MEMS time-of-flight thermal mass flow meter

摘要

An apparatus comprising a micromachined (a.k.a. MEMS, Micro Electro Mechanical Systems) silicon flow sensor, a flow channel package, and a driving circuitry, which operates in a working principle of thermal time-of-flight (TOF) to measure gas or liquid flow speed, is disclosed in the present invention. The micromachining technique for fabricating this MEMS time-of-flight silicon thermal flow sensor can greatly reduce the sensor fabrication cost by batch production. This microfabrication process for silicon time-of-flight thermal flow sensors provides merits of small feature size, low power consumption, and high accuracy compared to conventional manufacturing methods. Thermal time-of-flight technology in principle can provide accurate flow speed measurements for gases regardless of its gas compositions. In addition, the present invention further discloses the package design and driving circuitry which is utilized by the correlated working principle.

主权项

1. A MEMS time-of-flight thermal mass flow meter comprising:
a micromachined time-of-flight (TOF) thermal mass flow sensor; an insertion type of flow channel package; and a single frequency drive functionality circuit; wherein, said micromachined time-of-flight thermal mass flow sensor has a suspending membrane to provide a heat insulated region for device operation; said micromachined time-of-flight thermal mass flow sensor has a first micro-thermistor in a serpentine pattern disposed on a top surface of said suspending membrane and functioning as a micro-heating element; said micromachined time-of-flight thermal mass flow sensor has a second micro-thermistor in a serpentine pattern disposed on said top surface of said suspending membrane, which is in parallel with and a definite distance from said micro-heating element and functioning as a micro-sensing element; said micromachined time-of-flight thermal mass flow sensor has four open slots on said suspending membrane, which are located in parallel on each side of said micro-heating element and said micro-sensing element to isolate lateral heat conduction for the purpose of enhancing measurement accuracy; said single frequency drive functionality circuit contains four basic building circuitries including a heater-driving generator circuit; a sensing signal conditioning circuit; a pre-phase-lag detector circuit; and a micro-controller circuit; said single frequency drive functionality circuit provides a sinusoidal heat wave with a certain frequency to elevate a temperature of micro-heating element; and said sinusoidal heat wave is carried away by a flowing media and causes a phase shift of said sinusoidal heat wave when said sinusoidal heat wave arrives on said micro-sensing element.