sensors Article

Passive Wireless Hermetic Environment Monitoring System for Spray Painting Workshop Lifeng Wang 1, *, Jingjing Ma 2 , Yan Huang 1 , Dan Tang 1 and Qing-An Huang 1 1 2

*

Key Laboratory of MEMS of the Ministry of Education, Southeast University, Nanjing 210096, China; [email protected] (Y.H.); [email protected] (D.T.); [email protected] (Q.-A.H.) Smart Integrated Sensor Engineering Center, Jiangsu R & D Center for Internet of Things, Wuxi 214135, China; [email protected] Correspondence: [email protected]; Tel.: +86-25-8379-2632

Academic Editor: Vamsy Chodavarapu Received: 12 June 2016; Accepted: 26 July 2016; Published: 1 August 2016

Abstract: Passive wireless sensors have the advantages of operating without a power supply and remote sensing capability. Hence, they are very suitable for some harsh environments, such as hermetic environments, rotating parts, or very high temperature environments. The spray painting workshop is such a harsh environment, containing a large amount of flammable paint mist and organic gas. Aiming at this special environment of spray painting workshop, a passive wireless hermetic environment monitoring system was designed, fabricated, and demonstrated. The proposed system is composed of a transponder and a reader, and the circuit design of each part is given in detail in this paper. The power and the data transmission between the transponder and the reader are realized by the inductive coupling mechanism. Utilizing the back scatter modulation and channel multiplexing, the frequency signals generated by three different environmental sensors—together with their interfaces in the transponder—are wirelessly read out by the reader. Because of the harsh environment of the spray painting room, the package of the monitoring system is quite important. Three different kinds of filter films for the system package were compared. The experimental results show that the composite filter film aluminum anodic oxide/polytetrafluoroethylene (AAO/PTFE) has the best performance. After fabrication, the measured temperature, humidity, and pressure sensitivities were measured and found to be 180 Hz/˝ C in the range of 0~60 ˝ C, 100 Hz/%RH in the range of 15~95 %RH, and 42 Hz/hPa in the range of 600~1100 hPa, respectively. Additionally, the remote sensing distance of the monitoring system reaches 4 cm. Finally, the passive wireless hermetic environment monitoring system was installed on the glass wall of the spray painting workshop and was successfully demonstrated. Keywords: passive wireless; environment monitoring; inductive coupling; spray painting workshop

1. Introduction The sensor technology has penetrated into industry and daily life in all aspects [1]. However, traditional sensors are not easy, or even unable, to measure some harsh environments, such as sealed environments, rotating parts, or very high temperature environments. The reason for this is that traditional sensors are active powered and/or wire connected. Aiming at these shortcomings of traditional sensors, passive wireless sensors have been invented and applied to these special environments [2–4]. The most widely used mechanism is inductive coupling [5]. The first passive wireless sensor was reported by Collins in 1967 [6], which measures intraocular pressure with a pair of flat coils. However, for a long time after this period, passive wireless sensors had not been given much attention. Until 1996, a totally integrated Inductor–capacitor (LC) type passive wireless intraocular pressure sensor was proposed by Puers et al. [7]. After 2000, with the Sensors 2016, 16, 1207; doi:10.3390/s16081207

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development of the micromachining process, passive wireless sensing technology began to develop quickly. Besides non-contact pressure detection, passive wireless sensing technology has been used to measure many other parameters [8–11]. A passive wireless humidity sensor which could be used to monitor the moisture in sealed package was proposed by Zhang at al. [12]. Using ferroelectric ceramic as the temperature sensing material, a passive wireless temperature sensor is reported in [13], which can work in environments with temperatures up to 700 ˝ C. In some cases, several parameters need to be monitored at the same time. Using several resonators with different resonant frequencies or Sensors 2016, 16, 1207 2 of 14 one resonator with multi-resonant frequencies, passive wireless multi-parameter sensing could be development of the micromachining process, passive wireless sensing technology to develop achieved [14–16]. Besides, adding back-scatter modulation together withbegan channel multiplexing into quickly. Besides non-contact pressure detection, passive wireless sensing technology has been used the inductive coupling system, a passive wireless multi-parameter sensing system could be easily to measure many other parameters [8–11]. A passive wireless humidity sensor which could be used realized [17,18]. to monitor the moisture in sealed package was proposed by Zhang at al. [12]. Using ferroelectric as the temperature sensingmulti-parameter material, a passive wireless temperature sensor is reported in [13], In thisceramic study, passive wireless sensing technology was used to monitor the which can work in environments with temperatures up to 700 °C. In some cases, several parameters environmental parameters of a spray painting workshop. In order to ensure the quality of spraying need to be monitored at the same time. Using several resonators with different resonant frequencies and the safety ofresonator the working environment, the environmental parameters—including or one with multi-resonant frequencies, passive wireless multi-parameter sensing couldthe be temperature, achieved [14–16]. Besides, adding back-scatter modulation together with channel multiplexing into For example, humidity, and pressure—of a spray painting workshop need to be monitored in real time. the inductive coupling system, a passive wireless multi-parameter sensing system could be easily temperature affects the rate of solvent evaporation. However, the air in the spray painting workshop realized [17,18]. contains a large amount of flammable paint mist sensing and organic wire-powered In this study, passive wireless multi-parameter technologygas, was so used to monitor the devices are parameters a spray painting workshop. In orderoutside to ensurethe the quality spraying andspray painting forbidden; environmental even the lamps usedoffor lighting are all installed glass of wall of the the safety of the working environment, the environmental parameters—including the temperature, workshop. Hence, the passive wireless sensing technology is very suitable for this situation, which humidity, and pressure—of a spray painting workshop need to be monitored in real time. For example, has the advantages operating a power However, supply the andairremote sensing capability. temperature of affects the rate ofwithout solvent evaporation. in the spray painting workshop In Section 2, contains a large amount of flammable paint mist and organic gas, so wire-powered devices are forbidden; the overall block diagram and the working principle of the system is introduced. Then, the circuit even the lamps used for all installed the glass wall of the spray workshop. design of each part is given inlighting detail.areBecause ofoutside the harsh environment of painting the spray painting room, the Hence, the passive wireless sensing technology is very suitable for this situation, which has the advantages package ofofthe monitoring system is quite important. Section 3 describes the package of the monitoring operating without a power supply and remote sensing capability. In Section 2, the overall block system. The measurement and demonstration the system shown in Section 4.is Finally, some diagram and the working principle of the system isofintroduced. Then,are the circuit design of each part given detail.in Because of the conclusions areingiven Section 5. harsh environment of the spray painting room, the package of the 2.

monitoring system is quite important. Section 3 describes the package of the monitoring system. The measurement and demonstration of the system are shown in Section 4. Finally, some conclusions are Circuitsgiven Design in Section 5.

