Spiking Chemical Sensor (SCS): A new platform for neuro-chemical sensing

Published versio

Towards a Reconfigurable Sense-and-Stimulate Neural Interface Generating Biphasic Interleaved Stimulus

Published versio

Pressure stimulated currents in rocks and their correlation with mechanical properties

The spontaneous electrification of marble samples was studied while they were subjected to uniaxial stress. The Pressure Stimulated Current (PSC) technique was applied to measure the charge released from compressed Dionysos marble samples, while they were subjected to cyclic loading. The experimental results demonstrate that, in the linear elastic region of the sample, no PSC is recorded, while beyond the stress limit (s>0.60), observable variations appear, which increase considerably in the vicinity of sample failure, reaching a maximum value just before the failure. The emitted current is reduced on each loading cycle and it has a reciprocal dependence to the normalized Young modulus. The MCD model, applied out of the vicinity of sample failure explains successfully the above findings. The existence of a "memory-like" behavior of the sample, could justify the weakness or absence of electrical earthquake precursors, during an aftershock sequence

Piezo stimulated currents in marble samples: precursory and concurrent-with-failure signals

International audienceThe Earth?s electric field transient variations are promising candidates of earthquake precursors. In order to study the physical mechanisms of such precursory signals, laboratory experiments of uniaxial compression were carried out. More specifically the behaviour of stressed marble samples from Penteli Mountain was investigated. The samples were subjected to a time-varying uniaxial compression at both variable and constant stress rates. During the first set of experiments weak electric currents were detected during pressure variations. Such Piezo Stimulated Currents (PSC) were detected while stress steps, both positive and negative were applied, the maximum stress never being greater than the elasticity limit. During the second set of experiments stress was applied at a constant rate starting from zero-stress and ending in fracture. In the region beyond the elastic limit a PSC was detected which after reaching a peak suffered a reversal in its polarity just before fracture. In a third set of experiments the same procedure was applied to previously structurally damaged samples taking care not to fracture them. In all cases the PSC followed the variation of stress and moreover it was observed that a linear relationship existed between the PSC maxima and the corresponding stress-rate maxima. The mechanism responsible for the described phenomena can be ascribed to the Moving Charged Dislocations model

Pressure Stimulated Currents (PSC)in marble samples

The electrical behaviour of marble samples from Penteli Mountain was studied while they were subjected to uniaxial stress. The application of consecutive impulsive variations of uniaxial stress to thirty connatural samples produced Pressure Stimulated Currents (PSC). The linear relationship between the recorded PSC and the applied variation rate was investigated. The main results are the following: as far as the samples were under pressure corresponding to their elastic region, the maximum PSC value obeyed a linear law with respect to pressure variation. In the plastic region deviations were observed which were due to variations of Young s modulus. Furthermore, a special burst form of PSC recordings during failure is presented. The latter is emitted when irregular longitudinal splitting is observed during failure

Correlation of pressure stimulated currents in rocks with the damage parameter

Pressure Stimulated Current (PSC) experiments were conducted on marble samples to correlate PSC with the damage parameter, D. The phenomena and procedures taking place in the vicinity of the fracture limit were observed and analytically described. PSC recordings were conducted by application of uniaxial compressional stress, both at a constant stress rate and at a constant deformation rate. A linear relationship was shown to exist between the emitted PSC and the damage parameter which quantifies the deviation from linear elasticity and the concentration of microcracks

Wavelet analysis on pressure stimulated currents emitted by marble samples

International audienceThis paper presents a wavelet based method of analysis of experimentally recorded weak electric signals from marble specimens which have undergone successive abrupt step loadings. Experimental results verify the existence of "memory effects" in rocks, as far as the current emission is concerned, akin to the "Kaiser effect" in acoustic emissions, which accompany rock fracturing. Macroscopic signal processing shows similarities and differences between the currents emitted during successive loading and wavelet analysis can reveal significant differences between the currents of each loading cycle that contain valuable information for the micro and macro cracks in the specimen as well as information for the remaining strength of the material. Wavelets make possible the time localization of the energy of the electric signal emitted by stressed specimens and can serve as method to differentiate between compressed and uncompressed samples, or to determine the deformation level of specimens

A Phase Error Correction System for Bioimpedance Measurement Circuits

Bioimpedance sensing is widely used across a spectrum of biomedical applications. Among the different system architectures for measuring tissue impedance, synchronous detection or demodulation (SD) stands out for its lock-in amplifier utilising in-phase (I) and quadrature (Q) demodulation signals to derive real and imaginary impedance components. Typically, the current injected into the tissue is controlled by a voltage-controlled current source (VCCS). However, the VCCS can introduce phase shifts leading to discrepancies in real/imaginary outputs, especially at the highest end of the operating frequency bandwidth. Such discrepancies can significantly impact diagnostic accuracy in applications reliant on precise tissue phase profiling, such as cancer and neuromuscular evaluations. In the present work, we propose an automatic phase error compensation stage for bioimpedance measurement systems to minimise this systematic error. Our experimental findings demonstrated a considerable reduction in phase error, with the Phase Error Compensated Synchronous Detection (PECSD) system exhibiting a maximum phase error of 2° (≤5% error) compared with the uncompensated SD system where error exceeded 20%. The improvements made by our proposed SD system hold great potential for enhancing the accuracy of impedance measurements, particularly in clinical diagnosis and disease detection

A 3 MHz Low-Error Adaptive Howland Current Source for High-Frequency Bioimpedance Applications

Bioimpedance is a diagnostic sensing method used in medical applications, ranging from body composition assessment to detecting skin cancer. Commonly, discrete-component (and at times integrated) circuit variants of the Howland Current Source (HCS) topology are employed for injection of an AC current. Ideally, its amplitude should remain within 1% of its nominal value across a frequency range, and that nominal value should be programmable. However, the method’s applicability and accuracy are hindered due to the current amplitude diminishing at frequencies above 100 kHz, with very few designs accomplishing 1 MHz, and only at a single nominal amplitude. This paper presents the design and implementation of an adaptive current source for bioimpedance applications employing automatic gain control (AGC). The “Adaptive Howland Current Source” (AHCS) was experimentally tested, and the results indicate that the design can achieve less than 1% amplitude error for both 1 mA and 100 µA currents for bandwidths up to 3 MHz. Simulations also indicate that the system can be designed to achieve up to 19% noise reduction relative to the most common HCS design. AHCS addresses the need for high bandwidth AC current sources in bioimpedance spectroscopy, offering automatic output current compensation without constant recalibration. The novel structure of AHCS proves crucial in applications requiring higher β-dispersion frequencies exceeding 1 MHz, where greater penetration depths and better cell status assessment can be achieved, e.g., in the detection of skin or breast cancer