Quantifying Elastic Properties of Environmental Biofilms using Optical Coherence Elastography

Biofilms are complex biomaterials comprising a well-organized network of microbial cells encased in self-produced extracellular polymeric substances ...

Northwestern University

Viene presentato un fotoacustico imaging system che incorpora una fotocamera commerciale ad ultrasuoni per l&#39;imaging in tempo reale dei piani bidimensionali (2D) proiezione in tessuto al tasso dei video (30 Hz). Il sistema utilizza un laser a ND: YAG Q-switched duplicato in frequenza per la generazione di fotoacustico. La fotocamera ad ultrasuoni &egrave; costituito da un chip 2-D 12 x 12 mm CCD con 120 x 120 elementi di telerilevamento piezoelettrici utilizzati per rilevare la distribuzione della pressione fotoacustico irradiata dalla destinazione. Un sistema di lenti ad ultrasuoni &egrave; posto davanti il chip a raccogliere le onde in arrivo fotoacustico, offrendo la capacit&agrave; di messa a fuoco e di imaging a diverse profondit&agrave;. Confrontato con altri fotoacustico esistente tecniche di imaging, il sistema basato su fotocamera &egrave; attraente perch&eacute; &egrave; relativamente poco costoso e compatto, e pu&ograve; essere adattata per applicazioni di imaging cliniche in tempo reale. Vengono presentati i risultati sperimentali che dettagliano l&#39;imaging in tempo reale fotoacustico di stringhe di gomma e obiettivi assorbenti sepolti nel tessuto del seno di pollo, e la risoluzione spaziale del sistema &egrave; quantificata.

Imaging fotoacustico di pieno campo in tempo reale utilizzando una telecamera ad ultrasuoni.

Eine photoakustische imaging-System, das eine kommerzielle Ultraschallkamera f&uuml;r Echtzeit-Bildgebung der zweidimensionalen (2D) Projektion Flugzeuge im Gewebe mit video Rate (30 Hz) umfasst, wird pr&auml;sentiert. Das System verwendet einen g&uuml;tegeschaltete verdoppelt ND: YAG gepulsten Laser f&uuml;r photoakustische Generation. Der Ultraschallkamera besteht aus einem 2-D 12 x 12 mm CCD-Chip mit 120 x 120 piezoelektrischen Sensor Elementen zum Auffinden der Photoakustischen Druckverteilung strahlte vom Ziel verwendet. Ein Ultraschall Linsensystem befindet sich vor dem Chip, die eingehende Photoakustischen Wellen, bietet so die M&ouml;glichkeit f&uuml;r Fokussierung und imaging in verschiedenen Tiefen zu sammeln. Im Vergleich mit anderen vorhandenen Photoakustischen bildgebende Verfahren, ist das kamerabasierte System attraktiv, weil es relativ preiswert und kompakt, und es f&uuml;r Echtzeit-klinische imaging-Anwendungen angepasst werden kann. Experimentelle Ergebnisse detailliert die Echtzeit photoakustische Bildgebung aus Gummi Zeichenfolgen und begraben absorbierende Ziele in Huhn Brustgewebe werden pr&auml;sentiert und die r&auml;umliche Aufl&ouml;sung des Systems wird quantifiziert.

Echtzeit fl&auml;chenhaften photoakustische Bildgebung mit Ultraschall-Kamera.

