A WIRELESS EMBEDDED DEVICE FOR PERSONALIZED

ULTRAVIOLET MONITORING

Navid Amini, Jerrid E. Matthews, Foad Dabiri, Alireza Vahdatpour

Hyduke Noshadi and Majid Sarrafzadeh

Computer Science Department, University of California, Los Angeles, CA 90095, U.S.A.

Keywords: Wireless, Embedded Systems, Ultraviolet, Erythema, Skin Cancer.

Abstract: The skin care product market is growing due to the threat of ultraviolet (UV) radiation caused by the

destruction of the ozone layer, increasing demand for tanning, and the tendency to wear less clothing.

Accordingly, there is a potential demand for a personalized UV monitoring device, which can play a

fundamental role in skin cancer prevention by providing measurements of UV radiation intensities and

corresponding recommendations. This paper highlights the development and initial validation of a wireless

and portable embedded device for personalized UV monitoring which is based on a novel software

architecture, a high-end UV sensor, and conventional PDA (or a cell phone). In terms of short-term

applications, by calculating the UV index, it informs the users about their maximum recommended sun

exposure time by taking their skin type and sun protection factor (SPF) of the applied sunscreen into

consideration. As for long-term applications, given that the damage caused by UV light is accumulated over

days, it displays the amount of UV received over a certain course of time, from a single day to a month.

1 INTRODUCTION

The skin is the largest organ of the body in both

mass and surface area and skin cancer is the most

common cancer among all existing cancers.

Unfortunately, the incidence of skin cancer has been

increasing dramatically (Ferguson 2005, Sue 2002)

and more than 1 million cases of skin cancer are

reported annually in the United States. There are

three different forms of skin cancer: Basal cell

carcinoma, squamous cell carcinoma and melanoma.

Basal cell carcinoma is cured by a local operation,

but squamous cell carcinoma and melanoma are

more dangerous, as they metastasise to other parts of

body. Melanoma is considered as the most lethal

form of skin cancer and its incidence and mortality

rates have increased dramatically in the past few

decades in the United States (Boscoe 2006). In the

year 2008, about 62,480 persons are expected to be

diagnosed with melanoma resulting in the death of

an estimated 8,420 individuals (ACS 2008).

Alarmingly, the incidence of melanoma is increasing

rapidly in children (Strouse 2005).

Overexposure to solar radiation, especially the

ultraviolet (UV) region (wavelengths 280–400 nm)

of the solar spectrum, is the predominant risk factor

for the development of all forms of skin cancer (Hu

2004, Jemal 2000).

While some sunlight is needed to synthesize

vitamin D, which is necessary for human health,

increased exposure to UV radiation is harmful; it is

well known that apart from the skin damage, the

solar UV radiation is extremely injurious regarding

the eyes (DeFabo 1983). During a field study

involving 94 volunteer subjects, the UV exposure of

seven anatomical sites during six different outdoor

activities was investigated (Herlihy 1994). The

results of this study verify the importance of UV

monitoring during outdoor activities to avoid skin

and eye damage.

Currently there is an internationally accepted

parameter, UV index, for measuring the intensity of

UV radiation (Wong 1995). A ground-based

instrument that measures the amount of UV light

from the sun at 5 different wavelengths between 306

and 320 nm is Brewer Spectrophotometer (RMI

2008) which is very widely-used to calculate UV

index. However, the price is too expensive and for

the correct operation an expert technician is

required. Another method used is the solar light 501

biometer which is a wide-band UV radiation

measurement device (Solar 2008). Although it is

220

Amini N., E. Matthews J., Dabiri F., Vahdatpour A., Noshadi H. and Sarrafzadeh M. (2009).

A WIRELESS EMBEDDED DEVICE FOR PERSONALIZED ULTRAVIOLET MONITORING.

In Proceedings of the International Conference on Biomedical Electronics and Devices, pages 220-225

DOI: 10.5220/0001541402200225

 SciTePress

easy to use, its high energy consumption and heavy

weight prevent it from being exploited in wireless

and small embedded devices.

