<PAGE>

                                                                     EXHIBIT 3.1

                          CERTIFICATE OF INCORPORATION
                                       OF
                                AIRSENSORS, INC.

                                ARTICLE 1.  NAME

     The name of this corporation is AirSensors, Inc.

                    ARTICLE 2.  REGISTERED OFFICE AND AGENT

     The address of the initial registered office of this corporation is 1209
Orange Street, Wilmington, County of New Castle, State of Delaware 19801, and
the name of its initial registered agent at such address is The Corporation
Trust Company.

                              ARTICLE 3.  PURPOSES

     The purpose of this corporation is to engage in any lawful act or activity
for which corporations may be organized under the General Corporation Law of
Delaware.

                               ARTICLE 4.  SHARES

4.1  Authorized Capital.  The total authorized shares of this corporation shall
     ------------------
consist of 50,000,000 shares of common stock having a par value of .$001 per
share and 500,000 shares of preferred stock having a par value of $.001 per
share.

4.2  Issuance of Common Stock in Series.  The common stock may be issued from
     ----------------------------------
time to time in one or more series, the shares of each series to have such
voting powers, full or limited, and such designations, preferences and relative,
participating, optional or other special rights and qualifications, limitations
or restrictions thereof as are stated and expressed herein or in the resolution
or resolutions providing for the issue of such series adopted by the Board of
Directors.

4.3  Issuance of Preferred Stock in Series.  The preferred stock may be issued
     -------------------------------------
from time to time in one or more series, the shares of each series to have such
voting powers, full or limited, and such designations, preferences and relative,
participating, optional or other special rights and qualifications, limitations
or restrictions thereof as are stated and expressed herein or in the resolution
or resolutions providing for the issue of such series adopted by the Board of
Directors.

4.4  Authority of the Board of Directors.  Authority is hereby expressly granted
     -----------------------------------
to the Board of Directors of this corporation, subject to the provision of this
Article 4 and to the limitations prescribed by law, to authorize the issue of
the common stock in one or more series, and one or more series of the preferred
stock, and with respect to each such series to fix by resolution or resolutions
providing for the issue of such series the voting power, full or limited, if
any, of the shares of such series and the designations, preferences and
relative, participating, optional or other special rights and the
qualifications, limitations or restrictions thereof.  The authority of the Board
of Directors

                                       1
<PAGE>

with respect to each series of common stock or preferred stock shall include,
but not be limited to, the determination or fixing of the following:

(a)  The designation of such series.
(b)  The dividend rate of such series, the conditions and dates upon which such
     dividends shall be payable, the relation which such dividends shall bear to
     the dividends payable on any other class or classes of stock and whether
     such dividends shall be cumulative or noncumulative.
(c)  Whether the shares of such series shall be subject to redemption by this
     corporation and, if made subject to such redemption, the times, prices and
     other terms and conditions of such redemption.
(d)  The terms and amounts of any sinking fund provided for the purposes or
     redemption of the shares of such series.
(e)  Whether the shares of such series shall be convertible into or exchangeable
     for shares of any other class or classes or of any other series of any
     class or classes of stock of this corporation and, if provision be made for
     conversion or exchange, the times, prices, rates, adjustments, and other
     terms and conditions of such conversion or exchange.
(f)  The extent, if any, to which the holders of the shares of such series shall
     be entitled to vote with respect to the election of directors or otherwise,
     including the right to elect a specified number or class of directors, the
     number or percentage of votes required for certain actions, and the extent
     to which a vote by class or series shall be required for certain actions.
(g)  The restrictions, if any, on the issue or reissue of any additional common
     stock or preferred stock.
(h)  The rights of the holders of the shares of such series upon the dissolution
     of, or upon the distribution of assets of, this corporation.

4.5  Dividends.  Subject to any preferential rights granted for any series of
     ---------
preferred stock, the holders of shares of the common stock shall be entitled to
receive dividends, out of the funds of this corporation legally available
therefor, at the rate and at the time or times as may be provided by the Board
of Directors.  The holders of shares of the preferred stock or common stock
shall be entitled to receive dividends to the extent provided by the Board of
Directors in designating the particular series of preferred stock or the common
stock.  The holders of shares of the commons tock shall not be entitled to
receive any dividends thereon other than the dividends referred to in this
section.

4.6  Voting.  The holders of shares of the common stock, on the basis of one
     ------
vote per share, shall have the right to vote for the election of members of the
Board of Directors of this corporation and the right to vote on all other
matters, except those matters in which a separate class of this corporation's
stockholders vote by class of

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<PAGE>

series. To the extent provided by resolution or resolutions of the Board of
Directors providing for the issue of the common stock, or a series of preferred
stock, the holders of each such series shall have the right to vote for the
election of members of the Board of Directors of this corporation and the right
to vote on all other matters, except those matters in which a separate class of
this corporation's stockholders vote by class or series.

