction of the transmitting antenna 12, and Fig. 5 is a diagram illustrating a portion of the measurement results of the VSWR characteristics in the Z-direction of the transmitting antenna 12. Fig. 6 is a diagram illustrating the radiation characteristics of the transmitting antenna. In the diagram, the measurement standard is -60 dB.

The inventors measured the impedance characteristics (VSWR characteristics) as antenna characteristics of the designed transmitting antenna 12. More specifically, the VSWR characteristics were measured with respect to positional changes in the X, Y, and Z directions, with the center of the chest surface of the subject 90 as the origin. The VSWR values were measured using a network analyzer.

Figure 4 illustrates the measurement results for the second quadrant of the X-Y coordinate system, i.e., the region where the X coordinate is 0 and negative values (-20 mm to -100 mm) and the Y coordinate is 0 and positive values (20 mm to 100 mm). Figure 5 illustrates the measurement results for the distance in the Z direction, i.e., the distance between the transmitting antenna 12 and the body surface of the subject 90, which is 0 mm to 50 mm.

As shown in Figures 4 and 5, the VSWR value is 2.0 or less within a 100 mm x 100 mm plane centered on the center of the chest surface of the subject 90 and within a space from -5 mm to 50 mm above the plane, and there is little variation with respect to positional changes in the X, Y, and Z directions.

Note that although the measurement results are not shown for the first, third, and fourth quadrants in the X-Y coordinate system, the VSWR values are 2.0 or less. Furthermore, although the results are not shown for -5 mm in the Z direction, the VSWR value is also 2.0 or less. For example, if the VSWR is 2.0 or less, transmission is approximately 90% efficient.

In this way, the transmitting antenna 12 is configured so that the VSWR value fluctuation with respect to position change in a direction parallel to the antenna plane is within a predetermined first range (e.g., 2.0), and the VSWR value fluctuation with respect to position change in the Z direction perpendicular to the antenna plane is within a predetermined second range (e.g., 2.0).

As shown in FIG. 5, the mismatch loss (return loss) is also less than 0.5 when the distance between the transmitting antenna 12 and the body surface of the subject 90 is between 0 mm and 50 mm, and the variation with respect to the position change in the Z direction is small.

Furthermore, as shown in FIG. 6, regarding the radiation characteristics as antenna characteristics, when the distance between the transmitting antenna 12 and the body surface of the subject 90 is 10 mm or less, the fluctuation in gain and external leakage is small. The fluctuation in gain in the Z direction is approximately 10 dB. However, when the distance exceeds 10 mm, the gain of the horizontally polarized wave in the first quadrant of the X-Y coordinate system is particularly reduced.

(Receiving unit 20)
As shown in Fig. 2, the receiving unit 20 has a receiving antenna 21 and a receiving circuit 22. The receiving antenna 21 functions as an antenna on the back side of the subject 90, and receives microwaves radiated from the transmitting antenna 12 that have passed through the heart 91 or its vicinity. The receiving circuit 22 has a demodulation unit (not shown), which demodulates the microwave signal received by the receiving antenna 21, for example, by envelope detection (amplitude detection) or phase detection. The receiving circuit 22 may also extract a specific frequency component by frequency analysis to demodulate the microwave signal. The receiving circuit 22 outputs the demodulated microwave signal to the transmission/reception controller 31 as a reception signal.

Figure 7A is a schematic diagram illustrating the receiving antenna 21 shown in Figure 2, and Figure 7B is a schematic diagram of the receiving antenna shown in Figure 7A viewed from the X direction.

The receiving antenna 21 includes a substrate 210, an antenna element 211, a power supply section 212, and a ground plate 213. The substrate 210 is a generally rectangular plate-shaped member with each side B1 measuring several tens of mm to two hundred mm, and a single antenna element 211 is disposed on one surface (X-Y plane) of the substrate 210. The surface of the antenna element 211 is referred to as the antenna surface of the receiving antenna 21. The antenna element 211 may be a patch antenna (microstrip antenna) with one side AL1 measuring several tens of mm to one hundred and several tens of mm, a dipole-type linear antenna, or a loop antenna. For example, the antenna element 211 is a patch antenna with an antenna length AL1. The antenna length AL1 of the patch antenna is calculated using the following formula (2).