&#x5149;&#x58F0;&#x6210;&#x50CF;&#x7CFB;&#x7EDF;&#xFF0C;&#x5176;&#x4E2D;&#x5305;&#x62EC;&#x4E8C;&#x7EF4; (2-d) &#x6295;&#x5F71;&#x5E73;&#x9762;&#x89C6;&#x9891;&#x7387; &#xFF08;30 Hz&#xFF09; &#x5728;&#x7EC4;&#x7EC7;&#x4E2D;&#x7684;&#x5B9E;&#x65F6;&#x6210;&#x50CF;&#x5546;&#x4E1A;&#x8D85;&#x58F0;&#x6CE2;&#x76F8;&#x673A;&#x88AB;&#x63D0;&#x4EA4;&#x3002;&#x7CFB;&#x7EDF;&#x4F7F;&#x7528; Q &#x5F00;&#x5173;&#x500D;&#x9891;&#x8109;&#x51B2;&#x7684;&#x6FC0;&#x5149;&#x5149;&#x58F0;&#x4EE3;&#x3002;&#x8D85;&#x58F0;&#x6CE2;&#x76F8;&#x673A;&#x5305;&#x62EC; 2 D 12 x 12 mm CCD &#x82AF;&#x7247;&#xFF0C;120 &times; 120 &#x538B;&#x7535;&#x654F;&#x611F;&#x5143;&#x4EF6;&#x7528;&#x4E8E;&#x68C0;&#x6D4B;&#x4ECE;&#x76EE;&#x6807;&#x8F90;&#x5C04;&#x7684;&#x5149;&#x58F0;&#x538B;&#x529B;&#x5206;&#x5E03;&#x3002;&#x8D85;&#x58F0;&#x6CE2;&#x955C;&#x5934;&#x7CFB;&#x7EDF;&#x88AB;&#x653E;&#x5728;&#x524D;&#x9762;&#xFF0C;&#x82AF;&#x7247;&#x6536;&#x96C6;&#x8FDB;&#x6765;&#x7684;&#x5149;&#x58F0;&#x6D6A;&#xFF0C;&#x63D0;&#x4F9B;&#x7684;&#x80FD;&#x529B;&#x4E3A;&#x91CD;&#x70B9;&#xFF0C;&#x5E76;&#x5728;&#x4E0D;&#x540C;&#x6DF1;&#x5EA6;&#x7684;&#x5F71;&#x50CF;&#x3002;&#x4E0E;&#x5176;&#x4ED6;&#x73B0;&#x6709;&#x7684;&#x5149;&#x58F0;&#x6210;&#x50CF;&#x6280;&#x672F;&#x76F8;&#x6BD4;&#xFF0C;&#x57FA;&#x4E8E;&#x76F8;&#x673A;&#x7684;&#x7CFB;&#x7EDF;&#x662F;&#x6709;&#x5438;&#x5F15;&#x529B;&#x56E0;&#x4E3A;&#x5B83;&#x662F;&#x76F8;&#x5BF9;&#x4FBF;&#x5B9C;&#x548C;&#x7D27;&#x51D1;&#xFF0C;&#x5B83;&#x53EF;&#x4EE5;&#x9488;&#x5BF9;&#x5B9E;&#x65F6;&#x4E34;&#x5E8A;&#x56FE;&#x50CF;&#x5904;&#x7406;&#x5E94;&#x7528;&#x7A0B;&#x5E8F;&#x3002;&#x5217;&#x51FA;&#x7684;&#x8BE6;&#x7EC6;&#x4ECB;&#x7ECD;&#x6A61;&#x80F6;&#x5B57;&#x7B26;&#x4E32;&#x548C;&#x9E21;&#x4E73;&#x817A;&#x7EC4;&#x7EC7;&#x4E2D;&#x7684;&#x57CB;&#x5730;&#x5438;&#x6536;&#x76EE;&#x6807;&#x7684;&#x5B9E;&#x65F6;&#x5149;&#x58F0;&#x6210;&#x50CF;&#x7684;&#x5B9E;&#x9A8C;&#x7ED3;&#x679C;&#xFF0C;&#x5E76;&#x91CF;&#x5316;&#x7CFB;&#x7EDF;&#x7684;&#x7A7A;&#x95F4;&#x5206;&#x8FA8;&#x7387;&#x3002;

&#x4F7F;&#x7528;&#x8D85;&#x58F0;&#x6CE2;&#x6444;&#x50CF;&#x673A;&#x5B9E;&#x65F6;&#x5168;&#x57DF;&#x5149;&#x58F0;&#x6210;&#x50CF;&#x3002;

A photoacoustic imaging system that incorporates a commercial ultrasonic camera for real-time imaging of two-dimensional (2-D) projection planes in tissue at video rate (30 Hz) is presented. The system uses a Q-switched frequency-doubled Nd:YAG pulsed laser for photoacoustic generation. The ultrasonic camera consists of a 2-D 12 x 12 mm CCD chip with 120 x 120 piezoelectric sensing elements used for detecting the photoacoustic pressure distribution radiated from the target. An ultrasonic lens system is placed in front of the chip to collect the incoming photoacoustic waves, providing the ability for focusing and imaging at different depths. Compared with other existing photoacoustic imaging techniques, the camera-based system is attractive because it is relatively inexpensive and compact, and it can be tailored for real-time clinical imaging applications. Experimental results detailing the real-time photoacoustic imaging of rubber strings and buried absorbing targets in chicken breast tissue are presented, and the spatial resolution of the system is quantified.

Real-time full-field photoacoustic imaging using an ultrasonic camera.

Un photoacoustique imaging system qui int&egrave;gre une cam&eacute;ra commerciale ultrasonique pour l&#39;imagerie en temps r&eacute;el des avions &agrave; deux dimensions (2d) projection en tissu au d&eacute;bit vid&eacute;o (30 Hz) est pr&eacute;sent&eacute;. Le syst&egrave;me utilise un laser puls&eacute; Q-switched Nd: YAG doubl&eacute; en fr&eacute;quence pour la g&eacute;n&eacute;ration de photoacoustique. L&#39;appareil &agrave; ultrasons se compose d&#39;une puce 2D 12 x 12 mm CCD 120 x 120 &eacute;l&eacute;ments capteurs pi&eacute;zo&eacute;lectriques, utilis&eacute;s pour d&eacute;tecter la distribution de pression photoacoustique &eacute;mise par la cible. Un syst&egrave;me de lentilles ultrasonique est plac&eacute; en face de la puce pour recueillir les vagues photoacoustique, fournissant la capacit&eacute; de mise au point et d&#39;imagerie &agrave; diff&eacute;rentes profondeurs. Par rapport aux autre photoacoustique existant, techniques d&#39;imagerie, le syst&egrave;me de cam&eacute;ra est attrayant parce qu&#39;il est relativement compact et peu co&ucirc;teux, et il peut &ecirc;tre adapt&eacute; pour des applications d&#39;imagerie cliniques en temps r&eacute;el. On pr&eacute;sente des r&eacute;sultats exp&eacute;rimentaux, d&eacute;taillant l&#39;imagerie photoacoustique en temps r&eacute;el des cordes de caoutchouc et des cibles qui absorbent enfouis dans les tissus de la poitrine de poulet, et la r&eacute;solution spatiale du syst&egrave;me est quantifi&eacute;e.