4.7  Repurchase of Shares.  This corporation may from time to time issue and
     --------------------
dispose of any of the authorized and unissued shares of common stock or
preferred stock for such consideration, not less than its par value, as may be
fixed from time to time by the Board of Directors, without action by the
stockholders.  The Board of Directors may provide for payment therefor to be
received by this corporation in cash, property or services. Any and all such
shares of the common stock or preferred stock of this corporation, the issuance
of which has been so authorized, and for which consideration so fixed by the
Board of Directors has been paid or delivered, shall be deemed fully paid stock
and shall not be liable to any further call or assessment thereon.

                            ARTICLE 5.  INCORPORATOR

     The name and mailing address of the incorporator are:

          Julie E. Benezet
          The Bank of California Center
          Seattle, Washington 98164

                              ARTICLE 6.  BY-LAWS

     The Board of Directors shall have the power to adopt, amend or repeal the
By-laws for this corporation, at a duly called meeting or by written consent in
accordance with the General Corporation Law of Delaware, subject to the power of
the stockholders to amend or repeal such By-laws by the affirmative vote of the
holders of not less than a majority of the outstanding shares and, to the
extent, if any, provided by resolution or resolutions of the Board of Directors
providing for the issue of a series of common stock or preferred stock, not less
than a majority of the outstanding shares of each such series, entitled to vote
thereon. The stockholders shall also have the power to adopt, amend or repeal
the By-laws for this corporation.

              ARTICLE 7.  PROVISIONS FOR COMPROMISE OR ARRANGEMENT

     Whenever a compromise or arrangement is proposed between this corporation
and its creditors or any class of them and/or between this corporation and its
stockholders or any class of them, any court of equitable jurisdiction within
the State of Delaware may, on the application in a summary way of this
corporation or of any creditor or stockholder thereof or on the application of
any receiver or receivers appointed for this corporation under the provisions of
(S) 291 of Title 8 of the Delaware Code or on the application of trustees in
dissolution or of any receiver or receivers appointed for this corporation under
the provisions of (S) 279 of Title 8 of the Delaware Code order a meeting of the
creditors

                                       3
<PAGE>

or class of creditors, and/or of the stockholders or class of stockholders of
this corporation, as the case may be, to be summoned in such manner as the said
court directs. If a majority in number representing three-fourths in value of
the creditors or class of creditors, and/or of the stockholders or class of
stockholders of this corporation, as the case may be, agree to any compromise or
arrangement and to any reorganization of this corporation as consequence of such
compromise or arrangement, the said compromise or arrangement and the said
reorganization shall, if sanctioned by the court to which the said application
has been made, be binding n all the creditors or class of creditors, and/or on
all the stockholders or class of stockholders, of this corporation, as the case
may be, and also on this corporation.

                         ARTICLE 8.  PREEMPTIVE RIGHTS

     No preemptive rights shall exist with respect to shares of stock or
securities convertible into shares of stock of this corporation.

                         ARTICLE 9.  CUMULATIVE VOTING

     The right to cumulative votes in the election of Directors shall not exist
with respect to shares of stock of this corporation.

            ARTICLE 10.  AMENDMENTS TO CERTIFICATE OF INCORPORATION

     This corporation reserves the right to amend or repeal, by the affirmative
vote of the holders of a majority of the outstanding shares and, to the extent,
if any, provided by resolution or resolutions of the Board of Directors
providing for the issue of a series of common stock or preferred stock, a
majority of the outstanding shares of each series, entitled to vote thereon, any
of the provisions contained in this Certificate of Incorporation; provided that
Articles 1 ("Name")., 2 ("Registered Office and Agent") and 3 ("Purposes") may
be amended by the affirmative vote of the holders of a majority of the
outstanding shares, and to the extent, if any, provided by resolution or
resolutions of the Board of Director providing for the issuance of a series of
common stock or preferred stock, a majority of the outstanding shares of each
series, entitled to vote thereon.  The rights of the stockholders of this
corporation are granted subject to this reservation, provided, however, that the
holders of the outstanding shares of a class shall be entitled to vote as a
class upon a proposed amendment if the amendment would increase or decrease the
aggregate number of authorized shares of such class, increase or decrease the
par value of the shares of such class, or alter or change the powers,
preferences or special rights of the shares of such class so as to affect them
adversely.  If any proposed amendment would alter or change the powers,
preferences, or special rights of one or more series of any class so as to
affect them adversely, but shall not affect the entire class, then only the
shares of the series so affected by the amendment shall be considered as a
separate class for the purposes of this Article 10.  Irrespective of the
provisions of this Article 10, the number of authorized shares of any such class
or classes of stock may be increased by the affirmative vote of the holders of a
majority of the stock