Here, λg is the length of one wavelength obtained by shortening the length λ of one wavelength of a microwave of frequency f in free space by the substrate 120 as a dielectric. The overall shape of the antenna element 211 is determined taking into consideration the size of the patch antenna, the power supply 212, impedance matching (50 Ω), etc. The power supply 212 is a conductive member for transmitting a high-frequency signal from the single antenna element 211 to the receiving circuit 22, and connects the antenna element 211 and the receiving circuit 22.

In addition, on the opposite side of the antenna surface on the substrate 210, a ground plate 213 is formed on the entire surface or part of the substrate 210. The surface of the ground plate 213 is called the ground surface. The ground plate 213 is formed, for example, at a distance equivalent to the thickness of the substrate 210 away from the antenna surface, and the distance between the ground plate 213 and the antenna surface (shown as B2 in FIG. 7B) is preferably about 2 mm. In addition, the ground surface has an area that covers the entire back of a subject 90 of average build. The ground surface is rectangular, and the length of one side is shorter than the shoulder width of the subject 90. For example, the length of one side can be within the range of 200 to 300 mm. The length of one side can be preferably 250 mm. This has the effect of increasing the transmitted microwaves and increasing the input to the receiving antenna 21.

<Design example of receiving antenna 21>
For example, when the frequency f is 430 MHz and the effective dielectric constant ε of the substrate 210 is 4.3, the antenna length AL1 of the receiving antenna 21 can be calculated to be 130 mm using the above formula (2).

<Antenna characteristics of receiving antenna 21>
The antenna characteristics include at least one of impedance characteristics and radiation characteristics. Fig. 8 is a diagram illustrating a portion of the measurement results of the VSWR characteristics with respect to the positional changes in the X and Y directions of the receiving antenna 21, and Fig. 9 is a diagram illustrating a portion of the measurement results of the VSWR characteristics with respect to the positional changes in the Z direction of the receiving antenna 21. Fig. 10 is a diagram illustrating the radiation characteristics of the receiving antenna 21. In the diagram, the measurement standard is -40 dB.

The inventors measured the impedance characteristics (VSWR characteristics) as the antenna characteristics of the designed receiving antenna 21. More specifically, the VSWR characteristics were measured with respect to position changes in the X, Y, and Z directions, with the center of the subject's 90 chest surface as the origin. Figure 8 illustrates the measurement results in the region where the X coordinate in the X-Y coordinate system is 0 mm, 40 mm, and 80 mm, and the Y coordinate is -40 mm, 0 mm, and 40 mm. Figure 9 also illustrates the measurement results for the distance in the Z direction, i.e., the distance between the receiving antenna 21 and the body surface of the subject 90, ranging from 0 mm to 50 mm.

As shown in Figure 8, the VSWR value is 2.0 or less within an 80 mm x 80 mm plane centered on the center of the back surface of the subject 90, and there is little variation with respect to positional changes in the X and Y directions. Note that, although the measurement results are not shown when the X coordinate is a negative value, the VSWR value is 2.0 or less.

In this way, the receiving antenna 21 is configured so that the VSWR value fluctuates within a predetermined first range (e.g., 2.0) in response to position changes in a direction parallel to the antenna surface.

On the other hand, as shown in FIG. 9, with respect to a change in position in the Z direction perpendicular to the antenna surface, the VSWR value and mismatch loss increase as the distance between the receiving antenna 21 and the body surface of the subject 90 increases.

Furthermore, as shown in FIG. 10, regarding the radiation characteristics as antenna characteristics, when the distance between the receiving antenna 21 and the body surface of the subject 90 is 5 mm or less, the gain and external leakage are small. On the other hand, when the distance exceeds 5 mm, the gain and external leakage increase. The reason why the gain increases despite the increase in mismatch loss is thought to be because the body of the subject 90 functions as a ground rather than the ground surface of the receiving antenna 21.

Therefore, it is believed that the radiation characteristics of the receiving antenna 21 can be improved by providing a larger ground surface to the receiving antenna 21. In addition, the electromagnetic wave shield described below is also effective in suppressing increases in the VSWR value (mismatch loss) and external leakage.

<Electromagnetic wave shield>
11 is a schematic diagram illustrating the installation of an electromagnetic shield. The electromagnetic shield 14 is composed of, for example, a first electromagnetic shield 14a arranged so as to cover the entire chest of the subject 90 and the transmitting/receiving antenna, and a second electromagnetic shield 14b arranged between the bed 95 and the receiving antenna 21. That is, the first electromagnetic shield 14a, the transmitting antenna 12, the body of the subject 90, the receiving antenna 21, and the second electromagnetic shield 14b are arranged on the bed 95 in this order from the chest side to the back side of the subject 90.