2.1. Overall2.Block Diagram Circuits Design The passive wireless hermetic environment monitoring system for the spray painting workshop is 2.1. Overall Block Diagram composed of aThe transponder and a reader; the overall blocksystem diagram thepainting systemworkshop is shown in Figure 1. passive wireless hermetic environment monitoring for theof spray composed of a transponder and a reader; the overall block diagram of the system is shown in Figure The powerisand the data transmission between the transponder and the reader are realized by way of 1. The power and the data transmission between the transponder and the reader are realized by way inductive coupling. Hence, the transponder can be used to monitor hermetic environments without of inductive coupling. Hence, the transponder can be used to monitor hermetic environments without wires or batteries. wires or batteries.

Figure 1. Overall block diagram of the passive wireless hermetic environment monitoring system. The system is composed of a reader and a transponder. The power and the data transmission between the transponder and the reader are realized by way of inductive coupling.

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Figure 1. Overall block diagram of the passive wireless hermetic environment monitoring system. The system is composed of a reader and a transponder. The power and the data transmission between The process the system is as follows. Firstly, the carrier generator together theworking transponder and theof reader are realized by way of inductive coupling.

with the E-class power amplifier in the reader generates a carrier signal. Then, the carrier signal in the reader is working process though of the system is as follows. Firstly, the carrier with the is then coupledThe to the transponder their inductors. The coupled carriergenerator signal intogether the transponder E-class power amplifier in the reader generates a carrier signal. Then, the carrier signal in the rectified and regulated as the voltage source for itself. With sufficient power supply, the reader temperature, is coupled to the transponder though their inductors. The coupled carrier signal in the transponder humidity, and the pressure sensors together with their interfaces in the transponder can each generate is then rectified and regulated as the voltage source for itself. With sufficient power supply, the a digital frequency signal, whose value is decided based on the environment. In order to realize the temperature, humidity, and the pressure sensors together with their interfaces in the transponder can monitoring of multiple parameters, the division is used In to order sequentially each generate a digitalenvironmental frequency signal, whose value is time decided based multiplexer on the environment. transmit three frequency signals. Then, theparameters, output signals of the time multiplexer division multiplexer are to realize the digital monitoring of multiple environmental the time division is used modulated to thetransmit carrier signal by the load modulation circuit the transponder, and the modulated to sequentially three digital frequency signals. Then, the in output signals of the time division multiplexer areat modulated the carrier signal byto thethe load modulation circuit in the transponder, carrier signal is, the sametotime, coupled back reader. Finally, the digital frequency signals and the modulated carrier signal is, at the same time, coupled back to the reader. Finally, the digital generated by the sensors and their interfaces are recovered from the modulated carrier signal by frequency signals generated by the sensors and their interfaces are recovered from the modulated the demodulation and shaping circuits. The detail designs of the transponder and the reader are carrier signal by the demodulation and shaping circuits. The detail designs of the transponder and given below. the reader are given below.

2.2. Design of the Transponder

2.2. Design of the Transponder

2.2.1. Part 1: Sensor Interface Circuits and Time Division Multiplexer 2.2.1. Part 1: Sensor Interface Circuits and Time Division Multiplexer

The function of the sensor interface circuit is to convert the capacitive sensor signal to a digital The function of the sensor interface circuit is to convert the capacitive sensor signal to a digital frequency signal. AA lotlotofofcircuits to frequency frequencysignals. signals.Here, Here, frequency signal. circuitscan canconvert convertcapacitive capacitive variations variations to wewe used theused multi-harmonic oscillator, because of itsoflow temperature drift the multi-harmonic oscillator, because its low temperature driftcharacterization. characterization. Figure of the themulti-harmonic multi-harmonic oscillator. In Figure the capacitor Cs Figure2 2shows showsthe the schematic schematic of oscillator. In Figure 2, the2,capacitor Cs representsa acapacitive capacitive sensor. sensor. During design process, we use capacitors to represents Duringthe thecircuit circuit design process, we variable use variable capacitors to represent capacitive sensors. sensors. The resistor Rf and ampop constitute an integralan circuit, which plays which represent capacitive The resistor Rf the andopthe amp constitute integral circuit, the the rolerole of frequency selection. The resistance R1 and R the positive and circuit, plays of frequency selection. The resistance R21constitute and R2 constitute thefeedback positivecircuit, feedback the diode D 1 and D2 have the function of bidirectional limiting of voltage. The output frequency f of and the diode D1 and D2 have the function of bidirectional limiting of voltage. The output frequency the multi-harmonic oscillator can be calculated by [19]: f of the multi-harmonic oscillator can be calculated by [19]:

f 

1

1 f “2R C ln(1  2R22R) 2 f sCs lnp1 ` 2R f R R q 1

(1)

(1)

1

Figure 2. Schematic of the sensor interface circuit. By this multi harmonic oscillator, the capacitor Cs

Figure 2. Schematic of the sensor interface circuit. By this multi harmonic oscillator, the capacitor Cs could be converted to frequency signal Vs. could be converted to frequency signal Vs .

There are three kinds of environmental sensors integrated in the transponder, but the monitoring has only data transmission channel. Therefore, the time divisionbut multiplexer There aresystem three kinds of one environmental sensors integrated in the transponder, the monitoring is used to only realizeone thedata time division multiplexing transmission. division multiplexer consists system has transmission channel. Therefore,The thetime time division multiplexer is used to

realize the time division multiplexing transmission. The time division multiplexer consists of the oscillator, the frequency divider and the multiplexer. Figure 3 shows the output signals of the time division multiplexer. It can be seen that the sync signal and the signals of three sensors are sequentially outputted, and the transmission time for each signal was designed to be 64 ms.

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of the oscillator, the frequency divider and the multiplexer. Figure 3 shows the output signals Sensors 2016, 16, 1207 4 ofof 14the It can be seen that the sync signal and the signals of three sensors 4are of 14 of the oscillator, the frequency divider and the multiplexer. Figurewas 3 shows the output sequentially outputted, and the transmission time for each signal designed to besignals 64 ms. of the

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time division multiplexer. It can be seen that the sync signal and the signals of three sensors are sequentially outputted, and the transmission time for each signal was designed to be 64 ms.

