Techniques, systems, and devices are described for implementing for implementing computation devices and artificial neurons based on nanoelectromechanical (NEMS) systems. In one aspect, a nanoelectromechanical system (NEMS) based computing element includes: a substrate; two electrodes configured as a first beam structure and a second beam structure positioned in close proximity with each other without contact, wherein the first beam structure is fixed to the substrate and the second beam structure is attached to the substrate while being free to bend under electrostatic force. The first beam structure is kept at a constant voltage while the other voltage varies based on an input signal applied to the NEMS based computing element.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A nanoelectromechanical system (NEMS) based computing element, comprising: a substrate; and two electrodes configured as a first beam structure and a second beam structure positioned in close proximity with each other without contact, wherein the first beam structure is fixed to the substrate and the second beam structure is attached to the substrate while being free to bend under electrostatic force, wherein the first beam structure is kept at a constant voltage while the other voltage varies based on an input signal applied to the NEMS based computing element. 2. The NEMS based computing element of claim 1, wherein, as a potential difference between the electrodes varies due to an applied input signal, the electrostatic force between the two electrodes varies that causes the second beam structure to move towards the first beam structure, resulting in a change in the effective capacitance between the two electrodes. 3. The NEMS based computing element of claim 1, wherein the resulting output voltage is proportional to a differences between the capacitances of the first and the second beam structures. 4. An artificial neural network, comprising: a plurality of nanoelectromechanical system (NEMS) based computing elements interfaced with one another and forming synaptic nodes, the NEMS based computing elements including: a substrate, and two electrodes configured as a first beam structure and a second beam structure, wherein the first beam structure is fixed to the substrate and the second beam structure is attached to the substrate while being free to bend under electrostatic force, wherein the first beam structure is kept at a constant voltage while the other voltage varies based on an input signal applied to the NEMS based computing element. 5. A nanoelectromechanical system (NEMS) based multiplier element, comprising: a substrate; a first pair of electrodes disposed on the substrate and configured as a first beam structure and a second beam structure positioned in close proximity with each other without contact, wherein the first beam structure is fixed to the substrate and the second beam structure is attached to the substrate while being free to bend under electrostatic force; a second pair of electrodes disposed on the substrate mirroring the first pair of electrodes and configured as a third beam structure and a fourth beam structure positioned in close proximity with each other without contact, wherein the third beam structure is fixed to the substrate and the fourth beam structure is attached to the substrate while being free to bend under electrostatic force; wherein the first pair of electrodes and the second pair of electrodes mirror each other such that the second and fourth beam structures are on the inside of the combined structure; and a fifth beam structure disposed on the substrate between the second and fourth beam structures and serves as an output electrode, wherein the first beam structure is coupled to a first voltage, the third beam structure is coupled to a second voltage that is the negative version of the first voltage, wherein the second and fourth beam structures are coupled to a third voltage; wherein the fifth beam structure is configured to output a fourth voltage which is proportional to the product of the first voltage and the third voltage. 6. The NEMS based multiplier element of claim 5, further comprising: a sixth beam structure mechanically coupled to the second beam structure such that the sixth beam structure is free to bend when the second beam structure is actuated, wherein the sixth beam structure is positioned between the second and fifth beam structures, and wherein the fifth and sixth beam structures form a first variable capacitor; a seventh beam structure mechanically coupled to the fourth beam structure such that the seventh beam structure is free to bend when the fourth beam structure is actuated, wherein the seventh beam structure is positioned between the fourth and fifth beam structures, and wherein the fifth and seventh beam structures form a second variable capacitor; wherein the fourth voltage is computed based on a capacitor divider formed by the first variable capacitor and the second first variable capacitor. 