The electromagnetic wave shield 14 has the function of blocking microwaves, and blocks the passage of microwaves other than transmitted microwaves (hereinafter referred to as "non-transmitted microwaves") that go around the outside of the subject's 90 body toward the receiving antenna 21. By installing the electromagnetic wave shield 14 not only on the chest side of the subject 90 but also on the back side of the subject 90, i.e., on the side of the receiving antenna 21 that is not in contact with the patient's body, the effect of blocking non-transmitted microwaves is improved.

In addition to the electromagnetic shield 14, a radio wave absorber (not shown) that absorbs microwaves can also be arranged. In this case, the following are arranged on the bed 95 from the chest side to the back side of the subject 90: first electromagnetic shield 14a, radio wave absorber, transmitting antenna 12, the body of the subject 90, receiving antenna 21, radio wave absorber, and second electromagnetic shield 14b. By arranging the radio wave absorber, electromagnetic waves that are not necessary for calculating cardiac output, including non-penetrating microwaves, are absorbed by the radio wave absorber and are less likely to reach the receiving antenna 21. This can further suppress the reception of non-penetrating microwaves by the receiving antenna 21.

The radio wave absorber can be used, for example, as a material for the casing of the receiving antenna 21. However, in order for the radio wave absorber to adequately absorb unnecessary electromagnetic waves, the radio wave absorber needs to have a certain thickness, and it is not realistic to obtain the effect of adequately suppressing non-penetrating microwaves using only the radio wave absorber. Therefore, by using the electromagnetic wave shield 14 and the radio wave absorber together as the material for the casing, it is possible to adequately suppress non-penetrating microwaves while suppressing the thickness of the casing.

<Increasing microwave transmission through the ground plane>
Fig. 12A is a schematic diagram for explaining the relationship between the size of the ground surface of the receiving antenna 21 shown in Fig. 7A and the size of the transmitted microwave, and Fig. 12B is a schematic diagram illustrating, as a comparative example, a case in which the ground surface of the receiving antenna 21 is made small. Note that in Figs. 12A and 12B, for convenience of explanation, there is a gap between the receiving antenna 21 and the body of the subject 90, but in reality, the patch antenna of the receiving antenna 21 and the body of the subject 90 are in close contact with each other.

When the receiving antenna 21 is used in close contact with the body of the subject 90, it is preferable to make the ground surface as large as possible. As shown in FIG. 12A, in this embodiment, the area of the ground surface of the receiving antenna 21 is at least larger than the area of the ground surface of the transmitting antenna 12.

The inventors discovered that by configuring the ground planes of the transmitting antenna 12 and the receiving antenna 21 in this way, it is possible to suppress the reception of non-penetrating microwaves among the microwaves radiated by the transmitting unit 10. This is because the area of the ground plane of the receiving antenna 21 is larger than the area of the ground plane of the transmitting antenna 12, and therefore the ability W1A of the receiving antenna 21 to transmit and receive transmitted microwaves is larger than the ability W2A of the receiving antenna 21 to transmit and receive non-penetrating microwaves.

For example, since the transmitting and receiving capabilities of the receiving antenna 21 for penetrating microwaves are roughly equal, the transmitting and receiving capability W1A is illustrated by an upward arrow in FIG. 12A. The same is true for the transmitting and receiving capability W2A for non-penetrating microwaves. Non-penetrating microwaves include, for example, microwaves that have passed through organs other than the heart 91 or its vicinity of the subject 90, diffracted waves that do not pass through the body of the subject 90 but are diffracted near the body surface, and reflected waves that are reflected off the body surface and then re-reflected by surrounding objects.

On the other hand, as shown in FIG. 12B, in the comparative example, the surface area of the ground plate 233 of the receiving antenna 23 is small, so that the body of the subject 90 functions as the ground rather than the ground plate 233. Therefore, the capacity W2B for transmitting and receiving non-penetrating microwaves exceeds the capacity W1B for transmitting and receiving penetrating microwaves, and the non-penetrating microwaves received by the receiving antenna 23 increase. As a result, in the comparative example, the noise components of the received signal output by the receiving unit 20 increase and the baseline level fluctuates, resulting in a decrease in the measurement accuracy of the cardiac output. For example, when the receiving antenna 23 receives microwaves that have passed through organs other than the heart 91 or its vicinity, there is a possibility that a measurement error in the cardiac output will occur due to the body movement or breathing of the subject 90. In addition, when the receiving antenna 23 receives diffracted waves or reflected waves, there is a possibility that a measurement error in the cardiac output will occur due to the surrounding movements of the person measuring, etc.