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<PAGE>

of the corporation entitled to vote thereon or decreased (but not below the
number of shares thereof then outstanding) by the affirmative vote of the
holders of a majority of the stock of the corporation entitled to vote thereon,
if so provided in any amendment which created such class or classes of stock or
which was adopted prior to the issuance of any shares of such class or classes
of stock, or in any amendment which was authorized by a resolution or
resolutions adopted by the affirmative vote of the holders of a majority of such
class or classes of stock.

     I, Julie E. Benezet, being the incorporator hereinbefore named for the
purpose of forming a corporation pursuant to the General Corporation Law of the
State of Delaware, do make this certificate, hereby declaring and certifying
that this is my act and deed and the facts herein stated are true, and
accordingly I have hereunto set my hand this 17th day of October, 1985.

                                /s/ Julie E. Benezet
                                --------------------------------
                                Julie E. Benezet, Incorporator

                                       5
<PAGE>

                           CERTIFICATE OF AMENDMENT
                                      OF
                          CERTIFICATE OF INCORPORATION
                                      OF
                               AIRSENSORS, INC.

     Pursuant to the provisions of Sections 103 and 242 of the Delaware
Corporation Law, the undersigned certify as follows:

1.  The Certificate of Incorporation of AirSensors, Inc. is amended by adding a
new Article 11 as folllows:

       ARTICLE 11 - LIMITATION OF DIRECTORS' LIABILITY

         A director shall not be personally liable to the corporation or its
       stockholders for monetary damages for breach of fiduciary duty as a
       director, except for liability (i) for any breach of the director's duty
       of loyalty to the corporation or its stockholders, (ii) for acts or
       omissions not in good faith or which involve intentional misconduct or a
       knowing violation of law, (iii) under Section 174 or Title 8 of the
       Delaware General Corporation Code, or (iv) for any transaction from which
       the director derived an improper personal benefit. This provision shall
       not eliminate or limit the liability of a director for any act or
       omission occurring prior to the date when this provision becomes
       effective.

2.  The foregoing amendment was adopted by the directors of the corporation and
by both more than a majority of the outstanding stock entitled to vote thereon
and more than a majority of each class entitled to vote thereon as a class on
April 18, 1990, in accordance with the provisions of Section 222 and 242 of the
Delaware Corporation Law.

     I, Rawley F. Taplett, certify that I am Chairman of the Board of
AirSensors, Inc. and am authorized to execute this Certificate of Amendment on
behalf of the corporation.

     Dated: June 13, 1990.
            --------------
                                   /s/ R.F. Taplett
                                   ---------------------
                                   Chairman of the Board


Attest:
/s/ Dale L. Rasmussen
---------------------
Secretary

                                       6
<PAGE>

                            CERTIFICATE OF AMENDMENT
                                       OF
                          CERTIFICATE OF INCORPORATION
                                       OF
                                AIRSENSORS, INC.


     Pursuant to the provisions of Sections 103 and 242 of the Delaware
Corporation Law, the undersigned certify as follows:

     1.  The Article IV, Section 4.1 of the Certificate of Incorporation of
AirSensors, Inc. is amended in its entirety to provide as follows:

     4.1  Authorized Capital.  The total authorized shares of this
          ------------------
corporation shall consist of 25,000,000 shares of common stock having a par
value of $.001 per share and 500,000 shares of preferred stock having a par
value of $.001 per share.

     2.  The foregoing amendment was adopted by the directors of the corporation
and by both more than a majority of the outstanding stock entitled to vote
thereon and more than a majority of each class entitled to vote thereon as a
class on February 2, 1993 in accordance with the provisions of Sections 222 and
242 of the Delaware Corporation Law.

     I, Rawley F. Taplett, certify that I am the Chairman of the Board of
Directors of AirSensors, Inc. and am authorized to execute this Certificate of
Amendment on behalf of the corporation.

     Dated February 9, 1993


                              /s/ Rawley F. Taplette
                              --------------------------------------------------
                              Chairman of the Board

ATTEST:


/s/ Dale Rasmussen
------------------
Secretary

                                       7
<PAGE>

                      CERTIFICATE OF OWNERSHIP AND MERGER

                                       OF

                                AIRSENSORS, INC.

