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7/25/2019 Sensor Principles and Microsensors Part 1a
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Introduction to BioMEMS & Medical Microdevices
Sensor Princip les and Microsensors Part 1Companion lecture to the textbook: Fundamentals of BioMEMS and Medical Microdevices, byProf. Steven S. Saliterman, www.tc.umn.edu/~drsteve
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Steven S. Saliterman, MD, FACP
What is a sensor?
A sensor converts one form of energy toanother, and in so doing detects andconveys information about some
physical, chemical or biologicalphenomena.
More specifically, a sensor is atransducer that converts the measurand(a quantity or a parameter) into a signalthat carries information.
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Steven S. Saliterman, MD, FACP
Features of an ideal sensor: Continuous operation without effecting the
measurand.
Appropriate sensitivity and selectivity. Fast and predictable response.
Reversible behavior.
High signal to noise ratio.
Compact Immunity to environment.
Easy to calibrate.
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Steven S. Saliterman, MD, FACP
Examples of Sensor Methods
Piezoelectric Sensors Direct Piezoelectric Effect
Acoustic Wave Propagation
Quart crystal microbalance MEMS Structures
Thermal Sensing
Thermal and Non-Thermal Flow Sensing
Electrochemical Sensors Ion Selective Field Effect Transistors
Optical Sensors
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Steven S. Saliterman, MD, FACP
Piezoelectric Sensors
Direct transduction from mechanical to electricaldomains and vice versa. May be used as sensors oractuators.
The reversible and linear piezoelectric effect manifests
as the production of a charge (voltage) uponapplication of stress (direct effect) and/or as theproduction of strain (stress) upon application of anelectric field (converse effect).
Three modes of operation depending on how thepiezoelectric material is cut: transverse, longitudinaland shear.
Amplifiers are needed to detect the small voltage.
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technolog y 20, no. 9:092001.
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Steven S. Saliterman, MD, FACP
SEM image of an etched feature in PZT ceramic
substrate with feature dimensions of 3 x 15 m.
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technolog y 20, no. 9:092001.
Example: Lead Zirconate Titanate (PZT)
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Steven S. Saliterman, MD, FACP
Piezoelectric Materials
Crystals Quart SiO2 Berlinite AlPO4 Gallium
Orthophosphate GaPO4 Tourmaline (complex chemical structure)
Ceramics Barium titanate BaTiO3 Lead zirconate titanate PZT, Pb [ZrxTi1-x] O3 ; x = 0,52
Other Materials Zinc oxide ZnO
Aluminum nitride AlN
Polyvinylidene fluoride PVDF
Adopted from Piezomaterials.com
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Steven S. Saliterman, MD, FACP
Direct and Converse Piezoelectric Effects
Adopted from bme240.eng.uci.edu
Con verse Piezoelectr ic Effect - Application of an electrical field
creates mechanical deformation in the crystal.
Direct Piezoelectr ic Effect - When a mechanical stress (compressive or
tensile) is applied a voltage is generated across the material.
.
Poll ing- Random
domains are aligned
in a strong electric
field at an elevated
temperature.
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Steven S. Saliterman, MD, FACP
Typical Piezoelectric Circuit
1
T FOut
T P
Q RV
C C R
TOut
F
QVC
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technology 20, no. 9:092001.
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Steven S. Saliterman, MD, FACP
Piezoelectric sensors maybe configured asdirect mechanical transducers or as resonators.
The observed resonance frequency andamplitude are determined by the physicaldimensions, material and mechanical andinterfacial inputs to the device.
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technology 20, no. 9:092001.
Configurations
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Steven S. Saliterman, MD, FACP
Two Modes of Operation
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technolog y 20, no. 9:092001.
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Steven S. Saliterman, MD, FACP
Approaches to Fabrication
There are essentially three approaches
to realizing piezoelectric MEMS devices:
1. Deposition of piezoelectric thin films on
silicon substrates with appropriateinsulating and conducting layers followed
by surface or silicon bulk micromachining
to realize the micromachined transducer
(additive approach).
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technolog y 20, no. 9:092001.
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Steven S. Saliterman, MD, FACP
2. Direct bulk micromachining of single
crystal or polycrystalline piezoelectrics and
piezoceramics (subtractive approach).
3. Integrate micromachined structures insilicon via bonding techniques onto bulk
piezoelectric substrates (integrative
approach).
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technolog y 20, no. 9:092001.
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Steven S. Saliterman, MD, FACP
Approaches to Fabrication
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technolog y 20, no. 9:092001.
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Steven S. Saliterman, MD, FACP
Piezoelectric Thin Films
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technolog y 20, no. 9:092001.
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Steven S. Saliterman, MD, FACP
Dry Etching Characteristics
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technolog y 20, no. 9:092001.
