計測自動制御学会東北支部40周年記念学術講演会
2004 年12 月22 日，23 日 日本大学工学部

講演番号：A09

超小型血流センサーを用いた血流の変化の測定
森田巧

坂野進1

Integrated Blood Flowmeter Using Micromachining TechnologyTakumi Morita, Susumu Sakano
1College of Engineering, Nihon University

1 Nakagawara-Tokusada , Tamura-cho, Koriyama , 963-8642 , Japan
Tel: +81 24 956 8774,Fax: +81 24 956 8860, E-mail: sakano@mech.ce.nihon-u.ac.jp

Abstract- The micro machining technology has been advanced on the basis of the semiconductor
manufacturing technology. In this study, the research on the manufacturing the integrated micro opticalsensor accumulated LD and PD on the semiconductor substrate is practiced. The fabrication method is thetechnology of photolithography and etching technology in the semiconductor manufacturing. The bloodflow meter is taken up as a typical application of the micro optical sensor.

1. Introduction

which a packaged semiconductor laser ismounted together with the detectors in a small
probe.In-vivo experiments concerning blood
perfusion in a finger capillary confirm thefeasibility of the blood flow meter.

Wearable devices that gather physiologicalinformation are highly demanded for bedsidemonitoring in hospitals, telenursing for elderly
people living alone at home, and long-term
health assessments to predict and prevent adultdiseases, and several wearable devices infinger-ring or wristwatch configurations havebeen developed. However, the incorporated
sensors are restricted to either pulse-wave types
or pulse oximeters containing light-emitting
diodes [1].
In these applications, it is mostimportant that the sensors are small and light so thatthey can be worn comfortably.
This paper discusses a new design for a verysmall lightweight blood flowmeter that permitsreal-time monitoring of capillary microcirculation fora wearable health monitoring system. The
hybrid-integrated
structureincludesan
InGaAsP/InP distributed feedback laser diode(DFB LD) with a wavelength of 1310 nm, anedge-illuminatedphotodiode(PD)andpolyimide waveguides on silicon substrate (2 ×3 mm 2 ). This flowmeter is much smaller
than a previously reported compact one in

2. Structure of Sensor
2.1 Conventional blood measurement Bloodflow measurements have been of special interest for
many years because they offer a promising tool forthe noninvasive examination of the physiological stateof the microcirculation. Impaired blood circulation
is a factor deeply involved in the etiologies of many
adult diseases. The first application of laser Doppler
velocimetry to blood flow was reported by Riva et al[2]. In 1975, Stern demonstrated that scattered lightfrom laser-illuminated skin is Doppler broadened andthat the Doppler width correlates with blood flow [3].
There are a number of ways to implement blood
flowmetry and some of those have been put into
clinical use. The most common technique involves
the use of optical fibers to conduct the He-Ne laser
light or laser diode (LD) light to the skin tissue andfrom the tissue to a photodetector [4-5]. However, theinstrument requires positioning and alignmentof individual optical components (such as lens77

and fiber) in three dimensions. As a result,
the whole instrument becomes bulky withdimensions of several ten centimeters, although
the probes are small. Such a large instrument
is not suitable as wearable devices.
Furthermore, movement of the fiber affects the output
signal [6].

LD2.2 Structure LD (Laser Diode), PD (PhotoDiode) and wave guide are constructed on thesilicon substrate. In general, LD, PD are formed
directly on the silicon substrate. Though themass production of the micro optical sensor ispossible, there are problems in the dispersion of
the reliability and functional properties of themanufactured sensors as mentioned above. TheLD and PD for the optical communication areused in this study. They have long life and highreliability, and small fluctuation of theproperties. LD and PD are bonded on thesilicon substrate and the polyimide lightwaveguide for the light scatters is formed using
photolithography technology. The effect of theexternal light from the outside must be avoided
in the optical sensor.

PDFig. 1. Fabrication of optical sensor
The light is scattered by the tissue andbackscattered light is collected on the detector (PD).
A small part of the light is scattered by moving
particles (mostly red blood cells) in the capillaries of asample volume of tissue and is Doppler shifted. This
Doppler-shifted light and the non-Doppler-shifted
light scattered by nonmoving structures of the tissue
interfere at the detector, which causes intensity
modulations. The Doppler frequency spectrum to bemeasured at the detector, in the case of a single
velocity value, peaks at the frequency corresponding
with the velocity. In the case of scattering fromtissue, it will have an approximately exponential
decay in the spectral domain because of the randomcharacter of the velocity vector of the blood perfusionin the capillaries (Red blood cells move in different
directions and at different velocities) and because ofmultiple scattering in the tissue. It has been shownthat in such cases the first moment ω of the3. Fabrication Method
The micro optical sensor is manufactured byforming the patterns on the silicon substrateand LD, PD are bonded on the silicon platform.
It is shown in Figure. 1. The passive alignment
technique using alignment mask is used foraccurately bonding LD and PD onto silicon
2platform ( 3 × 2mm ). LD is a DFB LD with awavelength of 1310 nm and PD is anedge-illuminated refracting-facet PD with asmall active area. LD has the lifetime of morethan several hundred thousand hours andreasonable wavelength stability with thetemperature. The polyimide waveguide isformed on the silicon platform. The convex
shaped edge is formed in the polyimide
waveguide for collimating the laser beam fromLD horizontally.

power spectrum S (ω ) of the frequency distributionof all possible Doppler frequencies, given byω = ∫ ω ⋅ S (ω ) ⋅ dω ,4. Measurement Principle(1)

is proportional to the averaged velocity times theconcentration of Doppler scattering particles, i.e., tothe flow of particles. We used a digital signal
processor unit (Online Applications SystemsCorporation) to derive the first moment ω (theA schematic diagram of the proposed integrated laser
Doppler blood flowmeter and a cross section of blood
circulation in the skin are shown in Fig. 2. Skin is
illuminated with a coherent light source (DFB LD).