Figure Outputsignals signalsofofthe thetime timedivision division multiplexing multiplexing circuit. ofof Figure 3. 3. Output circuit. The Thesync syncsignal signaland andthe thesignals signals Figure 3. Output signals of the time division multiplexing circuit. Theeach syncsignal signal is and the signals of 64 three sensors are sequentially outputted. The transmission time for designed to be three sensors are sequentially outputted. The transmission time for each signal is designed to be 64 ms. ms.three sensors are sequentially outputted. The transmission time for each signal is designed to be 64 ms.

2.2.2. Part 2: Rectifier, Regulator, and Load Modulation Circuit 2.2.2. Part 2: Rectifier, Regulator, and Load Modulation Circuit 2.2.2. Part 2: Rectifier, Regulator, and Load Modulation Circuit The rectifier together with the regulator converts the received ac carrier signal to a stable dc The rectifier together with the regulator converts the received ac carrier signal to a stable dc The rectifier together thesupply regulator the received ac carrier signal to a stable dc voltage, which is used as the with power forconverts the transponder itself. The load modulation circuit voltage, which is used as the power supply for the transponder itself. The load modulation circuit voltage, which is used as the power supply for the transponder itself. The load modulation circuit modulates the low frequency data signals from the time division multiplexer to the high frequency modulates thethe low frequency divisionmultiplexer multiplexertotothe the high frequency modulates low frequencydata datasignals signalsfrom from the the time time division high frequency carrier signal. The schematic ofofthe rectifier, regulator, and load modulation circuit is shown in Figure 4. carrier signal. The schematic the rectifier, regulator, and load modulation circuit is shown in Figure carrier signal. The schematic of the rectifier, regulator, and load modulation circuit is shown in Figure L14.isLthe planar inductor that receives the carriersignal signalfrom from reader. The diode bridge plays 1 is planar inductor that thethe reader. Thediode diode bridge plays 4. L1the is the planar inductor thatreceives receivesthe thecarrier carrier signal from the reader. The bridge plays thethe therole role of rectifier. The diode D , together with the capacitor C , filters the signal after rectification. 2filtersthe of rectifier. The diode 3, 33,together thesignal signalafter after rectification. role of rectifier. The diodeDD together with with the the capacitor capacitor CC22, , filters rectification. Finally, a regulator chip UU TPS71550 [20], thedc dcvoltage voltage more smooth and stable. 1 ,1U Finally, a regulator chip , 1TPS71550 [20], isisused used to make make the the dc voltage more smooth and stable. Finally, a regulator chip , TPS71550 [20],is used to make more smooth and stable.

Figure 4. Schematic of the rectifier, regulator, and load modulation circuit. L1 is the planar inductor Figure 4. 4. Schematic circuit. LL11isisthe theplanar planarinductor inductor Figure Schematicofofthe therectifier, rectifier,regulator, regulator,and andload load modulation modulation circuit. that receives the carrier signal from the reader. The diode bridge plays the role of rectifier. The diode that receives the carrier signal from the reader. The diode bridge plays the role of rectifier. The diode thatDreceives the carrier signal from the reader. The diode bridge plays the role of rectifier. The diode 3, together with the capacitor C2, filters the signal after rectification. The regulator chip U1 (TPS71550) D3D, together with the capacitor C , filters the signal after rectification. The regulator chip U (TPS71550) 2 1 3, is together 2, filters the signal afterThe rectification. The regulator chip 1 (TPS71550) used to with makethe thecapacitor dc voltageCmore smooth and stable. NMOS transistor M1 as well asUthe resistor is used toto make the dc voltage smooth The NMOS NMOStransistor transistorM1 M1asaswell wellasasthe the resistor is used make voltagemore more smooth and and stable. stable. The resistor R4 forms the the loaddcmodulation circuit. R4R4 forms the load modulation circuit. forms the load modulation circuit.

The load modulation circuit consists of the NMOS transistor M1 and the resistor R4. The mechanism of the load modulation can be simply explained as follows. The The load modulation modulation circuit ofofthethe NMOS transistor M1 low and the R4V . mTheR4 . The load circuit consists consists NMOS transistor M1 frequency and resistor thesignal resistor changes the on/off state of M 1, so the equivalent load impedance in the reader that coupled from the mechanism of the load modulation can be simply explained as follows. The low frequency signal Vm The mechanism of the load modulation can be simply explained as follows. The low frequency transponder synchronously and the change of the load impedance of thethat reader finallyfrom leadsthe changes the on/off state of M 1changes, , so the equivalent load impedance in the reader coupled signal Vm changes the on/off state of M1 , so the equivalent load impedance in the reader that coupled to the amplitude variation changes, of the carrier signal. The result isload that the input low frequency signal Vm is transponder synchronously the change of the impedance the reader finally from the transponder synchronously and changes, and the change of the loadofimpedance of the leads reader modulated to the high frequency carrier signal. Hence, the load modulation we used here actually to the amplitude variation of the carrier signal. The result is that the input low frequency signal Vm is

finally leads to the amplitude variation of the carrier signal. The result is that the input low frequency modulated to the high frequency carrier signal. Hence, the load modulation we used here actually signal Vm is modulated to the high frequency carrier signal. Hence, the load modulation we used here actually belongs to the AM modulation. For better recovery of the sensor data, the frequency of the sensor signal must be at least one order of magnitude lower than the carrier signal [21]. Besides, a large

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5 of 14 modulation. For better recovery of the sensor data, the frequency of the sensor signal must be at least one order of magnitude lower than the carrier signal [21]. Besides, a large modulation depth is also very helpful, which can be acquired from the large impedance variation of modulation depth is also very helpful, which can be acquired from the large impedance variation of the load modulation circuit and the high Q factors of the transponder inductor and the reader the load modulation circuit and the high Q factors of the transponder inductor and the reader inductor. inductor. Figure 5 shows the signal waves of the load modulation circuit. In Figure 5a, the bottom wave is Figure 5 shows the signal waves of the load modulation circuit. In Figure 5a, the bottom wave is the unmodulated sensor signals from the time division multiplexer, the top wave is the modulated the unmodulated sensor signals from the time division multiplexer, the top wave is the modulated carrier signal at the inductor. In InFigure Figure5b, 5b,the the bottom wave is the modulated signals carrier signal at thetransponder transponder inductor. bottom wave is the modulated signals at at the thetransponder transponderinductor, inductor,and and the top wave is the modulated carrier signal at reader the reader inductor. the top wave is the modulated carrier signal at the inductor. It It can canbe beseen seenthat that sync signal the three sensors’ signals are successfully modulated to the thethe sync signal andand the three sensors’ signals are successfully modulated to the carrier carrier signal. The frequency of the carrier signal in our system is 5.1 MHz. signal. The frequency of the carrier signal in our system is 5.1 MHz.