Imagerie photoacoustique de plein champ en temps r&eacute;el &agrave; l&#39;aide d&#39;un appareil &agrave; ultrasons.

2 &#x6B21;&#x5143; (2 D) &#x6295;&#x5F71;&#x9762;&#x306B;&#x304A;&#x3051;&#x308B;&#x30D3;&#x30C7;&#x30AA; &#x30EC;&#x30FC;&#x30C8; (30 Hz) &#x7D44;&#x7E54;&#x5185;&#x306E;&#x30EA;&#x30A2;&#x30EB;&#x30BF;&#x30A4;&#x30E0; &#x30A4;&#x30E1;&#x30FC;&#x30B8;&#x30F3;&#x30B0;&#x306E;&#x305F;&#x3081;&#x306E;&#x5546;&#x696D;&#x8D85;&#x97F3;&#x6CE2;&#x30AB;&#x30E1;&#x30E9;&#x3092;&#x7D44;&#x307F;&#x8FBC;&#x3093;&#x3060;&#x30B7;&#x30B9;&#x30C6;&#x30E0;&#x3092;&#x30A4;&#x30E1;&#x30FC;&#x30B8;&#x30F3;&#x30B0;&#x5149;&#x97F3;&#x97FF;&#x304C;&#x63D0;&#x793A;&#x3055;&#x308C;&#x307E;&#x3059;&#x3002;&#x30B7;&#x30B9;&#x30C6;&#x30E0;&#x5468;&#x6CE2;&#x6570;&#x304C; 2 &#x500D;&#x306B; Q &#x30B9;&#x30A4;&#x30C3;&#x30C1; Nd:YAG &#x30D1;&#x30EB;&#x30B9; &#x30EC;&#x30FC;&#x30B6;&#x30FC;&#x5149;&#x97F3;&#x97FF;&#x751F;&#x6210;&#x3092;&#x4F7F;&#x7528;&#x3057;&#x307E;&#x3059;&#x3002;&#x8D85;&#x97F3;&#x6CE2;&#x30AB;&#x30E1;&#x30E9; 2 D 12 x 12 &#x30DF;&#x30EA;&#x30E1;&#x30FC;&#x30C8;&#x30EB; CCD &#x30C1;&#x30C3;&#x30D7;&#x306E;&#x30BF;&#x30FC;&#x30B2;&#x30C3;&#x30C8;&#x304B;&#x3089;&#x653E;&#x5C04;&#x3055;&#x308C;&#x308B;&#x5149;&#x97F3;&#x97FF;&#x5727;&#x529B;&#x5206;&#x5E03;&#x306E;&#x691C;&#x51FA;&#x306B;&#x4F7F;&#x7528;&#x3055;&#x308C;&#x308B; 120 x 120 &#x5727;&#x96FB;&#x30BB;&#x30F3;&#x30B5;&#x30FC;&#x7D20;&#x5B50;&#x3067;&#x69CB;&#x6210;&#x3055;&#x308C;&#x307E;&#x3059;&#x3002;&#x8D85;&#x97F3;&#x6CE2;&#x30EC;&#x30F3;&#x30BA; &#x30B7;&#x30B9;&#x30C6;&#x30E0;&#x306F;&#x3001;&#x7126;&#x70B9;&#x3092;&#x5F53;&#x3066;&#x3001;&#x7570;&#x306A;&#x308B;&#x6DF1;&#x3055;&#x3067;&#x30A4;&#x30E1;&#x30FC;&#x30B8;&#x30F3;&#x30B0;&#x306E;&#x80FD;&#x529B;&#x3092;&#x63D0;&#x4F9B;&#x3059;&#x308B;&#x7740;&#x4FE1;&#x306E;&#x5149;&#x97F3;&#x97FF;&#x6CE2;&#x3092;&#x53CE;&#x96C6;&#x3059;&#x308B;&#x305F;&#x3081;&#x306B;&#x3001;&#x30C1;&#x30C3;&#x30D7;&#x306E;&#x524D;&#x306B;&#x914D;&#x7F6E;&#x3055;&#x308C;&#x307E;&#x3059;&#x3002;&#x305D;&#x306E;&#x4ED6;&#x65E2;&#x5B58;&#x306E;&#x97F3;&#x97FF;&#x30A4;&#x30E1;&#x30FC;&#x30B8;&#x30F3;&#x30B0;&#x6280;&#x8853;&#x3068;&#x6BD4;&#x8F03;&#x3057;&#x3066;&#x3001;&#x30AB;&#x30E1;&#x30E9; &#x30D9;&#x30FC;&#x30B9;&#x306E;&#x30B7;&#x30B9;&#x30C6;&#x30E0;&#x306F;&#x6BD4;&#x8F03;&#x7684;&#x5B89;&#x4FA1;&#x3001;&#x30B3;&#x30F3;&#x30D1;&#x30AF;&#x30C8;&#x3067;&#x3042;&#x308A;&#x3001;&#x30EA;&#x30A2;&#x30EB;&#x30BF;&#x30A4;&#x30E0;&#x306E;&#x81E8;&#x5E8A;&#x753B;&#x50CF;&#x51E6;&#x7406;&#x30A2;&#x30D7;&#x30EA;&#x30B1;&#x30FC;&#x30B7;&#x30E7;&#x30F3;&#x3092;&#x5408;&#x308F;&#x305B;&#x308B;&#x3053;&#x3068;&#x304C;&#x3067;&#x304D;&#x308B;&#x305F;&#x3081;&#x9B45;&#x529B;&#x7684;&#x3067;&#x3059;&#x3002;&#x30B4;&#x30E0;&#x7D10;&#x3068;&#x57CB;&#x6CA1;&#x5438;&#x53CE;&#x306E;&#x30BF;&#x30FC;&#x30B2;&#x30C3;&#x30C8;&#x9D8F;&#x80F8;&#x306E;&#x30C6;&#x30A3;&#x30C3;&#x30B7;&#x30E5;&#x306E;&#x30EA;&#x30A2;&#x30EB;&#x30BF;&#x30A4;&#x30E0;&#x5149;&#x97F3;&#x97FF;&#x30A4;&#x30E1;&#x30FC;&#x30B8;&#x30F3;&#x30B0;&#x3092;&#x8A73;&#x8FF0;&#x5B9F;&#x9A13;&#x306E;&#x7D50;&#x679C;&#x3092;&#x8868;&#x793A;&#x3001;&#x304A;&#x3088;&#x3073;&#x30B7;&#x30B9;&#x30C6;&#x30E0;&#x306E;&#x7A7A;&#x9593;&#x5206;&#x89E3;&#x80FD;&#x306E;&#x5B9A;&#x91CF;&#x5316;&#x3057;&#x307E;&#x3059;&#x3002;

