{"product_id":"exploratory-investigation-of-ultrasound-interrogated-passive-sensors-based-on-an-acoustic-metamaterial-von-lucrezia-maini","title":"Exploratory Investigation of Ultrasound Interrogated Passive Sensors based on an Acoustic Metamaterial","description":"Wireless technologies have significantly influenced the development of new\nsensing concepts for continuous health monitoring and disease detection.\nCompared to wired solutions, wireless sensors overcome limitations such as\nrisk of infection and discomfort caused by tethered connections. Wireless\nsystems are classified as passive (powerless) and active (powered). Active\nsolutions face significant challenges both in terms of power management\nand fabrication, requiring the integration of complex electronic components\nand circuits. Furthermore, active devices may require power source\nreplacement, which can lead to health risks and complications for the\npatient. In contrast, passive devices present reduced complications thanks\nto their powerless nature and simpler architecture. Wireless devices\ntypically rely on electromagnetic coupling interrogation for powering or\ndata transmission. Electromagnetic waves, while being a common approach\nfor sensing interrogation, are limited by overheating risks associated with\nhigh energy absorption and scattering in tissue. Moreover, the development\nof customized receivers for these sensing applications requires significant\ndesign investment.\nDue to their mechanical nature, acoustic waves achieve comparable\npenetration depths to electromagnetic waves at lower power levels.\nFurthermore, standardized clinical equipment such as echographs can be\nutilized for interrogation in the MHz regime (ultrasound). Acoustic sensors\nbased on ultrasound interrogation have already been explored, but they are\nmostly limited by the spatial resolution of commercially-available\ntransducers, often insufficient to measure variations of biomedical\nparameters of interest (e.g. pressure, temperature). This thesis presents a\nnew approach to perform intracorporeal sensing, investigating the\nadvantages of frequency resolution and ultrasound interrogation. In\nparticular, this is achieved exploiting the high resonant states generated by\nan acoustic metamaterial. Metamaterials (from Greek: μϵτα, \"beyond\"\nconventional matter), engineered structures by design, exhibit properties\nbeyond those of conventional materials. While fundamental research on\nmetamaterials spans more than three decades, their application to\nultrasound for the development of new and innovative medical devices is\nstill in the early stages.\nThe acoustic metamaterial presented in this thesis consists of\nthree-dimensional silicon micropillars (radius: 35 μm), arranged in a\nhoneycomb lattice, and embedded in a polymeric matrix (PDMS,\npolyimethylsiloxane), which also acts as an encapsulation material. This\ndesign combines the high amplitude of the resonance mode of the\nmetamaterial with the temperature and pressure sensitivity introduced by\nthe presence of the PDMS matrix. The objectives of this thesis are focused\non the demonstration of (1) temperature and (2) pressure sensing\ncapabilities, within ranges of interest for medical applications. Specifically,\ntemperature sensitivity is evaluated in the 36◦ ÷ 41◦C range and pressure\nsensitivity in the 0 ÷ 200 mbar range. Temperature applications are\nrelevant for the detection of infections in failing implants. Pressure sensing\nrequirements were selected in collaboration with our clinical partners from\nthe Deutsches Herzzentrum der Charité, DHZC, Charité Hospital. In\nparticular, pressure specifications were defined for bi-atrial pressure\nmonitoring, as a key indicator of relevant cardiovascular conditions, such as\nheart failure.\nThe metamaterial (henceforth, PDMS-Meta) was initially characterized in\nwater. Its response was compared to a bilayer of silicon and PDMS\n(henceforth, Bilayer), and to the metamaterial without the PDMS matrix\n(henceforth, Si-Meta). These two structures were utilized to elucidate the\nphysical mechanism behind the temperature sensitivity. The temperature\nresolution achieved by the PDMS-Meta is below 0.1 K (0.03 K), with a\ntemperature sensitivity of −2.9 · 10−3 K-1. The physical origin of\ntemperature sensitivity was investigated by experiments and Finite\nElement Method (FEM) simulations and explained as a\ntemperature-dependency of the bulk modulus of the PDMS.\nTemperature characterization was repeated in presence of tissue mimicking\nmaterials, TMMs—imaging samples with acoustic properties comparable to\nthose of human muscle—and with animal tissue (pork loin) to assess the\neffect of scattering and attenuation on the temperature performance.\nTemperature sensitivity was comparable in the three media\n(−3.4 · 10−3 K-1, −3 · 10−3 K-1, −3.5 · 10−3 K-1, in water and in presence\nof the TMM and tissue, respectively), although the temperature resolution\ndegraded (0.02 K, 0.12 K, 0.18 K, in water, TMM and tissue). The\nachieved temperature resolution in presence of tissue is comparable to the\nresolution of infrared cameras utilized in medical thermometry (0.1 K).\nThe measurement location was observed to strongly influence the\ntemperature results in presence of highly inhomogeneous media as an effect\nof the multiple interferences introduced by the tissue.\nFinally, pressure characterization of the Bilayer, PDMS-Meta and Si-Meta\nwas performed in water with a bulge-test setup. Pressure sensitivity was\nsignificantly higher in the PDMS-Meta and the Bilayer, although opposite\nin sign (−4.3 · 10−6 mbar-1 and 11 · 10−6 mbar-1, respectively) in\ncomparison to the Si-Meta (−0.5 · 10−6 mbar-1). Pressure resolution was\ncomparable in the PDMS-Meta and Bilayer (11.6 mbar vs 18.3 mbar,\nrespectively), but significantly lower in the Si-Meta (224.8 mbar). The\norigin of pressure sensitivity was investigated by FEM simulations. In the\nBilayer, the primary mechanism was identified as a geometrical effect in\nthe PDMS layer. For the PDMS-metamaterial, the pressure sensitivity is\npotentially attributed to a strain-dependent variation in the speed of sound\nwithin the PDMS. The achieved pressure resolution enables the detection\nof pressure changes equivalent to systolic and diastolic pressure values\n(13 mbar vs 187 mbar) in ideal conditions (water).\nAs a next step, alternative metamaterial designs could be investigated to\nexploit anisotropy with respect to the direction of interrogation of the\nultrasound source. This approach could be particularly useful in\nmulti-modal sensing to decouple each contribution. Furthermore, the\ncurrent spatial dependency of the results should be addressed, for instance\nwith a multichannel setup with enhanced time averaging modality, to\nenable the interrogation of the sensor at multiple locations with improved\nsignal resolution.\nThe presented sensor opens the way to a new class of zero-power devices\nbased on acoustic metamaterials and ultrasound interrogation to perform\nremote sensing with limited integration and, potentially, exposure\ncomplications for the patient.\u003cdiv class=\"aw-variant-hidden-subtitle-div\" id=\"aw-variant-subtitle-9783866288454\"\u003e\u003ch3\u003e\u003c\/h3\u003e\u003c\/div\u003e","brand":"Autorenwelt Shop","offers":[{"title":"Softcover - 9783866288454","offer_id":55805779083589,"sku":"9783866288454","price":98.0,"currency_code":"EUR","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0940\/0622\/files\/9628fe8f-0495-4079-a59f-310a246f9827.jpg?v=1773383563","url":"https:\/\/shop.autorenwelt.de\/products\/exploratory-investigation-of-ultrasound-interrogated-passive-sensors-based-on-an-acoustic-metamaterial-von-lucrezia-maini","provider":"Autorenwelt Shop","version":"1.0","type":"link"}