(a)

(b) Figure Thesignal signalwaves wavesofofthe theload loadmodulation modulation circuit. circuit. (a) Figure 5. 5.The (a) The Thebottom bottomwave waveisisthe theunmodulated unmodulated sensor signals from the time division multiplexer, the top wave is the modulated carrier signalsignal at the at sensor signals from the time division multiplexer, the top wave is the modulated carrier transponder inductor; (b) The bottom wave is the modulated signals at the transponder inductor, and the transponder inductor; (b) The bottom wave is the modulated signals at the transponder inductor, the top wave is the modulated carrier signal at the reader inductor. and the top wave is the modulated carrier signal at the reader inductor.

2.3 Design of the Reader

2.3. Design of the Reader 2.3.1. Part 3: Carrier Generator and E-Class Power Amplifier 2.3.1. Part 3: Carrier Generator and E-Class Power Amplifier In our passive wireless sensing system, the carrier signal not only transmits sensor data but also provides power for the transponder. Therefore, a carrier signal with large amplitude is needed. Firstly, an oscillator chip LTC6900 [22] is used to generate a 50% duty cycle square wave. The output

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In our our passive passive wireless sensing system, the carrier signal not only transmits sensor data but also In Sensors 2016, 16, 1207 wireless sensing system, the carrier signal not only transmits sensor data but also 6 of 14 provides power for the the transponder. transponder. Therefore, Therefore, aa carrier carrier signal signal with with large large amplitude amplitude is is needed. needed. provides power for Firstly, an an oscillator oscillator chip chip LTC6900 LTC6900 [22] [22] is is used used to to generate generate aa 50% 50% duty duty cycle cycle square square wave. wave. The The output output Firstly, frequency of of LTC6900 is is adjustable from kHz to to 20 20 MHz, which is high high enough forfor ourour system. frequency LTC6900 adjustable from 1 kHz MHz, which is high enough system. frequency of LTC6900 is adjustable from 11 kHz to 20 MHz, which is enough for our system. However, the amplitude the output wave is less than 5 V, which is too weak to power the However, the amplitude of the output wave is less than 5 V, which is too weak to power the transponder. However, the amplitude of the output wave is less than 5 V, which is too weak to power the transponder. Hence, the output of the oscillator chip needs to be amplified. The E-class power Hence, the output oscillator chip needs tochip be amplified. Theamplified. E-class power which transponder. Hence, of thethe output of the oscillator needs to be The amplifier, E-class power amplifier, which has very high efficiency, is used here to amplify the output wave of the oscillator has very high efficiency, is used here to amplify the output wave of the oscillator chip. Figure amplifier, which has very high efficiency, is used here to amplify the output wave of the oscillator 6 chip. Figure shows the the schematic ofpower the E-class E-class power amplifier. Vcc is iswave the output output wave from the the shows the 66schematic ofschematic the E-classof amplifier. Vcamplifier. is the output from the oscillator chip. chip. Figure shows the power V the wave from oscillator chip. If If the theofcapacitance capacitance of C C33 and andthe (inMOS parallel) the MOS MOS transistor M22 and and the the parameters of If the capacitance C3 and (in of parallel) transistor M2 transistor and the parameters ofparameters the LCR branch oscillator chip. (in parallel) the M of the LCR branch (L 2 , C 4 , and R 5 ) are regulated just right, the LCR branch will be on its resonant state (L , C , and R ) are regulated just right, the LCR branch will be on its resonant state and the carrier 2 4branch 5(L2, C4, and R5) are regulated just right, the LCR branch will be on its resonant state the LCR and the carrier carrier amplitude on inductor Lthe 2 will reach the value. maximum value. When the LCR branch is on amplitude onamplitude inductor L reachL maximum When the LCR branch is on its resonant 2 will and the on inductor 2 will reach the maximum value. When the LCR branch is on itsstate, resonant state, the the amplitude amplitude of the the output carrier signal will be be decided by the thesupply dc power power supply the amplitude of the output carrier signal will signal be decided bydecided the dc power of the E-class its resonant state, of output carrier will by dc supply of the E-class amplifier. The output amplitude of the carrier signal reaches 63 V when the dc power amplifier. The output amplitude of the carrier signal reaches 63 V when the dc power supply of the E-class amplifier. The output amplitude of the carrier signal reaches 63 V when the dc power is supply is12set set to 12 12 V. V. set tois V. to supply

Figure 6. 6. Schematic of of thethe E-class power amplifier. When thethe LCR branch (L2(L 2, C4, and R5) is on its Figure Schematic E-class power amplifier. When LCR branch is on Figure 6. Schematic of the E-class power amplifier. When the LCR branch (L ,C R5)Ris its its 2 ,4,Cand 4 , and 5 ) on resonant state, the amplitude of the output carrier signal will reach the maximum value. resonant state, the amplitude of the output carrier signal will reach the maximum value. resonant state, the amplitude of the output carrier signal will reach the maximum value.

2.3.2. Part 4: Demodulation Demodulation and Shaping Circuits 2.3.2. Part 4: Demodulation and Shaping Circuits 2.3.2. Part 4: and Shaping Circuits After thethereader reader inductor receives thethe modulated signal from thethe transponder inductor, Afterthe readerinductor inductor receives modulated signal from transponder inductor, After receives the modulated signal from the transponder inductor, demodulation and shaping circuits are needed to recover the sensor data. The demodulation circuit demodulation and shaping circuits needed recover sensor data. The demodulation circuit demodulation and shaping circuits areare needed to to recover thethe sensor data. The demodulation circuit is realized by using a diode together with a capacitor and two resistors. The schematic of thethe realized using diodetogether togetherwith witha acapacitor capacitorand andtwo tworesistors. resistors.The The schematic is is realized byby using a adiode schematic of of the demodulation circuit is shown in Figure 7. The diode has the property of unidirectional conductivity, demodulation circuit is shown Figure 7. The diode property of unidirectional conductivity, demodulation circuit is shown in in Figure 7. The diode hashas thethe property of unidirectional conductivity, so so thethe capacitor C55Cwill will be be charged if the the input signal Vii V is positive positive and will discharge if V Vifii is is negative. capacitor will charged if the input signal is positive and will discharge V is negative. so the capacitor C be charged if input signal V is and will discharge if 5 i inegative. The charging and the discharging processes are carried out repeatedly and alternatively, which The chargingand andthe the discharging processes out repeatedly andand alternatively, which realize The charging processesare arecarried carried out repeatedly alternatively, which realize the envelope detection of the input V i. Appropriate value selection of the resistors and the the envelope detection of theof input Vi . Appropriate value selection of the resistors and theand capacitor realize the envelope detection the input Vi. Appropriate value selection of the resistors the capacitor can minimize the distortion of the demodulated signal. can minimize the distortion of the demodulated signal. capacitor can minimize the distortion of the demodulated signal.