The use of lightweight embedded systems to

assist in biomedical applications is being pursued by

many researchers and will become available as soon

as required sensors are made available. Hence, given

that the damage caused by UV light is accumulated

over days, there is a potential need for an embedded

device that monitors the amount of UV received

over a certain course of time, from a single day to a

month and gives corresponding advice. In recent

years, the concern over personal exposure to solar

UV has led to the development of numerous

personal (e.g., lapel or wristband) or hand-held

devices. These come with a variety of features, but

in general require input on skin type and degree of

protection and subsequently provide an audible

warning when sun exposure should cease. The

aforementioned devices solely show the current UV

index and they are not able to make accurate

measurements (OS 2008, EPP 2008). Further, none

of them has taken the received amount of UV during

for instance, one week, into consideration.

This work highlights the development and initial

validation of a wireless and portable embedded

device for personalized UV monitoring which is

based on a novel software architecture, written in

Python and is compatible with all Symbian OS cell

phones, a high-end UV sensor, ML8511 introduced

in 2008 by OKI Semiconductor (OKI 2008), and

conventional PDA (or a cell phone). The main

market for this wireless embedded device includes:

1- Children, since reducing UV exposures in early

life is fundamental to skin cancer prevention in

children. 2- Sun protection of outdoor workers in

occupational situations. 3- Sun protection of the

general population in recreational situations. 4-

Beach users and 5- Protection of photosensitive

patients.

This paper will start with preliminary notions

concerning the UV monitoring embedded device in

Section 2. Afterwards, the hardware and software

structure of this device will be presentred in Section

3. An example of the gathered data in a typical day

will be demonstrated in Section 4. Finally, Section 5

concludes this paper and discusses future research

directions.

2 PRELIMINARIES

This section presents the definition of related

concepts used in the design of the personalized UV

monitoring device.

2.1 UV Index

The Global Solar UV index (UVI) (Maddodi 2008,

HKO 2008) describes the level of solar UV radiation

at the Earth’s surface. Generally, providing the

public with an easy-to-understand daily forecast of

UV intensity is the main purpose of the UV index.

The values of the index range from zero upward –

the higher the index value, the greater the potential

for damage to the skin and eye, and the less time it

takes for harm to occur. An index of 0 corresponds

to zero UV irradiation (darkness). The UV index is

an open-ended linear scale defined as follows:

400

250

∫

λλ=

erer

d)(s.E.kUVI

(1)

where E

is the solar spectral irradiance (see the

previous section) expressed in W/(m

) at

wavelength λ and dλ is the wavelength interval used

in the summation. s

(λ) is the erythema reference

action spectrum, and k

is a constant equal to 40

/W.

The determination of the UVI can be through

measurements or model calculations. Two

measurement approaches can be taken: The first is to

use a spectroradiometer and to calculate the UVI

using the above formula. The second is to use a

broadband detector that has been calibrated and

programmed to give the UVI directly.

Although the weather stations assign a unique

UVI to a large area, for several reasons, the

measured noon UV index can be different from the

forecast, sometimes by as much as 100%; the

forecasted UV index does not include the effects of

atmospheric pollutants or haze which can

substantially decrease UV intensity, especially in

urban areas. On the other hand, the forecast does not

take into account variable surface reflection (e.g.,

sand, water, or snow), which can substantially

increase individual’s exposure at the beach or on

ski-slopes. The following facts demonstrate how the

environment or terrain affects the level of UV

radiation that we are exposed to (UNEP 2008):

1- Wet fresh snow can reflect as much as 85% of

UV radiation this means that snow reflection can

double overall UV exposure. Similarly, white

A WIRELESS EMBEDDED DEVICE FOR PERSONALIZED ULTRAVIOLET MONITORING

221

water and sand can intensify the UVI by up to

50% and 20% respectively.

2- Every 100 meters increase in altitude results

in the UVI increase of 100%. This is because at

higher altitudes a thinner atmosphere absorbs

less UV radiation.

3- 25% of the UV is reflected from white-water

reflection.

4- 80% of UV rays pass through a cloud.

Therefore, even with cloud cover, the UVI can

be adequately high.

5- Concrete buildings reflect 15% of the received

UV.

6- Shade can reduce UV by 50% or more.

The foregoing facts show that quantitative

measurements and research on UV radiation in

different environments and settings are vital in

developing and assessing UV-preventative strategies

for the reduction of skin cancer and other UV-

related problems for humans.

