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High temperature measurements are needed in industrial applications .

High temperature sensors capable of operating in harsh environments are needed to prevent disasters .

Most existing temperature sensors do not satisfy the needs.

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A contactless passive sensing device(Hybrid MEMS) is described for high temperature measurements.

Inductive telemetric measurement systems is used for contactless measurement using passive sensors.

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Passive autonomous sensors - those that are just passive elements, interrogated wirelessly by a readout unit.

Self-powered autonomous sensors - those that have a power-harvesting module or are supplied power by an electromagnetic field.

Hybrid MEMS temperature sensor is a Passive autonomous sensor.

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BLOCK DIAGRAM

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Sensing element is placed in harsh/remote area.

Read out unit in safety zone.

Two elements are connected by a wireless communication channel.

Most passive sensors use telemetric communication consisting of 2 inductors.

Measured quantity is usually read as reflected impedance.

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Components of MEMS

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Image of the hybrid telemetric MEMS.11

Developed using Metal MUMPs process.

Layout is organized into 36 cells having capacitive behavior and connected in parallel.

Built over a silicon nitride isolation layer with a 1µm air gap.

Working principle –structural deformation due to increase in temperature.

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Microscope image of interdigitated capacitor

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A single cell is based on a cascade of bent beam structures.

Consist of V-shaped beam anchored at 2 ends.

Thermal expansion induces displacement of central apex.

Central apex is connected to an interdigitated comb.

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Bent Beam structure.15

Movement of central apex causes displacement one electrode towards the fixed one.

Change in capacitance occurs. Maximum temperature 623K

(left) at 298 K and (right) at 500 K.16

Equivalent model of the interdigitated capacitor and an impedancediagram measured at 270 ◦C [(a) modulus and (b) phase].

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Impedance module of the interdigitated capacitor measured at differentTemperatures(100 ◦Cto 330 ◦C.)

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3 different zones has been identified,

1. In the lower frequencies, an increase in the parasitic resistance.

2. In the middle frequency, the increasing

of the capacitance.

3. In the higher frequencies, as the temperature increases, the resonant frequency decreases.

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Microscope image of the inductor A1 realized by thick-film deposition on alumina.

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Microscope image of the inductor B1 realized by photolithography 22

Equivalent model of the planar inductor and impedance diagrams at different temperatures.(23 ◦C to340 ◦C)

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3 different zones have has been identified

1. A resistive behavior is shown at lower frequencies.

2. At higher frequencies, a resonant frequency is visible due to capacitance behavior.

3. In middle frequencies purely inductive behavior is obtained

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Hybrid telemetric MEMS is placed in harsh environment.

Conditioning electronics is into the safe zone.

Readout inductor, is placed close to the hybrid MEMS.

Two inductors constitute a telemetric coupled system.

Readout inductor is a planar spiral fabricated in thick-film technology.

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It has 30 windings, each of 250 μm width and spaced 250 μm.

External diameter is 50 mm wide.

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BLOCK DIAGRAM OF INDUCTIVE TELEMETRY

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Link wirelessly two devices through inductive coupling.

Measurement information is acquired by the sensing element.

Sent through the communication channel using the magnetic coupling.

Read as reflected impedance by the conditioning electronics and elaborated by the readout unit.

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Modulus and phase of the impedance measured from the terminals of the readout inductor. 31

Min-Phase method measures a frequency fo.

Impedance of the terminals of the readout inductor is also measured.

Capacitive value of the sensor is related to the frequency at which the phase, in a short frequency interval, is at its minimum value.

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An IR heater of 500 W is provided to rise temperature upto 350 ◦C.

Pt100 thermo resistance measure the internal temperature at different points.

PC is connected to multimeter , impedance analyser through IEEE-488 bus.

PC is also connected to power control.

It monitors the temperature inside and controls it.

Two MEMS sensors are placed, one to impedance analyzer, one for telemetric measurement.

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35Modules of hybrid sensor measured using impedance analyzer at different temperatures.

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Phase of hybrid sensor measured using impedance analyzer at different temperatures

Observed that increase in temperature generates a decrease of the values of the resonant frequencies, since the sensor capacitance value increases.

Capacitances measured using 2 methods shows a quasi linear relationship.

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Capacitance sensor values directly measured and compared with the calculated ones. 38

39Temperature values measured with the Pt100 and compared with the Min-Phase and 3-Resonances calculated values.

Passive wireless sensor is capable of operating in harsh environments for high-temperature measurements.

The values measured by the two techniques have demonstrated good agreement with the reference values.

Inductive telemetric systems offer solutions to specific applications for contactless measurement.

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“Passive Hybrid MEMS for High-Temperature Telemetric Measurements” Daniele Marioli, Member, IEEE, Emilio Sardini, Member, IEEE, and Mauro Serpelloni

Y. Wang, Y. Jia, Q. Chen, and Y. Wang, “A passive wireless temperature sensor for harsh environment applications”

D. Marioli, E. Sardini, M. Serpelloni, B. Andò, S. Baglio, N. Savalli,and C. Trigona, “Hybrid telemetric MEMS for high temperature measurements into harsh industrial environments,”

Bruno Andò, Salvatore Baglio, Senior Member, IEEE, Nicolò Savalli, and Carlo Trigona Cascaded “Triple-Bent-Beam” MEMS Sensor for Contactless Temperature Measurements in Non accessible Environments.

“Inductive Telemetric Measurement Systems for Remote Sensing”,Daniele Marioli, Emilio Sardini and Mauro Serpelloni

“Passive and Self-Powered Autonomous Sensors for Remote Measurements”,Emilio Sardini and Mauro Serpelloni 41

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