&#x8D85;&#x97F3;&#x6CE2;&#x30AB;&#x30E1;&#x30E9;&#x3092;&#x7528;&#x3044;&#x305F;&#x30EA;&#x30A2;&#x30EB;&#x30BF;&#x30A4;&#x30E0; &#x30D5;&#x30EB;&#x30D5;&#x30A3;&#x30FC;&#x30EB;&#x30C9; &#x30FB;&#x5149;&#x97F3;&#x97FF;&#x30A4;&#x30E1;&#x30FC;&#x30B8;&#x30F3;&#x30B0;&#x3002;

&#xBE44;&#xB514;&#xC624; &#xB808;&#xC774;&#xD2B8; (30hz)&#xC5D0;&#xC11C; &#xC870;&#xC9C1;&#xC5D0; &#xC788;&#xB294; 2 &#xCC28;&#xC6D0; (2d) &#xD22C;&#xC601; &#xD3C9;&#xBA74;&#xC758; &#xC2E4;&#xC2DC;&#xAC04; &#xC774;&#xBBF8;&#xC9D5;&#xC5D0; &#xB300; &#xD55C; &#xC0C1;&#xC5C5;&#xC801;&#xC778; &#xCD08;&#xC74C;&#xD30C; &#xCE74;&#xBA54;&#xB77C; &#xD1B5;&#xD569; &#xC2DC;&#xC2A4;&#xD15C; &#xC774;&#xBBF8;&#xC9D5; photoacoustic &#xC81C;&#xACF5; &#xB429;&#xB2C8;&#xB2E4;. &#xC2DC;&#xC2A4;&#xD15C; photoacoustic &#xC138;&#xB300;&#xC6A9; nd &#xC8FC;&#xD30C;&#xC218; 2 &#xBC30;: Q &#xC2A4;&#xC704;&#xCE58; yag &#xD384;&#xC2A4; &#xB808;&#xC774;&#xC800;&#xB97C; &#xC0AC;&#xC6A9;&#xD569;&#xB2C8;&#xB2E4;. &#xCD08;&#xC74C;&#xD30C; &#xCE74;&#xBA54;&#xB77C; 2 D 12 &times; 12 m m CCD &#xCE69; 120 x 120 &#xC555; &#xAC10;&#xC9C0; &#xC694;&#xC18C; &#xB300;&#xC0C1;&#xC5D0;&#xC11C; &#xBC29;&#xC0AC; photoacoustic &#xC555;&#xB825; &#xBD84;&#xD3EC;&#xB97C; &#xD0D0;&#xC9C0; &#xD558;&#xB294; &#xB370; &#xC0AC;&#xC6A9; &#xB418;&#xB294; &#xAD6C;&#xC131; &#xB429;&#xB2C8;&#xB2E4;. &#xCD08;&#xC74C;&#xD30C; &#xB80C;&#xC988; &#xC2DC;&#xC2A4;&#xD15C; &#xCE69; &#xCD08;&#xC810; &#xBC0F; &#xB2E4;&#xB978; &#xAE4A;&#xC774;&#xC5D0; &#xC774;&#xBBF8;&#xC9D5; &#xAE30;&#xB2A5;&#xC744; &#xC81C;&#xACF5; &#xD558;&#xB294; &#xB4E4;&#xC5B4;&#xC624;&#xB294; photoacoustic &#xD30C;&#xB3C4; &#xC218;&#xC9D1; &#xC55E;&#xC5D0; &#xBC30;&#xCE58; &#xB429;&#xB2C8;&#xB2E4;. &#xB2E4;&#xB978; &#xAE30;&#xC874; photoacoustic &#xC774;&#xBBF8;&#xC9D5; &#xAE30;&#xBC95;&#xC5D0; &#xBE44;&#xD574; &#xCE74;&#xBA54;&#xB77C; &#xAE30;&#xBC18; &#xC2DC;&#xC2A4;&#xD15C;&#xC740; &#xC0C1;&#xB300;&#xC801;&#xC73C;&#xB85C; &#xC800;&#xB834; &#xD558; &#xACE0; &#xCEF4;&#xD329;&#xD2B8;&#xD55C;, &#xADF8;&#xB9AC;&#xACE0; &#xC2E4;&#xC2DC;&#xAC04; &#xC784;&#xC0C1; &#xC774;&#xBBF8;&#xC9D5; &#xC560;&#xD50C;&#xB9AC;&#xCF00;&#xC774;&#xC158;&#xC5D0; &#xB9DE;&#xCD9C; &#xC218; &#xC788;&#xAE30; &#xB54C;&#xBB38;&#xC5D0; &#xB9E4;&#xB825;&#xC801;. &#xACE0;&#xBB34; &#xBB38;&#xC790;&#xC5F4; &#xBC0F; &#xCE58;&#xD0A8; &#xC720; &#xBC29; &#xC870;&#xC9C1;&#xC5D0; &#xBB3B;&#xD600; &#xD761;&#xC218; &#xB300;&#xC0C1;&#xC758; &#xC2E4;&#xC2DC;&#xAC04; photoacoustic &#xC601;&#xC0C1; &#xC801; &#xC2E4;&#xD5D8; &#xACB0;&#xACFC; &#xC81C;&#xC2DC; &#xD558; &#xACE0; &#xC2DC;&#xC2A4;&#xD15C;&#xC758; &#xACF5;&#xAC04; &#xD574;&#xC0C1;&#xB3C4; &#xACC4;&#xB7C9;.