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Steven S. Saliterman, MD, FACP
Illustration of Surface Micromachining
(a) Substrate silicon wafer.(b) Silicon substrate surface is thermally
oxidized.
(c) Bottom electrode such as a (1 1 1) platinum
film is deposited.
(d) The piezoelectric thin film is deposited and
annealed.
(e) Top electrode metal such as Cr/Au is
deposited.
(f) The entire piezoelectric, electrodes and
passive layer stack is patterned and etch to
expose the substrate silicon.
(g) Substrate silicon is etched from the front
side using anisotropic wet etchant orisotropic vapor phase XeF2etchant while
protecting the transducer stack.
(h) Alternatively, the substrate silicon is
anisotropically etched from backside to
release the transducer structure.
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technolog y 20, no. 9:092001.
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Steven S. Saliterman, MD, FACP
Piezoelectric Effects
The piezoelectric effect is a linear phenomenon wheredeformation is proportional to an electric field:
is the mechanical strain,
is the piezoelectric coefficient,
is the electric field,
is the displacment (or charge density) linearly, and
is the stress.
Where
S
d
E
D
T
S dE and D dT
These equations are known as the conversepiezoelectric effectand the direct piezoelectric effectrespectively.
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Steven S. Saliterman, MD, FACP
Piezoelectric Constitutive Equations
, , 1 to 6; and , , 1 to 3,
is the strain,
is the dielectric displacement (or charge density),
is the electric field
Eji ij kl k
Tm nl lm ln
Where
i j m k l n
S
D
E
S s T d E
D d T E
(The superscripts and refer to measurement at a constant field and stress. )
,
is the stress, and
, and are the elastic compliances.E Tij kl ln
E T
T
s d
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Steven S. Saliterman, MD, FACP
Surface Acoustic Waves
Generation of surface acoustic waves (SAW)in quartz by interdigitated transducers:
Gardner, JW, VK Varadan and OO Awadelkarim, Microsensors, MEMS andSmart Devices. John Wiley & Sons, Ltd. W. Sussex (2001).
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Steven S. Saliterman, MD, FACP
Delay-line SAW
Typically with a sensing film such polyimide deposited on thesurface in the area between the interdigitated transducers:
Gardner, JW, VK Varadan and OO Awadelkarim, Microsensors, MEMS and
Smart Devices. John Wiley & Sons, Ltd. W. Sussex (2001).
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Steven S. Saliterman, MD, FACP
Two Port Delay Line and Resonator
Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technolog y 20, no. 9:092001.
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Steven S. Saliterman, MD, FACP
The change in SAW velocity is related to the mass of athin loss-less film on the sensor surface (left):
1 2
1 2
is the SAW velocity,
and are the substrate material constants,
is the SAW frequency,
is the height of the layer, and
is the density of the thin film lay
( )
R
R
R
Where
V
k k
f
h
Vk k fh
V
er.
0
0
0 0
is the frequency change,
is the intial SAW frequency,
is the phase shift, and
is the total degrees of phase in the sensor delay path
(as measured be
R
Where
f
f
fVV f
tween the centers of the IDTs)
The change in SAW velocity can be determined
experimentally by measuring the phase shift or thefrequency shift (right).
Calculating SAW Velocity
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Steven S. Saliterman, MD, FACP
Quartz Crystal Microbalance (QCM)
Mass-sensitive devices suitable for detecting a variety ofanalytes. Thin AT-cut quartz wafer with a diameter of 0.25-1.0 inches, sandwiched between two metal electrodeswhich are used to establish an electric field acrossthecrystal:
Cahayaalone.blogspot.comChimique.usherbrooke.ca
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Steven S. Saliterman, MD, FACP
Sauerbrey Equation
Mass changes on the QCM surface result in afrequency change according to the Sauerbreyequation:
0
20
is the change in frequency,
is the resonant frequency of the quartz resonator,
is the mass change,
is the active vibrating area
is the is the shear mod
2
Q
Q Q
Where
f
f
m
A
f mf
A
ulus of the quartz, and
is the the density of quartzQ
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Steven S. Saliterman, MD, FACP
MEMS Structures
Construction:a) Cantilever beam,
b) Bridge structure,
c) Diagram ormembrane.
Detection Methods: Electrical,
Magnetic,
Optical,
Acoustic.
Gardner, JW, VK Varadan and OO Awadelkarim, Microsensors, MEMS and
Smart Devices. John Wiley & Sons, Ltd. W. Sussex (2001).
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Steven S. Saliterman, MD, FACP
Cantilever Beam
The displacementxof the beam is related to
the applied force and length of the beam:3
is Young's modulus,
is the second moment of inertia,
i
or ( is the spring constant)3
m
m
x
x x m mm m
Where
E
I
F
lx F F k x k
E I
s the force or point load, and
is the length.l
Gardner, JW, VK Varadan and OO Awadelkarim, Microsensors, MEMS and
Smart Devices. John Wiley & Sons, Ltd. W. Sussex (2001).
