Wireless Temperature and Illuminance Sensor Nodes
With Energy Harvesting from Insulating Cover ofPower Cords for Building Energy Management System
Masanobu Honda, Takayasu Sakurai, and Makoto Takamiya
University of Tokyo
Tokyo, JapanAbstract—A new energy harvesting with low installation cost is
proposed to enable stable power supply to battery-less wirelesssensor nodes for energy management systems. Two electrodes(copper tapes) are attached on the insulating cover of two-wirepower cords and the leakage electric-field energy is harvested by
the capacitive coupling between the electrodes and the corewires. The proposed energy harvesting does not require anadditional ground connection and the current in the powercords. 3-4V, 1.4W is harvested with 20-cm electrodes from 100V AC power supply. Temperature and illuminance sensor nodes
with the proposed energy harvesting and ZigBee modules for thebuilding energy management system are demonstrated. Both thetemperature and illuminance are measured and transmitted to awireless receiver within a 100-m radius every 250s.
Index Terms--Energy harvesting, energy management system,
wireless sensor node, temperature, illuminanceI.

INTRODUCTION

In the building energy management system (BEMS),
sensor nodes are required to monitor the indoor environment(e.g. temperature, humidity, and illuminance) and themeasured data are used to control the air conditioning and thelighting of the building for reducing the energy consumption.
The requirements of the sensor nodes for BEMS are: (1) lowcost installation, (2) low operational cost, and (3) stable andcontinuous monitoring. The conventional sensor nodes withwires for power supply and communication increase theinstallation cost. The conventional wireless sensor nodes withbatteries require regular battery replacement, which increases
the operational cost. The energy harvesting (e.g. solar cell,thermoelectric generator, and vibration energy harvester) is apromising approach to eliminate the need for batteryreplacement. The energy harvesting, however, does notguarantee the continuous monitoring, because the energy
source is not always available. To solve the problems, thispaper focuses on an energy harvesting from the insulating
cover of power cords.

This work was partly supported by JSPS KAKENHI Grant Number
26630149.

In the conventional energy harvesting from leakage
magnetic-field energy from the insulating cover of powercords [1]-[4], the current in the power cords is required, which
does not guarantee the continuous monitoring, because themagnetic-field is not available when the current is zero. In theconventional energy harvesting from leakage electric-fieldenergy from the insulating cover of power cords [5], a
dedicated ground connection (i.e. attaching a metal plate on aconcrete wall with conductive adhesives after peeling off thepaint on the wall) is required, which increases the installation
cost. To solve the problems, a new energy harvesting from theinsulating cover of power cords (EHICPC), which does not
require the current in the power cords and the dedicatedground connection, is proposed in this paper. The proposed
EHICPC enables the low-cost installation, the low-cost
operation, and the stable and continuous monitoring.
In Section II, the operation principle and measured resultsof the proposed EHICPC are shown. In Section III, thedemonstration of temperature and illuminance sensor nodes
with EHICPC and ZigBee modules for BEMS is shown. InSection IV, EHICPC is compared with the previously
published energy harvestings from the insulating cover ofpower cords. Section V draws the conclusions of this paper.
II.

PROPOSED ENERGY HARVESTING FROM INSULATING
COVER OF POWER CORDS (EHICPC)

A. Operation Principle
Fig. 1 shows an operation principle of the proposed
EHICPC. Two electrodes (copper tapes) with the length of L
are attached on the insulating covers of two-wire power cords,
respectively. The electrodes are capacitively coupled to thecore wires, and the leakage electric-field energy from the corewires is harvested. The two electrodes are connected to a fullwave rectifier and AC input is converted to DC output. Fig. 2
shows a photo of the two-wire power cords with the twoelectrodes for EHICPC.

L

COUT

VOUT

100μF

Powercord

Thick (VCTFK)Electrode for energy harvesting
Insulating
coverCore wireThin (VFF)

Fig. 3. Photo of thin (VFF) and thick (VCTFK) power cords.

Fig. 1. Operation principle of proposed energy harvesting from the insulating
cover of power cords (EHICPC).

10Thin cord
L=20cmVOUT [V]864Measured

2Simulated

00102030
Time [min]40

Fig. 4. Measured and simulated waveforms of VOUT of thin power cordwith L = 20cm.
Fig. 2. Photo of the two-wire power cords with the two electrodes for EHICPC.