Figure 7. 7. Schematic Schematic of of the the demodulation demodulation circuit. circuit. The The envelope envelope detection detection of of the the input input V Vii is is realized realized by by Figure Figure 7.which Schematic of property the demodulation circuit. The envelope detection of the input Vi is realized by the diode, has the of unidirectional conductivity. thethe diode, which hashas thethe property of of unidirectional conductivity. diode, which property unidirectional conductivity.

Figure 8a 8a shows shows the the input input modulated modulated signal signal and and the the output output demodulated demodulated signal signal of of the the Figure Figure 8a shows the input modulated signal and the output demodulated signal of demodulation circuit: circuit: the the signal signal wave wave below below is is the the modulated modulated signal signal and and the the signal signal wave wave above above is isthe demodulation demodulation circuit: the signal wave below is the modulated signal and the signal wave above is the demodulated signal. It can be seen that the demodulated signal has a relatively small amplitude,

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the demodulated signal. It can be seen that the demodulated signal has a relatively small amplitude, and, lot of of glitches. glitches. So So the the shaping shaping circuit, circuit, which which contains contains the the voltage voltage follower follower and and, at at the the same same time, time, aa lot and the hysteresis comparator, is necessary. Figure 8b shows the signals of the shaping circuit: the hysteresis comparator, is necessary. Figure 8b shows the signals of the shaping circuit: the the signal signal wave wave above above is is the the output output of of the the voltage voltage follower follower and and the the signal signal wave wave below below is is the the final final output output signal signal from the hysteresis comparator. It can be seen that through the inductive coupling based back-scatter from the hysteresis comparator. It can be seen that through the inductive coupling based back-scatter modulation, diode based and the the shaping process, the modulation, diode based demodulation, demodulation, and shaping process, the sensor sensor data data generated generated by by the the transponder transponder is is finally finally outputted outputted from from the the reader. reader.

(a)

(b) Figure 8. 8. (a) (a) The The input input modulated modulated signal signal and and the the output output demodulated demodulated signal signal of of the the demodulation demodulation Figure circuit: the signal wave below is the modulated signal, and the signal wave above is the circuit: the signal wave below is the modulated signal, and the signal wave above is the demodulated demodulated signal; (b) (b)The Thesignals signals shaping circuit: the signal is the of output of thefollower, voltage signal; of of thethe shaping circuit: the signal wavewave aboveabove is the output the voltage follower, and the signal wave below the final output signal from the hysteresis comparator. and the signal wave below is the finalisoutput signal from the hysteresis comparator.

Figure 9 shows the photograph of the fabricated reader and the transponder. The area of the Figure 9 shows the photograph of the fabricated reader and the transponder. The area of the reader and transponder are both 5 cm × 8.8 cm, and the sizes of the inductors of the reader and the reader and transponder are both 5 cm ˆ 8.8 cm, and the sizes of the inductors of the reader and the transponder are both 4 cm × 4 cm. Three environment monitoring sensors, including the capacitive transponder are both 4 cm ˆ 4 cm. Three environment monitoring sensors, including the capacitive temperature sensor, the capacitive humidity sensor, and the capacitive pressure sensor, are mounted temperature sensor, the capacitive humidity sensor, and the capacitive pressure sensor, are mounted on on the transponder. Both the temperature and humidity sensors are the capacitive structures filled the transponder. Both the temperature and humidity sensors are the capacitive structures filled with with corresponding sensitive dielectric materials. More details can be found in our previous works corresponding sensitive dielectric materials. More details can be found in our previous works [15,23]. [15,23]. The capacitive pressure sensor is a commercial product, SCB10H from VTI [24], in which the The capacitive pressure sensor is a commercial product, SCB10H from VTI [24], in which the pressure pressure sensing mechanism is based on the bending of a silicon diagram. sensing mechanism is based on the bending of a silicon diagram.

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Figure 9. Photograph of the reader and the transponder. The sizes of the inductors of the reader and

Figure 9. Photograph of the reader and the transponder. The sizes of the inductors of the reader and the transponder are both 4 cm × 4 cm. The inductive coupling between these two inductors realizes the transponder are both 4 cm ˆ 4 cm. The inductive coupling between these two inductors realizes the passive wireless sensing. the passive wireless sensing. Figure 9. Photograph of the reader and the transponder. The sizes of the inductors of the reader and the transponder are both 4 cm × 4 cm. The inductive coupling between these two inductors realizes Package ofpassive thepainting Transponder wirelessworkshop, sensing. In athespray two kinds of contaminants are produced during the painting

3. Package of the Transponder

3.

process: the paint mist and the organictwo gas.kinds Amongofthem, the paint mist the main factor that leads In a spray painting workshop, contaminants areis produced during the painting 3. Package of the Transponder to the sensor failure. The diameter of most paint mists are less than 10 μm, and they are very easy to process: the paint mist and the organic gas. Among them, the paint mist is the main factor that leads adhere to no package is mounted, the paint mists will deposit on sensor during chips and quickly In objects. afailure. sprayIfpainting workshop, two kinds contaminants are produced the painting to the sensor The diameter of most paintof mists are less than 10 µm, and they are very easy to lead to sensor process: thefailure. paint mist and the organic gas. Among them, the paint mist is the main factor that leads adhere to objects. If no package is mounted, the mists willthe deposit on sensor chips and quickly hermetically sealed is paint not suitable which includes toHowever, the sensorthe failure. The diameter of package most paint mists are lessfor than 10transponder, μm, and they are very easy to leadthe to humidity sensor failure. sensor If and pressure sensor. In circumstance of the spray painting adhere to objects. no the package is mounted, thethe paint mists will deposit on sensor chipsworkshop, and quickly However, the hermetically notpermeable suitable for thebut transponder, whichtoincludes the the package of the transpondersealed shouldpackage not onlyisbe to air also be resistant the lead to sensor failure. deposition of the paint mist. Figure sealed 10 shows thethe schematic of the package ofspray the transponder. Firstly, humidity sensor and pressure sensor. In thetransponder, painting the However, thethe hermetically package iscircumstance not suitable forofthe whichworkshop, includes thethe transponder is mounted on the baseboard. thecircumstance transponder is covered with thetofilm fixing sensor and the pressure sensor. In the thebe spray painting workshop, package ofhumidity the transponder should not only be Then, permeable to air butof also resistant the deposition of cap.the The filter film film fixing cap is used for paint mist. Finally, the be film fixing package of on the transponder should notofonly be permeable totransponder. air but also resistant to is the the paint mist. Figure 10the shows the schematic theresisting package of the Firstly, thecap transponder covered with the porous used for blocking dust of and particles. deposition of the paintcap, mist.which Figureis10 shows the schematic thelarge package of the transponder. Firstly,