&#xC2E4;&#xC2DC;&#xAC04; &#xC804;&#xCCB4; &#xD544;&#xB4DC; photoacoustic &#xC774;&#xBBF8;&#xC9D5; &#xCD08;&#xC74C;&#xD30C; &#xCE74;&#xBA54;&#xB77C;&#xB97C; &#xC0AC;&#xC6A9; &#xD558; &#xC5EC;.

Se presenta un sistema que incorpora una c&aacute;mara comercial ultras&oacute;nica para la proyecci&oacute;n de imagen en tiempo real de aviones de la proyecci&oacute;n de dos dimensiones (2D) en tejido en las tasa de video (30 Hz) de la proyecci&oacute;n de imagen de fotoac&uacute;stica. El sistema utiliza un l&aacute;ser pulsado frecuencia-doblado Q-switched para generaci&oacute;n de fotoac&uacute;stica. La c&aacute;mara ultras&oacute;nica consiste en un chip de 2-D 12 x 12 mm CCD con 120 x 120 elementos sensores piezoel&eacute;ctricos utilizados para la detecci&oacute;n de la distribuci&oacute;n de presi&oacute;n fotoac&uacute;stica irradiada del objetivo. Un sistema ultras&oacute;nico de la lente se coloca delante el chip para recoger las ondas entrantes de fotoac&uacute;stica, proporcionando la capacidad de enfoque y proyecci&oacute;n de imagen a diferentes profundidades. En comparaci&oacute;n con otro fotoac&uacute;stica existente, t&eacute;cnicas de imagen, el sistema basado en c&aacute;maras es atractivo porque es relativamente barato y compacto, y puede ser adaptado para aplicaciones en tiempo real de im&aacute;genes cl&iacute;nicas. Se presentan resultados experimentales que detalla la proyecci&oacute;n de imagen en tiempo real fotoac&uacute;stica de cadenas de goma y objetivos absorbentes enterrados en tejido de pechuga de pollo, y se cuantifica la resoluci&oacute;n espacial del sistema.

La proyecci&oacute;n de imagen fotoac&uacute;stica de campo completo en tiempo real usando una c&aacute;mara ultras&oacute;nica.

The dispersive properties of surface waves on an isotropic elastic body with elastic moduli and mass density that depend on depth have been analyzed in the high frequency range, for the case of axially symmetric surface waves, which are of interest for point loading of a body. The method of approach requires some simplifications, but the final analysis yields simple expressions for the displacements, for the case that the two elastic moduli and the mass density each have different dependencies on depth. In a high-frequency approximation expressions are obtained for the displacements and the stresses. The condition that the surface tractions vanish at the free surface yields the dispersion equation which relates the surface wave velocity to the wavenumber. Conditions have been derived for a class of examples for which this equation yields a real valued surface wave velocity, and the displacement amplitudes decay exponentially with depth. Results for the surface wave velocity as a function of the wavenumber have been compared with numerical results which were obtained when the continuous inhomogeneity with depth is replaced by an equivalent layering. For some typical cases of increasing and decreasing material properties with depth, excellent agreement has been obtained between analytical and numerical results.

