Compact Sensor Array Research Articles

Multiplexed Piezoelectric Electronic Skin with Haptic Feedback for Upper Limb Prosthesis

AbstractUpper limb amputation severely impairs tactile perception, limiting daily activities. Developing a near‐natural replacement with prosthetic devices requires improving user sensory experiences during object interactions. The ideal upper limb prosthesis should provide real‐time sensory feedback, mirroring natural experiences. Current prostheses struggle with providing adequate tactile feedback due to sensory limitations. Inspired by the sensory properties of skin, we present a micro‐fabricated, multiplexed electronic skin (e‐skin) with actuators for sensory feedback in upper limb amputation. The piezoelectric‐capacitive sensor array detects static pressure, temperature, vibration, and texture, with integrated actuators stimulating the skin to provide real‐time feedback. The sensors integrate with actuators via readout electronics, making the system standalone and easy to use. The flexible, compact sensor array design (two pixels within a 1 cm² footprint) detects a wide range of pressure (0.5–10 kPa), temperature (22–60 °C), vibration (35–100 Hz), and texture (2.5–45 Hz), suitable for daily use. The e‐skin, attached to a prosthetic finger, is tested for feasibility on human volunteers with wrist‐mounted actuators. Statistics are used to quantitatively assess system performance. The integration of multiplexed sensors and actuators enhances tactile feedback, improving the quality of life for people with upper limb amputations.

Stable organic self-assembled microwire lasers for chemical vapor sensing

Organic microlasers hold great potentials in fabricating on-chip sensors for integrated photonic circuits due to their chemical versatility and reactivity. However, chemical vapor detection is still challenging for organic microlaser sensors, as it requires not only optical gain and self-assembly capability, but also rapid response to stimuli and long-term stability under high excitation power. In this work, a new laser dye 4,7-bis(9-octyl-7-(4-(octyloxy)phenyl)-9H-carbazol-2-yl)benzo[c][1,2,5]thiadiazole (BPCBT) is designed and synthesized, which self-assembles into microwires showing strong intramolecular charge transfer (ICT) photoluminescence with >80% quantum efficiency. It enables the lasing from BPCBT microwires under a low threshold of 16 μJ·mm−2·pulse−1 with significantly improved stability over conventional organic microlasers. The stimulated emission amplifies the fluorescence change in the BPCBT microwires under chemical vapors including various acid, acetone, and ethanol vapors, indicating high sensitivity and high selectivity of organic microlaser sensors desirable for compact sensor arrays in integrated photonics.

A novel multi-site damage localization method based on near-field signal subspace fitting using uniform linear sensor array

Damage diagnose imaging methods based on guided waves have been widely developed to depict the position and area of damage in structural health monitoring (SHM). Among them, compact sensor array based imaging methods have been gradually applied with high accuracy, such as phased array imaging, spatial filter imaging, multiple signal classification imaging and so on. However, when the multi-site damage appears nearly, the performance of these methods usually degrades. On one hand, limited to the array aperture, traditional methods cannot distinguish adjacent damage sites. On another hand, some subspace decomposition based methods also fail, suffering from the correlation between scattered array signals from different damage sites. To realize localization of multi-site damage, a novel near-field signal subspace fitting based multi-site damage localization method is proposed in this paper. This method constructs the cost function, which describe the equivalence relation between the signal subspace and array manifold matrix. Then localization of multi-site damage could be realized through multidimensional search for the optimization of cost function. The proposed method is verified on the aluminum panel with 3 damage sites. Experimental results show that the proposed method can realize multi-site damage localization with the angle errors less than 4° and the distance errors less than 35 mm.

Selective Detection of Formaldehyde By a Flame-Made Sensor Array for Environmental Monitoring