Therefore, in this embodiment, it is preferable to make the ground surface of the receiving antenna 21 as large as possible in order to suppress non-transmitting microwaves and reduce their effect on the received signal of the receiving unit 20.

On the other hand, the inventors have found that if the ground surface of the receiving antenna 21 is made large enough to extend beyond the body of the subject 90, the non-penetrating microwaves reach the protruding parts of the antenna surface directly, and the non-penetrating microwaves contained in the received signal increase. In this case as well, the non-penetrating microwaves increase, and the measurement accuracy of the cardiac output may decrease. Therefore, in order to reduce the effect on the received signal of the receiving unit 20, it is preferable to make the ground surface of the receiving antenna 21 large, but within a range that does not extend beyond the body of the subject 90.

The inventors measured the size of the ground plate 213 as 250 mm square, which does not extend beyond the subject's body, when the subject 90 is an adult of average build and the receiving frequency is 430 MHz, and confirmed that this provides an effect of suppressing non-transmitted microwaves. In addition, the inventors measured the size of the ground plate 213 as 250 mm x 320 mm, which is vertically long with the longitudinal direction extending from the head to the feet of the subject 90, and confirmed that this provides an effect of further suppressing non-transmitted microwaves. In this way, by configuring the ground plate 213 vertically long, the ground surface of the receiving antenna 21 can be further enlarged without it extending beyond the subject's body.

The measurement device and antenna set of this embodiment described above provide the following advantages:

The area of the ground surface of the receiving antenna 21 of the antenna set, which is installed on the back side of the subject 90, is larger than the area of the ground surface of the transmitting antenna 12, which is installed on the chest side of the subject 90, so that the reception of non-penetrating microwaves can be suppressed and the transmission of penetrating microwaves and/or the reception of penetrating microwaves can be increased. As a result, the cardiac output measurement sensor 100 can prevent or suppress a decrease in the measurement accuracy of cardiac output.

Second Embodiment
In the first embodiment, a case where an antenna set consisting of a transmitting antenna (second antenna) having a plurality of antenna elements and a receiving antenna (first antenna) having a single antenna element is used is described. In the second embodiment, a case where an antenna set consisting of a transmitting antenna (first antenna) having a single antenna element and a receiving antenna (second antenna) having a plurality of antenna elements is used is described. In order to avoid duplication of explanation, detailed explanation of the same configuration as in the first embodiment is omitted.

Figure 13 is a schematic block diagram showing the entire cardiac output measurement sensor 100 of the second embodiment. Also, Figure 14A is a schematic diagram illustrating the transmitting antenna 62 shown in Figure 13, and Figure 14B is a schematic diagram of the transmitting antenna 62 shown in Figure 14A viewed along the -X direction.

(Transmitter 60)
13, the transmitting unit 60 has a transmitting circuit 61 and a transmitting antenna 62. The function of the transmitting unit 60 of this embodiment is basically the same as that of the transmitting unit 10 of the first embodiment, but the transmitting circuit 61 is configured to supply a high-frequency signal to a transmitting antenna 62 having a single antenna element.

The transmitting antenna 62 functions as a chest-side antenna for the subject 90. As shown in Figures 14A and 14B, the transmitting antenna 62 includes a substrate 620, an antenna element 621, a power supply section 622, and a ground plate 623. The antenna element 621 and the power supply section 622 are formed on the substrate 620, which is an overall rectangular plate with a short side C1 of 40 mm to 80 mm and a long side C2 of 100 mm to 300 mm, for example.

The antenna element 621 is a patch antenna that is narrow (strip-shaped) along the X direction. The surface of the antenna element 621 is called the antenna surface of the transmitting antenna 62. The power supply unit 622 is a conductive member for supplying a high-frequency signal from the transmitting circuit 61 to the antenna element 621, and connects the antenna element 621 to the transmitting circuit 61. The power supply unit 622 is even narrower than the antenna element 621 and is formed integrally with the antenna element 621.