Table I Parameters in EHICPCThickness of cord
ThinThickCore wire 1

AC
100V
C1
30pF

10cm
Length20cm
ofelectrodes
30cm
(L)
40cm

◯◯◯◯

Electrode 1

C2

C48pF

40pF

C3C540pF

8pF

COUT
100μF

VOUTElectrode 2

Core wire 2◯
Electrode 1

B. Measured Results
To systematically quantify the harvested power, EHICPCwith different L and two types of power cords are measured.
Table I summarize the parameters in EHICPC. Fig. 3 shows aphoto of the thin (VFF) and thick (VCTFK) power cords.
Fig. 4 shows a measured waveform of the output voltage(VOUT) of thin power cord with L = 20cm. To understand theoperation principle of EHICPC, an equivalent circuit ofEHICPC is made and compared with the measured result. Fig.
5 shows the equivalent circuit of EHICPC of thin power cordwith L = 20cm. C1 is the capacitance between two wires. C3and C4 are the capacitance between the electrode and thenearby wire. C2 and C5 are the capacitance between theelectrode and the distant wire. Fig. 4 also shows a simulated

C340pFCore
wire 1

C2

C1

C58pF

30pF

8pF

Core
wire 240pF

C4Electrode 2Fig. 5. Equivalent circuit of EHICPC of thin power cord with L = 20cm.

waveform of VOUT with the equivalent circuit in Fig. 5. The
simulated waveform shows very good match with themeasured waveform, which shows the validity of theequivalent circuit in Fig. 5.
Fig. 6 shows measured waveforms of VOUT of thin andthick power cord with L = 20cm. VOUT of the thick power cord
is lower than that of the thin power cord, because C3 and C4 ofthe thick power cord are smaller than those of the thin powercord. Fig. 7 shows measured waveforms of VOUT of thin power
108
VOUT [V]I HARVEST 

COUTVOUTt(1)where COUT is the output capacitance in Fig. 1 and t is the time.
Fig. 8 shows measured L dependence of IHARVEST in the thinpower cord. IHARVEST is proportional to L. For example,IHARVEST is 400nA at L = 20cm, and IHARVEST / L is 20nA/cm.
III.

L=20cmWIRELESS TEMPERATURE AND ILLUMINANCE SENSORNODES WITH EHICPCIn this section, battery-less temperature and illuminancesensor nodes with the proposed EHICPC and ZigBee modulefor BEMS is demonstrated.

64200204060
Time [min]80Fig. 6. Measured waveforms of VOUT of thin and thick power cord with L= 20cm.

108VOUT [V]cord with L = 10cm, 20cm, 30cm, and 40cm. VOUT increases
with increasing L. The harvested current (IHARVEST) iscalculated by642Thin cordFigs. 9 (a) and (b) show a block diagram and a photo of thewireless and battery-less temperature and illuminance sensor
nodes with the proposed EHICPC, respectively. AC input
voltage is rectified to DC output voltage (VOUT) using four
diodes (1N914) and a 100-F electrolytic capacitor. An FET(2SK4150) to isolate VOUT and the power supply voltage (VDD)
is very important in the energy harvesting. Without the FET,
COUT is not charged, because IHARVEST (400nA) is muchsmaller than the peak supply current of RF module (17mA). Avoltage detector (AP4400A) is a key component to control theFET. Fig. 10 shows a measured waveform of VOUT of thesensor nodes with the proposed EHICPC of a thin power cordwith L = 20cm. The voltage detector has hysteresis between
3V and 4V. At start-up, when VOUT is increased from 0V to 4V,
the voltage detector turns off the FET to isolate VOUT from VDD.
When VOUT is 4V, the voltage detector turns on the FET, VOUT
is connected to VDD, and COUT charges VDD. Then, thetemperature sensor (MCP9700) and the illuminance sensor(TEMT6000) start the sensing operation, and the 2.4GHz

0VOUT

0

20

4060
Time [min]80

100
COUTFig. 7. Measured waveforms of VOUT of thin power cord with L = 10cm,20cm, 30cm, and 40cm.

100μF

Voltage
Detector

FETVDD
TemperatureSensor
IlluminanceSensor

RFModule

Harvested current(IHARVEST) [nA](a)1000

Thin cord
800

600
400

43mm200001020L [cm]30Fig. 8. Measured L dependence of IHARVEST in thin power cord.