Introduction Formaldehyde is a carcinogenic pollutant omnipresent in indoor air due to emission from wood-based furniture, textiles, and paints [1]. But it is formed also outdoors from biofuel combustion, forest fires and photooxidation of smog [2]. Therefore, its exposure is strictly regulated worldwide (e.g., World Health Organization < 80 ppb for short-term exposure). However, reliable and portable devices for on-site monitoring do not exist. Currently, formaldehyde emission testing is carried out by sampling via sorption tubes and subsequent off-site laboratory analysis by gas chromatography. This is expensive, time-consuming, and thus not applicable for distributed indoor air quality monitoring or personal exposure assessment. Chemical sensors are promising for these applications as they are compact, low-cost and simple-in-use. Current sensors, however, typically fail to fulfill the necessary sensitivity and selectivity requirements to detect relevant formaldehyde concentrations below 100 parts per billion (ppb) in ambient air, which contains hundreds of interfering compounds. Here, we present a highly sensitive, selective and compact sensor array of flame-made metal-oxide sensors for real-time quantification of formaldehyde at 90% relative humidity (RH) in gas mixtures. Method Sensing nanoparticles of Pt-, Si-, Pd- and Ti-doped SnO2 are produced by flame-spray pyrolysis and directly deposited onto microsensor substrates by thermophoresis. The individual sensors are assembled to an array (E-nose) by wire-bonding them on a leadless chip carrier, which is placed inside a Teflon sensor chamber. Sensing films are heated to 400 °C with a Pt back heater and the E-nose is characterized in synthetic gas mixtures with a gas mixing setup at 90% RH [3]. The E-nose is tested in gas mixtures containing formaldehyde, acetone, ammonia and ethanol and a multilinear linear regression model is applied to obtain individual analyte concentrations [4]. Results and Conclusions The E-nose consists of four nanostructured and highly porous Pt-, Si-, Pd- and Ti-doped SnO2 sensing films precisely deposited onto silicon wafer-based microsubstrates by flame spray pyrolysis (Figure 1a, b). Flame-made sensing particles are deposited (black patterns) within the designated area of the interdigitated electrodes, while the heater and electrode pads are shielded by the shadow mask and not contaminated by particles. This technique is scalable and be readily applied to wafer-level processing (69 sensors in a single step [5]).The individual sensors offer a sensing film consisting of a highly porous and nanostructured network of nanoparticles (Figure 1b). As a result, they are highly sensitive for formaldehyde concentrations <10 ppb even at 90% RH with fast response dynamics (response time 140 s) as shown in Figure 2. Even concentrations as low as 5 ppb are detected with high signal-to-noise ratio >25. Each dopant induces different analyte selectivity, enabling selective detection of formaldehyde in gas mixtures by multivariate linear regression. We apply this for formaldehyde detection in complex gas mixtures of formaldehyde, acetone, NH3, and ethanol at realistic concentrations and humidity. Formaldehyde is thereby detected with an average error of ≤9 pbb at concentrations 30–180 ppb despite the much higher concentrated interferants.As a result, based on its compact size and low price, this device is promising for monitoring of formaldehyde in indoor and outdoor air. When interconnected, such next-generation low-cost detectors could enable distributed chemical recognition [6] for air quality in “smart” buildings and “future” cities.

Coprime Sensing via Chinese Remaindering Over Quadratic Fields—Part II: Generalizations and Applications

The practical application of a new class of coprime arrays based on the Chinese remainder theorem (CRT) over quadratic fields is presented in this paper. The proposed CRT arrays are constructed by ideal lattices embedded from coprime quadratic integers. The geometrical constructions and theoretical foundations were discussed in the accompanying paper in great detail, while this paper focuses on aspects of the application of the proposed arrays in two-dimensional (2D) remote sensing. A generalization of CRT arrays based on two or more pairwise coprime ideal lattices is proposed with closed-form expressions on sensor locations, the total number of sensors and the achievable DOF. The issues pertaining to the coprimality of any two quadratic integers are also addressed to explore all possible ideal lattices. Exploiting the symmetry of lattices, sensor reduction methods are discussed with the coarray remaining intact for economic maximization. In order to extend conventional angle estimation techniques based on uniformly distributed arrays to the method that can exploit any coarray configurations based on lattices, this paper introduces a hexagon-to-rectangular transformation to 2D spatial smoothing, providing the possibility of finding more compact sensor arrays. Examples are provided to verify the feasibility of the proposed methods.

Magnetoencephalography with a Cs-based high-sensitivity compact atomic magnetometer.

