"COMSOL仿真问题解答及操作指南"

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COMSOL基本操作指南以及常见仿真问题的答疑解答可以帮助用户更好地掌握COMSOL多物理仿真软件的操作技巧和解决常见问题的方法。该指南通过对COMSOL的基本操作进行详细的讲解和示范，帮助用户快速上手并且熟练掌握软件的使用。同时，针对COMSOL使用过程中可能遇到的问题，包括但不限于网格生成、物理场设置、边界条件设置、后处理结果等方面，这些问题进行了吐血整理，给出详细的解决方法和步骤，以帮助用户更好地解决实际问题。 2012年COMSOL NEWS杂志所涵盖的内容非常丰富多样，包括多物理仿真、声学、电磁学、热传导、流体力学等领域。该杂志报道了一些前沿技术和应用案例，涉及到了领域的多个方面。例如，通过数值仿真进行拓扑优化，改进了丰田混合动力汽车电子元件的冷却效果；还有报道了一种源自 Cochlear™ 的全新可植入式人工耳蜗听力植入装置的设计，以及能量收集器的建模优化。在COMSOL NEWS 中，关于多物理仿真的报道是一个重要的话题。多物理仿真是指在一个计算模型中，同时考虑多种物理场耦合的现象，如机械、热、流体以及电磁学等。这些不同的物理现象之间相互影响，需要通过仿真软件进行综合分析。COMSOL正是这样一种能够进行多物理仿真的软件，它可以很好地模拟解决多物理场耦合的问题。从2012年COMSOL NEWS可以看出，COMSOL软件在多领域的应用案例中发挥了重要的作用。通过COMSOL多物理仿真软件，研究人员和工程师们得以进行各种复杂物理现象的模拟和分析，取得了很多有价值的成果和发现。通过COMSOL仿真技术的应用，研究人员不仅能够更好地理解问题背后的物理机制，而且还能够得到有针对性的解决方案和设计改进。总之，在COMSOL基本操作指南以及常见仿真问题的答疑解答的指引下，以及COMSOL NEWS中涉及的各个领域的应用案例，我们可以发现，COMSOL软件在实际工程和科学研究中发挥着越来越重要的作用，并且取得了许多令人瞩目的成就。期待COMSOL在未来能够继续推出更多更加高效的仿真工具和技术，为科研人员和工程师们提供更好的支持和帮助。

he desire to get rid of batteries and

power lines motivates a wide range

of research. In the quest for systems that

are energy autonomous, the concept of en-

ergy harvesting attracts much attention.

Combine this idea with operation at the

micro level and the ‘what if’ scenarios be-

come even more enticing.

For researchers at Siemens Corporate

Technology in Munich, there was a strong

attraction for exploring the potential of an

energy harvesting MEMS (Micro Electro-

Mechanical System) generator. Dr. Ingo

Kuehne explains, “Our remit is broad.

We are looking to develop

platform technologies for

tomorrow rather than spe-

ciﬁc products; however,

it makes sense to demon-

strate the value of our re-

search. Together with our

partner Continental AG

we decided to focus on an

application with clear com-

mercial potential. Our ulti-

mate goal is to design the

MEMS generator to be as

small, light and strong as

possible with enough en-

ergy to power a system un-

der a range of conditions.” They chose to

design a microgenerator for an innovative

Tire Pressure Monitoring System (TPMS)

driven by motion.

Because TPMS are traditionally pow-

ered by batteries, they tend to be mounted

on the wheel rim. With no reliance on a

battery, such a system could be placed in-

side the tire and would be in a position to

measure much more than pressure (Figure

1). It could monitor temperature, friction,

wear and torque; assist with optimal track-

ing and engine control; and convey all this

critical information wirelessly. It would also

be maintenance free, low cost and environ-

mentally friendly.

Yet, locating the device within the tire

requires that the assembly be extremely

robust and able to withstand gravita-

tional acceleration up to 2,500 g. More-

over, in order to avoid tire imbalance it

would have to be very light, and in terms

of operational life it would need to match

that of a tire, a minimum of 8 years.

From Mechanical Stress into

Electrical Energy

Mounted to one spot on the inside of a

tire, a piezoelectric microgenerator would

be able to harvest energy from the compres-

sion created each time that particular area

of the tire touched the ground. The canti-

lever was designed to incorporate a thin

ﬁlm of self-polarized piezoelectric ceramic

material with a silicon carrier layer, which

provides mechanical stability and stores

harvested mechanical energy (Figure 2).