Surface waves on a half space with depth-dependent properties.

Non-propagating evanescent fields play an important role in the development of nano-photonic devices. While detecting the evanescent fields in far-field can be accomplished by coupling it to the propagating waves, in practice they are measured in the presence of unwanted propagating background components. It leads to a poor signal-to-noise ratio and thus to errors in quantitative analysis of the local evanescent fields. Here we report on a plasmonic near-field scanning optical microscopy (p-NSOM) technique that incorporates a nanofocusing probe for adiabatic focusing of propagating surface plasmon polaritons at the probe apex, and for enhanced coupling of evanescent waves to the far-field. In addition, a harmonic demodulation technique is employed to suppress the contribution of the background. Our experimental results show strong evidence of background free near-field imaging using the new p-NSOM technique. Furthermore, we present measurements of surface plasmon cavity modes, and quantify their contributing sources using an analytical model.

Quantitative imaging of rapidly decaying evanescent fields using plasmonic near-field scanning optical microscopy.

Near-field optical techniques exploit light-matter interactions at small length scales for mechanical sensing and actuation of nanomechanical structures. Here, we study the optical interaction between two mechanical oscillators--a plasmonic nanofocusing probe-tip supported by a low frequency cantilever, and a high frequency nanomechanical resonator--and leverage their interaction for local detection of mechanical vibrations. The plasmonic nanofocusing probe provides a confined optical source to enhance the interaction between the two oscillators. Dynamic perturbation of the optical cavity between the probe-tip and the resonator leads to nonlinear modulation of the scattered light intensity at the sum and difference of their frequencies. This double-frequency demodulation scheme is explored to suppress unwanted background and to detect mechanical vibrations with a minimum detectable displacement sensitivity of 0.45 pm/Hz(1/2), which is limited by shot noise and electrical noise. We explore the demodulation scheme for imaging the bending vibration mode shape of the resonator with a lateral spatial resolution of 20 nm. We also demonstrate the time-resolved aspect of the local optical interaction by recording the ring-down vibrations of the resonator at frequencies of up to 129 MHz. The near-field optical technique is promising for studying dynamic mechanical processes in individual nanostructures.

Dynamic near-field optical interaction between oscillating nanomechanical structures.

Morphological parameters are commonly used to predict transport and metabolic kinetics in biofilms. Yet, quantification of biofilm morphology remains challenging because of imaging technology limitations and lack of robust analytical approaches. We present a novel set of imaging and image analysis techniques to estimate internal porosity, pore size distributions, and pore network connectivity to a depth of 1 mm at a resolution of 10 µm in a biofilm exhibiting both heterotrophic and nitrifying activities. Optical coherence tomography (OCT) scans revealed an extensive pore network with diameters as large as 110 µm directly connected to the biofilm surface and surrounding fluid. Thin-section fluorescence in situ hybridization microscopy revealed that ammonia-oxidizing bacteria (AOB) distributed through the entire thickness of the biofilm. AOB were particularly concentrated in the biofilm around internal pores. Areal porosity values estimated from OCT scans were consistently lower than those estimated from multiphoton laser scanning microscopy, though the two imaging modalities showed a statistically significant correlation (r = 0.49, p < 0.0001). Estimates of areal porosity were moderately sensitive to gray-level threshold selection, though several automated thresholding algorithms yielded similar values to those obtained by manually thresholding performed by a panel of environmental engineering researchers (±25% relative error). These findings advance our ability to quantitatively describe the geometry of biofilm internal pore networks at length scales relevant to engineered biofilm reactors and suggest that internal pore structures provide crucial habitat for nitrifier growth.

Morphological analysis of pore size and connectivity in a thick mixed-culture biofilm.

Biofilms are soft multicomponent biological materials composed of microbial communities attached to surfaces. Despite the crucial relevance of biofilms to diverse industrial, medical, and environmental applications, the mechanical properties of biofilms are understudied. Moreover, most of the available techniques for the characterization of biofilm mechanical properties are destructive. Here, we detail a model-based approach developed to characterize the viscoelastic properties of soft materials and bacterial biofilms based on experimental data obtained using the nondestructive dynamic optical coherence elastography (OCE) technique. The model predicted the frequency- and geometry-dependent propagation velocities of elastic waves in a soft viscoelastic plate supported by a rigid substratum. Our numerical calculations suggest that the dispersion curves of guided waves recorded in thin soft plates by the dynamic OCE technique are dominated by guided waves, whose phase velocities depend on the viscoelastic properties and plate thickness. The numerical model was validated against experimental measurements in agarose phantom samples with different thicknesses and concentrations. The model was then used to interpret guided wave dispersion curves obtained by the OCE technique in bacterial biofilms developed in a rotating annular reactor, which allowed the quantitative characterization of biofilm shear modulus and viscosity. This study is the first to employ measurements of elastic wave propagation to characterize biofilms, and it provides a novel framework combining a theoretical model and an experimental approach for studying the relationship between the biofilm internal physical structure and mechanical properties.