The UV index measurements and forecasts for

cities in many countries around the world are now

routinely posted on the internet by various

meteorological agencies (see Table 1 for UV index

categories). In summer in Europe, the solar UV

index typically peaks at values from 5 at high

latitudes (Scandinavia) to around 7 in central regions

such as the United Kingdom, France or central

Europe and up to 9 or 10 in Southern Europe. In the

United States maximum measured UV indices range

from 10 to 12 in the Southern continental United

States to 5 in Alaska while in Canada peak values

reach 8 in the southern cities. Generally, the highest

reported UV index measurements in the Northern

hemisphere have been recorded at high altitude. For

example, Bogota in Colombia, at over 2500m above

sea level, has registered a UV index of 16 and for

Mauna Loa volcano in Hawaii, at 3400m above sea

level, a UV index of 17 has been reported (Parisi

2000).

Table 1: UV index intensity.

UV index Extent

0-2 Low

3-5 Moderate

6-7 High

8-10 Very high

11+ Extreme

2.2 Sensor Characteristics

The spectral sensitivity characteristics of photo

diode used in ML8511, which are based on thin-film

Silicon-on-Insulator Technology (SOI), are shown in

Figure 1. Although this is a silicon photo diode, it is

highly sensitive and at the same time is selective

only to the UV-A (wavelengths of 320 to 400 nm)

and UV-B (wavelengths of 280 to 320 nm); this is

because of its SOI structure.

0.25

0.5

0.75

1.25

280 320 360 400 440 480 520 560 600

Wavelength (nm)

Sensitivity (Relative Value)

Figure 1: Spectral sensitivity characterisitics of the

ML8511.

3 THE UV MONITOR DEVICE

In this section the hardware and software structure

of the personalized UV monitoring device is

explained.

3.1 System Design

Figure 2 shows the schematic diagram of our

personalized UV monitoring system. The UV sensor

shown in the figure is a photo diode that uses a thin-

film SOI. With an additional filter, the accordance

with the erythema action spectrum curve of the

human skin has been further improved. A voltage

proportional to the amount of electrical current is

output by a current-to-voltage conversion amplifier,

comprised of an operational amplifier and resistor,

Rf. The output voltage can be linked directly to the

analog-to-digital converter (ADC), where it is

converted into a digital signal and input into the

processor of Atmel ATmega 128L microcontroller

via an interface (I/O). The resulting digital signal is

processed by the microcontroller to determine the

current UV index (see Table 2 and (2)) and

thereafter it sends the UV index data to the RN-24

Bluetooth adapter. The Bluetooth adapter sends its

received data without any changes to the Nokia N95

cell phone where the main software of our

embedded device is running. The software was

written in Python and is compatible with all

Symbian OS cell phones. As mentioned before, the

software has two parts. First, it shows the current

BIODEVICES 2009 - International Conference on Biomedical Electronics and Devices

222

Figure 2: Schematic diagram of the personalized UV monitoring system.

UV index (from 0 to 20) and maximum exposure

time based on the skin type of the user, SPF of the

applied sunscreen and current UV index. Second, it

shows the UV history of the person together with the

amount of UV (UV dose) that the person received

during the past day/week/month. The software also

saves the average of UV indices during one hour of

operation.

The calculation of the UV index is performed

using equation (2); in the darkness, the sensor output

and corresponding output of the ADC are equal to

0.993 V and 320 respectively. Therefore, in order to

derive the UV index, it is required to subtract 320

from the current ADC output and scale it as shown

in (2). In this equation, the ceiling function and the

multiplication by 0.2 show that our accuracy in UV

index calculation is not better than 0.2.

The software takes the skin type of the user and

the SPF number (from 0 to 100) of the applied

sunscreen (0 in case of no sunscreen), respectively

as the input.

ADC

UVI

OUTPUT

20)

320

( ×

⎥

⎦

⎥

⎢

⎣

⎢

−

(2)

The information in the Table 3 were used in the

software to calculate how long one can stay in the

sun without sunscreen before he/she starts to burn

(i.e., before minimum erythemal dose, occurs).

Table 3 also shows the tolerable MEDs with respect

to solar light for each of four possible skin types.

The flowchart of the software is shown on Figure

3. In addition to the UV history, both the current UV

index and maximum exposure time are shown on the

cell phone screen.