The team had settled on a triangular

design for the spring-loaded piezoelec-

tric cantilever, as such a shape enables a

Modeling Optimizes a Piezoelectric Energy Harvester

Used in Car Tires

Siemens is using ﬂuid-structure interaction simulation to ensure the cost-eﬀective optimization

of a cantilever in a MEMS generator designed to power a tire pressure monitoring system.

BY JENNIFER HAND

COAUTHORED BY DR. INGO KUEHNE AND DR. ALEXANDER FREY, SIEMENS AG

Figure 1. TPMS mounting options — on the rim or on the inner lining of the tire.

Figure 2. Schematic of the piezoelectric MEMS generator energy

harvester. The cantilever is made of two materials and electrical

energy is transferred through the circuit from the cantilever.

“ Our ultimate goal is

to design the MEMS

generator to be as small,

light and strong as

possible with enough

energy to power a

system under a range

of conditions.”

1 2 // COMSOL NEWS 2 0 1 2

MULTIPHYSICS

sIemens coRPoRaTe Technology, munIch, geRmany

uniform stress distribution in the surface

direction. “Typical cantilever designs have

substantial mass and are heavy with a

concentrated weight at the tip. This is ﬁne

for the conventional method of continuous-

ly exciting a cantilever at its natural fre-

quency. However, the high dynamic forces

we are dealing with prevent us from us-

ing this method of excitation,” comments

Dr. Alexander Frey. “We had to adopt an

unconventional approach and avoid mass

and its concentration. This in turn gave us

a more serious problem because damping

becomes much more critical.”

The big question for the Siemens team

was how to optimize the design of the can-

tilever in order to minimize damping. It

appeared that air damping was the domi-

nant effect, and the aerodynamic proﬁle

was a critical parameter. While the cantile-

ver area was limited to 100 mm

the layer

thicknesses were design parameters that

could be freely changed. “We needed to

ﬁnd suitable values for these parameters

so that we could ensure that the mechani-

cal oscillation would

continue for as long as

possible, and transfer as

much of the mechanical

energy as possible to

the electrical domain,”

comments Dr. Frey.

“We really needed

a numerical tool to

determine the optimal

structure and ensure

that enough energy was

being produced.”

Fluid and

Structure:

An Open

Relationship

Identifying the trans-

fer of mechanical en-

ergy to the surrounding

air as being critical, the

team ﬁrst conducted a

Fluid-Structure Interaction (FSI) analy-

sis of the cantilever. Dr. Kuehne explains,

“We started with static simulations and

these gave us some initial values. Then,

a time-dependent analysis allowed us to

see a range of physical effects and under-

stand the impact of the surrounding air

on the damping of the cantilever.” (Fig-

ures 3 and 4)

Figure 3. 2D Fluid-Structure Interaction simulation showing the resulting

velocity ﬁeld caused by feeding mechanical cantilever energy into the

disordered kinetic energy of the surrounding gas.

Figure 4. 2D simulations of ﬂuid-structure

interaction on a cantilever’s deﬂection at a

gas pressure of 1 bar for varied

carrier thickness.

Dr. Ingo Kuehne holding one of the wafers used in the production of

the MEMS Energy Harvester prototypes.

One of the wafers used with prototype

designs of the MEMS Energy Harvester.

COMSOL NEWS 2 0 1 2 // 1 3

MULTIPHYSICS

sIemens coRPoRaTe Technology, munIch, geRmany

Members of the team went on to con-

duct a 3D FSI simulation and to consider

the cantilever deﬂection as a function of

external pressure and carrier thickness

(Figures 5 and 6). They examined the

maximum stress required for initial deﬂec-

tion at each thickness where, as Dr. Frey

reports, “We conﬁrmed quantitatively that

increasing the thickness of the cantilever

led to an improvement in the damping be-

havior of the MEMS harvester.”

Optimizing Cantilever

Size and Shape

“With COMSOL Multiphysics simula-

tion software we learned how to numeri-

cally describe the behavior of our structure

to then allow us to conduct research in the

laboratory,” comments Dr. Kuehne. In or-

der to compare the simulated behavior

with experiments, the cantilever was pe-

riodically excited and the generated piezo-

electric voltage was recorded.