Nondestructive characterization of soft materials and biofilms by measurement of guided elastic wave propagation using optical coherence elastography.

Microbial granular biofilms are spherical, multi-layered aggregates composed of communities of bacterial cells encased in a complex matrix of hydrated extracellular polymeric substances (EPS). While granular aggregates are increasingly used for applications in industrial and municipal wastewater treatment, their underlying mechanical properties are poorly understood. The challenges of viscoelastic characterization for these structures are due to their spherical geometry, spatially heterogeneous properties, and their delicate nature. In this study, we report a model-based approach for nondestructive characterization of viscoelastic properties (shear modulus and shear viscosity) of alginate spheres with different concentrations, which was motivated by our measurements in granular biofilms. The characterization technique relies on experimental measurements of circumferential elastic wave speeds as a function of frequency in the samples using the Optical Coherence Elastography (OCE) technique. A theoretical model was developed to estimate the viscoelastic properties of the samples from OCE data through inverse analysis. This work represents the first attempt to explore elastic waves for mechanical characterization of granular biofilms. The combination of the OCE technique and the theoretical model presented in this paper provides a framework that can facilitate quantitative viscoelastic characterization of samples with curved geometries and the study of the relationships between morphology and mechanical properties in granular biofilms.

Towards mechanical characterization of granular biofilms by optical coherence elastography measurements of circumferential elastic waves.

Self-assembled nanodielectrics (SANDs) consist of alternating layers of polarized phosphonate-functionalized azastibazolium π-electron (PAE) and high- dielectric metal oxide (ZrO or HfO) films. SANDs are desirable gate dielectrics materials for thin-film transistor applications because of their excellent properties such as low-temperature fabrication, large dielectric strength, and large capacitance. In this paper, we investigate the cross-plane thermal boundary conductance of SANDs using the frequency domain thermoreflectance (FDTR) technique. First, we characterize the thermal conductance of PAE self-assembled monolayers (SAMs), inverted-PAE (IPAE) SAMs, and mixed PAE-IPAE SAMs, sandwiched between thin gold and silica (SiO) films at the top and bottom surfaces. Next, we quantify the thermal conductance of SAND- with different numbers () of PAE-ZrO layers and thicknesses ranging between 4.7 and 11.3 nm. From the FDTR measurements, we observe that the thermal boundary conductance of the SAMs can be tuned between 42.1 ± 4.6 MW/(m K) and 52.4 ± 2.5 MW/(m K), based on the relative density of the PAE and IPAE chromophores. In the SAND- samples, we observe a monotonic decrease in the thermal conductance with increasing . We use the measured thermal conductance data in a series resistance model to estimate a thermal interface conductance of 695 MW/(m K) for the contact between the PAE chromophore and the zirconium dioxide films, which is an order of magnitude larger than the SAMs. We attribute the improved thermal conductance to stronger adhesion between the PAE chromophore and the zirconium dioxide films, as compared to the weakly bonded SAMs to the gold and silicon dioxide films.

Cross-Plane Thermal Conductance of Phosphonate-Based Self-Assembled Monolayers and Self-Assembled Nanodielectrics.

Two-dimensional transitional metal halides have recently attracted significant attention due to their thickness-dependent and electrostatically tunable magnetic properties. However, this class of materials is highly reactive chemically, which leads to irreversible degradation and catastrophic dissolution within seconds in ambient conditions, severely limiting subsequent characterization, processing, and applications. Here, we impart long-term ambient stability to the prototypical transition metal halide CrI by assembling a noncovalent organic buffer layer, perylenetetracarboxylic dianhydride (PTCDA), which templates subsequent atomic layer deposition (ALD) of alumina. X-ray photoelectron spectroscopy demonstrates the necessity of the noncovalent organic buffer layer since the CrI undergoes deleterious surface reactions with the ALD precursors in the absence of PTCDA. This organic-inorganic encapsulation scheme preserves the long-range magnetic ordering in CrI down to the monolayer limit as confirmed by magneto-optical Kerr effect measurements. Furthermore, we demonstrate field-effect transistors, photodetectors, and optothermal measurements of CrI thermal conductivity in ambient conditions.

Ambient-Stable Two-Dimensional CrI  Organic-Inorganic Encapsulation.

Granular biofilms are dense spherical complex biological systems composed mainly of multi-microbial cells, water, and extracellular polymeric substances (EPS). They facilitate efficient purification and settling of activated sludge in wastewater treatment processes. The viscoelastic properties of these complex biofilm systems are important characteristics that control their growth and dictate how they respond to hydrodynamic forces and chemical stimuli. However, the viscoelastic properties of granular biofilms are poorly understood. In this paper, we study granular biofilms' viscoelastic properties using optical coherence elastography (OCE), a nondestructive method that integrates optical coherence tomography (OCT) with elastic wave propagation. While quantitative viscoelastic characterization of granular biofilms is challenging due to their heterogeneous properties, we show that elastic waves are suitable for this purpose. First, we employ guided elastic waves in a thin section of a granular biofilm to reveal a two-layered profile for the viscoelastic properties. Next, we utilize circumferential elastic waves that propagate near the surface of a non-sectioned spherical biofilm to quantify the layered system's viscoelastic properties. To the best of our knowledge, this work is the first quantitative study that characterizes the layered viscoelastic properties of granular biofilms. The measurement approach may provide a platform to study the interplay between the viscoelastic properties and other characteristics of granular biofilms such as the complex microbial system, morphology, and oxygen distribution.

