Flexible Acoustic Sensor Research Articles

Ultrafast response and highly sensitivity of flexible acoustic sensor based on the controllable hierarchical Nano/Micro-Structure

Flexible and highly sensitive acoustic sensors have become more and more essential for successful military detection. It puts a big barrier for the large-scale production and application. In this work, we have a low-cost and facile approach constructing a hierarchical nano/micro-structure based on the nanosheets of MXene (Ti3C2Tx) and the gold micro-wrinkles on polydimethylsiloxane (PDMS) surface. The period micro-wrinkles can be easily controlled by the thickness of gold layer and the pre-strain on PDMS through the uniaxial stretching method. The formed hierarchical structure can endow the high sensitivity (15 kPa−1 when applied pressure less than 50 Pa), an ultra-fast response time of 15 ms, a minimum detection of 2 Pa, which can achieve the precise acoustic detection of low frequency. Moreover, the flexible sensor also can detect the large pressure about 1000 Pa, and show stable repeatability over 1500 cycles at 400 Pa.

Ultra-Broadband Flexible Thin-Film Sensor for Sound Monitoring and Ultrasonic Diagnosis.

Small-scale and flexible acoustic probes are more desirable for exquisite objects like human bodies and complex-shaped components than conventional rigid ones. Herein, a thin-film flexible acoustic sensor (FA-TES) that can detect ultra-broadband acoustic signals in multiple applications is proposed. The device consists of two thin copper-coated polyvinyl chloride films, which are stimulated by acoustic waves and contact each other to generate the triboelectric signal. Interlocking nanocolumn arrays fabricated on the friction surfaces are regarded as a highly adaptive spacer enabling this device to respond to ultra-broadband acoustic signals (100Hz-4MHz) and enhance sensor sensitivity for film weak vibration. Benefiting from the characteristics of high shape adaptability and ultrawide response range, the FA-TES can precisely sense human physiological sounds and voice (≤10kHz) for laryngeal health monitoring and interaction in real-time. Moreover, the FA-TES flexibly arranged on a 3D-printed vertebra model can effectively and accurately diagnose the inner defect by ultrasonic testing (≥1MHz). It envisions that this work can provide new ideas for flexible acoustic sensor designs and optimize real-time acoustic detections of human bodies and complex components.

A Flexible, Acoustic Localized Sensor with Mass Block-Beam Structure Based on Polydimethylsiloxane-Silver Nanowires.

The flexible strain sensor is a fast-moving technology and has been used in many fields. The array design and application based on flexible strain sensors have been the current research hotspots. However, there are few reports on research of acoustic positioning using the flexible sensor array. Herein, we designed and realized the consistent fabrication of a thin-film, acoustic sensor array. The acoustic sensing research of the sensor was demonstrated as well. We used a convenient fabrication method to design a flexible acoustic sensor using silver nanowires coated on a thin polydimethylsiloxane (PDMS) film with mass block-beam structure. The acoustic sensor can record sound within a frequency domain of 20-2000 Hz and volume detection range of 83-108 dB. The sensor's resonance frequency is 380 Hz, horizontal distance sound detection limit is 5 cm, and vertical detection limit is 3.5 cm. We also achieved 360° azimuth detection in two-dimensional space with a detection accuracy of 15°. In three-dimensional space, the flexible acoustic sensor array was designed with two flexible acoustic sensors to detect the position of the sound source. This research first proposes the use of flexible acoustic sensors to test the sound source orientation.

Design Analysis and Human Tests of Foil-Based Wheezing Monitoring System for Asthma Detection

We present a flexible acoustic sensor that has been designed to detect wheezing (a common symptom of asthma) while attached to the chest of a human. We adopted a parallel-plate capacitive structure using air as the dielectric material. The pressure (acoustic) waves from wheezing vibrate the top diaphragm of the structure, thereby changing the output capacitance. The sensor is designed in such a way that it resonates in the frequency range of wheezing (100–1000 Hz), which presents twofold benefits. The resonance results in large deflection of the diaphragm that eradicates the need for using signal amplifiers (used in microphones). Second, the design itself acts as a low-pass filter to reduce the effect of background noise, which mostly lies in the >1000-Hz frequency range. The resulting analog interface is minimal, and thus consumes less power and occupies less space. The sensor is made up of low-cost sustainable materials (aluminum foil) that greatly reduce the cost and complexity of manufacturing processes. A robust wheezing detection (matched filter) algorithm is used to identify different types of wheezing sounds among the noisy signals originating from the chest that lie in the same frequency range as wheezing. The sensor is connected to a smartphone via Bluetooth, enabling signal processing and further integration into digital medical electronic systems based on the Internet of Things (IoT). Bending, cyclic pressure, heat, and sweat tests are performed on the sensor to evaluate its performance in simulated real-life harsh conditions.

A sensitivity-enhanced flexible acoustic sensor using side-polished fiber Bragg grating

A miniature flexible fiber Bragg grating (FBG) acoustic sensor with enhanced pressure sensitivity was fabricated by using a side-polished configuration of ∼54 μm depth and ∼15 mm length. The photoelectromechanical response of the sensor suspended as a dual-end-fixed beam was characterized based on the acoustic-induced strain interaction with fiber gratings. The opto-mechanical response of the sensor to bending strain was firstly investigated and exhibited about 11 times larger in wavelength shift, in comparison with a conventional bare FBG. Then acoustic testing demonstrated an acoustic pressure-induced wavelength shift of 0.041 nm/Pa and a noise equivalent acoustic signal level of ∼1.66 mPa/Hz1/2 in the frequency region around 2.5 kHz. Also, a relative flat frequency response with a fluctuation of less than 12.9 dB was achieved in the measurement between 400 Hz and 20 kHz, which is in well agreement with the result obtained by a reference condenser microphone. Along with strain-sensitive nanomaterials, the use of the side-polished FBG could be further extended for highly sensitive acousto-ultrasonic sensors in structural health monitoring and wearable applications.

Direction of Arrival Estimation and Localization Using Acoustic Sensor Arrays

Sound source localization has numerous applications such as detection and localization of mechanical or structural failures in vehicles and buildings or bridges, security systems, collision avoidance, and robotic vision. The paper presents the design of an anechoic chamber, sensor arrays and an analysis of how the data acquired from the sensors could be used for sound source localization and object detection. An anechoic chamber is designed to create a clean environment which isolates the experiment from external noises and reverberation echoes. An FPGA based data acquisition system is developed for a flexible acoustic sensor array platform. Using this sensor platform, we investigate direction of arrival estimation and source localization experiments with different geometries and with different numbers of sensors. We further present a discussion of parameters that influence the sensitivity and accuracy of the results of these experiments.