                                      AND

                            IMPCO TECHNOLOGIES, INC.

                                      WITH

                                AIRSENSORS, INC.

                                       AS

                             SURVIVING CORPORATION

     Pursuant to Title 8, Chapter 1, Delaware General Corporation Law (S)253
("DGCL"), the undersigned, being respectively the President and Secretary of
AirSensors, Inc., hereby adopt the following Certificate of Ownership and Merger
for the purpose of merging IMPCO Technologies, Inc. into AirSensors, Inc.
("Surviving Corporation") and changing the name of the Surviving Corporation to
IMPCO Technologies, Inc.

(1)  The names of the corporations being merged are AirSensors, Inc. and IMPCO
     Technologies, Inc.  Both corporations are organized under the laws of the
     State of Delaware.
(2)  AirSensors, Inc. owns more than 90% of the outstanding shares of each class
     of the stock of IMPCO Technologies, Inc.
(3)  The name of the Surviving Corporation is AirSensors, Inc. and it is to be
     governed by the laws of the State of Delaware.  The name of the Surviving
     corporation shall be changed to IMPCO Technologies, Inc. upon the
     effectiveness of the merger, pursuant to the Resolution of the board of
     Directors of AirSensors, Inc. approving the merger and attached as Exhibit
     A.
(4)  The Resolution and Plan of Merger (the "Plan") between AirSensors, Inc. and
     IMPCO Technologies, Inc. has been approved, adopted, certified, executed
     and acknowledged in accordance with Chapter 1, DGCL.  The Plan was
     unanimously approved by the holder of all of the outstanding stock of IMPCO
     Technologies, Inc. by written consent of the stockholder of IMPCO
     Technologies, Inc. on July 10, 1997.
(5)  The Certificate of Incorporation of AirSensors, Inc. shall be the
     Certificate of Incorporation of the Surviving Corporation, except that
     Article I shall be amended in its entirety as follows:

                                ARTICLE 1.  NAME


            The name of this corporation is IMPCO Technologies, Inc.

                                       8
<PAGE>

(6)  The Plan is on file at the principal place of business of the Surviving
     Corporation at 16804 Gridley Place, Cerritos, California  90703.  A copy of
     the Plan will be furnished by the Surviving Corporation, on request and
     without cost, to any stockholder of any constituent corporation.
(7)  Attached as Exhibit A and incorporated herein by reference is a copy of the
     Resolution of the Board of Directors of AirSensors, Inc. to merge IMPCO
     Technologies, Inc. into AirSensors, Inc.  This Resolution was adopted by
     the Board of Directors on July 10, 1997.
(8)  The person to contact regarding this filing is William G. Pusch, whose
     telephone number is 206-628-7744.
     IN WITNESS WHEREOF, this Certificate of Ownership and Merger has been
signed on September 8, 1997.

                         AIRSENSORS, INC.

                         By  /s/ Robert M. Stemmler
                            -------------------------------------
                               Robert M. Stemmler, President

                         By  /s/ Dale L. Rasmussen
                            -------------------------------------
                               Dale L. Rasmussen, Secretary

     We, Robert M. Stemmler and Dale L. Rasmussen, declare under the penalties
of perjury that we are the President and Secretary, respectively, of AirSensors,
Inc., a Delaware corporation, that we have examined this Certificate of
Ownership and Merger and that to the best of our knowledge and belief, it is
true, correct and complete.

     DATED:  September 8, 1997, 2001


                         /s/ Robert M. Stemmler
                         -----------------------------------------
                         Robert M. Stemmler

                         /s/ Dale L. Rasmussen
                         -----------------------------------------
                         Dale L. Rasmussen

                                       9
<PAGE>

                                   EXHIBIT A

                         RESOLUTION AND PLAN OF MERGER

     WHEREAS, IMPCO Technologies, Inc. has operated as a wholly owned subsidiary
of AirSensors, Inc. since it was acquired by AirSensors, Inc. in 1989; and

     WHEREAS, there is no longer any reason to continue the business activities
of IMPCO Technologies, Inc. as a wholly owned subsidiary of AirSensors, Inc. and
certain administrative expenses can be eliminated by merging IMPCO Technologies,
Inc. with and into AirSensors, Inc. as permitted by Section 253(a) of the
Delaware General Corporation Law ("DGCL"); and

     WHEREAS, it is desirable that AirSensors, Inc., as the surviving
corporation, change its name from AirSensors, Inc. to IMPCO Technologies, Inc.
upon the effective date of the merger as permitted by Section 253(b) of the
DGCL; it is therefore:

     RESOLVED, that IMPCO Technologies, Inc. be merged with and into AirSensors,
Inc. pursuant to the DGCL as hereinafter provided, so that the separate
existence of IMPCO Technologies, Inc. shall cease as soon as the merger shall
become effective, and thereupon, AirSensors, Inc. shall continue as the
surviving corporation to exist under, and be governed by, the laws of the State
of Delaware; and

     FURTHER RESOLVED, that AirSensors, Inc., as the surviving corporation,
change its corporate name to IMPCO Technologies, Inc. upon the effective date of
the merger; and

     FURTHER RESOLVED, that the merger and name change referred to in the
foregoing resolutions be effective upon the date of filing of the Certificate of
Ownership and Merger with the Secretary of State of Delaware; and

     FURTHER RESOLVED, that the terms and conditions of the proposed merger
(hereinafter, the "plan of merger") are as follows:

     (a) From and after the effective time of the merger, all of the estate,
property, rights, privileges, powers and franchises of IMPCO Technologies, Inc.
shall become vested in and be held by AirSensors, Inc. as fully and entirely and
without change or diminution as the same were before held and enjoyed by IMPCO
Technologies, Inc., and AirSensors, Inc. shall assume all of the obligations of
IMPCO Technologies, Inc., all in accordance with Section 259 of the DGCL.

     (b) All of the outstanding shares of stock of IMPCO Technologies, Inc. are
now owned by AirSensors, Inc., and upon the effective time of the merger they
shall be surrendered and extinguished.

     (c) The Certificate of Incorporation and Bylaws of AirSensors, Inc., both
as amended, as in effect immediately prior to the effective time of the merger
shall be the

                                       10
<PAGE>

Certificate of Incorporation and Bylaws of AirSensors, Inc., except
that Article 1 of the Certificate of Incorporation shall be amended as follows:

                                ARTICLE 1.  NAME

            The name of this corporation is IMPCO Technologies, Inc.

     FURTHER RESOLVED, that the President and the Secretary of AirSensors, Inc.
be, and each is hereby authorized and directed to make and execute a Certificate
of Ownership and Merger setting forth a copy of this Resolution and Plan of
Merger and the date of adoption thereof, and to cause the same to be filed and
recorded as provided by law, and to do all acts and things whatsoever, within
the State of Delaware and in any other appropriate jurisdiction, necessary or
proper to effect this Resolution and Plan of Merger.

                                       11
<PAGE>

                           IMPCO TECHNOLOGIES, INC.
                           ------------------------

                            CERTIFICATE OF AMENDMENT
                                      TO
                       THE CERTIFICATE OF INCORPORATION

     IMPCO Technologies, Inc. (the "Corporation"), a corporation organized and
existing under and by virtue of the General Corporation Law of the State of
Delaware (the "Delaware Corporation Law").

     DOES HEREBY CERTIFY:

     FIRST: That at a meeting of the Board of Directors of the Corporation duly
held on August 17, 2000, resolutions were duly adopted setting forth a proposed
amendment to the Certificate of Incorporation of the Corporation, declaring said
amendment to be advisable and directing that it be considered at the next annual
meeting of the stockholders of the Corporation. The resolution setting forth the
proposed amendment is as follows:

         RESOLVED, that the Certificate of Incorporation of this corporation
     be, and it hereby is, subject to approval by the stockholders of this
     corporation, amended to restate Article IV, Section 4.1 in its entirety to
     read in full as follows:

               "4.1 Authorized Capital.  The total authorized shares of
                    ------------------
          this corporation shall consist of 100,000,000 shares of common
          stock having a par value of $.001 per share and 500,000 shares
          of preferred stock having a par value of $.001 per share."

     SECOND: That thereafter, pursuant to said resolution of the Board of
Directors, at the annual meeting of stockholders of the Corporation duly called
and held on October 19, 2000, upon notice in accordance with Section 222 of the
Delaware Corporation Law, the necessary number of shares as required by statute
was voted in favor of the amendment.

     THIRD: That said amendment was duly adopted in accordance with the
provisions of Section 242 of the Delaware Corporation Law.

     FOURTH:  That the capital of the Corporation shall not be reduced under or
by reason of said amendment.

     IN WITNESS WHEREOF, IMPCO Technologies, Inc. has caused this Certificate of
Amendment to be signed by its President and its Secretary this 8th day of
December, 2000.


By: /s/ Robert M. Stammler                   By: /s/ Dale L. Rasmussen
   _________________________                     ________________________
   Name: Robert M. Stammler                      Name: Dale L. Rasmussen
   Title: President                              Title: Secretary


                                       12