With Industry 4.0 becoming increasingly pervasive, the importance and usage of sensors has increased several folds. Industry 4.0 refers to a new phase in the industrial revolution that mainly focuses on interconnectivity, automation, machine learning, and real-time data. Real-time structural health monitoring (SHM) of components in the industrial process is one of the crucial and important component of Industry 4.0. SHM of components exposed to high-temperature ( $\sim 650^{\circ }\text{C}$ ) is becoming increasingly important nowadays. However, harsh and high temperature environments impose a great challenge towards their implementation. This review is an attempt to demonstrate the development, application, limitations and recent advancement of the existing sensors used for SHM. Some sensors such as eddy current (EC) sensors and fiber Bragg grating (FBG) sensors have been discussed in detail. A phenomenological study of the electromagnetic sensor for the SHM of engineering components that are exposed to high temperature has been addressed. State-of-the-art fabrication methodologies such as low temperature co-fired ceramic (LTCC) technology for such type of sensors for high temperature SHM applications have been elucidated. Future challenges and opportunities for SHM applications of high temperature sensors have been highlighted.

Recent Advancements in the Development of Sensors for the Structural Health Monitoring (SHM) at High-Temperature Environment: A Review

Efficient extraction of Rb+ and Cs+ by a precipitation flotation process with ammonium phosphowolframate as precipitant

This brief presents a resistor-based CMOS temperature sensor with a duty-cycle-modulated output. A dynamic-biased resistive analog front-end (AFE) is proposed to generate voltages with positive and negative temperature dependencies. The voltages are then converted into a digital-friendly duty-cycle-modulated output, which can be proceeded by digital systems directly. Fabricated in a standard 0.13- $\mu \text{m}$ CMOS process, this sensor occupies a silicon area of 0.025 mm2 and can operate with a supply voltage as low as 0.8 V. It has a measured inaccuracy of ±0.85 °C ( $3\sigma $ ) from −40 °C to 85 °C after a two-point calibration. Measured at room temperature, it shows a resolution of 0.226 °C in a 0.25-ms conversion time while dissipating 12.5 $\mu \text{W}$ .

A Dynamic-Biased Resistor-Based CMOS Temperature Sensor With a Duty-Cycle-Modulated Output

It is common in the field of printed electronics that polydimethylsiloxane (PDMS) be used as a dielectric layer for capacitive sensors because of its high elasticity and restoration force. However, capacitive sensors with the PDMS dielectric layer have a lower sensitivity than those with an air-gap structure that has been fabricated by the conventional micro-electromechanical system (MEMS) process. This paper presents a productive method for fabricating air-gap structures for touch sensors by roll-to-roll slot-die coating. The air-gap is formed by coating and removing a sacrificial layer. Cantilever-structured capacitive touch sensors with an air-gap are fabricated as follows: First, the bottom electrode, the dielectric layer, and the poly(vinyl alcohol) (PVA) sacrificial layer are roll-to-roll slot-die-coated on a flexible substrate. In addition, the spacer layer is spin-coated. On the sacrificial and spacer layers, the top electrode and structural layer are formed by spin-coating. Then, the air-gap and cantilever structure are made by removing the sacrificial layer in water. The cantilever-structured sensor samples are examined in terms of sensitivity, hysteresis, and repeatability. In particular, the electrical performance of the samples is compared to those with the PDMS dielectric layer. Experimental results show that the cantilever-structured sensor samples have significantly higher sensitivity compared to those with the PDMS dielectric layer.

Fabrication and Characterization of Roll-to-Roll-Coated Cantilever-Structured Touch Sensors.

This paper presents a second-order discrete-time Sigma-Delta (SD) Analog-to-Digital Converter (ADC) with over 80 dB Signal to Noise Ratio (SNR), which is applied in a signal conditioning IC for automotive piezo-resistive pressure sensors. To reduce the flicker noise of the structure, choppers are used in every stage of the high gain amplifiers. Besides, to reduce the required area and power, only the CIC filter structure is adopted as a decimation filter. This filter has a configurable structure that can be applied to different data rates and input signal bandwidths. The proposed ADC was fabricated and measured in a 0.18-µm CMOS process. Due to the application of only a CIC filter, the total active area of the SD-ADC and reference generator is 0.49 mm2 where the area of the decimation filter is only 0.075 mm2. For the input signal bandwidth of 1.22 kHz, it achieved over 80 dB SNR in a 2.5 MHz sampling frequency while consuming 646 µW power.