In recent years, substantial progress has been made in developing a new generation of magnetoencephalography (MEG) with a spin-exchange relaxation free (SERF)-based atomic magnetometer (AM). An AM employs alkali atoms to detect weak magnetic fields. A compact AM array with high sensitivity is crucial to the design; however, most proposed compact AMs are potassium (K)- or rubidium (Rb)-based with single beam configurations. In the present study, a pump-probe two beam configuration with a Cesium (Cs)-based AM (Cs-AM) is introduced to detect human neuronal magnetic fields. The length of the vapor cell is 4 mm, which can fully satisfy the need of designing a compact sensor array. Compared with state-of-the-art compact AMs, our new Cs-AM has two advantages. First, it can be operated in a SERF regime, requiring much lower heating temperature, which benefits the sensor with a closer distance to scalp due to ease of thermal insulation and less electric heating noise interference. Second, the two-beam configuration in the design can achieve higher sensitivity. It is free of magnetic modulation, which is necessary in one-beam AMs; however, such modulation may cause other interference in multi-channel circumstances. In the frequency band between 10 Hz and 30 Hz, the noise level of the proposed Cs-AM is approximately 10 f T/Hz1/2, which is comparable with state-of-the-art K- or Rb-based compact AMs. The performance of the Cs-AM was verified by measuring human auditory evoked fields (AEFs) in reference to commercial superconducting quantum interference device (SQUID) channels. By using a Cs-AM, we observed a clear peak in AEFs around 100 ms (M100) with a much larger amplitude compared with that of a SQUID, and the temporal profiles of the two devices were in good agreement. The results indicate the possibility of using the compact Cs-AM for MEG recordings, and the current Cs-AM has the potential to be designed for multi-sensor arrays and gradiometers for future neuroscience studies.

Polar coastal soundscapes: Tridimensional mapping of benthic biophony and ice geophony with a compact sensor array

Polar areas show fast changes linked to global warming. The reduction of the ice pack and the melting of the ice sheet modify the conditions of living of marine fauna. We propose the simultaneous monitoring of the ice and benthic fauna using passive acoustics. Thanks to a compact sensor array of 4 hydrophones (2m*2m*2m), we detected, localized and mapped in three dimensions ({azimuth, elevation} or {x, y, z}) the biophonic and geophonic contributions made up of short and wideband pulses. Tridimensional maps of benthic biophony and ice geophony of Antarctic and Arctic 7 days-long recording sessions (2015, 2016) are built and analyzed over a surface of the order of 1 km2. Benthic invertebrates emit high energetic pulses with peak frequencies ranging from 2 to 55 kHz, most of them below 15 kHz. Geophony is structured into two parts. The ice sheet, located several kilometers or tens of kilometers away, creates a stable spatial distribution of low energetic pulses (representing the majority of pulses in the soundscape) modulated by the temporal variability. The movements of isolated icebergs or pack ice produce localized acoustic events identifiable by the high sound levels and the stable peak frequencies of the emitted pulses.

High-Accuracy Reference-Free Ultrasonic Location Estimation

This paper presents a novel reference-free ultrasonic indoor location system. Unlike most previous proposals, the mobile device (MD) determines its own position based only on ultrasonic signals received at a compact sensor array and sent by a fixed independent beacon. No radio frequency or wired timing reference signal is used. Furthermore, the system is privacy aware and one way in that the receive-only MD determines its own position based on ultrasonic signals received from fixed transmit-only beacons. The MD uses a novel hybrid angle of arrival (AoA)-time of flight (ToF) with timing lock algorithm to determine its location relative to the beacons with high accuracy. The algorithm utilizes an AoA-based location method to obtain an initial estimate of its own location. Based on this, it estimates the timing offsets (TOs) between the MD clock and the beacon transmissions. The average TO and the known periodicities of the beacon signals are then used to obtain a second more accurate MD location estimate via a ToF method. The system utilizes wideband spread spectrum ultrasonic signaling in order to achieve a high update rate and robustness to noise and reverberation. A prototype system was constructed, and the algorithm was implemented in software. The experimental results show that the method provides 3-D accuracy better than 9.5 cm in 99% of cases, an 80% accuracy improvement over the conventional AoA-only method.

A compact sensor array for blind separation of sources

Discusses the separation of N source signals recorded simultaneously by M (M/spl ges/N) receivers. To solve this cocktail party problem, the authors propose to collect a set of microphones making up an array with a few centimeters in diameter. On each sensor, signals are received with different time delays. The linear memoryless conventional model for source separation is then not suitable. However, when time delays are small in comparison to the coherence time of each source, the authors show that this problem can be simplified building up a particular set of instantaneous mixtures involving derivatives of sources with respect to time. Sources can then be extracted using an adapted second-order method. When more microphones than sources are available, it is shown how to deal with noisy mixtures. The validity of the proposed approach is confirmed by computer simulations. Finally, the method is applied to an experiment where two-source signals are extracted from their mixtures observed with two omnidirectional microphones in a normal room.