ENERGY HARVESTED FROM RESPIRATORY EFFORT

David Cavalheiro

1,2

, Ana Catarina Silva

, Stanimir Valtchev

, J. Pamies Teixeira

and Valentina Vassilenko

1,3

NMT- Tecnologia, Inovação e Consultoria, Lda., Portugal

Electrical Engineering Department, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Lisboa, Portugal

Physics Department, Faculdade de Ciências e Tecnologia - Universidade Nova de Lisboa, Lisboa, Portugal

Mechanical and Industrial Engineering Department, Faculdade de Ciências e Tecnologia

Universidade Nova de Lisboa, Lisboa, Portugal

Keywords: Respiratory effort, Energy harvesting, Piezoelectric power converter.

Abstract: Presently, a high cost of some medical equipment is due not only the sophisticated technology, but also

because the cost of his maintenance. The electronic devices implanted in the human body are examples for

this constant maintenance, requiring sophisticated medical operations. Extra weight and volume addition to

the electronic devices are also a disadvantage, limiting the autonomy of such devices. An alternative to

replace the batteries as power sources is to obtain the energy from the human body. In this work we present

our prototype of Breathing Energy Transducer (BET) for an efficient energy conversion at fixed 2.6V from

chest movements during breathing. A series of experiments were performed in order to calculate the power

that could be generated from the respiratory effort during normal and deep breathings.

1 INTRODUCTION

Currently, the energy supply for the portable and

autonomous equipment comes almost exclusively

from the battery. Unfortunately the maintenance of

those sources of energy brings disadvantages due to

the need for frequent recharging or replacement. In

many cases the battery brings extra weight and

volume to the electronic equipment, limiting its

autonomy. Some possible alternative methods to

replace the batteries as power source, or to achieve

better maintenance of existing (or smaller) batteries,

are the so called Energy Harvesting (EH) methods,

i.e. to obtain energy from the environment. For the

medical equipment, there is also a possibility to

recover and store energy generated by the human

body in its usual activities.

This article we explore a possibility to obtain and

convert an energy from the chest expansion during

the normal and deep breathings. The harvested

energy is either converted to a fixed 2.6V value, by

an extremely efficient converter developed by our

team for this purpose. The low amount of energy

harvested from the chest expansion can be enough

for the proper functioning of certain systems, e.g.

MEMS systems.

2 ENERGY SOURCE

There are several techniques to obtain energy from

the environment, either for storage or for direct

supplying the electronic consumers. The energy

harvesting device generates electrical energy from

the environment applying different conversion

methods. In an early work, S. W. Angrist calls this

conversion a “Direct Energy Conversion” (Angrist,

1971). In the present time the converters are

carefully designed for each different source of

environmental power. They are expected to have

high conversion efficiency, mostly due to the lowest

values of energy collected from the environment.

Kinetic, thermal and electromagnetic energy are

some of the possible examples of energy source.

2.1 Kinetic Energy

This source of energy is one of the most readily

available to be converted from the human body. The

mechanical deformation of a certain structure and

the displacement of a mass are the basic principles

of the kinetic energy conversion. Using the principle

of piezoelectricity is one method to convert

mechanical deformations and movements into

388

Cavalheiro D., Silva A., Valtchev S., Pamies Teixeira J. and Vassilenko V..

ENERGY HARVESTED FROM RESPIRATORY EFFORT.

DOI: 10.5220/0003876703880392

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2012), pages 388-392

ISBN: 978-989-8425-91-1

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

electrical energy.

Grate research has been carried out to collect as

much energy as possible from the human body. A

work done by T. Starner and J. Paradiso presents the

actively and passively dissipated energy during the

simple human activities(Starner and Paradiso, 2004).

One of the most explored energy sources from the

human body were the energy generated through the

force applied by the foot in a piezoelectric insole

during a walk (Kymissis et al., 1998).

Breathing is another possible source of energy.

The mechanical energy of the exhaled air can be

converted to the electricity. For example, using a

special mask with a turbine it possible to generate

the mechanical power of approximately 1W

(Starner, 1996).

From other side, the mechanical chest

movements during breathing can be used as another

way to harvest energy. In this process the

piezoelectric effect can be used to convert the

mechanical strain into electricity. It was estimated

that breathing with a mean frequency of the 10

breaths per minute can develop a mechanical power

of 0.83W (Starner, 1996).