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Steven S. Saliterman, MD, FACP
Bridge Structure
The sinusoidal solution for displacementxof a bridgestructure is:
2
2
is a constant,
is Young's modulus,
sin and (the buckling force)
m
y m mCritical
m m
Where
A
E
F E Ix A F
E I y l
is the second moment of inertia,
is the force andis the length.
m
y
I
Fl
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Steven S. Saliterman, MD, FACP
MEMS Sensor Piezoelectric Pressure
Piezoresistive pressure sensor
with reference pressure cavityinside chip.
Esashi, Masayoshi. 2012. Revolution of Sensors in Micro-Electromechanical
Systems. Japanese Journal of App l ied Physics 51, no. 8:080001.
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Steven S. Saliterman, MD, FACP
MEMS Sensor Capacitive Pressure
Integrated capacitive
pressure sensor fabricated
by wafer level packaging.
Esashi, Masayoshi. 2012. Revolution of Sensors in Micro-Electromechanical
Systems. Japanese Journal of App l ied Physics 51, no. 8:080001.
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Steven S. Saliterman, MD, FACP
Principle and photograph of SAW passive wireless
pressure sensor and example of measurement
(change in time converted into phase).
MEMS Sensor SAW Pressure
Esashi, Masayoshi. 2012. Revolution of Sensors in Micro-Electromechanical
Systems. Japanese Journal of App l ied Physics 51, no. 8:080001.
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Steven S. Saliterman, MD, FACP
Common two-wire tactile sensor network that
sequentially selects sensors.
MEMS Sensor Tactile Sensor
Esashi, Masayoshi. 2012. Revolution of Sensors in Micro-Electromechanical
Systems. Japanese Journal of App l ied Physics 51, no. 8:080001.
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Steven S. Saliterman, MD, FACP
Schematic of event-
driven (interrupt)
tactile sensor
network, example of
operation, and
photographs of
prototype IC.
MEMS Sensor Tactile Sensor
Esashi, Masayoshi. 2012. Revolution of Sensors in Micro-Electromechanical
Systems. Japanese Journal of Applied Physics 51, no. 8:080001.
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Steven S. Saliterman, MD, FACP
Poly-Si surface
micromachined integrated
accelerometer (cross
sectional structure and
photographs of two-axis
accelerometer).
MEMS Sensor - Accelerometer
Esashi, Masayoshi. 2012. Revolution of Sensors in Micro-Electromechanical
Systems. Japanese Journal of Applied Physics 51, no. 8:080001.
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Steven S. Saliterman, MD, FACP
Schematic ofaccelerometer with
thick epitaxial poly-Si
layer and photograph
of resonant gyroscope.
MEMS Sensor - Accelerometer
Esashi, Masayoshi. 2012. Revolution of Sensors in Micro-Electromechanical
Systems. Japanese Journal of Applied Physics 51, no. 8:080001.
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Steven S. Saliterman, MD, FACP
Automotive sensor
for yaw rate andacceleration.
MEMS Sensor Yaw & Acceleration
Esashi, Masayoshi. 2012. Revolution of Sensors in Micro-Electromechanical
Systems. Japanese Journal of App l ied Physics 51, no. 8:080001.
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Steven S. Saliterman, MD, FACP
MEMS Sensor - Gyroscope
Esashi, Masayoshi. 2012. Revolution of Sensors in Micro-Electromechanical
Systems. Japanese Journal of Applied Physics 51, no. 8:080001.
Two-axis resonant
gyroscope used for image
stabilization (photograph
and schematic).
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Steven S. Saliterman, MD, FACP
Apollo 11 Gyroscope 1969
Gyroscope image courtesy of https://www.flickr.com/photos/blafetra/14524883649
https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwi295PchoLLAhXF5yYKHUfeAD0QjRwIBw&url=https://www.flickr.com/photos/blafetra/14524883649&psig=AFQjCNHgcqRL12hoF057586YtNGz1JnqyQ&ust=14559103176540407/25/2019 Sensor Principles and Microsensors Part 1a
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Steven S. Saliterman, MD, FACP
Sensor Fusion:Adafruit BN0055
Absolute Orientation(Euler Vector, 100Hz) Threeaxis orientation data based on a 360 sphere.
Absolute Orientation(Quaterion, 100Hz) Fourpoint quaternion output for more accurate datamanipulation.
Angular Velocity Vector(100Hz)Three axis of 'rotation speed' in rad/s.
Acceleration Vector(100Hz)Three axis of acceleration (gravity + linear motion)in m/s^2.
Magnetic Field Strength Vector(20Hz) Three axisof magnetic field sensing in micro Tesla (uT).