In addition, on the side of the substrate 620 opposite the antenna surface, a ground plate 623 is formed on the entire surface or part of the substrate 620. The surface of the ground plate 623 is called the ground surface. The ground plate 623 is formed, for example, at a distance equivalent to the thickness of the substrate 610 away from the antenna surface, and the distance between the ground plate 623 and the antenna surface (shown by C3 in FIG. 14B) is preferably about 2 mm.

<Design Example of Transmitting Antenna 62>
For example, when the frequency f is 430 MHz and the effective dielectric constant ε of the substrate 620 is 4.3, the antenna length AL2 of the receiving antenna 21 can be calculated to be 130 mm from the antenna length AL2=λg/2. The length AL3 in the width direction can be, for example, 20 mm to 40 mm (e.g., 30 mm).

The inventors have discovered that by configuring the antenna element 621 to have a narrow width along the X direction, it is possible to reduce non-penetrating microwaves and increase transmitted microwaves that have penetrated the heart or its vicinity without compromising the antenna gain (i.e., transmission output).

The transmitting antenna 62 is preferably placed near the center of the chest of the subject 90. Since the transmitting antenna 62 has a narrow shape in the X direction, it can be placed near the body surface close to the heart 91 while being maintained parallel to the receiving antenna 71, regardless of the shape of the subject 90's chest, particularly the presence or absence of breasts and the shape of the breasts.

<Radiation characteristics of transmitting antenna 62>
Fig. 15A is a diagram illustrating a simulation result of the radiation intensity of the transmitting antenna 62 shown in Fig. 14A, and Fig. 15B is a diagram illustrating a simulation result of the radiation intensity of a transmitting antenna having a wide antenna element as a comparative example. In Fig. 15A and Fig. 15B, the parts where the microwave intensity is strong are shown in dark gray, and the parts where the microwave intensity is weak are shown in light gray.

As shown in FIG. 15A, in this embodiment, microwaves radiate from the transmitting antenna 62 and pass through the heart 91 or its vicinity. The transmitted microwaves that pass through the heart or its vicinity are received by the receiving antenna 71 installed on the back of the subject 90 while maintaining sufficient intensity.

On the other hand, as shown in FIG. 15B, in the comparative example, the microwaves radiated from the transmitting antenna 63, which has a wider antenna element than the transmitting antenna 62, are diffused to places in the body other than the heart or its vicinity, and the strength of the microwaves reaching the heart or its vicinity is reduced, and the strength is significantly reduced by the time they reach the receiving antenna 71.

(Receiving unit 70)
As shown in Fig. 13, the receiving unit 70 has a receiving antenna 71 and a receiving circuit 72. Fig. 16A is a schematic diagram illustrating the receiving antenna 71 shown in Fig. 13, and Fig. 16B is a schematic diagram of the receiving antenna shown in Fig. 16A as viewed along the X direction.

The receiving antenna 71 functions as an antenna on the back side of the subject 90. The receiving antenna 71 includes a substrate 710, an antenna array 711, and a ground plate 712. The antenna array 721 is formed on the substrate 710, which is an overall rectangular plate with each side D1 being 200 mm to 250 mm.

The antenna array 711 is composed of multiple antenna elements r1 to rx (hereinafter collectively referred to as "antenna elements r"), which are arranged in a lattice pattern on the same plane (X-Y plane) on the surface of the planar substrate 710. The antenna array 711 has, for example, a substantially square lattice array structure. The surface of the antenna array 711 is referred to as the antenna surface of the receiving antenna 71.

In addition, on the opposite side of the antenna surface on the substrate 710, a ground plate 712 is formed on the entire surface or part of the substrate 710. The surface of the ground plate 712 is referred to as the ground surface of the receiving antenna 71. The ground surface of the receiving antenna 71 can have an area that covers the entire back of a subject 90 of average build. The ground surface is rectangular, and the length of one side is shorter than the shoulder width of the subject 90. For example, the length of one side can be within the range of 200 to 300 mm. Since the area of the ground surface of the receiving antenna 71 is larger than the area of the ground surface of the transmitting antenna 62 installed on the chest side of the subject 90, reception of non-penetrating microwaves can be suppressed.

The ground plate 712 is formed, for example, at a distance equivalent to the thickness of the substrate 710 away from the antenna surface, and the distance between the ground plate 712 and the antenna surface (shown as D2 in FIG. 16B) is preferably about 5 mm. This has the effect of increasing the transmitted microwaves and directing the input of the receiving antenna 71.