However, the mechanical energy cannot be

converted completely in electricity due to losses in

harvesters and the other mechanisms. As a rule, the

electronic devices must have extremely high

efficiency both in energy conversion (harvestes) and

energy consumption (the control circuits). Larger

losses in the various components are translated into

lower conversion efficiencies. Usually the data

presented in the literature consider that the

mechanical generator have 50% efficiency; the

turbine + generator reach 40% efficiency; the

piezoelectric generator have 11% efficiency and the

double (including mechanical to mechanical and

other) conversion reach 12.5% efficiency (Starner,

1996).

3 POWER EXTRACTED FROM

HUMAN BREATH

In the present work were performed a series of

experiments in order to analyse the power generated

from human respiratory effort. For this purpose we

develop a Breath Energy Transducer (BET) working

as a piezoelectric generator.

The piezoelectric effect characterizes a class of

certain crystalline structures that become electrically

polarized when subjected to pressure. The reverse

effect is also known, i.e. when electric field is

applied to the crystal, its dimensions change

according to the applied electric field (inverse

piezoelectric effect). Initially, quartz was the most

well-known piezoelectric material, but now mostly

ceramic materials based in metal-oxide are used due

to the lower price.

The piezoelectric generator used to harvest

energy from chest expansion, contain one

piezoelectric transducer (Breath Energy Transducer),

producing electric charge when subjected to

compression. The generated voltage in this kind of

transducers may be high, but the value of the

produced current is (unfortunately) low. Some

piezoelectric systems tend to achieve better

performance through applying higher frequencies of

mechanical vibrations.

3.1 Breath Energy Transducer

The Breath Energy Transducer (BET) is a home-

made prototype of piezoelectric generator with

sensor composed by Macro Fibers (MFC) that offers

high performance, durability and flexibility. It

consists of rectangular piezoceramic rods (wires)

sandwiched between layers of epoxy polymer,

electrodes and polyimide film. The piezoelectric

sensor used in this work is the M-1700-P2 (170mm

x 7mm), developed for NASA. It presents a

capacitance of 91nF, free strain of -670ppm and a

blocking force of -42N.

Figure 1: Piezoelectric Breath Energy Transducer.

A BET was attached to a band (Figure 1), which

allow it fixing around the chest of a person.

3.2 Respiratory Effort Transducer

For measuring the amplitude of the chest during the

breathing was used a commercial respiratory effort

transducer SS5LB from BIOPAC

, also fixed

around the chest of a person (Figure 2). It measures

the respiratory effort and transmits the signal from

the chest expansion and contraction. The transducer

was applied to determine the depth of the breathing

and to calculate the breathing rate. By this

measurement it was possible to compare the normal

breathing to the deeper one, and to observe the

ENERGY HARVESTED FROM RESPIRATORY EFFORT

389

power generated by the harvesting piezoelectric

tape.

Figure 2: Respiratory effort transducer SS5LB and its

location.

The respiratory effort transducer was connected

to the BIOPAC

MP35 measuring system with

internal microprocessor to control the data

acquisition and recording software BSL Pro.

This measuring unit was necessary for

comparing the recorded breathings to the power

converted by the piezoelectric Breath Energy

Transducer.

4 EXPERIMENTAL RESULTS

The first step on the experimental procedure was to

find a correlation between the power consumed by

the load resistor, attached to the piezoelectric BET,

and the chest expansion while breathing normally

and deeply. The relation between the SS5LB sensor

signal and the SS5LB extension is shown in

Figure 3.

Considering that the maximum output of the SS5LB

sensor is proportional to the maximum depth of

breathing, a relation between the chest expansion (in

mm) and the output signal is possible to be achieved

for each individual person. This calibration have

allowed to find the relation between the chest

expansion and sensor extension (in mm), useful for

the proper construction of the Breath Energy

Transducer.

Figure 3: Relation between SS5LB output and SS5LB

extension.

The second step was aimed at finding the ideal

load for the piezoelectric Breath Energy Transducer.

Figure 4 shows the continuous power absorbed

during the loads in the range from 1kΩ to 2MΩ.

Figure 4: Power produced by the piezoelectric BET at

different loads.

