The introduction of commercial foil-strain gauges in the 1950s revolutionized the study of structural and mechanical engineering, as well as material science. These sensors provide an unprecedented window into the fundamental behavior of materials and solids. Coupled with the advent of inexpensive computing power, strain gauges allow engineers to monitor the behavior of structures in the field easily. Refined over the years, the basic foil gauge now meets the demands of a vast array of applications and environmental conditions in both research and production.
Unfortunately, conventional foil strain gauges are limited in their capability to measure small strain fields. They suffer from diminishing sensitivity, signal, and fatigue life as they get smaller. The current generation of miniaturized foil gauges boasts theoretical gauge lengths of 200μm (e.g., Tokyo Sokki Kenkyujo QFLG-02), but has low signal and sensitivity (at maximum 1μm resolution) and lifetimes (1x106 strain cycles under ideal conditions). Further, foil gauges function best under uniform strain field. To insure good signal, a uniform strain field over the whole of their polyimide-backing layer is preferable, thus increasing the effective gauge length to the size of the gauge’s polyimide substrate – 3.5 mm for the QLFG-02.
A similar technology – semiconductor strain gauges – shows promise for measuring small strain fields. Commercial gauges of this type are available with gauge lengths of approximately 700 μm and sensitivity approximately 75 times greater then foil gauges (Micro Flexitronics - L2-350 series). However, they suffer from large non-linear temperature behavior, and also require uniform strain fields similar to their foil counter parts.
In addition, both types of strain gauge require expensive, bulky sense equipment to achieve good strain sensitivity as well as exotic surface preparation and bonding to insure that the strain in the substrate is conveyed to the sensor. These issues restrict both of these sensors primarily to laboratory applications. Micro electro-mechanical systems (MEMS) offer a promises as a means for overcoming these limits. As early as the 1980s, the piezoelectric characteristics of silicon and silicon oxides led researchers to develop MEMS-based strain gauges . Since then, researchers have investigated various approaches and fabrication technologies including optical , capacitive -, and resonant  methods. Resonating sensors are of particular interest due to their simple design and potentially high sensitivity. Most recently, work at the University of California at Berkeley -, and the University of Southampton  demonstrates that a dual-ended tuning fork (DETF) design offers promise as a micro strain sensor. In addition, advances in bonding techniques suggest that installation and hermetic sealing of MEMS strain sensors can be achieved on a chip scale without exotic surface preparation. Finally, the fact that MEMS structures are typically fabricated using IC processing techniques, makes integration of the sensor and its control electronics apossibility, allowing for in situ installation of these sensors on preexisting devices.
May 31, 2004
Lippmann, J. M. (2004). Design and Fabrication of MEMS Resonant Strain Sensor in SOI: Research Report. United States: University of California, Berkeley.
Kuanzishwa kwa vifaa vya kibiashara vya kupima mvuto katika miaka ya 1950 kulibadilisha sana utafiti wa uhandisi wa muundo na mashine, na vilevile sayansi ya vifaa. Sensorer hizi hutoa dirisha lisilo na kifani katika tabia ya msingi ya vifaa na imara. Pamoja na kuanzishwa kwa nguvu za kompyuta zisizo za gharama kubwa, vipimo vya mtiririko huruhusu wahandisi kufuatilia tabia ya miundo shambani kwa urahisi. Kwa miaka mingi, kipimo cha msingi cha foil sasa kinakidhi mahitaji ya matumizi mengi na hali za mazingira katika utafiti na uzalishaji. Kwa bahati mbaya, kawaida foil strain gauges ni mdogo katika uwezo wao wa kupima maeneo madogo strain. Wao hupatwa na kupungua kwa hisia, ishara, na maisha ya uchovu wanapoongezeka. Mfano wa kisasa wa gauges ya foil miniaturized ina urefu wa gauge ya 200mm (kwa mfano, Tokyo Soke-Ken-Kyu-Gyu QFLG-02), lakini ina ishara ya chini na unyeti (kwa azimio la juu la 1mm) na maisha ya maisha (mzunguko wa mkazo wa 1x106 chini ya hali bora). Zaidi ya hayo, gauges foil kazi bora chini ya uwanja wa mtiririko sawa. Kwa upande mwingine, kwa sababu ya hali ya chini ya mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiriririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko wa mtiririko. Teknolojia kama hiyo <unk> semiconductor strain gauges <unk> inaonyesha ahadi kwa ajili ya kupima mashamba madogo strain. Vipimo vya kibiashara vya aina hii vinapatikana na urefu wa kipimo cha karibu 700 μm na unyeti wa karibu mara 75 zaidi kuliko vipimo vya foil (Micro Flexitronic - L2350-L2350-L2350-L2350-L2350-L2350-L2350-L2350-L2350-L2350-L2350-L2350-L2350-L2350-L2350-L2350-L2350-L3450-L3450-L3450-L3450-L3450-L3450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L4450-L. Hata hivyo, wao kuteseka kutoka tabia kubwa yasiyo ya linear joto, na pia zinahitaji usawa strain mashamba sawa na sehemu zao foil counter. Kwa kuongezea, aina zote mbili za strain gauge zinahitaji vifaa vya gharama kubwa, vya sensorer ili kufikia unyeti mzuri wa strain, pamoja na maandalizi ya uso wa ajabu na kuunganisha ili kuhakikisha kwamba strain katika substrate inasafirishwa kwa sensor. Masuala haya kupunguza wote wawili wa sensorer hizi hasa kwa maombi ya maabara. Microelectromechanical Systems (MEMS) ni njia ya kuimarisha uwezo wa kuendesha gari. Katika miaka ya 1980, kipimo cha piezoelectric cha silicon na oksidi ya silicon kilifanya watafiti wa MIT kuunda kipimo cha strain. Tangu wakati huo, watafiti wamechunguza mbinu mbalimbali na teknolojia za utengenezaji ikiwa ni pamoja na optical, capacitive-, na mbinu resonant. Sensorer resonating ni ya maslahi maalum kutokana na muundo wao rahisi na uwezekano wa unyeti wa juu. Kazi ya hivi karibuni katika Chuo Kikuu cha California katika Berkeley na Chuo Kikuu cha Southampton inaonyesha kwamba muundo wa tuning fork ya mwisho mbili (DETF) inatoa ahadi kama sensor ya micro strain. Kwa kuongezea, maendeleo katika mbinu za kuunganisha yanaonyesha kwamba usakinishaji na kufungwa kwa hermetic ya sensorer za mvuto wa MEMS zinaweza kupatikana kwenye kipimo cha chip bila maandalizi ya uso wa kigeni. Mwishowe, ukweli kwamba miundo ya MEMS ni kawaida fabricated kutumia IC mbinu za usindikaji, hufanya ushirikiano wa sensor na udhibiti wake wa elektroniki uwezekano, kuruhusu kwa ajili ya in-situ ufungaji wa sensorer hizi juu ya vifaa zilizopo. Mei 31, 2004 Lippmann, J. M. Ujenzi wa Mifumo ya Utafiti wa Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo ya Mifumo. Marekani: Chuo Kikuu cha California, Berkeley.