“Comparison of the simulation with

physical testing revealed that the overall

damping behavior was actually higher.

The obvious explanation was that we were

losing energy because of intrinsic losses in

the material. We assumed an accepted val-

ue for this internal damping, and after tak-

ing these correction factors into account,

we arrived at the same results. This reas-

sured us that our simulation process with

COMSOL was reliable and that we could

continue to investigate the performance of

the cantilever using different parameter

values.” The team was then able to move

on to optimizing system components and

system integration (Figure 7).

The use of COMSOL was critical to the

development of the physical prototypes. Ac-

cording to Dr. Kuehne, it takes three people

four months to do one technological run,

which typically consists of one batch of up

to 25 wafers. “One run usually results in a

couple of complete prototypes, depending on

layout. Testing takes a further two months.

In particular, the extra expense of a clean

room infrastructure results in development

costs of more than 100,000 Euros for a sin-

gle prototype run over six months. In con-

trast, you can measure a 2D simulation in

hours and a 3D simulation in days. In that

sort of time it is easy to simulate the per-

formance of up to 2,000 different prototypes

within COMSOL Multiphysics.”

Dr. Frey concludes, “Without COMSOL

and the option of numerical modeling we

would have to make numerous physical

structures that would have been time-con-

suming and expensive. Instead, we were

able to get on with the process of optimiz-

ing the MEMS design.” n

research PaPer

www.comsol.com/papers/11860/

Figure 7. Prototype of a piezoelectric MEMS energy harvesting module and surrounding system.

Figure 5. 3D Fluid-Structure Interaction simulation showing

the deﬂection of the triangular cantilever.

Figure 6. 3D simulations of ﬂuid-structure interaction

on a cantilever’s deﬂection as a function of gas

pressure with a carrier thickness of 250 µm.

“In that sort of time it is easy to simulate the

performance of up to 2,000 diﬀerent prototypes

within COMSOL Multiphysics.”

1 4 // COMSOL NEWS 2 0 1 2

MULTIPHYSICS

sIemens coRPoRaTe Technology, munIch, geRmany

edical ultrasound imaging has

made great advances and provides

ever more detailed diagnostic informa-

tion. With the help of new ultrasound

probe technology and signal processing,

it’s possible to greatly increase sensitiv-

ity, bandwidth, ﬁ eld of view and other

key parameters. Bandwidth, in partic-

ular, is important; it provides not only

greater image quality and thus diagnos-

tic power by supporting many different

frequency bands, it also means doctors

need fewer probes (the name given to

the handheld units placed on the body).

Miniaturization makes it possible to de-

ploy cost-effective ultrasound systems

in many more applications and put

them into use throughout a hospital or

in specialty practices (Figure 1).

The design of the probes is bringing

new advances. The quality of the ﬁ nal

image is tightly related to the materials

used in probe manufacturing and the un-

derstanding of their interactions.

This is exactly where a number of re-

searchers at Esaote S.p.A. in Florence,

Italy, are focusing their efforts. This

company’s principle activity is the manu-

facture and sale of diagnostic ultrasound

imaging systems. Our ﬁ rm has 1,350 em-

ployees, of which 20% are active in R&D,

and annual global sales are in excess of

300 million Euros.

Material Models

Ultrasound transducers (Figure 2) in-

volve specialized materials, manufactured

through processes with specialized ma-

chines and layers as thin as 30 microns.

This means that making multiple proto-

types for testing is expensive. Further, we

need to answer questions that can’t be ad-

dressed by measurements or theoretical

models. Often, we require information that

the material suppliers themselves often

don’t have on hand, usually because they do

Optimizing Ultrasound Piezo-Disk Transducers

The development of probes is pushing the design of ultrasound imaging forward. Thanks to COMSOL

Multiphysics, Esaote has been able to investigate how to improve their performance, including bandwidth

and steering performance.

BY LORENZO SPICCI AND MARCO CATI, R&D DEPARTMENT, ESAOTE S.P.A.

Figure 1. The performance of ultrasonic diagnostic systems such as MyLabOne (left) depends heavily on probes placed on the skin (right).

“A COMSOL model

provides results in one

month that otherwise

would take a year and

many prototypes

to achieve.”

COMSOL NEWS 2 0 1 2 // 1 5

MULTIPHYSICS

esaoTe s.P.a., floRence, ITaly

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