In this embodiment, a small loop antenna element or a dipole-type linear antenna can be applied as each antenna element r. In the example shown in Figures 16A and 16B, each antenna element r is a substantially rectangular small loop antenna element. The size of the antenna element r is smaller than the size of the heart 91, and each side of the antenna element r is, for example, within 20 mm, preferably within 12 mm. This configuration has the effect of increasing the transmitted microwaves. The overall size of the antenna array 711 is set to a size equal to or larger than the size of the heart 91 when viewed from the back side of the subject 90. For example, it is a rectangular shape with one side E1 of 100 to 150 mm.

The total number of antenna elements r is preferably 4 to 150 inclusive. For example, in the example shown in FIG. 16A, the antenna array 711 is composed of 49 antenna elements r1 to r49, 7 in each direction.

In this way, by arranging the antenna elements r in a lattice pattern and configuring it so that the antenna element r suitable for measurement can be selected, the antenna positioning operation can be simplified. The antenna element r that maximizes the strength of the microwaves transmitted through the heart 91 or its vicinity is selected by the receiving unit 70. The inventor has found that, in order to be able to select the antenna element r most suitable for measurement from the antenna elements r arranged in a lattice pattern as described above, it is effective to arrange the antenna elements r taking into consideration the size of the heart 91.

In addition, unlike the first embodiment, in this embodiment, the receiving antenna side is configured in an array rather than the transmitting antenna. With this configuration, the relative position of the transmitting antenna with respect to the subject 90 is fixed, so that the transmission state (intensity distribution) of the microwaves inside the body during measurement can be made constant, making it possible to receive the transmitted microwaves with greater accuracy. It has also been found that by configuring the receiving antenna in an array, it is possible to simultaneously simplify the operation of positioning the antenna.

For example, in the example shown in FIG. 16A, each antenna element r is a small loop antenna element having a roughly rectangular shape with one side measuring a1, and the antenna array 711 is composed of 49 antenna elements r1 to r49, seven in each direction.

Dummy antenna elements may also be arranged in the vicinity of the outer periphery of the antenna array 711. That is, the receiving antenna 71 has multiple dummy antenna elements d arranged to surround the antenna array 711 on the substrate 710 adjacent to the antenna surface. This makes it possible to equalize the surrounding environment (conditions) of the antenna elements due to the presence of adjacent antenna elements between the outermost antenna element and the innermost antenna element of the antenna array 711.

The receiving circuit 72 demodulates the microwave signal received by the receiving antenna 71. In this embodiment, since the receiving antenna 71 has multiple antenna elements, one of the multiple antenna elements is selected by a switching circuit (not shown), and the microwave signal is received by the selected antenna element. Note that the unselected antenna element is connected to ground.

<Design example of receiving antenna 71>
For example, when the frequency f is 430 MHz and the effective dielectric constant ε of the substrate 710 is 4.3, the total length (effective length) of the circumference of the antenna element r is λg/10. As a result, one side of the antenna element r can be calculated to be about 10.8 mm. In addition, when the interval between adjacent antenna elements r is 1.7 mm, the overall size of the antenna array 711 can be calculated to be about 100 mm square.

In the above example, the side D1 of the substrate 710 is 200 mm to 250 mm, but the present invention is not limited to this. The substrate 710 and the ground plate 712 may be elongated with the longitudinal direction extending from the head to the feet of the subject 90. The short-side length of the ground plate 712 is shorter than the shoulder width of the subject 90. For example, the short-side length may be within a range of 200 mm to 300 mm. The long-side length may be within a range of 200 mm to 320 mm. The substrate 710 and the ground plate 712 may be sized, for example, 250 mm by 320 mm. Furthermore, the antenna array 711 may be configured to have a total of 81 antenna elements r1 to r81, 9 in each direction.

Third Embodiment
In the second embodiment, a case where an antenna set consisting of a transmitting antenna (first antenna) having a single patch antenna element and a receiving antenna (second antenna) having a plurality of small loop antenna elements is used is described. In the third embodiment, a case where an antenna set consisting of a transmitting antenna (first antenna) having a single small loop antenna element and a receiving antenna (second antenna) having a plurality of small loop antenna elements is used is described. The third embodiment has the same configuration as the second embodiment except for the configuration of the transmitting antenna. In order to avoid duplication of explanation, detailed explanation of the same configuration as the second embodiment is omitted.