Layered viscoelastic properties of granular biofilms.

Hydrogel-encapsulated catalysts are an attractive tool for low-cost intensification of (bio)-processes. Polyvinyl alcohol-sodium alginate hydrogels crosslinked with boric acid and post-cured with sulfate (PVA-SA-BS) have been applied in bioproduction and water treatment processes, but the low pH required for crosslinking may negatively affect biocatalyst functionality. Here, we investigate how crosslinking pH (3, 4, and 5) and time (1, 2, and 8 h) affect the physicochemical, elastic, and process properties of PVA-SA-BS beads. Overall, bead properties were most affected by crosslinking pH. Beads produced at pH 3 and 4 were smaller and contained larger internal cavities, while optical coherence tomography suggested polymer cross-linking density was higher. Optical coherence elastography revealed PVA-SA-BS beads produced at pH 3 and 4 were stiffer than pH 5 beads. Dextran Blue release showed that pH 3-produced beads enabled higher diffusion rates and were more porous. Last, over a 28-day incubation, pH 3 and 4 beads lost more microspheres (as cell proxies) than beads produced at pH 5, while the latter released more polymer material. Overall, this study provides a path forward to tailor PVA-SA-BS hydrogel bead properties towards a broad range of applications, such as chemical, enzymatic, and microbially catalyzed (bio)-processes.

Tailoring polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel beads by controlling crosslinking pH and time.

Two-dimensional (2D) semiconductors exhibit unique physical properties at the limit of a few atomic layers that are desirable for optoelectronic, spintronic, and electronic applications. Some of these materials require ambient encapsulation to preserve their properties from environmental degradation. While encapsulating 2D semiconductors is essential to device functionality, they also impact heat management due to the reduced thermal conductivity of the 2D material. There are limited experimental reports on in-plane thermal conductivity measurements in encapsulated 2D semiconductors. These measurements are particularly challenging in ultrathin films with a lower thermal conductivity than graphene since it may be difficult to separate the thermal effects of the sample from the encapsulating layers. To address this challenge, we integrated the frequency domain thermoreflectance (FDTR) and optothermal Raman spectroscopy (OTRS) techniques in the same experimental platform. First, we use the FDTR technique to characterize the cross-plane thermal conductivity and thermal boundary conductance. Next, we measure the in-plane thermal conductivity by model-based analysis of the OTRS measurements, using the cross-plane properties obtained from the FDTR measurements as input parameters. We provide experimental data for the first time on the thickness-dependent in-plane thermal conductivity of ultrathin MoS nanofilms encapsulated by alumina (AlO) and silica (SiO) thin films. The measured thermal conductivity increased from 26.0 ± 10.0 W m K for monolayer MoS to 39.8 ± 10.8 W m K for the six-layer films. We also show that the thickness-dependent cross-plane thermal boundary conductance of the AlO/MoS/SiO interface is limited by the low thermal conductance (18.5 MW m K) of the MoS/SiO interface, which has important implications on heat management in SiO-supported and encased MoS devices. The measurement methods can be generalized to other 2D materials to study their anisotropic thermal properties.

Quantitative Characterization of the Anisotropic Thermal Properties of Encapsulated Two-Dimensional MoS Nanofilms.

Grain-boundary engineering is an effective strategy to tune the thermal conductivity of materials, leading to improved performance in thermoelectric, thermal-barrier coatings, and thermal management applications. Despite the central importance to thermal transport, a clear understanding of how grain boundaries modulate the microscale heat flow is missing, owing to the scarcity of local investigations. Here, thermal imaging of individual grain boundaries is demonstrated in thermoelectric SnTe via spatially resolved frequency-domain thermoreflectance. Measurements with microscale resolution reveal local suppressions in thermal conductivity at grain boundaries. Also, the grain-boundary thermal resistance - extracted by employing a Gibbs excess approach - is found to be correlated with the grain-boundary misorientation angle. Extracting thermal properties, including thermal boundary resistances, from microscale imaging can provide comprehensive understanding of how microstructure affects heat transport, crucially impacting the materials design of high-performance thermal-management and energy-conversion devices.

Oluwaseyi Balogun

Theoretical and Applied Mechanics Program,
Civil and Environmental Engineering Department,
Mechanical Engineering Department

Northwestern University

Quantifying Elastic Properties of Environmental Biofilms using Optical Coherence Elastography

Oluwaseyi Balogun

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Theoretical and Applied Mechanics Program,Civil and Environmental Engineering Department,Mechanical Engineering Department

Northwestern University

Quantifying Elastic Properties of Environmental Biofilms using Optical Coherence Elastography

Theoretical and Applied Mechanics Program,
Civil and Environmental Engineering Department,
Mechanical Engineering Department