is mounted on the baseboard. Then, the transponder is covered with the film fixing cap. The filter film the transponder is mounted on the baseboard. Then, the transponder is covered with the film fixing on the film fixing cap is used for resisting paint mist. Finally, the film fixing cap is covered with the cap. The filter film on the film fixing cap is used for resisting paint mist. Finally, the film fixing cap is porouscovered cap, which is used for blocking dust and large particles. with the porous cap, which is used for blocking dust and large particles.

Figure 10. Schematic of the package of the transponder. Firstly, the transponder is mounted on the baseboard. Then, the transponder is covered with the film fixing cap. The filter film on the film fixing cap is used for resisting paint mist. Finally, the film fixing cap is covered with the porous cap, which is used blocking dust and large particles. Figure 10. Schematic of the package thetransponder. transponder. Firstly, thethe transponder is mounted on the on the Figure 10.for Schematic of the package ofofthe Firstly, transponder is mounted baseboard. Then, the transponder is covered with the film fixing cap. The filter film on the film baseboard. Then, the transponder is covered with the film fixing cap. The filter film on thefixing film fixing Therefore, thefor filter film plays the most important role in packagewith of the Based cap is used resisting paint mist. Finally, the film fixing capthe is covered the transponder. porous cap, which cap is used for resisting paint mist. Finally, the film fixing cap is covered with the porous cap, which is on the environment of thedust spray painting workshop, we designed a composite film that is composed is used for blocking and large particles.

for blocking dust and large ofused a porous aluminum anodic oxideparticles. (AAO) base film and a polymeric polytetrafluoroethylene (PTFE) Therefore, the filter plays the most important role or in the packageparticles of the transponder. film. The AAO base film film filters chemical macromolecules impurity in the air, Based and on the environment of the spray painting workshop, we designed a composite film that is composed provides flow channels for air. The polymeric PTFE film is used to obtain a hydrophobic surface, Therefore, the filter film plays the most important role in the package of the transponder.inBased on of a porous aluminum anodic oxide (AAO) base film a polymeric polytetrafluoroethylene (PTFE) the environment of the spray painting workshop, weand designed a composite film that is composed of film. The AAO base film filters chemical macromolecules or impurity particles in the air, and a porous aluminum anodic oxide (AAO) base film and a polymeric polytetrafluoroethylene (PTFE) provides flow channels for air. The polymeric PTFE film is used to obtain a hydrophobic surface, in

film. The AAO base film filters chemical macromolecules or impurity particles in the air, and provides flow channels for air. The polymeric PTFE film is used to obtain a hydrophobic surface, in other words, to prevent paint mist adhesion. The fabrication of the AAO/PTFE composite film is not very

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complex. surfacepaint oxide film of the prepared aluminum is removed by alkali otherFirstly, words, the to prevent mist adhesion. The fabrication of the wafer AAO/PTFE composite film is solution. not Sensorsthe 2016,anodic 16, 1207 oxidation process is performed for the first time and then the oxide film 9 of 14 Secondly, is also very complex. Firstly, the surface oxide film of the prepared aluminum wafer is removed by alkali removed. Thirdly, the the anodic oxidation forthe thefirst second time, followed by the solution. Secondly, anodic oxidationprocess process is is performed performed for time and then the oxide other words, to prevent paint mist adhesion. The fabrication of the AAO/PTFE composite film is not film is also treatment removed. Thirdly, thetreatment. anodic oxidation process is performed for the second time, hole enlarging and heat Fourthly, using the spin coating process, a followed hydrophobic very complex. Firstly, the surface oxide film of the prepared aluminum wafer is removed by alkali by the hole enlarging treatment is and heat treatment. Fourthly, using the spin coating is process, a and microporous PTFEthe membrane coated on the film.for Finally, the PTFE hardened solution. Secondly, anodic oxidation process is AAO performed the first time andfilm then the oxide in hydrophobic and microporous PTFE membrane is coated on the AAO film. Finally, the PTFE film is vacuum temperature drying oven. The SEM photographs of the and thefollowed section view filmconstant is also removed. Thirdly, the anodic oxidation process is performed for surface the second time, in vacuum constant temperature drying oven.11. TheIn SEM photographs of the surface and the of thehardened AAO/PTFE composite film are shown in Figure Figure 11a, the average diameter by the hole enlarging treatment and heat treatment. Fourthly, using the spin coating process, aof the section view of the AAO/PTFE composite film are shown in Figure 11. In Figure 11a, the average holeshydrophobic is about 200and nm. Figure 11bPTFE shows that theisAAO is covered with the PTFE layer, microporous membrane coatedfilm on the AAO film. Finally, the PTFE filmand is the diameter of the holes is about 200 nm. Figure 11b shows that the AAO film is covered with the PTFE vacuumseeps constant oven.film. The SEM and the PTFEhardened materialin already intotemperature the holes ofdrying the AAO The photographs thicknesses of the thesurface AAO film and the layer, and the PTFE material already seeps into the holes of the AAO film. The thicknesses of the section view of the AAO/PTFE composite film are shown in Figure 11. In Figure 11a, the average PTFEAAO layerfilm are about µmlayer and are 1.5 µm, respectively. and the 10 PTFE about 10 μm and 1.5 μm, respectively. diameter of the holes is about 200 nm. Figure 11b shows that the AAO film is covered with the PTFE layer, and the PTFE material already seeps into the holes of the AAO film. The thicknesses of the AAO film and the PTFE layer are about 10 μm and 1.5 μm, respectively.