As it can be seen from the graphic in the Fig. 4, a

maximum of dissipated power is reached with a

resistive value of load around 200kΩ, where will

continuously dissipating 620μW. This load has been

used in the experiments to achieve a relation

between the chest expansions and the extracted

power values from the Breath Energy Transducer.

The third step consists in finding the relation

between the chest expansion, and the power

delivered to the load (200kΩ). For this purpose were

performed a series of experiments: a healthy person

with 1.64m of height and 60kg of weight were asked

to perform six normal breathings and six deep

breathings. A typical resulting signal in an SS5LB

output is given in Figure 5. In this graphic the first

six signals are related to normal breathings followed

by the next six signals related to deep breathings. As

it was expected, the normal breathings give lower

SS5LB output signals (peak to peak) than the deep

breathings.

Figure 5: SS5LB output signal, in V(t).

An oscilloscope was used to measure the AC

voltage delivered to the load. Resulting graphics of

obtained signals for normal and deep breathings are

presented in Figure 6 and Figure 7, respectively.

From the oscilloscope data were also obtained the

RMS voltages, allowing calculates the values for an

active power available at the (resistive) consumer.

This power is given by equation 1, resulting in

BIODEVICES 2012 - International Conference on Biomedical Electronics and Devices

390

19μW and 50μW for normal and deep breathing,

respectively.

=









(1)

Figure 6: Oscilloscope output signal for normal

breathings.

Figure 7: Oscilloscope output signal for deep breathings.

Previously, it was found a relation between the

chest expansion in normal and deep breathings,

resulting in an expansion between 2 cm and 3.18 cm

while breathing normal, and an expansion between

3.54cm and 4.05cm while breathing deeply. With

this relation, it is possible to affirm that for a specific

person, an expansion of the chest with 4cm can

provide an average power of 50μW to any electronic

sensor that presents ideal input impedance, around

200kΩ.

An extremely efficient converter from Linear

Technology was used to convert the AC signals

generated by the generator tape due to the chest

expansions. The converter was configured to outputs

a value of 2.6V, to a capacitor of 47μF. The

experimental results are shown in Figure 8 and

Figure 9. In both figures, the yellow signal

represents the rectified voltage from the

piezoelectric BET, and the blue signal show the

output value of the capacitor.

Figure 8: Output value for charging during normal

breathing.

Figure 9: Output value for charging during deep breathing.

As it can easy observe, the normal breathing

during around 25 seconds will allow charging the

capacitor until 2.5V, while deep breathing will take

less time, around 20 seconds. The obtained results

for the charging time have a clear correlation with

less voltage, and consequently less power, generated

during the normal breathing than during the deep

one.

5 CONCLUSIONS

The experimental study performed in this work

shows that the mechanical movements of the chest

during the breathing can be used as an energy source

harvested from the human respiratory effort.

Obtained results also showed that deep breathing is

able to generate almost 3 times more power than

normal breathing.

The proposed prototype of piezoelectric Breath

Energy Transducer using an efficient converter was

able to generate enough power to charge a capacitor

of 47μF to a fixed value of 2.6V due to its

ENERGY HARVESTED FROM RESPIRATORY EFFORT

391

mechanical deformation caused by respiratory effort

movements. This capacitor of 47μF charged until

2.6V could be sufficient as to act as an electric

source to any system that presents very low power

consumption.

In the future, the output power value of BET can

be improved by better adapting of electronic circuits.

Another important improvement will be obtained by

the optimizing present mechanical construction in

order to enable maximum compression in the

piezoelectric tape at minimum breathing effort.

REFERENCES

Angrist, S. W., "Direct energy conversion", Allyn and

Bacon, Inc. Boston, 1971.

Starner, T., Paradiso, J., 2004. "Human generated power

for mobile electronics", C. (ed), Low-Power

Electronics, CRC Press, Chapter 45.

Starner, T., “Human Powered Wearable Computing”, IBM

Systems Journal, Vol. 35, No. 3 & 4, pp. 618-629,

(1996).

Kymissis, J., Kendall, C., Paradiso, J., Gershenfeld, N.,

1998. “Parasitic power harvesting in shoes”, in Proc.

2nd Int. Symp. Wearable Computing, pp. 132–139.

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