7. A NEMS based adder/multiplier element, comprising: a linearly cascaded NEMS based multiplier elements, wherein each NEMS based multiplier element includes: a first pair of electrodes disposed on the substrate and configured as a first beam structure and a second beam structure positioned in close proximity with each other without contact, wherein the first beam structure is fixed to the substrate and the second beam structure is attached to the substrate while being free to bend under electrostatic force; a second pair of electrodes disposed on the substrate mirroring the first pair of electrodes and configured as a third beam structure and a fourth beam structure positioned in close proximity with each other without contact, wherein the third beam structure is fixed to the substrate and the fourth beam structure is attached to the substrate while being free to bend under electrostatic force; wherein the first pair of electrodes and the second pair of electrodes mirror each other such that the second and fourth beam structures are on the inside of the combined structure; and a fifth beam structure disposed on the substrate between the second and fourth beam structures and serves as an output electrode, wherein the first beam structure is coupled to a first voltage, the third beam structure is coupled to a second voltage that is the negative version of the first voltage, wherein the second and fourth beam structures are coupled to a third voltage; wherein the fifth beam structure is configured to output a fourth voltage which is proportional to the product of the first voltage and the third voltage. 8. A device based on nanoelectromechanical system (NEMS) elements, comprising: a substrate; nanoelectromechanical system (NEMS) elements formed over the substrate, each NEMS element including two electrodes configured as a first beam structure and a second beam structure positioned in close proximity with each other without contact to allow for relative motion therebetween under an electrostatic force in response to an electrical signal applied to the NEMS element; and an array of SONAR (Sound Navigation and Ranging) devices formed over the substrate, each SONAR device operable to produce a sonic signal directed to the NEMS elements so that sonic signals from the SONAR devices form sonic communication links within the NMES elements. 9. An ion-gas sensor device, comprising: a substrate including an array of pillars and troughs; a microfan component including a first stack and a second stack of layers of a piezoelectric composite material formed on the pillars of the substrate and protruding over the troughs, the first stack of layers to sense the flow of ions in a gas and the second stack of layers actuate to drive the ions to a detection region of the device at a controlled flow rate; a layer of a radioactive material formed in the trough of the substrate to ionize the gas when flowed above the layer; and an array of electrodes formed in the detection region to detect ion mobility of the ions of the gas. 10. The device as in claim 9, wherein the microfan component amplifies the controlled flow rate based on resonance of the second stack of layers. 11. The device as in claim 9, wherein the flow of the gas is controlled by shedding air vortices close to a tip of the second stack and re-circulating the gas in loops above or below surface of the second stack. 12. The device as in claim 9, wherein the radioactive material includes a Ni-63 thin film. 13. The device as in claim 9, wherein the piezoelectric composite material includes a stack of SiO2—TiPt—PZT-Pt layers. 14. The device as in claim 9, wherein: the second stack of layers is configured to have a width of substantially 200 μm and a length of substantially 800 μm that protrudes over the trough of the substrate, and the first stack of layers is configured to have a width of substantially 200 μm and a length of substantially 1000 μm that protrudes over the trough of the substrate. 15. A chip-size gas analyzer, comprising: a chipscale ionization source configured to generate ions of the target compounds in the gas flowing through the sensor; a gas pump module configured to pump the ions of the target compounds into an area of chemical sensing; and a detection module configured to detect and identify target compounds. 16. The chip-size gas analyzer of claim 15, wherein the chipscale ionization source includes an electron-emitting radioactive material for harvesting energized electrons which can be used to ionize molecules. 17. The chip-size gas analyzer of claim 15, wherein the electron-emitting radioactive material is integrated with a CMOS-compatible structure. 18. The chip-size gas analyzer of claim 15, wherein the electron-emitting radioactive material is 63Ni films. 19. The chip-size gas analyzer of claim 15, wherein the gas pump module includes piezoelectric fans, wherein a piezoelectric fan comprises a PZT plate including a fixed end attached to a substrate and free end suspended above the substrate. 20. A monolithic ultrasonic fingerprint scanner, comprising: an acoustic matching layer to provide a contact surface for a finger to make contact; an array of piezoelectric transducers disposed beneath the acoustic matching layer, wherein each of the piezoelectric transducers is operable to generate an incident acoustic wave or an incident acoustic pulse toward the acoustic matching layer and receive reflected acoustic waves or acoustic pulses off of an object being detected; and a CMOS die electrically coupled to the array of piezoelectric transducers to receive and process the piezoelectric transducers outputs produced in response to the reflected acoustic waves or the acoustic pulses. 21. The monolithic ultrasonic fingerprint scanner of claim 20, wherein the incident acoustic wave or an incident acoustic pulse is reflected off valleys and hills of the skin on a finger at different times with different amplitudes to create echo singles of different amplitudes and delays to represent features of a fingerprint. 22. The monolithic ultrasonic fingerprint scanner of claim 20, wherein each of the piezoelectric transducers communicates with any other piezoelectric transducer in the array of piezoelectric transducers by sending proper phasing of acoustic pulses at desired angles.