Linear Acceleration Vector(100Hz) Three axis oflinear acceleration data (acceleration minus gravity)in m/s^2.
Gravity Vector(100Hz) Three axis of gravitationalacceleration (minus any movement) in m/s^2.
Temperature(1Hz) Ambient temperature indegrees celsius.
Courtesy of Adafruit
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Steven S. Saliterman, MD, FACP
Thermosensors
Platinum resistor:
Linear, stable, reproducible.
Material property dependency on
temperature, Thermocouples (e.g.. Type K)
Thermistor: a semiconductor device
made of materials whose resistancevaries as a function of temperature.
Thermodiode and Thermotransistor.
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Steven S. Saliterman, MD, FACP
Thermocouple
Potentiometric devices fabricated by the joining of twodifferent metals forming a sensing junction: Based on the thermoelectric Seebeck effectin which a
temperature difference in a conductor or semiconductorcreates an electric voltage:
is the electrical voltage,
is the Seebeck coefficient expressed in volts/K , and
is the temperature difference ( - ).
s
S ref
s
WhereV
T T T
V T
Gardner, JW, VK Varadan and OO Awadelkarim, Microsensors, MEMS and
Smart Devices. John Wiley & Sons, Ltd. W. Sussex (2001).
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Steven S. Saliterman, MD, FACP
Thermodiode and Thermotransistor
When ap-ndiodeis operated in a constant current (IO)circuit, the forward voltage (Vout) is directly proportionalto the absolute temperature(PTAT).
is the Bolzman constant,
is temperature,
is the charge on an electron,
is the operating current and
is the saturation current.
ln 1out
b
S
B
S
Where
k
T
q
I
I
k T IVq I
Gardner, JW, VK Varadan and OO Awadelkarim, Microsensors, MEMS and
Smart Devices. John Wiley & Sons, Ltd. W. Sussex (2001).
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Steven S. Saliterman, MD, FACP
Thermal Flow Sensing
Hot wire or hot element anemometers.
Based on convective heat exchange takingplace when the fluid flow passes over the
sensing element (hot body). Operate in constant temperature mode or in
constant current mode.
Calorimetric sensors.
Based on the monitoring of the asymmetryof temperature profile around the hot bodywhich is modulated by the fluid flow.
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Steven S. Saliterman, MD, FACP
Thermal Flow Sensor
The heat transferred per unit time from a resistive wireheater to a moving liquid is monitored with athermocouple:
Gardner, JW, VK Varadan and OO Awadelkarim, Microsensors, MEMS and
Smart Devices. John Wiley & Sons, Ltd. W. Sussex (2001).
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Steven S. Saliterman, MD, FACP
In a steady state, the mass flow rate can bedetermined:
The volumetric flow rate is calculated asfollows:
1 2
2 1
is the mass flow rate,
is the heat transferred per unit time,is the specific heat capacity of the fluid and
, are temperature.
( )
m
h
m
hm
m
Where
Q
Pc
T T
PdmQ T T
dt c
is the volumetric flow rate,
is the mass flow rate and
is the density.
V
m
m
mV
m
Where
Q
Q
QdV
Q dt
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Steven S. Saliterman, MD, FACP
Thermal Flow Sensor with Thermopile
Silvestri, S. and E. Schena Micromachined Flow Sensors in Biomedical
Applications. Micromachines2012, 3, 225-243
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Steven S. Saliterman, MD, FACP
Non-Thermal Flow Sensors
Cantilever type flow sensors Measuring the drag-force on a cantilever beam.
Differential pressure-based flow sensors When a fluid flow passes through a duct, or over a surface, it produces a
pressure drop depending on the mean velocity of the fluid.
Electromagnetic
Laser Doppler flowmeter The phenomenon is due to the interaction between an electromagnetic or
acoustic wave and a moving object: the wave is reflected back showing afrequency different from the incident one.
Lift-force and drag flow sensors Based on the force acting on a body located in a fluid flow.
Microrotor Rotating turbine
Resonating flow sensors Temperature effects resonance frequency of a vibrating membrane.
Silvestri, S. and E. Schena Micromachined Flow Sensors in Biomedical
Applications. Micromachines2012, 3, 225-243
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Steven S. Saliterman, MD, FACP
Cantilever Type Sensor
Silvestri, S. and E. Schena Micromachined Flow Sensors in Biomedical
Applications. Micromachines2012, 3, 225-243
Able to Sense Direction
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Summary
A sensor is a transducer that converts themeasurand(a quantity or a parameter) into asignal that carries information.
Thepiezoelectric effectis a linearphenomenon where deformation isproportional to an electric field.
Mass changes on the QCM surface result in afrequency change according to the Sauerbreyequation.
MEMS Structures and Sensors Thermo Sensors Flow Sensors Magnetic Sensors