Electronic technique and circuit topology for accurate distance-independent contactless readout of passive LC sensors

Demori, Marco; Baù, Marco; Ferrari, Maurizio; Ferrari, Vittorio

doi:10.1016/j.aeue.2018.05.019

Cited by 27 publications

(18 citation statements)

References 13 publications

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“…As discussed in [ 23 ], with C P ≠ 0, Equation (16) no longer allows extraction of f S and Q S independently from the coupling factor k , which now is in the expression of Z 1P and affects Re{ Z 1P }, not only as a scaling factor. In particular, it has been shown by a numerical analysis of Equation (16) that Re{ Z 1P } has two maxima, corresponding, respectively, to a primary resonance near f S and a secondary resonance near

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Section: Analysis Of the Interrogation Techniquesmentioning

confidence: 99%

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Interrogation Techniques and Interface Circuits for Coil-Coupled Passive Sensors

et al. 2018

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Coil-coupled passive sensors can be interrogated without contact, exploiting the magnetic coupling between two coils forming a telemetric proximity link. A primary coil connected to the interface circuit forms the readout unit, while a passive sensor connected to a secondary coil forms the sensor unit. This work is focused on the interrogation of sensor units based on resonance, denoted as resonant sensor units, in which the readout signals are the resonant frequency and, possibly, the quality factor. Specifically, capacitive and electromechanical piezoelectric resonator sensor units are considered. Two interrogation techniques, namely a frequency-domain technique and a time-domain technique, have been analyzed, that are theoretically independent of the coupling between the coils which, in turn, ensure that the sensor readings are not affected by the interrogation distance. However, it is shown that the unavoidable parasitic capacitance in parallel to the readout coil introduces, for both techniques, an undesired dependence of the readings on the interrogation distance. This effect is especially marked for capacitance sensor units. A compensation circuit is innovatively proposed to counteract the effects of the parasitic input capacitance, and advantageously obtain distance-independent readings in real operating conditions. Experimental tests on a coil-coupled capacitance sensor with resonance at 5.45 MHz have shown a deviation within 1.5 kHz, i.e., 300 ppm, for interrogation distances of up to 18 mm. For the same distance range, with a coil-coupled quartz crystal resonator with a mechanical resonant frequency of 4.432 MHz, variations of less than 1.8 Hz, i.e., 0.5 ppm, have been obtained.

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.…”

Section: Analysis Of the Interrogation Techniquesmentioning

confidence: 99%

“…One of the challenges of the contactless readout of passive sensors is to adopt reading techniques independent of the coupling between the primary and secondary coils [ 20 , 23 ]. This, in turn, would ensure that the readings are not affected by the interrogation distance.…”

Section: Introductionmentioning

confidence: 99%

Interrogation Techniques and Interface Circuits for Coil-Coupled Passive Sensors

et al. 2018

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“…Approaches theoretically independent of the distance have been proposed both in the time-domain [3,4] and in the frequency-domain [2]. In the latter case, measuring the real part of the impedance at the readout coil allows to obtain the resonant frequency and the quality factor of the LC sensor [5,6]. The present work investigates on the limitations of such technique when considering unavoidable parasitic capacitances in parallel to the readout coil due to the connected electronics and cables.…”

Section: Introductionmentioning

confidence: 99%

Contactless Readout of Passive LC Sensors with Compensation Circuit for Distance-Independent Measurements

et al. 2018

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Contactless readout of passive LC sensors composed of a capacitance sensor connected to a coil can be performed through an electromagnetically coupled readout coil set at distance d. Resonant frequency fs and Q-factor QS of the LC sensor can be extracted from the measurement of the impedance at the readout coil by using a technique theoretically independent of d. This work investigates the effects on the measurement accuracy due to the unavoidable parasitic capacitance CP in parallel to the readout coil, which makes the measured values of fs and QS dependent on d. Numerical analysis and experimental tests confirm such dependence. To overcome this limitation, a novel electronic circuit topology for the compensation of CP is proposed. The experimental results on assembled prototypes show that for a LC sensor with fs ≈ 5.48 MHz a variation of less than 200 ppm across an interrogation distance between 2 and 18 mm is achieved with the proposed compensation circuit.

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“…Similarly, contactless interrogation can be achieved through an electromagnetic link between two coupled coils [17,18]. In [19][20][21][22], a primary coil is connected to the interrogation circuit, while a secondary coil is connected to a resonant sensor; i.e., a mechanical resonator such as a quartz crystal microbalance (QCM), a micro electro-mechanical system (MEMS) or an electrical resonant sensor such as an LC-tank circuit. The measurement principle can exploit both frequency-domain and time-domain techniques [21,22].…”

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confidence: 99%

“…In [19][20][21][22], a primary coil is connected to the interrogation circuit, while a secondary coil is connected to a resonant sensor; i.e., a mechanical resonator such as a quartz crystal microbalance (QCM), a micro electro-mechanical system (MEMS) or an electrical resonant sensor such as an LC-tank circuit. The measurement principle can exploit both frequency-domain and time-domain techniques [21,22]. This approach relies on completely passive sensors; i.e., they do not require any active electronic circuits on board to operate.A different approach exploits RFID technologies in the low frequency (LF), high frequency (HF) and ultra-high frequency (UHF) ranges [23].…”

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Low-Frequency RFID Signal and Power Transfer Circuitry for Capacitive and Resistive Mixed Sensor Array

et al. 2019

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This paper presents a contactless measurement system for a mixed array of resistive and capacitive sensors exploiting a low-frequency radio-frequency identification (RFID)-based approach. The system is composed of a reader unit which provides power to and exchanges measurement data with a battery-less sensor unit. The sensor unit is based on a transponder operating at 134.2 kHz and a microcontroller. The microcontroller sequentially measures the elements of the sensor array composed of n capacitive and m resistive sensors which share a common terminal. The adopted technique measures the charging time of a resistor–capacitor (RC) circuit, where the resistor or the capacitor can be either the sensing element or a reference component. With the proposed approach, the measured values of the resistive or capacitive elements of the sensor array are first-order independent from the supply voltage level. A prototype has been developed and experimentally tested with resistive elements in the range 400 kΩ–1.2 MΩ and capacitive elements in the range 200 pF–1.2 nF showing measurement resolution values of 1 kΩ and 5 pF, respectively. Operative distances up to 3 cm have been achieved, with readings taken faster than one element of the array per second.

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Electronic technique and circuit topology for accurate distance-independent contactless readout of passive LC sensors

Cited by 27 publications

References 13 publications

Interrogation Techniques and Interface Circuits for Coil-Coupled Passive Sensors

Interrogation Techniques and Interface Circuits for Coil-Coupled Passive Sensors

Contactless Readout of Passive LC Sensors with Compensation Circuit for Distance-Independent Measurements

Low-Frequency RFID Signal and Power Transfer Circuitry for Capacitive and Resistive Mixed Sensor Array

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