Table 2: UV indices corresponding to sensor and ADC

outputs (Vcc = 3.0 V).

Sensor output voltage ADC output UV index

0.993 320-345 0

1.073 345-370 1

1.153 370-395 2

1.233 395-420 3

1.313 420-445 4

1.393 445-470 5

1.473 470-495 6

1.553 495-520 7

1.633 520-545 8

1.713 545-570 9

1.793 570-595 10

1.873 595-620 11

1.953 620-645 12

2.033 645-670 13

2.113 670-695 14

2.193 695-720 15

2.273 720-745 16

2.353 745-770 17

2.433 770-795 18

2.513 795-820 19

2.593 820-845 20

3.2 Exposure Time

At present, the majority of countries, on the basis of

the recommendations of the COST-713 (Vanicek

2000), have adopted four skin types as a function of

tanning capacity.

A WIRELESS EMBEDDED DEVICE FOR PERSONALIZED ULTRAVIOLET MONITORING

223

Figure 3: Software operation (it receives the new UV

index each 15 seconds and stores to average for each

hour).

The principal characteristics of these skin types,

defined by the DIN 5050 standard, were shown in

Table 3, which also indicates the dose (in J/m2)

needed to produce one MED.

According to Table 3, a person with a skin type

of 3, in a UV index of 10, will start to sunburn after

just 20 minute of unprotected exposure to the sun:

[200 (min) / 10 (UVI) = 20 min], (3)

and by using an SPF 30 sunscreen this becomes 600

minutes, or 10 hours:

[20 (min) × 30 (SPF) = 600 min].

(4)

4 EXPERIMENTAL RESULTS

In this section we see an example of the gathered

data in a typical day. Figure 4 and Table 4 show an

example of our personal cell phone software. The

data were gathered on a partially cloudy day in June

in Los Angeles and we kept the device fixed on the

roof of an eight-story building. Therefore, it can

represent the amount of UV that an individual has

absorbed in a typical day.

Table 3: Skin types and corresponding tolerated MEDs

and maximum exposure time.

Skin

type

Color, burning

and tanning in

the sun

Tolerable

MEDs

Maximum

exposure

time

White, always

burns, never tans

2 hecto

J/m

67 min /

UVI

Yellow and white,

usually burns,

sometimes tans

4 hecto

J/m

100 min /

UVI

Yellow and black,

sometimes burns,

usually tans

5.75 hecto

J/m

200 min /

UVI

Black, rarely

burns, always tans

8.5 hecto

J/m

300 min /

UVI

In Table 4, as it can be seen, the first row values are

the UV indices at the exact hours of 8:00, 9:00, etc.

However, the second row shows the average amount

of UV index during each hour.

Moreover, for each day we calculate the

parameter UV dose that is:

UV Dose = Average UV × Exposure time. (5)

While the UV index is a measure of UV

intensity, it is the accumulative dose that is

important for human exposures to solar UV.

5 CONCLUSIONS

In this paper we adopt OKI ML8511 UV sensor to

implement a real-time and personalized UV

monitoring.

The personalized UV monitoring device

explained in this paper can be put on the hat, can be

a necklace, skin patch and even a clip-on. Therefore,

it is not obtrusive and can decrease the incidence of

the skin cancer in an efficient way. Since the system

is small and accurate, it proved to be a very feasible

commercial product.

This device will enable users to embed UV

sensor functions in a variety of portable devices,

offering them the ability to check their UV exposure

wherever they are.

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224

0.0

2.0

4.0

6.0

8.0

10.0

12.0

5:45

7:15

8:00

8:45

9:30

0:1

11:0

1:4

12:3

3:1

14:0

4:4

15:30

6:1

17:4

19:1

0:0

20:4

Time

UV Index

Figure 4: Example of personal UV monitor software (UV index was updated each 15 seconds throughout a partially cloudy

day).

Table 4: Example of personal UV monitor software (average data).

Time 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00

UV index

(ending on the hour)

1.2 2.2 4 5.4 6.2 9 5.6 5.8 4.6 2.4 1.2 0.0

Hourly mean UV

index

1.6 3.1 4.2 5.4 7.8 7.4 6.1 5.5 3.9 2.2 0.8 0.0

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