Figure 17A is a schematic diagram illustrating a transmitting antenna of the third embodiment, and Figure 17B is a schematic diagram of the transmitting antenna shown in Figure 17A viewed along the -X direction.

The transmitting antenna 82 includes a substrate 820, an antenna element 821, and a ground plate 822. The transmitting antenna 82 functions as an antenna on the chest side of the subject 90. The antenna element 821 is not particularly limited, but is preferably formed on the substrate 820, which is an entirely rectangular plate with a short side F1 of 90 mm to 110 mm and a long side C2 of 180 mm to 200 mm.

The antenna element 821 is a small loop antenna element that is approximately rectangular with one side a1. The size of the small loop antenna element is small compared to the size of the heart 91, with one side a1 being, for example, within 20 mm, preferably within 12 mm. The surface of the antenna element 821 is referred to as the antenna surface of the transmitting antenna 82.

The arrangement of the antenna element 821 on the substrate 820 is not particularly limited, but for example, the antenna element 821 may be arranged approximately in the center of the substrate 820 in the short direction of the substrate 820. For example, when F1 is 100 mm, b1 may be set to approximately 50 mm. In addition, it is preferable that the antenna element 821 is arranged at a position other than the end of the substrate 820 in the long direction of the substrate 820.

In addition, on the side of the substrate 820 opposite the antenna surface, a roughly rectangular ground plate 822 is formed on the entire surface or part of the substrate 820. The surface of the ground plate 822 is referred to as the ground surface. The area of the ground surface of the transmitting antenna 82 is smaller than the area of the ground surface of the receiving antenna installed on the back side of the subject 90. In other words, the area of the ground surface of the antenna on the back side of the subject 90 is larger than the area of the ground surface of the antenna on the chest side, so that reception of non-penetrating microwaves can be suppressed.

The ground plate 822 is formed, for example, at a distance equivalent to the thickness of the substrate 820 away from the antenna surface, and the distance between the ground plate 822 and the antenna surface (indicated by F3 in FIG. 17B) is preferably about 2 mm.

In the above example, the transmitting antenna 82 having one small loop antenna element is placed on the chest side of the subject 90, but the transmitting antenna 82 can also be placed on the back side of the subject 90. In this case, the area of the ground surface of the transmitting antenna 82 is designed to be larger than the area of the ground surface of the receiving antenna on the chest side.

As described above, the measurement device and antenna set of the present invention have been described in the embodiments. However, it goes without saying that a person skilled in the art can make additions, modifications, and omissions to the present invention as appropriate within the scope of its technical concept.

For example, in the above embodiment, a case has been described in which one of the antenna sets is an antenna array and the other is a patch antenna. However, the present invention is not limited to such a case, and can also be applied, for example, to a case in which both of the antenna sets are loop antennas or patch antennas.

10 Transmission unit,
11 Transmission circuit,
12 transmitting antenna,
121 antenna array,
122 ground plate,
13 signal cable,
14 electromagnetic wave shielding,
20 receiving unit,
21 receiving antenna,
211 antenna element,
212 power supply unit,
213 Ground plate,
22 receiving circuit,
30 device body,
31 transmit/receive controller,
32 control unit,
33 memory unit,
34 Input/Output I/F,
35 communication I/F,
41 touch panel,
51 PC,
60 transmitting unit,
61 transmitting circuit,
62 transmitting antenna,
621 antenna element,
622 power supply unit,
623 Ground plate,
70 receiving unit,
71 receiving antenna,
711 Antenna Array,
712 Ground plate,
72 receiving circuit,
95 beds,
100 Cardiac output measurement sensor.

Claims (17)