(a)

(b)

Figure 11. SEM photographs of the aluminum anodic oxide/polytetrafluoroethylene (AAO/PTFE)

Figure 11. SEM photographs of the aluminum anodic oxide/polytetrafluoroethylene (AAO/PTFE) composite film (a) the(a) surface view; (b) the section view. (b) composite film (a) the surface view; (b) the section view. Figure 11. SEM photographs of the aluminum anodic oxide/polytetrafluoroethylene (AAO/PTFE) A contrast experiment was carried out to compare the performance of the fabricated composite composite film (a) the surface view; (b) the section view. filter film with two otherwas kinds of filter films, PTFE filmthe and polyvinylidene fluoride (PVDF)composite film. A contrast experiment carried out to compare performance of the fabricated and PVDF films are of both large-scale commercial polymeric materials. They have (PVDF) good air film. filter The filmPTFE with two other kinds filter films, PTFE film and polyvinylidene fluoride A contrast experiment was carried out to compare the performance of the fabricated composite permeability, goodfilms corrosionboth resistance, and low surface tension. Othermaterials. films that They have similar The PTFE andwith PVDF large-scale commercial have filter film two otherare kinds of filter films, PTFE film and polymeric polyvinylidene fluoride (PVDF) film.good properties as above, such as polypropylene films [25] and Nafion films [26], may be possible air permeability, resistance, andcommercial low surface tension. Other films that have similar The PTFE andgood PVDFcorrosion films are both large-scale polymeric materials. They have good air candidates. Here, we mainly investigated the change of water vapor flux and the antipollution permeability, good resistance,films and [25] low and surface tension. filmsbe that have similar properties as above, suchcorrosion as polypropylene Nafion filmsOther [26], may possible candidates. properties of each filter film after being exposed for a long time to pollution in the spray painting properties asinvestigated above, such the as polypropylene films [25]flux andand Nafion films [26], may be possible Here,workshop. we mainly change of water vapor the antipollution properties of each Figure 12 gives the transient responses of the humidity sensors before and after 600 h candidates. Here, exposed we mainly investigated the change of in water vapor painting flux and workshop. the antipollution filter paint film after being for a long time to pollution the spray Figure mist contamination; the sensors were covered by the AAO/PTFE film, the PTFE film, and the 12 properties of each filter film after being exposed for before a long and time to pollution in themist spray painting givesPVDF the transient responses of photographs the humidity h paint contamination; film, respectively. The ofsensors the polluted films areafter also 600 shown in Figure 12. It can be workshop. Figure 12 gives the transient responses of the humidity sensors before and after 600 h the sensors were by the AAO/PTFE PTFE film, workshop, and the PVDF film, respectively. seen that, aftercovered a long time period of workingfilm, in thethe spray painting the composite filter paint mist contamination; the sensors were covered by the AAO/PTFE film, the PTFE film, and the film AAO/PTFE minimum pollution andshown the smallest change vapor flux. The photographs ofhas thethe polluted films are also in Figure 12.ofItwater can be seen that, after a long PVDF film, respectively. The photographs of the polluted films are also shown in Figure 12. It can be time period of after working intime the spray workshop, thepainting composite filter film has the seen that, a long periodpainting of working in the spray workshop, the AAO/PTFE composite filter minimum pollution and the smallest change of water vapor flux. film AAO/PTFE has the minimum pollution and the smallest change of water vapor flux.

(a)

(b)

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(b) Figure 12. Cont.

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(c)

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Figure 12. Transient responses of the humidity sensors covered by different filter films before and

Figure 12. Transient responses of the humidity sensors covered by different filter films before and after after 600 h paint mist contamination, (a) AAO/PTFE film; (b) PTFE film; and (c) polyvinylidene 600 h paint mist contamination, (a) AAO/PTFE film; (b) PTFE film; and (c) polyvinylidene fluoride fluoride (PVDF) film. (PVDF) film.

4. Measurement and Demonstration

4. Measurement and Demonstration

By using the OMEGA205 C340 temperature and humidity chamber (made by Vötsch Industrietechnik), the temperature and humidity characterizations of the passive wireless monitoring By using the OMEGA205 C340 temperature and humidity chamber (made by Vötsch system were measured. In Figure 13a, the variation of the output frequency is about 11 kHz when the Industrietechnik), the temperature and humidity characterizations of the passive wireless monitoring temperature changes from 0 °C to 60 °C. Hence, the average temperature sensitivity of the monitoring system were measured. In Figure 13a, the variation of the output frequency is about 11 kHz when system is 180 Hz/°C. Figure 13b shows that the output frequency changes about 8 kHz when the the temperature changes from 0 ˝ C to 60 ˝ C. Hence, the average temperature sensitivity of the humidity varies from 15 %RH to 95 %RH, and(c) the humidity sensitivity can be calculated as 100 monitoring system is 180 Hz/˝ C. Figure 13b shows that the output frequency changes about 8 kHz Hz/%RH. 12. Transient responses of the to humidity sensors by different filter filmscan before and when theFigure humidity varies from 15 %RH %RH, andcovered the humidity sensitivity be calculated The pressure characterization of the 95 passive wireless monitoring system was measured by the as after 600 h paint mist contamination, (a) AAO/PTFE film; (b) PTFE film; and (c) polyvinylidene 100 Hz/%RH. GY-600 pressure chamber (made by XiangHe, GuoRuiZhi Test Equipment Co., Ltd., Beijing, China). fluoride (PVDF) film. The pressure characterization of the passive wireless monitoring system was in measured by the The measured relationship between the pressure and the output frequency is shown Figure 13c. The variationchamber of and the output frequency is aboutGuoRuiZhi 21 kHz when theEquipment pressure changes fromBeijing, 600 hPa China). to GY-600 pressure (made by XiangHe, Test Co., Ltd., 4. Measurement Demonstration 1100 hPa. So the pressure between sensitivitythe of the monitoring is 42 Hz/hPa. The measured relationship pressure and system the output frequency is shown in Figure 13c. By using the OMEGA205 C340 temperature and humidity chamber (made by Vötsch The variation of the output frequency is about 21 kHz when the pressure changes from 600 hPa to Industrietechnik), the temperature and humidity characterizations of the passive wireless monitoring 1100 system hPa. Sowere the measured. pressure sensitivity of the thevariation monitoring system 42 Hz/hPa. In Figure 13a, of the outputisfrequency is about 11 kHz when the The passive wireless transmission distance of the monitoring system was also The test temperature changes from 0 °C to 60 °C. Hence, the average temperature sensitivity of measured. the monitoring platform as iswell the measurement result shown infrequency Figure 14.changes Whenabout the distance between system 180 as Hz/°C. Figure 13b shows thatisthe output 8 kHz when the the humidityand varies 15 %RH to 95 %RH, the humidity canisbestill calculated as properly. 100 transponder thefrom reader reaches 4 cm, theand output signal ofsensitivity the reader working Hz/%RH. Under fixed inductor size and input power, adjusting the resonant frequency of the transponder and pressure characterization of thecould passive monitoring was measured by distance. the the readerThe to the carrier signal frequency be wireless an efficient way tosystem increase the telemetry GY-600 pressure chamber (made by XiangHe, GuoRuiZhi Test Equipment Co., Ltd., Beijing, China). Because the wall of the spray painting workshop is made of glass, the effect of glass in the distance The measured relationship between the pressure and the output frequency is shown in Figure 13c. measurement needs to be considered. However, the measurement result shows that glass has no The variation of the output frequency is about 21 kHz when the pressure changes from 600 hPa to influence on the passive wireless sensing distance. 1100 hPa. So the pressure sensitivity of the monitoring system is 42 Hz/hPa. (a)

(b)

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(b) Figure 13. Cont.