A Sigma-Delta ADC for Signal Conditioning IC of Automotive Piezo-Resistive Pressure Sensors with over 80 dB SNR

In engineering practice, instruments, such as accelerometer and laser interferometer, are widely used in vibration measurement of structural parts. A method for using a triaxial fluxgate magnetometer as a microvibration sensor to measure low-frequency pendulum microvibration (not translational vibration) is proposed in this paper, so as to detect vibration from low-frequency vibration sources, such as large rotating machine, large engineering structure, earthquake, and microtremor. This method provides vibration detection based on the environmental magnetic field signal to avoid increased measurement difficulty and error due to different relative positions of permanent magnet and magnetometer on the device under test (DUT) when using the original magnetic measurement method. After fixedly connecting the fluxgate probe with the DUT during the test, the angular displacement due to vibration can be deduced by measuring the geomagnetic field’s magnetic induction intensity change on the orthogonal three components during the vibration. The test shows that the microvibration sensor has angular resolution of over 0.05° and maximum measuring frequency of 64 Hz. As an exploring test aimed to detect the microvibration of earth-orbiting satellite in the in-orbit process, the simulation experiment successfully provides the real-time microvibration information for attitude and orbit control subsystem.

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Digital Fluxgate Magnetometer for Detection of Microvibration

The invention discloses a chip-level atomic clock air chamber and a manufacturing method thereof An SOI silicon chip is used, a cavity is manufactured on a silicon layer used as a substrate and is used for placing of alkali metal and inflating of inert gas, glass is used for sealing the cavity, finally supporting materials are arranged on one side of a silicon layer used as a device layer to protect a device, and accordingly manufacturing of the high-stability chip-level atomic clock air chamber is completed Only by one-time key static bonding, manufacturing of the atomic clock air chamber can be completed, the problem of bad stability due to poor static bonding quality is avoided, and finished product rate is improved The air chamber is simple and reasonable in structure, so that the manufactured air chamber is small in size, easy to use, low in manufacturing cost and suitable for industrial production

Chip-level atomic clock air chamber and manufacturing method thereof

A scalable decimation filter ASIC for high resolution digital magnetometer with sigma-delta modulator feedback loop

The invention discloses a low-power-consumption chip level atomic clock physical packaging device which comprises an external package, an upper support, a lower support, a frame space device and an internal element. The external package is composed of a ceramic package body and a base. The internal element comprises a laser, a photoelectric detector, an alkaline atom bubble air chamber, a 1/4 wave plate and a C-field bias module. The C-field bias module comprises a permanent magnet assembly which generates a magnetic field in the physical packaging axial direction. The magnetic field generated by a permanent magnet can totally or partially replace a magnetic field generated by a coil in original chip level atomic clock physical packaging, currents flowing through the coil can be minimum, and therefore energy consumption of chip level atomic clock packaging can be greatly reduced.

Low-power-consumption chip level atomic clock physical packaging device

High order ΣΔ interface is a practical choice for high resolution MEMS sensors. Previous researches are mainly about the determination of the coefficients of multiple feedback ΣΔ interfaces. In the work presented here, a systematic method for the design of feed forward ΣΔ interface is proposed. Simulations show that the utilizing the proposed method, feed forward method and the traditional multiple feedback structures have almost the same peak SQNRs when a compensator pole is added to the feed forward structure. However, feed forward structure has many advantages, so the proposed method is a promising alternative method for the multiple feedback structure.

Donghai Qiao

Papers

Digital Fluxgate Magnetometer for Detection of Microvibration

Chip-level atomic clock air chamber and manufacturing method thereof

A scalable decimation filter ASIC for high resolution digital magnetometer with sigma-delta modulator feedback loop

Low-power-consumption chip level atomic clock physical packaging device

Design of feed-forward ΣΔ interface for MEMS based accelerometers