1. A measuring device for non-invasively measuring the amount of blood pumped by a subject's heart, comprising:
an antenna set including: a transmitting antenna installed on one of the chest side and the back side of the subject so as to face the heart; and a receiving antenna installed on the other of the chest side and the back side of the subject so as to face the heart, for receiving a transmitted wave which is an electromagnetic wave radiated from the transmitting antenna and transmitted through the living body of the subject;
A calculation unit that calculates the blood volume based on the transmitted wave,
Each of the transmitting antenna and the receiving antenna has a substrate on which an antenna surface including an antenna element is disposed, and a ground surface on the substrate opposite to the antenna surface;
A measuring device, wherein the area of the ground surface of a back-side antenna of the antenna set that is installed on the back side of the subject is larger than the area of the ground surface of a chest-side antenna that is installed on the chest side of the subject. the chest-side antenna is configured such that a variation in antenna characteristics falls within a predetermined first range with respect to a position change in a direction parallel to the antenna plane when the chest-side antenna is placed on the chest side of the subject, and a variation in the antenna characteristics falls within a predetermined second range with respect to a position change in a direction perpendicular to the antenna plane when the chest-side antenna is placed on the chest side of the subject,
The measurement device according to claim 1, wherein the back side antenna is configured such that a variation in the antenna characteristics falls within a predetermined first range with respect to a change in position in a direction parallel to the antenna surface when the back side antenna is placed on the back side of the subject. The measurement device according to claim 2, wherein the antenna characteristics include at least one of impedance characteristics and radiation characteristics. the chest-side antenna has an antenna characteristic VSWR value of 2.0 or less within a 100 mm×100 mm plane centered on the center of the subject's chest surface and within a space ranging from −5 mm to 50 mm above the plane;
4. The measurement device according to claim 3, wherein the VSWR value, which is the antenna characteristic of the back-side antenna, is 2.0 or less within a plane of 80 mm x 80 mm centered at the center of the subject's back surface. The measurement device according to any one of claims 1 to 4, wherein the ground surface of the receiving antenna has an area that entirely covers the chest or back of the subject of average build. The measurement device according to claim 5, wherein the ground surface of the receiving antenna is rectangular and the length of the short side is shorter than the shoulder width of the subject. The measuring device according to claim 6, wherein the short-side length is within a range of 200 mm to 300 mm. The measurement device according to any one of claims 1 to 7, wherein one of the transmitting antenna and the receiving antenna is a first antenna including only one of the antenna elements, and the other antenna is a second antenna having an array structure including a plurality of the antenna elements on the antenna surface. The measurement device according to claim 8, wherein the second antenna has an array structure on the antenna surface that includes a plurality of small loop antenna elements. The measurement device according to claim 9, wherein the ground plane of the second antenna is spaced apart from the antenna plane. The measurement device according to any one of claims 8 to 10, wherein the second antenna has a lattice array structure on the antenna surface in which the antenna elements are arranged in a lattice pattern, and has a plurality of dummy antenna elements arranged on the substrate adjacent to the antenna surface so as to surround the lattice array structure. the transmitting antenna is the first antenna including a patch antenna as the antenna element,
the antenna surface and the ground surface of the transmitting antenna are substantially rectangular;
12. The measurement device according to claim 8, wherein an area of the ground plane of the receiving antenna is larger than an area of the antenna plane of the transmitting antenna. the transmitting antenna is the first antenna including a small loop antenna as the antenna element,
The ground plane of the transmitting antenna is substantially rectangular.
12. The measurement device according to claim 8, wherein an area of the ground plane of the receiving antenna is larger than an area of the antenna plane of the transmitting antenna. The receiving antenna has a substantially square lattice array structure in which a plurality of antenna elements are arranged in a lattice on the antenna surface, and the ground surface is 250 mm square or larger,
The measurement device according to claim 12 or 13, wherein a width in a short side direction of the antenna element of the transmitting antenna is smaller than a width of the lattice array structure. the transmitting antenna is the second antenna having the array structure including a plurality of small loop antennas as the antenna elements on the antenna surface,
the receiving antenna is the first antenna including a patch antenna as the antenna element,
12. The measurement device according to claim 8, wherein an area of the ground plane of the receiving antenna is larger than an area of the antenna plane of the transmitting antenna. The measurement device according to any one of claims 1 to 15, wherein the antenna set has the transmitting antenna as a chest-side antenna and the receiving antenna as a back-side antenna. 1. An antenna set for a measurement device for non-invasively measuring the amount of blood pumped by a subject's heart, comprising:
the antenna set includes a transmitting antenna installed on one of the chest side and the back side of the subject so as to face the heart, and a receiving antenna installed on the other of the chest side and the back side of the subject so as to face the heart, and for receiving a transmitted wave which is an electromagnetic wave radiated from the transmitting antenna and transmitted through the living body of the subject;
Each of the transmitting antenna and the receiving antenna has a substrate on which an antenna surface including an antenna element is disposed, and a ground surface on the substrate opposite the antenna surface;
An antenna set, wherein an area of the ground plane of the receiving antenna is greater than an area of the ground plane of the transmitting antenna.