4067mm(b)Fig. 9. (a) block diagram and (b) photo of wireless and battery-lesstemperature and illuminance sensor node with proposed EHICPC.

V.

5EHICPC with low installation cost is proposed to enablestable power supply to battery-less wireless temperature andilluminance sensor nodes for BEMS. IHARVEST is 400nA andPHARVEST is 1.4W at L = 20cm, which enables the wirelesssensor node operation every 250s and the range of radiocommunication is within 100m. Not just BEMS, EHICPCcould be applied to wide range of applications where thepower codes are available (e.g. structural health monitoringand traffic management).

VOUT [V]43250s2Thin cord
L=20cm

1CONCLUSIONS

0510
1520Time [min]253025Fig. 10. Measured waveform of VOUT of sensor nodes with EHICPC of thinpower cord with L = 20cm.

ZigBee module (TWE-001L-DPC-WA) transmits themeasured data. During the wireless transmission, VDD rapidly
decreases, because IHARVEST (400nA) is much smaller than thepeak supply current of RF module (17mA). When VOUT isreduced to 3V, the voltage detector turns off the FET. Then,
VOUT is charged to 4V again. Therefore, the sensing operationand the wireless transmission are done every 250s. The
harvested energy per operation (EHARVEST) and the harvested
power (PHARVEST) are calculated byC
EHARVEST  OUT VOUT(final) 2  VOUT(initial)22

PHARVEST EHARVESTT(2)(3)

where VOUT(final) (= 4V) and VOUT(initial) (= 3V) are final andinitial VOUT per charging, respectively. T (= 250s) is thecharging period. In Fig. 10, EHARVEST is 350J and PHARVEST is1.4W.
Fig. 11 shows a measured power supply current of ZigBee
module at VDD = 3.3V. The first peak shows the activation ofthe module and the second peak shows the wirelesstransmission. Fig. 12 shows a measured breakdown of energy
in the wireless sensor node. The total energy per operation is268J, which is less than EHARVEST of 350J. The RF moduleand FET consume 76% and 23% of total energy.
Figs. 13 (a) and (b) show measured time dependence oftemperature and illuminance in a meeting room for 24 hours,
respectively. By using the developed battery-less wirelesssensor node, both the temperature and the illuminance are
simultaneously measured every 250s.
IV.

COMPARISON WITH PREVIOUS WORKS

The proposed EHICPC is compared with the previously
published energy harvestings from the insulating cover ofpower cords. Table II shows a comparison of the energy
harvestings from the insulating cover of power cord. Unlike
the conventional energy harvesting from the insulating coverof power cords, EHICPC does not require the current in thepower cords and the dedicated ground connection, whichenables the low-cost installation and the stable monitoring.

Supply current [mA]

0VDD=3.3V

20Transmission

15Activation

105001020
Time [ms]30

Fig. 11. Measured power supply current of ZigBee module at VDD = 3.3V.

Component

Energy/Operation[μJ]

RFmodule

204

FET

62

Illuminancesensor2Temperature
sensor0.32

Voltagedetector

0.004

Leakage ofcapacitor

0.002

Total

268

FET
(23%)
RF module(76%)

Fig. 12. Measured breakdown of energy in wireless sensor node.

REFERENCES

Temperature [℃]

28[1]2726[2]252423[3]2212:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AMTime

[4]

(a)

Illuminance [lx]

600

[5]

4002000
12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AMTime(b)Fig. 13. Measured time dependence of (a) temperature and (b) illuminancein meeting room for 24 hours.
Table II Comparison of energy harvestings from insulating cover of power
cords
[1]
PowerSource

[2]

[3]

Magnetic field[5]

This work

Electric fieldPiezoelectricbimorph andpermanent
magnetComponent
for energy
harvesting

Current
Transformer

Operation
w/o current
in power cord

No

NoNo

Yes✓

Yes✓

DedicatedgroundNo✓

No ✓No✓

YesNo ✓Harvested

20-cm
electrodes

Voltage 1.1-1.3V 2.2-4.7V

NA

19.8-21V

3-4V

Current

NANANA

NA

400nA

Power940μW

1890μW@4A AC1120μW@10A AC

8μW

1.4μW

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