flow of the blood flow) as continuous output

78

signals.

dark current: 0.03-0.28 nA) as a detector. In a
conventional flowmeter, a spatial filter, such asa pinhole or a slit, or an optical fiber isnormally placed in front of the PD to pick up
the time-varying laser speckle, which isproduced by the scattered light from the tissue[12, 13]. On the other hand, in our flowmeter,
by using a PD with light-sensitive area of 15
m ×65 m, we eliminated the need for such
additional components.
The absence of
optical fibers rules out disturbances due tomovement artifacts in the signal.
The silicon cap, which has titanium deposited(thickness: 200 nm) on its inner wall, prevents
light emitted from the backside facet of the LD
and scatteredfrom the edge of the waveguide.

silicon substrate
DFB LDPDwaveguidestratum corneum
epidermisff +∆fskincapillaries
dermisFig.2.

Blood flowmeter and cross sectionin the skin

6. Blood Perfusion Measurement
5. Integrated Blood Flowmeter

We performed some measurements of blood
perfusion from the fingertip of some volunteers.
The fabricated device was attached directly tothe fingertip with minimum pressure.

We designed the small sensor structure
integrated with the LD and PD without fibers.
Figure 3 is a schematic diagram of the proposed
blood flowmeter. The device consists of onlya LD, PD, fluorinated polyimide wave guide,and silicon cap on the same silicon platform (2× 3 mm2), which functions as an optical bench
and a heat sink. An InGaAsP/InP DFB LD with awavelength of 1310 nm, a power of 5 mW, and athreshold current value of Ith = 10 mA ware used as alight source. In the conventional instruments,visible light (600-800 nm) is mainly used.
However, we chose near-infrared laser(wavelength of 1310 nm) because of the very
high transmittance at 1310 nm , although there
is some small absorption of water. This highpenetration is due to the low absorption andscattering coefficients of the tissue at thiswavelength. In the wavelength region of350-1200 nm, melanin is the major absorber ofradiation in the epidermis, especially at shorterwavelength.
We can expect that anear-infrared laser may make measurements indeeper lying blood vessels, where blood flow ishigher. Our InGaAsP/InP DFB LD has alifetime of more than several hundred thousandhours. Forming a convex-shaped edge in thewaveguide eliminated the need for a lens.
This collimates the laser beam horizontally.
The full-width at half-maximum (FWHM) ofthe horizontal far-field pattern (FFP) wassmaller than 1°. We used an edge-illuminatedrefracting-facet PD (responsively: 0.91 A/W,

Sensor chip +Preliminary amplifierelectric circuit including
display, wireless circuitand battery

Sensorchip

Si capPD
DFB LD

polyimide waveguideSi substrate

1 mm

Fig.3.

Proposed laser blood flowmeter

In order to test the dynamic response of
microcirculation, the upper arm was occluded
with a pressurized cuff. Fig. 4 shows a typicalflow signal [Eq. (1)] as a function of time (laserpower: 3.5 mW). It is clearly seen that uponocclusion with the pressurized cuff inflated to200 mmHg there is a rapid drop in the flow
signal, indicating poor circulation. The flow
signal shows small variations with the heartbeat.
The heartbeat frequency is easily distinguishedin the signals, except for the sections with79

occlusion. This signal is in agreement withthat is obtained by a commercially available
laser Doppler flowmeter (Cyber Med
CDF-1000, Online Applications SystemsCorporation). A typical example is shown inFig. 5. We see that the signal spectrum obtainedchanges much depending on smoking. We canalso see abrupt occurrence of a low-frequency
signal. With this portable micro sensor, we canobtain such data immediately by carrying this.

can be easily handled in clinical situations and has
great potential for a wearable health monitoring
system.
Further developments, especially
miniaturization of the electronic circuit, are inprogress.
References[1 ] S. Rhee, B. H. Yang, K. Chang, andH. H . Asad a: Pro c. 20 t h Annual
In tern ational Conf er ence of th e
I EE E Eng ine er ing in Med ic in e andBio log y Society, Hong Kong, Oct.
29-Nov . 1, pp. 1906-1909,1998 .
[2 ] C. Riva, B. Ross, and G. B. Benedek, Invest.
Opthalmol., vol. 11, pp. 936-944, 1972.
[3 ] M. D. Stern, Nature (London), vol. 254, pp.
56-58, 1975.
[4 ] D. Watkins and G. A. Holloway, Jr., IEEE
Transactions on Biomedical Engineering, vol.
BME-25, no. 1, pp. 28-33, 1978.
[5 ] R. W. Wunderlich, R. L. Folger, D. B.
Giddon, and B. R. Ware, Rev. Sci. Instrum.,vol. 51, no. 9, pp. 1258-1262, 1980.
[6 ] F. F. M. de Mul, J. van Spijker, D. van derPlas, J. Greve, J. G. Aarnoudse, and T. M.
Smits, Appl. Opt., vol. 23, no. 17, pp.
2970-2973, 1984.

Fig. 4. Flow signal of fingertip

Fig. 5. Variation of frequency spectrum

7. Conclusions
We have constructed an integrated laser blood
flowmeter by micro machining and surface
mounting techniques. The device is 1.5 mm
thick × 2 mm wide × 3 mm long. Using
this flowmeter, we performed in-vivo
measurement of blood perfusion in the fingertip.
Because of its small size together with its highperformance, this integrated blood flowmeter80