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(c) Figure 13. Output frequency versus (a) temperature; (b) humidity; (c) pressure.

The passive wireless transmission distance of the monitoring system was also measured. The test platform as well as the measurement result is shown in Figure 14. When the distance between the transponder and the reader reaches 4 cm, the output signal of the reader is still working properly. Under fixed inductor size and input power, adjusting the resonant frequency of the transponder and the reader to the carrier signal frequency could be an efficient way to increase the telemetry distance. Because the wall of the spray painting workshop is(c) made of glass, the effect of glass in the distance measurement needsFigure to be13. considered. However, the measurement result shows that glass has no Output frequency versus (a) temperature; (b) humidity; (c) pressure. Figure 13. Output sensing frequency versus (a) temperature; (b) humidity; (c) pressure. influence on the passive wireless distance. The passive wireless transmission distance of the monitoring system was also measured. The test platform as well as the measurement result is shown in Figure 14. When the distance between the transponder and the reader reaches 4 cm, the output signal of the reader is still working properly. Under fixed inductor size and input power, adjusting the resonant frequency of the transponder and the reader to the carrier signal frequency could be an efficient way to increase the telemetry distance. Because the wall of the spray painting workshop is made of glass, the effect of glass in the distance measurement needs to be considered. However, the measurement result shows that glass has no influence on the passive wireless sensing distance.

Figure 14.14. Measurement of of passive wireless transmission distance. This ruler shows thethe passive Figure Measurement passive wireless transmission distance. This ruler shows passive wireless transmission distance between the transponder and the reader reaches 4 cm. wireless transmission distance between the transponder and the reader reaches 4 cm.

After the measurement, the passive wireless hermetic environment monitoring system is After the measurement, the passive wireless hermetic environment monitoring system is installed installed on the glass wall of the spray painting workshop for demonstration. Figure 15a is the on the glass wall of the spray painting workshop for demonstration. Figure 15a is the photograph of photograph of the transponder and reader installed on the glass wall of the spray painting workshop. the transponder and reader installed on wireless the glass wall of the spray This painting workshop. The one with Figure 14. Measurement of passive transmission distance. ruler shows passive The one with porous cap inside the glass wall is the transponder, which monitors thetheenvironmental porous cap insidetransmission the glass distance wall is the transponder, which monitors the environmental parameters of wireless between the transponder and the reader reaches 4 cm. parameters of the spray painting workshop, and the one directly facing the transponder outside the the spray painting workshop, and the one directly facing the transponder outside the glass wall is the glass wall is the reader, which receives data from the transponder and at the same time provides Afterreceives the measurement, the transponder passive wireless environment monitoring reader, which data from the andhermetic at the same time provides powersystem for it. is power for it. installed on the glass wall of the spray painting workshop for demonstration. Figure 15a is the data Figure 15b is a screenshot of the monitoring software, which could display both real-time photograph of the transponder and reader installed on the glass wall of the spray painting workshop. and historical records of the passive wireless monitoring system. Output results of four monitoring The one with porous cap inside the glass wall is the transponder, which monitors the environmental systems are shown on the screen at the same time. Among them, No. 1 and No. 2 monitoring systems parameters of the spray painting workshop, and the one directly facing the transponder outside the are installed in isone No.receives 3 and No. are inthe another room.and at the same time provides glass wall theroom, reader,and which data4 from transponder power for it.

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Figure 15b is a screenshot of the monitoring software, which could display both real-time data and historical records of the passive wireless monitoring system. Output results of four monitoring systems are16,shown Sensors 2016, 1207 on the screen at the same time. Among them, No. 1 and No. 2 monitoring systems 12 of 14 are installed in one room, and No. 3 and No. 4 are in another room.

(a)

(b) Figure 15. 15. Demonstration Demonstration of the monitoring monitoring systems systems in in spray spray painting painting workshop workshop (a) (a) Installation Installation of of Figure of the the transponder and reader on the glass wall of the spray painting workshop; (b) A screenshot of the the transponder and reader on the glass wall of the spray painting workshop; (b) A screenshot of the monitoring software software showing showing both both real-time real-time data data and and history history records. records. monitoring

5. Conclusions 5. Conclusions A passive wireless hermetic environment monitoring system was designed, fabricated and A passive wireless hermetic environment monitoring system was designed, fabricated and demonstrated for the spray painting workshop. The proposed system is composed of a transponder demonstrated for the spray painting workshop. The proposed system is composed of a transponder and a reader, and circuit design of each part is given in detail. Because the spray painting workshop and a reader, and circuit design of each part is given in detail. Because the spray painting workshop contains a large amount of paint mist, the package of the transponder was designed carefully. Three contains a large amount of paint mist, the package of the transponder was designed carefully. different filter films for the package were compared. The experimental results show that the Three different filter films for the package were compared. The experimental results show that composite filter film AAO/PTFE has the minimum pollution and the smallest change of water vapor the composite filter film AAO/PTFE has the minimum pollution and the smallest change of water flux. After fabrication, the temperature, humidity and pressure characterizations and the remote vapor flux. After fabrication, the temperature, humidity and pressure characterizations and the remote sensing distance of the monitoring system were measured. Finally, the passive wireless hermetic sensing distance of the monitoring system were measured. Finally, the passive wireless hermetic environment monitoring system was installed on the glass wall of the spray painting workshop and environment monitoring system was installed on the glass wall of the spray painting workshop and was successfully demonstrated. was successfully demonstrated. Acknowledgments: This work is supported by the National Natural Science Foundation of China (61401084, 61136006) and the National High Technology Research and Development Program of China (2015AA042602). Author Contributions: Lifeng Wang and Qing-An Huang conceived and designed the monitoring system; Yan Huang and Dan Tang designed the circuits and did the measurements; Jingjing Ma designed and fabricated the package; Lifeng Wang, Jingjing Ma and Yan Huang did the demonstration; Lifeng Wang wrote the paper. Conflicts of Interest: The authors declare no conflict of interest.

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